The photon does have a lifespan?

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In summary, a photon is born when it is created from an electron or positron, and it 'dies' when it is absorbed by another particle. However, the observational evidence suggests that there is no limited lifespan for a photon, as the oldest photons we measure from the distant edge of the observable universe are identical to newly generated photons. Some may argue that a photon could be considered 'dead' once its wavelength has redshifted to the point where it is greater than the radius of the observable universe, but as far as the photon is concerned, no time has elapsed. The absorption of a photon is determined by its energy, not its wavelength, so the size of the universe does not affect it.
  • #1
artevolved
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it is born.
 
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  • #2
artevolved said:
it is born.

It 'lives' until it runs into an electron or a positron, then it 'dies', to be 'reborn' again when the electron (or positron) falls back to a lower energy level and 'gives birth' to the photon.
 
  • #3
The "oldest" photons we measure have come to us from the most distant edge of the "observable universe". They have traveled for billions of years. (google "observable universe") So far as we can tell those photons are identical to newly generated photons. So, the observational evidence is that there seems to be no limited lifespan of a photon.
 
  • #4
Bobbywhy said:
The "oldest" photons we measure have come to us from the most distant edge of the "observable universe". They have traveled for billions of years. (google "observable universe") So far as we can tell those photons are identical to newly generated photons. So, the observational evidence is that there seems to be no limited lifespan of a photon.

I'd think a photon could be considered "dead" when it has red shifted to the point that its wavelength is greater then the radius of the observable universe. At that point we could never receive the entire wave. Granted that the universe is not old enough for that to have happened yet.
 
  • #5
'As far as the photon is concerned', no time has elapsed, despite the fact that we see it as having traveled for billions of years.
 
  • #6
Absorption of a photon is a question of energy, not wavelength. The two are related, of course, but I don't see how the size of the universe matters
 

1. What is a photon's lifespan?

A photon's lifespan is the amount of time it exists before it is either absorbed or scattered.

2. How long is a photon's lifespan?

The lifespan of a photon can vary greatly depending on its energy level and environment. In a vacuum, a photon can travel for billions of years without being absorbed or scattered.

3. Does a photon's lifespan affect its speed?

No, the speed of light is constant regardless of a photon's lifespan. However, a photon's energy level can affect its speed, with higher energy photons traveling faster.

4. What happens to a photon after its lifespan?

After its lifespan, a photon can either be absorbed by an atom or scattered by another particle. If it is absorbed, its energy is transferred to the absorbing particle. If it is scattered, its direction and energy can be altered.

5. Can a photon's lifespan be changed?

No, a photon's lifespan is determined by its energy level and environment. However, certain factors such as gravitational fields and high energy collisions can affect a photon's lifespan.

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