字幕表 動画を再生する 英語字幕をプリント No. The plant length is, as we know, the smallest length. But is there a smallest time scale like something smaller than nanoseconds? Yes, yes, you take the plant length. It's a length. It's much smaller in my hand and you divide it by the speed of light. Well, is it really the smallest interval of time? I mean, we don't know that, but if we wanted to construct a very short interval of time, uh, from the plank link, who would just take the plank length off 10 to the minus 35 meters and divide by the speed of light, which is three times 10 to the eight meters per second. And lo and behold, if we do, that division will get the plank time, which is something like 10 to the minus 43 seconds on. That is meant to be the time after which the Big Bang has gone into the realm of physics that we know according to most people's beliefs. Because you really can't test that out. No one could measure it. Of course, it's still far. What's so much smaller than the plant Nana's scale? I think the the shortest time interval that people have been able to measure is called in at us. I think is an at our second. It's about 10 to the minus 18 of a second. So this is where smaller than that. So the plank time before that there's a big bang plant length of time on. Then, after that, laws of physics are as we know it. We don't know what happened before now. What is the significance of that time? Well, I think the most significant aspect of it is that we certainly haven't got any idea of what physics is like a that length scale or time scale. So that's something about the this idea of the foamy anus of off space and time. It would be done on that length scale, and it's got something to do with some physics We don't understand involving quantum mechanics and gravity. So what's its use? Its its uses primarily in theories, in the sense of trying to understand when you might expect quantum gravity effects to have to come into place. So when we need to really understand how to quantum gravity at the moment, we don't really understand that we have models to try and do it, but so we were happy to push models using classical gravity down to about that scale that we probably shouldn't. But I think most people that that scale would throw their hands up in the air and say, We don't know what's going on. We need to have a proper quantum theory of gravity.