![]() Feel free to discuss anything related to this post or ask questions in the comments below. Leonard Susskind discusses an array of topics including uncertainty, the Schrödinger equation, and how things evolve with time. If you enjoyed this post or any of my others, follow and subscribe to my blog. This means total information about particles does not even exist and so the universe can not be classically deterministic. Improving knowledge of one means information on the other is being lost. This means perfect knowledge of a particle's position means knowledge on its momentum can't exist and vice versa. If there is no way to measure something then we can go as far as saying it does not exist. ![]() Quantum mechanics suggests that this is not entirely true. This would include precisely predicting all human behavior because ultimately, human's decisions come from particles acting in a way which conforms to the laws of physics. If we knew where every single particle in the world was right now and put it in a computer, we could run a simulation which would precisely predict all interactions between particles and we would actually have an exact simulation of the world. No matter how hard you try, you will never be able to know both the speed and the position of an object.Ĭlassical physics is entirely deterministic. The uncertainty principle turns out to be a fundamental property of the universe and is nothing to do with how good your technology is. Trying to improve the velocity measurement messes up your position measurement. If you wanted to not change its speed a lot, you would have to use long wavelength light but then you wouldn't have a good idea of where the electron was. Trying to improve your position measurement meant you've messed up your velocity measurement. The problem is that after you hit the electron with a photon the first time, you've changed its speed and so its not actually moving at speed v. You would have to hit the electron with a photon, wait an amount of time, hit the electron with a photon again and then do the distance between the two points divided by the time you waited for. This is fine if you only want to know the position of the electron but what happens when you want to also know the velocity? ![]() The problem with this is that short wavelength light has a high momentum. To get a more precise position, you have to use short wavelength light. It would be pretty hard to know where an electron was using light with wavelength 1m because all it would tell you is the location of the electron to within a meter. If you shine low frequency, low energy, high wavelength light at it, you won't have a good idea of where the object is. If you want to measure something, the most direct way to do so is by looking at it and so you shine photons on it so that you can see it. This is what the uncertainty principle boils down to. This equation tells us that the momentum of a photon is inversely related to its wavelength. Putting these two equations together gives
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