Latest / Daniel and Kelly’s Extraordinary Universe / Listener Questions 45: Gravity and Black holes

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Listener Questions 45: Gravity and Black holes · Daniel and Kelly’s Extraordinary Universe

• 0:08
  Speaker 1: Hey, Daniel, do you ever get tired of answering questions
• 0:11
  Speaker 1: from listeners?
• 0:12
  Speaker 2: Not so far, But you know, ask me again in
• 0:14
  Speaker 2: another five years.
• 0:15
  Speaker 1: Oh, what's going to happen in five years?
• 0:18
  Speaker 2: I might have a different answer.
• 0:20
  Speaker 1: Some places you get the same questions over and over.
• 0:22
  Speaker 2: You know, there are a lot of common themes in
• 0:24
  Speaker 2: these questions, that's true.
• 0:25
  Speaker 1: And do you have like pre prepared answers ready to go?
• 0:28
  Speaker 2: You can't really do that because every question's a little
• 0:31
  Speaker 2: bit different. And for me, the fun part is figuring
• 0:34
  Speaker 2: out like what somebody misunderstood to lead to their confusion
• 0:38
  Speaker 2: and helping them unravel that.
• 0:41
  Speaker 1: So you kind of just like program an AI to
• 0:43
  Speaker 1: answer questions for you, kind of like they do now
• 0:45
  Speaker 1: with like customer service lines.
• 0:47
  Speaker 2: You could definitely program an AI to answer questions, but
• 0:50
  Speaker 2: it would generate nonsense.
• 0:51
  Speaker 1: Sometimes, isn't the answer nonsense? In physics, especially quantum mechanics, the.
• 0:57
  Speaker 2: Most amazing thing about the universe is that it doesn't
• 0:59
  Speaker 2: see aim to be nonsense. It seems to actually make sense.
• 1:03
  Speaker 1: So far, Maybe I'll ask you again in five years.
• 1:06
  Speaker 2: Maybe in five years you'll have replaced me with an AI.
• 1:09
  Speaker 1: Maybe in five years will all be replaced by AIS
• 1:12
  Speaker 1: and only AIS will be listening to this, but maybe
• 1:15
  Speaker 1: not I.
• 1:15
  Speaker 2: I Hi.
• 1:31
  Speaker 1: I'm Jorge, a me cartoonists and the author of Oliver's
• 1:34
  Speaker 1: Great Big Universe him.
• 1:36
  Speaker 2: You know, I'm a professor of physics and I do
• 1:38
  Speaker 2: experiments at CERN, and I don't think that I'm an AI.
• 1:42
  Speaker 1: But you could be. Are you saying.
• 1:46
  Speaker 2: We never know philosophically where our consciousness comes from. We
• 1:49
  Speaker 2: could all actually be AIS.
• 1:51
  Speaker 1: Yeah, we could. I guess there's several possibilities, right, Like
• 1:54
  Speaker 1: we could be in a simulation or something and we
• 1:55
  Speaker 1: could all be AIS. Or you know, if the people
• 1:59
  Speaker 1: were really Jesus, all right, then technically we are kind
• 2:02
  Speaker 1: of artificial intelligence because we were made by another intelligence.
• 2:05
  Speaker 2: Yeah, it certainly could be. Or we could all just
• 2:07
  Speaker 2: be cylons, you know, thinking we're humans, programmed to think
• 2:10
  Speaker 2: we are humans, but silicon underneath. Yeah.
• 2:15
  Speaker 1: On a TV show that sadly got canceled.
• 2:19
  Speaker 2: That was a great show.
• 2:20
  Speaker 1: But anyways, welcome to our podcast, Daniel and Jorge Explain
• 2:22
  Speaker 1: the Universe, a production of iHeartRadio.
• 2:24
  Speaker 2: In which we use our consciousness simulated or not, artificial
• 2:28
  Speaker 2: or not, to try to understand the nature of the universe.
• 2:31
  Speaker 2: Whether it's real or not, and whether our subjective experience
• 2:35
  Speaker 2: is organic or not. We think it's worthwhile to try
• 2:38
  Speaker 2: to understand what's out there, to try to make it
• 2:41
  Speaker 2: all work in our minds, to ask questions and seek answers,
• 2:45
  Speaker 2: and that's what this podcast is all about.
• 2:47
  Speaker 1: Yeah, sometimes I feel like by intelligence is simulated, Like
• 2:49
  Speaker 1: I'm just pretending to be intelligent.
• 2:52
  Speaker 2: What's the difference between being intelligent and effectively pretending?
• 2:56
  Speaker 1: Oh? Good point, that's an intelligent answer. And I don't
• 2:59
  Speaker 1: mean that in a fix. I mean that in an
• 3:01
  Speaker 1: unartificial sense.
• 3:04
  Speaker 2: Sometimes I feel like the most important function I serve
• 3:06
  Speaker 2: for my students is asking them dumb questions about their research.
• 3:10
  Speaker 2: And often I see it spark good ideas. They're like,
• 3:13
  Speaker 2: well that doesn't make any sense, but it gives me
• 3:15
  Speaker 2: a good idea about something I could do.
• 3:18
  Speaker 1: So you're incentivized to ask dumb questions.
• 3:21
  Speaker 2: I just simulate knowing what I'm doing, and somehow the
• 3:24
  Speaker 2: people around me get stuff done.
• 3:26
  Speaker 1: Sounds like you could program an AI to ask dumb
• 3:28
  Speaker 1: questions and then you don't have to do anything.
• 3:31
  Speaker 2: Yeah, exactly. I think often I could be replaced by
• 3:33
  Speaker 2: a cardboard cutout of myself. Just having students explain what
• 3:36
  Speaker 2: they're doing to me helps them understand what they're doing wrong.
• 3:39
  Speaker 1: Yeah, and it has pre program answers like or questions like, huh,
• 3:43
  Speaker 1: that's really interesting. Have you checked the error bars?
• 3:47
  Speaker 2: Are you sure about those assumptions?
• 3:49
  Speaker 1: That's it. Just have it on loop. People come in,
• 3:51
  Speaker 1: they press a button, You're in a Caribbean island doing nothing.
• 3:54
  Speaker 2: Yeah. Or they just pull a string behind me, or
• 3:56
  Speaker 2: I'm just like a stuffed Teddy bear.
• 3:58
  Speaker 1: Yeah, there you go.
• 4:00
  Speaker 2: Maybe we should actually make merch stuffed versions of us.
• 4:03
  Speaker 2: They pull the back of you and you go hmm,
• 4:05
  Speaker 2: and they pull the back of me and it goes chuckle.
• 4:07
  Speaker 1: Yeah. Perfect, And then someone could just repidate the entire
• 4:10
  Speaker 1: podcast without us.
• 4:11
  Speaker 2: There just stings. You could build a robot to pull
• 4:16
  Speaker 2: the strings and we'd be done.
• 4:18
  Speaker 1: Yeah. Oh man, but I guess you need someone to
• 4:21
  Speaker 1: press the record book.
• 4:23
  Speaker 2: I have students who can do that.
• 4:25
  Speaker 1: Perfect. But yeah, it is a pretty interesting and amazing universe.
• 4:28
  Speaker 1: Whether it's simulated or not, or whether we are simulated
• 4:30
  Speaker 1: or not, and whether we are artificial or not. We
• 4:34
  Speaker 1: have questions about what's going on in this universe, about
• 4:36
  Speaker 1: how it all works.
• 4:37
  Speaker 2: Scientists have questions and are busy doing experiments to try
• 4:40
  Speaker 2: to get answers. But we're not the only ones with questions.
• 4:44
  Speaker 2: Everybody out there asks questions about the nature of the
• 4:47
  Speaker 2: universe since the first people have looked up in the
• 4:49
  Speaker 2: night sky and wondered what all those twinkling lights were.
• 4:52
  Speaker 2: Being curious is just part of being human and looking
• 4:55
  Speaker 2: for answers is doing science, whether or not you're getting
• 4:58
  Speaker 2: paid for it.
• 4:58
  Speaker 1: Yeah, it's not just a job of sign this to
• 5:00
  Speaker 1: ask questions about geners. It's your job. It's everybody's job
• 5:03
  Speaker 1: to look at the cosmos and wonder why it's all
• 5:05
  Speaker 1: there and how it all works.
• 5:06
  Speaker 2: One of our goals on this podcast is to find
• 5:09
  Speaker 2: answers for you, but also to stimulate your questions, to
• 5:12
  Speaker 2: get you to think about the things you don't understand,
• 5:15
  Speaker 2: to hear what we're saying and then try to click
• 5:17
  Speaker 2: it together in your mind and when it doesn't quite fit.
• 5:20
  Speaker 2: We love if you reached out to us to ask
• 5:22
  Speaker 2: us your questions about the universe. We'll always answer them
• 5:26
  Speaker 2: to questions at Danielandjorge dot com.
• 5:29
  Speaker 1: Yeah, everybody has questions, the kids, adults, and everyone in between,
• 5:32
  Speaker 1: and sometimes we'd like to answer those questions here on
• 5:34
  Speaker 1: the podcast.
• 5:35
  Speaker 2: We absolutely do, so feel free to write to us
• 5:37
  Speaker 2: and ask us your questions. Sometimes I'll get a question
• 5:40
  Speaker 2: that I think, hmm, I bet other people want to
• 5:42
  Speaker 2: know the answer that, and so we'll answer it here
• 5:44
  Speaker 2: on the podcast.
• 5:45
  Speaker 1: Do you sometimes think, oh, nobody else wants to know
• 5:47
  Speaker 1: the answer to that? Do you have the opposite feeling?
• 5:50
  Speaker 2: I do sometimes get personal questions about people's life path
• 5:53
  Speaker 2: and stuff like that, and so yeah, that's individualized answers
• 5:57
  Speaker 2: that don't need to be on the podcast.
• 5:59
  Speaker 1: Do you get a quot question that it's like so
• 6:01
  Speaker 1: complicated you don't think anyone else would be interested.
• 6:05
  Speaker 2: I get a lot of people sending me their personal
• 6:07
  Speaker 2: theories of the universe, and I'm not sure anybody else
• 6:10
  Speaker 2: really wants to read those hundreds of pages written by
• 6:13
  Speaker 2: retired engineers.
• 6:14
  Speaker 1: But what if they're right? Oh? I see, But then
• 6:17
  Speaker 1: it becomes your theory, and then you want everyone to
• 6:21
  Speaker 1: read about it.
• 6:22
  Speaker 2: No. I read those theories and give them critiques, and
• 6:24
  Speaker 2: if there was something to it, then yeah, you'd hear
• 6:26
  Speaker 2: about it well.
• 6:27
  Speaker 1: As Daniel say, we'd like to answer questions here on
• 6:29
  Speaker 1: the podcast, and so on. Today's episode will be tackling
• 6:36
  Speaker 1: listener questions number forty five, Gravity and black holes. That's
• 6:42
  Speaker 1: the theme of the questions today, gravity and black holes.
• 6:44
  Speaker 2: Yeah, black holes and gravity seem to be on people's
• 6:47
  Speaker 2: minds the week that these questions came in.
• 6:50
  Speaker 1: Yeah, and so we have some great questions here about
• 6:53
  Speaker 1: famous physics experiments, the event horizons of black holes, and
• 6:57
  Speaker 1: what happens since the Big Bang. Pretty deep questions, deep
• 7:01
  Speaker 1: in time and space. So we'll just jump right in.
• 7:04
  Speaker 1: Our first question comes from Sean from Canada.
• 7:06
  Speaker 3: Hey, Daniel and Jorge, this is Sean calling from Canada.
• 7:09
  Speaker 3: I have a question about the observer effect. What would
• 7:12
  Speaker 3: happen if the observer was on the inside of the
• 7:16
  Speaker 3: event horizon of a black hole and the experiment being
• 7:19
  Speaker 3: observed was on the outside of the event horizon of
• 7:22
  Speaker 3: a black hole? Would it know that it's being observed?
• 7:27
  Speaker 3: Would the waves collapse and all that stuff?
• 7:31
  Speaker 2: Yeah, let me know.
• 7:32
  Speaker 1: Thanks, interesting question. I guess the gist of it is
• 7:35
  Speaker 1: that what happens if you're inside of a black hole
• 7:38
  Speaker 1: can't tell what's going on outside of the black hole.
• 7:40
  Speaker 2: Yeah, there's a lot of really interesting stuff going on
• 7:42
  Speaker 2: in this question. It's about black holes, it's about quantum mechanics,
• 7:45
  Speaker 2: it's about all that kind of stuff. Of course, inside
• 7:48
  Speaker 2: a black hole, you can see things that are happening
• 7:51
  Speaker 2: outside a black hole, right. A black hole is where
• 7:54
  Speaker 2: information cannot escape from, but new information can always arrive,
• 7:58
  Speaker 2: Like photons can fall in do black holes, and if
• 8:00
  Speaker 2: you were inside a black hole, those photons could still
• 8:03
  Speaker 2: reach you. So from within a black hole, you can
• 8:06
  Speaker 2: observe things happening in the outside of the universe. But
• 8:09
  Speaker 2: I love this question because it touches on this complicated
• 8:12
  Speaker 2: quantum mechanical issue of observing things changing them right. Often
• 8:17
  Speaker 2: in quantum mechanics we say that observation changes an experiment,
• 8:20
  Speaker 2: And he's wondering, if you're doing that observation while you're
• 8:23
  Speaker 2: inside a black hole, can you change an experiment that's
• 8:26
  Speaker 2: outside a black hole.
• 8:28
  Speaker 1: Because I guess in quantum mechanics, once you observe something
• 8:33
  Speaker 1: it like, it changes the wave function of it right exactly.
• 8:35
  Speaker 2: And this is something in quantum mechanics that's not very
• 8:38
  Speaker 2: well understood. So often when you push the boundaries and
• 8:40
  Speaker 2: come up with crazy thought experiments, the answer is we
• 8:43
  Speaker 2: don't know or we have no idea because actually our
• 8:46
  Speaker 2: theory quantum mechanics doesn't make any sense, so it's probably
• 8:49
  Speaker 2: important to like sum up what is the observer effect
• 8:52
  Speaker 2: in quantum mechanics what we're talking about here.
• 8:55
  Speaker 1: But I guess maybe I have many more basic questions
• 8:57
  Speaker 1: about the setup here. So like the observer, you are
• 9:00
  Speaker 1: inside the black hole, and this is I guess, assuming
• 9:02
  Speaker 1: you survive going into the black hole.
• 9:04
  Speaker 2: Right, yeah, I assume. I assume you survive. If you're
• 9:06
  Speaker 2: observing the experiment.
• 9:07
  Speaker 1: Like you have a camera and you take it inside
• 9:09
  Speaker 1: of the black hole and you somehow survive, you would
• 9:12
  Speaker 1: still be getting information from outside the black hole, but
• 9:14
  Speaker 1: you wouldn't, I guess. See, like the whole universe, like
• 9:17
  Speaker 1: I think we've talked about this before, the whole universe
• 9:19
  Speaker 1: would look like one pinpoint to you.
• 9:21
  Speaker 2: That's right, All light that arrives on the black hole
• 9:24
  Speaker 2: would arrive to you and just one point. So like
• 9:27
  Speaker 2: the entire event horizon would be collapsed to a single
• 9:30
  Speaker 2: point in your vision. The rest every other direction from
• 9:33
  Speaker 2: your perspective would be towards the singularity. Because remember that
• 9:37
  Speaker 2: black holes are curvatures of space time, and so changing
• 9:42
  Speaker 2: the way space is organized inside the black hole.
• 9:45
  Speaker 1: Okay, So now the scenario is that there's maybe like
• 9:47
  Speaker 1: an electron just outside the black hole, and it's about
• 9:50
  Speaker 1: to veer to the right or to the left depending
• 9:52
  Speaker 1: on some magnetic field right because it has some quantum
• 9:55
  Speaker 1: uncertainty about that. And then the question is could you
• 9:58
  Speaker 1: see that, Like, could the photon from that electron reach you?
• 10:02
  Speaker 1: Would it reach you?
• 10:02
  Speaker 2: So a photon from that electron definitely could reach you.
• 10:05
  Speaker 2: If the electron gives off a photon that can fall
• 10:08
  Speaker 2: in the black hole, and then it can reach you
• 10:10
  Speaker 2: inside the black hole absolutely.
• 10:12
  Speaker 1: What about like time, doesn't time slow down at the
• 10:15
  Speaker 1: surface of a black hole, or doesn't it stand still?
• 10:17
  Speaker 2: So time does get slowed down by gravity. Places that
• 10:20
  Speaker 2: have strong curvature feel time going more slowly. So for example,
• 10:24
  Speaker 2: if you're near a black hole and you're looking at
• 10:26
  Speaker 2: the rest of the universe, your time is going more slowly.
• 10:28
  Speaker 2: You see the rest of the universe going more quickly.
• 10:31
  Speaker 2: Or if you're watching somebody fall into a black hole,
• 10:33
  Speaker 2: you see their time slow down. So from the outside
• 10:36
  Speaker 2: you can't actually see somebody fall into a black hole.
• 10:39
  Speaker 2: You're right, if time slows down so much as they
• 10:41
  Speaker 2: approach the event horizon, that it's not until, like time
• 10:44
  Speaker 2: equals infinity, that they actually fall in from your perspective.
• 10:48
  Speaker 2: But if you're the person falling into the event horizon,
• 10:52
  Speaker 2: then you just fall past the event horizon. You don't
• 10:54
  Speaker 2: notice these effects.
• 10:55
  Speaker 1: The electron would just fly right in from your perspective
• 10:58
  Speaker 1: inside the.
• 10:58
  Speaker 2: Black hole, inside the black hole exactly, but.
• 11:00
  Speaker 1: Really outside of the black hole, it wouldn't happen for infinity.
• 11:03
  Speaker 2: From the point of view of a distant observer watching
• 11:05
  Speaker 2: you fall in, it wouldn't happen until time egals infinity,
• 11:08
  Speaker 2: or until something else falls in the black hole and
• 11:11
  Speaker 2: grows it so that it encompasses you. That's the reason
• 11:14
  Speaker 2: that like real black holes in the universe can actually grow,
• 11:17
  Speaker 2: that they don't have to wait until time equals infinity
• 11:19
  Speaker 2: for things to fall in, because there's a whole series
• 11:21
  Speaker 2: of things falling in. Each one grows the event horizon
• 11:25
  Speaker 2: for the previous one.
• 11:26
  Speaker 1: Okay, so you can get information from inside the black hole,
• 11:29
  Speaker 1: and I guess you're not really watching the electron. You're
• 11:31
  Speaker 1: just watching whether it veers to the rider to the left, right,
• 11:34
  Speaker 1: something to texts the electron going right or left or something.
• 11:37
  Speaker 2: Yeah, I think the setupiece interested in is like an
• 11:40
  Speaker 2: electron is in a superposition of two possible states, like
• 11:42
  Speaker 2: does it go left or right? And somehow you maybe
• 11:44
  Speaker 2: use a photon to detect left versus right, and that
• 11:47
  Speaker 2: photon falls into the black hole. And he's wondering if
• 11:51
  Speaker 2: observing that photon inside the black hole collapses the way
• 11:55
  Speaker 2: functioning the experiment outside the black.
• 11:57
  Speaker 1: Hole right, because I guess since you're inside the black hole,
• 12:01
  Speaker 1: there's like no way for the electron to know whether
• 12:04
  Speaker 1: you saw it or not exactly.
• 12:06
  Speaker 2: That's where this cool quantum mechanics black hole paradox comes in,
• 12:09
  Speaker 2: because if you take away the black hole, we had
• 12:11
  Speaker 2: the sort of classic observer effect that the electron can
• 12:13
  Speaker 2: still be fifty percent chance left, fifty percent chance right
• 12:17
  Speaker 2: until its wave function is collapsed. When does the wave
• 12:20
  Speaker 2: function collapse? Well, nobody really knows the answer to that,
• 12:23
  Speaker 2: but one ridiculous but standard description or quantum mechanics says
• 12:28
  Speaker 2: that the electron's wave function is collapsed when is observed
• 12:32
  Speaker 2: by a classical object like a person or a big
• 12:35
  Speaker 2: detector or something. So the photon can bounce off of
• 12:38
  Speaker 2: the electron without collapsing its wave function because it's still
• 12:41
  Speaker 2: a quantum object. But then when that photon carrying that
• 12:43
  Speaker 2: information hits a screen or a detector or an eyeball
• 12:47
  Speaker 2: or something like that, a classical object, it collapses the
• 12:50
  Speaker 2: whole wave function. And that's when the electron decided, okay
• 12:53
  Speaker 2: I went left or okay I went right.
• 12:55
  Speaker 1: But does it collapse only for the observer or for
• 12:58
  Speaker 1: the entire universe? If if you observe it, but I
• 13:01
  Speaker 1: don't know what you observe, is it still a quantum
• 13:03
  Speaker 1: object to me?
• 13:04
  Speaker 2: Oh? Great question? And the answer to that depends on
• 13:07
  Speaker 2: your quantum mechanics philosophy. So in standard quantum mechanics Copenhagen interpretation,
• 13:12
  Speaker 2: it collapses for everybody, and it collapses instantly across space
• 13:16
  Speaker 2: and time. Those two objects are entangled. The photon and
• 13:19
  Speaker 2: the electron are quantum mechanically entangled, meaning that they share
• 13:23
  Speaker 2: a fate. They're connected to each other. If the electron
• 13:25
  Speaker 2: goes left, then the photon looks a certain way, and
• 13:27
  Speaker 2: if electron goes right, the photon looks another way. So
• 13:30
  Speaker 2: in your standard interpretation, as soon as you observe the photon,
• 13:33
  Speaker 2: that collapses the electron for everybody. But in other interpretations,
• 13:37
  Speaker 2: to quantum mechanics like Carlo Ravelli's relational quantum mechanics. Then
• 13:42
  Speaker 2: it only collapses for the person doing the observation. One
• 13:45
  Speaker 2: person can collapse it for themselves, somebody else could have
• 13:47
  Speaker 2: it be uncollapsed, and a third person can collapse it
• 13:50
  Speaker 2: in another way. So there's different theories of quantum mechanics
• 13:53
  Speaker 2: in the standard one that people typically think about and
• 13:55
  Speaker 2: we complain about a lot because it doesn't make much sense.
• 13:58
  Speaker 2: It's collapsed for everybody.
• 14:00
  Speaker 1: It also sort of depends on the idea of short
• 14:02
  Speaker 1: Anger's box, right, doesn't it? Like if I wrap a
• 14:04
  Speaker 1: box or on you the observer and the electron, like,
• 14:07
  Speaker 1: it's still a quantum object to me, no matter whose
• 14:10
  Speaker 1: interpretation I think about, does it the cat is both
• 14:12
  Speaker 1: alive and dad and you saw it and not saw
• 14:14
  Speaker 1: it at the same time.
• 14:15
  Speaker 2: Yeah, that is the paradox rate by Schrodinger's box, that
• 14:18
  Speaker 2: things can be unobserved but still be classical. So in
• 14:21
  Speaker 2: the standard Copenhagen interpretation we say classical objects collapse the
• 14:25
  Speaker 2: wave function and quantum objects do not. The problem with
• 14:27
  Speaker 2: the standard quantum mechanics is that there's no definition of
• 14:30
  Speaker 2: what's a classical and what's a quantum object, so it's
• 14:33
  Speaker 2: sort of a useless distinction. But in the standard interpretation
• 14:37
  Speaker 2: then you would still become collapse the wave function because
• 14:40
  Speaker 2: you'd be a classical object and your observation collapses it.
• 14:43
  Speaker 2: Even if I don't know what you've seen before. You're
• 14:45
  Speaker 2: not a quantum object, so you can't be in a superposition.
• 14:48
  Speaker 1: Okay, so that this is an extra twist to it. Now,
• 14:50
  Speaker 1: let's say that you're the observer and you're inside of
• 14:52
  Speaker 1: a black hole and you saw the electron go right
• 14:55
  Speaker 1: or left. I think Sean is asking, how does that
• 14:58
  Speaker 1: affect things that the wavefund collapse for the electron or
• 15:01
  Speaker 1: is it still unknown for the rest of the universe.
• 15:03
  Speaker 2: This is a really great and very very difficult question,
• 15:07
  Speaker 2: and before we answer it, I want to compare it
• 15:09
  Speaker 2: to a similar complicated question, which is just about entangled
• 15:12
  Speaker 2: objects that are really far apart right. A similar question
• 15:15
  Speaker 2: you might ask, is, well, well, if the photon is
• 15:18
  Speaker 2: really far away from the electron when it's observed, how
• 15:21
  Speaker 2: does the electron know to collapse? If the photon flies
• 15:25
  Speaker 2: for a thousand light years before it gets observed, how
• 15:28
  Speaker 2: does the electron then collapse instantly across time? These questions
• 15:32
  Speaker 2: are related because they have to do with apparently sending
• 15:35
  Speaker 2: impossible information. And this is a classic question in quantum
• 15:39
  Speaker 2: mechanics theory, right, And this is the paradox posed by
• 15:42
  Speaker 2: Einstein decades and decades ago when he can plain the
• 15:44
  Speaker 2: quantum mechanics makes no sense because it requires things to
• 15:48
  Speaker 2: violate special relativity to collapse instantly across time. Things outside
• 15:52
  Speaker 2: of each other's light cones somehow, causing each other to change.
• 15:56
  Speaker 1: So, in the case of it entangled quantum paricles, the
• 15:59
  Speaker 1: answer that but it does travel faster than light in
• 16:01
  Speaker 1: a way, right, Like, once you collapse one half of
• 16:05
  Speaker 1: it a few light years away, it sort of instantly
• 16:08
  Speaker 1: changes what you have in front of you exactly.
• 16:10
  Speaker 2: And there's a really crucial subtlety here. You're totally right
• 16:13
  Speaker 2: that the collapse happens instantaneously across space and time. So
• 16:16
  Speaker 2: quantum mechanics is what we call non local. And that's
• 16:19
  Speaker 2: because the wave function is broad. It doesn't just exist
• 16:22
  Speaker 2: in one place. Don't think of it like one particle
• 16:24
  Speaker 2: doing something to the other particle. It's one big quantum state,
• 16:28
  Speaker 2: and you collapse it anywhere. It collapses everywhere simultaneously. That
• 16:32
  Speaker 2: does happen instantaneously across space and time. But and this
• 16:35
  Speaker 2: is the crucial nuance, it doesn't send any information. So
• 16:38
  Speaker 2: collapsing the wave function with a photon really really far
• 16:42
  Speaker 2: apart doesn't send information to the electron. You can't use
• 16:45
  Speaker 2: it to like send signals faster than the speed of light.
• 16:48
  Speaker 2: Though a lot of people imagine that quantum mechanics entanglement
• 16:51
  Speaker 2: can do that, you can't actually send information. Just collapses
• 16:55
  Speaker 2: the whole wave function simultaneously. It's not a mechanism for
• 16:58
  Speaker 2: information transmission.
• 17:00
  Speaker 1: I see. I think what you're saying is that, like
• 17:01
  Speaker 1: there's no rule to how big a quantum system can
• 17:04
  Speaker 1: be or how far apart its parts can be. So
• 17:08
  Speaker 1: like even a half, if I have one half here
• 17:09
  Speaker 1: and another half, you know, millions of lighters a way,
• 17:12
  Speaker 1: it's just still one quantum system. There's no rule in
• 17:14
  Speaker 1: quantum mechanics that says, oh, no, you're too far apart.
• 17:16
  Speaker 1: Now you're two separate quantum systems. You're actually like still
• 17:18
  Speaker 1: the same system exactly.
• 17:20
  Speaker 2: And quantum mechanics explicitly is non local. Stuff can happen
• 17:24
  Speaker 2: coordinated across space and time. It doesn't have to be
• 17:28
  Speaker 2: like this thing bumps into that thing which is right
• 17:30
  Speaker 2: next to it. Very weird property of quantum mechanics that
• 17:33
  Speaker 2: we really don't fully understand.
• 17:35
  Speaker 1: Okay, and so now the question is, what if half
• 17:38
  Speaker 1: of my system is inside of a black hole? Is
• 17:40
  Speaker 1: it still one system?
• 17:41
  Speaker 2: Great question, and the answer depends on your theory of
• 17:44
  Speaker 2: quantum gravity, because now this is a question that involves
• 17:47
  Speaker 2: quantum mechanics. We're talking about quantum particles and wave functions,
• 17:51
  Speaker 2: and it involves event horizons, so gravitational effects. And the
• 17:55
  Speaker 2: truth is we don't know how to marry those two things.
• 17:58
  Speaker 2: So I'm sorry, Sean, you're asking a question we don't
• 18:01
  Speaker 2: really know the answer to because we don't have a
• 18:03
  Speaker 2: theory of quantum gravity.
• 18:05
  Speaker 1: Meaning like we don't know how like if you distorted
• 18:08
  Speaker 1: gravity a lot, like in a black hole, you don't
• 18:10
  Speaker 1: know how it affects this idea of like a quantum
• 18:13
  Speaker 1: system being the two halves even though they're far apart exactly.
• 18:16
  Speaker 1: We just don't know it might affect it or it
• 18:17
  Speaker 1: might not affect it exactly.
• 18:19
  Speaker 2: We don't know if gravity collapses wave functions or not,
• 18:22
  Speaker 2: or if gravity is fundamentally quantum mechanical and allows things
• 18:25
  Speaker 2: to be in superpositions even as they cross event horizons.
• 18:28
  Speaker 2: We don't have the answer to that, but I can
• 18:31
  Speaker 2: speculate an analogy to the other scenario where you have
• 18:34
  Speaker 2: two quantum particles really far apart, basically outside of each
• 18:38
  Speaker 2: other's light cones, which is sort of like being outside
• 18:41
  Speaker 2: of each other's event horizons. There's still the wave function
• 18:44
  Speaker 2: does collapse, but no information is transmitted. So I suspect
• 18:47
  Speaker 2: that what happens here is that if you observe the
• 18:50
  Speaker 2: photon inside the black hole, it does collapse the wave
• 18:54
  Speaker 2: function of the electron outside the black hole, but without
• 18:57
  Speaker 2: transmitting any information and so not breaking that rule of
• 19:01
  Speaker 2: black holes.
• 19:02
  Speaker 1: WHOA Does that mean you could now communicate from inside
• 19:06
  Speaker 1: of a black hole to the outside of a black hole.
• 19:08
  Speaker 2: No. In the same way that you can't use quantum
• 19:10
  Speaker 2: entangled particle collapse to send information, you also can't send
• 19:15
  Speaker 2: information from inside and event horizon using the collapse of
• 19:18
  Speaker 2: a quantum object across that event horizon. That's the analogy.
• 19:23
  Speaker 1: So I wonder for like, practically speaking, you didn't really
• 19:26
  Speaker 1: collapse it because you're inside of a black hole and
• 19:28
  Speaker 1: nobody will ever know what you saw, So pretty much
• 19:31
  Speaker 1: in the rest of the universe. The half that's outside
• 19:34
  Speaker 1: is still quantum unknown.
• 19:36
  Speaker 2: Yeah, that's very insightful because the reason you can't send
• 19:39
  Speaker 2: information across quantum particles faster than light is that you
• 19:43
  Speaker 2: can't know whether it's collapsed. Like if I have a
• 19:45
  Speaker 2: quantum particle and you have a quantum particle and they're entangled,
• 19:48
  Speaker 2: I can measure mine, which would collapse yours if you
• 19:51
  Speaker 2: haven't already measured it, But you can't tell if I've
• 19:53
  Speaker 2: collapsed at All you can do is measure your particle
• 19:55
  Speaker 2: and get like spin up or spin down, or left
• 19:57
  Speaker 2: or right. You can never tell that I've collapsed it.
• 20:00
  Speaker 2: That information doesn't get transmitted. And so in the same way,
• 20:03
  Speaker 2: if somebody observes that photon inside the event horizon, somebody
• 20:07
  Speaker 2: else looking at the electron can't tell whether the electrons
• 20:10
  Speaker 2: wave function has been collapsed or not.
• 20:11
  Speaker 1: Okay, So then the answer for Sean is that we
• 20:14
  Speaker 1: have no idea. That's just a comment answer we give
• 20:18
  Speaker 1: you on the podcast, because nobody knows how gravity or
• 20:21
  Speaker 1: extreme gravity like black holes effects quantum mechanics and quantum
• 20:25
  Speaker 1: systems and wave collapse. But our best guess here on
• 20:27
  Speaker 1: the podcast is that it probably does collapse it, but
• 20:30
  Speaker 1: maybe it doesn't matter, so it doesn't really collapse it.
• 20:33
  Speaker 2: Yeah, that's a great summary.
• 20:35
  Speaker 1: Well, let's get to our other questions here today about
• 20:37
  Speaker 1: black holes and about the big Dang and magnetic fields.
• 20:41
  Speaker 1: So let's get to those, but first let's take a
• 20:43
  Speaker 1: quick break. Right. We're taking listener questions here today and
• 20:59
  Speaker 1: at least trying to answer them. Although sometimes the answer
• 21:02
  Speaker 1: is we don't nobody knows.
• 21:03
  Speaker 2: Sometimes the answer is, great question, I wish I knew
• 21:06
  Speaker 2: the answer.
• 21:07
  Speaker 1: Yeah, if you have the answer, write it to us
• 21:09
  Speaker 1: in one hundred page summary and then Daniel will read
• 21:12
  Speaker 1: it and let you know.
• 21:13
  Speaker 2: That's right. Really, the answer some of these questions requires
• 21:16
  Speaker 2: us to develop theories of quantum gravity, and to figure
• 21:19
  Speaker 2: out how to develop those theories, we want to look
• 21:21
  Speaker 2: inside black holes, which is impossible, so we're a little
• 21:24
  Speaker 2: bit stuck sometimes.
• 21:25
  Speaker 1: Well, you can look inside of a black hole, just
• 21:27
  Speaker 1: can't tell anyone what you saw.
• 21:30
  Speaker 2: Yeah, that's right. That physicist who fell into a black
• 21:32
  Speaker 2: hole knows the answers, just can't get any awards for it.
• 21:36
  Speaker 1: Yeah, that physicists solved everything. Let's throw a Nobel Prize
• 21:40
  Speaker 1: medal inside the black hole for them that million dollars
• 21:46
  Speaker 1: also or million coroner. I'm sure they can find a
• 21:49
  Speaker 1: good use for it in there. All right. So our
• 21:51
  Speaker 1: second question comes from Ryan, who lives in northern Virginia.
• 21:54
  Speaker 4: Hello, Daniel and Hore. My name is Ryan and I
• 21:57
  Speaker 4: live in northern Virginia. I have a question for you
• 21:59
  Speaker 4: today about black holes, more specifically about their magnetic fields.
• 22:03
  Speaker 4: If the Earth's magnetic field comes from its liquid outer core,
• 22:07
  Speaker 4: where does a black holes magnetic field come from? Considering
• 22:10
  Speaker 4: there's no liquid core in the black hole and nothing
• 22:13
  Speaker 4: is supposed to be able to escape the event horizon,
• 22:16
  Speaker 4: I'm left to guess that the accretion disk is the
• 22:18
  Speaker 4: big driver of the magnetic field. But that's just a guess.
• 22:22
  Speaker 4: Thanks for considering my question, Love the show.
• 22:24
  Speaker 1: Awesome great question, Ryan. You know I don't know the
• 22:27
  Speaker 1: answer here, and I'm gonna guess maybe the answer is again,
• 22:30
  Speaker 1: we don't know because it deals with black holes.
• 22:33
  Speaker 2: No, this one I think we do know the answer to. Actually, well,
• 22:37
  Speaker 2: I know physics knows something, all right.
• 22:40
  Speaker 1: Well, let's see. Ryan's question is where does a black
• 22:43
  Speaker 1: hole's magnetic field come from? Because I guess black holes
• 22:46
  Speaker 1: have a magnetic field. Do we know that for sure.
• 22:49
  Speaker 2: Well, we do measure very strong magnetic fields near black holes.
• 22:53
  Speaker 1: How do we measure them?
• 22:54
  Speaker 2: How do we measure them? Great question? Well, we can
• 22:56
  Speaker 2: see the effect, right. Sometimes black holes have enormous jets
• 22:59
  Speaker 2: of stuff that shoot up and down on their north
• 23:02
  Speaker 2: and south poles, and we think that comes from the
• 23:05
  Speaker 2: magnetic field, like funneling particles up and down, sort of
• 23:08
  Speaker 2: the same way that the Earth's magnetic field causes northern lights.
• 23:12
  Speaker 2: Charged particles coming towards the earth magnetic field get funneled
• 23:15
  Speaker 2: up towards the north and south poles. Particles falling into
• 23:17
  Speaker 2: a black hole sometimes will miss because the magnetic field
• 23:20
  Speaker 2: will deflect them up and down, and you get these enormous,
• 23:23
  Speaker 2: like thousands of light years long jets of stuff shooting
• 23:27
  Speaker 2: out of black holes. We think from the magnetic fields.
• 23:29
  Speaker 1: Well, I guess, first of all, we think those are
• 23:32
  Speaker 1: black holes and that those jets are coming from black holes.
• 23:35
  Speaker 1: Don't Like, we haven't actually seen the inside of what's
• 23:37
  Speaker 1: inside of those jets.
• 23:38
  Speaker 2: We've study those jets in some great detail, and we
• 23:41
  Speaker 2: have really pretty good models that predict those jets. Recently,
• 23:44
  Speaker 2: we imaged a couple of black holes and saw ripples
• 23:47
  Speaker 2: in the accretion disk around them, and so we're able
• 23:49
  Speaker 2: to like really pin down the details of the magnetic
• 23:52
  Speaker 2: field near the black hole. I mean, we'd love to
• 23:54
  Speaker 2: send a probe near the black hole and measure those directly,
• 23:57
  Speaker 2: but there's a lot of indirect ways to measure those
• 23:59
  Speaker 2: magnetic fields, just by seeing the impact to have on
• 24:02
  Speaker 2: charge particles near the black hole.
• 24:05
  Speaker 1: And I guess the other question is, how do he
• 24:06
  Speaker 1: knows those magnetic fields are coming from the black hole
• 24:08
  Speaker 1: enough from the stuff around the black hole.
• 24:10
  Speaker 2: Yeah, that's a great question, and we don't know the
• 24:12
  Speaker 2: answer to that. We're sure that the stuff around the
• 24:15
  Speaker 2: black hole can make a magnetic field. Those are charged particles.
• 24:18
  Speaker 2: They're moving in a circle, so you have a current
• 24:20
  Speaker 2: moving in a circle that always generates a magnetic field.
• 24:22
  Speaker 2: The second part is thinking about whether a black hole
• 24:25
  Speaker 2: on its own could have a magnetic field even without
• 24:29
  Speaker 2: the accretion disc, even without the stuff swirling around it.
• 24:32
  Speaker 2: Whether just the black hole itself can have a magnetic
• 24:35
  Speaker 2: field is a really interesting question.
• 24:37
  Speaker 1: Do we know the answer? Does a black hole on
• 24:40
  Speaker 1: its own have an inherent magnetic field?
• 24:42
  Speaker 2: So we can answer that question theoretically, We've never seen
• 24:45
  Speaker 2: a black hole all by itself, without an accretion disk
• 24:48
  Speaker 2: and measured it. But according to general relativity, black holes
• 24:51
  Speaker 2: can have magnetic fields. And that's because black holes can
• 24:55
  Speaker 2: do two crucial things. One they can have an electric
• 24:58
  Speaker 2: charge and two they can can spin. And essentially anything
• 25:02
  Speaker 2: with an electric charge that spins has a magnetic field.
• 25:05
  Speaker 1: But you're saying it's all theoretical though.
• 25:07
  Speaker 2: It's theoretical because we've never observed a black hole without
• 25:10
  Speaker 2: any stuff around it and measured its magnetic field. That
• 25:13
  Speaker 2: would be an awesome test.
• 25:14
  Speaker 1: Of this theory, I see. So basically we don't know.
• 25:21
  Speaker 2: Yeah, that's true of lots of things. I suppose. We're
• 25:23
  Speaker 2: not sure about it, but we do have a pretty
• 25:25
  Speaker 2: good idea. And lots of our models of spinning black
• 25:28
  Speaker 2: holes and black holes with charge have been tested indirectly.
• 25:31
  Speaker 2: We've never done this exact test.
• 25:34
  Speaker 1: Okay, So you're saying theoretically black holes do have magnetic
• 25:39
  Speaker 1: fields because they somehow preserve it, right even though you
• 25:42
  Speaker 1: when you throw charge particles in it with spin in
• 25:45
  Speaker 1: it and magnetic fields, presumably that doesn't get destroyed by.
• 25:48
  Speaker 2: The black hole exactly. And Ryan is asking about, like
• 25:51
  Speaker 2: where that magnetic field might come from. Because you can't
• 25:53
  Speaker 2: see anything beyond the event horizon, So you can't have
• 25:56
  Speaker 2: like swirling matter within the event horizon and causing this
• 26:01
  Speaker 2: magnetic field. Why not, Because the details of anything like
• 26:04
  Speaker 2: that happening within the event horizon is shielded by the
• 26:07
  Speaker 2: event horizon. You can only know a few things about
• 26:10
  Speaker 2: what's happening inside the event horizon. You can know the
• 26:13
  Speaker 2: total mass, you can know the electric charge, and you
• 26:16
  Speaker 2: can know the spin.
• 26:17
  Speaker 1: Meaning even if there are a bunch of electron spinning
• 26:19
  Speaker 1: inside of a black hole, the magnetic field they would
• 26:22
  Speaker 1: generate couldn't leak out of the black hole. Is that
• 26:25
  Speaker 1: what you're saying, Because the space would just be pointing inwards.
• 26:29
  Speaker 2: A lot of the details of what's happening to those
• 26:31
  Speaker 2: electrons you wouldn't be sensitive to, Like if one electron
• 26:34
  Speaker 2: zigs up or zigs down, you couldn't sense that from
• 26:37
  Speaker 2: the outside. You can, however, sense that there are a
• 26:40
  Speaker 2: bunch of electrons, and you can sense that they're spinning overall,
• 26:43
  Speaker 2: because you can measure the total spin of the black
• 26:46
  Speaker 2: hole and the total electric charge of the black hole.
• 26:49
  Speaker 2: Like when electron falls into a black hole, just before
• 26:53
  Speaker 2: it falls in, it has an electric field, and when
• 26:55
  Speaker 2: it falls in, that electric field is now frozen on
• 26:57
  Speaker 2: the outside of the black hole. Whatever happened to the
• 27:00
  Speaker 2: electron after it falls in can no longer change that
• 27:03
  Speaker 2: electric field. It's sort of frozen there. So you can
• 27:05
  Speaker 2: tell that something has fallen in and that it had charge,
• 27:08
  Speaker 2: but the details what happens afterwards you're shielded from.
• 27:12
  Speaker 1: So then are you saying, like, to get the magnetic
• 27:14
  Speaker 1: field of a black hole, you just multiply its charged
• 27:17
  Speaker 1: by its spin somehow, and that gives you like what
• 27:20
  Speaker 1: you would feel as a magnetic field outside of the
• 27:22
  Speaker 1: black hole. But those are like overall numbers, not related
• 27:26
  Speaker 1: to anything in detail inside of it.
• 27:28
  Speaker 2: Exactly in the same way that an electron has a
• 27:31
  Speaker 2: little magnetic field. Right where does the magnetic field an
• 27:34
  Speaker 2: electron come from. It doesn't have a magnetic charge, It
• 27:37
  Speaker 2: has an electric charge, and it has quantum spin. Those
• 27:40
  Speaker 2: two things combined to give the electron a tiny little
• 27:43
  Speaker 2: magnetic direction, a magnetic dipole. And you can't tell what's
• 27:47
  Speaker 2: going on inside the electron. We think maybe it's a
• 27:49
  Speaker 2: fundamental particle. We have no idea. We can't see inside,
• 27:52
  Speaker 2: and it doesn't matter. We know it has an overall
• 27:54
  Speaker 2: charge and an overall spin, and so the overall charge
• 27:57
  Speaker 2: and spin of a black hole similarly gives it a
• 28:00
  Speaker 2: magnetic moment. It's a magnetic dipole.
• 28:03
  Speaker 1: I wonder if, like Ryan's question was more like, you know,
• 28:06
  Speaker 1: how can a black hole have a magnetic field if
• 28:08
  Speaker 1: nothing can escape it? You know what I mean? Like,
• 28:11
  Speaker 1: if the electromagnetic field it has is due to the
• 28:14
  Speaker 1: stuff inside of the black hole, how can its magnetism
• 28:17
  Speaker 1: escape the black hole?
• 28:18
  Speaker 2: Yeah, that's a great question. We have a whole episode
• 28:20
  Speaker 2: on how black holes can have magnetic fields and electric
• 28:24
  Speaker 2: fields and digs into the details of this question. Very briefly, though,
• 28:28
  Speaker 2: The answer is that the overall charge is essentially spread
• 28:32
  Speaker 2: out on the event horizon. So something falls into a
• 28:35
  Speaker 2: black hole, you're not getting information from within the event horizon.
• 28:38
  Speaker 2: You're just getting information from the event horizon. So think
• 28:42
  Speaker 2: about the event horizon itself as now having that charge
• 28:45
  Speaker 2: and having that spin. There might be crazy stuff going
• 28:48
  Speaker 2: on inside, weird quantum effects or singularities orringularities or whatever.
• 28:52
  Speaker 2: You can't tell, but you can tell that something charged
• 28:55
  Speaker 2: fell in, and you can tell without getting any information
• 28:58
  Speaker 2: about what's going on. Inside the event horizon.
• 29:01
  Speaker 1: It sort of sounds like you're saying that the black
• 29:03
  Speaker 1: hole's magnetic field comes from its surface, Like it's the
• 29:06
  Speaker 1: surface of the black hole. That's basically you know, phasing
• 29:09
  Speaker 1: out to the rest of the universe, and you know,
• 29:12
  Speaker 1: emanating an electric charge and an electric field, and that's
• 29:15
  Speaker 1: why we can see it.
• 29:16
  Speaker 2: Yeah, that's a good way to think about it. The
• 29:17
  Speaker 2: event horizon, or the surface of it equivalently, has three
• 29:20
  Speaker 2: properties mass, spin, and charge, and we can measure those
• 29:24
  Speaker 2: and those have an effect on the rest of the
• 29:26
  Speaker 2: universe right the same way, like the mass of the
• 29:28
  Speaker 2: black hole, even though it's contained within the event horizon,
• 29:31
  Speaker 2: still curves space outside the event horizon and can affect
• 29:34
  Speaker 2: the trajectories of stuff. Think of that as a property
• 29:37
  Speaker 2: of the event horizon. It doesn't matter what's going on
• 29:40
  Speaker 2: inside behind the screen of the event horizon, if things
• 29:42
  Speaker 2: are swirling around or not. All you know is the
• 29:45
  Speaker 2: overall mass, the overall charge, and the overall spin, and
• 29:48
  Speaker 2: that can create a magnetic field.
• 29:50
  Speaker 1: But again, time slows down almost to a standstill near
• 29:53
  Speaker 1: the event horizon. How does the magnetic field ever get out?
• 29:57
  Speaker 1: Don't have to wait to infinity to feel that magnetic.
• 30:00
  Speaker 2: Yes, so time near the black hole is really really
• 30:03
  Speaker 2: slowed down, not slowed down totally to infinity. So black
• 30:06
  Speaker 2: holes can radiate information for example, like if a black
• 30:10
  Speaker 2: hole gets accelerated by another black hole, it can radiate
• 30:13
  Speaker 2: a gravitational wave, or if it has charge, it will
• 30:16
  Speaker 2: also radiate photons. Again, these are coming from the surface
• 30:19
  Speaker 2: of the black hole, not from within it, so we're
• 30:22
  Speaker 2: not breaking the rules of black holes, but they can
• 30:24
  Speaker 2: radiate that information. And you're right that things near black
• 30:27
  Speaker 2: holes are slowed down, and so it does take longer.
• 30:30
  Speaker 2: And like those gravitational waves are slowed down by the
• 30:33
  Speaker 2: time dilation of the gravitational field. So without that effect,
• 30:37
  Speaker 2: those gravitational waves would look much crazier and the photons
• 30:40
  Speaker 2: would be much higher frequency. But they're stretched out and
• 30:44
  Speaker 2: red shifted by that time dilation, not all the way
• 30:46
  Speaker 2: to infinity, because the curvature isn't infinity outside the black hole.
• 30:50
  Speaker 1: All right, Well, it sounds like the answer for Ryan
• 30:52
  Speaker 1: is that a black hole's magnetic field comes from its surface.
• 30:55
  Speaker 1: It's event horizon basically, or at least we can practically
• 30:58
  Speaker 1: think of it as coming from the surface and the
• 31:00
  Speaker 1: event horizon and that's why we're able to see it
• 31:03
  Speaker 1: and experience it. We think, we think we don't know
• 31:07
  Speaker 1: for sure because it's a black hole.
• 31:10
  Speaker 2: We don't know for sure anything. We don't even know
• 31:12
  Speaker 2: if we exist or if this is a simulation. And
• 31:14
  Speaker 2: also remember that most of the encnic fields we've measured
• 31:17
  Speaker 2: probably do mostly come from the accretion disk of stuff
• 31:21
  Speaker 2: around them. But that's where he says we don't know
• 31:23
  Speaker 2: for sure.
• 31:24
  Speaker 1: All right, Well, let's get to our last question of
• 31:26
  Speaker 1: the day, which is about the expanding universe and gravity
• 31:31
  Speaker 1: and the Big Bang. But first let's take another quick break.
• 31:46
  Speaker 1: All right, we're answering listener questions here, our favorite kind
• 31:49
  Speaker 1: of episode where we take your questions that you send
• 31:52
  Speaker 1: in and we try to answer them, usually with answers
• 31:55
  Speaker 1: that are not we don't know.
• 31:58
  Speaker 2: We do our best.
• 32:00
  Speaker 1: Sometimes nobody knows which is an answer technically it is.
• 32:03
  Speaker 2: And I wonder if that's like really satisfying because it
• 32:06
  Speaker 2: means for the listener like, Ooh, I'm at the forefront
• 32:09
  Speaker 2: of human knowledge or really disappointing because like the rest
• 32:12
  Speaker 2: of humanity is still left unsatisfied.
• 32:15
  Speaker 1: Yeah, I guess it is pretty exciting, right to be
• 32:17
  Speaker 1: to like come up against the boundary of human knowledge, right, yeah, exactly,
• 32:22
  Speaker 1: Like when I ask you a question and you don't
• 32:23
  Speaker 1: know the answer, I'm like, Wow, I am at the
• 32:25
  Speaker 1: boundary of Daniel's knowledge of the universe.
• 32:28
  Speaker 2: Now, the boundary of Daniel's knowledge not the same as
• 32:31
  Speaker 2: the boundary knowledge. Let's not make that.
• 32:34
  Speaker 1: Mistake, or at least the boundary of the research you've
• 32:38
  Speaker 1: been able to do for the last hour before the podcast.
• 32:41
  Speaker 2: Exactly, I am at the boundary of human knowledge in
• 32:43
  Speaker 2: one time is a little corner of the vast sphere
• 32:47
  Speaker 2: of human knowledge.
• 32:49
  Speaker 1: Well, we're all here with you, and so our last
• 32:51
  Speaker 1: question of the day comes from Argent phor Daniel.
• 32:54
  Speaker 5: I have a question. Just got me thinking while I
• 32:57
  Speaker 5: was on the shore. We've come to understand that gravity
• 33:01
  Speaker 5: is bending of space time, and that's objects which would
• 33:06
  Speaker 5: normally travel in a straight line tend to take a
• 33:09
  Speaker 5: curve path around the body, which is distorting space time.
• 33:13
  Speaker 5: We also know that space itself is expanding in the
• 33:16
  Speaker 5: universe for the last ever since Big Bang happened. Do
• 33:20
  Speaker 5: we think the effects of gravity have changed over the
• 33:24
  Speaker 5: last couple billion years or do we expect it to
• 33:28
  Speaker 5: be different later now that we know that space itself
• 33:31
  Speaker 5: is expanding or stretching or thinning out, whatever you may
• 33:34
  Speaker 5: call it. Will that effect the way gravity acts and
• 33:38
  Speaker 5: behaves or has it changed over the years?
• 33:41
  Speaker 2: What do you reckon?
• 33:42
  Speaker 1: Awesome question? What do we reckon? Daniel? Do we know
• 33:45
  Speaker 1: the answer? In this case?
• 33:47
  Speaker 2: I reckon that Urgent probably takes really long showers to
• 33:49
  Speaker 2: have such deep thoughts about the whole.
• 33:51
  Speaker 1: History of the universe, which is awesome. Thank you Argent
• 33:55
  Speaker 1: for such a great question.
• 33:56
  Speaker 2: So, as usual, we have some ideas about how this works,
• 34:00
  Speaker 2: but there's lots that we still don't understand, especially about
• 34:03
  Speaker 2: the expanding and the accelerating expansion of the universe.
• 34:07
  Speaker 1: Okay, let me see if I understand Argent's question. He's
• 34:09
  Speaker 1: in the shower and he's wondering, you know, the universe
• 34:12
  Speaker 1: since the Big Bang has, first of all, it expanded
• 34:15
  Speaker 1: really fast. Space itself expanded really fast, and space today
• 34:18
  Speaker 1: is still expanding, and there's more and more space growing
• 34:21
  Speaker 1: and being created. The universe is expanding due to something
• 34:24
  Speaker 1: called dark energy. And I think his question is like,
• 34:27
  Speaker 1: is gravity affected by this expansion of space? Like do
• 34:31
  Speaker 1: we know if gravity itself has been the same and
• 34:35
  Speaker 1: for the last fourteen billion years or is there an
• 34:37
  Speaker 1: indication that maybe as a universe expands it could be
• 34:40
  Speaker 1: changing the effects of gravity like this gravity space dependent.
• 34:44
  Speaker 1: What do you reckon, Daniel, I.
• 34:46
  Speaker 2: Think there's a crucial piece of the history of the
• 34:48
  Speaker 2: universe that you sort of yaddiyauted over there, because you're right,
• 34:51
  Speaker 2: the things did expand very quickly in the beginning, but
• 34:54
  Speaker 2: then then expansion actually decelerated because the stuff in the
• 34:57
  Speaker 2: universe slowed down the expansion. And then later on, like
• 35:01
  Speaker 2: six billion years ago, it started picking up again and
• 35:04
  Speaker 2: it started to accelerate the expansion. So this is funny,
• 35:07
  Speaker 2: sort of like zigzag in the history of the universe.
• 35:09
  Speaker 2: It wasn't always just accelerating expansion. It was always expansion,
• 35:13
  Speaker 2: but there was a period when that expansion was decelerating.
• 35:15
  Speaker 2: I emphasized that not just because it's a cool zigzag,
• 35:18
  Speaker 2: but to underline something which I think is in crucial
• 35:20
  Speaker 2: to answering Argin's question, which is that's part of gravity.
• 35:24
  Speaker 2: Gravity is not just things pulling themselves together, it's also
• 35:28
  Speaker 2: space expanding. That is general relativity, our framework that we
• 35:32
  Speaker 2: have and what Argent describes as like things moving through
• 35:34
  Speaker 2: bent space time that allows for the universe to expand.
• 35:38
  Speaker 2: That's sort of part of what gravity is.
• 35:40
  Speaker 1: Well, what do you mean, like it's in the equations
• 35:44
  Speaker 1: of our theories of gravity for the universe to expand
• 35:46
  Speaker 1: due to dark energy.
• 35:48
  Speaker 2: It's part of general relativity that the universe can expand
• 35:51
  Speaker 2: under certain conditions. So the broad answer to Argent's question is,
• 35:54
  Speaker 2: we think the rules of the universe, the rules of
• 35:57
  Speaker 2: gravity and space time and general relativity have not changed
• 36:00
  Speaker 2: changed over the last fourteen billion years, and we can
• 36:02
  Speaker 2: describe all of these weird epics of the universe using
• 36:05
  Speaker 2: one consistent framework, and that's sort of amazing. So the
• 36:08
  Speaker 2: rules haven't changed, even though the conditions do change from
• 36:11
  Speaker 2: year to year and things get further apart and whatever.
• 36:14
  Speaker 2: So there are specific conditions under which general relativity predicts
• 36:18
  Speaker 2: the universe will expand and that that expansion will accelerate.
• 36:22
  Speaker 2: If you have a bunch of energy inherent in space
• 36:24
  Speaker 2: stored in a field that has high potential energy, then
• 36:27
  Speaker 2: general relativity says space will expand and that expansion will accelerate.
• 36:32
  Speaker 2: So we see that happening in the universe. We look
• 36:34
  Speaker 2: back at the history of the universe, we see it's
• 36:36
  Speaker 2: expanding we see that expansion is accelerating, and so we say, oh,
• 36:39
  Speaker 2: there must be some energy stored in a field somewhere
• 36:42
  Speaker 2: with a lot of potential energy that's causing this. We
• 36:45
  Speaker 2: don't know what that is. We don't know what that
• 36:46
  Speaker 2: field is, We have no explanation for it. But general
• 36:49
  Speaker 2: relativity can accommodate that well.
• 36:51
  Speaker 1: I think what you're saying is that physicists have a
• 36:54
  Speaker 1: set of equations that explain the universe, and that set
• 36:57
  Speaker 1: of equations has gravity in it, and it also as
• 37:00
  Speaker 1: expansion of the universe in it. So it's like they're
• 37:02
  Speaker 1: all actually kind of connected already into theories of physics.
• 37:05
  Speaker 2: Yes, exactly.
• 37:06
  Speaker 1: So it's not like one of them we don't know
• 37:08
  Speaker 1: if one of them is doing something the other one
• 37:09
  Speaker 1: doesn't know.
• 37:10
  Speaker 2: That's right. And when people say gravity colloquially, they mean
• 37:12
  Speaker 2: like stuff attracting and things falling towards planets and whatever.
• 37:16
  Speaker 2: When physicists say gravity, they mean the whole shebang, They
• 37:19
  Speaker 2: mean the whole theory of space, time and all of
• 37:21
  Speaker 2: its consequences. Because moving from like a Newtonian view of
• 37:25
  Speaker 2: gravity as a force to an Einsteinian view of gravity
• 37:28
  Speaker 2: as motion of stuff through space time has all of
• 37:31
  Speaker 2: these consequences, not just oh, light is also bent by gravity,
• 37:36
  Speaker 2: but also the universe can expand and it could also collapse.
• 37:39
  Speaker 2: All of these things are consequences of this geometric view
• 37:42
  Speaker 2: of the universe we have from general relativity, and we
• 37:45
  Speaker 2: think that those rules have not changed. That the same
• 37:47
  Speaker 2: rules applied in the very very beginning and in the
• 37:49
  Speaker 2: middle point when things were decelerating, and now when things
• 37:52
  Speaker 2: are accelerating. So in the broadest sense, the rules of
• 37:55
  Speaker 2: gravity general relativity have not changed over the course of
• 37:58
  Speaker 2: the universe.
• 38:00
  Speaker 1: I see, like the rules by which you mean the equations,
• 38:02
  Speaker 1: But I wonder if Argin means, like, you know, imagine
• 38:04
  Speaker 1: there's a term in your equations for gravity. I wonder
• 38:07
  Speaker 1: if he could mean that, you know, has that term
• 38:09
  Speaker 1: the equation change as the universe grew? Like could it
• 38:13
  Speaker 1: that be something the equations don't take into account, or
• 38:15
  Speaker 1: it could it be something we haven't noticed.
• 38:17
  Speaker 2: Or or what. Yeah, there's a couple of ways in
• 38:19
  Speaker 2: which that could be true. First of all, we assume
• 38:21
  Speaker 2: that dark energy or whatever this is, this potential field
• 38:25
  Speaker 2: that's causing the accelerating expansion in the universe. We assume
• 38:28
  Speaker 2: that that's constant everywhere in space and everywhere in time,
• 38:31
  Speaker 2: and mostly that works. I mean, it said that we
• 38:33
  Speaker 2: can explain the whole history of the universe, and that's
• 38:35
  Speaker 2: mostly true, but there are some discrepancies, like we measure
• 38:38
  Speaker 2: it early in the universe, we measure it late in
• 38:39
  Speaker 2: the universe, and those two numbers don't quite agree. You
• 38:42
  Speaker 2: can read more about that. It's called the Hubble tension. Essentially,
• 38:46
  Speaker 2: that's predicting the rate of expansion, and different measurements don't
• 38:49
  Speaker 2: quite agree. So that's quite interesting. So it might be
• 38:51
  Speaker 2: that the dark energy is changing over time, and again
• 38:53
  Speaker 2: that wouldn't mean a change in the rules, but it
• 38:55
  Speaker 2: would mean some change in the conditions, which is affecting
• 38:58
  Speaker 2: like your experience of the Union. And also, maybe more importantly,
• 39:02
  Speaker 2: the second sense is that the density of stuff in
• 39:04
  Speaker 2: the universe is definitely decreasing. Like things used to be
• 39:07
  Speaker 2: really hot and dense and now they're very cold and
• 39:09
  Speaker 2: very far apart, and so there's definitely like less sense
• 39:13
  Speaker 2: of gravity in the universe. Because the mass density of
• 39:16
  Speaker 2: stuff in the universe is going down, space goes up,
• 39:19
  Speaker 2: the amount of mass doesn't change, so the density decreases,
• 39:22
  Speaker 2: things get further and further apart. You're feeling less gravity
• 39:26
  Speaker 2: from distant galaxies than you were before because they're now
• 39:29
  Speaker 2: further away from you, and that's going to keep going.
• 39:31
  Speaker 1: Mm So I guess technically you would be feeling more
• 39:34
  Speaker 1: the gravity of Earth right as the universe gets more
• 39:37
  Speaker 1: empty and empty, right, Like, I'm way more in the
• 39:40
  Speaker 1: future regardless of what I what I do.
• 39:45
  Speaker 2: If you're relying on distant gravities to lift you up
• 39:47
  Speaker 2: off the surface of the Earth and make you feel light,
• 39:49
  Speaker 2: then I have bad news for you.
• 39:51
  Speaker 1: Yes, as my diet plan forget as epic.
• 40:00
  Speaker 2: Yeah, exactly, I suggest hitting the gym instead of relying
• 40:03
  Speaker 2: on distant galaxies. But I'm not a health expert. Don't
• 40:06
  Speaker 2: take advice from me.
• 40:07
  Speaker 1: Well, I wonder if Argine's question then maybe more simply
• 40:11
  Speaker 1: is like, you know, if I have a black hole
• 40:13
  Speaker 1: the same mass and I see it bend light around it,
• 40:16
  Speaker 1: is it going to bend light the same way now
• 40:19
  Speaker 1: in the future, in the past when the universe was
• 40:22
  Speaker 1: maybe more scrunched together, or is that light can we
• 40:25
  Speaker 1: bend differently depending on what the universe is doing, Like,
• 40:27
  Speaker 1: especially like let's say we're going through a period where
• 40:30
  Speaker 1: space is expanding faster and faster, or where we're hitting
• 40:33
  Speaker 1: you know, in that zig zag, where we're hitting a
• 40:35
  Speaker 1: point of maximum expansion, that light is going to bend
• 40:37
  Speaker 1: a little bit differently right than it would in a
• 40:39
  Speaker 1: period of not so fast expansion.
• 40:41
  Speaker 2: All right, So now you've pushed this into a corner
• 40:43
  Speaker 2: of general relativity that we don't understand very well.
• 40:46
  Speaker 1: So the answer is we don't know, We don't know.
• 40:48
  Speaker 2: And also fascinatingly because we don't even understand our own theory,
• 40:52
  Speaker 2: like general relativity has no problem with having black holes
• 40:55
  Speaker 2: in an expanding universe, but we don't know how to
• 40:57
  Speaker 2: do that. Calculation like Einstein's equation are nasty and they're
• 41:01
  Speaker 2: very very difficult to solve. We can only solve them
• 41:04
  Speaker 2: in very specialized, simplified settings, like you have a black
• 41:07
  Speaker 2: hole in an otherwise empty universe that we can solve,
• 41:11
  Speaker 2: or you have a universe that's expanding, but the matter
• 41:14
  Speaker 2: in it is totally uniform, like dust sprinkled everywhere. We
• 41:17
  Speaker 2: don't know how to solve the equations for a black
• 41:19
  Speaker 2: hole in an expanding universe or a universe with like
• 41:23
  Speaker 2: chunky stuff in it. So we have all these approximations
• 41:26
  Speaker 2: and so the specific question you just asked, like what
• 41:28
  Speaker 2: happens to a black hole in an expanding universe? We
• 41:31
  Speaker 2: don't know how to do that calculation, but we think
• 41:35
  Speaker 2: that the rules are not changing, right, and so for
• 41:38
  Speaker 2: a black hole, gravity is basically the same as it
• 41:41
  Speaker 2: was a billion years ago and five billion years ago,
• 41:43
  Speaker 2: Like the nature of space itself is not changing. It
• 41:46
  Speaker 2: doesn't thin out, you know, as the universe expands, and
• 41:49
  Speaker 2: that expansion accelerats, you just get more space, and that
• 41:51
  Speaker 2: space behaves, we think, according to the same rules, and
• 41:54
  Speaker 2: so Bend's light the same way as it always did.
• 41:57
  Speaker 1: All right, Well, then the answer origin seems to be
• 41:59
  Speaker 1: that you don't think that the rules of the universe
• 42:01
  Speaker 1: are changing, meaning like what the physicists would consider to
• 42:04
  Speaker 1: be gravity, which is the whole set of equations. You
• 42:06
  Speaker 1: don't think that's changing. But maybe the effects of a
• 42:09
  Speaker 1: black hole might be changing, except you don't know how
• 42:12
  Speaker 1: to calculate it.
• 42:12
  Speaker 2: That's right. And there was even this fast on any
• 42:14
  Speaker 2: paper a few months ago about how like black holes
• 42:17
  Speaker 2: might be driving the expansion of the universe, right, that
• 42:20
  Speaker 2: black holes might actually be like weird clusters of dark energy.
• 42:23
  Speaker 2: So just to highlight like how little we understand the
• 42:27
  Speaker 2: expansion of the universe, and how tricky it is to
• 42:30
  Speaker 2: do these kind of calculations in any sort of realistic setting.
• 42:33
  Speaker 1: Yeah, or in the shower.
• 42:36
  Speaker 2: The shower is probably the best place to do these calculations.
• 42:39
  Speaker 1: Yeah. Well, if it wasn't for gravity, you couldn't take
• 42:42
  Speaker 1: a shower. You definitely any gravity to shower.
• 42:44
  Speaker 2: Oh my gosh, wow, thank you gravity. We should be
• 42:47
  Speaker 2: saying every time we have a shower. Yeah.
• 42:48
  Speaker 1: If not for gravity, we'd all be a little bit stinkier,
• 42:51
  Speaker 1: or we'd all have to take baths in zero gravity,
• 42:55
  Speaker 1: which I think is dangerous, isn't it, Like you would
• 42:57
  Speaker 1: you would very quickly drown because the water would just sing.
• 43:00
  Speaker 2: Golf you maybe, But again, don't take health advice from
• 43:04
  Speaker 2: this podcast. That is outside our area of expertise.
• 43:07
  Speaker 1: Yeah, don't take health advice from a cartoonist, a physicist.
• 43:12
  Speaker 2: Stay on your diet whatever it was before this podcast.
• 43:15
  Speaker 1: That's right. Listen to a real doctor, not the academic kind, exactly.
• 43:21
  Speaker 2: You know what the best thing about.
• 43:22
  Speaker 1: Getting your PhD is, there's the best thing.
• 43:25
  Speaker 2: Every meeting is now a doctor's appointment.
• 43:28
  Speaker 1: There you go. I'm sure everyone loves doctor's appointments. Does
• 43:32
  Speaker 1: that mean that this podcast is a doctor's appointment for
• 43:35
  Speaker 1: the thousands of people who listen to.
• 43:37
  Speaker 2: Us, I guess so. Yeah, oh man, keep your pants on, everyone, Yeah,
• 43:42
  Speaker 2: keep your pants.
• 43:42
  Speaker 1: How I'm not gonna grab anything or ask you to cough.
• 43:46
  Speaker 2: No, the only things we're probing are the nature of
• 43:48
  Speaker 2: the universe. The only black holes we're investigating are the
• 43:52
  Speaker 2: theoretical kind. That's right.
• 43:54
  Speaker 1: That's right, only only physical dark matter that we're interested in.
• 43:59
  Speaker 1: All right, Well, that answers Arjie's question and everybody's question again,
• 44:03
  Speaker 1: and another interesting journey to the edge of human knowledge
• 44:07
  Speaker 1: and the realization of how much we know and still
• 44:10
  Speaker 1: have yet to know about the universe, which is kind
• 44:12
  Speaker 1: of exciting.
• 44:13
  Speaker 2: That's right. So keep asking questions. You'll be surprised how
• 44:16
  Speaker 2: quickly you can get.
• 44:18
  Speaker 1: To the edge of human knowledge or the edge of
• 44:20
  Speaker 1: a black hole.
• 44:21
  Speaker 2: Apparently, or the edge of this doctor's appointment, or.
• 44:23
  Speaker 1: The edge of this podcast. So we hope you enjoyed that.
• 44:27
  Speaker 1: Thanks for joining us, See you next time.
• 44:35
  Speaker 2: For more science and curiosity. Come find us on social media,
• 44:38
  Speaker 2: where we answer questions and post videos. We're on Twitter, disport, Instant,
• 44:43
  Speaker 2: and now TikTok and remember that. Daniel and Jorge Explain
• 44:46
  Speaker 2: the Universe is a production of iHeartRadio. For more podcasts
• 44:50
  Speaker 2: from iHeartRadio, visit the iHeartRadio Apple Apple Podcasts, or wherever
• 44:55
  Speaker 2: you listen to your favorite shows.
• 45:00
  Speaker 3: Th