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How would we see a near-light speed object emitting light?

How would we see a near-light speed object emitting light?

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2 Answers

Biswajit Das
askIITians Faculty 55 Points
8 years ago
An observer in the path of this object would not be able to see this unless this hit the observer. In fact all the light emitted by the object would, sort of, accumulate and would burst on the observer as the beam of light (all the light rays accumulated) and the object would reach the observer at same time.
shubham sharda
360 Points
8 years ago

Consider an object travelling near the speed of light relative to us (let it be a spaceship or a star), which is emitting light (consider it monochromatic resulting from a two level electronic transition).

Regarding the different relative time in the object itself (since it's travelling at high speeds) and the time of an observer (say in Earth), what would happen to the number of photons that we would see emitted by that object, i.e. photons/second, as it increases speed ?

I believe that we would see that the object would be emitting less and less photons (per unit time) as its speed increases because the time for radiative recombination, i.e. the time required to produce a photon, would pass slower. Is this true?

If yes: It is possible that we may fail to detect matter when we look to the outer space and think that nothing is there? Relating the fact that no radiation detectable from that point and that the relativistic mass is especially high, could it, or why cannot, this be related to dark matter?

Note: I am NOT referring to change of energy caused by red-shift, I am referring to change of the number of photons per unit time!

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