RE: quantum field theories are problematic

[Brent Meeker]

I think he is drawing an unwarranted conclusion.  The fact that a physical
clock must have finite extent doesn't mean it can't work.  Diffeomorphism
invariance is a requirement we impose on our theories to reflect the fact that
choice of coordinates is a matter of description, not physics.  To suppose that
somehow restricts what clocks can measure is to turn the principle on it's
head.

Brent Meeker

>-Original Message-
>From: Stephen Paul King [mailto:[EMAIL PROTECTED]
>Sent: Sunday, May 08, 2005 3:19 AM
>To: Brent Meeker
>Cc: Stephen P. King
>Subject: Re: quantum field theories are problematic
>
>
>Dear Brent,
>
>Did you understand the discussion of the implication of Diffeomorphism
>invartiance? That is the key point to Hitoshi's point. This requirement that
>the laws of physics are invariant under any possible coordinate
>transformation requires that one's clocks and rules be definable only on
>infinitesimal points. This destroys the possibility of defining a "physical
>clock" and thus the "multi-fingered time" idea collapses.
>
>Stephen
>
>
>- Original Message -
>From: "Brent Meeker" <[EMAIL PROTECTED]>
>To: "Stephen Paul King" <[EMAIL PROTECTED]>
>Sent: Saturday, May 07, 2005 2:22 PM
>Subject: RE: quantum field theories are problematic
>
>
>>
>>
>>>-----Original Message-
>>>From: Stephen Paul King [mailto:[EMAIL PROTECTED]
>>>Sent: Sunday, May 08, 2005 12:41 AM
>>>To: Brent Meeker
>>>Subject: Re: quantum field theories are problematic
>>>
>>>
>>>Dear Brent,
>>>
>>>Did you read Hitoshi's take on the problem on his website:
>>>www.kitada.com?
>>>
>>>Thanks for the reference, I will find the book and read it.
>>>
>>>Stephen
>>
>> Yes I read it. Hitoshi seems confused to me.  First, he supposes that the
>> singularity theorems of Penrose and Hawking arise from imposing a global
>> coordinate system.  This is not so; the singularities are not artifacts of
>> coordinate choice.
>>
>> Second, his discussion of time corresponds to what is called
>> "many-fingered"
>> time in GR - it's just the observation that physical time, as measured by
>> a
>> clock, is different for each different path the clock takes through
>> spacetime.
>> But that time is not necessarily the "t" that multiplies the Hamiltonian
>> in
>> exp(-itH).  That "t" is just a coordinate and there is not uncertainity
>> relation between it and the energy.  Physical time is what is measured by
>> a
>> physical clock.
>>
>> Modeling an ideal clock in QM is non-trivial.  Asher Peres has a good
>> discussion of it in his text book "Quantum Theory, Concepts and Methods".
>> The
>> time that is measured by coupling such a physical clock to other QM events
>> does
>> have an uncertainity relation with energy.
>>
>> Brent Meeker
>>
>
>

RE: quantum field theories are problematic

[Jesse Mazer]

Stephen Paul King:
Dear Jesse,
   I thought that you knew that there are serious problems with all known 
forms of QFT!

See, for example:
http://www.cgoakley.demon.co.uk/qft/
Yes, I've heard there are some conceptual problems with them, questions 
about whether the renormalization is mathematically well-founded, but 
there's no getting around the fact that they make excellent predictions. Any 
improved theory of quantum fields would presumably have to reproduce the 
same predictions in the domains where they've been tested, and explain why 
renormalization gives the right answers in these cases even if it isn't 
really well-founded in general (the author of the webpage you cite seems to 
want to just throw away renormalization completely and not explain why it 
works so well in practice, which seems like bad science to me). Do you think 
it's plausible that a theory involving a preferred reference frame would 
reproduce the predictions of a Lorentz-invariant theory?

Jesse