Re: Time dilation and expanding space

Robert Karl Stonjek wrote:
"Tom Roberts" <tjroberts137@xxxxxxxxxxxxx> wrote in message
news:qS8Fh.175$iw4.7@xxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Robert Karl Stonjek wrote:
The frequency of light is like a clock in itself - if the frequency is
lower then the clock at the source is slower as measured by an observer
who also measures that redshift. [...]
This is true regardless of the cause of redshift
Not true. Doppler shift is a different relationship than "time
dilation". And you completely ignore the possibility that an observer
can measure a BLUEshift....

I don't see how the frequency of light can be lower at the destination than
the source without all other observations of the source indicating that the
clocks are running slower

The usual method of measuring redshift would not work if what you claim were true. In order to measure the redshift of a distant galaxy one must ASSUME that frequencies of atomic lines in that galaxy are THE SAME as they are here on earth. That directly implies that atomic clocks there run at the same rate as identical atomic clocks here.

Of course in GR that assumption is valid.

In some sense you are double counting. If redshift corresponded to clock slowing at the source, you would not obtain the correct values.... And of course for BLUE-shifted light your claim breaks down completely. In simplified terms, the Doppler shift due to relative motion is first order in v/c, while the "time dilation" is second order in v/c; so the EM signal from an approaching clock is BLUE-shifted even though its "time dilation" goes the other way.


I don't see how it can be otherwise.

It cannot be as you claim and still agree with observations. And of course GR simply predicts otherwise. In GR, every clock ticks at its usual rate wherever it is located and however it might be moving. Measurements of red- and blue-shifts of EM signals sent from the clock will vary depending on the relative motion of source clock+emitter and receiver detector+clock, plus the difference in "gravitational potential" between them.

Light is NOT a "clock". Period. But the phase function of a light wave is an invariant 4-vector function on the manifold (this is the wave optics approximation to Maxwell's equations). That invariance directly relates to the observed local invariance of c and the measured relationships among c, frequency, and wavelength.

Your claim being valid would destroy those relationships. So you need to improve your ability to imagine things which are unfamiliar to you.


Tom Roberts
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Relevant Pages

  • Re: Explaining Time Dilation
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