Quantum Gravity?

Do you use the word God because you can't explain otherwise how it
happens?

Tsk tsk tsk. Sloppy. Very sloppy.

wrote:
Do you use the word God because you can't explain otherwise how it
happens?

"God does not play dice" is a famous quote of Einstein, in
which he expressed, in jokingly colorful language, his serious
opinion that some deterministic law lies behind the apparently
probabilistic quantum mechanics. It's still a matter of
controversy, though many would say that the answer is in, and
Einstein was wrong. When physicists use the God-playing-dice
phrase now, the reference is to that opinion of Einstein; it's
not meant literally as a statement about God.


Tsk tsk tsk. Sloppy. Very sloppy.

Save your breath for the real ways that S. is sloppy.

Russell wrote:
"God does not play dice" is a famous quote of Einstein, in
which he expressed, in jokingly colorful language, his serious
opinion that some deterministic law lies behind the apparently
probabilistic quantum mechanics.

It's not quite that simple (as you alluded to below). The one
generally accepted axiom of QM -- the Evolution postulate, as couched
in Schroedinger's equation -- is deterministic. The probabilistic
element only enters into Lueder's Rule or the Projection postulate,
which is not widely accepted as a fundamental postulate of QM.

That's really the whole impetus behind "interpretations" and
"measurement theory": trying to find a way to get a semblance of
projection without the extra axiom.

All that you can say, as Bohm pointed out directly after writing up a
book summarizing the standard (Evolution + Projection) formulation is
that the determinism is non-local and the probabilistic element comes
from ignoring what's "outside" the system -- just like it does in
classical physics (where "outside" means both "outside the domain of
interest" AND "outside/under the macroscopic realm").

In fact, you get the probabilistic behavior any time you cut off ANY
part of the external environment; the resulting state (relative states)
exhibit the very type of "collapse" (from pure state to mixed states)
you want. The probabilistic behavior is not fundamental but comes from
tracing over the external (and/or microscopic) modes, no different than
in classical physics.

The one question that usually arises is what about the entire universe?
If it has a quantum (pure) state that evolves deterministically, then
absent an extra axiom like Projection, literally nothing will happen in
the universe so-modelled. That's the famous Problem of Time in quantum
cosmology.

But the problem seriously begs the question: i.e., that there even IS
such a thing as a universal configuration space to draw out a state
space from, never mind that the universe might be in one of the states.

Number one, you need not even have a global "t" coordinate in the first
place, if the global structure of the spacetime is contorted in such a
way that time can loop. And even if not, then as Smolin was one of the
first to point out, it STILL need not be the case, even in a globally
hyperbolic spacetime where there is a "t" coordinate, that you have a
configuration space or a pure quantum state.

In that case, for all intents and purposes, the entire Universe is an
open system, relative states become a necessity, boundaries with the
external environment become a necessity, and everything has to be done
locally. The result is that probability enters the picture.

Not just in quantum theory, but even in classical physics!

In .com, on
06/09/2005
at 04:57 PM, said:

The one question that usually arises is what about the entire
universe?
If it has a quantum (pure) state that evolves deterministically,
then absent an extra axiom like Projection, literally nothing will
happen in the universe so-modelled.

That's only true if it has an exact energy, i.e., is in an eigenstate
of the Hamiltonian. If it's not an energy eigenstate then it will
evolve over time.

--
Shmuel (Seymour J.) Metz, SysProg and JOAT http://patriot.net/~shmuel

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Shmuel (Seymour J.) Metz wrote:
The one question that usually arises is what about the entire
universe?
If it has a quantum (pure) state that evolves deterministically,
then absent an extra axiom like Projection, literally nothing will
happen in the universe so-modelled.

That's [i.e. The Problem of Time, which is what this is in reply to, as you would know if you hadn't deleted the rest of the quote above which said it was referring to that!] only true if it has an exact energy,

Oh, for God's sake, people! Will you PLEASE look up what you're
replying to before you reply (and try not to delete it!)

The Problem of Time
http://search.yahoo.com/search?p=%22...lem+of+Time%22

Energy and eigenvalues have nothing to do with nothing. The problem of
time is related solely to diffeomorphism gauge invariance.