Cosmological Redshift

[NotBrad]

Could somebody explain cosmological redshift in layman's terms please? My puny brain cannot handle it.

LOL LET ME KNOW IF YOU GET THE SECRET MESSAGE

[CraigD]

Cosmological redshift is pretty simple.

 

Assume space expands, like a compressed and dried sponge that has been soaked with water. Everything in it becomes uniformly longer in every direction, including the wavelength of all existing electromagnetic radiation. This is cosmological redshift.

[NotBrad]

So you are saying that the light has changed wavelength at a different rate than the surrounding reference distances?

[CraigD]

So you are saying that the light has changed wavelength at a different rate than the surrounding reference distances?

That depends on what you mean by “reference distance”.

 

According to General Relativity like the FLWR metric, the wavelength of light change increases by exactly the same factor as the distance between any two points in space.

 

So if by reference distance you mean the distance between 2 points with zero relative velocity and acceleration, no, the wavelength of light changes at the same rate as this.

 

If by “reference distance” you mean something like the distance traveled in 1 s by light in a vacuum, or the diameter of 1 kg iron sphere in a vacuum at 273 K, then yes, the wavelength of light changes at a different rate than this, because these “reference distances,” don’t change due to the metric expansion of space.

 

This difference is important, because if everything expanded equally, it would be impossible to measure, and wouldn’t be able to explain any of the cosmological problems.