Clocks and rulers

[swansont]

So given equivalence, there is the question as to whether the ruler changes (or should I say, appears to change) length at various points in the gravitational well. If it doesn't then there doesn't seem to between the supposedly equivalent effects resulting from acceleration and gravity.

Kinematic time dilation is due to speed, not acceleration, so this is moot.

[MigL]

The units of frequency are events per second, where in the case of light the events are wave cycles or peaks, if you will.

So light is a clock. And it is affected by time dilation ( gravitational and kinematic ).

So if the 'clock that is a light wave changes due to time dilation, its frequency changes. And frequency being intimately associated with its speed, c ( which cannot change ) means that wavelength changes inversely. And that is what we measure, the wavelength shift.

We are, in effect, comparing two clocks, the one in our frame ( observer ) with the one of a frame deeper in the gravitational well. And we are doing this simply by comparing the light in two different frames.

This effect is not, nor can it be evident, if you consider just one frame. Just think about it, in its own frame everything is as normal. There is no change in its own frame.

So yes, the change is frame dependent, or if you will, the observer needs to be in a different frame to measure any comparative time dilation.

[disarray]

The units of frequency are events per second, where in the case of light the events are wave cycles or peaks, if you will.

So light is a clock. And it is affected by time dilation ( gravitational and kinematic ).

So if the 'clock that is a light wave changes due to time dilation, its frequency changes.

 

So my perhaps ridiculous question is why we can't just say that light or EM waves change (frequency and wavelength) and therefore that we observe certain effects such as slower metabolism/decay rates, rather than bringing in the added metaphor that spacetime stretches and therefore we observe these effects.

[Markus Hanke]

 

rather than bringing in the added metaphor that spacetime stretches and therefore we observe these effects.

 

 

Spacetime is completely flat in SR, there is no "stretching".

 

 

 

why we can't just say that light or EM waves change (frequency and wavelength) and therefore that we observe certain effects

 

The effects of SR aren't merely optical illusions explainable by changes in light, they are real effects with real physical consequences. The "atmospheric muon" case is a good example in that regard.

[disarray]

 

 

Spacetime is completely flat in SR, there is no "stretching."

Yet metaphors referring to the bending, warping, folding, and stretching of spacetime are commonplace terms, even among physicists.

 

The effects of SR aren't merely optical illusions explainable by changes in light, they are real effects with real physical consequences. The "atmospheric muon" case is a good example in that regard.

 

But yet, it is maintained that the ruler never physically changes length, though it physically ages at a different rate (in comparison with the inertial frame).

[StringJunky]

Spacetime is completely flat in SR, there is no "stretching."

Yet metaphors referring to the bending, warping, folding, and stretching of spacetime are commonplace terms, even among physicists.

 

Spacetime is completely flat in SR, there is no "stretching."

Yet metaphors referring to the bending, warping, folding, and stretching of spacetime are commonplace terms, even among physicists.

 

The effects of SR aren't merely optical illusions explainable by changes in light, they are real effects with real physical consequences. The "atmospheric muon" case is a good example in that regard.

 

But yet, it is maintained that the ruler never physically changes length, though it physically ages at a different rate (in comparison with the inertial frame).

 

 

SR describes the local case where gravity is not taken into account i.e, locally, spacetime is 'flat'

 

Edited August 12, 2016 by StringJunky

[swansont]

Yet metaphors referring to the bending, warping, folding, and stretching of spacetime are commonplace terms, even among physicists.

When discussing GR. Not SR.

So my perhaps ridiculous question is why we can't just say that light or EM waves change (frequency and wavelength) and therefore that we observe certain effects such as slower metabolism/decay rates, rather than bringing in the added metaphor that spacetime stretches and therefore we observe these effects.

The effect is from time slowing down. Changes in EM waves are a result of relativity, not a cause.

[Strange]

But yet, it is maintained that the ruler never physically changes length, though it physically ages at a different rate (in comparison with the inertial frame).

This again seems to mix up the change in units (length of ruler, clock ticking rate) with the total elapsed (distance travelled, time passed).

 

The ruler changes length, as observed by different observers. Whether it "physically" changes length depends what you mean by the word "physically". If you mean "what we measure" then yes, it physically changes. If you mean some sort of internal structural/chemical change, then no.

[disarray]

The effect [of slowed metabolism] is from time slowing down. Changes in EM waves are a result of relativity, not a cause.

 

Ok, but is it just as reasonable to say that the changes in the EM waves cause (or result in) the slowing of metabolism, as it is to say that changes in spacetime (i.e., time dilation) cause (or result in) the slowing of metabolism.

Edited August 12, 2016 by disarray

[swansont]

Ok, but is it just as reasonable to say that the changes in the EM waves cause (or result in) the slowing of metabolism, as it is to say that changes in spacetime (i.e., time dilation) cause (or result in) the slowing of metabolism.

No, it is not.