Why do lightwaves shift in color as they move away? Is it because they lose energy?

Question

Why do lightwaves shift in color as they move away? Is it because they lose energy?

Answer 1

An individual photon does not lose energy.  But your measurement of that energy depends on your frame of reference.  That's part of special relativity.

Answer 2

If the source of the wave is moving relative to you, you will perceive a change in wavelength.  The frequency and wavelength of the wave are related to its velocity (frequency * wavelength = velocity).

Wavelength is the measure of the distance between consecutive maximum (or minimum) points on the wave (analogy to water waves would be distance from crest to crest).

The maximum (or minimum) points of waves are repeated by the source at a certain time interval (equal to the inverse of its frequency).

If the source is moving, the distance between consecutive maximum (or minimum) points on a wave is the wavelength of the wave when the source isn't moving plus or minus the distance it traveled in the time interval between consecutive points (the plus or minus depends on the direction it is moving).

You've witnessed this with soundwaves.  Think of a siren on a fire truck or police car or ambulance when it is coming towards you and then listen to it change when it is moving away from you going the opposite way.  In the first case, the wavelength was decreased and in the second, the wavelength was increased.

This phenomenon is called Doppler effect.

Answer 3

no its not, light does not lose energy slowly, it loses all its energy at once or not at all, they shift in color because as they move away from you they appear to get stretched out, think of it in terms of sound waves, as something with a siren gets closer, the pitch goes up, shorter wavelength, as it goes further away, longer wavelength, this is because each bit of the wave is emitted slightly further away than the last bit and so takes longer to get to you, hence the wavelength increases, same thing with light, hope that helps, if not check out    http://www.falstad.com/ripple/    set the second to top box to "1 Moving src" turn down the speed and frequency and look closely at the waves in front and behind source.