Re:Physics Without Probability (2015) [video]
by Koshkin on Tuesday January 05, 2021 @05:20PM
(#25651992)
To be fair, the parent was talking about "classical systems," not about the applicability of quantum-mechanical principles to macroscopic objects.
Re:Physics Without Probability (2015) [video]
by lisper on Tuesday January 05, 2021 @09:16PM
(#25654016)
But there is in reality no such thing as a classical system. The world we live in is quantum. Its behavior approaches that of a classical system as the number of entangled degrees of freedom grows, to the point where classical physics becomes a damn good approximation. But reality never actually becomes classical. The wave function does not actually collapse. And grains of sand do not have actual positions and momemta.
Re:Physics Without Probability (2015) [video]
by simiones on Wednesday January 06, 2021 @01:36AM
(#25655186)
Whether this is actually true or not remains an open question, but it is indeed the expected consequence of QM. However, there is as yet no experiment showing any kind of quantum behavior for huge objects (closest is a few hundred million atoms as far as I know).
Still, the point was about a classical model, not about physical reality being classical or quantum. To rephrase, my point was that even in a classical model there are quantities that can't practically be measured (even though classical mechanics as a model assumes all objects have definite positions and momentums), and that doesn't stop us from accepting in such a model that they are 'real'. So, the idea of property that is 'real' but not really measurable already exists in classical physics, it is not an invention of exotic interpretations of QM.
No, they don't. The uncertainty principle applies just as much to grains of sand as it does to electrons. The only reason they appear to have definite position and momentum is that their masses are large, so a very small velocity produces a very large momentum which gives them a very small wavelength, much smaller than their physical extent. But the uncertainty principle still applies. With the right technology you could do a two-slit experiment on grains of sand. See: https://www.wired.com/story/even-huge-molecules-follow-the-q...