-1

If (in our mind) we reverse the velocity of every elementary particle in the Universe, does time reverse too? And if so does the same happen to the development of the all the wavefunctions and the expansion of space, both of which I find hard to believe?

Deschele Schilder
  • 1
  • Possibly related: http://physics.stackexchange.com/q/34479/50583, http://physics.stackexchange.com/q/257350/50583, http://physics.stackexchange.com/q/63811/50583 among many others. It's not entirely clear to me what scenario exactly you're envisioning here - we do not have a theory in which "velocity of particles", "wavefunctions" and "expansion of space" simultaneously are well-defined meaningful concepts. – ACuriousMind Jan 24 '17 at 19:58
  • I mean all the relative (or maybe the absolute velocities of elementary particles relative to the CMBR) velocities that elementary particles have, and simply turn these 180 degrees. – Deschele Schilder Jan 24 '17 at 21:56

1 Answers1

0

On a classical scale, Newton's laws cannot tell you the direction of time. On a quantum scale, the notion of velocity is meaningless. So no.

I think the nearest answer you might get to quantum scale effects involving time and elementary particles is CPT Symmetry

And if so does the same happen to the development of the all the wavefunctions and the expansion of space, both of which I find hard to believe?

I am not sure what implications you mean to convey here, sorry :)

  • In the hidden variables interpretation of QM velocity is certainly not meaningless. But the Copenhagen interpretation came to be the preferred one which is due to the decisions of some hotshots in the old days. The coin could just as well had landed with the other face upwards. In a classical setting, I could certainly tell when time is going forwards or backwards. Why shouldn't you? CPT symmetry is a local phenomenon, not a global one, and what does reversing time mean in the CPT symmetry theorem (which is one of the deepest results in QFT)? – Deschele Schilder Jan 24 '17 at 22:07
  • Hi I bought Nick Herbert's Quantum Reality book about ten years ago, which lists 8 interpretations and to me interpretations are based on your own personal preferences, so I gave up. Self learning the math is time consuming and weird enough for me :) Sure, common sense tells both of us which way time is running, but the quantum world does not run on common sense, and the physical laws can't tell me either. My "answer" is a bit terse, my apologies for that, entropy and the slight possibility of time reversal would have been a better choice than CPT . –  Jan 24 '17 at 23:38
  • @Countto10-Well, whatever the answer, at the moment I consider it more important to take a little walk with our dog in the starlit night!;-) – Deschele Schilder Jan 25 '17 at 00:08
  • That is exactly it, no matter how caught up in physics we get, we are always brought back to the ordinary world. I myself am looking for a dog to buy soon, possibly a collie. But you know the old joke, humans trying to understand QM is like a dog trying to understand how his food comes in cans...... –  Jan 25 '17 at 00:40
  • 1
    @HaHa! You're right. Though you haven't our dog yet! – Deschele Schilder Jan 25 '17 at 10:11