Latest / Daniel and Kelly’s Extraordinary Universe / What's the real speed limit of the Universe?

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What's the real speed limit of the Universe? · Daniel and Kelly’s Extraordinary Universe

• 0:02
  Speaker 1: Yeah, or hey, do you find yourself speeding up or
• 0:11
  Speaker 1: slowing down as we get older? Kind of both both?
• 0:15
  Speaker 1: How's that possible? Well, I'm faster at falling asleep on
• 0:17
  Speaker 1: the couch, that's true. I'm faster at finding a place
• 0:20
  Speaker 1: to sit down as soon as I get somewhere, But
• 0:22
  Speaker 1: I'm getting slower at the same time that time seems
• 0:25
  Speaker 1: to go faster. Do you think there's like a maximum
• 0:28
  Speaker 1: speed to that if we live to be like nine
• 0:31
  Speaker 1: years old, like Yoda with the years just passed by
• 0:33
  Speaker 1: in a blink. Well, first of all, I definitely want
• 0:35
  Speaker 1: to be Yoda. I don't want to look like Yoda
• 0:38
  Speaker 1: when I'm Somebody needs to tell Yoda about sunscreen. Although
• 0:41
  Speaker 1: my ears are getting bigger, but my light serious skills
• 0:44
  Speaker 1: are getting worse. As long as you can still do
• 0:47
  Speaker 1: those flips, well you know what he said. He said,
• 0:50
  Speaker 1: do or do not? There is no try. Hi am
• 1:07
  Speaker 1: or Handma cartoonists and the creator of PhD comics. Hi,
• 1:10
  Speaker 1: I'm Daniel. I'm a particle physicist and a professor at
• 1:13
  Speaker 1: U C Irvine, and I don't think I will ever
• 1:15
  Speaker 1: do a backflip in my whole life. Oh, I feel
• 1:18
  Speaker 1: bad for you. You've never done a backflip or a
• 1:20
  Speaker 1: front flip except underwater. I've done one underwater, but you know,
• 1:24
  Speaker 1: not like standing on the ground. And I feel like
• 1:26
  Speaker 1: I've sort of passed the age where you could like
• 1:28
  Speaker 1: learn to do that in the future. I still do backflips.
• 1:32
  Speaker 1: You can do a standing backflip. Yeah, that's amazing. I
• 1:35
  Speaker 1: think we have to see a video of that. Yeah. Well,
• 1:38
  Speaker 1: usually do it at those trampoline places. Yeah. I can
• 1:43
  Speaker 1: do backflips while skydiving. Yeah. Have you skydive? Actually have
• 1:47
  Speaker 1: jumped out of an airplane once? Did you do a backflip?
• 1:50
  Speaker 1: We did all sorts of crazy maneuvers, but I had
• 1:53
  Speaker 1: somebody strapped to my back, so it's sort of like
• 1:55
  Speaker 1: a double backflip. You had someone strapped to your back,
• 1:58
  Speaker 1: or someone had you strapped through their front. It was
• 2:00
  Speaker 1: basically like Baby Buern skydiving. Welcome to our podcast Daniel
• 2:03
  Speaker 1: and Jorge Explain the Universe, a production of My Heart
• 2:06
  Speaker 1: Radio in which our goal is to make your brain
• 2:09
  Speaker 1: and do backflips as you understand the incredible beauty and
• 2:12
  Speaker 1: mystery of our universe. We seek to dive into all
• 2:16
  Speaker 1: of the crazy mysteries about how things work unraveled the
• 2:19
  Speaker 1: explanations that humanity has discovered for what's actually out there
• 2:24
  Speaker 1: in the universe and what rules it is following. We
• 2:27
  Speaker 1: talk about all of that on the podcast and make
• 2:29
  Speaker 1: sure we can explain all of it to you. That's right.
• 2:32
  Speaker 1: It is a vast universe moving slowly and fast at
• 2:35
  Speaker 1: the same time, and we are here to help you
• 2:37
  Speaker 1: do those mental gymnastics to put it all inside of
• 2:40
  Speaker 1: your brain. We hope that you get that feeling of
• 2:42
  Speaker 1: satisfaction when you land that triple backflip of understanding quantum
• 2:46
  Speaker 1: mechanics and general relativity in squeezing all that into your brain.
• 2:50
  Speaker 1: Do you think we usually stick de landing on the podcast.
• 2:52
  Speaker 1: I think we usually stick something somewhere at the wall.
• 2:56
  Speaker 1: Usually we just throw back points at the wall and
• 2:58
  Speaker 1: and I hope something sticks. Thank God for good editors.
• 3:01
  Speaker 1: But it is a wonderful and interesting universe with all
• 3:04
  Speaker 1: kinds of rules in it. It seems that kind of
• 3:07
  Speaker 1: govern how things can happen, what things can do, what
• 3:10
  Speaker 1: particles and energy and forces and waves can do out there.
• 3:13
  Speaker 1: That gives us this interesting and very complex universe that
• 3:17
  Speaker 1: we live in, and a very human thing to do
• 3:19
  Speaker 1: when understanding the universe is to try to figure out
• 3:22
  Speaker 1: what are the rules, What are the laws, what are
• 3:24
  Speaker 1: the limits, what are the things that we are not
• 3:26
  Speaker 1: allowed to do. It's like we're still children pushing up
• 3:29
  Speaker 1: against the boundaries, trying to understand what's allowed and what's not.
• 3:34
  Speaker 1: And now we're translating that to understanding what things in
• 3:37
  Speaker 1: the universe can do. What is a particle allowed to
• 3:40
  Speaker 1: do when it whizzes around a black hole? How fast
• 3:42
  Speaker 1: can it go when it rides the shock wave from
• 3:45
  Speaker 1: a supernova? Wait? Are we trying to figure out the
• 3:46
  Speaker 1: rules so we can break them or so we can
• 3:49
  Speaker 1: avoid getting into trouble? What does that mean? To get
• 3:52
  Speaker 1: into trouble? As the universe gonna punish us if we
• 3:54
  Speaker 1: go faster than the speed of light. No dessert for
• 3:56
  Speaker 1: a week, we might get a time out from the universe.
• 4:00
  Speaker 1: No screen time for a few millennium go over the
• 4:02
  Speaker 1: black hole and have your time dilated. No. I think
• 4:04
  Speaker 1: we are trying to break the rules because that helps
• 4:07
  Speaker 1: us understand what the rules are. I mean, if you
• 4:09
  Speaker 1: think that there's a hard and past rule in physics
• 4:11
  Speaker 1: and then you break it, then you discover the universe
• 4:14
  Speaker 1: is different from the way you thought it was. And
• 4:16
  Speaker 1: that's exactly the process of science. That's what we are
• 4:19
  Speaker 1: hoping to do, right, to pull back the veil of
• 4:21
  Speaker 1: our ignorance and understand how the universe actually is. But wait,
• 4:25
  Speaker 1: if you break a rule, then it wasn't really a rule,
• 4:28
  Speaker 1: was it. No, it wasn't a rule. But then you
• 4:30
  Speaker 1: try to figure out what the new rule is, what
• 4:32
  Speaker 1: the real rule is. We hope we think that the
• 4:35
  Speaker 1: universe does follow some set of rules, and that we
• 4:38
  Speaker 1: can approximate or learn those rules over time. Well, the
• 4:41
  Speaker 1: universe definitely rules, and there are lots of amazing things
• 4:45
  Speaker 1: to consider and discover, including those rules themselves. It seems
• 4:48
  Speaker 1: like the universe does kind of have limits about what
• 4:51
  Speaker 1: you can and can't do in it. It certainly does.
• 4:53
  Speaker 1: There are things that happen in the universe and things
• 4:55
  Speaker 1: that just don't ever happen, And something we do a
• 4:58
  Speaker 1: lot in science is take to that and wonder like,
• 5:01
  Speaker 1: why is it a muon doesn't ever decay directly to
• 5:05
  Speaker 1: an electron? Why is it that the universe is made
• 5:07
  Speaker 1: of these particles and never those kinds of particles? And
• 5:10
  Speaker 1: we think that all of these things are clues that
• 5:12
  Speaker 1: there are reasons for the universe to do one thing
• 5:15
  Speaker 1: and never some other thing, And we're trying to uncover
• 5:18
  Speaker 1: those rules and deduce from them what the underlying mechanics
• 5:21
  Speaker 1: are of the workings of the universe. Daniel wonder if
• 5:25
  Speaker 1: that's a philosophically impossible task. I mean, isn't it impossible
• 5:29
  Speaker 1: to prove a negative which means you can never prove
• 5:32
  Speaker 1: that a rule can't be broken, which means you can
• 5:34
  Speaker 1: never prove that something is a rule that's certainly true.
• 5:36
  Speaker 1: And a great example of that is a deep question
• 5:39
  Speaker 1: about the nature of matter, like is matter itself stable?
• 5:42
  Speaker 1: We are made of protons. We think that protons might
• 5:45
  Speaker 1: live forever, but we don't know because we've never seen
• 5:48
  Speaker 1: a proton fall apart. Like you put a proton out
• 5:51
  Speaker 1: into empty space, we don't know how long they last.
• 5:54
  Speaker 1: We've watched a bunch of protons for a bunch of
• 5:56
  Speaker 1: years and none of them fell apart. That doesn't mean
• 5:58
  Speaker 1: that eventually one day they might all fall apart. We
• 6:01
  Speaker 1: can't prove that they won't, so we should just give up. Man,
• 6:05
  Speaker 1: you can never prove anything, you know. What we can
• 6:07
  Speaker 1: do is make statistical limits. We can say we're very
• 6:09
  Speaker 1: confident that the lifetime of a proton is longer than
• 6:12
  Speaker 1: the current age of the universe. We don't know if
• 6:15
  Speaker 1: it's infinity or if it's just very, very long, but
• 6:17
  Speaker 1: that doesn't mean we don't know anything. We certainly know
• 6:20
  Speaker 1: that the lifetime of our proton is not ten minutes
• 6:23
  Speaker 1: or one minute, right, or we wouldn't even be here.
• 6:26
  Speaker 1: So we can certainly learn things about the universe, even
• 6:28
  Speaker 1: if we can never know for sure what those rules are.
• 6:33
  Speaker 1: I am nine certain that is unsatisfactory and welcome to philosophy.
• 6:39
  Speaker 1: But the universe does seem to have sort of rules
• 6:41
  Speaker 1: that things seem to fall on. One of them. Maybe
• 6:43
  Speaker 1: the biggest one that affects our everyday live is the
• 6:46
  Speaker 1: speed of light that let me you all the time,
• 6:48
  Speaker 1: Like when you're going to the post office and stuff,
• 6:50
  Speaker 1: you're like, oh, I wish I could drive there faster.
• 6:52
  Speaker 1: But this dang speed of light. Yeah, I mean it
• 6:54
  Speaker 1: affects everything, right, It means there's a speed limit to
• 6:57
  Speaker 1: how fast things can happen. Because it doesn't just apply
• 6:59
  Speaker 1: to the life, It applies to everything in the universe. Right, Yeah,
• 7:02
  Speaker 1: that's true. It probably applies to the people listen to
• 7:05
  Speaker 1: this podcast because it limits how fast that download can happen.
• 7:09
  Speaker 1: You write, everything in the universe, all information, and all matter,
• 7:13
  Speaker 1: is limited to the speed of light. That means if
• 7:16
  Speaker 1: you want to download all of the Explain the Universe
• 7:18
  Speaker 1: back catalog and it's seven point twenty one gigabytes or whatever,
• 7:22
  Speaker 1: it's gonna take a while because information takes time to transit.
• 7:26
  Speaker 1: I wonder how many people out there cursing the speed
• 7:28
  Speaker 1: of light because they can't hear our voices fast enough.
• 7:31
  Speaker 1: One maybe or zero. I think that our voices arrive
• 7:34
  Speaker 1: at just the right speed. We're like wizards in the
• 7:39
  Speaker 1: Lord of the Rings. We arrived precisely when we intended
• 7:41
  Speaker 1: to arrive. Yeah, that's true. Although maybe people are out
• 7:44
  Speaker 1: there listening to us at like two x speed, and
• 7:46
  Speaker 1: so we already are breaking the rules. I wonder if
• 7:49
  Speaker 1: anyone puts this at speed of light, plate this podcast
• 7:55
  Speaker 1: is finished as soon as you started it. Yeah, maybe
• 7:57
  Speaker 1: before it started. Maybe people are out there listening to
• 8:00
  Speaker 1: us at half speed because we're going too quickly, or
• 8:03
  Speaker 1: maybe somebody's playing us at negative speed, which would reveal
• 8:07
  Speaker 1: some interesting and deep secrets about the universe. If you
• 8:10
  Speaker 1: play the podcast backwards, you actually hear the rules of
• 8:12
  Speaker 1: the antimatter universe, the anti rules of the antimatter universe,
• 8:16
  Speaker 1: which means what you should do, which maybe should be
• 8:19
  Speaker 1: any religion. I forgot what this podcast is supposed to
• 8:21
  Speaker 1: be about. Now it's about anti religion. I think we
• 8:24
  Speaker 1: kind of went a little off key there. It's about
• 8:27
  Speaker 1: the speed of light and the speed of things in
• 8:29
  Speaker 1: the universe. Because it's easy to be a very basic
• 8:31
  Speaker 1: principle in the universe, right the information, light particles, they
• 8:35
  Speaker 1: don't seem to be able to go faster than a
• 8:37
  Speaker 1: very specific number out there in the universe. Yeah, this
• 8:40
  Speaker 1: is a discovery made just about a hundred and twenty
• 8:42
  Speaker 1: years ago that the universe does seem to have a
• 8:45
  Speaker 1: speed limit. No matter how fast you're going, you throw
• 8:47
  Speaker 1: that baseball out of your spaceship, it will never go
• 8:50
  Speaker 1: faster than a certain speed. No light, no photon, no particle,
• 8:54
  Speaker 1: nothing in the universe, no information even seems can transfer
• 8:58
  Speaker 1: from one place in the universe to another faster than
• 9:01
  Speaker 1: this stubborn speed limit. It's fascinating, and it's forced us
• 9:04
  Speaker 1: to rethink the nature of space and time and simultaneity
• 9:08
  Speaker 1: and all sorts of crazy stuff. Or at least, that's
• 9:11
  Speaker 1: what it seems like. We haven't seen anything move faster
• 9:14
  Speaker 1: than the speed of light. But you gotta wonder if
• 9:17
  Speaker 1: maybe there are exceptions to that rule I made. There
• 9:19
  Speaker 1: are special situations or circumstances in which that could happen,
• 9:24
  Speaker 1: and so do they. On the podcast, we'll be asking
• 9:26
  Speaker 1: the question, what's the fastest that a charged particle can go? Now?
• 9:36
  Speaker 1: Charges is like a particle that's had a lot of coffee,
• 9:39
  Speaker 1: or it's just pumped up with excitement, or just the
• 9:42
  Speaker 1: plane of electromagnetic charge. I can't speak to the emotions
• 9:45
  Speaker 1: of these particles or their caffeine intake, certainly not. And
• 9:49
  Speaker 1: I think, like a molecule, caffeine is probably much much
• 9:52
  Speaker 1: bigger than an electron. So I don't even know how
• 9:54
  Speaker 1: that would work. How do electrons zip coffee? Right, there's
• 9:58
  Speaker 1: a philosophy question for you without an answer. Maybe if
• 10:01
  Speaker 1: the electron is part of the caffeine molecule technically, then
• 10:03
  Speaker 1: it would be supercharged. Yeah, that's right. Our electrons that
• 10:07
  Speaker 1: are part of caffeine, do they have a different experience
• 10:10
  Speaker 1: than electrons that are part of something heavy and slow? Yeah?
• 10:13
  Speaker 1: I guess it depends on whether they like coffee or not.
• 10:15
  Speaker 1: Are they part of a latte molecule or expressing molecule.
• 10:19
  Speaker 1: I think they probably have a lot of fun. But
• 10:21
  Speaker 1: back to the question at hand. It's interesting that there
• 10:23
  Speaker 1: is an overall speed limit to the universe, something that
• 10:26
  Speaker 1: nothing can ever exceed. But practically speaking, there are also
• 10:29
  Speaker 1: other limits to how fast particles can go, especially if
• 10:32
  Speaker 1: they have other attributes to them, mass or charge, and
• 10:36
  Speaker 1: in this case we're thinking about the old fashioned electromagnetic charge,
• 10:40
  Speaker 1: and so this is an interesting question, and as usually,
• 10:43
  Speaker 1: we were wondering how many people out there had thought
• 10:44
  Speaker 1: about this, whether charge particles have a different speed limit
• 10:48
  Speaker 1: than non charged particles. So thank you very much to
• 10:50
  Speaker 1: everybody out there who answers these questions on the podcast.
• 10:53
  Speaker 1: It's a lot of fun for us to hear what
• 10:55
  Speaker 1: you are thinking. And if you would like to share
• 10:57
  Speaker 1: your thoughts on the podcast, please don't be shy right
• 11:00
  Speaker 1: to us. Two questions at Daniel and Jorge dot com.
• 11:03
  Speaker 1: Just think about it for a second. How fast do
• 11:05
  Speaker 1: you think charge particles can go? Here's what people had
• 11:09
  Speaker 1: to say. My quick answer it will be like ninety
• 11:13
  Speaker 1: nine point nine of speed of light. But does just
• 11:17
  Speaker 1: a guess with speed of light minus plunks, constant multiply
• 11:23
  Speaker 1: something that makes units consistent. As far as I know,
• 11:26
  Speaker 1: the maximum speed would be the speed of light. And
• 11:30
  Speaker 1: it's only particles that have mass that cannot achieve speed
• 11:35
  Speaker 1: of light, so I think that would be the speed
• 11:37
  Speaker 1: of light. I suppose my answer depends on whether or
• 11:40
  Speaker 1: not charge particles have mass, and I'm honestly not sure
• 11:42
  Speaker 1: if they do or not. If they are masthless, my
• 11:45
  Speaker 1: I would guess that they travel at the speed of light.
• 11:48
  Speaker 1: But if they do have mass and their mass is
• 11:50
  Speaker 1: non zero, I would say they travel at a significant
• 11:52
  Speaker 1: fraction of the speed of light, maybe upwards of speed
• 11:55
  Speaker 1: of light. Uh. The fastest charge particle could move in space,
• 11:58
  Speaker 1: I would think would be the speed of light, if
• 12:02
  Speaker 1: not the speed of light. All right, everyone seemed to
• 12:10
  Speaker 1: have the speed of light as the limit, or at
• 12:12
  Speaker 1: least ninety nine a lot of nine in these answers.
• 12:15
  Speaker 1: I give it a nine out of ten for that
• 12:17
  Speaker 1: vault attempt. Yeah, most people seem on board the idea
• 12:20
  Speaker 1: that the speed of light is the speed limit, but
• 12:23
  Speaker 1: that massive particles can't reach the speed of light. So
• 12:27
  Speaker 1: people definitely know there's a limit to things, and that
• 12:29
  Speaker 1: limit is less for things that have mass, and so
• 12:33
  Speaker 1: the question is discharge also give them a different speed limit. Well,
• 12:37
  Speaker 1: let's dig into this topic generally speaking, Daniel, what is
• 12:40
  Speaker 1: the speed limit that the universe seems to have so
• 12:42
  Speaker 1: special relativity? Einstein's description of space and time and motion
• 12:46
  Speaker 1: and how all those things interact tells us that the
• 12:49
  Speaker 1: speed limit is the speed of light in a vacuum,
• 12:52
  Speaker 1: which is about three hundred million meters per second, which
• 12:57
  Speaker 1: is first of all, a very very fast number. It's huge, right,
• 13:01
  Speaker 1: three hundred million meters in a second is an extraordinary
• 13:05
  Speaker 1: distance to traverse in just one second. And on the
• 13:08
  Speaker 1: other hand, it's very very slow because things in the
• 13:11
  Speaker 1: universe are far apart. So even if you can fly
• 13:15
  Speaker 1: three millions in a second, it can still take you
• 13:17
  Speaker 1: years to get to the next star, thousands of years
• 13:20
  Speaker 1: to get across the galaxy, and millions of years to
• 13:23
  Speaker 1: get to other galaxies. Yeah, although I wassuming you don't
• 13:26
  Speaker 1: want to go that far, it is pretty much instantaneous, right,
• 13:31
  Speaker 1: if you're not the traveling type or want to go
• 13:33
  Speaker 1: to another galaxy or planet, it's pretty much instantaneous, right,
• 13:37
  Speaker 1: at least to our brains. Yeah, it's pretty much instantaneous.
• 13:40
  Speaker 1: You know, light takes about a nanosecond to go afoot,
• 13:44
  Speaker 1: So if you're looking at something like your computer screen,
• 13:46
  Speaker 1: it's about a foot away, you're seeing the computer screen
• 13:49
  Speaker 1: as it looked a nanosecond ago. But you know, the
• 13:53
  Speaker 1: human eye also can't really distinguish things that happen faster
• 13:56
  Speaker 1: than like a thirty milliseconds. So for all extents and
• 13:59
  Speaker 1: purpose is it's instantaneous on the sort of scale of
• 14:02
  Speaker 1: things that we live in, right, But I guess it
• 14:04
  Speaker 1: is interesting this idea that there's nothing instantaneous kind of
• 14:07
  Speaker 1: in the universe, right that the even light or pretty
• 14:10
  Speaker 1: much anything just information in general, things, events, the actual
• 14:15
  Speaker 1: existence of things can't sort of move faster in this
• 14:18
  Speaker 1: universe than the speed of light. Yeah, it makes our
• 14:21
  Speaker 1: universe local. It means that you can only be influenced
• 14:24
  Speaker 1: by things around you. And what we mean by around
• 14:27
  Speaker 1: you depends on that speed of light. If the speed
• 14:30
  Speaker 1: of light was much much faster than things that could
• 14:33
  Speaker 1: influence you, things that we would say are local would
• 14:35
  Speaker 1: be things that are also further away. If the speed
• 14:37
  Speaker 1: of light was much much slower than the universe would
• 14:40
  Speaker 1: be sort of more local. You could only be influenced
• 14:42
  Speaker 1: by things that were closer to you. We talked in
• 14:44
  Speaker 1: the podcast several times about this concept of a light cone,
• 14:47
  Speaker 1: the sort of cone of things in your past that
• 14:49
  Speaker 1: can influence you. Things that are nearby can influence you
• 14:53
  Speaker 1: fairly recently. Things that are really really far away can
• 14:55
  Speaker 1: only influence you from the past. Things that happen in
• 14:58
  Speaker 1: like Andromeda right now can't affect us, and that can
• 15:01
  Speaker 1: be good news. Right If aliens are building a death
• 15:03
  Speaker 1: ray and shooting get at us, then it won't arrive
• 15:05
  Speaker 1: here for quite a little while. Yeah, I feel like
• 15:08
  Speaker 1: it's a very philosophical question too, and an impact just
• 15:11
  Speaker 1: on the very nature of existence. Like a giant pink
• 15:15
  Speaker 1: unicorn suddenly appeared on top of Jupiter. To us, that
• 15:19
  Speaker 1: wouldn't really exist until several minutes later, right, because that
• 15:23
  Speaker 1: information would take some time to get to us. As opposed,
• 15:25
  Speaker 1: it depends on what you mean by exists. We wouldn't
• 15:28
  Speaker 1: know it existed, We couldn't prove that it existed, So
• 15:31
  Speaker 1: in that sense, it wouldn't be real in the way
• 15:33
  Speaker 1: that it wouldn't appear in our experiments, right, But to
• 15:36
  Speaker 1: somebody else on Jupiter, they would be able to see it, right, Yeah,
• 15:39
  Speaker 1: that's what I mean that for us, it wouldn't exist,
• 15:42
  Speaker 1: right Yeah, in the same way that if the Sun disappeared,
• 15:45
  Speaker 1: we wouldn't notice for eight minutes because it takes that
• 15:48
  Speaker 1: long for light from the Sun to reach here. So
• 15:51
  Speaker 1: the universe as we see it is not the universe
• 15:53
  Speaker 1: as it is right now. And more deeply, relativity says
• 15:57
  Speaker 1: that there is no sort of universal definition of right now,
• 16:02
  Speaker 1: that time and the universe depends on where you are
• 16:05
  Speaker 1: and how fast you are going. This sort of requires
• 16:08
  Speaker 1: us to give up this concept that there is a
• 16:10
  Speaker 1: universe that's marching forward in time uniformly, sort of an
• 16:14
  Speaker 1: ancient Newtonian view, right. And so it's called the speed
• 16:17
  Speaker 1: of light, but it should actually be called the speed
• 16:19
  Speaker 1: of anything in the universe. We just call it the
• 16:21
  Speaker 1: speed of light because basically light is the only thing
• 16:24
  Speaker 1: we know that can go at that speed, or the
• 16:27
  Speaker 1: first thing we knew that could go at that speed. Yeah,
• 16:29
  Speaker 1: it really should be called the speed of everything, or
• 16:31
  Speaker 1: maybe the speed of anything. But it's the sort of
• 16:34
  Speaker 1: maximum speed limit of any kind of information, any field.
• 16:37
  Speaker 1: For example, in the universe, when it wiggles, information can't
• 16:40
  Speaker 1: move through that field faster than the speed of light,
• 16:43
  Speaker 1: and so that limit applies to every field, including the
• 16:45
  Speaker 1: electromagnetic field, for which photons are a ripple in that field,
• 16:49
  Speaker 1: and because they have no mass, they can move at
• 16:52
  Speaker 1: that maximum speed. It's true for any massless ripple in
• 16:55
  Speaker 1: a field. So, for example, we think that gravitational waves
• 16:59
  Speaker 1: travel at the feed of light as well, because those
• 17:01
  Speaker 1: ripples in the gravitational field, or equivalently, ripples in the
• 17:05
  Speaker 1: curvature of space, so we think those also move at
• 17:08
  Speaker 1: the speed of light. And if there are other particles
• 17:10
  Speaker 1: out there we haven't discovered that are massless, they would
• 17:13
  Speaker 1: also move at the speed of light. Are there other
• 17:16
  Speaker 1: particles we've discovered that are massless gluons, which are the
• 17:19
  Speaker 1: particles that helped transmit the strong force. They are also massless,
• 17:22
  Speaker 1: so they move at the speed of light. But gluons
• 17:25
  Speaker 1: are weird because they interact very strongly with themselves, and
• 17:28
  Speaker 1: so you never sort of see a gluon by itself.
• 17:30
  Speaker 1: They conform weird states like glue balls, but those have
• 17:34
  Speaker 1: energy inside of them, so they have mass, So the
• 17:36
  Speaker 1: glue balls don't move at the speed of light, even
• 17:38
  Speaker 1: if individual gluons do. Interesting, so photons are the only
• 17:43
  Speaker 1: particles that we know of that can move at the
• 17:45
  Speaker 1: speed of light. Well, I think gluons count is moving
• 17:47
  Speaker 1: at the speed of light, even though they don't go
• 17:49
  Speaker 1: very far. Gravitational waves aren't a particle. If gravity is
• 17:53
  Speaker 1: quantized and made of gravitons, then those are probably massless
• 17:57
  Speaker 1: and would move at the speed of light. But we
• 17:58
  Speaker 1: don't know if gravitons exist. Yeah, so, so technically photons
• 18:02
  Speaker 1: are the only particle we know of. What do you
• 18:03
  Speaker 1: have against gluhons? You know, then you say a little
• 18:07
  Speaker 1: while ago that they don't quite you don't never see
• 18:09
  Speaker 1: them move with the speed of light. Yeah, you can't
• 18:11
  Speaker 1: like shoot a gluon across the universe and have a
• 18:14
  Speaker 1: travel like a photon. But you know a gluon which
• 18:16
  Speaker 1: is exchanged between two quarks, that does happen at the
• 18:18
  Speaker 1: speed of light. The speed of information of the strong
• 18:21
  Speaker 1: force is the speed of light. All right, Well, photons
• 18:24
  Speaker 1: and gluons, I guess they they're stuck together in that category.
• 18:27
  Speaker 1: But again, maybe give us an into the sense. What
• 18:30
  Speaker 1: does it mean to move at the speed of light?
• 18:32
  Speaker 1: What is it like? It's a fun question. What is
• 18:34
  Speaker 1: it like to move at the speed of light. You
• 18:36
  Speaker 1: would like to be able to put yourself in that
• 18:38
  Speaker 1: frame and say, I'm moving along with a photon. What
• 18:41
  Speaker 1: is the photon? See? It's not something you can really
• 18:44
  Speaker 1: do because photons don't have a frame. Like if a
• 18:47
  Speaker 1: spaceship is flying by the Earth, you can put yourself
• 18:49
  Speaker 1: in this frame where the spaceship is at rest and say, okay,
• 18:52
  Speaker 1: I'm moving with the spaceship. What do I see? I
• 18:55
  Speaker 1: see the same thing as the spaceship. You can't do
• 18:57
  Speaker 1: that with a photon because the photon is never at rest.
• 19:00
  Speaker 1: There's no like frame you can put yourself in to
• 19:02
  Speaker 1: say I'm moving with the photon. Photons always move at
• 19:06
  Speaker 1: the speed of light relative to anybody, So no matter
• 19:08
  Speaker 1: where you are in the universe and how fast you're going,
• 19:10
  Speaker 1: that photon is zipping away from you at the speed
• 19:13
  Speaker 1: of light, and so you can't sort of like put
• 19:15
  Speaker 1: yourself in the point of view of a photon. M mmm.
• 19:18
  Speaker 1: So there's sort of like pure motion, right, because they
• 19:22
  Speaker 1: don't have mass, so they don't have a substance to them,
• 19:24
  Speaker 1: so all of their energy is in their speed. Yeah,
• 19:27
  Speaker 1: all of their energy is in their speed exactly. They
• 19:29
  Speaker 1: are just motioned. There's nothing to them, Like if you
• 19:33
  Speaker 1: could catch up with a photon, it was sort of
• 19:35
  Speaker 1: disappear in a puff of motionlessness. You know, they are
• 19:39
  Speaker 1: only motion, but it's it's like a wiggle in the
• 19:41
  Speaker 1: like a kinetic field. Right, Yeah, it's the motion of
• 19:44
  Speaker 1: that field. But isn't it a wiggle like a little perturbation. Yeah,
• 19:49
  Speaker 1: pure kinetic energy. Right, And people right in they're confused
• 19:52
  Speaker 1: about that because they say, well, it's energy, and energy
• 19:55
  Speaker 1: is mc squared, So doesn't that mean the photon has mass? Right?
• 19:59
  Speaker 1: And the wrinkle there is that equals mc squared only
• 20:02
  Speaker 1: applies to particles at rest, because the m there applies
• 20:05
  Speaker 1: to its rest mass. There's another term there which we
• 20:08
  Speaker 1: don't often talk about. The full equation is like E
• 20:10
  Speaker 1: squared equals M squared c to the fourth plus p
• 20:14
  Speaker 1: squared c square. There's a term there for momentum, and
• 20:17
  Speaker 1: so for a particle that has mass and momentum, there
• 20:19
  Speaker 1: are two terms there. There's the mass term and the
• 20:22
  Speaker 1: momentum term. Photons don't have any mass, so they just
• 20:26
  Speaker 1: have the momentum term. The equation for photon is E
• 20:29
  Speaker 1: equals pc momentum times the speed of light. So photons
• 20:33
  Speaker 1: are really weird because they don't have mass, but they
• 20:36
  Speaker 1: do have momentum, so they can like push things. Right,
• 20:39
  Speaker 1: that's how solar sales work. Right. They catch sunlight and
• 20:42
  Speaker 1: they transfer that momentum to motion, and that's how you
• 20:45
  Speaker 1: can sail out of the solar system. So photons do
• 20:49
  Speaker 1: have momentum and they go at the speed of light,
• 20:51
  Speaker 1: but there are a couple of caveats to that, maybe
• 20:55
  Speaker 1: not just for photons, but for everything else. Let's dig
• 20:58
  Speaker 1: into the ways that the rules that don't apply. But first,
• 21:01
  Speaker 1: let's take a quick break. All right, we're talking about
• 21:16
  Speaker 1: the speed limit of the universe and how it applies
• 21:19
  Speaker 1: to a charged particle, because I guess the charged particle
• 21:22
  Speaker 1: is a little bit different. Yeah, particles that have charge
• 21:25
  Speaker 1: also have mass, and the rules for massive particles and
• 21:29
  Speaker 1: for charge particles are a little bit different than the
• 21:32
  Speaker 1: rules for massless chargeless photons. Yeah, we've been talking about
• 21:37
  Speaker 1: how the speed limit applies to photons, which I guess
• 21:40
  Speaker 1: it does, but it almost only applies to photons and
• 21:44
  Speaker 1: I guess gluons. But it limits how fast photons can go.
• 21:48
  Speaker 1: But there are caveats to that rule. Right, it's not
• 21:50
  Speaker 1: necessarily the case that photons go at the speed of light. Yeah,
• 21:54
  Speaker 1: there are caveats to that rule. When we say that
• 21:57
  Speaker 1: photons always travel at the speed of light, when we mean,
• 22:00
  Speaker 1: but we don't often say, is that that's true in
• 22:03
  Speaker 1: your local inertial frame. If space is not curved, basically
• 22:07
  Speaker 1: the playground of special relativity, operate in flat space and
• 22:12
  Speaker 1: have things whizzing around near each other, that's what you're
• 22:15
  Speaker 1: going to observe. But if space is curved or expanding,
• 22:18
  Speaker 1: or things are really really far away from you, then
• 22:21
  Speaker 1: you can no longer apply those rules, and things start
• 22:25
  Speaker 1: to get really weird. It seems like a very limiting
• 22:28
  Speaker 1: caveat I mean local flat space. That's almost never true.
• 22:32
  Speaker 1: And if you're there, then you're bending space, which means
• 22:35
  Speaker 1: it doesn't apply to that's true, although you're not that massive,
• 22:39
  Speaker 1: and so you don't really bend space. Oh thanks, I've
• 22:42
  Speaker 1: been working out, and no matter how curved the universe is,
• 22:47
  Speaker 1: you can always find a locally flat approximation to it. Right,
• 22:51
  Speaker 1: space is always flat. In a local approximation, you can
• 22:54
  Speaker 1: always put a tangent on some surface and say, oh,
• 22:57
  Speaker 1: in this vicinity, I can assume I'm in flats space,
• 23:00
  Speaker 1: and that's sort of the issue is that special relativity
• 23:02
  Speaker 1: applies in our local vicinity where we can assume things
• 23:05
  Speaker 1: are flat, but then over larger distances we can't really
• 23:09
  Speaker 1: make that assumption, and that's why things break down. Well,
• 23:12
  Speaker 1: I guess the question is how do they break down
• 23:14
  Speaker 1: when when space is not flat, when it's a little
• 23:17
  Speaker 1: curved or a lot curve, does like go faster than
• 23:20
  Speaker 1: the speed of light or slower than the speed of light.
• 23:22
  Speaker 1: The space is curved between you and another galaxy, then
• 23:24
  Speaker 1: you have two different frames. You have your frame, you
• 23:27
  Speaker 1: have the frame in that galaxy, and how you translate
• 23:30
  Speaker 1: velocity from one frame to another is a little bit arbitrary.
• 23:34
  Speaker 1: You can do it in lots of different ways because
• 23:36
  Speaker 1: space is curved between you. We talked about this once
• 23:39
  Speaker 1: in the podcast. That has to do with like comparing
• 23:42
  Speaker 1: whether two vectors are parallel and comparing their length, and
• 23:46
  Speaker 1: if space is curved between two points, then how you
• 23:49
  Speaker 1: move that vector over that space depends on the path
• 23:52
  Speaker 1: that you've taken. So it's sort of not well defined
• 23:55
  Speaker 1: in the sense that there's like many ways that you
• 23:58
  Speaker 1: could do it and get different and service so you
• 24:01
  Speaker 1: can't really compare velocities in two different frames, if this
• 24:05
  Speaker 1: curvature or expansion between them. Yeah, it gets really tricky
• 24:09
  Speaker 1: and complicated, and we spend a whole hour talking about this.
• 24:12
  Speaker 1: I remember, but I guess what's the takeaway? There are
• 24:14
  Speaker 1: many ways to compute the velocity of a photo going
• 24:17
  Speaker 1: from between here and another galaxy. But do some of
• 24:19
  Speaker 1: these solutions tell you that this light is moving faster
• 24:22
  Speaker 1: or slower than the speed of light? Or do they
• 24:24
  Speaker 1: all tell you it's moving slower than the speed of light?
• 24:26
  Speaker 1: Some of them tell you that those photons are moving
• 24:28
  Speaker 1: faster than the speed of light, and some of them
• 24:30
  Speaker 1: tell you that the photons are moving slower than the
• 24:32
  Speaker 1: speed of light. So there's an infinite number of ways
• 24:34
  Speaker 1: that you could do this, compare velocities in one galaxy
• 24:38
  Speaker 1: to another because there are different reference frames. There's also
• 24:40
  Speaker 1: sort of a standard way that we do it, which
• 24:42
  Speaker 1: is that we just try to like extrapolate our frame
• 24:45
  Speaker 1: out to the end of the universe, even though we
• 24:46
  Speaker 1: know that doesn't really work. And those galaxies are moving
• 24:49
  Speaker 1: away from us faster than the speed of light, so
• 24:51
  Speaker 1: things seem to be breaking that speed of light limit.
• 24:53
  Speaker 1: Because you've done this thing of extending your inertial frame
• 24:56
  Speaker 1: out to the end of the universe, which you're not
• 24:58
  Speaker 1: technically allowed to do. The other way you can look
• 25:00
  Speaker 1: at it is to say they have their frame, we
• 25:02
  Speaker 1: have our frame, and space is expanding between those frames.
• 25:05
  Speaker 1: So nothing's breaking the speed of light limit. It's just
• 25:07
  Speaker 1: that space itself is growing and in its own frame,
• 25:11
  Speaker 1: everything is moving less than the speed of light. That's
• 25:13
  Speaker 1: what I mean when I say there's like different ways
• 25:15
  Speaker 1: you could assign that velocity. They're all sort of reasonable
• 25:18
  Speaker 1: and give you different answers. So there are those important capiats,
• 25:21
  Speaker 1: But in your local inertial frame, like your the laboratory,
• 25:25
  Speaker 1: the measurements you're going to actually make, you're never going
• 25:27
  Speaker 1: to observe anything going faster than the speed of light.
• 25:30
  Speaker 1: M M, I see. So even the local bending of
• 25:32
  Speaker 1: space can only slow down the speed of light. Is
• 25:34
  Speaker 1: that what you're saying? Like, if I'm orbiting a black hole,
• 25:37
  Speaker 1: for example, and space has really warped around me and
• 25:40
  Speaker 1: I run those experiments, what what would I see there?
• 25:42
  Speaker 1: I think you're breaking the assumption because we're talking about
• 25:45
  Speaker 1: a local flat frame, and if you're near a black hole,
• 25:47
  Speaker 1: then you're definitely not in a local, flat frame. So
• 25:50
  Speaker 1: I would say that if your space is pretty local
• 25:52
  Speaker 1: and pretty flat, you're always going to see photons moving
• 25:55
  Speaker 1: at the speed of light. So there's one caveat we
• 25:57
  Speaker 1: haven't talked about yet. But if you are near a
• 26:00
  Speaker 1: black hole or something else than spaces bendy and crazy
• 26:03
  Speaker 1: and the velocities get insane, and you could see photons
• 26:06
  Speaker 1: moving at zero velocity. For example, as a photon climbs
• 26:09
  Speaker 1: out of the gravity well or tries to climb out
• 26:13
  Speaker 1: of the gravity well of a black hole, to you,
• 26:15
  Speaker 1: it appears to go at zero velocity. Right, photons are
• 26:17
  Speaker 1: contained within a black hole. How could they do that
• 26:20
  Speaker 1: if they were moving at the speed of light Because
• 26:22
  Speaker 1: the bending nous of space there makes all these velocities
• 26:25
  Speaker 1: a little wonky to calculate. But would you ever see
• 26:28
  Speaker 1: it go faster? Probably not right. That only happens when
• 26:32
  Speaker 1: you have space expanding. Yeah, I believe that's true. The
• 26:35
  Speaker 1: bending of space can only effectively slow down the speed
• 26:39
  Speaker 1: of light that you observe. In order things to appear
• 26:41
  Speaker 1: to go fasten the speed of light, you need space
• 26:43
  Speaker 1: to expand rather than to curve. Well, there's another caveat
• 26:46
  Speaker 1: to this also is that the space has to be empty. Yes,
• 26:49
  Speaker 1: that's right. The limit that we talk about is the
• 26:51
  Speaker 1: speed of light in a vacuum, as if there's nothing
• 26:53
  Speaker 1: out there in space for these photons to interact with.
• 26:56
  Speaker 1: But we know that light slows down as it passes
• 26:59
  Speaker 1: through material hills or at the index of refraction tells
• 27:02
  Speaker 1: you the speed of light through that material. So light
• 27:06
  Speaker 1: traveling through glass goes slower than light traveling through a vacuum,
• 27:10
  Speaker 1: Like traveling through air goes a little bit slower than
• 27:12
  Speaker 1: light traveling through a vacuum. And that's not because somehow
• 27:15
  Speaker 1: the air molecules or the glass molecules like effect the
• 27:19
  Speaker 1: space that the light travels in. It's because light keeps
• 27:21
  Speaker 1: running into things, right, like trying to move through a
• 27:24
  Speaker 1: crowded room. The float that keeps bumping into the air
• 27:26
  Speaker 1: and glass molecules and then getting re emitted on the
• 27:29
  Speaker 1: other side. But it still has to sort of something
• 27:31
  Speaker 1: has to happen when they bump. The speed that we're
• 27:34
  Speaker 1: talking about here is basically the average speed from one
• 27:37
  Speaker 1: side of the material to the other side of the material.
• 27:39
  Speaker 1: You can think about it as the light sort of
• 27:40
  Speaker 1: zig zagging between molecules or atoms that it's interacting with
• 27:44
  Speaker 1: each of those zigs or each of those zags, it's
• 27:46
  Speaker 1: still moving at the speed of light. Of photon is
• 27:49
  Speaker 1: always moving at the speed of light, but it sort
• 27:51
  Speaker 1: of gets absorbed. It takes time to get re emitted,
• 27:54
  Speaker 1: and so that sort of slows it down. It's like
• 27:56
  Speaker 1: if you send your teenager on an errand to the
• 27:58
  Speaker 1: store and they stop and chat at their friends house
• 28:00
  Speaker 1: every block, it's can take them a lot longer to
• 28:02
  Speaker 1: get there, even if they're driving at top speed between
• 28:05
  Speaker 1: all of their friends houses. That's an interesting neighborhood you
• 28:08
  Speaker 1: live in where your teenagers is driving and stopping to
• 28:12
  Speaker 1: talk to their friends at the same time. Hopefully they
• 28:15
  Speaker 1: are being the speed limit there. Fortunately, I don't have
• 28:17
  Speaker 1: teenagers who can drive yet, so maybe my analogies will
• 28:20
  Speaker 1: improve when I have some data. So it's if space
• 28:24
  Speaker 1: is empty and it's not bend deep or distorted or expanding,
• 28:29
  Speaker 1: then light goes at the speed of light. But now
• 28:31
  Speaker 1: what about particles that are not light? Pretty much everything
• 28:34
  Speaker 1: else besides gluons. What if a particle, for example, has mass. Yes,
• 28:39
  Speaker 1: so photons can go with the speed of light if
• 28:41
  Speaker 1: they're in a vacuum and not near a black hole,
• 28:43
  Speaker 1: for example. But electrons, particles with mass, they can never
• 28:48
  Speaker 1: actually reach the speed of light. Oh yeah, is there
• 28:50
  Speaker 1: a particular reason for that. It's sort of interesting and philosophical.
• 28:53
  Speaker 1: It's not like there's a lower speed limit for electrons.
• 28:56
  Speaker 1: It's not like electrons can only go speed of light
• 29:00
  Speaker 1: and they're always pegg there. It's just that they ask
• 29:02
  Speaker 1: emp tonically can approach the speed of light, So there's
• 29:05
  Speaker 1: no actual limit there. They just get closer and closer
• 29:08
  Speaker 1: and closer to the speed of light as you add
• 29:10
  Speaker 1: more energy, but they never actually get to the speed
• 29:14
  Speaker 1: of light. Yeah, that's weird. So you're saying that it's
• 29:16
  Speaker 1: a speed limit, not because like if I just create
• 29:20
  Speaker 1: an electron or a proton or a cord going at
• 29:23
  Speaker 1: the speed of light, maybe can that can happen. It's
• 29:26
  Speaker 1: just that for any electron or a particle with mass
• 29:29
  Speaker 1: that starts address I can, I can never get it
• 29:32
  Speaker 1: to the speed of light. A particle with mass moving
• 29:34
  Speaker 1: at the speed of light would have infinite kinetic energy.
• 29:37
  Speaker 1: So if you could create a particle with infinite kinetic energy,
• 29:40
  Speaker 1: then yes, it would be moving at the speed of light. Otherwise,
• 29:43
  Speaker 1: taking a particle and getting it to the speed of
• 29:45
  Speaker 1: light would require giving it infinite kinetic energy. And the
• 29:48
  Speaker 1: key concept, of course is that these particles have mass.
• 29:50
  Speaker 1: So why is it that having master means that you
• 29:53
  Speaker 1: require infinite energy to get to the speed of light,
• 29:55
  Speaker 1: whereas a photon with a non infinite energy can move
• 29:58
  Speaker 1: at the speed of light it and the key concept there,
• 30:01
  Speaker 1: of course, is the mass of the particle. Mass is
• 30:04
  Speaker 1: this property of particles like resist changes to their motion.
• 30:08
  Speaker 1: So you have an electron, it's gonna stay at rest
• 30:10
  Speaker 1: unless you give it a push, and it's going to
• 30:12
  Speaker 1: stay at certain velocity unless you give it a push.
• 30:15
  Speaker 1: And mass is that ability to resist changes in motion.
• 30:18
  Speaker 1: So it takes energy to speed it up. So you
• 30:20
  Speaker 1: give the electron to push, it speeds up as it
• 30:22
  Speaker 1: gets faster and faster, though it takes bigger pushes more
• 30:26
  Speaker 1: energy to take it up the next level and speed.
• 30:29
  Speaker 1: It's not a linear relationship, right, And that's just kind
• 30:31
  Speaker 1: of how the universe is, right, Like, that's just what
• 30:35
  Speaker 1: mass is. It's not like they have mass and therefore
• 30:38
  Speaker 1: they're hard to push the more you go. It's like
• 30:41
  Speaker 1: the definition of mass is the fact that some particles
• 30:44
  Speaker 1: gets harder and harder to push. Yeah, I think it's
• 30:46
  Speaker 1: important to understand what things we understand and what things
• 30:49
  Speaker 1: we just like observe and define. Right. We have observed
• 30:53
  Speaker 1: that things that have internal energy in them have this
• 30:56
  Speaker 1: property of inertia. An electron has some internal energy to it,
• 31:00
  Speaker 1: protons have some internal energy to it, the mass of
• 31:03
  Speaker 1: the corks and then also the mass of the binding
• 31:05
  Speaker 1: energy between the corks. Anything with internal energy seems to
• 31:08
  Speaker 1: have this property of inertia, of resisting changes to its motions.
• 31:12
  Speaker 1: So yeah, sort of a deep philosophical mystery why that is,
• 31:14
  Speaker 1: Why do we live in the universe that way and
• 31:16
  Speaker 1: not some other way? But it's something that we've observed
• 31:19
  Speaker 1: in the universe and try to describe in our theories,
• 31:21
  Speaker 1: and those theories are very effective when we test them
• 31:24
  Speaker 1: out in nature, So that's why we believe they are true,
• 31:27
  Speaker 1: even if we don't know why the universe is this
• 31:29
  Speaker 1: way and not some other way. Yeah, it's a massive issue.
• 31:32
  Speaker 1: And how is this related to the Higgs boson and
• 31:34
  Speaker 1: the Higgs field, because I know everyone talks about how
• 31:37
  Speaker 1: the Higgs field is what gives particles mass. Is this
• 31:40
  Speaker 1: inertial mass that's related to the speed of light, related
• 31:43
  Speaker 1: to the Higgs field and Higgs boson. So most generally
• 31:46
  Speaker 1: mass is just internal stored energy of some kind, and
• 31:50
  Speaker 1: most of the mass in your body doesn't come from
• 31:52
  Speaker 1: the mass of the particles of your body. So for example,
• 31:56
  Speaker 1: you're mostly protons and neutrons, and those protons have massive
• 32:00
  Speaker 1: from their corks, but they also have mass from how
• 32:02
  Speaker 1: those corks are bound together. So the internal stored energy
• 32:06
  Speaker 1: the proton is mostly the energy of those particles bound together.
• 32:10
  Speaker 1: A little bit of the mass of the proton does
• 32:12
  Speaker 1: come from the mass of those particles, like the corks
• 32:14
  Speaker 1: that are inside the proton, and those corks they get
• 32:17
  Speaker 1: their inertial mass from the Higgs boson, but again it's
• 32:20
  Speaker 1: internal stored energy. The corks themselves, like the true theoretical object,
• 32:25
  Speaker 1: is massless, but as the cork moves through the universe,
• 32:28
  Speaker 1: it interacts with this Higgs field and it creates this
• 32:31
  Speaker 1: like effective cork, this object which is moving differently because
• 32:34
  Speaker 1: of its interactions with the Higgs field in such a
• 32:37
  Speaker 1: way that it moves as if it had mass. So
• 32:39
  Speaker 1: it is inertial mass that we're talking about, and some
• 32:42
  Speaker 1: of the inertial mass in the universe comes from the
• 32:44
  Speaker 1: Higgs boson, but not all of it, right, In fact,
• 32:46
  Speaker 1: most of it doesn't come from the Higgs field and
• 32:48
  Speaker 1: Higgs boson. Most of it just comes from this fact
• 32:51
  Speaker 1: of the universe that things with energy are are hard
• 32:55
  Speaker 1: to move in the universe and impossible to get moving
• 32:58
  Speaker 1: at the speed of light. Yeah, exact, you often hear
• 33:00
  Speaker 1: their frame that as things approach the speed of light,
• 33:03
  Speaker 1: they get more massive, as if like an electron is
• 33:06
  Speaker 1: getting as heavy as a car for example, if it
• 33:09
  Speaker 1: goes near the speed of light. And as some sort
• 33:11
  Speaker 1: of an old fashioned idea that is trying to convey
• 33:14
  Speaker 1: to you this concept that as something approaches the speed
• 33:16
  Speaker 1: of light, it takes more energy to move it up
• 33:19
  Speaker 1: in velocity than it did when it was moving slower.
• 33:22
  Speaker 1: We don't really think about things literally gaining mass. It's
• 33:25
  Speaker 1: just that it takes a bigger push to notch them
• 33:27
  Speaker 1: up to the next level of velocity. Right, Although it's
• 33:30
  Speaker 1: kind of true, right, I mean, the idea is that
• 33:33
  Speaker 1: mass is the resistance to movement or to increasing your movement.
• 33:36
  Speaker 1: Then yeah, as it gets harder, because the universe, as
• 33:39
  Speaker 1: it gets harder, technically it is sort of gaining mass, right,
• 33:43
  Speaker 1: It doesn't really hang together though, Like if you want
• 33:46
  Speaker 1: to use that mass and F equals m A, it
• 33:48
  Speaker 1: doesn't really work because then that mass is like weirdly
• 33:51
  Speaker 1: directionally dependent, because if you're moving along the x axis
• 33:55
  Speaker 1: for example, now you have like a lot of mass
• 33:57
  Speaker 1: along the x axis, but you don't have that mass
• 34:00
  Speaker 1: along the y axis, right, Like turnting can give you
• 34:02
  Speaker 1: a push along the y axis with a certain force
• 34:04
  Speaker 1: and you get one acceleration, but if they give you
• 34:06
  Speaker 1: a push along the x axis with that same force,
• 34:09
  Speaker 1: they get a different acceleration. The more general way to
• 34:12
  Speaker 1: think about it is just in terms of momentum. This
• 34:14
  Speaker 1: this equation for relativistic momentum which includes this factor. So
• 34:18
  Speaker 1: we just leave mass as the rest mass of an object,
• 34:21
  Speaker 1: like how massive would it be if it was at rest,
• 34:23
  Speaker 1: and this extra resistance to accelerating at high speeds. We
• 34:28
  Speaker 1: fold that into the definition of momentum, which then helps
• 34:31
  Speaker 1: fix up F equals I may, which in the end
• 34:33
  Speaker 1: is just F equals the derivative of momentum with respect
• 34:36
  Speaker 1: to time. So this is whole topic of relativistic kinematics,
• 34:39
  Speaker 1: which I think we dug into in another episode. Yeah,
• 34:42
  Speaker 1: I think what you're trying to say is that an
• 34:44
  Speaker 1: electron looks less massive depending on which angle you're looking
• 34:47
  Speaker 1: at it, Like the electron has a good angle and
• 34:50
  Speaker 1: a bad angle. I think the concept of relativistic mass
• 34:53
  Speaker 1: things actually getting heavier as you get to higher mass,
• 34:56
  Speaker 1: doesn't really hang together if you try to propagate it
• 34:58
  Speaker 1: through all the equations. But it's sort of an old
• 35:00
  Speaker 1: fashioned way of thinking about things. All right, that's how
• 35:03
  Speaker 1: mass effects how fast you can go in the universe.
• 35:05
  Speaker 1: Now let's talk about how other things might affect how
• 35:08
  Speaker 1: fast you can move through the universe, including whether space
• 35:12
  Speaker 1: is empty or not. So let's get into that. But
• 35:14
  Speaker 1: first let's take another quick break. All Right, we're asking
• 35:30
  Speaker 1: the question what is the fastest that a charge particle
• 35:32
  Speaker 1: or pretty much any particle can go, right, because there
• 35:35
  Speaker 1: are a lot of caveats to this idea that nothing
• 35:37
  Speaker 1: can move faster than the speed of light. One of
• 35:39
  Speaker 1: those caveats was that space had to be empty. But
• 35:42
  Speaker 1: what happens if space is not empty? Yeah, we talked
• 35:45
  Speaker 1: about photons moving through glass, photons moving through water, but
• 35:48
  Speaker 1: you might imagine, well, what about space between here and Andromeda?
• 35:51
  Speaker 1: For example? That's mostly empty, right, Or what about the
• 35:54
  Speaker 1: space outside of Earth in our solar system that's mostly empty? Right?
• 35:58
  Speaker 1: Photons surely spend most of their time whizzing around basically
• 36:01
  Speaker 1: at the speed of light. What turns out, space is
• 36:03
  Speaker 1: almost never empty. The space in our solar system is
• 36:07
  Speaker 1: filled with particles from the Sun. The Sun pumps out
• 36:10
  Speaker 1: a solar wind of protons and electrons and other stuff
• 36:13
  Speaker 1: that's always blowing through the Solar system. So photons traveling
• 36:16
  Speaker 1: through our solar system are constantly running into these protons
• 36:19
  Speaker 1: and these electrons and interacting with them. Really interesting. So
• 36:23
  Speaker 1: you're saying, like the space between us and the Sun
• 36:26
  Speaker 1: is not perfectly clear. There's all kinds of stuff in it,
• 36:28
  Speaker 1: which means that the speed of light in our solar
• 36:30
  Speaker 1: system is slower than the speed of light, a tiny, tiny,
• 36:34
  Speaker 1: tiny little bit slower. This is very dilute. Is like
• 36:36
  Speaker 1: not very many protons per cubic meter, you know, between
• 36:39
  Speaker 1: us and Jupiter, for example, but there are some. And
• 36:42
  Speaker 1: so if you're talking technically, like our photons that bounce
• 36:45
  Speaker 1: off Jupiter and then come back to Earth, are those
• 36:47
  Speaker 1: moving at the speed of light? Technically they're moving at
• 36:50
  Speaker 1: a little bit less than the speed of light. And
• 36:52
  Speaker 1: that's also true for photons from Andromeda, for example, because
• 36:56
  Speaker 1: the space between us and other galaxies is also not empty, right, yeah,
• 37:01
  Speaker 1: because there's a lot of stuff in between us and
• 37:03
  Speaker 1: and Drama. Not. Even though it's hard to see what
• 37:05
  Speaker 1: the naked eye, you probably imagine the university these clusters
• 37:07
  Speaker 1: of stars grouped into galaxies, and that's basically where everything is.
• 37:12
  Speaker 1: But don't forget that the universe is mostly gas, right.
• 37:15
  Speaker 1: Stars are a tiny fraction in the universe, So really
• 37:17
  Speaker 1: you should be thinking about the gas in those galaxies,
• 37:20
  Speaker 1: and it's also gas between the galaxies. Think of the
• 37:24
  Speaker 1: universe not as a bunch of dots of stars clustered
• 37:27
  Speaker 1: into galaxies, but like a cosmic web of gas filaments,
• 37:30
  Speaker 1: and where those filaments overlap and intersect, then you have
• 37:32
  Speaker 1: these deep pools that form stars and visible light and
• 37:35
  Speaker 1: all that cool stuff. But between the galaxies there are
• 37:38
  Speaker 1: these very long tendrils of gas between Us and Andromeda,
• 37:42
  Speaker 1: for example, a huge amount of gas. They estimate like
• 37:45
  Speaker 1: a significant fraction of all the matter in the universe
• 37:49
  Speaker 1: are kind of matter is actually between galaxies, not in galaxies. Yeah,
• 37:54
  Speaker 1: like of the matter in the universe is basically small, right, Yeah,
• 38:00
  Speaker 1: they call this the warm hot intergalactic medium. I'm not
• 38:04
  Speaker 1: even gonna talk about why they call it warm hot.
• 38:08
  Speaker 1: But the acronym for it is w H I M,
• 38:10
  Speaker 1: which you know, they didn't choose on a whim, but
• 38:12
  Speaker 1: they did because it spells out whim. It's just a
• 38:15
  Speaker 1: whimsical name, you know, for something that's warm hot. Now,
• 38:17
  Speaker 1: why do they call it warm hot because it's not
• 38:20
  Speaker 1: cool warm. They call it warm hot because it's sort
• 38:23
  Speaker 1: of between warm and hot. And remember, if you were
• 38:26
  Speaker 1: out there in space, you would freeze your tissue off.
• 38:29
  Speaker 1: But these particles are fairly high speed, and so we
• 38:32
  Speaker 1: say that they have a fairly high temperature. This intergalactic
• 38:36
  Speaker 1: plasma can actually be fairly hot on a temperature scale,
• 38:39
  Speaker 1: even though it's very very dilute, so it doesn't contain
• 38:41
  Speaker 1: a lot of heat. But because of the speed of
• 38:43
  Speaker 1: the particles, they say it's fairly hot, not fast enough
• 38:47
  Speaker 1: to call it actually hot, not slow enough to call
• 38:49
  Speaker 1: it is warm. So it's sort of like warm too hot,
• 38:52
  Speaker 1: So they call it warm hot. It's not a whim
• 38:55
  Speaker 1: or a hymn, it's a whim. It should be W
• 38:59
  Speaker 1: T H I M, but then it'll be like with them,
• 39:02
  Speaker 1: I get the lukewarm intergalactic medium, wouldn't really fly there, No,
• 39:06
  Speaker 1: I suppose not, And so that slows down photons that
• 39:09
  Speaker 1: are moving through the universe between galaxies. So when you're
• 39:12
  Speaker 1: looking up at the night sky and know that all
• 39:14
  Speaker 1: the photons that are traveling towards you were traveling a
• 39:16
  Speaker 1: little bit less than the speed of light, even the
• 39:19
  Speaker 1: ones coming from other galaxies. But wait, wait, wait, isn't
• 39:22
  Speaker 1: the space between our galaxies also expanding? So space everywhere
• 39:26
  Speaker 1: is expanding, right, and the expansion happens simultaneously at every
• 39:30
  Speaker 1: point in space at the same rate for things are
• 39:32
  Speaker 1: near each other. However, that's a pretty small effect. And
• 39:34
  Speaker 1: also things that near each other have gravity, so the
• 39:37
  Speaker 1: gravity and Dromeda is actually pulling it towards us faster
• 39:40
  Speaker 1: than space is expanding between us. So you can basically
• 39:44
  Speaker 1: ignore the expansion of space when you're thinking about photons
• 39:47
  Speaker 1: from Andromeda, because they're like in our local gravitational bubble, right,
• 39:50
  Speaker 1: But it's it's still expanding, which is speeding up the
• 39:53
  Speaker 1: speed of light a little bit. But you're saying that
• 39:55
  Speaker 1: the effect of the whimsical gas in between is slowing
• 39:58
  Speaker 1: it down more than the expand sin is speeding it up. Yes,
• 40:01
  Speaker 1: so the expansion would be moving and Dromeda away from us,
• 40:03
  Speaker 1: but gravity is holding Andromeda in place, sort of the
• 40:05
  Speaker 1: same way that gravity holds the Earth around the Sun.
• 40:08
  Speaker 1: You're right there, the photons from Andromeda are moving through
• 40:10
  Speaker 1: expanding space. Because they're moving towards us, that would actually
• 40:13
  Speaker 1: be slowing down their effective speed. Okay, now let's talk
• 40:16
  Speaker 1: about charge particles. We know that particles with mass have
• 40:20
  Speaker 1: extra limitation with respect to the speed of light, and
• 40:24
  Speaker 1: we know that space is not empty. Does having a
• 40:26
  Speaker 1: charge affect you more than having mass? Like, does it
• 40:30
  Speaker 1: somehow give you a boost through this plasma or does
• 40:33
  Speaker 1: it slowly down more? Well, interestingly, there are no particles
• 40:37
  Speaker 1: that have charge and don't have mass. Right so the
• 40:40
  Speaker 1: photon has no charge and no mass. But if you're
• 40:42
  Speaker 1: a charge particle number one, that means that you have
• 40:44
  Speaker 1: mass like the electron and the corks. All the particles
• 40:48
  Speaker 1: that have charged also have mass, So that right away
• 40:50
  Speaker 1: means if you have charge, you can't go at the
• 40:52
  Speaker 1: speed of light. Really wouldn't that make you think they're
• 40:54
  Speaker 1: somehow related? Yeah, it's a really fascinating clue and one
• 40:57
  Speaker 1: that we just don't understand at all. Possible that one
• 41:00
  Speaker 1: day in the future we will discover a massless charged particle,
• 41:04
  Speaker 1: but none exists currently in our universe that we know about. Well,
• 41:08
  Speaker 1: gluons have charged, they just don't have electromagnetic charge, right,
• 41:12
  Speaker 1: that's right. They have color charge charged for the strong force. Yeah,
• 41:15
  Speaker 1: that's a really good point. And we do sometimes discover
• 41:18
  Speaker 1: new categories of particles, like the Higgs boson was a
• 41:21
  Speaker 1: particle like no particle we had seen before. It's the
• 41:24
  Speaker 1: first scale or particle that we've ever found before, a
• 41:27
  Speaker 1: particle without any spin. And so it's possible to discover
• 41:31
  Speaker 1: new categories of particles that we haven't seen before in
• 41:33
  Speaker 1: the universe, or we might discover that that's impossible for
• 41:36
  Speaker 1: some reason we haven't learned yet. But the higgs boson
• 41:39
  Speaker 1: has massed to it, right, it interacts with itself, but
• 41:42
  Speaker 1: it does the higgs boson have charge. The higgs boson
• 41:45
  Speaker 1: doesn't have electric charge. No, But it was interesting because
• 41:48
  Speaker 1: it also doesn't have quantum spin like all the other
• 41:50
  Speaker 1: particles do. So the higgs boson does have mass but
• 41:53
  Speaker 1: no charge. The higgs boson has mass but no charge.
• 41:56
  Speaker 1: But we don't have any particles that have charge but
• 41:58
  Speaker 1: no mass. Oh, it seems so if you have charge,
• 42:01
  Speaker 1: then you usually have mass. That's the pattern so far.
• 42:04
  Speaker 1: We don't know if that's a hard and fast rule
• 42:06
  Speaker 1: or just sort of like a coincidence or electromagnetic charge.
• 42:09
  Speaker 1: I should say, right, yes, exactly, electromagnetic charge. So now,
• 42:13
  Speaker 1: if you're a proton flying through space on an electron
• 42:15
  Speaker 1: flying through space, you obviously can't move at the speed
• 42:18
  Speaker 1: of light just because you have mass. So if you're
• 42:21
  Speaker 1: charged particle, that also means you have mass, which means
• 42:23
  Speaker 1: you can't travel at the speed of light. How does
• 42:25
  Speaker 1: the charge affect your motion? Does it make you go
• 42:27
  Speaker 1: faster or slower through this plasma in the universe? Well? Both.
• 42:31
  Speaker 1: First of all, it allows you to go really fast
• 42:34
  Speaker 1: because having a charge means that you can get accelerated
• 42:36
  Speaker 1: by cosmic electric fields or magnetic fields. For example, you
• 42:40
  Speaker 1: can be near a black hole or a pulsar, which
• 42:42
  Speaker 1: have very very strong magnetic fields and you can gain
• 42:45
  Speaker 1: huge acceleration. And so it allows you to sort of
• 42:48
  Speaker 1: like tap into cosmic accelerators to get to really really
• 42:51
  Speaker 1: high energies. But then on the flip side, it also
• 42:55
  Speaker 1: slows you down because particles that have charge interact with photons,
• 42:59
  Speaker 1: and the unit verse is filled with photons, if photons
• 43:02
  Speaker 1: left over from the Big Bang, from the cosmic microwave
• 43:05
  Speaker 1: background radiation that's everywhere in the universe, and so charge
• 43:09
  Speaker 1: particles flying through the universe interact with those photons, which
• 43:13
  Speaker 1: constantly sap their energy. Mm I think you're saying that.
• 43:16
  Speaker 1: You know, if you have charge, that means that you
• 43:19
  Speaker 1: can be pulled by something that has the opposite charge
• 43:23
  Speaker 1: ahead of you, right, But it could also maybe slow
• 43:24
  Speaker 1: you down if the thing is behind you. Absolutely could.
• 43:26
  Speaker 1: You have magnetic fields and electric fields from cosmic objects
• 43:30
  Speaker 1: can accelerate or decelerate these particles. But also just the
• 43:33
  Speaker 1: whole universe is filled with a fog. If you're an
• 43:35
  Speaker 1: electron and you're flying through the universe, there really is
• 43:38
  Speaker 1: no empty space. You see photons everywhere and they're all
• 43:42
  Speaker 1: interacting with you. And there's this effect that if a
• 43:44
  Speaker 1: particle is moving really really really really really fast, then
• 43:48
  Speaker 1: it tends to interact with this cosmic microwave background photons
• 43:52
  Speaker 1: in a way that SAPs its energy and turns it
• 43:54
  Speaker 1: into other particles. And so there's basically like an effective
• 43:57
  Speaker 1: limit to how fast a charge particle can move through
• 44:00
  Speaker 1: the universe because of its interaction with the cosmic microwave
• 44:04
  Speaker 1: background radiation. Meaning like, if I'm a proton flying through
• 44:07
  Speaker 1: space and uh I hit a photon head on, it's
• 44:10
  Speaker 1: going to slow me down, right, because the photon has momentum. Right,
• 44:14
  Speaker 1: You're gonna interact with that photon, and some of your
• 44:16
  Speaker 1: energy is going to get used up to create a
• 44:18
  Speaker 1: new particle, like a delta particle or some other low
• 44:21
  Speaker 1: mass particle, and then you can go fly off in
• 44:23
  Speaker 1: another direction, but you've lost some of that energy. What
• 44:25
  Speaker 1: if the photon hits you from behind, when did it
• 44:27
  Speaker 1: push you? Yeah, that's possible, and photons move faster than protons,
• 44:31
  Speaker 1: so they can catch up to a proton and give
• 44:33
  Speaker 1: it a little push. But the overall effect from a
• 44:36
  Speaker 1: proton like flying through this fob of photons, is that
• 44:40
  Speaker 1: it gets slowed down. It's like compressing the space in
• 44:43
  Speaker 1: front of it. You mean, like, there's an average speed
• 44:45
  Speaker 1: of all the photons in the universe, and if you're
• 44:47
  Speaker 1: going faster than that average speed, then you'll hit the
• 44:51
  Speaker 1: photons kind of like bugs in your windshield. I'm not
• 44:53
  Speaker 1: sure how to calculate the average speed of a photon.
• 44:55
  Speaker 1: But think about like the number of directions that a
• 44:58
  Speaker 1: photon could hit you. In. Most of the those ways
• 45:00
  Speaker 1: it would slow you down. In only a few ways
• 45:02
  Speaker 1: they would speed you up because you're you're moving in
• 45:05
  Speaker 1: a certain direction relative to the maybe the average direction
• 45:08
  Speaker 1: of all the photons. Yeah, that's right. And also, as
• 45:11
  Speaker 1: you move really fast through space, you tend to contract
• 45:13
  Speaker 1: the space in front of you, which increases the density
• 45:16
  Speaker 1: of the photons in front of you that you're hitting.
• 45:18
  Speaker 1: So there's a special relativistic effect there also, And what
• 45:21
  Speaker 1: this means is that really really high energy particles gets
• 45:24
  Speaker 1: slowed down. So we have cosmic accelerators out there, the
• 45:27
  Speaker 1: centers of galaxies and pulsars whatever, spewing out super high
• 45:31
  Speaker 1: energy charged particles, but then they basically screeched to a halt.
• 45:34
  Speaker 1: It's really really hard to have charged particles a crazy
• 45:37
  Speaker 1: high energy in the universe because the universe is kind
• 45:39
  Speaker 1: of like sticky for those charged particles. And that means
• 45:42
  Speaker 1: something really cool. It means that if you see one
• 45:44
  Speaker 1: of these particles, it can't have come from very far
• 45:47
  Speaker 1: away because very very high energy particles can't go very
• 45:51
  Speaker 1: far at our universe, they're sort of local, or they
• 45:53
  Speaker 1: started off with a super duper duper crazy amount of
• 45:56
  Speaker 1: energy to start with. Yeah, exactly, they would have to
• 45:59
  Speaker 1: have double bonkers energy if they come from really far away.
• 46:02
  Speaker 1: So you're saying that the whole universe is filled with
• 46:05
  Speaker 1: a little bit of light pollution, which kind of slows
• 46:07
  Speaker 1: everything down, makes it even harder to go at the
• 46:10
  Speaker 1: speed of light. And as time goes on, that light pollution,
• 46:14
  Speaker 1: the cosmic microwave background radiation is cooling, and so this
• 46:18
  Speaker 1: effect is fading because the universe is expanding, that light
• 46:21
  Speaker 1: is cooling, it's getting more and more dilute. So as
• 46:23
  Speaker 1: time goes on, the universe gets like less sticky for
• 46:26
  Speaker 1: charge particles, which means that these charged particles, these protons
• 46:29
  Speaker 1: coming out of cosmic accelerators can go faster and faster
• 46:33
  Speaker 1: as time goes on, or further and further at their
• 46:36
  Speaker 1: top speed. You mean like this light pollution of the
• 46:38
  Speaker 1: universe is kind of dissipating in a way. Yeah, precisely.
• 46:41
  Speaker 1: The fog is clearing very very slowly, Isn't the universe
• 46:45
  Speaker 1: also filled with like quantum vacuum energy, like particles popping
• 46:50
  Speaker 1: in and out. All space has quantum fields in it,
• 46:52
  Speaker 1: and those quantum fields can never relax down to zero,
• 46:55
  Speaker 1: so there's always some energy and space. We think that's
• 46:59
  Speaker 1: very very small. We also think that might be what's
• 47:01
  Speaker 1: causing the expansion of the universe. It's not something that
• 47:05
  Speaker 1: we understand very well. So then, if something is flying
• 47:08
  Speaker 1: through space, does it interact with those that vacuum quantum
• 47:12
  Speaker 1: fields particles popping up? It doesn't necessarily slow it down,
• 47:15
  Speaker 1: It just gives it inertia. So interacting with the Higgs
• 47:17
  Speaker 1: field is how the particle gets mass. It doesn't have
• 47:20
  Speaker 1: to slow it down. So it's possible to interact with
• 47:22
  Speaker 1: these quantum fields without slowing down. All right. Well, then
• 47:25
  Speaker 1: now to wrap it up and to answer the question
• 47:27
  Speaker 1: we set out to answer at the beginning, Daniel, what's
• 47:29
  Speaker 1: the fastest that a charge particle can go? Super duper
• 47:32
  Speaker 1: duper duper duper fast, but not actually the speed of
• 47:36
  Speaker 1: light and not for very far in the universe? You mean,
• 47:40
  Speaker 1: po Yeah, there's no actual limit, right, These particles can
• 47:45
  Speaker 1: keep approaching the speed of light but never actually get there.
• 47:48
  Speaker 1: And for charge particles, they just can't do it for
• 47:51
  Speaker 1: very far. So even if I did a perfect backflip
• 47:54
  Speaker 1: at the Olympics. You would only give me a nine.
• 47:57
  Speaker 1: I would give you a warm hot score. Yes, our right. Well,
• 48:00
  Speaker 1: another reminder that the universe has these strange rules. If
• 48:04
  Speaker 1: you think about them, they're kind of strange. But that's
• 48:07
  Speaker 1: kind of the job that we as humans have is
• 48:09
  Speaker 1: to figure out what are the rules and when can
• 48:13
  Speaker 1: you break them? And that's the job of us experimentalists
• 48:15
  Speaker 1: to go out there and actually try to break the
• 48:17
  Speaker 1: rules of the universe. All right, Well, we hope you
• 48:19
  Speaker 1: enjoyed that. Thanks for joining us, See you next time.
• 48:30
  Speaker 1: Thanks for listening, and remember that Daniel and Jorge explain
• 48:32
  Speaker 1: the Universe is a production of I Heart Radio. For
• 48:35
  Speaker 1: more podcast from my heart Radio, visit the i heart
• 48:39
  Speaker 1: Radio app, Apple Podcasts, or wherever you listen to your
• 48:42
  Speaker 1: favorite shows. Yeah,