Lost energy of red shifted photons

In summary, photons that experience a change in frequency due to gravity or other red-shifting effects will lose energy, but total energy is conserved. The energy is not lost in any specific form, but rather the frequency of the photon is changed relative to the observer's frame. This is also true for red or blue shift due to relative motion. In the case of cosmological expansion, the frequency of the photon may appear to change, but it is still unchanged relative to its original rest frame. Time dilation plays a role in this phenomenon, and further study of it may provide more insight.
  • #1
MikeGomez
344
16
Photons which have experienced a change in frequency (red shift) due to gravity(or other red shifting affects), have necessarily lost energy. But total energy is conserved. Can someone please explain in what form is the energy lost?

Also related to the red shifted light subject:
Electrons emit and absorb energy in quantum values. However, after an adequate amount of red shifting, photons of a given emission will lose the ability to excite the same (equivalent) electron to that higher energy state. What is the tolerance? For example say an electron in the outer shell of some atom can be excited to higher state by photon of 5500 angstroms. What would happen when the electron encounters a red shifted photon of 5505 angstroms. Will the electron be excited to a certain extent, but be unstable?
 
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  • #2
Imagine you're in a car accident: you get rear ended by a 1000 kg car going 10 m/s while you're stationary (in a really big truck). The energy of the collision is 50,000J.

Now imagine you're in a similar collision, but this time you are moving at 5 m/s. What's the energy of the collision now? Did the universe lose energy somewhere?
 
  • #3
MikeGomez said:
Photons which have experienced a change in frequency (red shift) due to gravity(or other red shifting affects), have necessarily lost energy. But total energy is conserved. Can someone please explain in what form is the energy lost?

For gravity, red shift or blue shift is NOT due to any change in frequency of the photons, but is rather due to the time rates being different for observers in different potentials. No energy change occurs. If a photon of a given frequency is created by some atomic transition in the vicinity of a star, then it will appear red-shifted compared with the energy of the same transition at some distance from the star, but it hasn't changed frequency.

Similar considerations apply for red or blue shift due to relative motion; the energy is unchanged relative to the location at which the photon was emitted, but appears different from a moving frame.

The situation isn't quite so clear-cut about red shift due to cosmological expansion, because it depends on how you describe the expansion, but even in that case the frequency of the photon is unchanged relative to its original rest frame.
 
  • #4
Redshifted photons are time dilated, so no net energy loss - er, what jonathan said.
 
  • #5
Jonathan Scott said:
For gravity, red shift or blue shift is NOT due to any change in frequency of the photons, but is rather due to the time rates being different for observers in different potentials. No energy change occurs.

Ahh, interesting. That makes the study of time dilation my next subject of interest.
 

1. What is the lost energy of red shifted photons?

The lost energy of red shifted photons refers to the decrease in the energy of light as it travels through the expanding universe. This phenomenon is known as redshift, and it is caused by the expansion of space itself.

2. How does redshift affect the energy of photons?

Redshift causes the wavelength of light to increase, which in turn decreases the energy of photons. This is because the energy of a photon is directly proportional to its wavelength, with longer wavelengths having lower energy.

3. Can redshift be observed in everyday life?

Yes, redshift can be observed in everyday life. The most common example is the red color of a sunset, which is caused by the redshift of sunlight as it passes through the Earth's atmosphere. Other examples include the redshift of distant galaxies and the redshift of light from stars as they move away from us.

4. How is the lost energy of red shifted photons measured?

The lost energy of red shifted photons can be measured using the redshift parameter, denoted by z. This parameter is calculated by comparing the observed wavelength of light to its rest wavelength. The higher the value of z, the greater the redshift and the greater the lost energy of photons.

5. What is the significance of understanding the lost energy of red shifted photons?

Understanding the lost energy of red shifted photons is crucial for studying the expansion of the universe and the evolution of galaxies. It also has implications for our understanding of fundamental physics, such as the theories of relativity and the nature of dark energy.

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