Why Does Light Lose Energy with Universe Expansion?

[sancharsharma]

Can anyone please explain the physical reason of why is light losing energy as universe is expanding?

 

[HallsofIvy]

Can you give a reference to that statement?

 

[mathman]

Can anyone please explain the physical reason of why is light losing energy as universe is expanding?

A simple way to look at is that the expansion is stretching the light waves. Longer wavelength is equivalent to lower energy.

 

[sancharsharma]

@mathman,
But the wavelength of light is not merely a distance between two points. As a support it doesn't follow lorentz length contraction. It is distance per cycle.
So are you sure that it is a valid argument to say that wavelength expands as universe expands?

 

[bcrowell]

@mathman,
But the wavelength of light is not merely a distance between two points. As a support it doesn't follow lorentz length contraction. It is distance per cycle.

Cosmological expansion isn't the same thing as Lorentz contraction.

So are you sure that it is a valid argument to say that wavelength expands as universe expands?

It is valid to describe cosmological Doppler shifts verbally as kinematic Doppler shifts, and it is also valid to describe them verbally as being due to the expansion of space. These are just two different ways of talking about the mathematics of general relativity.