Cosmological redshift and photon energy loss in SR

In summary, the conversation discusses the energy loss of redshifted photons in the context of space expansion. The use of special relativity is questioned and it is suggested that general relativity may be necessary to fully understand the issue. It is also mentioned that the current understanding of conservation of energy in general relativity is undefined.
  • #1

vsemenov

2
0
This might be a tired topic but please help me to understand.

Assume a photon moving in vacuum, ignore potential interstellar medium absorption and re-emission since it is not relevant to discussion of space expansion in this context.

Redshifted photons will undergo energy loss between *right after* emission at source and *right before* absorption at destination. Since photons always travel at c and experience no acceleration, increase in wavelength must occur in one and same inertial frame. Therefore we can apply special relativity. In special relativity, energy is conserved as long as reference frame remains static. If we were to consider the photon right before absorption, it should be already redshifted and lost energy through unknown means, yet we can not know since as soon as we observe SR no longer applies. So either I'm misunderstanding SR, or energy is being lost can not be explained by SR. So where does this energy go? How can a photon experience a change in total energy during one inertial frame when it does not experience time in the instance of that inertial frame?
 
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  • #2
Your reasoning leading you to the fact that SR is sufficient to discuss this problem eludes me. I certainly do not think it does. Even in a globally (spatially) flat universe, the metric is still non-minkowski, so GR need not reduce to SR.

Edit: Quick google search turns this up, which appears to be relevant: http://arxiv.org/ftp/physics/papers/0511/0511178.pdf
 
  • #3
Nabeshin said:
Your reasoning leading you to the fact that SR is sufficient to discuss this problem eludes me. I certainly do not think it does. Even in a globally (spatially) flat universe, the metric is still non-minkowski, so GR need not reduce to SR.

Edit: Quick google search turns this up, which appears to be relevant: http://arxiv.org/ftp/physics/papers/0511/0511178.pdf

Thanks. So propagation through expanding space has to be treated with GR, and currently conservation of energy is undefined in GR. So energy loss in cosmological redshift is either not a problem or unknown?
 

1. What is cosmological redshift?

Cosmological redshift is a phenomenon in which the light from distant objects in the universe, such as galaxies or quasars, appears to be shifted towards longer wavelengths (redshifted) due to the expansion of the universe. This effect is similar to the Doppler shift, but is caused by the stretching of space rather than the relative motion of the objects.

2. How does cosmological redshift affect photon energy?

Cosmological redshift causes a decrease in the energy of photons as they travel through expanding space. This is because the wavelength of light determines its energy, and as the universe expands, the wavelength of the light is stretched, resulting in a decrease in energy. This effect is known as photon energy loss.

3. What is the relationship between cosmological redshift and the speed of light?

While the speed of light is constant, the wavelength of light can change due to the expansion of the universe. As a result, the speed of light remains unchanged, but the wavelength and frequency of light are affected, leading to the redshift of light from distant objects.

4. How does special relativity play a role in cosmological redshift and photon energy loss?

Special relativity, which describes the relationship between space and time, is essential in understanding cosmological redshift and photon energy loss. It explains how the expansion of the universe can affect the wavelength of light and the energy of photons, as well as how the speed of light remains constant despite these changes.

5. Are there any other factors that can contribute to cosmological redshift and photon energy loss?

While the expansion of the universe is the primary cause of cosmological redshift and photon energy loss, there are other factors that can also play a role. These include the presence of matter and energy in the universe, as well as the effects of gravity. However, the expansion of the universe remains the dominant factor in these phenomena.

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