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> Unlike general relativity, quantum mechanics, and particle physics, thermodynamics embeds a direction of time. This is the bit that irks me. Quantum mechanic
by mathgenius 8y ago
> Unlike general relativity, quantum mechanics, and particle physics, thermodynamics embeds a direction of time.
This is the bit that irks me. Quantum mechanics, the real QM that physicists actually use, involves collapse of the wavefunction. This is absolutely time-asymmetric. But in all these discussions of "why is time one-way?" this never seems to be mentioned. Apparently QM is not a real theory, and just a placeholder until we can work something out properly. Irk!
- jblow 8y agoMany physicists do not believe that collapse of the wavefunction is a thing.
- deleted 8y ago[deleted]
- mathgenius 8y agoOk, but why is there no discussion at all? I stand by my irk.
- whatshisface 8y agoYou can get every conclusion you want out of QM without any wavefunction collapses, so there's no need to discuss it (depending on your purpose) and if you're an MW-er you'd argue that, further, there's no reason to believe that it even happens. Since there are several self-consistent "piles of words" that all talk about the same math but contradict each other, (Does the wavefunction collapse? Does 1600s literature simulate the simulacrum?) not talking about it seems completely justified.
- mathgenius 8y ago> You can get every conclusion you want out of QM without any wavefunction collapses I don't think so. > "piles of words" I definitely agree about the piles. Maybe ordinary language is just to feeble for this stuff.
- kgwgk 8y agoWhat do you mean by “no discussion at all”? Looking for [“arrow of time” wavefunction] in your favorite search engine will return thousands of links.
- danharaj 8y agoIt only looks like the wave function collapses if you fail to take into account that the ones doing the experiment are quantum mechanical as well. If you could run an experiment where you account for the interaction between the apparatus and the observer, a meta experiment if you will, you would not see the wave function collapse that the observer thinks they observed.
- mathgenius 8y agoYes, this is known as "the church of the larger Hilbert space", or perhaps "Wigner's friend".
- empath75 8y agoInstead of the ‘collapse of a wave function’ think of it as entanglement of the wave function with the observer. The point at which the future evolution of the wave function and the observer become connected with each other.
- mathgenius 8y agoYes there are many perspectives to take. The basic problem with your suggestion is that it does not explain how anything actually "happens". Unitary evolution is a theory where nothing changes. People seem to think that they can evoke decoherence, or similar, and these issues disappear. But they do not. Anyway, I'm not positing any solution, I am just saying that it irks me that all these ideas are dismissed whenever it comes to the problem of the asymmetry of time. It just seems bizarre to me.
- antidesitter 8y agoWhat do you mean by “unitary evolution is a theory where nothing changes”?
- mathgenius 8y agoFor any two state vectors, |u> and |v>, unitary evolution preserves the amplitude <u|v>: <u|U^\dag U|v> = <u|v>.
- monktastic1 8y agoSure, if U operates on both |u> and |v>, their inner product doesn't change. But why does this mean that "nothing ever changes?" |u> can evolve independently of |v>, after all. OTOH, I can understand the argument that nothing ever happens. One reasonable requirement for something to happen is that it should not be able to "unhappen," which is why some are looking for the possibility of irreversible decoherence.
- mathgenius 8y ago
- csomar 8y ago> Apparently QM is not a real theory, and just a placeholder until we can work something out properly. Irk! There is no QM theory. There are interpretations (like the Copenhagen interpretation). We don't know the truth as of yet. (which is exactly what Hawking has been trying: creating a unified physics between QM and General relativity).