字幕列表 影片播放 列印英文字幕 Yes, there's there's a letter in nature by a group that tells us that the radius of the proton is about 4% smaller than what we thought. Itwas to. The person's got a size and we always thought we understood the size of the proton. It was well defined. We could explain. It's a way of measuring its was had been developed that would could be accounted for through the theories of quantum electrodynamics, which is probably the best tested theory we have. Proton, of course, is a fairly small object. It's very light and is radius is extremely small life actually written it down here if you want to see it, so there it is. The radius of the proton is no 0.84 fem two meters wasif empty meter. If empty meter is 10 to the minus 15th of a meter. What was it? Well, that's a good question. I'll write it down. Well, that was the old Val Iwas again. I'm rounding it to two significant figures. No 20.87 times, 10 to the minus 15 meters. So that's the That's the new Radius. And that's the Old Radius. So the pro tone has shrunk by 4% is 4% smaller than we thought it was before These beautiful new, accurate measurements. It might not sound like a very big distance in natural size natural meters, but actually when you as a percentage of the what we've previously thought, it's quite a big difference. This group of physicists and Switzerland lived on this fantastic experiment, and they've taken it over six years to do it. What is it? 10 years They've had the debtor for over six years. Basically, they've seen that the Proton seems to have got smaller in size than we thought. It wa ce by about 4% which of course, doesn't sound very much. But in terms of understanding it from the theoretical standpoint where we thought we had the theory that would explain the size of the proton and it seemed to work very well. A 4% shift is a huge difference. What does it mean? Well, does it mean, for example, I'm 4% thinner that I was Unfortunately not so, although I can just about put a notch in my belt and reduce my waistline by 4% isn't because the proton has suddenly become smaller. Are we missing something? Is there an extra ingredient? Perhaps the theory as it stands is correct, but there's an extra thing in there that we haven't yet picked up on. So there's the proton, and here's the electron on. We know that the Proton is positively charged. It carries most of the mass of the atom because it's about 1800 times heavier than the electron on the electron. Being negatively charged is moving around is orbiting around the proton somewhat like the way in which the Earth is orbiting around the sun. Yeah, how do you two find the size of an object that's fuzzy? You know, Where do you take your tape measure to? Where's the edge edge of it? Where does the fuzziness stop? And, of course, it's not very well defined that way, so you don't do it that way. The way you define the sizes, you look for something else, an event that depends upon the size of the proton, but something else that you can measure, which you can measure very accurately. I've scale up the proton to the size of a cricket ball, and here's my electron, so I have to scale up the size of the electoral bit as well, and quantum mechanics tells us that the size of the electron orbit is about three kilometers. The radius of the orbit is three kilometers. The electron in this classical picture will be orbiting away about two miles away. Now, in fact, of course, the laws of quantum mechanics mechanics tell us that the electoral isn't behaving like a classically orbiting particle. It has a wave function on. It could be here, there and anywhere, and we have to describe that by showing away or probability density. But it means that the probability density cloud of the electron is extending a distance of something like three kilometers or two miles around. This this broken so you don't try on measure simply the size of the proton. By getting a met a tape measure and measuring out to the edge, you look for something else. And the particular thing that people look for is the fact that in an atom a hydrogen atom, for example, which consists of a proton and an electron, if you the electrons go around the proton. Okay, so so they're going around them and depending on which orbit they're in. They either go close to the props are not far away from the proton, but you can. If you excite that election, then you can move it from one orbit to another orbit on the beauty of quantum mechanics, and the thing that makes it so testable is that that difference between one orbit and the other orbit is well defined is called discrete. It's not a continuous change. There's a There's an actual discreet changing energy. So now if you pump in a bit of energy for a ton of light, smack it in on the on the electron, the electron would jump up. And if you've pumped in the right amount, you know there was the amount that you need to make it jump up to the next level. It's like jumping up a step. That's where the electron moves up to the next orbit circles around. And then as it comes back down, it will release energy again of that Sam about, and you can detect that energy. Now it turns out, in quantum electrodynamics that the the those energy steps those gaps depend upon the size of the proton. I mean, what what are they actually doing? There's something quite certain about what they've done is what they've essentially taken is the highest, not some sort of modified hearts tonight. So you'll know from chemistry that hydrogen atoms that are made up of a sort of central proton electron everything around okay on what these guys have done is they sort of taken that model. But they've replaced the electron with something else. They've still got the proton, but they replaced the election with its with a member of the the next member of the left on family, which is the mule. Now the new one has properties like the electron. Except for its mass. Its mass is around 200 times bigger than the electron. Now this meal, I'm being a lot heavier. It sort of hang around much more, more closely to the to the Proton itself, and then they do the same experiment again. They believe they understand how much energy should take you from one new one level to the next energy level. They do that, and they find that the amount of energy they required or the amount that's released when the new one decays because it decays extremely quickly is around 4% different toe what they expected. And they realized that actually, the Proton radius is a little bit less than we previously thought. And I said, This is quite profound implications for the rest of physics. If true, the first thing you should always be asking. And this is what the experimentalists will have been asking themselves over and over and over again, and why it's taken him so long to actually publish this debtor. In the end, remember, they've had this result, I think, for about six years is have we got the experiment right way doing it correctly? Are we doing the right measurements? Are we interpreting those measurements correctly? So that's the first thing. That's kind of the conservative approach that you very careful. Then you move on to the to me, and I get all excited because I start thinking, Oh, perhaps this. This is a manifestation off a new force that's kicking in that's over on top of the of the usual force that's arising from quantum electrodynamics. Perhaps there's some hint of a new ingredient that we haven't yet been able to see. I think for me that this sort of the important thing is it? It actually put into question, if true, one of sort of the theories that we thought was most correct, that we held most there. And that's quantum electrodynamics saying the proton is 4% smaller. Is that just like saying Mount Everest in a couple of centimeters shorter than we realize there is a really big deal? It's a bigger deal than saying that's Everest is a couple of centimeters shorter because you could explain Mount Everest being a couple of centimeters shorter with acceptable physics. It just means perhaps way don't know the constituents of Mount Everest quite as well as we thought we did. And in fact it's a bit more massive than we thought and the pull of gravity is pulled it down a couple of centimeters. Or perhaps our experimental equipment's not quite as accurate a cz. We thought here the really ex citing aspect of this would be if conventional physics can't do it. If once you've tested things like the experiment tested all the systematics that go with the experiment, you reduce those errors down to that minimum. There's still this difference and that that difference needs to be explained by something. And then then you begin to move into questions off. Perhaps our underlying theory. The theory of that of light and matter at the quantum level needs modifying.