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suppose a white light is passed in space, after certain distance it dissapears. my question is whether the light loses its energy or whether the dark absorbs the energy.If it loses what is the energy form its changed into?
- lourde (age 25)
madras veterinary college, chennai- India
The main effect you may be thinking of is just that the light spreads
out. As it does, its intensity in any one place goes down, keeping
total energy constant.
On a much longer time scale, effects of General Relativistic
cosmology become important. The space the light is in is expanding,
diluting its energy further. The wavelengths stretch out too, so there
is also less energy per photon. That's why the background radiation
from the Big Bang no longer looks like light from something like the
surface of the Sun but rather consists of microwaves. In this process
the light energy density goes down faster than the volume goes up, so
it looks like energy is being lost. Howver, I believe that the
resolution is that a gravitational potential energy term goes up,
keeping the total amount of energy constant.
There can also be simple absorption by dust, which converts the
energy to thermal vibrations in the dust. Some is then re-radiated as
lower frequency radiation. This process does not seem to have been very
important on a cosmological scale.
(republished on 07/29/06)
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