Re: Is 'time' time or is it not.

On 2005-08-30, I.Vecchi <vecchi@xxxxxxxxxxxxx> wrote:
> Igor Khavkine ha scritto:

>> For both non-relativistic and special relativistic theores, there exist
>> both classical and quantum formulations. In this sense, QM does not
>> treat time any different than we would expect. As to general relativity,
>> the main problems lie in the technical difficulties of constructing
>> quantum theories that take GR into account. Once these difficulties are
>> taken care of, at some point in the future, a quantum theory that takes
>> general relarivity into account (provided that gravitational fields
>> remain fixed and classical), would treat time in the same way as GR.
>>
>> Hope this helps.
>
> It sure does, but I would surmise that not any function provides
> credible time. Shouldn't clock readings be monotonously increasing?
> What about the result by Unruh & Wald showing that any physical clock
> has a non-null probability of running backwards ([1], cf. [2])?
> Can you briefly elaborate on why a quantum gravity theory where
> "gravitational fields remain fixed and classical" is a realistic
> perspective?

> [1] Unruh & Wald "Time and the interpretation of quantum gravity" Phys.
> Rev. D40, 2598--2614 (1989)
> [2] http://math.ucr.edu/home/baez/week167.html

Thanks for the interesting references. I finally had a chance to look at
them. However, I must clarify what I meant above. I was talking about
formulating quantum theory (which includes quantum field theory) on
curved backgrounds, where the background is considered fixed. From what
I understand, the greatest difficulty is the construction of non-linear
quantum fields on the curved space-times. However, the difficulties are
mostly of technical nature, due to the singularity of the field operator
valued distributions, and will most likely be worked out with time. I
wouldn't presume to say anything with as much confidence about a quantum
theory of the gravitational field itself. There, the difficulties are
more than technical, as illustrated in the references you provided.

Igor

.