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What if gravity were much stronger? · Daniel and Kelly’s Extraordinary Universe

0:08
Speaker 1: Hey, Jorge, I have a pitch for a new kind
0:12
Speaker 1: of superhero. I think we're all full up on superheroes.
0:16
Speaker 1: I don't know, but this one, this one stayed with me,
0:18
Speaker 1: will be scientifically accurate. So it'll be like a super physicist.
0:24
Speaker 1: Does he happen to um you know where glasses live
0:27
Speaker 1: in California and be called Daniel not at all? No, No,
0:31
Speaker 1: So you've heard of Magneto, one of the X Men's,
0:34
Speaker 1: those who can control things with magnetism. Of course, So
0:39
Speaker 1: I was thinking, let's have a whole team of superheroes,
0:41
Speaker 1: one for each fundamental force and have them be like accurate. Interesting,
0:46
Speaker 1: except I vote not to be the weak force. So
0:49
Speaker 1: there's going to be like a Gravito then, and a
0:52
Speaker 1: strong Eto. Yeah, and Gravito would be really really really weak,
0:56
Speaker 1: but super patient and in the end will control the
0:59
Speaker 1: shape of the universe. Oh, the bad guys win. That's
1:03
Speaker 1: a twist. You gotta keep the sequels coming until maybe
1:06
Speaker 1: the week Fource gets super strong block twist. Hi'm Poor
1:25
Speaker 1: handmy cartoonist and the creator of PhD Comics. Hi I'm Daniel.
1:28
Speaker 1: I'm a particle physicist and a professor at UC Irvine
1:32
Speaker 1: and I have a superpower, which is that I can
1:34
Speaker 1: sometimes pronounce the title of my job sometimes. What kind
1:38
Speaker 1: of superpower is that it only works in extreme situations
1:41
Speaker 1: through like the Hulk. Well, one listener wrote in to
1:43
Speaker 1: complain that I sometimes mispronounced the word physicist. And I'll
1:47
Speaker 1: admit it's a tricky word. I stumble over it. Physicist, businessicist,
1:53
Speaker 1: It's got a terrible name to it. I guess you
1:56
Speaker 1: never have to say the word very often because you're
1:58
Speaker 1: just surrounded by physicist all the time. Yeah, we say
2:01
Speaker 1: the word physics a lot, but we don't call ourselves
2:04
Speaker 1: physicists very often. You call yourself professors, I guess, explorers
2:10
Speaker 1: of the universe. So when we're feeling grandiose, I see
2:16
Speaker 1: he's walking to the office every day and you're like, hello,
2:18
Speaker 1: fellow explorers of the universe, what's your plan for napping today?
2:23
Speaker 1: Fellow nappers of the universe? Hello, fellow diviners of truth.
2:28
Speaker 1: But you know you are a cartoonist, which means you
2:30
Speaker 1: do cartoons. So you think, since I do physics, I
2:33
Speaker 1: should be a physics ist. But it's not physics ist,
2:36
Speaker 1: it's physicist. Well, English is not my first language, so
2:39
Speaker 1: I'm not even going to pretend to know the difference.
2:42
Speaker 1: And you know, in French, someone who does physics is
2:45
Speaker 1: a physicist, so I think a lot of French physicists
2:48
Speaker 1: call themselves physicians. Interesting. I wonder if people then confuse
2:52
Speaker 1: you with real doctors. I don't real ask people to
2:55
Speaker 1: take off their pants nearly as often. But anyway, we
2:57
Speaker 1: welcome to our podcast. Daniel and Jorge explain the ever.
3:00
Speaker 1: It's a production of I Heart Radio, where we are
3:02
Speaker 1: all explorers of the universe seeking to understand the nature
3:06
Speaker 1: of this bonker's reality, which seems to follow rules as
3:10
Speaker 1: weird and strange as they may be. We encourage you
3:13
Speaker 1: to join us in our journey to understand the nature
3:16
Speaker 1: of those rules and to pick away slowly at the
3:19
Speaker 1: mysteries that remain. Yeah, because it is a pretty mysterious universe,
3:22
Speaker 1: full of head scratching things that happen and mysterious objects
3:26
Speaker 1: out there that are just floating in space, begging us
3:29
Speaker 1: to ask the question what is it? And what's going
3:31
Speaker 1: on with you? And it's not just those of us
3:33
Speaker 1: who can't pronounce our job titles who are curious about
3:36
Speaker 1: the nature of the universe, wondering how the universe works
3:39
Speaker 1: and where it came from and how it all fits
3:40
Speaker 1: together is something almost everybody out there does. Who doesn't
3:44
Speaker 1: want to know where the universe came from and what
3:47
Speaker 1: its final fate will be. Yeah, because curiosity is a
3:50
Speaker 1: very human trade. Everyone looks at the universe and wonderus.
3:55
Speaker 1: You know, what's going on? How did that come to be?
3:57
Speaker 1: And why are we here? And how is it that
3:59
Speaker 1: we are here asking these questions on a podcast, and
4:02
Speaker 1: curiosity is sort of our brand or Hey, we work
4:04
Speaker 1: a lot on projects and encourage people to be curious,
4:07
Speaker 1: from this podcast to our books to our TV show.
4:09
Speaker 1: Do you ever get curious about curiosity? Like? Why are
4:13
Speaker 1: humans so curious? Interesting? Sounds almost like the plot of
4:16
Speaker 1: a movie that's coming out in PBS Kids pretty soon.
4:20
Speaker 1: That sounds like a wonderful journey to me. It is.
4:24
Speaker 1: That is the name of our special for eleanor Wonderus Fly,
4:28
Speaker 1: which is coming out in April, so if you have kids,
4:30
Speaker 1: but please take it out. It's a movie we wrote,
4:32
Speaker 1: It's got awesome songs in it, and it's all about
4:34
Speaker 1: why we ask questions, and we ask questions about the universe,
4:37
Speaker 1: but we also want to hear about your questions. The
4:40
Speaker 1: fact that you're listening to this podcast means that you
4:43
Speaker 1: are curious not just about how butterfly wings evolve, but
4:46
Speaker 1: about how space and time fit together, what we can
4:49
Speaker 1: see at the edge of the universe, and how the
4:51
Speaker 1: universe might fundamentally be different if we tweaked the deepest
4:54
Speaker 1: laws of nature. So, if you are curious about how
4:57
Speaker 1: the universe works and you have a question that you
4:59
Speaker 1: haven't heard an inswer two please it'll be shy right
5:02
Speaker 1: to us two questions at Daniel and Jorge dot com.
5:05
Speaker 1: We answer everybody's questions. Yeah, because everybody has questions. This
5:08
Speaker 1: is a very active podcast. I feel like you cannot
5:11
Speaker 1: just listen to us talking about questions or answering questions.
5:14
Speaker 1: You can also ask questions and you will answer them,
5:16
Speaker 1: and sometimes we even answer them here on the podcast. Yeah,
5:19
Speaker 1: some questions are super fun and I think other listeners
5:22
Speaker 1: would like to hear the answer to them, or they're
5:24
Speaker 1: a little bit tricky and I have to go read
5:26
Speaker 1: something or think carefully about exactly how to praise the
5:29
Speaker 1: answer because there's a lot of subtleties involved, and there's
5:32
Speaker 1: just a lot of fun to talk about on the podcast.
5:34
Speaker 1: Because I know that at least one person out there
5:36
Speaker 1: wants to hear the answer. Yeah, and so today on
5:38
Speaker 1: the podcast will be tackling listener questions. Number twenty seven
5:48
Speaker 1: is twenty seven time we answer listening to questions, Daniel,
5:51
Speaker 1: and I feel like maybe at this point which is
5:52
Speaker 1: dropped the numbers and just go with like, you know,
5:55
Speaker 1: just a fun subtitle, you know, like they do in
5:57
Speaker 1: movies now where there are so many sequels that you
5:59
Speaker 1: don't use. No verst listener questions, no way home and
6:03
Speaker 1: listener questions, return listeners, strike back, listener questions, the questions awakened.
6:12
Speaker 1: Hopefully we won't get to listen to your questions the
6:15
Speaker 1: last question no hopefully yes? Right, but isn't that the
6:19
Speaker 1: goal of all of physics and physicists is to get
6:23
Speaker 1: to the last question ever know the goals to answer
6:25
Speaker 1: today's questions, which will generate tomorrow's questions. We live for questions.
6:29
Speaker 1: We don't want to figure everything out. We want to
6:31
Speaker 1: continuously ask questions. Right, You just want to be able
6:34
Speaker 1: to say your physicists forever. Today I can't say I'm
6:38
Speaker 1: a physicist, so I'm hoping to one day figure that out.
6:43
Speaker 1: You gotta activate that superpower. There. You got to figure
6:46
Speaker 1: out your triggers. But yeah, we have some awesome questions
6:49
Speaker 1: here from listeners like you and there are they're all
6:52
Speaker 1: over the place, or about the observable universe and the
6:55
Speaker 1: cosmic microwave background there about gravity and the forces, and
6:58
Speaker 1: they're also about the disappearing universe. And Daniel, just to
7:03
Speaker 1: be clear, nobody was required to take off their pants
7:06
Speaker 1: to ask these questions. Right, we have a strict Pence
7:08
Speaker 1: policy in this podcast. Right, I'm wearing pants. We don't
7:11
Speaker 1: actually have a strict pants policy. So I have no idea.
7:13
Speaker 1: I can make no statement about what pants these people
7:16
Speaker 1: are or are not wearing. But if you'd like, in
7:19
Speaker 1: the future, I will inquire about what people are wearing
7:22
Speaker 1: when they record these questions. That's maybe not I think
7:26
Speaker 1: we should be pants agnostic. Yeah, yeah, let's be pant
7:29
Speaker 1: pant agnostic. Yeah, alright, well let's jump into it. Our
7:32
Speaker 1: first question here comes from Jeff, and Jeff has a
7:35
Speaker 1: question about the observable universe and the cosmic microwave background. Hi, Daniel,
7:41
Speaker 1: Jorge and special guests contributors. I'm Jeff from Alltown, p A.
7:46
Speaker 1: If the observable universe extends only as far as light
7:50
Speaker 1: as that time to reach us, and that faston the
7:54
Speaker 1: light expansion precludes us from ever seeing galaxies beyond. How
7:59
Speaker 1: is it we can still image the cosmic microwave background,
8:04
Speaker 1: which should predate any cosmic structures. Thank you again for
8:08
Speaker 1: keeping us educated, wondering, curious, and entertained. Awesome. Thank you
8:15
Speaker 1: Jeff for that question, and a shout out to Allentown, Pennsylvania. Daniel.
8:18
Speaker 1: I feel like Jeff asked a pretty good gotcha question,
8:21
Speaker 1: Like I'm wondering how we're going to answer this one.
8:23
Speaker 1: Jeff has a question which really exposes a lot of
8:25
Speaker 1: subtle issues in understanding how far we can see in
8:29
Speaker 1: the universe as the universe is expanding, and as that
8:33
Speaker 1: expansion is accelerating, and so there are a couple of
8:36
Speaker 1: interesting issues here, like what is the oldest thing we
8:39
Speaker 1: can see? And what is it that we cannot see
8:43
Speaker 1: in the universe? Right right, There's a lot of sort
8:45
Speaker 1: of concepts here in this question, Like, first of all,
8:47
Speaker 1: it's the idea of the observable universe. Then also the
8:52
Speaker 1: expansion of the universe, which is presumably maybe at some
8:54
Speaker 1: point going faster than light, and then there's also the
8:57
Speaker 1: concept of the cosmic microwave background, which is kind of
9:00
Speaker 1: like the revenant light from The Big Bang exactly. And
9:04
Speaker 1: so the basic concept to understand is that as we
9:07
Speaker 1: look further and further away, we're seeing things that are
9:10
Speaker 1: older and older. We're looking back in time, and that's
9:13
Speaker 1: just because it takes time for light to get to
9:16
Speaker 1: us from Earth. So we're looking at a distant star
9:19
Speaker 1: that's really far away. We're not seeing it as it
9:22
Speaker 1: is today. We're seeing it as it was when that
9:24
Speaker 1: light left it, and it doesn't look like that today,
9:27
Speaker 1: and it's probably in a different location today. And so
9:30
Speaker 1: as we look further away, we see further back in time,
9:34
Speaker 1: which is actually super awesome and really useful for doing
9:37
Speaker 1: science because we get to see the history of the universe,
9:40
Speaker 1: not just the way it looks today. Right. Yeah, And
9:42
Speaker 1: the whole reason is that light takes a while to
9:44
Speaker 1: get two places. Right, Like, light isn't infinitely fast. It
9:48
Speaker 1: has the speed of light and it's a it's limited,
9:50
Speaker 1: and so space is so big that there's still stuff
9:53
Speaker 1: like coming at us, like coming at us that started
9:56
Speaker 1: maybe billions and billions of years ago. That's right. There
9:59
Speaker 1: are f photons arriving today that left their location billions
10:03
Speaker 1: of years ago and they are just now arriving. You
10:05
Speaker 1: can imagine, like our past light cone. You know, things
10:08
Speaker 1: that are closer can have left more recently and be
10:11
Speaker 1: arriving right now, and things that were really far away
10:15
Speaker 1: the light had to leave a long time ago in
10:18
Speaker 1: order to reach us right now. But those two photons
10:20
Speaker 1: can be arriving at the same moment from different locations
10:23
Speaker 1: and also different times in the past. Yeah, and it's
10:26
Speaker 1: sort of coming at us from all directions, which is
10:29
Speaker 1: which makes it more of a bubble, right than a
10:31
Speaker 1: cone kind of right, it's more of like a bubble
10:33
Speaker 1: around us, which is as far as we can see,
10:35
Speaker 1: because anything further the light just hasn't reached us. Yeah.
10:38
Speaker 1: In one dimensions, it would be like a light triangle,
10:41
Speaker 1: and two dimensions would be like a light cone. But
10:43
Speaker 1: you're right, in three dimensions, it's sort of harder to imagine.
10:46
Speaker 1: It's like a conoid. It would be the geometrical term.
10:49
Speaker 1: I think you need a superpower just to pronounce that. There.
10:54
Speaker 1: And so as we look further back in time, we're
10:56
Speaker 1: looking further into the past, and so we can see,
10:58
Speaker 1: for example, how Gala seas formed. We can see things
11:01
Speaker 1: that happened a billion years after the Big Bang, we
11:04
Speaker 1: can see things that happened five million years after the
11:07
Speaker 1: Big Bang. We can keep looking further and further back
11:10
Speaker 1: in time, right, And so there's this sort of bubble
11:13
Speaker 1: around us of things we can see. But also at
11:15
Speaker 1: the same time, the universe is expanding, so the bubble
11:19
Speaker 1: and the things in it are sort of flying away
11:22
Speaker 1: from us, or at least getting stretched away from us,
11:24
Speaker 1: which is kind of makes it tricky, right, It does
11:26
Speaker 1: make it tricky. The whole thing is pretty complicated and
11:29
Speaker 1: hard to hold in your head. First, let's imagine the
11:31
Speaker 1: universe was not expanding. Then, you know, the bubble we
11:33
Speaker 1: could see would be growing as time went on, and
11:36
Speaker 1: we have no problem seeing the cosmic marcrowave background. We
11:39
Speaker 1: could see things before structure formed. Right, You don't have
11:43
Speaker 1: to see a galaxy in order to see stuff. You
11:45
Speaker 1: just need to see light. So the cosmic microwave background
11:49
Speaker 1: is light from the first plasma before structure was formed.
11:52
Speaker 1: When the universe became transparent. We can't really see before
11:55
Speaker 1: that because the universe was opaque, but we can see
11:59
Speaker 1: past the earliest galaxies all the way to the cosmic
12:02
Speaker 1: microwave background radiation. Right, So that's if the universe was
12:06
Speaker 1: not expanding. Now Jeff says, well, the universe is expanding,
12:09
Speaker 1: and it's expanding fast in the light, which means some
12:12
Speaker 1: parts of the universe we will never see. And he's right.
12:15
Speaker 1: There are things that are so distant past, like sixty
12:18
Speaker 1: five billion light years, where the light will never reach
12:20
Speaker 1: us because the universe is expanding. As we'd like to say,
12:24
Speaker 1: you know, if Hussain Bolt is running towards you and
12:26
Speaker 1: somebody's laying track in front of him faster than he's running,
12:29
Speaker 1: he's never going to get to you. So there are
12:31
Speaker 1: photons moving at us, but they're moving through parts of
12:34
Speaker 1: the universe that are receding fast in the speed of light,
12:36
Speaker 1: so they will never reach us. Right. It's like we
12:39
Speaker 1: can see this bubble around us, but there's also sort
12:41
Speaker 1: of another bubble that's maybe bigger than that of stuff
12:44
Speaker 1: we haven't seen yet. And then we'll also never see
12:48
Speaker 1: because at the same time that we're seeing this bubble,
12:50
Speaker 1: space is expanding, and so there's maybe stuff out there
12:53
Speaker 1: beyond the bubble we can see that may we'll never see, right,
12:56
Speaker 1: because it's moving it too fast. That's right. The current
12:58
Speaker 1: edge of the observable universe is forty six billion light
13:01
Speaker 1: years away, but there's another edge sixty three billion light
13:05
Speaker 1: years away, and stuff beyond that we will never see, Like,
13:08
Speaker 1: it doesn't matter how long you wait, we will never
13:11
Speaker 1: see it because the universe is expanding so fast that
13:13
Speaker 1: those photons will always be moving through space that's moving
13:17
Speaker 1: away from us faster than the speed of light, and
13:20
Speaker 1: so we would just never see it, assuming, of course,
13:23
Speaker 1: the current cosmological model is correct and that expansion continues
13:26
Speaker 1: in the same way that it does. But then Jeff's
13:28
Speaker 1: question is, so, then how is it possible to see
13:31
Speaker 1: the CNB If there are parts of the universe that
13:34
Speaker 1: are moving away from us so fast, we'll never see them, right, Yeah,
13:37
Speaker 1: that's kind of mind blowing to think about. Like, at
13:38
Speaker 1: sixty five billion light years, there's like a son right
13:42
Speaker 1: there that's shining and it's throwing a photon at us,
13:45
Speaker 1: but that photon is like sort of fighting against the
13:48
Speaker 1: stretching of space and just will never get to us.
13:51
Speaker 1: That's right. It's moving through its space at the speed
13:54
Speaker 1: of light, but the distance between us and that photon
13:57
Speaker 1: is actually increasing. Right, The proper stance between us and
14:01
Speaker 1: that photon is growing even though it's moving through space
14:04
Speaker 1: towards us, right, because space in front of it is expanding.
14:07
Speaker 1: It's like there's news space growing between us and that
14:10
Speaker 1: photon rate that's higher than three hundred million meters per second. Right.
14:16
Speaker 1: And if we were relying on seeing light from the
14:19
Speaker 1: CNB that came from super far away cosmic marketway background plasma,
14:23
Speaker 1: then Jeff is right, we would never be able to
14:25
Speaker 1: see it. What we are seeing when we look at
14:27
Speaker 1: the CNB is not light that was emitted from that
14:30
Speaker 1: far away. It was actually emitted from pretty close to us.
14:33
Speaker 1: It's just taken forever to get here because the universe
14:36
Speaker 1: has expanded while those photons fly through the universe. Right.
14:40
Speaker 1: I think maybe what Jeff is thinking is that, you know,
14:43
Speaker 1: there is a background of like light that came from
14:46
Speaker 1: the Big Bang, And you know the word background means
14:48
Speaker 1: like it's in the back, right, So he's probably manna
14:51
Speaker 1: be thinking that this cosmic background comes from like way
14:54
Speaker 1: further out, like since the further out we look, the
14:57
Speaker 1: further back in time we look. He's thinking maybe the
15:00
Speaker 1: source of this light is like the you know, the
15:03
Speaker 1: basically the background of the universe, and so he's wondering, like,
15:06
Speaker 1: if the background is moving away from us faster than light,
15:09
Speaker 1: then how can that background get to us? But you're saying,
15:11
Speaker 1: I think, is that it's not really like in the back,
15:14
Speaker 1: it's like everywhere. It is, in fact, everywhere the CNB
15:17
Speaker 1: was admitted everywhere. There's a patch of the universe where
15:20
Speaker 1: we are right now. There used to be plasma right here,
15:23
Speaker 1: and it emitted CNB light, and that CNB light is
15:26
Speaker 1: flying away from us, and it's been flying away from
15:29
Speaker 1: us fo the whole universe, and it's now almost forty
15:32
Speaker 1: six billion light years away right, not exactly forty six
15:35
Speaker 1: billion light years, because it was admitted a little bit
15:38
Speaker 1: after the universe started, like you know, a few hundred
15:40
Speaker 1: thousand light years. And similarly, the CNB light that we
15:43
Speaker 1: are seeing right now was emitted from stuff which is
15:46
Speaker 1: now almost at the edge of the observable universe, right,
15:50
Speaker 1: so it did have time to get here. It's within
15:52
Speaker 1: the edge of the observable universe. Interestingly, though, when it
15:56
Speaker 1: admitted it, it was much much closer, like it was
15:59
Speaker 1: probably only a few tens of millions of light years
16:02
Speaker 1: away when it emitted that light. But the universe has
16:05
Speaker 1: been expanding so much that took thirteen billion years to
16:09
Speaker 1: cross what was originally forty two million light years, right.
16:13
Speaker 1: The same mystery for the stars that are at that business, right,
16:15
Speaker 1: like the library getting from the edge of the servile universe,
16:18
Speaker 1: is from stars that they used to be closer to us. Exactly.
16:21
Speaker 1: So the patch of the universe which now occupies like
16:24
Speaker 1: a sphere with radius forty six billion light years, used
16:27
Speaker 1: to be much much smaller. At the universe is expanding rapidly,
16:31
Speaker 1: and so basically we are seeing what used to be
16:33
Speaker 1: a tiny little bubble of the universe. Something which was
16:37
Speaker 1: fifty million light years away from us at the very
16:39
Speaker 1: beginning of the universe is now outside the edge of
16:43
Speaker 1: the observable universe. Will probably never see it because it's
16:45
Speaker 1: all expanded. So the CNB light we're seeing today started
16:48
Speaker 1: out forty two million light years away, has been struggling
16:51
Speaker 1: to get to us for billions of years, and has
16:53
Speaker 1: now just arrived. We see it today, and we think
16:56
Speaker 1: the plasma that admitted it that stuff is now forty
17:00
Speaker 1: six billion light years away, right. I think that maybe
17:02
Speaker 1: the key point here is that the cosmic microwave background
17:06
Speaker 1: was sort of like made everywhere in all directions at
17:09
Speaker 1: the same time, you know, Like it wasn't like one
17:11
Speaker 1: event that flashed and then now the light is getting
17:14
Speaker 1: to us. It's like even where we are right now,
17:17
Speaker 1: like this batch of space that I'm occupying here in
17:20
Speaker 1: my podcast studio, like this space around me generated some
17:25
Speaker 1: microwave background radiation at some point in the past, but
17:28
Speaker 1: now that light has just gone right. It's like it's
17:31
Speaker 1: when when, and in all directions. But the same thing
17:34
Speaker 1: happened all over space, like between here and the observable
17:37
Speaker 1: universe the edge of it. There was stuff being generated
17:40
Speaker 1: at every point. Yeah, And I think a lot of
17:42
Speaker 1: people have a misconception that the universe started as a
17:45
Speaker 1: point and then expanded and at some moment it was
17:48
Speaker 1: this little ball of plasma that admitted that light, and
17:51
Speaker 1: they wonder, like, why is it we can see it
17:53
Speaker 1: right now, and you're write the answer is that that's true.
17:57
Speaker 1: But it wasn't just a little ball. The whole univer
18:00
Speaker 1: verse was filled with this plasma. The big band wasn't
18:02
Speaker 1: just when one spot, it was everywhere, and so everywhere
18:06
Speaker 1: in the universe had these little balls of plasma. And
18:08
Speaker 1: as time goes on, we continue to see the CMB,
18:11
Speaker 1: but we see different slices of it. We see light
18:14
Speaker 1: from different pieces of that infinite universe plasma. Right, I
18:17
Speaker 1: wonder if I have a good analogy, is kind of
18:19
Speaker 1: like a rubber band, Like if you're stretching a rubber band,
18:21
Speaker 1: but also all of the rubber band was emitting light.
18:25
Speaker 1: You would see the light that your patch of space emitted,
18:28
Speaker 1: and you're part of the rubber band, but you also
18:30
Speaker 1: over time be seeing the light those generated over other
18:34
Speaker 1: parts of the rubber band. Yeah, and if you think
18:36
Speaker 1: about what's going to happen in a very very far future,
18:38
Speaker 1: we will always see some CMB, but you know, there
18:41
Speaker 1: is a limit of what fraction of the universe we
18:43
Speaker 1: will see. So eventually the CNB will just get red
18:46
Speaker 1: shifted into invisibility. Like the CNB right now is very
18:51
Speaker 1: long wavelengths compared to the light that was emitted at
18:53
Speaker 1: the time. It used to be a very hot plasma
18:56
Speaker 1: hundreds of thousands of degrees. It used to be you know,
18:59
Speaker 1: very high frequent and see wavelength, and it's gotten red
19:02
Speaker 1: shifted down to very long wavelengths, down to like two
19:05
Speaker 1: point seven degrees Calvin. So that's just going to keep happening.
19:08
Speaker 1: The wavelength is gonna get longer and longer until eventually
19:10
Speaker 1: becomes essentially invisible. Right, And I think what's interesting what
19:13
Speaker 1: you just said is that you know, the cosmic microwave background,
19:17
Speaker 1: then we'll be changing over the next couple of billion years,
19:19
Speaker 1: like the picture of it is gonna wiggle and ripple
19:22
Speaker 1: because it's coming from different parts of the universe each
19:25
Speaker 1: time you take the picture exactly, and so as we
19:27
Speaker 1: look at it it does change that it doesn't change
19:29
Speaker 1: very rapidly. Um. You know, we took the original picture
19:32
Speaker 1: of the CNB thirty years ago, and then we're taking
19:35
Speaker 1: more and more refined pictures of it, and over those
19:38
Speaker 1: time periods it doesn't really change in any significantly observable way.
19:41
Speaker 1: So we are seeing slightly different slices of the universe.
19:44
Speaker 1: But you know, in the way that like a star
19:46
Speaker 1: doesn't change very much when you look at it from
19:47
Speaker 1: one year to the next. On these time scales of
19:50
Speaker 1: twenty thirty years, nothing really is changing. If we keep
19:53
Speaker 1: watching it for millions and billions of years and keep
19:56
Speaker 1: doing astronomy for that long and then we will see
19:58
Speaker 1: different slices of the universe. M M. Yeah, And I
20:01
Speaker 1: think Jeff is right that at some point in the future,
20:05
Speaker 1: like the observable universe is going to reach the point
20:07
Speaker 1: where we can't see anything, including the cosmic microwave background. Right, Like,
20:11
Speaker 1: at some point in the future, um, this cosmic microwave
20:15
Speaker 1: is going to disappear. I think we'll always be able
20:17
Speaker 1: to see some CNB, but it will just red shift
20:20
Speaker 1: away to infinity. There's always going to be some point
20:23
Speaker 1: in the universe where light is just now arriving from
20:26
Speaker 1: wherever it was admitted. And since the CNB was everywhere
20:29
Speaker 1: in the universe, there will always be some CNB whose
20:33
Speaker 1: light is just now arriving. But that's going to get
20:35
Speaker 1: more and more stretched out as time goes on, and
20:38
Speaker 1: eventually you'll disappear, right, let's get stretched into nothingness. Oh yes,
20:42
Speaker 1: it disappear in the sense that the wavelength will reach
20:45
Speaker 1: infinity and therefore it be like essentially unobservable. Like if
20:48
Speaker 1: the CNB has a wavelength of the galaxy, then you
20:51
Speaker 1: need a galaxy size detector to see it, and so yeah,
20:54
Speaker 1: it would be invisible to us MM, so it will
20:56
Speaker 1: sort of disappear, So like if humans had come around,
20:59
Speaker 1: may be a couple of billion years later, whichever alien
21:02
Speaker 1: species comes up a few billion years from now may
21:05
Speaker 1: not maybe even be able to see this kind of
21:08
Speaker 1: baby picture of the universe. Yeah, And whenever I think
21:10
Speaker 1: about that, I realized it's lucky that we live now
21:13
Speaker 1: so we can sort of see this stuff in the universe.
21:16
Speaker 1: It makes me wonder what used to be observable in
21:18
Speaker 1: the universe five billion years ago that now we will
21:21
Speaker 1: never see and couldn't discover. What pictures are we missing?
21:25
Speaker 1: What clues? Will we never get to the deep nature
21:28
Speaker 1: of the universe because we came along fourteen billion years
21:31
Speaker 1: after the party started. Yeah, we missed the cosmic microwave
21:35
Speaker 1: foreground because we got here too late. We procrastinated Daniel
21:39
Speaker 1: in our evolution. We shouldn't have spend so much time
21:42
Speaker 1: in the primordial sludge. Yeah, it was pretty warm and cozy.
21:45
Speaker 1: I gotta say, all right, Well that answers the question
21:48
Speaker 1: for Jeff Um. You're right, the same bee will disappear
21:51
Speaker 1: one day, but not for a while because we are
21:54
Speaker 1: still seeing it and because it was generated by every
21:57
Speaker 1: point in space. All right, let's get into our next question, Um,
22:00
Speaker 1: this one is about gravity, magnetism and the different forces.
22:04
Speaker 1: So we'll get to that, but first let's take a
22:06
Speaker 1: quick break. Al Right, we are answering listener questions. Today.
22:22
Speaker 1: We talked about a great question about the server universe
22:25
Speaker 1: and the cosmic microwave background, and now we have a
22:28
Speaker 1: question here about the forces. And this is kind of
22:30
Speaker 1: what you're referencing before, Daniel, about superheroes based on the
22:33
Speaker 1: different forces, because we have different forces in the universe. Yeah,
22:37
Speaker 1: we have these different forces in the universe, and we
22:39
Speaker 1: don't understand why some of them are stronger than others
22:42
Speaker 1: and some of them are weaker. And we think that
22:44
Speaker 1: maybe in the early universe they might have all been
22:46
Speaker 1: one force that had one strength, but we're not sure. Interesting,
22:51
Speaker 1: we had the Avengers before The Avengers was the prequel.
22:55
Speaker 1: It's sort of like, you know, how the Power Rangers
22:57
Speaker 1: can come together into one superpower Ranger. Uh huh, we
23:01
Speaker 1: think the reverse might have happened in our universe. Interesting,
23:04
Speaker 1: it's a prequel. All right. Well, then let's get to
23:06
Speaker 1: the question. This one is from on God who wonders
23:09
Speaker 1: about gravity and magnetism. Hi, Daniel and Jorge really like
23:12
Speaker 1: your podcast because it teaches so much about physics in space.
23:17
Speaker 1: So I got me. I'm wondering what would happen if
23:22
Speaker 1: gravity was as strong as magnetism would So, if the
23:27
Speaker 1: universe started with gravity being as strong as magnetism, what
23:32
Speaker 1: would happen? Would the universe even start expanding or not?
23:37
Speaker 1: Or were it get even donser somehow? Also, what would
23:40
Speaker 1: happen if right now, if the universe is normal, but
23:45
Speaker 1: then right now gravity all of a sudden becomes as
23:50
Speaker 1: strong as magnetism, where it create mega black holes and
23:54
Speaker 1: then things that are so done that time goes backwards.
23:58
Speaker 1: But the bending of the like cone? What would happen?
24:02
Speaker 1: Thank you very much, good luck with the podcast. Oh man,
24:05
Speaker 1: what an awesome question. Thank you on God you do?
24:07
Speaker 1: You have so much going on in your in your
24:09
Speaker 1: little head. That's amazing. That is a future physicist for sure. Yeah,
24:14
Speaker 1: let's get him practicing the how to say the word
24:16
Speaker 1: physicists as soon as possible. Clearly not a prove requisite, however,
24:20
Speaker 1: for becoming one. So maybe it should be Danny should
24:24
Speaker 1: be pants essential pronunciation, not necessarily. I mean, how are
24:28
Speaker 1: you going to recruit more of you if you can't
24:30
Speaker 1: even say the word. So you're saying we should have
24:34
Speaker 1: more physicists in the world. I'm saying you should have
24:37
Speaker 1: more trained physicists. And how to pronounce your job title.
24:41
Speaker 1: It's all about priorities. Yeah, but their question is pretty interesting, uh,
24:46
Speaker 1: And it's about the forces. So the main question is
24:49
Speaker 1: what if gravity was as strong as magnetism? And so
24:52
Speaker 1: gravity is one force, magnetism is another force. And actually
24:55
Speaker 1: gravity you always say is very weak compared to magnetism. Yeah,
25:00
Speaker 1: gravity is the weakest of the forces by a long shot,
25:04
Speaker 1: like not by a tiny little bit or a factor
25:07
Speaker 1: of ten, but by a factor of ten to the
25:10
Speaker 1: thirties seven. You know, like a billion is ten with
25:13
Speaker 1: twelve zeros in front of it. This is ten with
25:16
Speaker 1: thirty seven zeros in front of it. It's really a
25:19
Speaker 1: huge number. They're just like not even on the same
25:22
Speaker 1: playing field at all. Yeah, Like magnetism is the thirty
25:25
Speaker 1: seven orders of magnitude stronger than gravity, meaning like if
25:28
Speaker 1: you have two things that have mass and electric charge,
25:31
Speaker 1: like the force they feel because of the electric charge
25:34
Speaker 1: is much much higher. Yeah, and you're using electric charge
25:37
Speaker 1: there because you know that magnetism is actually part of
25:39
Speaker 1: a unified idea of electro magnetism. Magnetism by itself isn't
25:44
Speaker 1: really a holistic concept. You need electricity to understand it
25:47
Speaker 1: as well. And that's because from different like frames of reference,
25:50
Speaker 1: the same phenomena will produce electricity or magnetism. So really
25:54
Speaker 1: it's one holistic concept we talk about. And as you say,
25:57
Speaker 1: magnetism is much much stronger than gravity. And you can
26:00
Speaker 1: discover this yourself in your kitchen. You know, you have
26:03
Speaker 1: kitchen magnets on your fridge, right, and they stick to
26:05
Speaker 1: your fridge. They don't fall down, even though the entire
26:08
Speaker 1: mass of the Earth, right, the whole planet is tugging
26:11
Speaker 1: on them. And yet a tiny kitchen magnet can totally
26:14
Speaker 1: resist that because magnetism is that much more powerful than gravity. Yeah,
26:19
Speaker 1: Like the kitchen magnet is being pulled towards the Earth
26:21
Speaker 1: by the whole earth gravity, but it's being pulled up
26:25
Speaker 1: by its magnetic attraction to the fridge. Yeah. I like
26:28
Speaker 1: to think that every time I get up in the morning,
26:30
Speaker 1: I'm beating the whole Earth. That's right. Bananas apparently are
26:35
Speaker 1: more powerful than the Earth. You can defeat its gravity.
26:39
Speaker 1: Yea banana and cereal, they'll get me up in the
26:41
Speaker 1: morning every day, and it beats gravity. And the other
26:44
Speaker 1: forces are also not equal, right. The strong force is
26:47
Speaker 1: a hundred and thirties seven times more powerful than electromagnetism,
26:52
Speaker 1: which is even more powerful than the weak force. But
26:54
Speaker 1: all of those are basically the same compared to gravity,
26:57
Speaker 1: which is almost zero compared to the other forces. And
27:00
Speaker 1: yet gravity is the one that dominates the structure of
27:04
Speaker 1: the universe, right. The nature of the Solar System, the
27:06
Speaker 1: shape of galaxies, all that is because of gravity. And
27:09
Speaker 1: that's because there is a lot of mass in the
27:11
Speaker 1: universe and gravity is very, very patient, and eventually it wins. Yeah.
27:15
Speaker 1: And the main reason, I know we've talked about this
27:17
Speaker 1: before is that for the other forces, they sort of
27:19
Speaker 1: cancel each other out. Like there's a plus you know,
27:23
Speaker 1: a magnetic force and a negative magnetic force, and if
27:25
Speaker 1: you're a plus charge or minus charge, you would feel
27:28
Speaker 1: one of them. But because they're able to cancel, they
27:31
Speaker 1: sort of cancel out generally in the universe. But gravity,
27:35
Speaker 1: it's always attracting. Yeah, Gravity, if you think about in
27:37
Speaker 1: terms of a force rather than the curvature of space time,
27:40
Speaker 1: it's basically just got one kind of charge, right, mass
27:43
Speaker 1: is always positive, and so all it can do is
27:45
Speaker 1: attract the other forces as you say it, positives and negatives,
27:49
Speaker 1: or you know, the strong force has three different kinds
27:52
Speaker 1: of color, but they can be balanced out. You can
27:54
Speaker 1: get things that are effectively neutral. It's impossible to get
27:57
Speaker 1: everything neutral gravitationally, unless you like spread everything out through
28:02
Speaker 1: the universe totally homogeneously. There will always be a gravitational
28:05
Speaker 1: force that tugs on things, so eventually gravity will wait,
28:09
Speaker 1: it will pull everything into a black hole, right. I
28:11
Speaker 1: think we covered this in our book or one of
28:12
Speaker 1: our books, where like if the whole Earth was positively
28:16
Speaker 1: charged and the whole Sun was negatively charged, like we'd
28:19
Speaker 1: be toasts, Like the whole Earth would just fly into
28:22
Speaker 1: the Sun super fast, because that's how strong the electroplanknetic forces.
28:27
Speaker 1: But because you know, we have an equal number of
28:30
Speaker 1: plus and minus force charges here on Earth and almost
28:33
Speaker 1: equal mound in the Sun like to the Earth, the
28:36
Speaker 1: Sun is neutral. It doesn't feel any electromagnetic attraction or
28:40
Speaker 1: repulsion exactly. And the reason is that mostly the universe
28:43
Speaker 1: was formed from neutral stuff because electromagnetism is so strong
28:47
Speaker 1: that charged particles sought each other out to balance each
28:51
Speaker 1: other out early on in the universe, and so the
28:54
Speaker 1: universe neutralized from the point of view of electromagnetism, long
28:57
Speaker 1: before gravity really had anything to say about anything. Yeah,
29:01
Speaker 1: and so I'm guess question is that gravity is weaker
29:03
Speaker 1: than the electromagnetic force. But what if it wasn't, Like,
29:06
Speaker 1: what if it was stronger at the beginning of time?
29:09
Speaker 1: And what would happen if it suddenly got stronger? And
29:11
Speaker 1: now it's a great question, and I love running these
29:14
Speaker 1: sort of mental simulations, like what would the universe look
29:17
Speaker 1: like if the knobs were different? And it's a really
29:19
Speaker 1: important question because let's just think about, like, why are
29:22
Speaker 1: the knobs set the way they are? Is it possible
29:24
Speaker 1: they could have been set differently or not? And so
29:27
Speaker 1: in this case, if gravity was just as strong as electromagnetisms,
29:31
Speaker 1: so we're cranking gravity up by ten to the thirty seven,
29:35
Speaker 1: then the whole universe would look very different from the
29:37
Speaker 1: very beginning. Remember that the structure of the universe that
29:40
Speaker 1: we see now galaxies and stars and planets and all
29:43
Speaker 1: this stuff, took a long time to form because gravity
29:46
Speaker 1: is so weak. So gravity was sort of on the
29:48
Speaker 1: sidelines while the universe was cooling, and all these particles
29:52
Speaker 1: buzzing around positive negative charges. The universe cools and the
29:55
Speaker 1: other forces are sort of in charge. So the strong force,
29:58
Speaker 1: for example, pulls together a bunch of quarks to make
30:01
Speaker 1: them neutral from the strong force point of view. So
30:03
Speaker 1: you get like protons, right, which are neutral from the
30:06
Speaker 1: strong force. And then electromagnetism takes over and it pulls
30:09
Speaker 1: protons and electrons together to make neutral atoms like hydrogen.
30:13
Speaker 1: And then finally, thousands and millions of years later, gravity
30:17
Speaker 1: does its job and clumps those together into stars. Now,
30:21
Speaker 1: if gravity was as strong as electromagnetism, then it would
30:24
Speaker 1: have been active much earlier on. It wouldn't have been
30:26
Speaker 1: waiting while electromagnetism form neutral atoms. It would have started
30:30
Speaker 1: clumping protons together before they even neutralized. You would get
30:33
Speaker 1: these like huge positively charged masses. Well, I guess you
30:37
Speaker 1: have to be clear, Like, it's not like gravity turn
30:39
Speaker 1: on at toping, Like it was always there from the beginning.
30:42
Speaker 1: It was just so weak compared to the electroc bannetic
30:44
Speaker 1: corps that basically the universe sort of egbarded for a
30:47
Speaker 1: long time. Exactly. It was irrelevant for a long time
30:49
Speaker 1: because more powerful forces were on the field. Only when
30:53
Speaker 1: those forces finished doing their jobs could gravity even play
30:57
Speaker 1: in the game, because it was the only thing left
30:59
Speaker 1: on the fee basically, And so if gravity was much
31:02
Speaker 1: much stronger than it would have been relevant earlier on
31:05
Speaker 1: and hydrogen, for example, might not have formed in the
31:08
Speaker 1: same way because gravity would have like tugged all those
31:12
Speaker 1: protons together instead of letting them seek out their electrons.
31:16
Speaker 1: And I don't want to overstate it, as you say,
31:18
Speaker 1: gravity is around, and even though it's weaker than the
31:21
Speaker 1: other forces, it does play a role in the early universe.
31:24
Speaker 1: We can see its effect on like the slashing of
31:26
Speaker 1: the barry on plasma. It just wasn't dominant, right or
31:29
Speaker 1: I wonder if even like neutrons or protons would have formed,
31:32
Speaker 1: like could gravity somehow mess up with the way the
31:34
Speaker 1: quarks like buying together could potentially if it was strong enough.
31:37
Speaker 1: In this scenario, though, gravity is as strong as electromagnetism,
31:42
Speaker 1: which is weaker than the strong force, So then in
31:44
Speaker 1: this scenario the strong force would still be stronger than gravity,
31:47
Speaker 1: so you would still form protons of course, would feel
31:49
Speaker 1: those color forces more strongly than they would feel gravity,
31:53
Speaker 1: so they would still form together. But then if it's
31:55
Speaker 1: the same strength as electromagnetism, then you know, gravity and
31:59
Speaker 1: elect a magnetism would be at a tug of war
32:02
Speaker 1: very early on, and you get very weird structures, So
32:05
Speaker 1: the universe would look totally different. You might get like
32:07
Speaker 1: black holes forming very very early on because gravity would
32:11
Speaker 1: be so powerful. Well, I feel like these physics scenarios
32:13
Speaker 1: never end well for us, Like it's always some crazy
32:18
Speaker 1: universe that comes out of it. It wouldn't end well
32:21
Speaker 1: for us. It would form some other, very different universe.
32:24
Speaker 1: It's hard to imagine what like stable structures would form,
32:27
Speaker 1: what it would look like. It might take trillions of
32:29
Speaker 1: years to develop complexity or only last for millions of years,
32:33
Speaker 1: we don't know, And it might evolve very very different
32:35
Speaker 1: forms of life that we can't even imagine, forms of
32:38
Speaker 1: life which you know would have podcasts and speculate about
32:41
Speaker 1: what the universe would be like if gravity was much weaker.
32:44
Speaker 1: I like our podcast better there, but I think I
32:48
Speaker 1: think maybe the main question here is like would you
32:50
Speaker 1: even see structure in this universe or would it all
32:53
Speaker 1: just immediately or very early on, just become all black
32:56
Speaker 1: holes Because if gravity is stronger than write things things,
32:59
Speaker 1: blacks are easier to make, black holes are easier to make.
33:02
Speaker 1: Although to make a black hole you need a lot
33:04
Speaker 1: of mass. And so one question is like, are you
33:07
Speaker 1: gonna get a lot of small clumps or is gravity
33:08
Speaker 1: gonna gather things together into a big clump. Because in
33:11
Speaker 1: the early universe, you know, things are very spread out,
33:14
Speaker 1: very smooth, and you have these micro fluctuations, these slight
33:17
Speaker 1: over densities that let you form structure. Now in this scenario,
33:21
Speaker 1: gravity is much much more powerful, so those over densities
33:24
Speaker 1: form structure much more quickly. But it's not clear to
33:27
Speaker 1: me whether you get a lot of little black holes
33:30
Speaker 1: or a bunch of really big black holes, or if
33:32
Speaker 1: you might just get things like neutron stars. Right, well,
33:35
Speaker 1: but if Grouty was thirty seven times stronger, like those
33:38
Speaker 1: neutron stars will probably become black holes much more quickly.
33:42
Speaker 1: That's right. Neutron stars in our universe wouldn't survive in
33:45
Speaker 1: that universe. But you might get like smaller objects which
33:48
Speaker 1: much less gravity there are still stable somehow, you know,
33:51
Speaker 1: the strong force could resist the force of gravity. In
33:54
Speaker 1: smaller scales, you might get like neutron stars the size
33:57
Speaker 1: of your hand instead of ten kilometers wide, for example.
34:01
Speaker 1: It's really hard to predict because we can't really calculate
34:04
Speaker 1: things using the strong force very well. It's too strong,
34:07
Speaker 1: it's too powerful, it's too chaotic, and so these kind
34:09
Speaker 1: of simulations are very hard to do. All right, Well,
34:12
Speaker 1: then the other part of the question is, like, what
34:13
Speaker 1: if gravity suddenly became stronger? Now, Like what if on
34:17
Speaker 1: Gut went to the control room of the universe and
34:19
Speaker 1: flipped the switch and suddenly we are sitting here, but
34:21
Speaker 1: then suddenly gravity is much stronger. On God, please do
34:25
Speaker 1: not do that. You would be like the double Fanos
34:28
Speaker 1: because everybody you know would die instantly if that happened.
34:32
Speaker 1: Oh my goodness, really straight to death. Well, imagine you're
34:36
Speaker 1: standing on Earth and all of a sudden gravity becomes
34:38
Speaker 1: ten to the thirty seven times more powerful, right, It
34:42
Speaker 1: would pulverize you. The tidal forces from Earth would tear
34:45
Speaker 1: you apart, you would get squished to the surface. You
34:48
Speaker 1: would just not survive. So you're saying Fantasy should have
34:51
Speaker 1: been a physicist, because otherwise he would have known what
34:54
Speaker 1: to do to do to be a little more fitting exactly,
34:58
Speaker 1: and not only would you not vibe, but most of
35:00
Speaker 1: the structures we know in the universe would collapse very
35:03
Speaker 1: very quickly, because you know, what we have today is
35:06
Speaker 1: a balance between gravity and the other forces. The reason
35:09
Speaker 1: the Earth doesn't collapse a new black hole is because
35:12
Speaker 1: it's internal tensile strength of the materials from the electromagnetic
35:15
Speaker 1: bonds are strong enough to prevent that. And the reason
35:18
Speaker 1: the Sun hasn't collapsed into a black hole is because
35:21
Speaker 1: it's powered by fusion, which is preventing its collapse. Now
35:25
Speaker 1: suddenly you're changing half of that equation. Gravity is much
35:28
Speaker 1: much stronger. Everything is going to collapse very very quickly.
35:31
Speaker 1: So the hearts of stars, for example, will instantly become
35:35
Speaker 1: super duper hot because the gravitational pressure. Basically every Sun
35:39
Speaker 1: goes supernova instantly. Well, the whole universe just goes up
35:43
Speaker 1: in a big explosion kind of and emplosion at the
35:47
Speaker 1: same time, like with the Earth, the Earth suddenly become
35:49
Speaker 1: a black hole. Yeah, the Earth becomes a black hole.
35:52
Speaker 1: The Sun goes supernova and leaves behind a black hole,
35:55
Speaker 1: and then you know, the eventual future of our universe
35:58
Speaker 1: we imagine is things driping further apart. But getting pulled
36:01
Speaker 1: together into black holes. And so basically this just speeds
36:05
Speaker 1: that up and turns everything into a black hole much
36:07
Speaker 1: much sooner than it otherwise would. Right, But then the
36:10
Speaker 1: universe is still expanding, So the gravity bring everything together
36:15
Speaker 1: or would the universe continue to expand. The universe would
36:17
Speaker 1: continue to expand we think that dark energy is not
36:20
Speaker 1: a function of the strength of gravity. But you know,
36:22
Speaker 1: there's a balance between dark energy and gravity. Dark energy
36:26
Speaker 1: is pulling the universe apart, and gravity is pulling stuff together.
36:29
Speaker 1: And currently that balance is at the level of like
36:32
Speaker 1: galaxy clusters. We think that gravity wins at the level
36:35
Speaker 1: of galaxy clusters. It holds that stuff together and prevents
36:38
Speaker 1: it from getting pulled apart by dark energy and anything
36:41
Speaker 1: further away, dark energy is winning. Now, if you make
36:44
Speaker 1: gravity much much stronger, then dark energy is still gonna
36:47
Speaker 1: win at some distances, but gravity is gonna win at
36:50
Speaker 1: much bigger things than it did before. So it's going
36:52
Speaker 1: to pull together superclusters and clusters of superclusters, and so
36:56
Speaker 1: you get these really big monster black holes that would
36:59
Speaker 1: contain like, you know, maybe all the stuff in our
37:01
Speaker 1: current observable universe. Yeah, I get called them mega black hole,
37:05
Speaker 1: which is a cool word. It is a super cool word.
37:08
Speaker 1: It's a mega cool word. It's make a cool world.
37:11
Speaker 1: There you go from a mega physicist. Alright, well, I
37:13
Speaker 1: think that answers the question. Things would be really different, right.
37:17
Speaker 1: The universe would have still formed, right, You would still
37:20
Speaker 1: get the Big Bang because that expansion is not depending
37:23
Speaker 1: on gravity like you said. But um, I guess the
37:27
Speaker 1: universe would have just a lot more black holes exactly.
37:30
Speaker 1: If gravity was much more powerful early on, you get
37:32
Speaker 1: very different structures and early black hole formation. If gravity
37:35
Speaker 1: suddenly turned on to be very powerful today, you would
37:38
Speaker 1: get in in supernova and then a lot of black holes.
37:41
Speaker 1: So I got pleased. Don't press that button, at least
37:43
Speaker 1: not yet. You know exactly. I know it's tempting. It's
37:47
Speaker 1: the big red button. You want to press it. The
37:49
Speaker 1: please take a step back, take a step back. Alright, Well,
37:53
Speaker 1: we have one more question here, and it's about things
37:56
Speaker 1: disappearing from space, from the universe. So let's get into that.
38:00
Speaker 1: But first let's take another quick break. We are answering
38:15
Speaker 1: questions from listeners, and our last question here is from
38:18
Speaker 1: Keith from Cleveland, who is wondering if things are going
38:22
Speaker 1: to disappear in the universe at some point. Hi, Daniel
38:25
Speaker 1: and Jorge. This is Keith from Cleveland. I love the
38:27
Speaker 1: podcast and I'm amazed at how much time you spend
38:30
Speaker 1: answering random listener questions. I don't know how Daniel has
38:33
Speaker 1: time left to be a working physicist and have an
38:35
Speaker 1: actual life outside of podcasting and question answering, But I'm
38:38
Speaker 1: going to add to that burden anyways by asking questions.
38:41
Speaker 1: And that is, have we been observing deep enough into
38:45
Speaker 1: space for a long enough time that something we used
38:48
Speaker 1: to be able to see has receded to a point
38:50
Speaker 1: where it can no longer be seen due to the
38:52
Speaker 1: expansion of the universe. For example, is our galaxy that
38:55
Speaker 1: we detected, say by, that has since disappeared for from
39:00
Speaker 1: our view because it is no longer within our hubble volume,
39:03
Speaker 1: and thus that galaxy's photons will now never reach us.
39:07
Speaker 1: Do we know of such an object? And if not,
39:09
Speaker 1: how long do we need to wait between observing a
39:11
Speaker 1: very distant object and it disappearing forever? Thanks so much
39:15
Speaker 1: and keep up the great work all right. Thank you.
39:17
Speaker 1: Keith from Cleveland. That's a little bit hard to say,
39:19
Speaker 1: Keith from Cleveland. I wonder if he became a physicists
39:24
Speaker 1: really extra hard to pronounce. This is his Keith from Cleveland. Yeah,
39:28
Speaker 1: but he asked a really cool question about the nature
39:31
Speaker 1: of the universe and what we can see in it.
39:33
Speaker 1: He also has a great question about the nature of Daniel. Daniel,
39:36
Speaker 1: how do you find at the time to do all
39:39
Speaker 1: everything you do? Time dilation? You know, you move fast
39:41
Speaker 1: enough and clocks go slow? Interesting? Interesting? Or do you
39:45
Speaker 1: get close to a black hole? Right? Is that great?
39:47
Speaker 1: Do you have one in your house? But then I
39:50
Speaker 1: would slow down and the rest of the universe would
39:52
Speaker 1: speed up, So then you need to put the rest
39:54
Speaker 1: of the universe near a black hole while you get
39:56
Speaker 1: your work done. So I see, maybe have a white
40:00
Speaker 1: hole in your house. You are Oh, you aren't called
40:03
Speaker 1: whitesn you figured it out. I am Carlott Holmes Elementary.
40:10
Speaker 1: But not to answer you keeps question. I am still
40:12
Speaker 1: a working physicist. I'm doing data analysis from the Large
40:14
Speaker 1: Agon Collider. I got undergrads and grad students and post
40:18
Speaker 1: docs working with me, and we're just having a lot
40:20
Speaker 1: of fun answering questions about the universe. Yeah. Yeah, you're
40:23
Speaker 1: still working as a physicist. You're just not pronouncing it
40:26
Speaker 1: as well as he could not part of the job.
40:28
Speaker 1: As far as I understand, you don't listen on your
40:31
Speaker 1: resume can pronounce my job title, Joe is. I can't
40:34
Speaker 1: even really spell it. There's so many scenes and asses
40:37
Speaker 1: in it. I get it wrong every single time. Do
40:39
Speaker 1: you spell it like a psychic baby? Yeah, it's like
40:41
Speaker 1: trying to spell the word license. It's like where does
40:43
Speaker 1: that see you go? And a good thing. I don't
40:45
Speaker 1: need a physics license because I couldn't spell either world
40:48
Speaker 1: my goodness or that you're a real doctor too, you'd
40:50
Speaker 1: be a physicians physicist licensee. Al Right, Well, this question
40:54
Speaker 1: was it sort of related to what we're talking about before,
40:57
Speaker 1: the idea that there are parts of space that we
41:00
Speaker 1: can see now and there are parts of space that
41:03
Speaker 1: we maybe we will never see because the universe is
41:05
Speaker 1: expanding faster and faster, And I think he's is asking like,
41:10
Speaker 1: have we gotten to that point yet, Like have we
41:12
Speaker 1: noticed that there are things we can't see anymore? Yeah,
41:14
Speaker 1: it's a really interesting question. You right, he's asking about
41:17
Speaker 1: whether things are falling off the edge of the observable universe.
41:21
Speaker 1: And first of all, he's right that things will fall
41:23
Speaker 1: off the edge of the observable universe. And that's because
41:25
Speaker 1: space is expanding faster than light, right, so space is
41:29
Speaker 1: stretching out right, Well, the observable universe expands that a
41:32
Speaker 1: light year per year. Space itself is expanding faster than that,
41:36
Speaker 1: and so there are things that are moving into parts
41:39
Speaker 1: of the universe that are expanding faster than the speed
41:41
Speaker 1: of light, where their photons will no longer ever reach us.
41:44
Speaker 1: So there are things falling off the edge of the
41:47
Speaker 1: observable universe. It's like, you know, somebody stretching out the
41:51
Speaker 1: fabric faster than we're looking at it, and so we're
41:53
Speaker 1: seeing a smaller and smaller fraction of the stuff in
41:56
Speaker 1: the universe. Well, but it's not sort of like alling off.
42:01
Speaker 1: It's more like the observable universe is growing, but it's
42:04
Speaker 1: just not there are things that are outpacing it, or
42:07
Speaker 1: they're running away from us faster than that bubble is expanding. Yeah,
42:11
Speaker 1: they're not falling off from the edge into like the
42:12
Speaker 1: mouth of dragons or something like that. We think there
42:15
Speaker 1: probably is still space out there for this stuff to
42:18
Speaker 1: be in, but it's sort of disappearing from our view.
42:20
Speaker 1: So you're right, the expansion is outpacing the speed of line, right,
42:23
Speaker 1: And it's not like it's they're falling out of our view.
42:26
Speaker 1: It's just that they never were in our view and
42:29
Speaker 1: they never will. Well, there's things in different categories. There's
42:32
Speaker 1: stuff that was observable and in the future will not
42:35
Speaker 1: be observable, things that sort of move out of the
42:38
Speaker 1: observable universe. There are things which started out not observable,
42:42
Speaker 1: and we're in parts of space that we're expanding faster
42:44
Speaker 1: than the speed of light and then briefly are observable
42:48
Speaker 1: and then fall out. And then there are things that
42:50
Speaker 1: never will be observable, things that, no matter how much
42:53
Speaker 1: time passes, photons from them will never reach us. Oh,
42:57
Speaker 1: you just blew my mind a little bit. That was
42:58
Speaker 1: like four categories of things. Let's let's maybe take one
43:02
Speaker 1: out a time. So there are our silver universe is expanding,
43:06
Speaker 1: there's stats of the stuff we can see for sure.
43:08
Speaker 1: We talked about before earlier in this episode. How there's
43:11
Speaker 1: things like out there beyond sixty five billion light years
43:14
Speaker 1: away that will never see because space is expanding and
43:18
Speaker 1: so it will never like our our silver universe will
43:20
Speaker 1: never catch up to that, right, that's right. It's sixty
43:23
Speaker 1: three billion light years in radius. Things further than that,
43:26
Speaker 1: the recession velocity is greater than the speed of light
43:29
Speaker 1: and always will be, and so those photons will never
43:32
Speaker 1: reach us because they'll always be in parts of space
43:35
Speaker 1: where the recession velocity is greater than the speed of light.
43:38
Speaker 1: So there are distance to us will always be getting larger,
43:41
Speaker 1: even though they're technically moving towards us through their space. Right.
43:45
Speaker 1: And when you say always, you mean as long as
43:46
Speaker 1: the universe keeps expanding, right, that's right. And this is
43:49
Speaker 1: assuming the current cosmological model and that the expansion continues
43:53
Speaker 1: in the way that it has, which is fascinating, you know,
43:55
Speaker 1: because there was very early expansion inflation the first few
43:58
Speaker 1: moments of the universe, and then there's late time expansion,
44:01
Speaker 1: this time around eight billion years after the universe started,
44:05
Speaker 1: when they started accelerating again, the sort of two modes
44:08
Speaker 1: of expansion. And what we're doing now is we're assuming
44:11
Speaker 1: that that recent expansion in the last few billion years
44:13
Speaker 1: just sort of continues forever. But we don't know, right,
44:16
Speaker 1: it could be different. It could be that the future
44:18
Speaker 1: is is something else, right, But as far as we know,
44:20
Speaker 1: it seems like there's stuff we can see stuff we
44:23
Speaker 1: will never see. And then very interestingly, he said, there
44:26
Speaker 1: are two kinds of things that we can see now
44:28
Speaker 1: but that we won't see in the future. So what
44:31
Speaker 1: are those two things? So one is stuff that has
44:34
Speaker 1: been in our observable universe, but eventually we'll fall out
44:38
Speaker 1: of our observable universe because it's moving within space. Well,
44:41
Speaker 1: because space is expanding. You know, things for example, that
44:44
Speaker 1: we're between us and forty two million light years away,
44:49
Speaker 1: very very early on in the universe, like around the
44:51
Speaker 1: CMB time. That's stuff we can see right now. Oh,
44:54
Speaker 1: I see you're saying. I would have thought like once
44:56
Speaker 1: we see something like we can see it forever. No,
45:00
Speaker 1: So if you go back to the very beginning, right
45:02
Speaker 1: T equal zero, technically we could see nothing, right, so
45:04
Speaker 1: we couldn't see any part of the observable universe was
45:07
Speaker 1: a sphere of zero volume. Then as time goes on,
45:10
Speaker 1: that expands and we start to be able to see
45:12
Speaker 1: things in the universe, right, and so things enter the
45:16
Speaker 1: observable universe. Not everything is going to enter that however,
45:19
Speaker 1: right there's still things so far away that they will
45:22
Speaker 1: never enter the observable universe because at the same time,
45:25
Speaker 1: space is expanding, so you know, you have this race
45:28
Speaker 1: between the observable universe, which is growing at one light
45:31
Speaker 1: year per year, and space expanding, which is tugging things
45:34
Speaker 1: away from us. So in the very beginning, nothing's in
45:36
Speaker 1: the observable universe. Then as time goes on, some things
45:40
Speaker 1: come into the observable universe and we can see them,
45:42
Speaker 1: though not everything. There's some things that will never enter
45:44
Speaker 1: the observable universe. But the stuff that falls into the
45:47
Speaker 1: observable universe that comes into the observa universe, so we
45:50
Speaker 1: can see it. Eventually, also it will leave because space
45:54
Speaker 1: is expanding fast in the speed of light, so that
45:57
Speaker 1: will win and eventually everything will get pulled out out
46:00
Speaker 1: of our universe. And even though technically the observing universe
46:03
Speaker 1: will be large, will essentially be nothing in it anymore. Right, Well,
46:07
Speaker 1: I think, maybe just to be clear, like the space
46:10
Speaker 1: within the observable universe right now, it's not expanding faster
46:13
Speaker 1: than the speed of light, but it's accelerating all the time,
46:16
Speaker 1: and space is stretching faster and faster. So I think
46:18
Speaker 1: what you're saying is that eventually the space within the
46:20
Speaker 1: observable universe. That stuff is gradually going to be going
46:24
Speaker 1: faster than the speed of light, and then at some
46:26
Speaker 1: point it's gonna you know, catch up to the observable
46:28
Speaker 1: universe and even pass it, in which case we won't
46:31
Speaker 1: be able to see it. Ye, So the bubble that
46:33
Speaker 1: we can see keeps growing, but stuff gets accelerated away
46:36
Speaker 1: from us faster than that bubble keeps growing, and so
46:39
Speaker 1: eventually everything sort of falls out of our I like
46:42
Speaker 1: to say falls out, but you're right, it's not like
46:44
Speaker 1: tripping over the edge. It's outpacing the growth of that bubble.
46:49
Speaker 1: I feel like it's it's a very exciting race. It's like,
46:51
Speaker 1: you know, the observable universe was winning, but then the
46:54
Speaker 1: expansion was winning, but then that one was losing. And
46:57
Speaker 1: there's some people caught in some stars in the middle
47:00
Speaker 1: that are unfortunately going to be winning but then losing.
47:03
Speaker 1: And it's a pretty pretty dramatic story. It's a pretty
47:05
Speaker 1: dramatic story. And you think about an individual thing, it
47:08
Speaker 1: starts out invisible, right, and essentially you can think about
47:12
Speaker 1: that is like having infinite red shift. Red shift in
47:15
Speaker 1: infinity is totally invisible. So things that are going to
47:18
Speaker 1: be in our observa universe, start out an infinite red shift,
47:21
Speaker 1: and then they come into our observa universe, and at
47:24
Speaker 1: some point in time they reach like their minimum red shift,
47:28
Speaker 1: and then they turn around and they start to grow
47:30
Speaker 1: their redshift again as the universe acceleration takes over and
47:34
Speaker 1: they go back to infinite redshift. So everything sort of
47:36
Speaker 1: starts in infinity, comes to a minimum redshift, and then
47:39
Speaker 1: goes to infinite red shift. Some things are always an
47:42
Speaker 1: infinite redshift and will never see them, those things past
47:45
Speaker 1: our eventual particle horizon. Well, I think keith question though,
47:49
Speaker 1: is like has that started to happen? Right? Like, has
47:52
Speaker 1: stuff within our absorbable universe started to accelerate faster than
47:57
Speaker 1: the speed of light? Because it's possible that it hasn't
47:59
Speaker 1: started right. Well, there's always something right at the edge.
48:02
Speaker 1: There's something that is falling off. Right, Since the universe
48:05
Speaker 1: started accelerating about eight billion years ago, things that are
48:08
Speaker 1: right there at the edge started to lose that race.
48:10
Speaker 1: So there's always something that's passing that threshold, but but
48:13
Speaker 1: not necessarily right. It could have been right because the
48:16
Speaker 1: universe's expressed out and it could be like like right, now,
48:18
Speaker 1: it could be that the observerable universe it's expanding at
48:22
Speaker 1: the speed of light. But it could be that maybe
48:23
Speaker 1: the expansion up to the point hasn't reached that right. Well,
48:26
Speaker 1: remember that the recession velocity is linear, that's hubbled laws.
48:30
Speaker 1: So things that are close to us are not moving
48:32
Speaker 1: away from us that fast, And as you go further
48:34
Speaker 1: and further away, things are moving away from us faster
48:36
Speaker 1: and faster, and that's linear. So as you go far
48:39
Speaker 1: enough away, there's always something that's moving away from us
48:41
Speaker 1: faster than the speed of light. Yes, but that thing
48:44
Speaker 1: could be outside of our observable universe right now, or
48:47
Speaker 1: it could be inside of our observable universe. Right If
48:49
Speaker 1: it's outside the observable universe, then right now we can
48:51
Speaker 1: see everything. But eventually it's going to catch up. So
48:55
Speaker 1: things are moving away from as faster as they're more distant. Currently,
48:58
Speaker 1: in order to be moving away from us faster than
49:00
Speaker 1: the speed of light, you only need to be about
49:02
Speaker 1: fifteen billion light years away, So most of the observable
49:05
Speaker 1: universe is moving away from us faster than the speed
49:08
Speaker 1: of light. Oh. Interesting, So there are things that are
49:13
Speaker 1: falling out of our view, but in the past, there wasn't,
49:16
Speaker 1: but now there is. I think there are always things
49:19
Speaker 1: that are falling out of our view if the universe
49:21
Speaker 1: is expanding and accelerating at the same rate. But wasn't
49:24
Speaker 1: the universe expanding slower before? Yeah, the expansion has been
49:27
Speaker 1: accelerating exactly. So now there are things falling out of
49:31
Speaker 1: the edge of our durable universe or getting outpaced by
49:34
Speaker 1: the expansion. I think is your phrase, which I think
49:36
Speaker 1: is better interesting. Alright, So Keith was right these I
49:40
Speaker 1: mean he was asking when that's going to happen, and
49:42
Speaker 1: you're saying it's already happened. We're losing the universe. Yeah,
49:46
Speaker 1: And Keith was asking whether we've seen something disappear, which
49:50
Speaker 1: is a really cool question and similar to your question
49:53
Speaker 1: before about like seeing the CMB change. So if you're
49:56
Speaker 1: like looking at an object that you know is really
49:58
Speaker 1: far away now, right, And remember that when we're talking
50:01
Speaker 1: about seeing an object that's really far away, there's a
50:03
Speaker 1: subtlety here. If we say something that we're seeing is
50:06
Speaker 1: forty six billion light years away, we mean that's where
50:10
Speaker 1: it is right now, right, So we're seeing light from
50:13
Speaker 1: it that was admitted when that object was closer to us,
50:16
Speaker 1: but now where it is is forty six billion light
50:19
Speaker 1: years away. That's when we mean when we say the
50:22
Speaker 1: edge of the observable universe. Right, we're not seeing that
50:24
Speaker 1: stuff today. We're seeing it from when it was actually
50:27
Speaker 1: closer from where it was when it sent us a photon. Anyway,
50:31
Speaker 1: we are looking at stuff at the edge of the
50:32
Speaker 1: observd a universe. And so for example, there's a galaxy
50:35
Speaker 1: people have looked at that might be the most distant object.
50:38
Speaker 1: You know, the CNB is older and more distant. But
50:41
Speaker 1: this is an object near the edge of the observable universe.
50:44
Speaker 1: It's called g n Z eleven and it was a
50:47
Speaker 1: galaxy formed about four hundred million years after the Big Bang.
50:51
Speaker 1: If you look at the pictures of it, it just
50:52
Speaker 1: sort of looks like a blob that the James Webb
50:54
Speaker 1: Space Telescope. Of course, we'll get very very crisp pictures
50:57
Speaker 1: of this object and help us understand like the early
51:00
Speaker 1: universe and galaxy formation. So this is a candidate for
51:03
Speaker 1: the kind of thing we expect to disappear from our
51:05
Speaker 1: universe because it's very close to the edge. Right, interesting,
51:09
Speaker 1: you know, but I guess you're saying that it's not
51:12
Speaker 1: gonna like blink out at some point where it's not
51:14
Speaker 1: going to blink out in the space of ten years.
51:15
Speaker 1: It's gonna slowly red shift into sort of blackness, right. Exactly.
51:20
Speaker 1: The reason the James Webb is a good telescope to
51:23
Speaker 1: look at it is because its wavelengths are already really
51:27
Speaker 1: red shifted into the I, R and two infrared wavelengths,
51:30
Speaker 1: and as the time goes on, it's just going to
51:32
Speaker 1: gradually get more and more red shifted until it gets
51:35
Speaker 1: to red shift of infinity. So you're right, it's not
51:38
Speaker 1: going to just disappear one day. It's gonna gradually get
51:41
Speaker 1: redder and redder. It's not going to be very dramatic, unfortunately,
51:44
Speaker 1: and it's gonna take a long time to really even
51:46
Speaker 1: notice any differences. These things take cosmological time periods to change,
51:51
Speaker 1: not days or weeks or years. Kase, just watch what
51:54
Speaker 1: you eat and you might live long enough to see
51:56
Speaker 1: it disappear. But it sort of makes me a little sad.
52:01
Speaker 1: I feel like you're telling me that we've already started to,
52:04
Speaker 1: you know, see less of the universe, like our view
52:06
Speaker 1: of the universe, like as has already started to disappear.
52:10
Speaker 1: Does that mean that, like what we see today is
52:12
Speaker 1: the most we'll see of the universe. Ever, while there
52:15
Speaker 1: are things disappearing, there are also things that we have
52:18
Speaker 1: not yet seen that we will see. Things that have
52:21
Speaker 1: been flying through the universe the whole history of the
52:23
Speaker 1: universe and have not yet arrived. But they will arrive
52:26
Speaker 1: because right now they're flying through space that's not moving
52:29
Speaker 1: away from us faster than the speed of light. They've
52:31
Speaker 1: made it inside the hubble radius, and they will eventually
52:34
Speaker 1: reach us. So, for example, there are things that are
52:36
Speaker 1: sixty three billion light years away the very first flashes
52:40
Speaker 1: they sent in the very early universe. Those will eventually
52:43
Speaker 1: reach us. Nothing else afterwards that they send will ever
52:47
Speaker 1: reach us, right so they'll very briefly dip into our
52:50
Speaker 1: observable universe at the very end of time. So there
52:54
Speaker 1: are some things where the light is still on its
52:56
Speaker 1: way that will reach us. But there are also things
52:59
Speaker 1: that right now there are ready disappearing from the universe.
53:02
Speaker 1: So every photon as it passes through the universe sort
53:04
Speaker 1: of passes through a different universe because space is expanding,
53:08
Speaker 1: and that expansion is changing with time. So photons that
53:10
Speaker 1: left a long time ago have had a chance to
53:13
Speaker 1: make it within the sphere that's no longer expanding faster
53:16
Speaker 1: than the speed of light, so they will eventually get here,
53:19
Speaker 1: although later photons from the same super distant objects won't
53:22
Speaker 1: get here. All right, Well, I think the answer for
53:24
Speaker 1: Keith is that things have started disappearing now, or they
53:28
Speaker 1: they are starting to disappear, but it might be a
53:31
Speaker 1: little bit before we stopped getting new things into our
53:36
Speaker 1: field of view. Like, we haven't peaked yet in terms
53:38
Speaker 1: of our view of the universe, but we will something
53:41
Speaker 1: That's right, the most distant thing we see will be
53:43
Speaker 1: sixty three billion night years away. We haven't yet seen that.
53:47
Speaker 1: We will see it very briefly at the end of time,
53:49
Speaker 1: and we will never see anything more distant than that.
53:52
Speaker 1: At the same time, there are some things which are closer,
53:54
Speaker 1: which spend more time in our abservable universe, but are
53:58
Speaker 1: already being outpaced by the accelerating expansion in the universe. Unfortunately,
54:02
Speaker 1: they don't blink out dramatically, They just sort of read
54:04
Speaker 1: shift away. All right, Well, um, stay tuned. I guess
54:07
Speaker 1: until the end of time we'll find out the answer
54:12
Speaker 1: that hopefully we'll be making this podcast until the end
54:14
Speaker 1: of time. Hopefully you'll learn how to pronounce the word
54:17
Speaker 1: physicists by then. That will take two or three universes,
54:20
Speaker 1: I think, Yeah, maybe in the next universe. You'll flick
54:23
Speaker 1: it out. In the next universe. All right, I'll put
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Speaker 1: it on my two do list for next universe. That's right,
54:28
Speaker 1: it's stay tuned for the sequel. Uh the universe. The
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Speaker 1: dark matter returns correctly pronounced with pants on. Alright, Well,
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Speaker 1: we hope you enjoyed that. Thanks for joining us, See
54:38
Speaker 1: you next time. Thanks for listening, and remember that Daniel
54:48
Speaker 1: and Jorge Explain the Universe is a production of I
54:51
Speaker 1: Heart Radio. For more podcast from my Heart Radio, visit
54:54
Speaker 1: the I Heart Radio app, Apple Podcasts, or wherever you
54:58
Speaker 1: listen to your favorite show. M