B The Red Light Shift and Space Debris

[wlc88]

Hi,

As I understand it the theory that the universe is expanding is in part based off the red light shift. My question is could atoms in space, dust etc cause the red light to travel faster. I realize that space isn’t a medium, but could the aforementioned atoms and dust exist in such measurement per cubic meter to cause this?

Many thanks

 

[kimbyd]

Hi,

As I understand it the theory that the universe is expanding is in part based off the red light shift. My question is could atoms in space, dust etc cause the red light to travel faster. I realize that space isn’t a medium, but could the aforementioned atoms and dust exist in such measurement per cubic meter to cause this?

Many thanks

That wouldn't create redshift. It would create dispersion. It can be tested by, for instance, observing far-away objects which have time-dependent properties. Far-away quasars are really good examples, because they tend to vary quite a bit in brightness. If different wavelengths of light traveled at different speeds, then you'd see the brightness changes happening at different times for different colors.

Measurements so far indicate that there is no significant dispersion yet detected.

 

[phinds]

Hi,

As I understand it the theory that the universe is expanding is in part based off the red light shift. My question is could atoms in space, dust etc cause the red light to travel faster. I realize that space isn’t a medium, but could the aforementioned atoms and dust exist in such measurement per cubic meter to cause this?

Many thanks

Sorry, but that doesn't even make sense. Light does not travel faster or slower, it travels at c. Period. Red shift is a FREQUENCY shift, not a speed shift.

 

[kimbyd]

Sorry, but that doesn't even make sense. Light does not travel faster or slower, it travels at c. Period. Red shift is a FREQUENCY shift, not a speed shift.

That's not strictly true, as light does travel at a slower speed when it travels through a medium. And it's also true that intergalactic space isn't strictly a vacuum. There's not much matter there, but there is some. So dispersion isn't completely absurd. But it definitely has nothing to do with redshift.

Current evidence is that the amount of dispersion is so small that it is basically unmeasurable. Incidentally, there are some proposed theories which predict some dispersion for extremely high-energy photons. But so far there hasn't been any evidence of that either.

 

[phinds]

... light does travel at a slower speed when it travels through a medium.

Current evidence is that the amount of dispersion is so small that it is basically unmeasurable

I was treating space as a vacuum and I think you just made my point.

 

[Drakkith]

Hi,

As I understand it the theory that the universe is expanding is in part based off the red light shift. My question is could atoms in space, dust etc cause the red light to travel faster. I realize that space isn’t a medium, but could the aforementioned atoms and dust exist in such measurement per cubic meter to cause this?

Many thanks

No. One of the unique properties of redshit is that it conserves spectral lines. That is, the pattern of emission and absorption lines created when light is emitted by or passes through a gas are scaled by the same factor as the redshift, but they still exist. Absorption and scattering by dust erases spectral lines, while absorption by single atoms and simple molecules merely adds more spectral lines, it does not scale the original lines.