Comments on Soul Physics: David Albert on symmetries of motion in quantum me...

Bryan, >> the best interpretation of time w...

2010-03-20T10:59:51.399-04:00

Bryan,

>> the best interpretation of time will be as an illusion

I would prefer the term 'approximation' instead of 'illusion'.

Notice that we dont know how it would be if there is no time (e.g. living in the Euclidean sector of a QFT). Obviously it would not be just 'everything standing still', because this experience of 'everything standing still' already assumes some internal time of the observer imho.

Thanks Wolfgang, that's a really interesting p...

2010-03-20T07:27:55.893-04:00

Thanks Wolfgang, that's a really interesting point -- amazingly, the Wheeler-deWitt equation doesn't have an explicit time parameter. And there is that literature of people like Carlo Rovelli who argue that, in quantum gravity, the best interpretation of time will be as an illusion. But then, it seems that the question of time reversal for these people would be a moot point: if there's no time, then there's no need to figure out what it means to reverse time.

Bryan, >> the conclusion that "nothing...

2010-03-20T05:12:52.115-04:00

Bryan,

>> the conclusion that "nothing ever happens" is obviously false.

H|psi> = 0 is the Wheeler-deWitt equation for quantum gravity and it is not clear that it is obviously false.

I don't know ... I occasionally read stuff by ...

2010-03-17T19:45:07.668-04:00

I don't know ... I occasionally read stuff by Peirce when I'm bored (or when I want to remind myself how dumb I am), and he has some remarks to the effect that Laplace says such and so but the only things that are real are point particles with their masses and spatial arrangements (or relative displacements or whatever) and the laws. But those things together don't specify velocities of the particles. To get velocities, you need all of that at two different times.

I don't have any other examples in mind, but I'm guessing that you could rig up something similar that required n different time slices.

That's interesting. I suppose in principle you...

2010-03-17T17:59:01.736-04:00

That's interesting. I suppose in principle you could have dynamical laws like that. Did you have any particular examples in mind?

Does rejecting the premiss that the instantaneous ...

2010-03-17T17:46:46.225-04:00

Does rejecting the premiss that the instantaneous state gives the complete dynamics really amount to rejecting determinism or just one variety of determinism? If you have in mind Laplacean-style determinism, where every state is determined by a complete characterization of any single state, then sure. But couldn't you give up on the premiss at stake and still think that every state is determined by, say, two or three or n other states? And if so, wouldn't that qualify as determinism?

You could reject that as well. That's basicall...

2010-03-17T16:37:33.534-04:00

You could reject that as well. That's basically the assumption that the equations of motion are deterministic. You could also give up the assumption of time-translation invariance. But then, at least in the case of the Schrödinger evolution, the equations of motion actually are deterministic for well-posed systems. And giving up time-translation invariance means giving up local energy conservation, which isn't a very plausible option either...

Couldn't you also reject the premiss that the ...

2010-03-17T16:27:16.287-04:00

Couldn't you also reject the premiss that the instantaneous microscopic state of a system at t is the complete dynamical condition for that system at t? What is at stake in that premiss?