From what I understand, red-shifting is when light from a distant source travels through expanding space which stretches out the wave making it appear more red by the time it reaches earth.
So if a light wave traveled far enough, would it “red-shift” all the way down the EM spectrum eventually losing its waviness and becoming a straight line?
In: Physics
I think you’re mistaken on quite what it means to be redshifted. It doesn’t change the amplitude of the wave (the up-and-down measurement), just the wavelength and frequency. So maybe it would eventually appear as a flat line to measuring devices that are less than infinitely sensitive, but theoretically no it could never become perfectly flat.
The decrease is exponential, the light loses a certain percentage of energy per time (assuming constant expansion of the universe). So it does, say, double the wavelength every billion years So it gets indeed larger and larger, without any boundary; but it never truly reaches infinity, becoming straight.
Maybe you can imagine the process as if the wiggling wave thing gets stretched with space, becoming lengthier; but to stretch it straight, space would have to increase infinitely.
There is no end to the EM spectrum. So it can keep being redshifted indefinitely.
There’s also a cap on how far light can go (based on the age of the universe).
The big example of this is the cosmic microwave background; this is the light that was emitted in the early stages of the universe – when the universe first stopped being opaque. This light has been redshifted (by universal expansion) as much as it is possible for any light to be redshifted, and it is currently microwave radiation (obviously), with a wavelength of around 1-2mm. Radio waves can work with wavelengths in the hundreds of kilometres. There is plenty of space for more redshifting.
Red shift is when the source of the wave is moving away from the receiver, so there is a physical change in the distance between the peaks and troughs of the waveform.
A higher frequency of light becomes more blue, and a lower frequency is more red.
The light is still considered to be coming in at the same speed, because it is a continuous wave of particles, but the swing from the “highest” to “lowest’ points take a longer time.
With a high enough speed, theoretically, the frequency of light could be so low that you receive individual photons, instead of a continuous wave, but each of those photons is still travelling at the speed of light. But that speed would be incredible, relativistic speeds.
As you look at larger and larger redshifts, the distance increases, and [asymptotes](https://en.m.wikipedia.org/wiki/Asymptote) at the distance to the edge of the observable universe. At the boundary, the redshift is infinite, which would (according to the definition 1+z=λ/λ0) imply that the observed wavelength is infinite too.
Really what this means is that light from beyond this distance is unobservable, it corresponds to light that hasn’t reached us. The interesting thing would be the extremely high redshifts as you get asymptotically close to the edge of the observable universe, though such light doesn’t exist anyway as the universe was opaque for the first 300k years.
Light isn’t changing as it gets redshifted instead the observer is moving and so the wave takes time to catch up with the eye and it is that movement which stretches out the wave.
No. Red shifting is only caused by the observer also moving, similar to the Doppler effect on sound. Otherwise, light will continue to travel infinitely at a constant rate because energy cannot be created or destroyed.
What you are describing would mean the observer would have to be traveling at the speed of light in order for it to essentially shift into net 0, but if you are traveling at the speed of light in front of a particle traveling at the speed of light then you will never be able to observe the particle in the first place. If you were going very close to the speed of light, on the other hand, the redshift would be a lot, but only ever approaching 0, never actually 0, if that makes any sense.
That is put very simply. Red shifting is actually caused by the expansion of the universe, but the idea still holds true. The rate of expansion of the universe would have to be the speed of light for the particles to no longer exist on the spectrum, but that has a few other challenging implications.
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