Speaker 1: Black holes make a gravitational wave. White chocolate is Daniel's save.
Speaker 2: What controls colors on our furry friends? It's biology, so.
Speaker 1: It depends particle colliders make mini booms. The big Bang
Speaker 1: filled the whole room.
Speaker 2: Biology, physics, archaeology, and forestry. Thank you for not asking
Speaker 2: about chemistry.
Speaker 1: What diseases you get from your cats? We'll find answers
Speaker 1: to all of that.
Speaker 2: Whatever questions keep you up at night, Daniel and Kelly's
Speaker 2: answers will make it all right.
Speaker 1: Welcome to another Listener Questions episode on Daniel and Kelly's
Speaker 1: Extraordinary Universe. Hello, I'm Kelly Wadersmith. I study parasites and space,
Speaker 1: and I'm excited to learn more about black holes today.
Speaker 2: Hi. I'm Daniel. I'm a particle physicist and I love cats,
Speaker 2: though I don't have nearly as many pets as exist
Speaker 2: on the Wienersmith Farm.
Speaker 1: Well, I mean that's hard to beat. So you're a
Speaker 1: cat person rather than a dog person, Is that what
Speaker 1: I'm hearing?
Speaker 2: Well, I grew up with cats, always loved cats, but
Speaker 2: my daughter is allergic cats. So now we have a
Speaker 2: dog and love my dog of course, and so kind
Speaker 2: of a dog person now but my daughter is getting
Speaker 2: shots so that she can tolerate cats, and we're hoping
Speaker 2: to get a cat soon.
Speaker 1: Oh exciting. Now are you going to adopt that cat?
Speaker 1: Where are you going to get the cat from?
Speaker 2: It? Was that? Or create the cat in collisions at
Speaker 2: the large hadron collider? So probably going to adopt it.
Speaker 1: Yeah, excellent. Well, we have a growing number of cats
Speaker 1: because we live on a farm in the woods and
Speaker 1: they find us and then they move in and I
Speaker 1: can never kick them out. We almost ended up with
Speaker 1: three beagles because they were also like dropped on the
Speaker 1: property and well saying no more animals. I am like
Speaker 1: simultaneously dumping pile of food in front of them. I
Speaker 1: can't help myself.
Speaker 2: Oh I see that was the other option. The option
Speaker 2: is adopt cats or have them adopt you, which is
Speaker 2: what you're doing on the farm.
Speaker 1: Yep, yep, although the goats I think I will be
Speaker 1: purchasing directly.
Speaker 2: Well, there's some sort of gravitational cat hole effect there,
Speaker 2: I think, because the more cats you get, the more
Speaker 2: they attract more cats, and then cats hear about your
Speaker 2: farm they're like, oh wow, it's a cat haven, and
Speaker 2: pretty soon you're gonna be a cat lady.
Speaker 1: Yeah, it's true. And we're also getting into chicken math.
Speaker 1: Have you heard about chicken math?
Speaker 2: Tell me about chicken math.
Speaker 1: It's when you decide you're going to get four chickens
Speaker 1: because it's not really that much work. So you actually
Speaker 1: get ten chickens, and then before you know what, the
Speaker 1: order you put in actually had a four in the front,
Speaker 1: and now you've got forty chickens. And anyway, I did
Speaker 1: duck math recently, and so now we have five ducks
Speaker 1: and two geese coming. My husband's not excited about the geese.
Speaker 1: We decided we were gonna name the geese Jacques Gusta
Speaker 1: and franc Scene Gusto. I think Jacques had two wives.
Speaker 1: One of them was Franccene. Anyway, we're very excited.
Speaker 2: Well, at least you have control over the names of
Speaker 2: the pets, even if not the species or number of them.
Speaker 2: Gives you a little bit of illusion of control.
Speaker 1: That's right. All that matters is that they let me
Speaker 1: snuggle them.
Speaker 2: And in this crazy universe that can sometimes feel out
Speaker 2: of our control, one way we can sort of establish
Speaker 2: a little bit of a finger hold on sanity is
Speaker 2: to think about the universe and try to understand it,
Speaker 2: try to grapple with the mysteries of the cosmos, and
Speaker 2: the best way to do that is to start by
Speaker 2: asking questions. Questions we have and questions that you have.
Speaker 1: Chicken math might not make sense, but Daniel and Kelly's
Speaker 1: answers do. So if you would like to submit your
Speaker 1: questions about the universe, write us at questions at danielands
Speaker 1: Kelly dot org. And it might take us a little
Speaker 1: while before your answer airs, because we are actually fairly
Speaker 1: well organized and we're about two months ahead of schedule,
Speaker 1: and we've got a bit of a list of questions.
Speaker 1: But you will get an answer from us, for sure.
Speaker 1: We respond to everyone that's.
Speaker 2: Right right to us with your questions at questions at
Speaker 2: Daniel and Kelly dot org. Everyone gets an answer, and
Speaker 2: some people get on the podcast. And today we have
Speaker 2: questions from three listeners about black holes, about furry pets,
Speaker 2: and about tiny little bangs. Our first question comes from
Speaker 2: Mark from Ireland about black holes. Here's Mark's question.
Speaker 3: Hi, Daniel and Kelly, this is Mark from Ireland and
Speaker 3: I have a question about merging black holes. When two
Speaker 3: black holes spiral towards each other to merge, they lose
Speaker 3: mass and in doing so, generates gravitational waves. The newly
Speaker 3: formed black hole will have a mass less than the
Speaker 3: sum of the two original black holes. My question is
Speaker 3: what actual mass is converted into gravitational waves and how
Speaker 3: does this happen? In trying to get my head around
Speaker 3: this phenomenon, I see there are lots of other interesting
Speaker 3: questions that might arise. Maybe you can explain the merging
Speaker 3: process and detail. I really enjoy the podcast and look
Speaker 3: forward to new episodes. Thank you and keep up the
Speaker 3: good work.
Speaker 1: Whoa great question. Okay, so I'm going to assume that
Speaker 1: we've never actually seen black holes collide and we are
Speaker 1: guessing what happens, or have we seen black.
Speaker 2: Holes Colyde, depends what you mean by seeing and black holes.
Speaker 2: But yes, we actually have seen black holes collide. We've
Speaker 2: observed these ingravitational waves collisions of dozens and dozens of
Speaker 2: pairs of black holes. Now it seems sort of fantastical
Speaker 2: and science fiction y, but it's our reality.
Speaker 1: Okay, So then what did you mean when you said
Speaker 1: it depends what you mean by black holes and observe,
Speaker 1: because it sounds like we have seen black holes collide.
Speaker 2: Yeah, I think most people in astronomy would say that
Speaker 2: we have seen black holes collide. Okay, but you know,
Speaker 2: we don't technically know that they are black holes. We've
Speaker 2: seen very dense, compact, dark objects which are consistent with
Speaker 2: black holes collide, that we've never really observed the event
Speaker 2: horizon directly, So there's an asterisk there on do we
Speaker 2: really know black holes are black holes? And in terms
Speaker 2: of seeing, we've observed the radiation generated by that collision,
Speaker 2: and that's what today's question is all about, how those
Speaker 2: black holes merge and the radiation they give off. So
Speaker 2: we've observed that gravitational radiation and it looks exactly like
Speaker 2: you would expect from black holes colliding. But I don't
Speaker 2: know if that counts as seeing it because it's not
Speaker 2: like visible light.
Speaker 1: Okay, all right, I got it. So let's start from
Speaker 1: the basics. What's a black hole?
Speaker 2: Right? So black hole famous prediction from classical general relativity. Right,
Speaker 2: This is Einstein's theory that space is curved. Gravity is
Speaker 2: not really a force. So what you think is gravity
Speaker 2: is actually just the effect of space time being curved.
Speaker 2: If you don't notice that space time is curved, it
Speaker 2: looks like something is bending the light or changing the
Speaker 2: path of the Earth. But it's actually just the curvature
Speaker 2: of space time. Space time curves in response to mass,
Speaker 2: and if you get enough mass in a small area,
Speaker 2: it curves space time so much that things get trapped.
Speaker 2: Space time is curved so that like light can't even escape.
Speaker 2: It's not like there's so much gravity it even pulls
Speaker 2: on photon. It's that space itself is bent so that
Speaker 2: inside a black hole, space only points towards the center.
Speaker 2: And so this creates the phenomenon we call the event horizon,
Speaker 2: beyond which anything that falls in is trapped. It will
Speaker 2: only move towards the center of the black hole. And
Speaker 2: so this is the defining feature of a black hole,
Speaker 2: the event horizon. This is the thing we haven't actually
Speaker 2: literally technically observed. We've seen lots of indirect evidence for
Speaker 2: black holes, but never actually observe the event horizon. And
Speaker 2: beyond the event horizon, we can't tell anything that happens.
Speaker 2: We can know the mass of the black hole, we
Speaker 2: can know if it has electric charge, we can know
Speaker 2: if it's spinning, but everything else is shrouded in mystery.
Speaker 1: We've done eleven of these listener questions episodes so far.
Speaker 1: In thinking back, I feel like most of them have
Speaker 1: had at least a question about a black hole. What
Speaker 1: do you think it is about black holes that keep
Speaker 1: people up at night?
Speaker 2: I think it's an incredible prediction of physics, something so
Speaker 2: strange and beyond our intuition. But macroscopic, right, like quantum
Speaker 2: mechanics makes all sorts of weirds about electrons, what they're
Speaker 2: secretly doing while you're asleep, whatever, But we'll never see
Speaker 2: those because they're microscopic. You can never observe them. Black
Speaker 2: holes are a prediction that are like technically you could
Speaker 2: see you could be near a black hole and observe
Speaker 2: it and see all this strange effects. So it feels
Speaker 2: sort of like magic, I think. And yeah, you're right,
Speaker 2: people are fascinated by black holes. It's a significant fraction
Speaker 2: of the questions that we get are about black holes.
Speaker 2: So yeah, absolutely, it's fantastic. It's wonderful. It's incredible that
Speaker 2: we've actually seen them, and we've seen these collisions. I
Speaker 2: remember in the late nineties deciding where to go to
Speaker 2: graduate school and what to work on, and I had
Speaker 2: an opportunity to work on this project Lego the gravitational
Speaker 2: wave observatory, and they were looking to see these black
Speaker 2: holes merging and the gravitational waves generated by them. And
Speaker 2: I remember thinking, they're never going to make that work.
Speaker 2: It's crazy, and so I decided not to work on that.
Speaker 2: And then of course they won the Nobel Prize. But
Speaker 2: you know, hey, maybe if I had worked on it,
Speaker 2: it wouldn't have worked out, and they wouldn't have won
Speaker 2: a Nobel Prize. So maybe they won the Nobel Prize
Speaker 2: because I didn't work on it.
Speaker 1: Anyway, hard to say, do you ever regret not going
Speaker 1: into black holes? Or are you totally happy with the
Speaker 1: path your life took?
Speaker 2: You know, there are always other options you could consider,
Speaker 2: but I'm pretty happy with how everything worked out, and
Speaker 2: so yeah, I don't worry too much about the counterfactuals.
Speaker 2: But it is amazing that humanity has figured out a
Speaker 2: way to observe these collisions. Einstein predicted this decades and
Speaker 2: decades ago, but he thought it was going to be
Speaker 2: impossible to observe because gravitational radiation is very, very weak,
Speaker 2: because gravity itself is not very powerful, and so you
Speaker 2: need an extraordinarily sensitive instrument to see this stretching and
Speaker 2: squeezing of space time, this gravitational radiation, unless, of course,
Speaker 2: you're right next to the black holes colliding, in which
Speaker 2: case the signal is very powerful and you're probably dead.
Speaker 1: I feel like that's another thing that gets people interested
Speaker 1: in the idea that observing this could kill you, but
Speaker 1: if you could survive what's on the other side, I
Speaker 1: just feel like it's amazing. But Okay, so we have
Speaker 1: observed collisions, and you said that we've observed a lot
Speaker 1: of them, and.
Speaker 2: It was a little bit of a surprise when we
Speaker 2: saw the first one. You know, we didn't know how
Speaker 2: often does this happen in the universe. We're building our
Speaker 2: first eyeball for gravitational waves, and how long it takes
Speaker 2: the sea one depends on how often they happen, and
Speaker 2: there were lots of predictions. Some people predicted that it
Speaker 2: would take decades to see one, but they saw one
Speaker 2: almost immediately after turning the thing on, and everyone's like,
Speaker 2: oh my gosh. Wow. So it turns out these collisions
Speaker 2: happen more often than people suspected.
Speaker 1: So does that mean we were totally off in our
Speaker 1: predictions for how many black holes there are or how
Speaker 1: much they're moving? Around what were we wrong about in particular.
Speaker 2: So we're not sure. Black hole formation is still kind
Speaker 2: of mystery. Super massive black holes or things we don't
Speaker 2: really understand, so something we're still trying to understand and
Speaker 2: we don't understand. Also the distribution of black hole masses.
Speaker 2: There seem to be some smaller ones, some bigger ones,
Speaker 2: but there aren't intermediate sized ones. So there's a lot
Speaker 2: we don't understand about black hole formation, how often it happens,
Speaker 2: how often they're close to each other, right, this kind
Speaker 2: of stuff, So a lot of really interesting astrophysics is
Speaker 2: being opened up by this study.
Speaker 1: No gold locks black holes, and Mark.
Speaker 2: Is interested in what happens when these two black holes
Speaker 2: form and where the mass goes, because you know, there's
Speaker 2: nothing free in the universe. If two black holes collide
Speaker 2: and produce gravitational waves, gravitational waves carry energy. They're stretching
Speaker 2: and squeezing of space time, and that energy has to
Speaker 2: come from somewhere, and it comes from the internal energy
Speaker 2: of the black hole system. These two things are orbiting
Speaker 2: each other and for them to collapse down into one,
Speaker 2: they have to lose that angular momentum, so they radiate
Speaker 2: it away in gravitational waves and Marx's questions trying to
Speaker 2: understand where the mass goes, because the mass of the
Speaker 2: resulting black hole is not just the sum of the
Speaker 2: masses of the two black holes that go in. It's
Speaker 2: smaller than that because energy is lost to gravitational waves.
Speaker 1: And we have talked in other episodes about how energy
Speaker 1: is mass, but maybe not. It's complicated, is that, right?
Speaker 2: Yeah, Mass is a measure of internal stored energy. Right,
Speaker 2: So like a proton's mass, it's not just the mass
Speaker 2: of the stuff that makes it up. It's the mass
Speaker 2: of the stuff that makes it up, plus the energy
Speaker 2: they have relative to each other. In fact, most of
Speaker 2: the mass of the proton comes from that energy, the
Speaker 2: binding energy of the quarks together. So if you have
Speaker 2: a black hole black hole system, two black holes orbiting
Speaker 2: each other, the mass of the whole system is the
Speaker 2: massive black hole one plus the massive black hole two
Speaker 2: plus their relative energy, and that's a lot. There's a
Speaker 2: lot of gravitational energy between those two black holes. Let's
Speaker 2: say black hole one is forty masses of the Sun,
Speaker 2: for example, and black hole two is thirty masses of
Speaker 2: the Sun. These are typical numbers. Then the energy of
Speaker 2: the whole system would be forty plus thirty plus whatever
Speaker 2: energy they have in their relative rotation, and that could
Speaker 2: be like thirty or forty or fifty, right, it depends
Speaker 2: on the configuration. So the total energy of the system
Speaker 2: could be much more than seventy. You could be one hundred,
Speaker 2: one hundred and twenty, this kind of thing. But a
Speaker 2: lot of that energy is lost when the two radiated
Speaker 2: away in order to combine. They have to radiate away
Speaker 2: some energy in order to combine, otherwise they would just
Speaker 2: or bit forever.
Speaker 1: And are they losing the energy of the black holes
Speaker 1: or are they losing the energy that surrounds the black
Speaker 1: holes or a little bit of both.
Speaker 2: Yeah, So this is a great question. And this is
Speaker 2: what Mark is asking, is like he wants to do
Speaker 2: some accounting. Is their mass actually lost? And I think
Speaker 2: he's interested in this because people think of black holes
Speaker 2: as something that can never lose mass, right at least
Speaker 2: in classical general relativity, And so he's wondering, like, is
Speaker 2: this a way for mass to escape somehow the black holes?
Speaker 2: And it's a little bit tricky. There's a couple of
Speaker 2: things to keep in mind. So the final black hole
Speaker 2: is smaller than the sum of the two original black holes,
Speaker 2: but always larger than either of them. So neither black
Speaker 2: hole shrinks. Both black holes grow.
Speaker 1: Nope, no, no, no, You've lost me. Don't they become
Speaker 1: one black hole when they merge.
Speaker 2: Yes, they become one black hole exactly, And so there's
Speaker 2: no shrinking of the event horizon. Like the final event
Speaker 2: horizon is bigger than either of the incoming event horizons. Okay,
Speaker 2: so no event horizon is shrinking. It's not like you're
Speaker 2: seeing behind the event horizon of either black hole. Both
Speaker 2: of them are growing, right, but the final is smaller
Speaker 2: than the sum of the two parts. It feels trickier.
Speaker 2: It feels like I'm cheating.
Speaker 1: Yes, so I guess what I'm not following is Okay,
Speaker 1: when they merge, I no longer think of them as
Speaker 1: two separate parts. They're just one part. But it sounds
Speaker 1: like you are still trying to keep accounting on two parts,
Speaker 1: but now they've become one. So what am I missing?
Speaker 2: Yeah? I think think about it from the point of
Speaker 2: view of black hole one. Okay, black Hole one has
Speaker 2: an event horizon, and it has a certain mass, and
Speaker 2: you could just be in its reference frame and it
Speaker 2: has another black hole orbiting it, right, and then that
Speaker 2: black hole radiates some energy and falls in and it
Speaker 2: gets gobbled up. Black Hole one grows. Right, So we
Speaker 2: followed all the rules of general relativity. The event horizon
Speaker 2: is not shrunk because it can never shrink, because if
Speaker 2: it did, you'd see things inside the event horizon. It
Speaker 2: has grown. Its mass has gone up. Right, in classical
Speaker 2: general relativity, black hole masses can only go up. So
Speaker 2: from the point of view of black hole one, the
Speaker 2: fact that black hole two is a black hole is
Speaker 2: kind of irrelevant. It's eaten some energy and it's grown.
Speaker 2: You can play the same game from the point of
Speaker 2: view a black hole two. Right, The thing is symmetric.
Speaker 2: Black Hole two grows, it gains mass, it's eating black
Speaker 2: hole one. The two merge. The final result is bigger
Speaker 2: than black hole two. Everything is happy from a general
Speaker 2: relativity point of view.
Speaker 1: Okay, so at the end you still have just one
Speaker 1: black hole, but that one black hole is bigger than
Speaker 1: black hole one or black hole two were originally.
Speaker 2: Yes, exactly, Okay, and so it feels like mass has
Speaker 2: been lost and we're playing some sort of shell game here.
Speaker 2: I think there's another thing to understand that might help people,
Speaker 2: which is, the mass of the black hole doesn't just
Speaker 2: depend on what's beyond the event horizon. You can make
Speaker 2: a black hole more massive without crossing the event horizon. So,
Speaker 2: for example, say I shoot Kelly into orbit around a
Speaker 2: black hole, hypothetically speaking, or Zach. Should we talk about Zaz? Yeah, yes,
Speaker 2: of course Zach is in orbit around a black hole. Okay,
Speaker 2: Now that black hole's mass grows even before Zach goes
Speaker 2: over the event horizon. Right, you tend to think like, oh,
Speaker 2: it's has to eat Zach before it grows to add
Speaker 2: to its mass. But the mass is a measure of
Speaker 2: the energy of the system, right, So the black hole's
Speaker 2: mass actually grows before Zach falls over the event horizon.
Speaker 1: So at what point does Zach become part of the
Speaker 1: system mm.
Speaker 2: Hmm, Well when he has a relationship to it, like
Speaker 2: it's a gravitationally bound to it, than to an external
Speaker 2: observer who's like a little bit further away, like it's
Speaker 2: a black hole, Zach's system. The whole thing has more
Speaker 2: mass than the black hole or than Zach does, and
Speaker 2: so you don't have to like add stuff to the
Speaker 2: black hole over the event horizon in order for the
Speaker 2: black hole to gain in mass. This is actually crucial
Speaker 2: for the way that black holes actually grow in the universe.
Speaker 2: You might have heard, for example, if you do throw
Speaker 2: your husband into a black hole, you'll never actually see
Speaker 2: him cross the event horizon because time slows down. And
Speaker 2: a lot of people write it and say, all right,
Speaker 2: but then how do black holes actually grow if nothing
Speaker 2: can cross the event horizon because time slows down. But
Speaker 2: the answer is that the event horizon grows before Zack
Speaker 2: reaches it. It grows out to meet him. He and
Speaker 2: the event horizon approach each other. And so if Zach
Speaker 2: was the last thing you ever threw into a black hole,
Speaker 2: it's true that he would never cross it, you'd never
Speaker 2: see him. But if after you throw Zach into a
Speaker 2: black hole, you feel bad and you throw him a sandwich,
Speaker 2: and that sandwich approaches the black hole, and as it
Speaker 2: approaches the black hole, it pulls the event horizon over Zack, right,
Speaker 2: because the event horizon comes out to meet the thing
Speaker 2: that's approaching it. Because again, the mass of the black
Speaker 2: hole depends on the stored energy, which includes the gravitational
Speaker 2: energy it has with things around it. So you shouldn't
Speaker 2: think of these things as just like boxes, right, Remember,
Speaker 2: mass it's not just like a measure of how much
Speaker 2: stuff is inside the black hole. It's a more comprehensive
Speaker 2: measure of the energy of that whole system. You don't
Speaker 2: have to be over the event horizon in order to
Speaker 2: be part of that system.
Speaker 1: So one, the next time you say biology is complicated,
Speaker 1: I'm going to just start laughing right away. But okay. Two,
Speaker 1: So if you threw Zach ten thousand sandwiches because you
Speaker 1: are like you're going to be there for a while,
Speaker 1: would the event horizon pass Zach faster than if you
Speaker 1: just threw him one sandwich because you don't really care
Speaker 1: about what happens in the long run.
Speaker 2: Mm hmm, yeah, absolutely, okay. And if you threw them
Speaker 2: in a series, then chicken sandwich number one would pass first,
Speaker 2: chicken sandwich number two, then chicken number three, and the
Speaker 2: last chicken sandwich would not cross the event horizon. So
Speaker 2: it's true, you can't see something cross the event horizon
Speaker 2: if it's the last thing that you throw. But in
Speaker 2: our universe there's never a last thing. There's always like
Speaker 2: more gas and more particles. And that's how black holes
Speaker 2: in the universe actually grow, all right, But back to
Speaker 2: Mark's question, what's going on here is that the mass
Speaker 2: of the whole system. Right, Let's say we start with
Speaker 2: our example of a forty and a thirty black hole,
Speaker 2: and together they have a mass of like one hundred
Speaker 2: and twenty, right, including all gravitational energy and rotational energy.
Speaker 2: As they inspirle, they radiate away a bunch of that energy.
Speaker 2: So the mass of the system was one twenty. It's
Speaker 2: radiated away I don't know sixty. So now the final
Speaker 2: black hole is sixty instead of one twenty. So sixty
Speaker 2: is bigger than forty and bigger than thirty, but smaller
Speaker 2: than forty plus thirty. But all that's happened is that
Speaker 2: some of that rotational gravitational energy has been radiated away.
Speaker 2: So even though the whole system started out with mass
Speaker 2: of one twenty, now it's down to sixty because it's
Speaker 2: radiated away half of its energy. I'm just making up
Speaker 2: these numbers. They're roughly correct in the order of magnitude,
Speaker 2: but I haven't done like any calculations. But that's the
Speaker 2: right way to think about it as the energy of
Speaker 2: the whole system.
Speaker 1: All right, Well, I think I understand black holes better now,
Speaker 1: although I say that after every explanation and then I
Speaker 1: get things wrong the next time we talk about it.
Speaker 1: But let's see what Mark from Ireland thinks of that explanation.
Speaker 3: Hi, Daniel and Kelly, thank you very much for that
Speaker 3: very informative answer to mike question. I think black holes
Speaker 3: are really amazing, and merging black holes are even more amazing.
Speaker 3: It's incredible that during the final fifth of a second
Speaker 3: of their inward spiral, that they are flying around one
Speaker 3: another at near relativistic speeds, often up to a rate
Speaker 3: of two hundred and fifty orbits a second, and radiate
Speaker 3: the equivalent of multiple solar masses of energy in the
Speaker 3: former gravitational waves. It really is crazy, crazy physics. Well,
Speaker 3: you've answered my questions very well, and thank you both
Speaker 3: for taking the time to do so. I'm sure you'll
Speaker 3: hear from me again at some stage in the future,
Speaker 3: and in the meantime, I'm going to keep listening in.
Speaker 1: All right, So now we are onto by all, from
Speaker 1: black holes to black spots. We are talking about patterns
Speaker 1: on our furry friends. Let's hear what Simon from Germany
Speaker 1: wanted to know about.
Speaker 4: Hi, Daniel N. Kelly Simon here from Germany. Thanks for
Speaker 4: a great podcast. They're a fine background to my daily
Speaker 4: run in the woods. I have a question here for Kelly,
Speaker 4: one that has puzzled me for quite some time, and
Speaker 4: it's in relation to the coloration of our furry friends.
Speaker 4: So if we take a dog, for example, who is
Speaker 4: black and white, and we zoom into the border between
Speaker 4: the two colors, presumably we have one skin cell or
Speaker 4: hair cell with black pigmentation and the neighboring cell as
Speaker 4: a white pigmentation. The question is how is this information
Speaker 4: passed down? Presumably the information is contained in a precursor cell,
Speaker 4: one splitting into a black and one into a white.
Speaker 4: The question is what is the mechanism for this? Thanks
Speaker 4: for a great podcast, guys, Keep up the good work,
Speaker 4: and I look forward to hearing some insight into this question.
Speaker 2: See biology also has really massively important questions.
Speaker 1: Are you being facetious?
Speaker 2: I can't tell no, I'm trying to make a gravitational pun.
Speaker 1: Oh good, excellent? Okay, sorry, went right over my head.
Speaker 1: All right, So this was actually a fairly difficult question
Speaker 1: to read about and to try to understand. And it's biology.
Speaker 1: So it depends.
Speaker 2: Let me see if I can interpret the question to
Speaker 2: make sure I understand what he's asking. Okay, I think
Speaker 2: he's basically trying to do some physics here, which is
Speaker 2: to like zoom in on the microprocesses involved. He's like
Speaker 2: looking at his dog and seeing there's white patches and
Speaker 2: black patches and wondering like what makes one bit white
Speaker 2: and one black? And he's trying to understand it by
Speaker 2: zooming in on the boundary and saying like, there's got
Speaker 2: to be a point where there's one cell that's white
Speaker 2: and one cell that's black, and that's where the difference is.
Speaker 2: And he wants to highlight like what's going on between
Speaker 2: those cells to understand why one turns white and black,
Speaker 2: but also obviously to zoom out and understand, like how
Speaker 2: do you get these patterns?
Speaker 1: Yes, And that's how I interpreted the question as well.
Speaker 1: And the answer is that if you are looking at
Speaker 1: animal patterns in general, it depends on the colors, it
Speaker 1: depends on the pattern shape, it depends on the animal.
Speaker 1: But Simon in particular referenced dogs and referenced white and black,
Speaker 1: and so I decided that I was going to hone
Speaker 1: in on that in particular, all right, because I needed
Speaker 1: a foothold for this question. And so in dogs, there
Speaker 1: are hair follicles or fur follicles that produce either black
Speaker 1: or brown colors, or yellow or white colors. So one
Speaker 1: follicle can produce either of those colors depending on the
Speaker 1: instructions that it's given. So it's not like you have
Speaker 1: different kinds of cells next to each other. It's all
Speaker 1: the same cell, but it just is following different sets
Speaker 1: of instructions.
Speaker 2: So they're just like printers, and they can get an
Speaker 2: instruction for a black hair or a white hair and
Speaker 2: they're happy to do it.
Speaker 1: That's right, Yes, exactly.
Speaker 2: Interesting, So who sends the instructions?
Speaker 1: So the instructions are encoded in a gene called a gooty,
Speaker 1: and this gene is important for coloration in a lot
Speaker 1: of different species, and the gene produces a hormone. The
Speaker 1: hormone gets released from the cell.
Speaker 2: I'm a little confused because a gene is part of
Speaker 2: your DNA, and so when you're saying the gene produces
Speaker 2: a hormone, do you mean the gene when it's transcribed
Speaker 2: into a protein is that hormone or the gene when
Speaker 2: transcribed into a protein. Is some little machine that makes
Speaker 2: the hormone or excuse my naive biologic question.
Speaker 1: No, No, that's a great question. I skipped a bunch
Speaker 1: of steps. So, as I understand it, the gene encodes
Speaker 1: for a hormone, and so when that gene is essentially
Speaker 1: read and turned into a protein, that protein is a
Speaker 1: hormone that subsequently gets released from the cell.
Speaker 2: The hair follicle cell, or some other kind of cell
Speaker 2: that's controlling the hair follicle cells.
Speaker 1: What I think is happening here is that hair follicle
Speaker 1: cells are producing this message and then also sharing it
Speaker 1: with nearby cells.
Speaker 2: Oh interesting, Okay, one.
Speaker 1: Gets released and it talks to the nearby cells. If
Speaker 1: you are a hair follicle next to a cell that
Speaker 1: has just released this hormone, then you produce white.
Speaker 2: Interesting.
Speaker 1: If you don't get that hormone message, you default to
Speaker 1: making black or brown?
Speaker 2: Wow? Fascinating right.
Speaker 1: So cells can do either, and so the question is
Speaker 1: why are some cells making the signal that say turn
Speaker 1: on white and why are some cells not making that
Speaker 1: signal and telling nearby cells to default to brown or black?
Speaker 2: I loveI we like follow the chain of logic here like,
Speaker 2: this is happening because of that, because of that, because
Speaker 2: of that, because of that, and now we're like detectives
Speaker 2: following the clues all the way back to the source.
Speaker 2: So are you going to tell us who the killer is?
Speaker 2: Who is making these decisions about whether to produce this hormone?
Speaker 1: You know, it's biology, so that the answer is never,
Speaker 1: you know, kernel mustard. It's much more complicated. So you've
Speaker 1: got this a gooty gene, And what determines whether or
Speaker 1: not genes are turned on or off is that there
Speaker 1: are these regions called promoters, and when something binds to
Speaker 1: the promoter, that can turn the gene on. And so
Speaker 1: it seems that whether or not this hormone is made
Speaker 1: or not has to do with some complicated interactions happening
Speaker 1: with the promoter for the genes. And so some cells
Speaker 1: have these promoters turned on, so they're making this make
Speaker 1: white message, and some genes don't get this promoter turned on,
Speaker 1: so they are not giving a message, and nearby cells
Speaker 1: make black or brown. Part of why I didn't get
Speaker 1: into the details is because it might help you understand
Speaker 1: exactly what's happening in this very particular instance. But to
Speaker 1: understand coloration in general, that's more a story about promoters
Speaker 1: getting turned on or off.
Speaker 2: So in general, then how do promoters get turned on
Speaker 2: or off? I mean, this is part of your DNA,
Speaker 2: what determines whether or not that DNA is getting turned
Speaker 2: on or off.
Speaker 1: In general, we don't understand what's happening super well here,
Speaker 1: and we understand this process a lot better in rodents
Speaker 1: in birds, and in part that's because we feel much
Speaker 1: more comfortable doing experiments on these animals in the lab.
Speaker 2: All that's kind of sad, I know.
Speaker 1: I know it is sad, But then you can also
Speaker 1: pick animals that have much simpler color patterns and fewer
Speaker 1: colors to boots, and that makes it easier to sort
Speaker 1: of get a handle on these sorts of things, whereas
Speaker 1: dogs have loads of different color patterns, and so trying
Speaker 1: to get a handle on all of the different ways
Speaker 1: these patterns can be made is much more complicated. The
Speaker 1: manuscript that I read even had a sentence being like,
Speaker 1: the situation in dogs is still unresolved, but they're doing
Speaker 1: their best to figure it out.
Speaker 2: Well, this is super interesting how we can go from
Speaker 2: like totally clues about it to understanding, Oh, follicles can
Speaker 2: print either color to understanding what controls what they print,
Speaker 2: and then follow that up the chain, and we're still
Speaker 2: crawling up the chain. It's incredible.
Speaker 1: It is incredible, And like I said, we've got a
Speaker 1: better handle on some species. And animal coloration in general
Speaker 1: is sort of fascinating. Like sometimes there are some animals
Speaker 1: that get it from their diet. For example, there are
Speaker 1: some fish that have red coloration that they get from
Speaker 1: the animals that they eat, and it just sort of
Speaker 1: like accumulates in their skin.
Speaker 2: That would be amazing if humans, for example, change color
Speaker 2: based on what they ate.
Speaker 1: Oh man, Yeah, there'd be very specific kinds of diets
Speaker 1: I imagine, And around Halloween you'd eat like a lot
Speaker 1: more carrots to get in the mood.
Speaker 2: Would be great, well, amazing. You could get a tan
Speaker 2: just by having lunch.
Speaker 1: That would be incredible and probably a lot safer than
Speaker 1: what we do now to get tans.
Speaker 2: All Right, So it turns out that Simon's question is
Speaker 2: cracked open a huge canyon of unresolved questions in biology.
Speaker 2: And not only do we not understand dogs, but the
Speaker 2: whole question of how animals get color is still an
Speaker 2: active area of research. And maybe having different answers in
Speaker 2: each species. Amazing.
Speaker 1: That's right, And so let's see if Simon feels like
Speaker 1: he learned anything from this answer.
Speaker 2: It sounds like Kelly read a lot of papers and
Speaker 2: learned a lot.
Speaker 1: Kelly read a lot of papers, learned a lot, and
Speaker 1: also learned that there's a lot that she doesn't know
Speaker 1: about how this stuff works out. So it was a
Speaker 1: learning experience for sure.
Speaker 2: All right, let's hear from Simon. Uh huh.
Speaker 4: Kelly definitely did learn something, and I think we as
Speaker 4: the audience, I've definitely learned something too. Thanks Kelly for
Speaker 4: the great insight into the invisible and incredibly complicated, it
Speaker 4: seems biological mechanisms behind something as simple as the coloration
Speaker 4: of our furry friends. I think understanding how it works
Speaker 4: at this very last step perhaps gives us some insight
Speaker 4: into how it works at the very first step. So
Speaker 4: if I go back to the very first cell directly
Speaker 4: after conceptions, say, where it splits into two, and then
Speaker 4: to four, and then to eight and so on, eventually
Speaker 4: giving rise to something that resembles a head, a torso,
Speaker 4: and four legs, to understand the finer details of how
Speaker 4: this information has passed down. How one cell knows to
Speaker 4: be a torso while as a direct neighbor knows to
Speaker 4: become a leg To understand how this transfer of information
Speaker 4: works from one cell division to the next will be
Speaker 4: fascinating to find out one day, But that's a question
Speaker 4: for another day. Maybe. Thanks Kelly for taking the time
Speaker 4: to look deeper into this mechanism and give us some
Speaker 4: insight into this very last step of cell division. Gave
Speaker 4: up the Great White cause.
Speaker 2: All right, we're back and we're moving on from the
Speaker 2: mysteries of biology to the mysteries of the very early universe?
Speaker 2: Which one do we understand less?
Speaker 1: Does it really need to be a competition? We don't
Speaker 1: understand much about anything.
Speaker 2: Some days it feels like Leonardo wanted to understand the
Speaker 2: relationship between particle collisions and the Big Bang. Here's his question.
Speaker 5: Hi, Kelly and Daniel loved the show. I heard particle
Speaker 5: accelerators being described as tiny banks as in The Big
Speaker 5: Bang but tiny in another podcast by doctor Katie Mack.
Speaker 5: I also know we measure the energy of impacts in
Speaker 5: giga electron votes, so can we also estimate the energy
Speaker 5: of the Big Bang in electron votes?
Speaker 6: And?
Speaker 5: If so, why are we not classifying accelerators in Meli
Speaker 5: or Fento banks and Easy because the number would be
Speaker 5: too unsatisfying. Grains from Brazil.
Speaker 1: All right, So, Daniel, I remember you telling me once
Speaker 1: that when you all turned on the particle collider for
Speaker 1: the first time, there was a little bit of a
Speaker 1: concern that maybe you would destroy the universe? Is that
Speaker 1: because you all thought you were going to kick off
Speaker 1: a tiny, big bang.
Speaker 2: Well, you know, anytime you do something that's never been
Speaker 2: done before, you don't know what's going to happen. That's
Speaker 2: the excitement of research, right, you know, you're exploring the unknown,
Speaker 2: you're potentially unleashing something you didn't expect. And so yeah,
Speaker 2: there's always a little frison of you know, enthusiasm and
Speaker 2: fear when that happens.
Speaker 1: But when I first infect a fish with a parasite,
Speaker 1: I don't worry that it's the end of humanity. Like,
Speaker 1: the scale feels very different here.
Speaker 2: Maybe you should think bigger, Kelly. Yeah, okay, for those
Speaker 2: of you worried at home, we didn't actually worry about
Speaker 2: that too much because the collisions we'd do with the
Speaker 2: particle colliders are not unusual in nature. They're very high
Speaker 2: energy collisions from particles slamming into the Earth's atmosphere all
Speaker 2: the time, much higher energy than what we achieve with
Speaker 2: the large a drunk collider. We didn't worry that we'd
Speaker 2: be collapsing the Higgs field or creating a black hole
Speaker 2: or anything like that. But it is a fascinating experiment
Speaker 2: because we are recreating conditions of the early universe. They're
Speaker 2: also conditions of our current universe, just not as widespread.
Speaker 2: And so it's often said that particle collisions recreate the
Speaker 2: Big Bang, and that's true in some sense, but there's
Speaker 2: also the potential there to sort of underscore misunderstandings about
Speaker 2: the Big Bang that we should probably clear up.
Speaker 1: Well, can we start with, like, what is the defining
Speaker 1: characteristic of a bang of any size? Small, medium, or large?
Speaker 2: Yeah, that's a good question. You know, in terms of
Speaker 2: the Big Bang, the Big Bang is more of a
Speaker 2: whiff than a bang, right, because the universe is expanding,
Speaker 2: but it's really sort of cooling. It's becoming older and colder.
Speaker 2: So the Big Bang is a description of how the
Speaker 2: universe is decreasing in density as time goes on. It's
Speaker 2: cooling down and getting more dilute. To run the clock backwards,
Speaker 2: the universe gets hotter and denser, and we can run
Speaker 2: backwards to a certain point what we call the plank
Speaker 2: time beyond which we know our theories don't work, and
Speaker 2: so everything is a question mark. And that's what we
Speaker 2: call the Big Bang is expansion from that moment. So
Speaker 2: it's a description of when the universe had very high
Speaker 2: energy density. It's not a tiny dot in empty space.
Speaker 2: The idea of a big bang, especially if you compare
Speaker 2: to particle collisions, makes it sound like something happening at
Speaker 2: one location, but the Big Bang was everywhere, and so
Speaker 2: the similarity between particle collisions and the Big Bang is
Speaker 2: that both have high energy density. Particle collisions of course,
Speaker 2: though in just one spot, the Big Bang was everywhere.
Speaker 1: Got it? Okay? And what kind of scale difference are
Speaker 1: we talking about in terms of energy between big and
Speaker 1: tiny bangs?
Speaker 2: Yeah, so it's a pretty big difference. We compare these
Speaker 2: things in a weird unit called electron volts, and it's
Speaker 2: sort of a generic unit of energy. You can also
Speaker 2: use it to measure mass, because we don't care about
Speaker 2: things like the speed of light, and so an electron
Speaker 2: volt is our unit, and to calibrate. For example, a
Speaker 2: proton has a mass of one giga electron vault, so
Speaker 2: a billion electron volts is the mass of a proton,
Speaker 2: and collisions that we can achieve here on Earth are
Speaker 2: in the scale of ten tarra electron vaults, so ten
Speaker 2: thousand times the mass of a proton. And that sounds
Speaker 2: pretty big, right, like ooh wow tarra Like that's a big.
Speaker 1: Number, But protons are pretty small.
Speaker 2: Protons are pretty small, exactly, And so the energy of
Speaker 2: the Big Bang in the same units is ten to
Speaker 2: the sixteen terra electron vaults, so ten to the fifteen
Speaker 2: times more energy than the collisions we have at the LHC.
Speaker 2: And ten of the fifteen is not a small number,
Speaker 2: you know, it's not fifteen times. It's ten to fifteen
Speaker 2: ten with fifteen zeros. If your bank account had one
Speaker 2: with fifteen zeros in it, you'd be very very rich,
Speaker 2: much much much richer than Elon Musk, probably like Elon
Speaker 2: Musk squared. So it's very very high energy.
Speaker 1: If particle physicists had enough money, would you guys try
Speaker 1: to make a particle collider you could do the Big
Speaker 1: Bang in because I'm not sure we can trust.
Speaker 2: You, guys, No, I think we would. And you know,
Speaker 2: the higher the energy collision, the more stuff you can make.
Speaker 2: Right we don't know what's out there in the sort
Speaker 2: of universe's menu of particles. And the incredible thing about
Speaker 2: these collisions is that you pour energy in and there's
Speaker 2: some sort of like quantum mechanical magic alchemy that happens,
Speaker 2: and the universe decides what from its menu to make,
Speaker 2: and it just sort of picks randomly from all the
Speaker 2: things that it can make, which means that if you
Speaker 2: pour enough energy into the collisions, you'll see everything the
Speaker 2: universe is capable of making. If you do it often enough,
Speaker 2: you don't even have to know what's out there. So
Speaker 2: it's like a way to explore the capacity of the
Speaker 2: universe without even knowing what it's capable of. You don't
Speaker 2: have to leave your house. It's like, hey, make me
Speaker 2: everything you can make right here. And as you turn
Speaker 2: up that energy, you get to explore higher and higher
Speaker 2: on nature's menu. And you could be just below the
Speaker 2: threshold and not make the thing because they don't have
Speaker 2: enough energy, and then you crank up the energy and
Speaker 2: boom it starts to pop out. So Yeah, we'd love
Speaker 2: to crank up the energy these things. We're still a
Speaker 2: factor of ten to fifteen away from the Big Bang,
Speaker 2: which means there could be particles that were made in
Speaker 2: the early universe and they're super duper massive and we
Speaker 2: haven't been able to make them yet. They could be
Speaker 2: made in collisions of cosmic rays in the atmosphere, but
Speaker 2: they're very short lived and we don't have detectors up
Speaker 2: there to see them.
Speaker 1: So check out Daniels go fundme for the next big
Speaker 1: particle collider.
Speaker 2: Leon artists question also asked, can we measure particle collisions
Speaker 2: in terms of milli or fempto bangs? And the answer
Speaker 2: is yes. So if you define one bang as ten
Speaker 2: to the sixteen TeV, then the Large Hadron Collider has
Speaker 2: collisions at about ten of the minus fifteen bangs or
Speaker 2: one femto bang, which, yeah, doesn't sound very impressive and
Speaker 2: not a great way to headline your science funding request.
Speaker 1: I don't know. I think femto bang sounds pretty.
Speaker 2: Cool, but it's also a way to sort of trace
Speaker 2: back the history of the universe. Like as the energy
Speaker 2: of your collisions goes up and up and up, you
Speaker 2: recreate conditions that existed everywhere in the universe further and
Speaker 2: further back in time and already ten TV one. Femto
Speaker 2: bang is pretty high energy. It takes you all the
Speaker 2: way back to like microseconds after the Big Bang because
Speaker 2: the energy started to fall off really really quickly. It
Speaker 2: becomes more gradual as time goes on. So we are
Speaker 2: probing conditions in a very very early universe microseconds after
Speaker 2: the Big Bang.
Speaker 1: Well, let's see if Leonardo is impressed by femto bangs.
Speaker 6: Hello, I'm also in teen Kelly, I'm also impressed by
Speaker 6: fento bank. Also, thanks for clarifying the differences between a
Speaker 6: particle collider and the early universe. I actually never considered
Speaker 6: that there could have been particle so massive. If that
Speaker 6: we will likely never be able to recreate. Thanks.
Speaker 2: All right, and today we have a special bonus question
Speaker 2: on gravitational and velocity based time dilation from ASTHMT. We
Speaker 2: decided we could squeeze in a fourth question for y'all,
Speaker 2: So here's Ozma's question about time dilation.
Speaker 7: Hello, I'm a smith, and my question is what would
Speaker 7: happen to time dialation if both high velocity and strong
Speaker 7: magnetic feeling interacted simultaneously. Would this cost time to slow
Speaker 7: down even more significantly or would there be no additional effect?
Speaker 7: Thank you?
Speaker 1: All right? So Daniel, I have been listening, well you talk,
Speaker 1: and I remember you told me there's two kinds of
Speaker 1: time dilation, gravity and velocity. But my brain is a sieve,
Speaker 1: so remind me what the difference between those is.
Speaker 2: Right, So there are two ways that clocks can appear slow. Now,
Speaker 2: clocks that you hold, that you have with you always
Speaker 2: run the same speed. But if Kelly gives Zach clock
Speaker 2: and then shoots them out of a cannon a very
Speaker 2: high speed relative to her, she will see Zach's clock
Speaker 2: running slow because velocity time dilation says moving clocks run slow. Now, Zach,
Speaker 2: with this telescope looking back at Kelly's clock, will disagree.
Speaker 2: He'll say, no, no, Kelly's clock is running slow. So that
Speaker 2: kind of time dilation is symmetric, meaning both wiener Smith's
Speaker 2: see the other one's clock running slow. And at least
Speaker 2: to this sort of confusion like whose clock is really
Speaker 2: slower and the answer is there is no really slower,
Speaker 2: they can argue forever and both be right. So it's
Speaker 2: sort of a marital trap for the two of them.
Speaker 1: Yeah, that's not great.
Speaker 2: But the other kind of time dilation, gravitational time dilation,
Speaker 2: is asymmetric, which means everybody can agree on it. So,
Speaker 2: for example, if Kelly does drop Zach near a black hole,
Speaker 2: she'll see his clock running slower, but he will see
Speaker 2: her clock running faster. They agree in this scenario, but
Speaker 2: whose clock is running slower or faster? Both of them
Speaker 2: see their own clocks running at normal speed. And so
Speaker 2: the cool thing here, and this is Ozma's question, is like,
Speaker 2: what happens when you have both? Do they constructively interfered,
Speaker 2: destructively interfered to his universe? Explode? What happens?
Speaker 1: I hope The answer is Kelly is right. Whatever time
Speaker 1: Kelly says is the correct time.
Speaker 2: The answer is they both contribute. So let's say, for example,
Speaker 2: that Kelly launches Zach into orbit. Right now, Zach is
Speaker 2: going really, really fast, and so his velocity means that
Speaker 2: his clock runs slower than clocks we have here on
Speaker 2: Earth from our point of view. Okay, but he's also
Speaker 2: further from the gravitational well of the Earth, so his
Speaker 2: clocks will run faster than ours. Because of the gravitational
Speaker 2: time dilation is less so we have actually gravitational time
Speaker 2: dilation right here on the surface of the Earth. Because
Speaker 2: of the Earth, we're all experiencing it all the time.
Speaker 2: Clocks out in deep space run faster. So from Kelly's
Speaker 2: point of view, Zach's clock runs slower because of velocity
Speaker 2: and faster because of gravity, and the gravity actually wins out.
Speaker 2: So the velocity time delation is like seven microseconds per
Speaker 2: day if he's up with GPS satellites, and forty five
Speaker 2: microseconds per day the other direction due to gravity. So
Speaker 2: overall gravity wins.
Speaker 1: So when I shoot him into orbit, because gravity is
Speaker 1: winning and it makes things faster, he should still be
Speaker 1: on time or early to the meetings. I let no
Speaker 1: excuse for being late, Is that right?
Speaker 2: I really feel like I don't want to get in
Speaker 2: the middle of here. Physics is not going to solve
Speaker 2: your marital.
Speaker 1: Problems, all right, all right, but baby sandwiches, well.
Speaker 2: Sandwiches yet well exactly now, from Zach's point of view,
Speaker 2: both of the effects make Earth's clocks slower. It's fascinating
Speaker 2: because from the Earth's point of view, we see the
Speaker 2: effects having different directions. But from Zach's point of view,
Speaker 2: he sees both effects having the same direction. He sees
Speaker 2: us moving quickly, which means our clocks run slow, and
Speaker 2: he sees a closer to a gravitational well of the earth,
Speaker 2: which means our clocks run slow.
Speaker 1: Oh see, now, I feel like you're citing with zech.
Speaker 1: This is no excuse.
Speaker 2: I feel like I need my lawyer present.
Speaker 1: All right, everybody, thanks for playing. Just a reminder that
Speaker 1: you too can send us questions at questions at danielant
Speaker 1: Kelly dot org. We answer every question, some of them
Speaker 1: end up on the show and we can't wait to
Speaker 1: hear from you.
Speaker 2: And some of our questions come from conversations on the discord.
Speaker 2: We encourage you to join our discord, where people ask
Speaker 2: and answer questions and make a bunch of nerdy jokes.
Speaker 2: You can find the invitation on our website Daniel and
Speaker 2: Kelly dot org.
Speaker 1: Daniel and Kelly's Extraordinary Universe is produced by iHeartRadio. We
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Speaker 2: We want to know what questions you have about this
Speaker 2: Extraordinary Universe.
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