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