May 21, 2024 • 50 mins
Daniel and Katie reveal the shocking truth about the balance between positive and negative particles.
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Speaker 1 (00:08):
Ay, Katie, did we use up all of our electricity
puns in the last episode we did together?
Speaker 2 (00:14):
I don't know. I mean, you're the one who's in charge.
Speaker 1 (00:17):
Yeah, but I'm trying to stay neutral on this.
Speaker 2 (00:20):
That's just because you think that puns have such a
high potential.
Speaker 1 (00:25):
They do, though, they do. They so much capacity for
humor in electricity.
Speaker 2 (00:30):
It's almost like electricity induces its own jokes.
Speaker 1 (00:35):
Let's see, we can get a few more, and it's
really down to the wire.
Speaker 2 (00:39):
You will find no resistance for me.
Speaker 1 (00:56):
Hi, I'm Daniel. I'm a particle physicist and a professor
at you see Irvine, and I'm endlessly fascinated by electricity
and its capacity for puns.
Speaker 2 (01:05):
My name is Katie Golden. I host an animal biology
podcast called Creature Feature, and I am a particle enthusiast.
I like particles, uh so I enjoy learning about them.
What's your favorite particle, Daniel.
Speaker 1 (01:24):
Oh, my favorite particle? Wow? I feel like now they're
all listening to me.
Speaker 2 (01:28):
Wonder just one?
Speaker 1 (01:32):
I guess I gotta go top quark because I studied
it from my phdtiss and it's the most massive of
all the particles in that way, kind of the weirdest.
Speaker 2 (01:41):
Oh okay, now, which one of the top particles is
your favorite? Pick one?
Speaker 1 (01:47):
Pick one. Well, that's actually quite hilarious because for my PhD,
I studied like six top quarks, like literally or six
that we found at the time. But the way particle
physics works is that you get more and more collisions
every year the things ramp up. So folks these days
doing their PhD have like tens of thousands of top
quarks they get to study. Wow, and I like names
for mine. I was like, oh, this is top quark
(02:09):
number four. Who I call this number two? Who I
call Sally. She's a bit weird, but I love her.
Speaker 2 (02:15):
That's it's adorable. It's like the the seven Dwarfs, except
it's the six quarks. Yeah, sleepy grumpy.
Speaker 1 (02:27):
I really got to know my top quarks. Well, how
about you? You said your pro particle. I'm glad to
hear that you're not anti particle.
Speaker 2 (02:33):
Yeah. No, I mean I like things existing. I'm pro
existence of there being stuff. I like stuff. I like
the way that stuff works. I like being able to
It's like rainy today, and I appreciate the physics of
being able to have some tea and you know that
(02:53):
it's it's just those are the simple things.
Speaker 1 (02:55):
Right, Like you're really sticking out a controversial position over
their pro.
Speaker 2 (02:58):
Stuff, prost stuff, pro existence, pro hot tea.
Speaker 1 (03:03):
And Welcome to the podcast Daniel and Jorge Explain the Universe,
a production of iHeartRadio in which we are pro stuff,
we are pro particles, we are pro the universe, and
we are especially pro you understanding the universe because we
think that not only is the universe incredible and majestic
and kinda crazy and weird, but that it's also understandable
(03:25):
that with our tiny little human brains, we can develop
mathematical models and intuitive understanding for what's going on out
there in the rest of the universe, from the tiniest
little particles to the most massive of super massive black
holes and everything in between, including me and you and
Katie's dog.
Speaker 2 (03:42):
Yes, Cookie is a very good physicist because she knows
that what goes up comes down when it comes to treats.
Speaker 1 (03:50):
When I talk them, your dog's name is Cookie, not Biscotti.
Speaker 2 (03:55):
She yeah, it's funny. We didn't change her name to
Italian when we moved here.
Speaker 1 (04:00):
And why is your dog named Cookie? Is it because
she's so delicious.
Speaker 2 (04:03):
It's wow. Well, no, I don't want to eat my
canine made out of dog meat. No, No, it's just
very very cute. When she was a little puppy, she's
very small and cute and kind of cream colored, so
she looked like a little biscotti, which is funny because
an Italian biscotti is actually just the general term for cookies,
(04:24):
like we say a biscotti, but that doesn't really make
any sense because it's like biscotti is plural, quick Italian
grammar lesson.
Speaker 1 (04:33):
And doesn't piscotti actually mean like cook twice.
Speaker 2 (04:35):
I think, yeah, I don't know if it just means
cooked twice. It really is just a general term for cookies,
and it's not necessarily the really hard ones that you
have to dunk to actually get any enjoyment out of.
It's just any cookie is called a biscato, and you know,
any kind of cookie is you know, like plural biscottis cookies.
Speaker 1 (04:55):
Until somebody invents the next generation of cookies and then
they can call it like triscotti or something.
Speaker 2 (04:59):
Right right by phosphate scotti. I don't know chemistry stuff,
but yeah, let's talk more about particles that are not
so visible as the biscotti particle.
Speaker 1 (05:11):
That's right, because we're not just here to talk about cookies.
We're here to understand the whole universe down to the
tiness of the particles it's made out of. And on
the podcast, we often talk about the mystery of electric charge.
What is it? Why do some particles have it, why
do other particles not have it? How does it all work?
And we usually think about it in terms of the
tiniest little individual particles. One is positive, one is negative,
(05:34):
one is neutral. But today we actually want to zoom
out and ask a much bigger, grander question about the
nature of electric charge.
Speaker 2 (05:42):
Yeah, you know, I got a fortune cookie message that
says you will have an electrifying experience. I'm really glad
it meant recording this podcast and not like I was
going to need to be resuscitated with those electric paddles.
Speaker 1 (05:55):
And it might still happen. I mean, this podcast could
be very shocking.
Speaker 2 (05:58):
Today we'll see, well, yeah, we'll see if my heart
can take it. But yeah, no, I mean it is interesting,
right because like electricity is, it's in everything. It's like
in our bodies, the heart rhythm, the cytostoism of our
heart is determined by electrical pulses our brain activity, Like
you are using electricity right now to think for your
(06:19):
brain to kind of understand this podcast. But then it's
also you know, it is throughout the universe in everything
in terms of how molecules stick to each other. So
it's a very interesting force in that, Like I feel
like we kind of only think about it when it's
really obvious, like lightning or getting shocked by your toaster,
(06:44):
but it is literally almost everywhere.
Speaker 1 (06:46):
It seems like it is almost everywhere, which makes us
inspired to think about it. In the grandest sense. We
can often learn something about the universe by trying to
zoom out by saying, well, what do all these particles
make or how do they come together? To determine the
biggest features of the universe its size, its shape, it's topology,
all this amazing stuff. So in today on the podcast,
we want to start from the little particles they're electric charges,
(07:09):
and zoom out to think about the whole universe. And
so today in the podcast, we'll be answering the question
what is the total electric charge of the universe?
Speaker 2 (07:25):
Twenty that's my guess. It just feels it feels right.
It feels like a good number. Twenty charge.
Speaker 1 (07:35):
You know, there is something interesting about the numerology of
the universe. If you imagine like writing down the final
equation of the universe or looking at the final numbers
in the final theory, you got to wonder, like why
those numbers are not some other numbers. You know, there
are some numbers that obviously are just human and not
important because they have units on them, and we make
(07:55):
up units and so anything with the units on it
is irrelevant. But you know, it's like the final theory
of string theory that explains the universe has like a
three in it or eleven in it. Then you got
to wonder, like why that number is the universe somehow?
Eleven ish right?
Speaker 2 (08:08):
M Yeah, it does have kind of an eleveny feeling
to it. I think that makes sense.
Speaker 1 (08:14):
That sounds like a delicious name for a cookie.
Speaker 2 (08:16):
Eleveny sounds like eleven to cookie. So I guess, like
when we're talking about like total electric charge, like I
don't even know where to start really, because it's like,
I mean, it could be positive, it could be negative,
it could be neutral. I don't know if they're like
if this is something that even could have a number, right, Like,
if it's a positive charge, could it have a positive
(08:37):
Is twenty even a possible answer?
Speaker 1 (08:39):
Tony actually is a possible answer. But we're gonna see
that there's a lot of sort of assumptions built into
this discussion about what's natural, what makes sense, what numbers
we would sort of accept, what numbers need explanation, and
what numbers don't need explanation, and so these kind of
questions I think are fascinating because they reflect not just
our understanding of the universe, but our attitudes about it,
(09:01):
our biases, our presuppositions about what kind of answers make sense.
So I was wondering, as usual, what people thought about
this question before we dove in. So I went out
there and I asked our group of volunteers what they
thought about this question. If you'd like to join this
not very illustrious, but very enthusiastic group of volunteers, please
write to me at questions at Danielandhorge dot com. So
(09:23):
think about it for a moment before you hear these answers.
What do you think the total electric charge of the
whole universe could be? Here's what people had to say.
Speaker 3 (09:32):
I would say zero, so that all the charges eventually
equal out. That would seem nice and symmetric. But since
that's almost certainly not the right answer, I'm gonna go
with plus five electron vaults.
Speaker 4 (09:47):
Well, I know there's the law of the conservation of energy,
so I guess it probably depends on what the charge
was of all the energy that existed during the Big Bang.
Given that Daniel and Jorge are explainers of the universe,
there are two people, and they're both very positive, I'm
going to say plus two.
Speaker 5 (10:01):
The electromagnetic field, as far as I understand it, can
be thought I was covering the entire universe, and I
don't see why that would have been created with a
non zero value. So I'm going to say the overall
electric charge is zero.
Speaker 6 (10:16):
Shouldn't this be zero because all this symmetry of particles
and charges and the words for maximizing entropy is this emulated.
I have my dear, I feel like the net electric
charge in the universe must be zero, but that's probably
not correct.
Speaker 7 (10:35):
I want to guess that it's the same as a
single electron, only because if every electron is just an
expression of the excitation of a single field, then that
whole field represents the charge of a single electron. Oh Man, Daniel,
I don't know, sounds good.
Speaker 2 (10:56):
I love the answer. That's like, it seems like it
should be zero, like neutral, but knowing that the universe
is weird, it's probably like five.
Speaker 1 (11:05):
That was basically your answer, right, I think that makes
a lot of sense.
Speaker 2 (11:08):
That basically sums up this is typically what I learned
from these recordings with you, is that it's like, well,
it seems like it should be something really like neat
and precise and tidy, and then it's something like five
point seven units of physics.
Speaker 1 (11:27):
It's true that the universe is chock full of surprises,
and the way that we think things should work isn't
always the way things actually work. But I think this
already raises that really fascinating issue. Like if I told
you the answer is zero, you'd be like, cool, that
kind of makes sense, and you might not even need
any more explanation because zero is just like a natural answer.
But if I tell you the answer is five, then
(11:48):
you're like, well, why five? Why not four? Why not seventeen? Right?
Then it needs an explanation. It tells us something about
the kind of answers we're willing to accept about these
deep questions about the universe.
Speaker 2 (11:58):
I'm not anti math, but like, I don't think math
is a natural thing for me, and certainly not like
the kind of math required to sum up all of
the charge of the universe, which sounds very time consuming.
How would you even go about, like what is the
mathematical process here? We're hopefully not counting the atoms and
(12:19):
their charges and just summing them up, because that seems
like it would take a whole afternoon.
Speaker 1 (12:26):
Yeah, that's exactly what we're doing. What when we talk
about the total electric charge of the universe, we really
just mean put all the protons on one side and
all the electrons on the other side and count them
up and add it all up.
Speaker 2 (12:40):
It sounds like doing taxes.
Speaker 1 (12:43):
Yeah, exactly, we're doing the accounting of the universe. It's
just one big Excel file. Actually, that's the way the
universe works. It's it's just a big Excel's bridge.
Speaker 2 (12:53):
Oh god, that's the darkest outcome.
Speaker 1 (12:56):
But you know, that's really how we define things. The
chargement of is the sum of the charges of things.
It's made out of Like if you have a cloud
of hydrogen gas. It's made of protons electrons, one proton
per electron, so the whole cloud is neutral. If you
added like one proton in there without an electron, then
the whole cloud would have an overall positive charge. So
(13:18):
that's really fascinating because the charge of an object really
is just the sum of the charges. There's nothing else
going on in there. It's very crisp, very clean to
calculate the charge of an object.
Speaker 2 (13:28):
So I noticed in a lot of the answers, which
I also kind of understand and agree with, that there
is this and what you said earlier, which is there's
this comfort with the idea of it being zero because
that seems balanced, right, Like this intuitive feeling that there
should be for every positively charged particle there should be
(13:48):
a negatively charged particle that they're for every proton there
should be an electron. Essentially, Why do you think there
is this assumption which I'm not necess really disagree with.
I just think that's interesting that that is a comfortable
stance for people to take, Like, what is it about
that neutrality that we like so much?
Speaker 1 (14:09):
Yeah, I think that's a great question and a deep one.
I think it just reflects our biases. You know, I
think we like to imagine that the universe makes sense,
that it runs on laws, and those laws are reasonable
and they make sense, and that they're not arbitrary, and
having the overall universe have it's sort of just an
arbitrary number for its charge. It needs an explanation, you know,
(14:30):
why eighteen? Why sixteen? And it takes a sort of
different philosophical approach to ask, like, well, doesn't zero also
need an explanation, Like if you have exactly the same
number of protons and electrons in the universe, doesn't that
also need some explanation. It's sort of an amazing coincidence.
Anytime you see a coincidence in nature, you wonder like, hmmm,
(14:52):
is there a reason for that? Is there some underlying
process we're not aware of that's making that happen, And
sometimes it does and sometimes it's not. You know, there's
a huge coincidence in our sky. The sun and the
moon are almost exactly the same size in our sky,
which makes for very dramatic eclipses. Is that a coincidence? Yeah? Absolutely,
There's no reason why the sun and the moon should
(15:12):
be the same size at all, Like they're very differently
sized objects, very different distances away from the Earth. It's
just a literally cosmic coincidence that they balance each other
in the sky and appeared to be the same size
other times. We think that there might really be an
underlying reason why the universe would have some cosmic coincidence.
So in the case of its total charge, we're just
(15:34):
adding up the protons and the electrons and counting them.
And I just want to go back to this for
one minute, because I think it's kind of amazing that
you can calculate the whole charge of the universe just
by adding up its bits, because you know that's not
true for other stuff, like for mass, right, you can't
just say, well, what's the mass of the universe. I'm
going to add up the mass of all the quarks
and the electrons. Because we've talked about lots of times
on the podcast, like the mass of the proton is
(15:56):
not just the mass of the things that's made out
of there's also energy in its bonds which contributes to
its mass. So mass is much more slippery of a
concept than electric charge. Electric charge is incredibly crisp and clean,
and so you actually can measure the electric charge of
the universe on an Excel spreadsheet is really just very
simple map, but the numbers are staggering, Like how many
(16:17):
protons are there in the universe is something like ten
to the eighty protons in the universe. And that's, of
course just the observable universe, just the part that we
can see and interact with, and that life has had
enough time to travel to us since the origin of
the universe. We think they're like ten with eighty zeros
after it, protons in that chunk of the universe. What
(16:39):
lies beyond, of course, we can't know.
Speaker 2 (16:41):
Yeah, this seems like the trickiest part, right is obviously
we cannot have a bean counter go throughout the whole
universe counting every single electron and proton, but we would
need to sort of, you know, almost like average out
like what our expectations are, Like take a slice of
the universe, figure out like if it's a representative sample
(17:04):
of the universe, and then scale that up or something.
I don't even know. Look, I'm thinking in terms of
sort of like biology studies and statistics and stuff, but
I don't even know if those kinds of things work
for the universe, right, because you could have. You could
take a reasonably large slice of the universe and try
to assume it's a representative sample of the whole universe.
(17:26):
But you know, then you could have an entire, massively
large area of the universe where you know the density
of stuff, or there's a presence of a black hole,
and things are completely different.
Speaker 1 (17:38):
Now, this is a really good point, and I think
that fundamentally we need to talk about the universe as
a whole, even beyond what we can see. Because imagine
the universe is infinite, right, It's still possible that it
has an equal number of electrons and protons, that the
total universe charge is neutral. But then you know where
any individual particle is going to be is going to
(17:58):
be a little bit random. So if you take an
observable universe sized scoop of that infinite universe, you could
take lots of different scoops one here, when they're one
exactly where we are, you might get exactly the same
number of electrons and protons, but that's actually quite unlikely.
You're very likely to get a slight difference in the
protons and electrons for any random scoop. Overall, they would
(18:19):
average out, but any observable universe scoop would probably have
a very small difference. And that's not something we can
practically measure, because, as you say, you have to go
touch every proton and every electron. But we can think
about the overall universe, and we can extrapolate from what
we've learned about the laws of physics and what we've
observed about the behavior of charges in our scoop to
(18:40):
think about what the overall charge of the universe is.
Speaker 2 (18:43):
Okay, So it's all about sort of trying to figure
out some underlying rule that we might be able to
safely assume applies to the rest of the universe, rather
than trying to get sort of a representative sample, like
we are looking for something that seems like a consistent
rule that should apply and scale up.
Speaker 1 (19:05):
Yeah, I think we can actually do both. We can
think about what would make sense, what the rules of
electricity and magnetism are, and whether we think the universe
should be neutral, and then we can do our best
to go out there and look to see if that
actually works, look for any evidence of deviation from that,
see if we can find hints that we could be
wrong about the nature of the universe.
Speaker 2 (19:26):
Okay, Well, I'm gonna go get my big old chalkboard
on wheels do some goodwill hunting style, like suddenly I'm
good at math inexplicably, and then maybe I'll come up
with the number. But we'll take a quick break and
we'll see what Daniel thinks of that number I come
up with. So, Daniel, I did some I just wrote
(20:00):
some random fractions, but I'm not really getting anywhere. I
think that I need more stuff to work with here
in my math exploration, because this is a thing, like
with theoretical math and theoretical physics, I have such a
hard time understanding where one even begins to try to understand,
like I would assume perhaps for this like there would
(20:21):
be some you would start with some experiments to see
if there is some kind of rule that it's consistent
in terms of the average charge of a system.
Speaker 1 (20:33):
And so we can start theoretically and think about like
how electromagnetism works. And as you say, thinking about the
rules is really important because it helps us understand, like, also,
can the electric charge of the universe change? Is it
possible for it to go up and down? Because if
it is, then it's very difficult to imagine the electric
charge of the universe is zero, or even to know
(20:54):
what the number is. But something that's super fascinating and
super important about electric charge really that it's deeply fundamental
to the nature of the universe and matter itself, is
that electric charge is conserved. That means that the total
electric charge we think can never change. Whatever that number is.
Add up all the pluses and all the minuses, and
you get some number zero or seven or whatever that
(21:16):
cannot change. Is no physical process in the universe that
can change that number. There's a wrinkle there. It doesn't
mean you can't create and destroy charged particles, right Like,
you can have a photon which has no charge, and
it can turn into an electron and its antiparticle the positron,
so that you have created new charged particles, but you
created a plus one and a minus one, so the
(21:38):
total charge hasn't changed. Photon with zero the positron and
electron pair total charge is still zero. So that kind
of stuff can happen. You can create and destroy charge particles,
but for some reason, the universe doesn't let you just
make an electron or just make a positron. You have
to keep those charges balanced.
Speaker 2 (21:57):
Interesting so when I rub my feet real fast against
the carpet, I'm wearing socks, and I have changed my
charge slightly, And so I assume though then I have
potentially also changed the charge of the carpet or something.
Right like, It's not like I don't just produce a
positive Well, actually, I guess I don't know what my
(22:18):
charges once I rubbed my socks real fast against the carpet.
All I know is that I have changed my state
somewhat so that when I touch a doorknob, I get
a little zap. But my assumption is that this is
not coming out of nowhere. There's some exchange happening exactly.
Speaker 1 (22:34):
That's a really deep insight right there. That if something
is conserved, then there has to be a current of it.
Then in order for you to get some of it,
it has to come from somewhere. It has to flow.
So if you're going to get a bunch of electrons,
you can't just create them from nothing. They have to
come from somewhere. Somewhere else has to lose electrons. If
you're going to gain electrons, or more specifically, if you're
(22:55):
going to gain negative charges, something else has to gain
positive charges either by losing a life netrons or creating
positrons or something. So this is like a conserved current
in the universe. You cannot just create charge out of nothing.
If you're getting it, it comes from somewhere, and that
tells you that it's like deeply ingrained in the nature
of reality itself. And there's lots of things in the
(23:16):
universe we see are almost conserved, like energy is mostly conserved.
And this is hard for people to grasp because they
think of that way of energy, that energy has to
come from somewhere and go to somewhere. But actually we
know that energy increases in the universe as it expands.
So energy is mostly conserved, but not Actually it's not
an exact symmetry or conservation of the universe. Same with
(23:38):
lots of other things we talk about, like lefton number
or other symmetries we have in particle physics. But this
one is exact. This one in the universe will never
ever let you violate. It's like down to the wire.
It will not give an inch on charge conservation.
Speaker 2 (23:51):
I don't want to go on a tangent, but you
said that the energy increases as the universe expands.
Speaker 1 (23:57):
Yeah, energy is only conserved if space is constant. But
if space is expanding, then is creating more space, and
that new space always comes with energy built in. It's
like the dark energy of the universe, So the total
energy of the universe is actually increasing if space is expanding.
We have a whole podcast about that.
Speaker 2 (24:15):
It's really fun, that's really cool. Yeah, I'm gonna listen
to it.
Speaker 1 (24:20):
But that's not true for electric charge. And I want
to disentangle two concepts here. We're talking a lot about
particles and antiparticles, and it's true that if you make
an electron, you also have to make its antiparticle. But
charge conservation is not the same thing as like matter
conservation or antimatter conservation. Matter particles can be positive or
they can also be negative. Antimatter particles can be positive
(24:42):
and they can be negative. So for example, electron we
call matter and it's negative. Proton we call matter and
it's positive. Antiproton would be negative, anti electron, the positron
would be positive. And it's a whole other question about
like matter antimatter symmetry in the universe. Like we think
that the treats matter and antimatter almost exactly the same
(25:02):
way but not quite right. But charge conservation is a
different thing than matter antimatter. Conservation matter anti matter is
another example of one where the universe is almost conserved,
almost symmetric, but not exactly. But charge conservation the universe
respects exactly.
Speaker 2 (25:18):
That's so interesting. It's like it makes it feel like
like electricity in charge is like much more. I mean,
I guess everything is fundamental, but it's like that this
is like the sort of one of the you know,
most fundamental aspects or causal aspects of the function of
the universe.
Speaker 1 (25:36):
Yeah, it seems like a deep clue about the nature
of reality itself. And you might ask, like, well, where
does it come from? Right? Why is it this way?
What does it tell us about the nature of reality?
And about one hundred years ago a mathematician Emmy Nuther
told us that everything that's conserved in the universe, anytime
there's a quantity that doesn't change, like momentum, is conserved
in a similar way. It tells you about some symmetry
(25:59):
in the universe that every conservation law, like conservation of
electric charge or conservation of momentum comes from some symmetry.
And that's a nuclear's theorem that every symmetry leads to
a conservation law. If there's a symmetry, it means some
quantity is conserved. And the case of momentum, the reason
momentum is conserved in the universe is because there's no
absolute location in space. Every place in the universe has
(26:21):
the same laws of physics. We think, it doesn't matter
if you do your experiment here or somewhere else, or
an alpha centauri, like, the fundamental laws of the universe
are the same. It's called translation invariance, and you do
a little bit of math, and out of translation in
variance comes conservation of momentum. So then you might ask, well,
what symmetry is it that creates conservation of electric charge?
(26:44):
Why do we have that? What does it tell us
about the universe? It's a little bit mathematical. It tells
us something about the phase of the electromagnetic field. The
electromagnetic field of these numbers that feel all of space
right and like, do you have an electric field here?
Do you have a magnetic field here? But those numbers
also have directions, like everywhere in space. The electromagnetic field
(27:04):
isn't just a number, it's an arrow. It points in
a certain direction, and the phase of that arrow, like
which direction it's actually pointing in, turns out to not
really matter. You can change that without changing the dynamics
of electromagnetism, and so it's a little bit mathematical and abstract,
but this is the quantity whose symmetry leads to conservation
(27:25):
of electric charge. And actually there's a whole set of
these symmetries, of these fundamental fields of the universe that
lead to conservation laws. We have an episode about these
gauge symmetries and how they lead to conservations and how
they're really deeply fundamental to the way the universe works.
So it's a little bit abstract, but conservation of electric
charge is telling us something about the nature of the
(27:45):
electromagnetic field and the symmetries of that field.
Speaker 2 (27:49):
If you changed the direction of an electromagnetic field, would
that have an impact on the direction of other electromagnetic
fields or what is just simply change direction and have
no impact on anything else.
Speaker 1 (28:06):
It absolutely would have an impact if you didn't have photons.
So photons are the things that actually preserve this symmetry.
Without photons, you can't have this symmetry in the universe.
Photons like zip around transmitting this information about the direction
of electric field changing from here to there. You can
actually deduce the existence of photons just by saying I
(28:26):
want an electromagnetic field and I wanted to have this
weird particular symmetry. For that to happen, you have to
have photons. And so that sort of like explains why
we have photons, why we have forces. In general, all
of the forces are actually there to preserve these symmetries.
So it's a really fascinating and deep new way to
think about the nature of forces. Encourage everybody interested in
(28:48):
this stuff to check out our episode about gauge symmetry.
But this tells us something about the nature of electric charge,
but it's still not something we really understand. Like we
kick the can down the road a little bit. We say, okay,
so just conserving the universe, Why well because of this
other weird symmetry in the universe. Why does it have
that other weird symmetry. We don't know. That's just like
something we observe, and this is the process of science, right,
(29:11):
We're like, why is this oh because of that?
Speaker 7 (29:13):
Well?
Speaker 1 (29:13):
Why that? Oh because of this other thing? Well why
that other thing, right, and so we're sort of at
that stage and we're like, we don't know what that
really means, but we do think the universe preserves it.
Speaker 2 (29:24):
Yeah, I mean that's interesting. I think it's also interesting
this sort of way you phrased it, which is that
like photons are here in order to maintain this neutrality
or this conservation. And look, I'm totally here for the ride,
so I believe you. But I also think it's interesting that, like, uh,
I think that sometimes like we have as humans, we
(29:46):
are extremely causal, right, Like we love a thing that
like had like this causes this, right X causes why
I push a ball? That's what causes the ball to
roll down the hill. I wonder like if you know
there's something I mean it it certainly seems like everything
is interlocking in this extremely precise way, but it's like, well,
(30:12):
could one option be like everything sort of happened all
at once, right, like in terms of like everything maybe interlocking,
but one thing doesn't necessarily cause another thing, or could
it be like that you have this fundamental rule about
charge being conserved, and then somehow like photons became this,
Like I mean, in biology, it's like called the spandrel,
(30:33):
where it's like this thing that doesn't at least initially
have any purpose, but it is just because of the
structure of the organism. This structure has to exist. Like
an architecture, you'll have a spandrel being like a section
of the wall when you have an archway like that
(30:53):
is sort of between the rectangle of the opening and
then the arch. There's like those little kind of like
curvy pizza slices which are the spandrels, and they don't
actually serve any structural purpose, but they just have to
exist because the arch is there. And so like I
find that kind of interesting of like how do we like,
(31:14):
what are some of the ways that we think about
these Like could photons just obviously we have use for
photons now and they fit in with everything in all
the other particles in the universe, But just like, are
these things just happening because of some fundamental rule basically
forced everything else into place? Or did everything just kind
of pop into place all at once? And now my
(31:35):
brain hurts, Yeah, we don't know.
Speaker 1 (31:38):
The answer to that question. We're struggling to figure it out.
We think that maybe understanding the nature of reality at
a deeper level, you know, quantum gravity. That might explain
where all these fields come from and why we have
them and why they have These symmetries could help us
understand why this exists in our universe. And there's some
people exploring theories that suggest that maybe charge is in conserved,
(32:00):
like maybe it's almost conserved, ben we've never seen it
be broken, but at some very tiny level, like very
very rarely can be broken. And most of these theories
suggest that our universe exists in higher dimensions, that like
it's more than just the three dimensions of space plus
one dimension of time that we're used to, but that
it's like five dimensional or six dimensional or ten dimensional
(32:22):
or whatever, and that maybe it's neutral in that ten
dimensional space, but in our like four dimensional subspace, maybe
it's not. You know, if you imagine the whole universe
is neutral, but you have like a random slice of it,
then particles can move in and out of that slice,
and that would look to you like charge is not conserved.
There's no data to support these ideas, but it's the
kind of things people are thinking about. You could create
(32:44):
charge non conservation in our universe by sort of expanding
the concept of the universe to something with more dimensions
in it. But if the universe does respect charge conservation,
that means that the total charge of the universe now
is the same as it was a minute ago, is
the same as it was in hours ago, is the
same as it was a billion years ago, Which means
that to figure out what the charge of the universe
(33:05):
is today, we only need to think about what the
charge of the universe was at the Big Bang or
when it began, right, and that will tell us what
the charge of the universe is still today. And that
relies really crucially on the charge never changing. So that's
why that's such an important part of this argument.
Speaker 2 (33:22):
Well, I'm excited to see a video of the Big Bang,
which Daniel clearly has, but let's take a little bit
of a break so I can hydrate before my mind
is blown. And then when we get back, Daniel's going
to explain exactly what happened during the Big Bang, leave
no detail undescribed. All right, Daniel, you promised, you promised
(33:55):
this big Bang? What happened there? What was up with that?
Speaker 1 (34:00):
Think you may have oversold this maybe a little bit.
You're right that the argument is if we know the
charge of the universe when it began. Then we know
the charge of the universe now because it hasn't changed.
So do we know the charge of the universe when
it began? Well, do we know how the universe began?
Unfortunately we don't, right, and people think about the Big Bang,
(34:21):
is this moment fourteen billion years ago when the universe began?
But really things are much fuzzier than that. What we
do know is fourteen billion years ago the universe was
in some very hot and dense state. We know that
because we see how the universe is progressing over time.
The further back we are looking in time, so we
can see the history of the universe. It's literally written
in the night sky.
Speaker 2 (34:42):
This is because light takes time to reach us, and
so we know based on the distance that it was, Like,
if stuff is closer, it's coming to us more recently
in time, and if stuff is further away, it's coming
to us further back in time.
Speaker 1 (34:58):
Right, like from that direction is arriving now that left
a long long time ago. So the images we are
seeing when we look really really far away are in
the deep, deep past, and what they tell us is
that the universe is getting colder. As it gets older,
it gets more spread out, more dilute, it gets chiller.
And if you run that clock backwards in time, then
the universe is getting hotter as you get backwards, and
(35:21):
more dense. So the universe started in some very hot
dense state and then spread out over time. And people
often think of the Big Bang as some dot of
matter spreading out into empty space. But the more accurate
picture is that the universe was already infinite, already filled
with an infinite amount of hot, dense stuff everywhere, and
(35:42):
the Big Bang is the expansion of that space, space
being created between those particles spreading out to make those
things colder and more dilute. That's our picture of the
Big Bang. And that's as far back as we can go.
Our theories of physics work really, really well back to
that hot dense state. Understanding how it is banded and
cooled and formed stuff. Kittens and ice cream and lava
(36:03):
and hamsters and all that good stuff before that, we
just really don't know.
Speaker 2 (36:07):
They don't mix particularly well those things anyway.
Speaker 1 (36:13):
Kitten ice cream, oh my gosh, really.
Speaker 2 (36:15):
And hamsters, they don't. They don't love lava.
Speaker 1 (36:18):
You could put a nice piscatti run on top of
that scoop of kitten ice cream. Perfectly you should name
your kitten cookie instead of your dog. But the pla
is that we don't know where that came from, right,
And so there's ideas, you know, it could be that
it decayed from some other unknown field like the Inflanton field,
or it could be as a bubble of exotic stuff
which turned into our universe. We don't really know. And
(36:41):
here's where we get sort of like philosophical, and we say, well,
probably it was born and neutral, because what else makes sense?
Speaker 2 (36:49):
Well, so if it's if we know it was super
hot and dense, is there something about heat and density
that could like tell us about the charge? Right, Like
do we know like if when we have really hot
dnse stuff, do we know the charge of those things?
And like could we somehow extrapolate like what is the
(37:10):
likely charge of like the it's like super super soup
of the initial universe.
Speaker 1 (37:20):
Yeah, so here's where we get into the evidence. The
only theoretical argument we have is the universe should be
neutral because it only makes sense for it to be
born neutral. And we're pretty sure that if it was
born neutral, it's still neutral, Well, do we have any
evidence to back that up. We can't actually look at
pictures from the very very early universe and look for
hints to see if there was any overall positive or
(37:41):
negative charge, because that really does affect how things oscillate.
So the oldest images that we have, the earliest measurements
we can make of the early universe, are from about
three hundred and eighty thousand years after that very very hot,
dense state. That's when things cool down enough that like
protons and electrons start to hang out to get into
neutral atoms, and then the universe became transparent. Before that,
(38:04):
it was hot and dense and opaque like the center
of the sun. After that moment became more transparent like
the air which let's light through. So we can still
see life from that last moment of opacity still shining
around the universe. That's the cosmic microwave background radiation we
talked about a lot on the podcast, and by looking
at patterns in that light, we can tell how that
(38:26):
gas or how that last moment of plasma was oscillating,
was sloshing around. We see all sorts of cool patterns
in that plasma that tell us like how much dark
matter there was in the universe, how much normal matter,
how many photons? The imprint of the ripples and the
cosmic microwave background radiation are an extraordinarily precise way to
understand the dynamics of that early plasma, and we can
(38:48):
actually use that to answer the question of whether there
was any overall charge very very far back in their
early universe.
Speaker 2 (38:56):
Okn, So how do we look at the charge of
this background radiation that we can actually observe on Earth.
Speaker 1 (39:03):
Well, the lucky thing is electromagnetism is super duper powerful,
Like it's so much more powerful than gravity that if
there was any positive charge or any negative overall charge
in those clouds of gas, we would see it because
it would overwhelm gravity. Mostly. When we look at the
cosmic backroway background radiation and use it to think about
like the sloshing and the oscillation of that gas in
(39:26):
the early universe, we see gravitational effects. We see dark
matter pulling it in, we see particles passing through each other.
We can think about the acoustic waves of pressure in
that gas, so we can see the gravitational effects if
there was any charge left over, any positive or negative
we would see a really strong effect because it would
overwhelm all that gravity. And yet when we look at
the data, we only see gravity effects. We see no
(39:49):
indication there that there's any positive or any negative charge
in the early universe clouds.
Speaker 2 (39:54):
Of gas that would indicate that maybe it is zero, right,
that it's neutral.
Speaker 1 (39:59):
You can't actually pinning down all the way to zero.
You can do a set a limit and say, look,
if there is an excess of protons or electrons, it's
got to be a tiny fraction, because if it was
any bigger, we would have seen it. And numerically what
that means is that, like, if there's an overall positive
or negative charge, it has to be less than one
part in ten to the twenty nine, which means like
(40:21):
for every ten of the twenty nine protons, there's ten
to the twenty nine electrons plus one.
Speaker 2 (40:27):
I may not know math, but I know that's that's tiny.
That's very small.
Speaker 1 (40:32):
It's very small.
Speaker 2 (40:33):
If you put that in as like a thing, I
couldn't see that thing.
Speaker 1 (40:39):
That's true. It is very very small. It's not exactly zero,
and ten to the twenty nine is a big number,
but it's actually small compared to the total number of
electrons and protons, which remember is like ten to the eighty,
So it's possible that the universe has a slightly positive or.
Speaker 2 (40:53):
Negative actually be infuriating. That would be so aggravating, And it.
Speaker 1 (40:57):
Could actually be that they're like ten to the fifty
more protons than electrons in the universe, which would still
be a tiny fraction of the ten to the eighty
protons and electrons in the universe. So that's what we
can learn from the cosmic microwave background radiation. But we
can keep fast forwarding in time for the universe and
look for effects in other dynamics, other structure that was
(41:17):
formed in the universe. That's actually a little bit more precise.
Speaker 2 (41:21):
Okay, I like this because I hate the idea that
we would just leave it at like it could be
zero or maybe, you know, tend to the twenty ninth ish,
We don't know.
Speaker 1 (41:30):
If you want definitive answers, cosmology is the wrong place
to look. So what happens next in the universe. The
protons and electrons have formed together to make hydrogen, then
that hydrogen fuses together very briefly like we're used to
thinking about fusion happening at the hearts of stars, which
formed hundreds of millions of years later. But for a
couple of minutes in the very early universe, things were
(41:53):
hot and dense enough that hydrogen could fuse together to
make heavier elements. It's like, briefly, the whole universe was
like the heart of a star, so that hydrogen made
some helium and very trace amounts of lithium. It didn't
last long enough to make anything heavier than that, and
the rate at which that happens tells us a huge
amount about the nature of reality at that moment, Like
(42:13):
we can measure the density of the protons at that
moment by the ratios of like how much helium was
made and how much lithium was made, because fusing two
protons together is really hard. You got to really push
them together with a lot of force. But you need
a huge amount of density in high temperature because protons
don't like to get together. They're both positively charged, they
repel each other. So you can learn a lot about
(42:34):
the density. And this is really precise science called Big
Bang nucleosynthesis that tells us a lot about the nature
of the universe back then, just by measuring these ratios,
the helium to hydrogen to lithium ratios, and it also
tells us about the positive and negative charges, because if
there was a bunch of extra protons flying around, that
(42:54):
would really change the rate of fusion, or if there
was a bunch of extra electrons flying around, because again
the electric force is really powerful and it would disrupt
or enhance the rate of the production of these heavier
elements in that moment. So by measuring these ratios, we
can get a limit on the total electric charge of
the universe now to one part in ten to the
thirty two, So it's like a thousand times more powerful
(43:17):
than the limit we get from the Cossack microwave background radiation.
Speaker 2 (43:20):
Okay, so intellectually I understand this is amazing and that
the science behind this is I mean, it's incredible right
to be able to do this kind of like deduction
and to do this calculation to this level of precision,
and that tend to the thirty two is a lot
more than tend to the twenty ninth because that is
(43:40):
the nature of exponential growth. And yet to my little
monkey brain, I'm like, these numbers are essentially the same,
and I like it's just real small, but the uncertainty
is still there. It's just real small.
Speaker 1 (43:56):
No, that's fair. I mean, on one hand, these are
very very precise studies, really incredible. We can learn this
much about the early universe from this trace information. And
on the other hand, it's nowhere near getting us close
to zero to understanding whether the universe is actually overall neutral.
But we can do even better. We can look in
the modern day universe to see if there are currents
(44:17):
flowing in the whole universe, like if the universe had
a bunch of positive charge here or a bunch of
negative charge there, if there was an imbalance in the
protons and electrons, that would create huge electric fields throughout
the whole universe, just the way like electrons and protons
can create electric fields in the atom or in materials
or between like your sock and the floor. If you
(44:38):
have an overall excess of electrons or protons somewhere, which
you'd have to have if there was an imbalance, then
you'd have electric fields. And we think we could see
that because those electric fields would steer cosmic rays. Cosmic
rays are just charged particles that hit the Earth like
tiny little asteroids like protons or sometimes heavier elements hit
the Earth, and we can measure them in our atmosphere
(44:58):
and using all sorts of cool time technology, and by
studying the patterns of those cosmic rays, we can use
them as probes of these cosmic electric fields and try
to figure out whether there is an overall positive or
negative charge to the universe.
Speaker 2 (45:12):
Okay, I mean that makes sense, right. You've got if
you have an imbalance that would cause this sort of
like sloshing of fields, and then we would see that
from here in cosmic rays that we receive.
Speaker 1 (45:26):
Yeah, and we've studied these cosmic rays. They're super interesting
for lots of other reasons, like what's even making them?
How do they get such high energy? The patterns of
them in the sky are very strange. We've analyzed them carefully,
and there's no evidence for an overall positive or negative
charge of the universe from cosmic rays. And we can
set a limit of one part in ten to the
thirty nine. So this is jumping up like seven more
(45:48):
orders of magnitude, improving this result by factor of ten million.
I hope that impresses you, Katie.
Speaker 2 (45:54):
Look again, intellectually, this is incredible, nothing but respect for
these scientists, And I understand that it is significant that
we keep increasing the precision of this estimation, meaning that
it looks more and more like it could probably be
zero or neutral. And yet you know, again there's a
(46:16):
little uncertainty, and the part of my brain that is
still a monkey does not like it.
Speaker 1 (46:24):
Well, you're right, we still don't actually know the answer,
and that's about as good as we can do so far.
We have other ways to look for electric fields, like
to look at the gravitational structure of the universe. You know,
if galaxies were overall positive or overall negative, it would
change the way they pull and tug on each other,
the way they move in galaxy clusters. And that's a
powerful way to look for excess charges, but it's not
(46:45):
as powerful as the cosmic ray limits. So those are
our best measurements so far about the overall neutrality of
the universe, about one part in ten to the thirty nine,
which is only like, you know, forty orders of magnitude
away from having a definitive answer to this question.
Speaker 2 (47:01):
I feel like at a certain point it's going to
be less of a math problem and more of a
problem to solve in therapy or I learned just to
accept uncertainty.
Speaker 1 (47:11):
Well, I think this is a really fascinating question because
we have a very strong answer from the theoretical side.
There's a very strong bias that says the universe should
be neutral when it was created, because again, no other
answer makes sense, and that's really just very philosophical. There's
no very strong theoretical argument there other than just like
a preference for zero is the most natural answer if
(47:32):
you have to pick one. But then the theory tells
us that once you picked one for the early universe,
once you create a universe, its charge is fixed. That
will just never change. And that's really cool experimentally because
it means we can measure the charge of the universe anytime.
We can measure it today. We can look for evidence
in the early universe, we can look for a thousand
years after the universe which created. We have lots and
(47:52):
lots of opportunities to make these measurements. So far, these
measurements tell us that the universe is mostly neutral, down
to about one part heart intended the thirty nine, which
I think is pretty good. But Katie's unimpressed. Maybe one
day we'll come up with another technique that lets us
push these measurements even further so we can get a
deeper answer to this question.
Speaker 2 (48:12):
Yeah, I mean, you know, And it's also a good lesson, like,
think real hard before you create your own universe, because
once you pick that charge, you can't change it later.
Speaker 1 (48:21):
That's you are literally stuck with it. There's no changing
the electric charge of the universe. But that's also not
something we understand. Right, we don't understand how the universe
was made or what its charge was in the beginning.
We also still don't really understand why charge is conserved.
This again, is just something we've observed. We've done a
zillion particle physics experiments looking for violation as rule and
(48:42):
never seen one. That doesn't mean that it doesn't happen occasionally, right,
We have these theoretical reasons that suggest that photons exist
to preserve electric charge, but again we don't really understand
why that is, and so it's possible that sneakily the
universe is changing its little bits of charge here and
there very occasionally under our newses.
Speaker 2 (49:02):
My therapist is going to be so confused when I
talk to her about like and then Daniel said that
we can't know if the charge doesn't change. I don't
know what to believe anymore. Who do I trust?
Speaker 1 (49:12):
I think you should just sit with your dog cookie
and have a nice cookie, and you have the therapy
right there.
Speaker 2 (49:17):
That is the best therapy, the buye cookie therapy.
Speaker 1 (49:22):
All right, Well, thanks everyone for joining us on this
exploration of the nature of the universe, not just its size,
not just its structure, but it's overall charged and what
that tells us about the nature of reality and what's
important to the universe For reasons we still don't understand.
The charge seems to be a fundamentally conserved quantity in
the universe, but we still don't actually know what the
(49:42):
total charge of the universe is. Thanks very much Kennie
for joining us today, and thanks everybody for listening.
Speaker 2 (49:48):
Thanks for having me.
Speaker 1 (49:49):
Tune in next time for more science and curiosity. Come
find us on social media where we answer questions and
post videos. We're on Twitter, Discorg, Insta, and now TikTok.
Thanks for listening, and remember that Daniel and Jorge Explain
the Universe is a production of iHeartRadio. For more podcasts
(50:11):
from iHeartRadio, visit the iHeartRadio, app, Apple podcasts, or wherever
you listen to your favorite shows.
Ay, Katie, did we use up all of our electricity
puns in the last episode we did together?
Speaker 2 (00:14):
I don't know. I mean, you're the one who's in charge.
Speaker 1 (00:17):
Yeah, but I'm trying to stay neutral on this.
Speaker 2 (00:20):
That's just because you think that puns have such a
high potential.
Speaker 1 (00:25):
They do, though, they do. They so much capacity for
humor in electricity.
Speaker 2 (00:30):
It's almost like electricity induces its own jokes.
Speaker 1 (00:35):
Let's see, we can get a few more, and it's
really down to the wire.
Speaker 2 (00:39):
You will find no resistance for me.
Speaker 1 (00:56):
Hi, I'm Daniel. I'm a particle physicist and a professor
at you see Irvine, and I'm endlessly fascinated by electricity
and its capacity for puns.
Speaker 2 (01:05):
My name is Katie Golden. I host an animal biology
podcast called Creature Feature, and I am a particle enthusiast.
I like particles, uh so I enjoy learning about them.
What's your favorite particle, Daniel.
Speaker 1 (01:24):
Oh, my favorite particle? Wow? I feel like now they're
all listening to me.
Speaker 2 (01:28):
Wonder just one?
Speaker 1 (01:32):
I guess I gotta go top quark because I studied
it from my phdtiss and it's the most massive of
all the particles in that way, kind of the weirdest.
Speaker 2 (01:41):
Oh okay, now, which one of the top particles is
your favorite? Pick one?
Speaker 1 (01:47):
Pick one. Well, that's actually quite hilarious because for my PhD,
I studied like six top quarks, like literally or six
that we found at the time. But the way particle
physics works is that you get more and more collisions
every year the things ramp up. So folks these days
doing their PhD have like tens of thousands of top
quarks they get to study. Wow, and I like names
for mine. I was like, oh, this is top quark
(02:09):
number four. Who I call this number two? Who I
call Sally. She's a bit weird, but I love her.
Speaker 2 (02:15):
That's it's adorable. It's like the the seven Dwarfs, except
it's the six quarks. Yeah, sleepy grumpy.
Speaker 1 (02:27):
I really got to know my top quarks. Well, how
about you? You said your pro particle. I'm glad to
hear that you're not anti particle.
Speaker 2 (02:33):
Yeah. No, I mean I like things existing. I'm pro
existence of there being stuff. I like stuff. I like
the way that stuff works. I like being able to
It's like rainy today, and I appreciate the physics of
being able to have some tea and you know that
(02:53):
it's it's just those are the simple things.
Speaker 1 (02:55):
Right, Like you're really sticking out a controversial position over
their pro.
Speaker 2 (02:58):
Stuff, prost stuff, pro existence, pro hot tea.
Speaker 1 (03:03):
And Welcome to the podcast Daniel and Jorge Explain the Universe,
a production of iHeartRadio in which we are pro stuff,
we are pro particles, we are pro the universe, and
we are especially pro you understanding the universe because we
think that not only is the universe incredible and majestic
and kinda crazy and weird, but that it's also understandable
(03:25):
that with our tiny little human brains, we can develop
mathematical models and intuitive understanding for what's going on out
there in the rest of the universe, from the tiniest
little particles to the most massive of super massive black
holes and everything in between, including me and you and
Katie's dog.
Speaker 2 (03:42):
Yes, Cookie is a very good physicist because she knows
that what goes up comes down when it comes to treats.
Speaker 1 (03:50):
When I talk them, your dog's name is Cookie, not Biscotti.
Speaker 2 (03:55):
She yeah, it's funny. We didn't change her name to
Italian when we moved here.
Speaker 1 (04:00):
And why is your dog named Cookie? Is it because
she's so delicious.
Speaker 2 (04:03):
It's wow. Well, no, I don't want to eat my
canine made out of dog meat. No, No, it's just
very very cute. When she was a little puppy, she's
very small and cute and kind of cream colored, so
she looked like a little biscotti, which is funny because
an Italian biscotti is actually just the general term for cookies,
(04:24):
like we say a biscotti, but that doesn't really make
any sense because it's like biscotti is plural, quick Italian
grammar lesson.
Speaker 1 (04:33):
And doesn't piscotti actually mean like cook twice.
Speaker 2 (04:35):
I think, yeah, I don't know if it just means
cooked twice. It really is just a general term for cookies,
and it's not necessarily the really hard ones that you
have to dunk to actually get any enjoyment out of.
It's just any cookie is called a biscato, and you know,
any kind of cookie is you know, like plural biscottis cookies.
Speaker 1 (04:55):
Until somebody invents the next generation of cookies and then
they can call it like triscotti or something.
Speaker 2 (04:59):
Right right by phosphate scotti. I don't know chemistry stuff,
but yeah, let's talk more about particles that are not
so visible as the biscotti particle.
Speaker 1 (05:11):
That's right, because we're not just here to talk about cookies.
We're here to understand the whole universe down to the
tiness of the particles it's made out of. And on
the podcast, we often talk about the mystery of electric charge.
What is it? Why do some particles have it, why
do other particles not have it? How does it all work?
And we usually think about it in terms of the
tiniest little individual particles. One is positive, one is negative,
(05:34):
one is neutral. But today we actually want to zoom
out and ask a much bigger, grander question about the
nature of electric charge.
Speaker 2 (05:42):
Yeah, you know, I got a fortune cookie message that
says you will have an electrifying experience. I'm really glad
it meant recording this podcast and not like I was
going to need to be resuscitated with those electric paddles.
Speaker 1 (05:55):
And it might still happen. I mean, this podcast could
be very shocking.
Speaker 2 (05:58):
Today we'll see, well, yeah, we'll see if my heart
can take it. But yeah, no, I mean it is interesting,
right because like electricity is, it's in everything. It's like
in our bodies, the heart rhythm, the cytostoism of our
heart is determined by electrical pulses our brain activity, Like
you are using electricity right now to think for your
(06:19):
brain to kind of understand this podcast. But then it's
also you know, it is throughout the universe in everything
in terms of how molecules stick to each other. So
it's a very interesting force in that, Like I feel
like we kind of only think about it when it's
really obvious, like lightning or getting shocked by your toaster,
(06:44):
but it is literally almost everywhere.
Speaker 1 (06:46):
It seems like it is almost everywhere, which makes us
inspired to think about it. In the grandest sense. We
can often learn something about the universe by trying to
zoom out by saying, well, what do all these particles
make or how do they come together? To determine the
biggest features of the universe its size, its shape, it's topology,
all this amazing stuff. So in today on the podcast,
we want to start from the little particles they're electric charges,
(07:09):
and zoom out to think about the whole universe. And
so today in the podcast, we'll be answering the question
what is the total electric charge of the universe?
Speaker 2 (07:25):
Twenty that's my guess. It just feels it feels right.
It feels like a good number. Twenty charge.
Speaker 1 (07:35):
You know, there is something interesting about the numerology of
the universe. If you imagine like writing down the final
equation of the universe or looking at the final numbers
in the final theory, you got to wonder, like why
those numbers are not some other numbers. You know, there
are some numbers that obviously are just human and not
important because they have units on them, and we make
(07:55):
up units and so anything with the units on it
is irrelevant. But you know, it's like the final theory
of string theory that explains the universe has like a
three in it or eleven in it. Then you got
to wonder, like why that number is the universe somehow?
Eleven ish right?
Speaker 2 (08:08):
M Yeah, it does have kind of an eleveny feeling
to it. I think that makes sense.
Speaker 1 (08:14):
That sounds like a delicious name for a cookie.
Speaker 2 (08:16):
Eleveny sounds like eleven to cookie. So I guess, like
when we're talking about like total electric charge, like I
don't even know where to start really, because it's like,
I mean, it could be positive, it could be negative,
it could be neutral. I don't know if they're like
if this is something that even could have a number, right, Like,
if it's a positive charge, could it have a positive
(08:37):
Is twenty even a possible answer?
Speaker 1 (08:39):
Tony actually is a possible answer. But we're gonna see
that there's a lot of sort of assumptions built into
this discussion about what's natural, what makes sense, what numbers
we would sort of accept, what numbers need explanation, and
what numbers don't need explanation, and so these kind of
questions I think are fascinating because they reflect not just
our understanding of the universe, but our attitudes about it,
(09:01):
our biases, our presuppositions about what kind of answers make sense.
So I was wondering, as usual, what people thought about
this question before we dove in. So I went out
there and I asked our group of volunteers what they
thought about this question. If you'd like to join this
not very illustrious, but very enthusiastic group of volunteers, please
write to me at questions at Danielandhorge dot com. So
(09:23):
think about it for a moment before you hear these answers.
What do you think the total electric charge of the
whole universe could be? Here's what people had to say.
Speaker 3 (09:32):
I would say zero, so that all the charges eventually
equal out. That would seem nice and symmetric. But since
that's almost certainly not the right answer, I'm gonna go
with plus five electron vaults.
Speaker 4 (09:47):
Well, I know there's the law of the conservation of energy,
so I guess it probably depends on what the charge
was of all the energy that existed during the Big Bang.
Given that Daniel and Jorge are explainers of the universe,
there are two people, and they're both very positive, I'm
going to say plus two.
Speaker 5 (10:01):
The electromagnetic field, as far as I understand it, can
be thought I was covering the entire universe, and I
don't see why that would have been created with a
non zero value. So I'm going to say the overall
electric charge is zero.
Speaker 6 (10:16):
Shouldn't this be zero because all this symmetry of particles
and charges and the words for maximizing entropy is this emulated.
I have my dear, I feel like the net electric
charge in the universe must be zero, but that's probably
not correct.
Speaker 7 (10:35):
I want to guess that it's the same as a
single electron, only because if every electron is just an
expression of the excitation of a single field, then that
whole field represents the charge of a single electron. Oh Man, Daniel,
I don't know, sounds good.
Speaker 2 (10:56):
I love the answer. That's like, it seems like it
should be zero, like neutral, but knowing that the universe
is weird, it's probably like five.
Speaker 1 (11:05):
That was basically your answer, right, I think that makes
a lot of sense.
Speaker 2 (11:08):
That basically sums up this is typically what I learned
from these recordings with you, is that it's like, well,
it seems like it should be something really like neat
and precise and tidy, and then it's something like five
point seven units of physics.
Speaker 1 (11:27):
It's true that the universe is chock full of surprises,
and the way that we think things should work isn't
always the way things actually work. But I think this
already raises that really fascinating issue. Like if I told
you the answer is zero, you'd be like, cool, that
kind of makes sense, and you might not even need
any more explanation because zero is just like a natural answer.
But if I tell you the answer is five, then
(11:48):
you're like, well, why five? Why not four? Why not seventeen? Right?
Then it needs an explanation. It tells us something about
the kind of answers we're willing to accept about these
deep questions about the universe.
Speaker 2 (11:58):
I'm not anti math, but like, I don't think math
is a natural thing for me, and certainly not like
the kind of math required to sum up all of
the charge of the universe, which sounds very time consuming.
How would you even go about, like what is the
mathematical process here? We're hopefully not counting the atoms and
(12:19):
their charges and just summing them up, because that seems
like it would take a whole afternoon.
Speaker 1 (12:26):
Yeah, that's exactly what we're doing. What when we talk
about the total electric charge of the universe, we really
just mean put all the protons on one side and
all the electrons on the other side and count them
up and add it all up.
Speaker 2 (12:40):
It sounds like doing taxes.
Speaker 1 (12:43):
Yeah, exactly, we're doing the accounting of the universe. It's
just one big Excel file. Actually, that's the way the
universe works. It's it's just a big Excel's bridge.
Speaker 2 (12:53):
Oh god, that's the darkest outcome.
Speaker 1 (12:56):
But you know, that's really how we define things. The
chargement of is the sum of the charges of things.
It's made out of Like if you have a cloud
of hydrogen gas. It's made of protons electrons, one proton
per electron, so the whole cloud is neutral. If you
added like one proton in there without an electron, then
the whole cloud would have an overall positive charge. So
(13:18):
that's really fascinating because the charge of an object really
is just the sum of the charges. There's nothing else
going on in there. It's very crisp, very clean to
calculate the charge of an object.
Speaker 2 (13:28):
So I noticed in a lot of the answers, which
I also kind of understand and agree with, that there
is this and what you said earlier, which is there's
this comfort with the idea of it being zero because
that seems balanced, right, Like this intuitive feeling that there
should be for every positively charged particle there should be
(13:48):
a negatively charged particle that they're for every proton there
should be an electron. Essentially, Why do you think there
is this assumption which I'm not necess really disagree with.
I just think that's interesting that that is a comfortable
stance for people to take, Like, what is it about
that neutrality that we like so much?
Speaker 1 (14:09):
Yeah, I think that's a great question and a deep one.
I think it just reflects our biases. You know, I
think we like to imagine that the universe makes sense,
that it runs on laws, and those laws are reasonable
and they make sense, and that they're not arbitrary, and
having the overall universe have it's sort of just an
arbitrary number for its charge. It needs an explanation, you know,
(14:30):
why eighteen? Why sixteen? And it takes a sort of
different philosophical approach to ask, like, well, doesn't zero also
need an explanation, Like if you have exactly the same
number of protons and electrons in the universe, doesn't that
also need some explanation. It's sort of an amazing coincidence.
Anytime you see a coincidence in nature, you wonder like, hmmm,
(14:52):
is there a reason for that? Is there some underlying
process we're not aware of that's making that happen, And
sometimes it does and sometimes it's not. You know, there's
a huge coincidence in our sky. The sun and the
moon are almost exactly the same size in our sky,
which makes for very dramatic eclipses. Is that a coincidence? Yeah? Absolutely,
There's no reason why the sun and the moon should
(15:12):
be the same size at all, Like they're very differently
sized objects, very different distances away from the Earth. It's
just a literally cosmic coincidence that they balance each other
in the sky and appeared to be the same size
other times. We think that there might really be an
underlying reason why the universe would have some cosmic coincidence.
So in the case of its total charge, we're just
(15:34):
adding up the protons and the electrons and counting them.
And I just want to go back to this for
one minute, because I think it's kind of amazing that
you can calculate the whole charge of the universe just
by adding up its bits, because you know that's not
true for other stuff, like for mass, right, you can't
just say, well, what's the mass of the universe. I'm
going to add up the mass of all the quarks
and the electrons. Because we've talked about lots of times
on the podcast, like the mass of the proton is
(15:56):
not just the mass of the things that's made out
of there's also energy in its bonds which contributes to
its mass. So mass is much more slippery of a
concept than electric charge. Electric charge is incredibly crisp and clean,
and so you actually can measure the electric charge of
the universe on an Excel spreadsheet is really just very
simple map, but the numbers are staggering, Like how many
(16:17):
protons are there in the universe is something like ten
to the eighty protons in the universe. And that's, of
course just the observable universe, just the part that we
can see and interact with, and that life has had
enough time to travel to us since the origin of
the universe. We think they're like ten with eighty zeros
after it, protons in that chunk of the universe. What
(16:39):
lies beyond, of course, we can't know.
Speaker 2 (16:41):
Yeah, this seems like the trickiest part, right is obviously
we cannot have a bean counter go throughout the whole
universe counting every single electron and proton, but we would
need to sort of, you know, almost like average out
like what our expectations are, Like take a slice of
the universe, figure out like if it's a representative sample
(17:04):
of the universe, and then scale that up or something.
I don't even know. Look, I'm thinking in terms of
sort of like biology studies and statistics and stuff, but
I don't even know if those kinds of things work
for the universe, right, because you could have. You could
take a reasonably large slice of the universe and try
to assume it's a representative sample of the whole universe.
(17:26):
But you know, then you could have an entire, massively
large area of the universe where you know the density
of stuff, or there's a presence of a black hole,
and things are completely different.
Speaker 1 (17:38):
Now, this is a really good point, and I think
that fundamentally we need to talk about the universe as
a whole, even beyond what we can see. Because imagine
the universe is infinite, right, It's still possible that it
has an equal number of electrons and protons, that the
total universe charge is neutral. But then you know where
any individual particle is going to be is going to
(17:58):
be a little bit random. So if you take an
observable universe sized scoop of that infinite universe, you could
take lots of different scoops one here, when they're one
exactly where we are, you might get exactly the same
number of electrons and protons, but that's actually quite unlikely.
You're very likely to get a slight difference in the
protons and electrons for any random scoop. Overall, they would
(18:19):
average out, but any observable universe scoop would probably have
a very small difference. And that's not something we can
practically measure, because, as you say, you have to go
touch every proton and every electron. But we can think
about the overall universe, and we can extrapolate from what
we've learned about the laws of physics and what we've
observed about the behavior of charges in our scoop to
(18:40):
think about what the overall charge of the universe is.
Speaker 2 (18:43):
Okay, So it's all about sort of trying to figure
out some underlying rule that we might be able to
safely assume applies to the rest of the universe, rather
than trying to get sort of a representative sample, like
we are looking for something that seems like a consistent
rule that should apply and scale up.
Speaker 1 (19:05):
Yeah, I think we can actually do both. We can
think about what would make sense, what the rules of
electricity and magnetism are, and whether we think the universe
should be neutral, and then we can do our best
to go out there and look to see if that
actually works, look for any evidence of deviation from that,
see if we can find hints that we could be
wrong about the nature of the universe.
Speaker 2 (19:26):
Okay, Well, I'm gonna go get my big old chalkboard
on wheels do some goodwill hunting style, like suddenly I'm
good at math inexplicably, and then maybe I'll come up
with the number. But we'll take a quick break and
we'll see what Daniel thinks of that number I come
up with. So, Daniel, I did some I just wrote
(20:00):
some random fractions, but I'm not really getting anywhere. I
think that I need more stuff to work with here
in my math exploration, because this is a thing, like
with theoretical math and theoretical physics, I have such a
hard time understanding where one even begins to try to understand,
like I would assume perhaps for this like there would
(20:21):
be some you would start with some experiments to see
if there is some kind of rule that it's consistent
in terms of the average charge of a system.
Speaker 1 (20:33):
And so we can start theoretically and think about like
how electromagnetism works. And as you say, thinking about the
rules is really important because it helps us understand, like, also,
can the electric charge of the universe change? Is it
possible for it to go up and down? Because if
it is, then it's very difficult to imagine the electric
charge of the universe is zero, or even to know
(20:54):
what the number is. But something that's super fascinating and
super important about electric charge really that it's deeply fundamental
to the nature of the universe and matter itself, is
that electric charge is conserved. That means that the total
electric charge we think can never change. Whatever that number is.
Add up all the pluses and all the minuses, and
you get some number zero or seven or whatever that
(21:16):
cannot change. Is no physical process in the universe that
can change that number. There's a wrinkle there. It doesn't
mean you can't create and destroy charged particles, right Like,
you can have a photon which has no charge, and
it can turn into an electron and its antiparticle the positron,
so that you have created new charged particles, but you
created a plus one and a minus one, so the
(21:38):
total charge hasn't changed. Photon with zero the positron and
electron pair total charge is still zero. So that kind
of stuff can happen. You can create and destroy charge particles,
but for some reason, the universe doesn't let you just
make an electron or just make a positron. You have
to keep those charges balanced.
Speaker 2 (21:57):
Interesting so when I rub my feet real fast against
the carpet, I'm wearing socks, and I have changed my
charge slightly, And so I assume though then I have
potentially also changed the charge of the carpet or something.
Right like, It's not like I don't just produce a
positive Well, actually, I guess I don't know what my
(22:18):
charges once I rubbed my socks real fast against the carpet.
All I know is that I have changed my state
somewhat so that when I touch a doorknob, I get
a little zap. But my assumption is that this is
not coming out of nowhere. There's some exchange happening exactly.
Speaker 1 (22:34):
That's a really deep insight right there. That if something
is conserved, then there has to be a current of it.
Then in order for you to get some of it,
it has to come from somewhere. It has to flow.
So if you're going to get a bunch of electrons,
you can't just create them from nothing. They have to
come from somewhere. Somewhere else has to lose electrons. If
you're going to gain electrons, or more specifically, if you're
(22:55):
going to gain negative charges, something else has to gain
positive charges either by losing a life netrons or creating
positrons or something. So this is like a conserved current
in the universe. You cannot just create charge out of nothing.
If you're getting it, it comes from somewhere, and that
tells you that it's like deeply ingrained in the nature
of reality itself. And there's lots of things in the
(23:16):
universe we see are almost conserved, like energy is mostly conserved.
And this is hard for people to grasp because they
think of that way of energy, that energy has to
come from somewhere and go to somewhere. But actually we
know that energy increases in the universe as it expands.
So energy is mostly conserved, but not Actually it's not
an exact symmetry or conservation of the universe. Same with
(23:38):
lots of other things we talk about, like lefton number
or other symmetries we have in particle physics. But this
one is exact. This one in the universe will never
ever let you violate. It's like down to the wire.
It will not give an inch on charge conservation.
Speaker 2 (23:51):
I don't want to go on a tangent, but you
said that the energy increases as the universe expands.
Speaker 1 (23:57):
Yeah, energy is only conserved if space is constant. But
if space is expanding, then is creating more space, and
that new space always comes with energy built in. It's
like the dark energy of the universe, So the total
energy of the universe is actually increasing if space is expanding.
We have a whole podcast about that.
Speaker 2 (24:15):
It's really fun, that's really cool. Yeah, I'm gonna listen
to it.
Speaker 1 (24:20):
But that's not true for electric charge. And I want
to disentangle two concepts here. We're talking a lot about
particles and antiparticles, and it's true that if you make
an electron, you also have to make its antiparticle. But
charge conservation is not the same thing as like matter
conservation or antimatter conservation. Matter particles can be positive or
they can also be negative. Antimatter particles can be positive
(24:42):
and they can be negative. So for example, electron we
call matter and it's negative. Proton we call matter and
it's positive. Antiproton would be negative, anti electron, the positron
would be positive. And it's a whole other question about
like matter antimatter symmetry in the universe. Like we think
that the treats matter and antimatter almost exactly the same
(25:02):
way but not quite right. But charge conservation is a
different thing than matter antimatter. Conservation matter anti matter is
another example of one where the universe is almost conserved,
almost symmetric, but not exactly. But charge conservation the universe
respects exactly.
Speaker 2 (25:18):
That's so interesting. It's like it makes it feel like
like electricity in charge is like much more. I mean,
I guess everything is fundamental, but it's like that this
is like the sort of one of the you know,
most fundamental aspects or causal aspects of the function of
the universe.
Speaker 1 (25:36):
Yeah, it seems like a deep clue about the nature
of reality itself. And you might ask, like, well, where
does it come from? Right? Why is it this way?
What does it tell us about the nature of reality?
And about one hundred years ago a mathematician Emmy Nuther
told us that everything that's conserved in the universe, anytime
there's a quantity that doesn't change, like momentum, is conserved
in a similar way. It tells you about some symmetry
(25:59):
in the universe that every conservation law, like conservation of
electric charge or conservation of momentum comes from some symmetry.
And that's a nuclear's theorem that every symmetry leads to
a conservation law. If there's a symmetry, it means some
quantity is conserved. And the case of momentum, the reason
momentum is conserved in the universe is because there's no
absolute location in space. Every place in the universe has
(26:21):
the same laws of physics. We think, it doesn't matter
if you do your experiment here or somewhere else, or
an alpha centauri, like, the fundamental laws of the universe
are the same. It's called translation invariance, and you do
a little bit of math, and out of translation in
variance comes conservation of momentum. So then you might ask, well,
what symmetry is it that creates conservation of electric charge?
(26:44):
Why do we have that? What does it tell us
about the universe? It's a little bit mathematical. It tells
us something about the phase of the electromagnetic field. The
electromagnetic field of these numbers that feel all of space
right and like, do you have an electric field here?
Do you have a magnetic field here? But those numbers
also have directions, like everywhere in space. The electromagnetic field
(27:04):
isn't just a number, it's an arrow. It points in
a certain direction, and the phase of that arrow, like
which direction it's actually pointing in, turns out to not
really matter. You can change that without changing the dynamics
of electromagnetism, and so it's a little bit mathematical and abstract,
but this is the quantity whose symmetry leads to conservation
(27:25):
of electric charge. And actually there's a whole set of
these symmetries, of these fundamental fields of the universe that
lead to conservation laws. We have an episode about these
gauge symmetries and how they lead to conservations and how
they're really deeply fundamental to the way the universe works.
So it's a little bit abstract, but conservation of electric
charge is telling us something about the nature of the
(27:45):
electromagnetic field and the symmetries of that field.
Speaker 2 (27:49):
If you changed the direction of an electromagnetic field, would
that have an impact on the direction of other electromagnetic
fields or what is just simply change direction and have
no impact on anything else.
Speaker 1 (28:06):
It absolutely would have an impact if you didn't have photons.
So photons are the things that actually preserve this symmetry.
Without photons, you can't have this symmetry in the universe.
Photons like zip around transmitting this information about the direction
of electric field changing from here to there. You can
actually deduce the existence of photons just by saying I
(28:26):
want an electromagnetic field and I wanted to have this
weird particular symmetry. For that to happen, you have to
have photons. And so that sort of like explains why
we have photons, why we have forces. In general, all
of the forces are actually there to preserve these symmetries.
So it's a really fascinating and deep new way to
think about the nature of forces. Encourage everybody interested in
(28:48):
this stuff to check out our episode about gauge symmetry.
But this tells us something about the nature of electric charge,
but it's still not something we really understand. Like we
kick the can down the road a little bit. We say, okay,
so just conserving the universe, Why well because of this
other weird symmetry in the universe. Why does it have
that other weird symmetry. We don't know. That's just like
something we observe, and this is the process of science, right,
(29:11):
We're like, why is this oh because of that?
Speaker 7 (29:13):
Well?
Speaker 1 (29:13):
Why that? Oh because of this other thing? Well why
that other thing, right, and so we're sort of at
that stage and we're like, we don't know what that
really means, but we do think the universe preserves it.
Speaker 2 (29:24):
Yeah, I mean that's interesting. I think it's also interesting
this sort of way you phrased it, which is that
like photons are here in order to maintain this neutrality
or this conservation. And look, I'm totally here for the ride,
so I believe you. But I also think it's interesting that, like, uh,
I think that sometimes like we have as humans, we
(29:46):
are extremely causal, right, Like we love a thing that
like had like this causes this, right X causes why
I push a ball? That's what causes the ball to
roll down the hill. I wonder like if you know
there's something I mean it it certainly seems like everything
is interlocking in this extremely precise way, but it's like, well,
(30:12):
could one option be like everything sort of happened all
at once, right, like in terms of like everything maybe interlocking,
but one thing doesn't necessarily cause another thing, or could
it be like that you have this fundamental rule about
charge being conserved, and then somehow like photons became this,
Like I mean, in biology, it's like called the spandrel,
(30:33):
where it's like this thing that doesn't at least initially
have any purpose, but it is just because of the
structure of the organism. This structure has to exist. Like
an architecture, you'll have a spandrel being like a section
of the wall when you have an archway like that
(30:53):
is sort of between the rectangle of the opening and
then the arch. There's like those little kind of like
curvy pizza slices which are the spandrels, and they don't
actually serve any structural purpose, but they just have to
exist because the arch is there. And so like I
find that kind of interesting of like how do we like,
(31:14):
what are some of the ways that we think about
these Like could photons just obviously we have use for
photons now and they fit in with everything in all
the other particles in the universe, But just like, are
these things just happening because of some fundamental rule basically
forced everything else into place? Or did everything just kind
of pop into place all at once? And now my
(31:35):
brain hurts, Yeah, we don't know.
Speaker 1 (31:38):
The answer to that question. We're struggling to figure it out.
We think that maybe understanding the nature of reality at
a deeper level, you know, quantum gravity. That might explain
where all these fields come from and why we have
them and why they have These symmetries could help us
understand why this exists in our universe. And there's some
people exploring theories that suggest that maybe charge is in conserved,
(32:00):
like maybe it's almost conserved, ben we've never seen it
be broken, but at some very tiny level, like very
very rarely can be broken. And most of these theories
suggest that our universe exists in higher dimensions, that like
it's more than just the three dimensions of space plus
one dimension of time that we're used to, but that
it's like five dimensional or six dimensional or ten dimensional
(32:22):
or whatever, and that maybe it's neutral in that ten
dimensional space, but in our like four dimensional subspace, maybe
it's not. You know, if you imagine the whole universe
is neutral, but you have like a random slice of it,
then particles can move in and out of that slice,
and that would look to you like charge is not conserved.
There's no data to support these ideas, but it's the
kind of things people are thinking about. You could create
(32:44):
charge non conservation in our universe by sort of expanding
the concept of the universe to something with more dimensions
in it. But if the universe does respect charge conservation,
that means that the total charge of the universe now
is the same as it was a minute ago, is
the same as it was in hours ago, is the
same as it was a billion years ago, Which means
that to figure out what the charge of the universe
(33:05):
is today, we only need to think about what the
charge of the universe was at the Big Bang or
when it began, right, and that will tell us what
the charge of the universe is still today. And that
relies really crucially on the charge never changing. So that's
why that's such an important part of this argument.
Speaker 2 (33:22):
Well, I'm excited to see a video of the Big Bang,
which Daniel clearly has, but let's take a little bit
of a break so I can hydrate before my mind
is blown. And then when we get back, Daniel's going
to explain exactly what happened during the Big Bang, leave
no detail undescribed. All right, Daniel, you promised, you promised
(33:55):
this big Bang? What happened there? What was up with that?
Speaker 1 (34:00):
Think you may have oversold this maybe a little bit.
You're right that the argument is if we know the
charge of the universe when it began. Then we know
the charge of the universe now because it hasn't changed.
So do we know the charge of the universe when
it began? Well, do we know how the universe began?
Unfortunately we don't, right, and people think about the Big Bang,
(34:21):
is this moment fourteen billion years ago when the universe began?
But really things are much fuzzier than that. What we
do know is fourteen billion years ago the universe was
in some very hot and dense state. We know that
because we see how the universe is progressing over time.
The further back we are looking in time, so we
can see the history of the universe. It's literally written
in the night sky.
Speaker 2 (34:42):
This is because light takes time to reach us, and
so we know based on the distance that it was, Like,
if stuff is closer, it's coming to us more recently
in time, and if stuff is further away, it's coming
to us further back in time.
Speaker 1 (34:58):
Right, like from that direction is arriving now that left
a long long time ago. So the images we are
seeing when we look really really far away are in
the deep, deep past, and what they tell us is
that the universe is getting colder. As it gets older,
it gets more spread out, more dilute, it gets chiller.
And if you run that clock backwards in time, then
the universe is getting hotter as you get backwards, and
(35:21):
more dense. So the universe started in some very hot
dense state and then spread out over time. And people
often think of the Big Bang as some dot of
matter spreading out into empty space. But the more accurate
picture is that the universe was already infinite, already filled
with an infinite amount of hot, dense stuff everywhere, and
(35:42):
the Big Bang is the expansion of that space, space
being created between those particles spreading out to make those
things colder and more dilute. That's our picture of the
Big Bang. And that's as far back as we can go.
Our theories of physics work really, really well back to
that hot dense state. Understanding how it is banded and
cooled and formed stuff. Kittens and ice cream and lava
(36:03):
and hamsters and all that good stuff before that, we
just really don't know.
Speaker 2 (36:07):
They don't mix particularly well those things anyway.
Speaker 1 (36:13):
Kitten ice cream, oh my gosh, really.
Speaker 2 (36:15):
And hamsters, they don't. They don't love lava.
Speaker 1 (36:18):
You could put a nice piscatti run on top of
that scoop of kitten ice cream. Perfectly you should name
your kitten cookie instead of your dog. But the pla
is that we don't know where that came from, right,
And so there's ideas, you know, it could be that
it decayed from some other unknown field like the Inflanton field,
or it could be as a bubble of exotic stuff
which turned into our universe. We don't really know. And
(36:41):
here's where we get sort of like philosophical, and we say, well,
probably it was born and neutral, because what else makes sense?
Speaker 2 (36:49):
Well, so if it's if we know it was super
hot and dense, is there something about heat and density
that could like tell us about the charge? Right, Like
do we know like if when we have really hot
dnse stuff, do we know the charge of those things?
And like could we somehow extrapolate like what is the
(37:10):
likely charge of like the it's like super super soup
of the initial universe.
Speaker 1 (37:20):
Yeah, so here's where we get into the evidence. The
only theoretical argument we have is the universe should be
neutral because it only makes sense for it to be
born neutral. And we're pretty sure that if it was
born neutral, it's still neutral, Well, do we have any
evidence to back that up. We can't actually look at
pictures from the very very early universe and look for
hints to see if there was any overall positive or
(37:41):
negative charge, because that really does affect how things oscillate.
So the oldest images that we have, the earliest measurements
we can make of the early universe, are from about
three hundred and eighty thousand years after that very very hot,
dense state. That's when things cool down enough that like
protons and electrons start to hang out to get into
neutral atoms, and then the universe became transparent. Before that,
(38:04):
it was hot and dense and opaque like the center
of the sun. After that moment became more transparent like
the air which let's light through. So we can still
see life from that last moment of opacity still shining
around the universe. That's the cosmic microwave background radiation we
talked about a lot on the podcast, and by looking
at patterns in that light, we can tell how that
(38:26):
gas or how that last moment of plasma was oscillating,
was sloshing around. We see all sorts of cool patterns
in that plasma that tell us like how much dark
matter there was in the universe, how much normal matter,
how many photons? The imprint of the ripples and the
cosmic microwave background radiation are an extraordinarily precise way to
understand the dynamics of that early plasma, and we can
(38:48):
actually use that to answer the question of whether there
was any overall charge very very far back in their
early universe.
Speaker 2 (38:56):
Okn, So how do we look at the charge of
this background radiation that we can actually observe on Earth.
Speaker 1 (39:03):
Well, the lucky thing is electromagnetism is super duper powerful,
Like it's so much more powerful than gravity that if
there was any positive charge or any negative overall charge
in those clouds of gas, we would see it because
it would overwhelm gravity. Mostly. When we look at the
cosmic backroway background radiation and use it to think about
like the sloshing and the oscillation of that gas in
(39:26):
the early universe, we see gravitational effects. We see dark
matter pulling it in, we see particles passing through each other.
We can think about the acoustic waves of pressure in
that gas, so we can see the gravitational effects if
there was any charge left over, any positive or negative
we would see a really strong effect because it would
overwhelm all that gravity. And yet when we look at
the data, we only see gravity effects. We see no
(39:49):
indication there that there's any positive or any negative charge
in the early universe clouds.
Speaker 2 (39:54):
Of gas that would indicate that maybe it is zero, right,
that it's neutral.
Speaker 1 (39:59):
You can't actually pinning down all the way to zero.
You can do a set a limit and say, look,
if there is an excess of protons or electrons, it's
got to be a tiny fraction, because if it was
any bigger, we would have seen it. And numerically what
that means is that, like, if there's an overall positive
or negative charge, it has to be less than one
part in ten to the twenty nine, which means like
(40:21):
for every ten of the twenty nine protons, there's ten
to the twenty nine electrons plus one.
Speaker 2 (40:27):
I may not know math, but I know that's that's tiny.
That's very small.
Speaker 1 (40:32):
It's very small.
Speaker 2 (40:33):
If you put that in as like a thing, I
couldn't see that thing.
Speaker 1 (40:39):
That's true. It is very very small. It's not exactly zero,
and ten to the twenty nine is a big number,
but it's actually small compared to the total number of
electrons and protons, which remember is like ten to the eighty,
So it's possible that the universe has a slightly positive or.
Speaker 2 (40:53):
Negative actually be infuriating. That would be so aggravating, And it.
Speaker 1 (40:57):
Could actually be that they're like ten to the fifty
more protons than electrons in the universe, which would still
be a tiny fraction of the ten to the eighty
protons and electrons in the universe. So that's what we
can learn from the cosmic microwave background radiation. But we
can keep fast forwarding in time for the universe and
look for effects in other dynamics, other structure that was
(41:17):
formed in the universe. That's actually a little bit more precise.
Speaker 2 (41:21):
Okay, I like this because I hate the idea that
we would just leave it at like it could be
zero or maybe, you know, tend to the twenty ninth ish,
We don't know.
Speaker 1 (41:30):
If you want definitive answers, cosmology is the wrong place
to look. So what happens next in the universe. The
protons and electrons have formed together to make hydrogen, then
that hydrogen fuses together very briefly like we're used to
thinking about fusion happening at the hearts of stars, which
formed hundreds of millions of years later. But for a
couple of minutes in the very early universe, things were
(41:53):
hot and dense enough that hydrogen could fuse together to
make heavier elements. It's like, briefly, the whole universe was
like the heart of a star, so that hydrogen made
some helium and very trace amounts of lithium. It didn't
last long enough to make anything heavier than that, and
the rate at which that happens tells us a huge
amount about the nature of reality at that moment, Like
(42:13):
we can measure the density of the protons at that
moment by the ratios of like how much helium was
made and how much lithium was made, because fusing two
protons together is really hard. You got to really push
them together with a lot of force. But you need
a huge amount of density in high temperature because protons
don't like to get together. They're both positively charged, they
repel each other. So you can learn a lot about
(42:34):
the density. And this is really precise science called Big
Bang nucleosynthesis that tells us a lot about the nature
of the universe back then, just by measuring these ratios,
the helium to hydrogen to lithium ratios, and it also
tells us about the positive and negative charges, because if
there was a bunch of extra protons flying around, that
(42:54):
would really change the rate of fusion, or if there
was a bunch of extra electrons flying around, because again
the electric force is really powerful and it would disrupt
or enhance the rate of the production of these heavier
elements in that moment. So by measuring these ratios, we
can get a limit on the total electric charge of
the universe now to one part in ten to the
thirty two, So it's like a thousand times more powerful
(43:17):
than the limit we get from the Cossack microwave background radiation.
Speaker 2 (43:20):
Okay, so intellectually I understand this is amazing and that
the science behind this is I mean, it's incredible right
to be able to do this kind of like deduction
and to do this calculation to this level of precision,
and that tend to the thirty two is a lot
more than tend to the twenty ninth because that is
(43:40):
the nature of exponential growth. And yet to my little
monkey brain, I'm like, these numbers are essentially the same,
and I like it's just real small, but the uncertainty
is still there. It's just real small.
Speaker 1 (43:56):
No, that's fair. I mean, on one hand, these are
very very precise studies, really incredible. We can learn this
much about the early universe from this trace information. And
on the other hand, it's nowhere near getting us close
to zero to understanding whether the universe is actually overall neutral.
But we can do even better. We can look in
the modern day universe to see if there are currents
(44:17):
flowing in the whole universe, like if the universe had
a bunch of positive charge here or a bunch of
negative charge there, if there was an imbalance in the
protons and electrons, that would create huge electric fields throughout
the whole universe, just the way like electrons and protons
can create electric fields in the atom or in materials
or between like your sock and the floor. If you
(44:38):
have an overall excess of electrons or protons somewhere, which
you'd have to have if there was an imbalance, then
you'd have electric fields. And we think we could see
that because those electric fields would steer cosmic rays. Cosmic
rays are just charged particles that hit the Earth like
tiny little asteroids like protons or sometimes heavier elements hit
the Earth, and we can measure them in our atmosphere
(44:58):
and using all sorts of cool time technology, and by
studying the patterns of those cosmic rays, we can use
them as probes of these cosmic electric fields and try
to figure out whether there is an overall positive or
negative charge to the universe.
Speaker 2 (45:12):
Okay, I mean that makes sense, right. You've got if
you have an imbalance that would cause this sort of
like sloshing of fields, and then we would see that
from here in cosmic rays that we receive.
Speaker 1 (45:26):
Yeah, and we've studied these cosmic rays. They're super interesting
for lots of other reasons, like what's even making them?
How do they get such high energy? The patterns of
them in the sky are very strange. We've analyzed them carefully,
and there's no evidence for an overall positive or negative
charge of the universe from cosmic rays. And we can
set a limit of one part in ten to the
thirty nine. So this is jumping up like seven more
(45:48):
orders of magnitude, improving this result by factor of ten million.
I hope that impresses you, Katie.
Speaker 2 (45:54):
Look again, intellectually, this is incredible, nothing but respect for
these scientists, And I understand that it is significant that
we keep increasing the precision of this estimation, meaning that
it looks more and more like it could probably be
zero or neutral. And yet you know, again there's a
(46:16):
little uncertainty, and the part of my brain that is
still a monkey does not like it.
Speaker 1 (46:24):
Well, you're right, we still don't actually know the answer,
and that's about as good as we can do so far.
We have other ways to look for electric fields, like
to look at the gravitational structure of the universe. You know,
if galaxies were overall positive or overall negative, it would
change the way they pull and tug on each other,
the way they move in galaxy clusters. And that's a
powerful way to look for excess charges, but it's not
(46:45):
as powerful as the cosmic ray limits. So those are
our best measurements so far about the overall neutrality of
the universe, about one part in ten to the thirty nine,
which is only like, you know, forty orders of magnitude
away from having a definitive answer to this question.
Speaker 2 (47:01):
I feel like at a certain point it's going to
be less of a math problem and more of a
problem to solve in therapy or I learned just to
accept uncertainty.
Speaker 1 (47:11):
Well, I think this is a really fascinating question because
we have a very strong answer from the theoretical side.
There's a very strong bias that says the universe should
be neutral when it was created, because again, no other
answer makes sense, and that's really just very philosophical. There's
no very strong theoretical argument there other than just like
a preference for zero is the most natural answer if
(47:32):
you have to pick one. But then the theory tells
us that once you picked one for the early universe,
once you create a universe, its charge is fixed. That
will just never change. And that's really cool experimentally because
it means we can measure the charge of the universe anytime.
We can measure it today. We can look for evidence
in the early universe, we can look for a thousand
years after the universe which created. We have lots and
(47:52):
lots of opportunities to make these measurements. So far, these
measurements tell us that the universe is mostly neutral, down
to about one part heart intended the thirty nine, which
I think is pretty good. But Katie's unimpressed. Maybe one
day we'll come up with another technique that lets us
push these measurements even further so we can get a
deeper answer to this question.
Speaker 2 (48:12):
Yeah, I mean, you know, And it's also a good lesson, like,
think real hard before you create your own universe, because
once you pick that charge, you can't change it later.
Speaker 1 (48:21):
That's you are literally stuck with it. There's no changing
the electric charge of the universe. But that's also not
something we understand. Right, we don't understand how the universe
was made or what its charge was in the beginning.
We also still don't really understand why charge is conserved.
This again, is just something we've observed. We've done a
zillion particle physics experiments looking for violation as rule and
(48:42):
never seen one. That doesn't mean that it doesn't happen occasionally, right,
We have these theoretical reasons that suggest that photons exist
to preserve electric charge, but again we don't really understand
why that is, and so it's possible that sneakily the
universe is changing its little bits of charge here and
there very occasionally under our newses.
Speaker 2 (49:02):
My therapist is going to be so confused when I
talk to her about like and then Daniel said that
we can't know if the charge doesn't change. I don't
know what to believe anymore. Who do I trust?
Speaker 1 (49:12):
I think you should just sit with your dog cookie
and have a nice cookie, and you have the therapy
right there.
Speaker 2 (49:17):
That is the best therapy, the buye cookie therapy.
Speaker 1 (49:22):
All right, Well, thanks everyone for joining us on this
exploration of the nature of the universe, not just its size,
not just its structure, but it's overall charged and what
that tells us about the nature of reality and what's
important to the universe For reasons we still don't understand.
The charge seems to be a fundamentally conserved quantity in
the universe, but we still don't actually know what the
(49:42):
total charge of the universe is. Thanks very much Kennie
for joining us today, and thanks everybody for listening.
Speaker 2 (49:48):
Thanks for having me.
Speaker 1 (49:49):
Tune in next time for more science and curiosity. Come
find us on social media where we answer questions and
post videos. We're on Twitter, Discorg, Insta, and now TikTok.
Thanks for listening, and remember that Daniel and Jorge Explain
the Universe is a production of iHeartRadio. For more podcasts
(50:11):
from iHeartRadio, visit the iHeartRadio, app, Apple podcasts, or wherever
you listen to your favorite shows.
Hosts And Creators
Daniel Whiteson
Kelly Weinersmith
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