Transcription
How do particles know it's time to decay?
Love that question. That's a great question. Yeah. Sorry about your name, David, because since you asked such a great question.
Um, so what's the best way of describing that is time? So they have a lifetime which is um, as I said before is to do with can you decay into something lighter. So there might be a reason you can't, right? Because things are conser like electric charge for example, electric charge is conserved. So, so you can't take a a positive charged thing and have it decay into a lighter negatively charged thing because you'd be you'd be inventing, you know, you can't destroy and create electric charge. You have to do it in pairs. It's conserved.
A very important example is the neutron and the proton. So, the neutron is a bit heavier than the proton. So the neutron can change into a proton and does, and does in in about 10 minutes or so. I suppose even quicker than like six minutes is it or eight minutes. Yeah, it's it's it's it's like you can count it out and watch and watch it happen. So if it's sat on its own it'll do that and it'll and and to conserve charge there'll be a positive thing will go as well and so so you'll so so basically it can do it. So, and the the the lifetime is really proportional to the difference in mass between the neutron and the proton, which is very tiny. So, if it was really big, if it was much heavier, it would decay quicker.
So, you've got there's the mass difference and then there's the number of things you can decay into, the number of ways you can do it. Yeah. But that's just a statistical average, the decay time. That's the That's the halflife. Yes. Half life. Okay. So there's a we fill out the time with some of them are decaying sooner or longer. So you it's not just as simple as you described where how much difference is there in the energy and the mass of what it is and what it can be because there's a variation in there and I interpret that question is how do you get that variation?
Oh well that that's that's quantum mechanics so it's statistical. Don't say that's the answer. Well, no, no, but it's [laughter] a bit you're right. It's a very deep question. Yeah. It's like and that bothered immensely the the early founders of quantum mechanics. So, people like Rutherford and those people who Neils Boore and all those people and Einstein it bothered a lot. God does not play dice with the universe. That's essentially what you're saying. You're saying why does God play dice as Einstein puts it.
So, so the reason he was laid on the mortgage for the [laughter] universe. So he plays nice to get some extra cash on the side. Papa got to make this money. [laughter] So I think it was Papa Papa got to make this money, baby. Come on. [laughter]
Wait, wait, but Bryce, I realized just while you were speaking that you did answer her question precisely because she said, you know, cuz why does some take longer than others and the difference in how many options it has coming out the other side and the mass difference and the mass difference. So that that'll say why one will decay in 5 minutes or 10 or or 10 hours. You can get that. Yeah. Okay.
Given that what is going on at the instant that it decays? [laughter] It's enough. It's because that give me insight into why some will decay sooner and some will decay later so that it averages out to that halflife.
So what's going on? So you can it's called the weak nuclear force that's changing these things. And so that's part of the standard model. So what actually happens when a neutron turns into a proton. So so a down quark turns into an up quark. So what happens is the down quark it you can think of is emitting a a particle force carrying or a force carrying particle comes off. It's a W minus W minus which then goes to an electron and a thing called an anti-electron neutrino actually but it goes so it's the W minus goes off and then you get a down quark which is a charge plus plus 2/3. Okay. So you get a you get a minus one/3 quark going to a plus 2/3 quark and then you get an electron that comes off. So all the charges are conserved. So you haven't invented electric, right? And also the sum of all the charges at the end is the same.
We got it. And when we think of a neutron decaying to a proton, all that's the in the engine process going on. That's the gear the gearing that's happening that you just described.
So it's the it's the same kind of picture as why does an electron bounce off another electron. So we'd say well because they've got negative charge and negative charges repel. But the particle physics picture of that is that a photon is exchanged between the electrons. So in this case it's this. It's not the electromagnetic force. It's called the weak nuclear force. Basically the down quark is changing into an up quark with ultimately the emission of an electron and a neutrino. And the W minus is the particle.
And in the end when that happens is statistical. We got to deal with that. Are we hiding our awareness of objective reality by dusting it into the bin of probability?
No, it's so it's not the same that that randomness is not the same as the randomness because we don't know everything. So in in terms of a gas, let's say, you know, there are things things are jiggling around. We don't keep track. We spoke about it earlier. We don't keep track of the billions of molecules in the gas. So there's some statistics comes in because we're averaging over a load of the quantum mechanics is not like that as far as we can tell the statistical nature of it is inherently it's built into the theory. It's built into nature and it bothered everybody.
So Einstein was just wrong. Yes. Well, Einstein didn't [laughter] like it. It is true that how to interpret that then it's a whole other episode, right? is so you've probably talked to people about the many worlds interpretation of quantum mechanics. No, that's all that's this thing that's all in this. How do you interpret those statistical predictions without the collapse wave function without invoking a statistical description? Yeah. I mean, so it seems that it's it's a fundamentally it's a fundamental part of the theory.
You know, my favorite part of particle decay. What's that? If you accelerate them. Right. Then they take longer to decay. That makes sense because Einstein's special theory of relativity. So yeah, that's going closer to the speed of light. So time literally is slowing down. Slowing down for the And so decay. It takes longer to decay. Yeah. Yeah. That's a beautiful thing. That's very cool, man. Yeah. Wow. All right.
Time for a few more. All right. Here we go. This is John. He says, "Hello, Lord. Nice." And Dr. Tyson, Dr. Cox, uh John from Arkansas here. You've both explained what a plank length is and how we will likely never get more accurate measurements beyond this supposed limit. I am wondering if light can have a wavelength that small and if energy would be measurable or could that be another infinity we need new physics to explain much like the singularity in a black hole. PS love the show and Chuck I figured I'd mention you first for a change [laughter] anyway. Yeah. Uh
There is there is an answer to this. I I'd love this question. Yeah. I would not have been able to answer this question. The the answer is that um so the smaller you make the wavelength of a photon, the higher the energy of so so there should be an energy associated with the wavelength that is a plank length is. Yes. And you find out that that's the the that energy density makes a black hole. [gasps] [screaming] [laughter] So I think when OH MY GOD. SO, AND THEN SO you think about it, the more you try to probe smaller and then the black hole would I I think Lenn Suskin calls it the UVIR connection. I think that's what he calls it. So the the upshot is that if you try to put more and more energy into a smaller and smaller space to see smaller things, the size of the black hole you make increases. It grows. That's why. So the more the more you try to see smaller things, the less you can see the small things because the the the black hole [laughter] gets The universe is diabolical. Yes. So it stops you. So you can't you can't probe it. So black holes are in the cosmological witness protection program. [laughter] You can't get in there. You just can't. No matter what you do, you're not gonna That's amazing. [clears throat] What a great question, bro. That was a That was awesome.
Okay. Just remind us briefly about a a plank length. Just put that on the map here. So you can construct units fundamental units from things like so from specifically the speed of light, the strength of gravity and plank's constant. So if you take those things and put them together, so you get meters out, you'll get the plank length. So it's Plank who figured out that it would be good to make units of measurement out of things on which everyone would agree. If you think you make meet an alien for example, then there's no point talking about a meter because what is it? It's the length of your arm or something like that. Oh no, no. It's 1 10 millionth the length of a quarter of the Earth from the North Pole to the equator through the Paris Observatory. Is that what it is? Yes. Right. Okay. That's why the circumference of the earth is 40 million meters which is and make that kilometers it's 40,000 km that's why that's that's why it's that even is the French did that but you're Brit so you don't care what they did. Yeah. So they're all arbitrary things that our planet or our bodies or whatever it is. But then you could say well but the speed of light planks constant and the strength of gravity everyone would agree on even aliens. So yeah because you can measure those. So whatever units you measure them in, you can put them together to make something that looks like a length. Gotcha. And that's the plank length. It happens to be very very tiny relative to us. Right. Very cool.
So can there be a fabric of spaceime that in other words you if you were to quantize general relativity, you would have to the plank length would be fundamental to that. Is that not right? Yeah. So we we think that's telling us something deep about the about the universe itself. Okay. So these are properties of the universe these things not properties of planets or exactly very very cool. [music] [music] [music] [music] [music]