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

On 2005-08-28, RHNL <rhnl@xxxxxxxxxxxx> wrote:
> Simply put: Is 'time' a constant or a variable?
>
> If it is a 'constant' why is it applied differently
> in QM and GR?
>
> If it is a 'variable', why do we call it 'time'?

You've put so many scare quotes around words in your post, I don't even
know what you mean by them. I do know what physicists mean by time, and
I can tell you what that is.

We live in a 4-dimensional space-time. This is a space (in the
mathematical sense of the word) where points are called events. We can
identify different events by what "happens" there. For example, a light
turns on, an abscent minded physicist bumps into a wall, an African
swallow drops a coconut, a radioactive atom decays, and a star going
supernova are all examples of events, each of wich helps us identify the
point in space-time where it occurs.

Time is a function on space-time. Given an event, an observer present at
it can look at her clock and read off a number. That's precisely the
definition of a function, an association of a number to a point of
space-time. Up to this point, the same description applies to any
physical theory.

In non-relativistic theories, once two clocks are synchronized, their
readings do not depend on the motion of the observers who carry them. If
these observers meet up again, their clock readings will agree.

In theories based on special relativity, the clock readings do depend on
the motion of the observers. So if two clocks are brought together after
an earlier synchronization, they will not necessarily give the same
readings. However, if we know details of the motion of the two observers
in between, special relativity gives us a recipe for translating between
the readings of different clocks.

In general relativity, the only alteration is now that the clock
readings depend not only on the motion of the observer that carries it,
but also on the gravitational fields that the observer encounters. GR
also suppies an improved recipe for translating between the clocks of
different observers.

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.

Igor

.

Relevant Pages

  • Re: Is time time or is it not.
    ... > We live in a 4-dimensional space-time. ... > readings do not depend on the motion of the observers who carry them. ... > these observers meet up again, their clock readings will agree. ...
    (sci.physics.research)
  • Re: Hafele & Keating, Einstein, Dingle,Cocke, and Scott Murray
    ... > observers which are not truly inertial. ... > sun just as the observer at the equator is rotating about the pole. ... >>Acceleration of a clock is not supposed to affect the rate of that clock. ... > mass against the pull of gravity you get gravitational potential energy. ...
    (sci.physics.relativity)
  • Re: Seriously, What Can We Do About It?
    ... Time dilation ... well before anyone knew what kind of clock would be used in the test. ... of all observers therefore remain as a universal common ... of and without any consideration of concepts like 'co-existence' ...
    (sci.physics.relativity)
  • Re: Download a new book on quantum mechanics and relativity.
    ... > an uniform motion in a straight line and a straight line is defined ... When Galileo discussed inertial observers he wrote about a person ... > interactions propagate instantaneously in your theory, the photon ... I apply a ruler to measure distance and I use a clock to measure ...
    (sci.physics)
  • Re: Download a new book on quantum mechanics and relativity.
    ... > an uniform motion in a straight line and a straight line is defined ... When Galileo discussed inertial observers he wrote about a person ... > interactions propagate instantaneously in your theory, the photon ... I apply a ruler to measure distance and I use a clock to measure ...
    (sci.physics.relativity)