Latest / Daniel and Kelly’s Extraordinary Universe / Listener Questions goes bananas!

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Listener Questions goes bananas! · Daniel and Kelly’s Extraordinary Universe

• 0:08
  Speaker 1: Hey, or hey, do you like your bananas really really fresh?
• 0:12
  Speaker 1: Or like gently decayed?
• 0:14
  Speaker 2: Decayded?
• 0:15
  Speaker 1: What do you mean, like a rotten You know, bananas
• 0:18
  Speaker 1: are on the spectrum from like crunchy and green to
• 0:22
  Speaker 1: black and mushy, and everybody likes them differently. Where do
• 0:25
  Speaker 1: you sit on that spectrum?
• 0:26
  Speaker 3: Mmm?
• 0:27
  Speaker 2: I like him yellow but with a little bit of
• 0:29
  Speaker 2: a speckle to them.
• 0:30
  Speaker 1: Mmmm, so slightly decayed.
• 0:33
  Speaker 2: Slightly decayed but only a little bit. But you know,
• 0:36
  Speaker 2: I'm flexible. It depends on the how desperate I am
• 0:39
  Speaker 2: for banana and.
• 0:40
  Speaker 1: How desperate you are to keep from decaying.
• 0:42
  Speaker 2: What do you mean the bananas help you live.
• 0:44
  Speaker 1: Longer, probably longer than chocolate.
• 1:02
  Speaker 2: Hi am Porgemake Cartoonists, an author of Oliver's Great Big Universe.
• 1:05
  Speaker 1: Hey, I'm Daniel. I'm a particle physicist and a professor
• 1:08
  Speaker 1: at U See or Irvine, and I honestly think bananas
• 1:11
  Speaker 1: and chocolate don't mix.
• 1:13
  Speaker 2: You've never had it together before?
• 1:15
  Speaker 1: Oh no, I've tried them. It's just not a good combination.
• 1:18
  Speaker 1: The texture just clashes.
• 1:20
  Speaker 3: Hmm.
• 1:21
  Speaker 2: I wonder if you had the right way, like on
• 1:23
  Speaker 2: a fondue. Have you had it on a fondue? Then
• 1:25
  Speaker 2: they're both kind of soft and uh and delicious.
• 1:30
  Speaker 1: Yeah, but the bananas still got that squishiness to it,
• 1:33
  Speaker 1: you know, where the chocolate is like smooth and luxurious.
• 1:37
  Speaker 2: M Do you like anything with your chocolate or are
• 1:39
  Speaker 2: you a chocolate purist?
• 1:41
  Speaker 1: No, Pretzels and chocolate's good. Bread and chocolate a good.
• 1:44
  Speaker 1: Some fruits with chocolate, like a raspberry with chocolate, it's good.
• 1:47
  Speaker 1: Cherries and chocolate. Blueberries and chocolate. Bananas just doesn't fit. It.
• 1:52
  Speaker 2: Sounds like you've done a lot of experimenting.
• 1:53
  Speaker 1: I like to think of myself as very thorough.
• 1:58
  Speaker 2: Thorough in your chocolate comes. But how thur are you though?
• 2:04
  Speaker 2: Have you tried chocolate covered sardines?
• 2:07
  Speaker 1: You know, sometimes you just want to explore, and sometimes
• 2:10
  Speaker 1: you want to be guided by the theory, And the
• 2:13
  Speaker 1: theory tells me chocolate sardines are disgusting.
• 2:17
  Speaker 2: Chocolate covered broccoli perhaps.
• 2:19
  Speaker 1: Chocolate covered garbage.
• 2:20
  Speaker 2: Yeah, did you just called broccoli garbage?
• 2:25
  Speaker 1: No, but I think the combination of chocolate and broccoli
• 2:27
  Speaker 1: is garbage in theory. In theory, I could be.
• 2:30
  Speaker 2: I don't know for sure. Yeah, you could be wrong.
• 2:32
  Speaker 1: Somebody out there tell me about your savory chocolate exploration.
• 2:36
  Speaker 2: That's right, and then write a paper about it, and
• 2:38
  Speaker 2: then maybe Daniel will believe you.
• 2:39
  Speaker 1: Yeah, I'll even cite your paper in.
• 2:41
  Speaker 2: Your own paper. Jour chocolate cover pretzels or about chocolate
• 2:46
  Speaker 2: covered sardines.
• 2:47
  Speaker 1: Yes, exactly, there's an academic field for everything.
• 2:50
  Speaker 2: But anyways, welcome to our podcast, Daniel and Jorge Explain
• 2:53
  Speaker 2: the Universe, a production of iHeartRadio, where we.
• 2:55
  Speaker 1: Don't just talk about chocolate or bananas or chocolate and bananas.
• 2:59
  Speaker 1: We talk about big questions about the universe, things that
• 3:02
  Speaker 1: actually matter, things that make you go hmm, I wish
• 3:05
  Speaker 1: I knew the answer to that question, or my life
• 3:08
  Speaker 1: would be different if I knew the answer to this question.
• 3:12
  Speaker 1: Those are the kind of questions we dig into on
• 3:14
  Speaker 1: the podcast. How big is the universe? Where did it
• 3:16
  Speaker 1: all come from? How does it all work? And we
• 3:18
  Speaker 1: want to answer not just the questions that are in
• 3:20
  Speaker 1: the minds of professional scientists, but your questions, the ones
• 3:24
  Speaker 1: that you struggle with when you're trying to make sense
• 3:27
  Speaker 1: of the universe, or the ones that keep you up
• 3:29
  Speaker 1: at night. So send us your questions to Questions at
• 3:32
  Speaker 1: Daniel and Jorge dot com. You'll get an.
• 3:34
  Speaker 2: Answer that's right. We'd like to address all kinds of questions,
• 3:37
  Speaker 2: the kind that make you think that the universe is
• 3:39
  Speaker 2: amazing and sometimes a little bit bananas, those amazing facts
• 3:42
  Speaker 2: about the universe that make the cosmos such a slippery
• 3:45
  Speaker 2: subject to study, but at the same time so darn appealing.
• 3:51
  Speaker 1: What seems to continuously amaze listeners is that I'm promising
• 3:55
  Speaker 1: on air to answer all of their questions, and then
• 3:58
  Speaker 1: I can email from somebody and they're amazed that I
• 4:00
  Speaker 1: actually write them back. I've got an email from a
• 4:02
  Speaker 1: listener this morning saying, wow, you really will do right
• 4:04
  Speaker 1: back to all of us. It's like, yes, call my bluff,
• 4:07
  Speaker 1: write to me with your questions. I really do want
• 4:09
  Speaker 1: to answer them.
• 4:10
  Speaker 2: Wellhy do you think they're surprised?
• 4:11
  Speaker 1: I think if there's a lot of science communicators out
• 4:13
  Speaker 1: there that don't respond to their emails and that publicly
• 4:16
  Speaker 1: complain about how many emails they get and are negative
• 4:19
  Speaker 1: and stand offish about it, and yeah, I take the
• 4:21
  Speaker 1: opposite approach, and so maybe that's surprising to people. I
• 4:24
  Speaker 1: am a busy guy. Of course, I got lots of
• 4:26
  Speaker 1: things going on. But to me, this is a real joy.
• 4:28
  Speaker 1: I don't want this podcast to just be a one
• 4:30
  Speaker 1: direction a lecture. I want it to be a conversation
• 4:32
  Speaker 1: with everybody out there who's excited about these things, who
• 4:35
  Speaker 1: doesn't have a friendly neighborhood physicist, They can ask these
• 4:38
  Speaker 1: questions too, So yeah, send us your questions, engage with us,
• 4:41
  Speaker 1: have a conversation.
• 4:43
  Speaker 2: Do you know any friendly neighborhood physicists for friendly physicists,
• 4:47
  Speaker 2: I think you know one, yeah, But anyways, we do
• 4:52
  Speaker 2: like to answer listener questions here and sometimes we'd like
• 4:54
  Speaker 2: to answer them here on the podcast, live or at
• 4:57
  Speaker 2: least pre recorded on the.
• 4:59
  Speaker 1: Internet, live and heavily edited.
• 5:03
  Speaker 2: Are we heavily edited? I didn't know that how heavily edited?
• 5:06
  Speaker 4: Are we?
• 5:07
  Speaker 2: Can I just say anything and someone's gonna censor me.
• 5:11
  Speaker 1: You should check out our behind the scenes episode where
• 5:13
  Speaker 1: we talked to Corey about how much he cuts and
• 5:15
  Speaker 1: how much he keeps. Mostly it all ends up on
• 5:17
  Speaker 1: the air, but sometimes, you know, we back up and
• 5:19
  Speaker 1: say things another way.
• 5:20
  Speaker 2: But we do like to answer questions answer to the
• 5:22
  Speaker 2: on the podcast. We'll be tackling listener questions number sixty five.
• 5:32
  Speaker 2: We're getting four closer to one number. We might have
• 5:35
  Speaker 2: to skip. Daniel, Well, we have three awesome questions here
• 5:39
  Speaker 2: today from listeners. We have questions about banana radiation, the
• 5:44
  Speaker 2: half life of tiny particles, and how fast things spin
• 5:48
  Speaker 2: around a black hole. I guess whether or not they're
• 5:51
  Speaker 2: bananas or not.
• 5:53
  Speaker 1: Whether that makes them go bananas?
• 5:55
  Speaker 2: What if they're half bananas?
• 5:59
  Speaker 1: You'll have to ask that question and find out.
• 6:02
  Speaker 2: All right, well, let's get right down to it. Our
• 6:04
  Speaker 2: first question comes from Samia, who hails from Morocco.
• 6:08
  Speaker 5: Hi Daniel Hi hot Hay, So, I have been pondering
• 6:11
  Speaker 5: something lately. How do scientists define the half life of nukelids?
• 6:16
  Speaker 5: I always assumed it was determined experimentally, but then I
• 6:20
  Speaker 5: stumbled upon those massive numbers in billions of years. An
• 6:24
  Speaker 5: example of this is potassium, commonly found in Hogey's favorite snack, bananas.
• 6:31
  Speaker 5: They have half life of one point four billion years.
• 6:34
  Speaker 5: So it's definitely not just experimental and also not a guesswork.
• 6:41
  Speaker 5: So I am really curious about the actual answer.
• 6:45
  Speaker 2: All right, interesting question, I guess. Samya's question is how
• 6:49
  Speaker 2: do you know stuff? Daniel, like, have you actually measured
• 6:54
  Speaker 2: the half life of some things that maybe take billions
• 6:56
  Speaker 2: of years to decay?
• 6:57
  Speaker 1: Yeah, it's a good question. And I like that what
• 6:59
  Speaker 1: he did in something very practical. Bananas of course. And
• 7:03
  Speaker 1: it's a good question how we can measure these things
• 7:05
  Speaker 1: that take like a billion years to happen, because we
• 7:07
  Speaker 1: haven't been doing science for a billion years.
• 7:10
  Speaker 2: Right right, humans haven't been around for for a billion years, right.
• 7:14
  Speaker 1: Yeah, So if something takes a billion years to happen,
• 7:16
  Speaker 1: you can't possibly measure it, right. But the answer here
• 7:19
  Speaker 1: lies in understanding what people mean when they say half life.
• 7:22
  Speaker 1: If the half life of potassium is one point four
• 7:24
  Speaker 1: billion years, that doesn't mean you have to wait one
• 7:27
  Speaker 1: point four billion years for anything to happen. The half
• 7:31
  Speaker 1: life is the time it takes on average for half
• 7:34
  Speaker 1: of the atoms to decay. So if you wait one
• 7:37
  Speaker 1: point four billion years, that means half of them are
• 7:39
  Speaker 1: decayed and half of them have not. But some of
• 7:41
  Speaker 1: them may have decayed very early on, in the first
• 7:44
  Speaker 1: few seconds you were watching, or the first few minutes
• 7:47
  Speaker 1: you were watching, because half life is per atom, it's
• 7:50
  Speaker 1: really the time for an atom to have a fifty
• 7:52
  Speaker 1: percent chance of decaying.
• 7:53
  Speaker 2: Well, what's kind of interesting about the half life is
• 7:55
  Speaker 2: that it's almost always true, right, Like if you have
• 7:59
  Speaker 2: a ton of them material, it'll take a certain number
• 8:02
  Speaker 2: of years to decay down to half, But if you
• 8:04
  Speaker 2: have a little bit of that material, you'll still take
• 8:06
  Speaker 2: the same amount of time to decay down to half
• 8:08
  Speaker 2: of that much material.
• 8:09
  Speaker 1: Yeah, because it's relative and it's per atom, right. Every
• 8:12
  Speaker 1: atom is independent. They don't affect each other. It doesn't
• 8:15
  Speaker 1: matter how many atoms you have. You start from one hundred,
• 8:18
  Speaker 1: it takes the half life to get down to fifty.
• 8:20
  Speaker 1: You start from a billion, it takes that half life
• 8:22
  Speaker 1: to get down from a billion to half a billion,
• 8:25
  Speaker 1: because you could just break that billion into chunks of
• 8:27
  Speaker 1: one hundred, each of which then decay down into fifties.
• 8:31
  Speaker 2: Right, Right, like a banana would take a billion years
• 8:33
  Speaker 2: to decay, whether it's a tiny little banana or a humongous,
• 8:36
  Speaker 2: galaxy sized banana.
• 8:38
  Speaker 1: Yeah, exactly, because they don't interact, right, they're all independent,
• 8:41
  Speaker 1: and so it doesn't matter how many you have. And
• 8:43
  Speaker 1: the key to understanding how you could measure something that
• 8:46
  Speaker 1: takes a billion years is that stuff is happening even
• 8:49
  Speaker 1: in the first few moments potentially, and that's because every
• 8:52
  Speaker 1: atom has the same probability. They don't have like an age.
• 8:55
  Speaker 1: It's not like a clock inside of them. It says, oh,
• 8:58
  Speaker 1: somebody's been watching me for a billion years or for
• 9:00
  Speaker 1: a million years, it's time for me to decay. Every
• 9:03
  Speaker 1: moment the atom has like a fresh chance to decay,
• 9:06
  Speaker 1: and it rolls a die. It's like a die with
• 9:08
  Speaker 1: sixty million sides or something, and one side says decay
• 9:11
  Speaker 1: and the other side say don't. And every moment the
• 9:13
  Speaker 1: universe is rolling that die. So the probability for an
• 9:16
  Speaker 1: individual atom to decay is constant in time, right, which
• 9:21
  Speaker 1: means there's always a chance for any atom to decay.
• 9:23
  Speaker 1: It's just a question of like how long it takes
• 9:26
  Speaker 1: for half of them to eventually hit that.
• 9:28
  Speaker 2: Number, or, as you said, how long it takes for
• 9:29
  Speaker 2: it to have that particular atom to have a fifty
• 9:32
  Speaker 2: percent chance of decaying exactly, Like, if you just give
• 9:35
  Speaker 2: it a minute, probably that it's going to decay is
• 9:38
  Speaker 2: probably super duper small. If you give it ten years,
• 9:41
  Speaker 2: it's a little bit bigger. If you give it a
• 9:42
  Speaker 2: billion years, then there's a fifty percent chance that it's
• 9:45
  Speaker 2: going to decay by.
• 9:46
  Speaker 1: Then, exactly. And even after a minute or a moment,
• 9:50
  Speaker 1: there's still a non zero chance of it decaying, right,
• 9:53
  Speaker 1: You have a single potassium atom, say the half life
• 9:55
  Speaker 1: is a billion years, I haven't even looked it up.
• 9:57
  Speaker 1: It still has a chance of decaying after the first
• 10:00
  Speaker 1: moment it rolls that die and it might hit it
• 10:02
  Speaker 1: the very first time, right, and decay right there, even
• 10:05
  Speaker 1: if it's half life is a billion years. A long
• 10:07
  Speaker 1: half life comes from having a small probability of decaying
• 10:11
  Speaker 1: at any given moment. A short half life comes from
• 10:13
  Speaker 1: having a high probability decaying. If like ninety percent of
• 10:16
  Speaker 1: the sides of that die, say, decay, then the stuff's
• 10:19
  Speaker 1: going to decay away pretty quickly.
• 10:21
  Speaker 4: Right.
• 10:21
  Speaker 2: But I think Tim would maybe have the same question
• 10:23
  Speaker 2: about the single atom, like, how do you know a
• 10:26
  Speaker 2: single atom of potassium takes a billion year to have
• 10:29
  Speaker 2: a fifty percent chance of decaying if you've never measured
• 10:32
  Speaker 2: one for billion years?
• 10:33
  Speaker 1: Yeah, And the key is not to look at a
• 10:35
  Speaker 1: single atom. So if you're looking for something really rare
• 10:38
  Speaker 1: to happen, but it could happen at any moment, or
• 10:40
  Speaker 1: you don't have to wait a billion years, it could
• 10:42
  Speaker 1: happen at any moment, the key is to look at
• 10:44
  Speaker 1: a lot of atoms. Right, If you have like one
• 10:46
  Speaker 1: in a billion chance for a potassium atom to decay
• 10:49
  Speaker 1: at any moment. Then you just need a billion of them,
• 10:52
  Speaker 1: or ten billion of them, or fifty billion of them,
• 10:54
  Speaker 1: and then you'll see one of them decay. So if
• 10:57
  Speaker 1: you start with a big enough blob of potassium atom,
• 11:00
  Speaker 1: you'll start to see them decay almost instantly. It'll still
• 11:03
  Speaker 1: take a billion years for half of them to decay,
• 11:05
  Speaker 1: because it's very rare for any individual one to decay.
• 11:08
  Speaker 1: But if you got lots of them, just like lots
• 11:11
  Speaker 1: of monkeys in your room with typewriters, pretty quickly one
• 11:13
  Speaker 1: of them is going to type up Shakespeare.
• 11:15
  Speaker 2: Right, But you're not measuring individual atom. Even if you
• 11:18
  Speaker 2: have a billion atoms of potassium, your experiment is not
• 11:21
  Speaker 2: going to be looking at an individual atom the decay.
• 11:25
  Speaker 1: It depends on the decay. Sometimes you can see an
• 11:27
  Speaker 1: individual decay if it's, for example, generates radiation, then you
• 11:31
  Speaker 1: could pick up a single particle. You know, we have
• 11:33
  Speaker 1: these very sensitive detectors that can see individual particles, So
• 11:37
  Speaker 1: in principle, yeah, you could see an individual atom decay.
• 11:40
  Speaker 1: In practice, you don't even have to be that sensitive,
• 11:43
  Speaker 1: so mostly you can just look for the decay products
• 11:46
  Speaker 1: and you'll see plenty of them, because the tricky is
• 11:48
  Speaker 1: it's not hard to have ten to the thirty atoms. Right.
• 11:51
  Speaker 1: Atoms are so small that just like a handful of
• 11:53
  Speaker 1: any element, is a huge number of atoms. So it's
• 11:56
  Speaker 1: not hard to get a huge number of them, which
• 11:58
  Speaker 1: means you can see really things happening just because you've
• 12:01
  Speaker 1: got so many little monkeys in that room all typing away.
• 12:05
  Speaker 2: I wonder when maybe the real answer or maybe the
• 12:07
  Speaker 2: best way to explain this is to explain that the
• 12:10
  Speaker 2: half life of something is really just an arbitrary number, right,
• 12:14
  Speaker 2: Like we just call it a halflight because that's something
• 12:16
  Speaker 2: that's kind of easy for our minds to graps, like, oh,
• 12:18
  Speaker 2: it's when fifty percent of it the case, But really
• 12:21
  Speaker 2: that number of the half life is just the rate
• 12:24
  Speaker 2: of dec and you can measure that also in like
• 12:26
  Speaker 2: not the halflight, but like the quarter life of something,
• 12:29
  Speaker 2: or the one tenth of a life of something or
• 12:31
  Speaker 2: the one million time of something, and all of those
• 12:34
  Speaker 2: rates are basically the same. They're all related, like once
• 12:37
  Speaker 2: you know one, you know all the other ones.
• 12:39
  Speaker 1: Yeah, there's definitely an arbitrary element there, right, The fact
• 12:42
  Speaker 1: that we choose to define the half life at fifty percent.
• 12:45
  Speaker 1: You're right, you could choose to define the quarter life
• 12:47
  Speaker 1: or the tenth life, or the ninety percent life or whatever.
• 12:50
  Speaker 1: Half life is an arbitrary choice, but it also does
• 12:54
  Speaker 1: reflect something which is not arbitrary, which is the decay probability.
• 12:57
  Speaker 1: So it determined by that decay probability. But you're right,
• 13:00
  Speaker 1: that decay probability at any given moment also could determine
• 13:03
  Speaker 1: the quarter life or the tenth life. It's just a
• 13:05
  Speaker 1: standard we choose for comparing things. And we know that
• 13:09
  Speaker 1: a short half life means a high probability to decay
• 13:11
  Speaker 1: at any moment. A long half life means a small
• 13:14
  Speaker 1: probabilities to decay at any moment. That's why you get
• 13:17
  Speaker 1: more of them. But you can actually measure things that
• 13:19
  Speaker 1: happen very very rarely as long as you have enough examples.
• 13:23
  Speaker 2: Right, So then, like if you wanted to measure the
• 13:25
  Speaker 2: half life or the dek rate of potassium, you wouldn't
• 13:28
  Speaker 2: have to wait a billion years. You would maybe just
• 13:30
  Speaker 2: wait one year or ten years and see how much
• 13:32
  Speaker 2: of that blob of potassium you have decays, and maybe
• 13:36
  Speaker 2: it's you know, one millionth or one billionth of the
• 13:39
  Speaker 2: material has decayed. But even that one billionth tells you
• 13:43
  Speaker 2: basically the rate of decay, which then lets you extrapolate
• 13:46
  Speaker 2: to what the half life would be.
• 13:47
  Speaker 1: Yeah, exactly. You don't have to observe half of the
• 13:50
  Speaker 1: decaying to measure the half life. You just have to
• 13:52
  Speaker 1: measure the decay rate. And as long as you have
• 13:54
  Speaker 1: enough examples, you'll see some decay and you can measure
• 13:57
  Speaker 1: that decay rate. You can even do crazy things like
• 13:59
  Speaker 1: measure sure the lifetime of a proton to be longer
• 14:02
  Speaker 1: than the age of a universe.
• 14:04
  Speaker 2: Which is true, right, that's what you've measured.
• 14:06
  Speaker 1: Yeah, because we've never seen a proton decay, so we
• 14:09
  Speaker 1: don't know do protons live forever or do they just
• 14:12
  Speaker 1: live a very very long time. And we've watched a
• 14:15
  Speaker 1: bunch of protons waiting to see if one of them
• 14:18
  Speaker 1: decays and never seen one, And so we can say, well,
• 14:21
  Speaker 1: the lifetime of a proton is at least ten to
• 14:23
  Speaker 1: the thirty one years, which is a huge number. Right.
• 14:27
  Speaker 1: The age of the universe is like ten to the
• 14:29
  Speaker 1: thirteen years.
• 14:30
  Speaker 2: But have you ever seen a proton decay?
• 14:32
  Speaker 1: Never seen a single one, never.
• 14:34
  Speaker 2: Seen never seen one. But you've also never seen an
• 14:36
  Speaker 2: electron decay. That's for electrons. You say that it never decays.
• 14:40
  Speaker 1: We say it never decays. We don't actually know that.
• 14:42
  Speaker 1: We just know that they're stable on time scales that
• 14:45
  Speaker 1: are much longer than the life of the universe. But yeah,
• 14:47
  Speaker 1: they could decay.
• 14:48
  Speaker 2: Did you just say that You say things without really
• 14:50
  Speaker 2: knowing them.
• 14:51
  Speaker 1: I mean, there's always a qualification when we say we
• 14:53
  Speaker 1: know something right. Nothing we know about physics could be true.
• 14:56
  Speaker 1: It could be that everything is upturned later or shown
• 14:59
  Speaker 1: to just be an approximate. In the case of an electron,
• 15:02
  Speaker 1: we call it stable because that's what stable means for us, Like,
• 15:05
  Speaker 1: it doesn't decay over billions and billions of years. It
• 15:07
  Speaker 1: might live forever, or it might decay after ten to
• 15:10
  Speaker 1: the fifty years. We definitely know a lot about the
• 15:12
  Speaker 1: lifetime of the electron, but we don't know everything about it.
• 15:15
  Speaker 2: But then, what's the difference between an electron and proton?
• 15:17
  Speaker 2: That makes you think that a proton has a lot
• 15:19
  Speaker 2: of half life but an electron does not.
• 15:21
  Speaker 1: Yeah, that's a good question, because the proton is not fundamental, right,
• 15:24
  Speaker 1: it's an assembly of smaller bits. We already know that
• 15:28
  Speaker 1: the electron might be fundamental might just be the electron
• 15:30
  Speaker 1: is made of the electron, in which case it's stable.
• 15:33
  Speaker 1: But if it's made of smaller things that could change
• 15:36
  Speaker 1: their configuration and turn into something else, it'd be more
• 15:38
  Speaker 1: likely to be unstable. And we know the proton is
• 15:41
  Speaker 1: made of smaller bits, right, there's just an arrangement of
• 15:43
  Speaker 1: quarks and the slightly different arrangements of those same quarks.
• 15:46
  Speaker 1: The neutron is not stable. The neutron only lasts for
• 15:49
  Speaker 1: like eleven minutes. You got a bunch of neutrons in space,
• 15:52
  Speaker 1: they'll decay really quickly. So it's sort of a mystery
• 15:54
  Speaker 1: why the proton is stable. And there's lots of juicy
• 15:58
  Speaker 1: theories out there that particle theorists life because they solve
• 16:00
  Speaker 1: other problems that predict the proton should decay, And all
• 16:04
  Speaker 1: those theories are ruined by the fact that the proton
• 16:06
  Speaker 1: doesn't decay. So there's a bunch of experiments out there
• 16:08
  Speaker 1: hoping to see a proton decay.
• 16:10
  Speaker 2: Interesting, Now, do you have a juicy theory about the
• 16:13
  Speaker 2: decay of bananas?
• 16:15
  Speaker 1: Yes?
• 16:16
  Speaker 2: Like, can you make banana juice? Is that such a thing?
• 16:18
  Speaker 1: It's called the smoothie. My theory is that when bananas decay,
• 16:20
  Speaker 1: they get way too juicy.
• 16:22
  Speaker 2: And griss mmm, too soft, too softly.
• 16:26
  Speaker 1: But it's really cool to think that you can say
• 16:28
  Speaker 1: something about protons over like ten to the thirty years,
• 16:32
  Speaker 1: even though no proton has existed that long, not even
• 16:35
  Speaker 1: a tiny fraction of that length.
• 16:37
  Speaker 2: Yeah, or even about potassium, right, it's amazing. We can
• 16:40
  Speaker 2: say that the potasium in a banana is not going
• 16:41
  Speaker 2: to decay for one point four billion years because we
• 16:45
  Speaker 2: know we've seen it decay, and it decays super duper slowly.
• 16:48
  Speaker 2: So from that you can extrapolate that it's going to
• 16:50
  Speaker 2: take I want and have billion years to decay to
• 16:53
  Speaker 2: half of its initial quantity.
• 16:55
  Speaker 1: Yeah, exactly. So if you want to see something do
• 16:57
  Speaker 1: something rare, just get a whole lot of them, that's
• 17:00
  Speaker 1: the answer.
• 17:01
  Speaker 2: Are you saying people should go out there and get
• 17:02
  Speaker 2: a lot of bananas.
• 17:06
  Speaker 1: If you want to see bananas do something right, If
• 17:07
  Speaker 1: you think bananas get up and dance in the middle
• 17:09
  Speaker 1: of the night and you think that's pretty rare, then yeah,
• 17:11
  Speaker 1: get a lot of bananas, watch them all at night
• 17:13
  Speaker 1: and see what they do.
• 17:15
  Speaker 4: Well.
• 17:15
  Speaker 2: The half life of bananas in my house is pretty short.
• 17:18
  Speaker 2: Now that my son is growing up and he's doing
• 17:20
  Speaker 2: all kinds of exercise, and he's downing those bananas pretty
• 17:24
  Speaker 2: pretty fast.
• 17:25
  Speaker 1: Does he do that thing kids do, which is like
• 17:27
  Speaker 1: just eat half a banana and then leave it around?
• 17:29
  Speaker 1: Is that what half life of banana means in your house?
• 17:32
  Speaker 4: Well?
• 17:32
  Speaker 2: I think he learned that for me. But yeah, he
• 17:34
  Speaker 2: takes a knife and he cuts a banana and then
• 17:36
  Speaker 2: he'll eat the other half the next day. All right, well,
• 17:39
  Speaker 2: great question, thank you, Samia, And let's get to our
• 17:42
  Speaker 2: other questions here today. We have questions about more bananas,
• 17:45
  Speaker 2: it seems, and black holes and or maybe both, So
• 17:49
  Speaker 2: let's dig into that. But first let's take a quick break.
• 18:05
  Speaker 2: All right, we're taking listener questions here today, and our
• 18:07
  Speaker 2: next question comes from Bill.
• 18:10
  Speaker 4: Hi, Daniel, and Jorre. This is Bill. I was thinking
• 18:12
  Speaker 4: about banana radiation and realized that while half lives of
• 18:15
  Speaker 4: various decays are well characterized, I can't find anything about
• 18:18
  Speaker 4: how long a decay actually takes. It must take some
• 18:21
  Speaker 4: time for an atom of one element to turn into
• 18:23
  Speaker 4: another element and various particles. Is this time unmeasurably short?
• 18:27
  Speaker 4: Does it vary for different types of decay? Thanks?
• 18:30
  Speaker 1: All?
• 18:30
  Speaker 2: Right, another banana radiation half Live question? Is that a
• 18:35
  Speaker 2: theme today? Were you feeling really bananas today?
• 18:38
  Speaker 1: It wasn't me. I think Bill and Sammy I just
• 18:40
  Speaker 1: wrote in about bananas decaying at the same moment.
• 18:43
  Speaker 2: It's sort of amazing at the same time, like the
• 18:46
  Speaker 2: same timestamp.
• 18:47
  Speaker 1: Yeah, I think some potassium particle must have triggered inside
• 18:49
  Speaker 1: their brains.
• 18:50
  Speaker 2: Yeah, exactly, what's the probability of that happening. It's bananas.
• 18:54
  Speaker 1: Their brains are banana tabled quantum bananament.
• 18:58
  Speaker 2: Well, you know you don't have to answer these in order, Daniel,
• 19:01
  Speaker 2: we could have saved spread out some of the banana
• 19:03
  Speaker 2: conversations across several listener question episodes.
• 19:07
  Speaker 1: I'm too busy answering listener emails to organize these.
• 19:09
  Speaker 2: I see, you're too busy directing your grad students to
• 19:11
  Speaker 2: answer the emails.
• 19:14
  Speaker 1: I am not allowed to get my grad students to
• 19:16
  Speaker 1: work on this project for free.
• 19:18
  Speaker 2: Absolutely no, oh for free? I see. But if you
• 19:22
  Speaker 2: pay them bananas, then it's totally kosher.
• 19:25
  Speaker 1: Do you want to pay my grad students out of
• 19:27
  Speaker 1: the podcast? Let's do it.
• 19:30
  Speaker 2: If we can pay them in bananas, Sure, that sounds
• 19:32
  Speaker 2: like a great deal. And it'll be good for them.
• 19:35
  Speaker 1: You know, the grad students here unionized recently, so bananas
• 19:37
  Speaker 1: are definitely off the table for payment.
• 19:39
  Speaker 2: Oh, I don't know, are they Have you read the
• 19:42
  Speaker 2: union rules? Maybe they make exceptions for bananas, don't they do?
• 19:48
  Speaker 1: That was not a clause on the bargaining table.
• 19:50
  Speaker 2: I see, I see to slippery a point of contention.
• 19:54
  Speaker 2: All right, Well back to the question. Bill has a question,
• 19:56
  Speaker 2: but it's a kind of a different question about banana
• 19:59
  Speaker 2: radiation and the case. He's not asking like how long
• 20:01
  Speaker 2: it takes a bit the potassium in a banana de decay,
• 20:03
  Speaker 2: but basically how long it takes for something to decay, Like,
• 20:06
  Speaker 2: if something decays, does it happen instantly or does it
• 20:09
  Speaker 2: take a certain amount of time.
• 20:11
  Speaker 1: Yeah, this is a super awesome question because it really
• 20:14
  Speaker 1: reveals the limits of our knowledge and also how those
• 20:18
  Speaker 1: limits have changed. I mean, the short answer is for
• 20:20
  Speaker 1: some things it's effectively instantaneous, because we can't measure how
• 20:24
  Speaker 1: fast it is, like an individual decay, how long does
• 20:27
  Speaker 1: it take one atom to turn into another kind, or
• 20:30
  Speaker 1: for a neutron to turn into a proton, or for
• 20:32
  Speaker 1: inverse beta decay to happen? For some processes, we can't
• 20:35
  Speaker 1: measure it, so we treat it as instantaneous though we
• 20:37
  Speaker 1: don't actually know what.
• 20:39
  Speaker 2: Do you mean we can measure like it happens too
• 20:41
  Speaker 2: fast or is just impossible to measure.
• 20:44
  Speaker 1: I don't think it's impossible to measure in principle, Like
• 20:46
  Speaker 1: if we had higher energy probes and we could look
• 20:49
  Speaker 1: inside and see the mechanics of what was happening, then
• 20:53
  Speaker 1: we would see that something is happening, and that takes time.
• 20:56
  Speaker 1: And because we can't see inside and we don't have
• 20:57
  Speaker 1: like fast enough measuring devices, it's as if it's instantaneous
• 21:01
  Speaker 1: in some cases but not in others. And we've made
• 21:04
  Speaker 1: some progress. So, for example, we used to treat beta
• 21:07
  Speaker 1: decay when a neutron turns into a proton and emits
• 21:11
  Speaker 1: an electron, as an instantaneous thing. We're like, well, this
• 21:14
  Speaker 1: is just one thing that happens. A neutron turns into
• 21:16
  Speaker 1: a proton and an electron boom, And like fifty years ago,
• 21:20
  Speaker 1: we couldn't see inside the neutron or the proton to
• 21:22
  Speaker 1: understand like what was actually happening there. We just treated
• 21:25
  Speaker 1: them all as point particles and we said there was
• 21:28
  Speaker 1: a before and there's an after and in the middle,
• 21:30
  Speaker 1: we don't know what happens. We just treat it as
• 21:32
  Speaker 1: an instantaneous step.
• 21:34
  Speaker 2: But I guess maybe more fundamentally, do you think these
• 21:37
  Speaker 2: things are happening instantaneously or do you think all of
• 21:40
  Speaker 2: these things decays particle interactions? Do they all take some time?
• 21:45
  Speaker 1: Everything in the universe definitely takes some time, even if
• 21:47
  Speaker 1: you're transitioning between fundamental states like say, for example, you
• 21:52
  Speaker 1: have a photon and it's turning into an electron and
• 21:54
  Speaker 1: a positron. Right, we don't know what's inside the photon.
• 21:57
  Speaker 1: We don't know what's inside the electron depositron, We don't
• 21:59
  Speaker 1: know what's happening there. So assume that those are fundamental
• 22:03
  Speaker 1: things in the universe. When a photon turns into an
• 22:05
  Speaker 1: electron apostoitron, you can ask like, is that instantaneous? Is
• 22:08
  Speaker 1: there a moment when it's a photon and then a
• 22:11
  Speaker 1: moment when it's an electron apositron and nothing in between.
• 22:14
  Speaker 1: The way to think about a quantum mechanically, which is
• 22:16
  Speaker 1: the right way to think about everything microscopically, is to
• 22:18
  Speaker 1: think about the probabilities changing. It's like one hundred percent
• 22:21
  Speaker 1: chance of being a photon, and then that probably starts
• 22:23
  Speaker 1: to drop, and now it's like fifty percent chance of
• 22:25
  Speaker 1: being a photon and fifty percent chance of being an electron,
• 22:27
  Speaker 1: an a positron, or two other particles. And then that
• 22:31
  Speaker 1: probability changes and now it's like one percent chance of
• 22:33
  Speaker 1: still being a photon. So the probability changes smoothly.
• 22:36
  Speaker 2: So you're saying, so there's two things that can happen
• 22:40
  Speaker 2: that can change, Like the actual electron can change, and
• 22:43
  Speaker 2: then the probability of it what it is can also change.
• 22:47
  Speaker 2: Are you saying like in quantum mechanics, nothing is ever
• 22:51
  Speaker 2: something like nothing is there an electron or nothing's ever
• 22:54
  Speaker 2: a proton or a photon. Things just have the probability
• 22:57
  Speaker 2: of being an electron or the probability of being a
• 22:59
  Speaker 2: photo if you probe them.
• 23:01
  Speaker 1: Yeah, exactly, And we can try to make it simpler
• 23:03
  Speaker 1: even just think about like what a single electron does.
• 23:06
  Speaker 1: We talked once in the podcast about like how an
• 23:08
  Speaker 1: electron changes from energy levels? Is that instantaneous when it
• 23:12
  Speaker 1: absorbs a photon, Does it like jump from one an
• 23:14
  Speaker 1: energy level to another, or does it move from that
• 23:17
  Speaker 1: energy level to the other. Well, the electron can't be
• 23:20
  Speaker 1: in between energy levels, so how does it like get
• 23:22
  Speaker 1: from here to there? What happens is that the probability
• 23:26
  Speaker 1: for it to be in the lower energy level starts
• 23:28
  Speaker 1: to drop, and the probability for it to be in
• 23:29
  Speaker 1: the higher energy level starts to raise, until it's effectively
• 23:32
  Speaker 1: one hundred percent.
• 23:33
  Speaker 2: Now do you know that for sure though? Or I mean,
• 23:35
  Speaker 2: isn't it technically possible for these probabilities to change instantaneously?
• 23:40
  Speaker 2: Because they're just math.
• 23:41
  Speaker 1: Right, they're just math. I love that we know this
• 23:45
  Speaker 1: for sure, only in the sense that this is how
• 23:48
  Speaker 1: the theory works, and the theory so far describes everything
• 23:51
  Speaker 1: we've seen, so it accurately predicts it. But there's always
• 23:54
  Speaker 1: bits of the theory that are like behind the curtain
• 23:56
  Speaker 1: that we can't see directly, and right now we're talking
• 23:58
  Speaker 1: about stuff we can't see, argument things that are not observed.
• 24:01
  Speaker 1: This is the calculation of what's happening really behind the scenes.
• 24:04
  Speaker 1: All you can do is shoot a photon at the
• 24:06
  Speaker 1: electron and measure its old energy level and it's new
• 24:08
  Speaker 1: energy level and make predictions for that. You can't see
• 24:11
  Speaker 1: these probabilities themselves transitioning. That's probably what you mean.
• 24:15
  Speaker 2: But you could potentially, right, I guess maybe that's what
• 24:18
  Speaker 2: I'm asking is that you can't see them change, or
• 24:22
  Speaker 2: that we don't have the technology to see them change. Like,
• 24:24
  Speaker 2: let's say I gave you magical powers, and I gave
• 24:26
  Speaker 2: you the ability to create this measuring device that has
• 24:28
  Speaker 2: infinite time resolution and infinite size resolution. Would you be
• 24:32
  Speaker 2: able to see these probability these change or would you
• 24:36
  Speaker 2: maybe see them change suddenly?
• 24:38
  Speaker 1: You can't see the probabilities directly, right, The probabilities or
• 24:41
  Speaker 1: consequences of the wave function, which is not something physical
• 24:43
  Speaker 1: we can measure. All we can do is measure the
• 24:45
  Speaker 1: electron and measure the photon. So if you gave me
• 24:48
  Speaker 1: infinite experimental powers, I could look set up a huge
• 24:51
  Speaker 1: number of these devices and shoot photons at them simultaneously,
• 24:55
  Speaker 1: and just like in the previous question, I could say, like, oh, look,
• 24:57
  Speaker 1: forty percent of the photons were absorbed or n twy
• 25:00
  Speaker 1: percent of them were absorbed. So that way I could
• 25:02
  Speaker 1: sort of measure the probabilities. But for an individual photon
• 25:05
  Speaker 1: an electron, I can't say, oh, here, this one has
• 25:08
  Speaker 1: a forty percent chance there, and that one has forty
• 25:10
  Speaker 1: percent chance here. I can calculate those things using the theory,
• 25:14
  Speaker 1: but I can't actually observe those things directly. And also crucially,
• 25:17
  Speaker 1: in the theory, probabilities never change suddenly. They always evolve
• 25:21
  Speaker 1: smoothly with time. That's again just part of the theory.
• 25:24
  Speaker 1: And you know, the theory could be totally wrong. We
• 25:27
  Speaker 1: have lots of questions about quantum mechanics and what's going
• 25:29
  Speaker 1: on inside this stuff that could be totally wrong. But
• 25:32
  Speaker 1: in our current picture, none of this stuff happens instantaneously.
• 25:35
  Speaker 1: But the way to think about it is the probabilities
• 25:37
  Speaker 1: changing smoothly, not the particles changing.
• 25:40
  Speaker 2: Instantly according to the theory, though.
• 25:42
  Speaker 1: Right according to the theory, and sometimes you can zoom
• 25:45
  Speaker 1: out and understand like the internal mechanisms of these particles,
• 25:48
  Speaker 1: like we were talking about earlier. We used to understand
• 25:51
  Speaker 1: a neutron just like changing into a proton and an
• 25:53
  Speaker 1: electron the way we just described, like, hey, there's a
• 25:56
  Speaker 1: probability for it to happen. Now we know though, about
• 25:59
  Speaker 1: what's going on inside the neutron, so we can talk
• 26:01
  Speaker 1: about what's actually happening and how long that takes. We've
• 26:04
  Speaker 1: like zoomed in and we can see, oh, when that
• 26:07
  Speaker 1: happens that's a down cork turning into an upcork and
• 26:10
  Speaker 1: emitting a w boson. We've like resolved this thing, which
• 26:13
  Speaker 1: you should just be a point in our theories. Now
• 26:15
  Speaker 1: we've like zoomed in and we've seen, oh no, it's
• 26:17
  Speaker 1: actually these little pieces interglocking and changing and doing their thing,
• 26:21
  Speaker 1: and that does take some time.
• 26:23
  Speaker 2: And how do you measure that time?
• 26:25
  Speaker 1: Then?
• 26:25
  Speaker 2: I know, in the large Hadron collider you have like
• 26:27
  Speaker 2: a series of detectors or their sensors, and you can
• 26:30
  Speaker 2: sort of trace the path and the track and the
• 26:33
  Speaker 2: what happens to these things after they smash up? Is
• 26:35
  Speaker 2: that how you tell how long something takes? Or are
• 26:37
  Speaker 2: you just guessing from the theory?
• 26:40
  Speaker 1: Just guessing from the theory the highest level of understanding
• 26:44
  Speaker 1: of the universe ever achieved by humans, Jorge calls guessing
• 26:48
  Speaker 1: from the theory. I love it. No, in some cases
• 26:53
  Speaker 1: this is just guessing from the theory. Like for example,
• 26:56
  Speaker 1: the dcay we just described talks about a w boson
• 26:58
  Speaker 1: a w boson for a very very short amount of
• 27:01
  Speaker 1: time ten to them, man is twenty four seconds, which
• 27:04
  Speaker 1: is much faster than anything we could actually measure. So
• 27:07
  Speaker 1: again we have a theoretical description of this, and we
• 27:09
  Speaker 1: think it takes that much time for this decay to
• 27:12
  Speaker 1: happen ten to minus twenty four seconds. But we could
• 27:14
  Speaker 1: never measure that.
• 27:15
  Speaker 2: For the probability to shift from being one thing to
• 27:18
  Speaker 2: the other.
• 27:18
  Speaker 1: Yes, exactly.
• 27:19
  Speaker 2: But I wonder if maybe Bill's question is like, when
• 27:21
  Speaker 2: it actually happens, does it take time or is it instantaneous?
• 27:25
  Speaker 2: Because you know, like these things are wiggles in some
• 27:29
  Speaker 2: quantum field out there in the universe. Do those wiggles
• 27:31
  Speaker 2: suddenly like pop into a different configuration or do they
• 27:36
  Speaker 2: you know, morph from one to the other.
• 27:38
  Speaker 1: The right way to think about it is that it
• 27:39
  Speaker 1: always takes time. Everything takes time. Nothing in the universe
• 27:42
  Speaker 1: is discontinuous. It's not like a slice where it's this
• 27:45
  Speaker 1: and then all of a sudden, it's that. Right. Everything
• 27:47
  Speaker 1: is smooth in the universe as far as we've discovered,
• 27:50
  Speaker 1: you know, and so even quantum mechanics, right, which likes
• 27:53
  Speaker 1: to have things be discrete and in chunks. It transforms
• 27:56
  Speaker 1: things smoothly through times. You look at the Shortener equation
• 28:00
  Speaker 1: for example, that's an equation for how wave functions change
• 28:03
  Speaker 1: through time as they interact with stuff and that's always smooth.
• 28:07
  Speaker 1: And so instead of thinking about like things popping from
• 28:10
  Speaker 1: one spot to another, you should think about their probabilities
• 28:12
  Speaker 1: as like sloshing around and so that always takes time.
• 28:15
  Speaker 2: That always takes time. And I guess part of Bill's
• 28:18
  Speaker 2: question was do different things take different amounts of time?
• 28:21
  Speaker 2: And that's the answer is yes, right, some things maybe
• 28:25
  Speaker 2: or maybe not.
• 28:26
  Speaker 1: Yes, absolutely different things take different amounts of time. For example,
• 28:30
  Speaker 1: the w boson is very short lived, but if you
• 28:32
  Speaker 1: decay and you use a photon instead, photons can live
• 28:35
  Speaker 1: for a very long time, and so some of these
• 28:37
  Speaker 1: decays can take much longer.
• 28:38
  Speaker 2: Wait, wait, wait, I feel like maybe there's two things here,
• 28:41
  Speaker 2: and I wonder if this is what's confusing Bill enough
• 28:44
  Speaker 2: for him to ask this question, which is, you know,
• 28:46
  Speaker 2: some things take a long time to decay, right, Like
• 28:49
  Speaker 2: they have a long half life, as we talked about
• 28:52
  Speaker 2: in the first third of the episode, like maybe a
• 28:54
  Speaker 2: potasting takes a billion years for half of them to decay, right,
• 28:58
  Speaker 2: because the probability of that is so small for it
• 29:01
  Speaker 2: to decay, So that there's that one thing the probability
• 29:04
  Speaker 2: over it to decay is small. Therefore the half life
• 29:07
  Speaker 2: is really long. But then when an individual potassium atom
• 29:10
  Speaker 2: actually decays, does that take an amount of time? And
• 29:14
  Speaker 2: it sounds like you said yes, but does it take
• 29:16
  Speaker 2: a different amount of time depending on the thing.
• 29:18
  Speaker 1: Yeah, so potassium atoms, they should all take the same
• 29:21
  Speaker 1: amount of time. But something else the decays in a
• 29:23
  Speaker 1: different wave. If it doesn't decay with a w boson,
• 29:26
  Speaker 1: for example, if it decays is through some other mechanism,
• 29:29
  Speaker 1: it can take longer or shorter.
• 29:30
  Speaker 2: What does that depend on?
• 29:31
  Speaker 1: Then it depends like on the mass of the particle involved.
• 29:34
  Speaker 1: The w boson, for example, is very heavy and so
• 29:36
  Speaker 1: it doesn't live for very long. It decays very very rapidly.
• 29:39
  Speaker 1: But if you decayed with another particle involved, you know,
• 29:42
  Speaker 1: for example, you didn't make a w boson, you made
• 29:44
  Speaker 1: a photon instead. Photons can live for a very long
• 29:46
  Speaker 1: time and so that decay process can take longer.
• 29:49
  Speaker 2: Is it possible for something to have like a short
• 29:51
  Speaker 2: half life but a long decay time and conversely like
• 29:55
  Speaker 2: something can have a long half life but a short
• 29:58
  Speaker 2: decay time.
• 29:59
  Speaker 1: Yeah, I don't think the twoth a connected at all.
• 30:02
  Speaker 1: If think, if you dug into it, there might be
• 30:04
  Speaker 1: some connections because the reason things decay quickly, is that
• 30:08
  Speaker 1: there was a high chance of decaying at any moment,
• 30:11
  Speaker 1: which probably means a stronger force, which might mean you
• 30:15
  Speaker 1: end up using gluons and photons rather than W and
• 30:17
  Speaker 1: Z bosons. So there might be some sort of loose
• 30:20
  Speaker 1: connection there.
• 30:21
  Speaker 2: All right, well, I guess. And then the last part
• 30:23
  Speaker 2: of Bill's question was are these times unmeasurably short? Have
• 30:27
  Speaker 2: we measured actually any of these decay times or are
• 30:31
  Speaker 2: they still beyond our technological reach.
• 30:33
  Speaker 1: Most of these things happen much faster than we could
• 30:36
  Speaker 1: actually measure, so we can't measure most of these decays
• 30:39
  Speaker 1: like to see them halfway. For example, you can see
• 30:42
  Speaker 1: them before, you can see them after. But as we
• 30:44
  Speaker 1: talked about in a recent episode about the fastest time slice,
• 30:47
  Speaker 1: and we're nowhere close to being able to measure things
• 30:49
  Speaker 1: like down to ten of the nights twenty four seconds.
• 30:51
  Speaker 2: Which is how fast you think these decays are happening,
• 30:53
  Speaker 2: like the actual the decay of the probability function. Yeah,
• 30:57
  Speaker 2: but what about bananas? Bananas? We can measure those pretty right.
• 31:02
  Speaker 1: Yeah, let's take days or weeks to decay, or in
• 31:04
  Speaker 1: your house, just minutes.
• 31:08
  Speaker 2: We are well within the bounds of our physical abilities.
• 31:13
  Speaker 1: It sounds like it's improving every day.
• 31:15
  Speaker 4: Yeah.
• 31:15
  Speaker 2: Yeah, he is getting bigger and so he's eating more.
• 31:18
  Speaker 1: I think there's a correlation there actually.
• 31:21
  Speaker 2: All right, well, thank you Bill for that great question.
• 31:23
  Speaker 2: Now let's get to our last question, and this one
• 31:26
  Speaker 2: is about black holes and whether things spiral into them
• 31:31
  Speaker 2: or whether they fall straight in sort of. We'll dig
• 31:34
  Speaker 2: into that, but first let's take another quick break.
• 31:49
  Speaker 3: All right.
• 31:49
  Speaker 2: We're answering listener questions here today, and our last question
• 31:52
  Speaker 2: is about black holes, and it comes from Julian from Brazil.
• 31:56
  Speaker 4: Hi, Daniel, My.
• 31:58
  Speaker 3: Question is about black holes. Does the matter closer to
• 32:02
  Speaker 3: the actual black hole spins faster than the matter that's
• 32:05
  Speaker 3: more distant from the center. I mean, is it more
• 32:08
  Speaker 3: like a galaxy where everything spins more or less at
• 32:11
  Speaker 3: the same speed because dark matter is holding everything together?
• 32:15
  Speaker 3: Or is it more like the solar system where mercury
• 32:18
  Speaker 3: spins around the sun? Why faster than neptune? That's it?
• 32:21
  Speaker 3: Big fan of the podcast, the books and everything.
• 32:23
  Speaker 2: Thanks by all right, interesting question here today. It's got
• 32:27
  Speaker 2: my head spinning a little bit. Is he asking how
• 32:31
  Speaker 2: fast things spin as they fall in or do they
• 32:36
  Speaker 2: spin faster as they fall in.
• 32:38
  Speaker 1: Yeah, I think he wants to know about the rotation
• 32:40
  Speaker 1: speed of the accretion disk, this disc of matter that's
• 32:43
  Speaker 1: like on deck to fall into the black hole. He's
• 32:45
  Speaker 1: wondering does it spin faster the outside or near the center.
• 32:49
  Speaker 1: And he's comparing that to his understanding of the Solar
• 32:51
  Speaker 1: System and the galaxy and those spinning systems, and he
• 32:54
  Speaker 1: wants to know, like which one is more.
• 32:56
  Speaker 2: Like the accretion disk, because I guess you know, he
• 32:58
  Speaker 2: mentions the Solar System and the planets, like the planets
• 33:02
  Speaker 2: around our Sun, they're all have different orbital speeds, right,
• 33:06
  Speaker 2: Like some take one hundred two hundred years to go
• 33:07
  Speaker 2: around the Sun, some take at less time.
• 33:09
  Speaker 1: Yeah, and not just orbital periods because they're going further,
• 33:13
  Speaker 1: but their actual like speed relative to the Sun is
• 33:16
  Speaker 1: different at different distances from the Sun. And that's also
• 33:20
  Speaker 1: true and really powerful and important for galaxies. Right, understanding
• 33:23
  Speaker 1: how stars are moving around the center of the galaxies,
• 33:26
  Speaker 1: how we discovered that dark matter was a thing. So
• 33:29
  Speaker 1: this is a really an important and interesting question.
• 33:31
  Speaker 2: Right And at the same time, like the planets are
• 33:33
  Speaker 2: spinning in place.
• 33:34
  Speaker 1: Too, right, Yeah, everything is spinning.
• 33:37
  Speaker 2: Yeah, that's a nice way to spin it all right,
• 33:40
  Speaker 2: So then I guess maybe step us through. What is
• 33:42
  Speaker 2: an accretion disk of a black hole?
• 33:44
  Speaker 1: Yeah, so an accretion disk is the stuff you see
• 33:47
  Speaker 1: sort of at the belt of the black hole. Right.
• 33:49
  Speaker 1: Most black holes are spinning and the stuff around them
• 33:52
  Speaker 1: is spinning. And that's because stuff doesn't just like fall
• 33:55
  Speaker 1: into a black hole. You might have a mental picture
• 33:57
  Speaker 1: of a black hole is like a giant space vacuum
• 33:59
  Speaker 1: sucking stuff up. But black holes just have gravity the
• 34:02
  Speaker 1: way anything else has gravity. Like you replace the Sun
• 34:05
  Speaker 1: with a black hole the same mass and the Earth's
• 34:07
  Speaker 1: orbit wouldn't change, wouldn't get like magically sucked in. And
• 34:10
  Speaker 1: things can orbit something with gravity and not fall in
• 34:13
  Speaker 1: the way the Earth orbits the Sun and doesn't fall
• 34:16
  Speaker 1: in the way the Sun orbits the center of the
• 34:18
  Speaker 1: galaxy and doesn't fall in. You can also orbit a
• 34:21
  Speaker 1: black hole and not fall in. So the accretion disc
• 34:24
  Speaker 1: is stuff that's near the black hole. It's come in
• 34:27
  Speaker 1: like at an angle, so it's whizzing around the black
• 34:30
  Speaker 1: hole before it falls in.
• 34:32
  Speaker 2: I feel like maybe we covered this in our book.
• 34:35
  Speaker 2: Frequently asked questions about the universe now available for sale,
• 34:37
  Speaker 2: But is the accretion disc of a black hole continuous
• 34:41
  Speaker 2: or does it only exist in the band, you know,
• 34:43
  Speaker 2: sort of like Saturn's rings. They don't go out there
• 34:46
  Speaker 2: into infinity. They sort of an extent to them.
• 34:50
  Speaker 1: There are definitely regions near a black hole where you
• 34:52
  Speaker 1: can be in a stable orbit, or regions where you can't,
• 34:54
  Speaker 1: Like if you get close enough to a black hole,
• 34:56
  Speaker 1: you're definitely just going to fall in and you're done,
• 34:59
  Speaker 1: unless you're a photon. So there's like a photon ring
• 35:02
  Speaker 1: where photons can orbit a black hole stabily, like where
• 35:05
  Speaker 1: if you shot a flashlight forwards, it would hit you
• 35:08
  Speaker 1: in the back of the head, for example. But stuff
• 35:10
  Speaker 1: with matter can't orbit there stable. It will just fall
• 35:12
  Speaker 1: towards the event horizon. So there's definitely like a region
• 35:16
  Speaker 1: near the black hole where you can't have any stable orbits,
• 35:18
  Speaker 1: and then regions further out where you could have stable orbits.
• 35:22
  Speaker 2: So maybe it does have an like an extent like
• 35:24
  Speaker 2: an outer limit in an inner limit.
• 35:26
  Speaker 1: It may, but there's an important difference between what's happening
• 35:29
  Speaker 1: in an accretion disk and what's happening with like planets
• 35:32
  Speaker 1: orbiting the Sun or the Sun orbiting the center of
• 35:35
  Speaker 1: the galaxy, and that's friction. Like in our orbit, we're
• 35:39
  Speaker 1: mostly not interacting with other stuff. We get like a
• 35:41
  Speaker 1: little bit of a tug from Jupiter now and then
• 35:43
  Speaker 1: and from Mars, but mostly we're alone in an orbit
• 35:47
  Speaker 1: and we're just orbiting the Sun, and the Sun is
• 35:49
  Speaker 1: orbiting the center of the galaxy, and it's mostly not
• 35:51
  Speaker 1: like bumping into stuff and losing energy, and so things
• 35:54
  Speaker 1: can be in stable orbits for billions of years. Right
• 35:57
  Speaker 1: the Earth has been going around the Sun for billions
• 35:59
  Speaker 1: of years. The Sun has been going around the center
• 36:01
  Speaker 1: of the galaxy all of that time, and that's pretty stable.
• 36:04
  Speaker 1: But an accretion disk is hot and nasty in a
• 36:07
  Speaker 1: very different way. There's a lot of interactions happening between
• 36:10
  Speaker 1: this stuff in the accretion disk.
• 36:12
  Speaker 2: Because I think, just like in our sun, you can
• 36:15
  Speaker 2: orbit a black hole for a long time, right, Like
• 36:17
  Speaker 2: you could you could be a planet with life when
• 36:20
  Speaker 2: it orbiting your black hole, and you think, like, and
• 36:23
  Speaker 2: that would be normal to you, Like instead of a sun,
• 36:25
  Speaker 2: you would have a dark circle in the sky.
• 36:27
  Speaker 1: Exactly. If you found a black hole that was all
• 36:29
  Speaker 1: by itself and didn't have an accretion disc, you could
• 36:31
  Speaker 1: put a planet there and it would orbit stabily and
• 36:33
  Speaker 1: be happy, no.
• 36:34
  Speaker 2: Problem, or even without an accretion disk, right, Like, if
• 36:37
  Speaker 2: you're maybe far enough away from it.
• 36:39
  Speaker 1: Yeah, if you're far enough away, then that's not a problem.
• 36:41
  Speaker 1: But in accretion disk, this stuff everywhere, and it's all
• 36:44
  Speaker 1: interacting and it's rubbing against itself. And that's why accretion
• 36:47
  Speaker 1: disks glow because they're hot, because they're bumping into each other,
• 36:50
  Speaker 1: they're moving fast. There's lots of energy exchange, so very
• 36:54
  Speaker 1: little stuff in the accretion disk is orbiting the way
• 36:56
  Speaker 1: our planet is orbiting or the Sun is orbiting the
• 36:59
  Speaker 1: center of the galaxy. Mostly it's spiraling in. So the
• 37:02
  Speaker 1: trajectory the dynamics of an accretion disc are very different
• 37:05
  Speaker 1: from the dynamics of the Solar system or the galaxy.
• 37:08
  Speaker 1: Almost nothing is moving in a circle or an ellipse.
• 37:11
  Speaker 1: Almost everything is moving in a spiral as it's losing
• 37:14
  Speaker 1: energy and falling in right.
• 37:16
  Speaker 2: Well, I think you said kind of the key word there,
• 37:17
  Speaker 2: which is friction, which is like, you know, you can
• 37:20
  Speaker 2: orbit the Sun or a black hole forever as long
• 37:21
  Speaker 2: as you're not losing energy. But once you start losing
• 37:24
  Speaker 2: energy because maybe things are bumping into you or you're
• 37:26
  Speaker 2: rubbing against other the space debris, then you're going to
• 37:30
  Speaker 2: start falling in.
• 37:31
  Speaker 1: Yeah, exactly. And the key concept here is angular momentum.
• 37:34
  Speaker 1: The thing that keeps the Earth in orbit around the
• 37:36
  Speaker 1: Sun and the Sun in orbit around the center of
• 37:37
  Speaker 1: the galaxy is its angular momentum. That's what keeps you going.
• 37:40
  Speaker 1: It makes a stable orbit. Things in the accretion disc
• 37:43
  Speaker 1: of the black hole will bump into each other, Like
• 37:45
  Speaker 1: how do you lose angular momentum? Something has to apply
• 37:47
  Speaker 1: a torque to you, and that's that other thing you
• 37:49
  Speaker 1: bumped into. So you knock something further away, and you
• 37:52
  Speaker 1: get knocked in closer to the accretion disk, and then
• 37:55
  Speaker 1: you start to fall in. So you actually gain energy, right,
• 37:58
  Speaker 1: you gain velocity. This is I think what Julian was
• 38:00
  Speaker 1: asking about. As you get closer to the black hole,
• 38:03
  Speaker 1: you've lost angular momentum. But now you're pointing towards the
• 38:07
  Speaker 1: core of the black hole. You're speeding up as you
• 38:09
  Speaker 1: come in, so you're getting faster. So you actually sort
• 38:11
  Speaker 1: of gain energy but lose angular momentum.
• 38:14
  Speaker 2: So you are spinning faster as you get closer.
• 38:17
  Speaker 1: You're moving fast, you have a higher velocity, but your
• 38:20
  Speaker 1: angular velocity is decreasing, You're not like whizzing around the
• 38:23
  Speaker 1: black hole as much. That's what was keeping you away
• 38:26
  Speaker 1: from the center, is that you were moving around it.
• 38:28
  Speaker 1: You're like missing the black hole. Like the reason the
• 38:30
  Speaker 1: Moon doesn't fall to the Earth is that it's enough
• 38:33
  Speaker 1: angular velocity to sort of miss the Earth even though
• 38:35
  Speaker 1: the Earth is pulling on it. But if you lose
• 38:38
  Speaker 1: that angular velocity, then the pull is just going to
• 38:40
  Speaker 1: pull you straight in towards the center, and it will
• 38:42
  Speaker 1: speed you up as you fall in the same way
• 38:45
  Speaker 1: that Like, if you drop a rock from the Moon
• 38:46
  Speaker 1: to the Earth and it falls in, it's going to
• 38:48
  Speaker 1: be going really fast. By the time it hits the
• 38:50
  Speaker 1: surface of the Earth. You're going to be going really
• 38:53
  Speaker 1: fast if you bump into a rock and the accretion
• 38:54
  Speaker 1: disk and head towards the black hole.
• 38:57
  Speaker 2: What did you slip on a banana near a black hole?
• 39:01
  Speaker 1: And then as you fall in you can blame it
• 39:02
  Speaker 1: on your son.
• 39:03
  Speaker 2: I told you, yeah, totally, not to cut the banana.
• 39:09
  Speaker 1: Are you telling me you cut bananas? I mean bananas
• 39:11
  Speaker 1: come with like a handy device. You can just peel
• 39:14
  Speaker 1: them and eat them. You don't need any utensils.
• 39:16
  Speaker 2: But yeah, but if you only want to eat half,
• 39:17
  Speaker 2: you can cut it, because otherwise you peel half and
• 39:19
  Speaker 2: then you got this hanging a peal that eventually looks close.
• 39:25
  Speaker 2: But if you cut a banana then it's clean.
• 39:26
  Speaker 1: I have this argument with my kids all the time.
• 39:28
  Speaker 1: They like to eat apples by cutting them, and I'm like,
• 39:29
  Speaker 1: you don't need to cut. You just hold in your hand.
• 39:32
  Speaker 1: You have teeth already. Like, it's beautiful, it's utensil free eating.
• 39:35
  Speaker 2: Sure, I mean that can say that about any kind
• 39:38
  Speaker 2: of eating. Dina, you can eat spaghetti without a fork
• 39:40
  Speaker 2: as well, why not.
• 39:44
  Speaker 1: They make this argument as well. They make this argument
• 39:46
  Speaker 1: as well.
• 39:47
  Speaker 2: Like, wow, dinner time must be really entertaining at your house.
• 39:53
  Speaker 2: Their facing a bull spaghetti. But anyways, black holes sort of.
• 40:00
  Speaker 2: I was like, you're saying that if you're far away
• 40:01
  Speaker 2: from the black hole and you start to fall in,
• 40:04
  Speaker 2: maybe you will start to spin faster, right, because the
• 40:06
  Speaker 2: stuff around the accretion in the accretion disk near the
• 40:09
  Speaker 2: black hole, that stuff is glowing and getting intense because
• 40:13
  Speaker 2: it is spinning so fast. Are you saying then that
• 40:15
  Speaker 2: once you fall into the black hole, then you slow down?
• 40:17
  Speaker 1: Well, I think that you're not spinning faster. As you
• 40:20
  Speaker 1: fall into the black hole, you're moving faster. So it's
• 40:23
  Speaker 1: a little bit of a nuance there between velocity and
• 40:25
  Speaker 1: angular velocity. Right, you're moving faster towards the center of
• 40:29
  Speaker 1: the black hole, but your angle relative to the black
• 40:31
  Speaker 1: hole is not changing anymore, and so you lost angler momentum.
• 40:35
  Speaker 1: You definitely have higher velocity, and that's why, as you say,
• 40:37
  Speaker 1: things glow right, these things are moving very very fast
• 40:40
  Speaker 1: and fast moving objects. If they have electric charge, they
• 40:43
  Speaker 1: will emit photons, and that's why the accretion disc of
• 40:46
  Speaker 1: black holes can be very very bright. That's why we
• 40:48
  Speaker 1: can see them. That picture of the black hole that's
• 40:50
  Speaker 1: so famous, Right, it's a ring around this black circle.
• 40:54
  Speaker 1: It's the accretion disc is what we're seeing. It's those
• 40:57
  Speaker 1: high speed particles as they fall in depens Once you
• 41:00
  Speaker 1: pass the event horizon, are you even going faster? That's
• 41:03
  Speaker 1: a question for quantum gravity. General relativity says depends on
• 41:06
  Speaker 1: the observer. If you're far away, then you'll never actually
• 41:09
  Speaker 1: see that person cross the event horizon because time slows down.
• 41:12
  Speaker 1: If you're that actual particle, you can measure your velocity
• 41:15
  Speaker 1: as you accelerate towards the singularity.
• 41:19
  Speaker 2: But I think we covered this in our book. Frequently
• 41:21
  Speaker 2: asked questions about the universe now for soil, for sue, yes,
• 41:25
  Speaker 2: that the accretioning disk is not sort of continuous down
• 41:28
  Speaker 2: to the black hole or even to the event horizon,
• 41:31
  Speaker 2: Like there's a gap right between the event horizon or
• 41:34
  Speaker 2: at least the shadow of the black hole and this
• 41:36
  Speaker 2: glowing disk.
• 41:37
  Speaker 1: Well, yeah, there's a gap where you can't have a
• 41:39
  Speaker 1: stable orbit, but you could still have stuff falling in actively.
• 41:42
  Speaker 1: Right So below, for example, the Photon ring, you can't
• 41:45
  Speaker 1: have anything orbiting that's outside the event horizon, but inside
• 41:49
  Speaker 1: the photon ring you can't have anything orbiting stabily there,
• 41:52
  Speaker 1: but you can still have stuff there. If it's falling
• 41:54
  Speaker 1: in actively and currently, then you could still see stuff there,
• 41:59
  Speaker 1: So it doesn't have to be empty.
• 42:00
  Speaker 2: There's stuff, But there is a little bit of a
• 42:02
  Speaker 2: gap there, right though.
• 42:03
  Speaker 1: It depends on the black hole, right if it's not
• 42:05
  Speaker 1: actively feeding, then yes, there will definitely be a gap there,
• 42:08
  Speaker 1: and you could imagine stable stuff orbiting further out from
• 42:10
  Speaker 1: the photon ring. But you know, if you dump like
• 42:13
  Speaker 1: a whole space ship full of gravy, for example, then
• 42:15
  Speaker 1: you can fill up that whole area with gravy particles briefly, right,
• 42:19
  Speaker 1: then they're all going to fall in. They can't stay
• 42:20
  Speaker 1: stably there in that gap.
• 42:22
  Speaker 2: Now, when you keep gravy in your house, do you
• 42:24
  Speaker 2: use utensils too?
• 42:26
  Speaker 1: We use a gravy boat and we just like pour
• 42:28
  Speaker 1: it all over the table.
• 42:29
  Speaker 2: Yeah, yeah, well you believe in the gravy boat. Okay,
• 42:31
  Speaker 2: I'm just trying to find out where your line is
• 42:33
  Speaker 2: for stability.
• 42:34
  Speaker 1: Super soaker is filled with gravy.
• 42:36
  Speaker 2: Gravy super soaker, Yeah, I just opened.
• 42:37
  Speaker 1: My mouth and the kids just shoot the gravy in.
• 42:39
  Speaker 4: You know.
• 42:42
  Speaker 2: That sounds like a lot more trouble than a spoon,
• 42:44
  Speaker 2: don't you, Because then you have to clean up. You
• 42:45
  Speaker 2: have to clean up the super soaker.
• 42:47
  Speaker 1: Yeah, well you got the fire hose afterwards. You know
• 42:49
  Speaker 1: it all cleans up pretty well. Tool.
• 42:52
  Speaker 2: That's another tool you need just to clean a super soaker.
• 42:54
  Speaker 1: Did you hear about that lady who made her entire
• 42:56
  Speaker 1: kitchen the inside of a washing machine so she could
• 42:58
  Speaker 1: just wash the whole kitchen but the press of a button.
• 43:00
  Speaker 2: I have not heard of this. Now, having a great idea,
• 43:04
  Speaker 2: isn't that like those public restrooms and parks do they
• 43:07
  Speaker 2: have in some cities where did you like just close
• 43:10
  Speaker 2: the door and then it turns into a washing machine
• 43:13
  Speaker 2: in there?
• 43:13
  Speaker 1: Yeah, exactly, great idea, And anybody with toddlers understands why
• 43:17
  Speaker 1: that's a good idea.
• 43:19
  Speaker 2: Just make your whole house that way.
• 43:20
  Speaker 1: Yeah exactly. It's just like make the whole plane out
• 43:22
  Speaker 1: of the black box, right.
• 43:24
  Speaker 2: Yeah, it'll clean itself up like a black hole and
• 43:26
  Speaker 2: as you clog it with too many too much gravy.
• 43:29
  Speaker 1: But people are really interested in studying the dynamics of
• 43:32
  Speaker 1: accretion disks because it tells us something about what's happening there. Like,
• 43:36
  Speaker 1: you can learn a lot about what's going on just
• 43:39
  Speaker 1: by looking at the velocity of stuff. Like one of
• 43:41
  Speaker 1: the ways that we know black holes exist is by
• 43:43
  Speaker 1: looking at stars orbiting them and seeing their velocity. We
• 43:46
  Speaker 1: can use that to measure the mass of the black hole,
• 43:49
  Speaker 1: Like the black hole the center of our galaxies is
• 43:51
  Speaker 1: a recent Nobel prize from studying the motion of stars
• 43:54
  Speaker 1: nearby that black hole. Their velocity tells us the mass.
• 43:58
  Speaker 1: It is. This incredibly powerful probe in the same way
• 44:01
  Speaker 1: that like, looking at the velocity of stars in the
• 44:03
  Speaker 1: galaxy told us how much mass there was because there
• 44:06
  Speaker 1: had to be mass to hold in all those high
• 44:08
  Speaker 1: speed stars, and so it's a really powerful way to
• 44:11
  Speaker 1: see things that you can't see directly.
• 44:13
  Speaker 2: All right, well, great question, thank you, Julian. And I
• 44:16
  Speaker 2: guess the basic answer for Julian is that, yeah, things
• 44:20
  Speaker 2: kind of spin at different speeds around a black hole,
• 44:23
  Speaker 2: just like they do around the Solar system.
• 44:25
  Speaker 1: Yeah, just like they do around the Solar system. Like
• 44:26
  Speaker 1: Mercury is going much faster than Earth, which is going
• 44:29
  Speaker 1: much faster than Saturn, which is going much faster than Neptune,
• 44:32
  Speaker 1: and so in accretion disc is a little bit more
• 44:33
  Speaker 1: like that, though there's a lot more bumping and grinding
• 44:35
  Speaker 1: going on in the accretion disk than in the Solar system.
• 44:38
  Speaker 2: Oh, you make it sound very sexy there, But it
• 44:41
  Speaker 2: sort of depends also on the mass, right, Like something
• 44:43
  Speaker 2: can be closed but moving slow, but something could be
• 44:45
  Speaker 2: far and moving fast.
• 44:46
  Speaker 1: There's going to be a lot of variation because in
• 44:48
  Speaker 1: decretion disc is a lot of chaos in it. But
• 44:50
  Speaker 1: in general, things will definitely be faster closer to the
• 44:52
  Speaker 1: black hole because they've fallen in that gravitational potential.
• 44:55
  Speaker 2: But within the accreasing disc there might be some things
• 44:58
  Speaker 2: moving faster than others. Right, yeah, all right, Well three
• 45:01
  Speaker 2: great questions, two of them about banana radiation. Boy, I
• 45:05
  Speaker 2: wonder if that de kay ratio is the ratio is
• 45:08
  Speaker 2: gonna be increasing over time. We're gonna hit one hundred
• 45:11
  Speaker 2: percent full life banana topics on our listener questions.
• 45:16
  Speaker 1: Tune in find out next time.
• 45:17
  Speaker 2: I guess that could be easily hagged, Like you just
• 45:19
  Speaker 2: have to coordinate with a couple of your friends, let's
• 45:22
  Speaker 2: say six friends, and then just have you all ask
• 45:25
  Speaker 2: a banana question at the same time. And then technically,
• 45:28
  Speaker 2: because of Daniel's your rules, you would have to have
• 45:32
  Speaker 2: a full banana episode.
• 45:33
  Speaker 1: Oh my gosh, let's go for it.
• 45:35
  Speaker 2: Oh man, that would be bananas.
• 45:37
  Speaker 4: All right.
• 45:37
  Speaker 2: Well, thanks again everyone who asked the question. We hope
• 45:40
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