# Can space-time expansion destroy light?

I know that light shifts from high frequency(like gama rays) to low frequency (like radio waves) when traveling throw a gravitational field, this is called red shifting. My question is: Is there a limit to this, what happens to the light wave when it can no longer stretch, does it get destroyed ?

Thanks, and sorry for the dumb question, just curios.

Edit: From my knowledge and the internet :) Electromagnetic spectrum it states that light is an electromagnetic wavelength and the frequency which the wavelength travels up and down and the distance it's travel it's called spectrum and in that spectrum there is a frequency that is visible to us, but the spectrum is very large, my question is just for curiosity, I want to know if we know what happens when the light gets beyond the spectrum, can it? And I know that the expanding of space-time makes the light stretch from a high frequency spectrum to a low one, but what happens when you go to the limit of the spectrum ? can the wavelength be stretch to the point of "breaking" ?

• do you mean black hole? if so any light that falls in is gone, lost, added to the black hole mass. Commented Oct 23, 2017 at 9:24
• No.. I mean the actual light that travels throw spacetime continuum and is stretched by the fabric of expanding spacetime. Does the stretching has a limit? What happens when the light can't stretch anymore does it break ? Commented Oct 23, 2017 at 11:11
• I'll try to mimic expert: from your inertial frame you will see that the light from a distant galaxy which seemingly moving away from you becoming redder which the observer in that galaxy don't see the changes. Again from his inertial frame he will see light from our galaxy becoming redder. Then again for galaxies that is far,far away will be already outside our horizon. Commented Oct 23, 2017 at 12:19
• @user6760 Your first comment is a bit misleading: if a photon "add[s] to...mass" it can only do so by being absorbed. If a photon is simply trapped, as is the case with photons near a star's core (which may take thousands of years to make their way to the surface), it still exists. Commented Oct 23, 2017 at 13:26
• There seems to be a misunderstanding about how gravity affects light. The gravitational red shift corresponds to the time dilation of that object. Light leaving a massive object can only red shift as far as the time is dilated. It won't shrink arbitrarily small unless you have an object just a smidge away from being a black hole. Commented Oct 23, 2017 at 13:35

The stretching has no limit. Light can be redshifted to infrared, then to microwaves, to radio waves. There is no limit. This is because there is no medium that carries the waves to be stretched. There is no limit of the spectrum. It runs from arbitrarily long wavelengths, to arbitrarily short.

Instead of thinking of waves being stretched you could use a model suggested by Feymann. Each photon is like a small clock with one hand. THe colour of the light is the time it takes for the hand to go round. The photons in visible light turn a thousand trillion times a second. Radio waves only a million times a second. There is no limit to how slowly the hand can turn. Red-shifting is the slowing of the hand. There is no need to think of something stretching, and nothing to "break".

• So the visualization in the link of the light being stretched is wrong ? link You can see till 23:55 Commented Oct 23, 2017 at 12:17
• No, Both are "wrong" in that both are models. I'm suggesting that the model of "stretching" is a useful model in some ways, but if it is confusing you into thinking that something can "break" you can use a different model, that is wrong in different ways. A better model than either of these is a mathematical model, such as in quantum electrodynamics. But no model is "right" only "useful". Commented Oct 23, 2017 at 13:11
• OK, let me recap.. the photon of light travels as a wave, is that right ? If so the expanding of spacetime is affecting the frequency which the photon vibrates, right? Commented Oct 23, 2017 at 13:35
• I found some interesting information here, is this correct ? Commented Oct 23, 2017 at 13:58
• "the photon of light travels as a wave": that is a model. It may be useful for some things. It is neither completely True, nor False. A more complete model requires maths. Commented Oct 23, 2017 at 14:32

Another way to look at redshift is to consider the wavelength, which gets "stretched". There's no limit to how long a wavelength can be - it could be millions of kilometres (or even light years!) - but there's a limit to the size of the antenna we can use to detect it. And redshifted photons have less energy, so extremely long wavelengths mean extremely low energy.

• I understand this, I'm just saying are we sure there is no limit ? Commented Oct 25, 2017 at 11:07
• Or you can think of, is there possible that the wavelength can have zero energy thus implying maximum "stretching", or can it go negative ? Commented Oct 25, 2017 at 11:09
• Light (photon) energy is inversely proportional to wavelength, so as wavelength approaches infinity, energy approaches zero. But this is asymptotic so energy can never get to zero. Also, wavelength can't exceed the size of the universe. It's likely that the Planck length is a limit to how small a wavelength can be. Commented Oct 25, 2017 at 20:19