Light travels 14 Billion light years from the centre of the Universe could redshift be caused by 'tired' light and not an expanding universe Light cannot have infinite energy so it must slow or stop?

Answer 1

Great question! This issue has been argued about and studied by astronomers for many years. The best experiments indicate that light never gets tired and never slows down. It does not need infinite energy to do this -- all light seems to travel at the speed of light "c" in a vacuum. Don't confuse this with light slowing down in materials. In fact it can stop. And don't think any of this is the last word on the subject. This is an active field of investigation due to dark matter, etc. See link below. Regarding infinite energy, this is a non-scientist's view. Photons are massless, and so they neither accelerate to c, nor do they expend energy to maintain c while they are traveling. No matter how far from the source a photon might go before it is absorbed, it is still one photon, and since this is a quantum of light, the smallest amount of light possible, when it is finally absorbed by something it imparts the same amount of energy as if it were absorbed immediately after being transmitted. This may or may not be an accurate analogy: an object in deep space moving relative to earth will keep moving for ever, except that particles of various size will surely impact it over time. These impacts will absorb some of the object's energy, but the object is not 'using up' energy in order to maintain its velocity. The difference here is that you can't absorb a fraction of a photon's energy. It's all or nothing. In closing. The redshift we see is due directly to the relative motion between the observer (us on earth) and the source (stars far from us). If we can set aside the "center of the universe idea" and look at just those areas where we can see farthest, the universe stretches pretty much "equidistant" in every direction. And the farther out we look, the faster (in general) that objects are moving away from us. This causes the Doppler effect we observe. Naturally we are looking back in time when we look farther out in space, but light arriving at the observer is the same light that left the source billions of years ago and followed the curve of spacetime through all that period to arrive here now. And in this case, the Doppler shift is clear player in the observed energy (frequency, wavelength) of the electromagnetic energy that arrives here to be scooped up by our collectors, be they optical telescopes, radio telescopes, or the like.