Doppler Shifting of Light: Simplification or Reality?

[pforeman]

Is red shifting of light from distant stars actually caused from them moving away from us, or is this a simplification.
Doesn't this break the rule of light always going the same speed.
Could the light rays be possibly lengthened because when the light left many yrs ago space was smaller, now it is bigger so the wavelengths are now, necessarily longer
Thanks for your help
Paul

 

[Orodruin]

Is red shifting of light from distant stars actually caused from them moving away from us, or is this a simplification.

At the scale where the curvature of spacetime is negligible, there is no problem with this interpretation. However, there is also no problem with your other interpretation (which is usually called cosmological redshift). The thing is that both interpretations are coordinate dependent and therefore dependent on how you choose to label events in spacetime with coordinates.

Doesn't this break the rule of light always going the same speed.

No.

 

[phinds]

Doesn't this break the rule of light always going the same speed.

No. Red shifted (and blue shifted as well, for that matter) light is still traveling at c relative to the receiver. Whether it is red or blue shifted is just a matter of how many wavefronts arrive in a given amount of time but all wavefronts are moving at c relative to the receiver.

 

[Vanadium 50]

Is your question "are the equations oversimplified"? The answer is no.

Is your question "Are the stories we tell ourselves to help understand the equations oversimplified"? Well, maybe some are. I haven't seen all of them for sure.

 

[vanhees71]

Well, often popular-science writers distort reports about scientific papers to such an extent that I need to look at the scientific paper to (hopefully) being able to understand what the popular-science writers write about ;-).

 

[pervect]

Is red shifting of light from distant stars actually caused from them moving away from us, or is this a simplification.
Doesn't this break the rule of light always going the same speed.
Could the light rays be possibly lengthened because when the light left many yrs ago space was smaller, now it is bigger so the wavelengths are now, necessarily longer
Thanks for your help
Paul

The idea of "tired light" has been discredited, but it's unclear if it's the same idea that you're proposing in part two. See for instance the wiki https://en.wikipedia.org/wiki/Tired_light. Basically, the theory as proposed by Zwicky made experimental predictions that were inconsistent with observations, which you can read about in the Wiki article. Whether or not your description is the same as Zwicky's is a question I can't answer, you might try more reading. If your understanding of your theory is detailed enough to make predictions, you can perhaps decide if this experiment falsifies your theory.

The idea the relative velocity causes red-shift in General Relativity is basically incorrect. General Relativity, the theory that actually predicts the red-shift in question, does not have an unambiguous way of determing the velocity of distant objects. I would point to Baez's et al paper, "The Meaning of Einstein Equation" as a reference on this point, though it may be too advanced for the thread.

I'll explain a bit more as simply as I can. The relative velocity between two objects at the same event in space-time is well defined. In order to compare the velocity of two objects that are not in the same event (same place in space at the same time), according to the theory, there needs to be a transport mechanism to transport the velocities to the same location, where they can then be compared.

Unfortunately, in General relativity, this transport process, called "parallel transport", depends on the path, so transporting the velocity of the distant object along two different paths can give two different results, as Baez et al points out in their paper

Note that with these rules, there is no problem at all with the velocity of light being constant and equal to c. For a beam of light and a material object / measuring instrument at the same place and time, the measuring instrument will always measure the velocity of said light beam to be a constant, equal to c. A purist might have some more to say about this, but this post is already too long.

General relativity can be concisely described as the geometry of space-time. Space time can be represented by a space-time diagram, so General realtivity can be described as the idea that space-time diagrams should be drawn on curved surfaces rather than flat sheets of paper. That's the simplest and not very complete answer I have to give some guide as to what General Relativity acutually has to say as a theory. I'd also like to make a bit of a push for being able to draw and interpret space-time diagrams as a fundamental tool for understanding first special, and to a limited extent as above, General, relativity.

 

[Orodruin]

The idea of "tired light" has been discredited, but it's unclear if it's the same idea that you're proposing in part two.

I think what he is describing in part two sounds much more like cosmological redshift than tired light.