Re: Time dilation and expanding space

This is not a problem in all other relativistic redshift as one can
explain
the phenomena using three spatial dimension and time (not together as
spacetime). Eg gravitational time redshift is explained by the
gravitational time dilation at the emitter (the frequency of light is
actually lower at the point of emission). This was measured by Pound
and
co
in the 60s.

One can not explain expanding space redshift in this way ..

As I explained you can, and in fact GR works even beyond the
horizon where the apparent recession speed reaches c and your
3D+time model fails. All you are showing is that the traditional
view cannot cope.


That is utter rubbish. 3D+Time copes with black holes etc and not all
spatial expansion involves faster than c totals. The fact of the matter is
that there is no 3D+ time equivalent for ANY spatial expansion. Also, there
are conditions where c is exceeded in SR. Two photons emitted in opposite
directions from some point move away from each other at 2c such that at 1s
there is a 2*c distance between them.

There is no cause for this spacetime expansion. In all other examples of
spacetime expansion or spacetime curvature, gravity or motion is involved.
But not with the expansion of spacetime.

Let me give you a clear analogy which you should be able to solve quite
easily if naked spacetime expansion is a valid concept:-
consider a volume evacuated to replicate the density of space (a near vacuum
by Earthly standards). Now, given whatever tools you need, including those
that exist only 'in principle', how would you go about expanding or
contracting the spacetime in this volume?

Few can even offer an 'in principle' example. Or maybe dark energy may be
called upon even though it was only dreamt up some 40~50 years after the
naked (away from gravitating bodies) expansion of spacetime became a widely
accepted concept (but not by Einstein).

nor account for how
light can change its frequency in transit. In the spacetime model we
can
point to light being stretched as it passes over expanding spacetime.
But
the accompanying explanation from a frame closer to the speed of light
or
from space and time separately is not forthcoming - simply put - there
isn't
one.

Here are three quotes from P403 of the above mentioned book:-
-) As an example, in the curved spacetime paradigm, the verbal picture
of
Einstein's field equation is the statement that "mass generates the
curvature of spacetime." When translated into the language of the flat
spacetime paradigm, this field equation is described by the verbal
picture
"mass generates the gravitational field that governs the shrinkage of
rulers
and the dilation of ticking clocks." Although the two versions of
Einstein'
s field equations are equivalent, their verbal pictures differ
profoundly.

-) Some problems are solved most easily and quickly using curved
spacetime
paradigm; others, using flat spacetime.

-) This freedom carries power. That is why physicists were not content
with
Einstein's curved spacetime paradigm, and have developed the flat
spacetime
paradigm as a supplement to it.

Sure, and for most physics problems even Newtonian gravity
is adequate. Physics is a practical science. Constant g on
the surface of the Earth is adequate for building design,
inverse square law does for most satellites, that plus
gravitational redshift and SR effects is good for GPS and
they use full blown GR when it comes to cosmology where
the simpler approximations run out of steam.


Three space plus time is not a simple approximation. As Thorne says - the
two are equivalent. You are confusing Newtonian approximation with two
different accounts of the same thing and with the same precision ie one can
use the standard GR model of clocks and rods to explain ANY GR phenomena,
except for the expansion of spacetime.

A manifold by definition can be mapped onto three dimensions+time. It
should be possible to do this with expanding spacetime (even if precision is
lost ie an approximation), after all, space is not changing in dimension -
space is not expanding.

What is the flat space equivalent of expanding space - the version using
rods and clocks? Only the concept of expanding spacetime fails this
simple
test of consistency.

No, it's not the model that fails, it is the attempt to map
the curved spacetime onto a flat surface that doesn't work
in such extreme situations.

Curved spacetime can always be mapped onto three dimensions+time. All valid
forms, anyway.

Let's start with the basics - can space expand or contract? The answer is
no.
What is the agent of spacetime expansion?
How would you replicate the expansion of spacetime *in principle*??

Saying that it is all too hard just doesn't wash.

And GR can not model time except where motion is involved. The closest you
get is a light cone that expands, but it is still a temporal snapshot. You
can not model a simple experiment where a clock is left on a massive body
for one hour as measured by that clock and show why that clock is losing
ever more time to a space based clock.

Consider three identical clocks A, B and C. Let all three clocks be in
space well away from any massive body. Let the clocks be synchronised. Let
two of the clocks B and C be conveyed to the massive body. Let one of the
clocks, B, be immediately conveyed back to clock A and the difference in
their measured time be compared. B will show that less time has passed than
A. GR has no problem modelling this.

Now, after some interval, let C be conveyed back to A and B (the conveyance
being identical for each trip to and from the massive body). C will have
measured less time than A OR B. GR can not model this because it involves
an interval that does not include any motion. Kip Thorne mentions the
'snapshot' nature of GR in his book, so I don't think I need to rigorously
prove this point.

Robert


.

Relevant Pages

  • Re: Time dilation and expanding space
    ... view cannot cope. ... that there is no 3D+ time equivalent for ANY spatial expansion. ... spacetime expansion or spacetime curvature, ... use the standard GR model of clocks and rods to explain ANY GR phenomena, ...
    (sci.astro)
  • Re: Simultaneity
    ... passed in both ships until the accelerations stopped. ... The clocks may tick for the same time in the ships at what each ship sees as ... spacetime that results means that time slips. ...
    (sci.physics.relativity)
  • Re: Length Of A Curve in Spacetime
    ... I am confused about the way time and clocks are supposed ... different paths in spacetime. ... Note that dy/dx is a dimensionless ratio. ... meaning that "proper time runs slower than coordinate time", ...
    (sci.physics.relativity)
  • Re: Time dilation and expanding space
    ... In all other examples of spacetime expansion or ... expanding or contracting the spacetime in this volume? ... Newtonian gravity is adequate. ... model of clocks and rods to explain ANY GR ...
    (sci.astro)
  • Re: Time dilation and expanding space
    ... and through that vacuum light travels at c. ... speed of a photon through space, which is always c and NEVER slower. ... account of gravity proper by QM), even if badly, ... There is no spacetime in QM. ...
    (sci.astro)