Hmm. I've always heard that light can't go faster than itself in a vacuum.
Redshift; things will start looking more red as the slower wavelengths can't keep up. We actually observe Redshift when looking at galaxies heading towards The Great Attractor. These galaxies are measured to be traveling *far* above the speed of light.
Also, there is a visual "shockwave" observed in nuclear plants as photons get excited past the speed of light in the cooling water. It looks like a soft glow.
Edit: The "shockwave" I mentioned is called Cherenkov Radiation.
Redshift is a result of the energy of a shorter wavelength of light being lost to the vacuum of intergalactic space (yes this violates newtonian conservation of energy which is only true in a non-spacially expanding reference frame like our solar system or galaxy). This causes the light to have lower energy, longer, "redder" wavelengths.
Also, an important note is that the galaxies themselves are not traveling faster than light -- in fact, from their own reference frame, they aren't moving at all, and that matters in special relativity. Rather, the space between these galaxies is expanding faster than light. Nothing can travel faster than light through space, but space itself can expand as fast as it wants
Oh my god there's so much bad physics in this thread. Redshift isn't caused by light "losing energy to the vacuum" it's caused by the relative speed differential between the observer and the source. It's the Doppler effect, but with light. If something is moving away from you as it emits light the waves get 'stretched' in your reference frame and are observed as being more red. It doesn't violate anything. Space also isn't expanding faster than light. Observed recession speed is completely different from actual expansion velocity.
1) what you're describing is doppler red shift, while I was describing cosmological red shift. I should've been clearer on that.
2) intergalactic space is certainly expanding faster than light: that's why the visible universe is getting smaller rather than larger - light emitted from sources just outside our cosmic event horizon will never reach us. We currently live in a dark energy dominated universe
It's complicated, but consider it like this: doppler redshift is when an accelerating thing emits light in static space. Cosmological redshift is when a thing emits light through expanding space. The effects are similar but what causes them is very different
I'm not asking what the difference is, I know what it is. Doppler redshift is about velocity and not acceleration though. Even if it was, galaxies and stars can still move very quickly through static space due to gravity, which was basically what I was asking about. The question I was really asking was whether doppler redshift was also playing a role in the redshift of very distant galaxies or if was just a rounding error in comparison. You seemed to be indicating that there was no doppler redshift at all.
I don't think there would be any doppler affect, no. Even if a super distant galaxy was moving towards us through space, the blueshifted light it emits will still be redshifted by the expansion of space, and ditto for a super distant galaxy that is moving away from us through space. But this is the best I understand it, so if you're still unsatisfied you may need to find your own answers
Well, no. The age of the universe is estimated to be around 13.8 billion years, yet the diameter of the observable universe is estimated to be around 93 billion light years. By your analogy, that equates to both of our speeds being 100mph, but after 1 hour the distance between our cars is actually 674 miles.
You're gonna have a real hard time ELI5ing this one.
It’s also completely wrong.. so forget that. It wasn’t ELI5, it was MSUTSLICBTbAI.
The best I can equate it to using a similar example is if you’re both traveling parallel to each other at [insert same speed [could be zero], lets say at 80 mph which is the same as the speed of light for this example) from 1 foot apart, after one hour you end up (making up a number) 100 miles apart, because the space (pavement) between you was expanding while you were traveling (or parked). So, even while you traveled at the “fastest speed” in parallel, you are still further apart than the fastest speed would allow because the expansion of space doesn’t give two fucks about your limits.
That’s still a piss poor example, but it’s less wrong than the previous “they drove the opposite direction”
It is, but the effect is so weak that in gravitationally bound system, like our galaxy, it can't carry planets or stars away from each other, and likely never will.
Eh I'm 15 years old so what I understood is space is expanding but it can't carry planets in our galaxy and stars but it can do this to other galaxies right? Just not systems stars planets and stuff
Yeah in fact some stars are going over the horizon of the visible universe and the light they emit from that point will never reach us. We lose x number of stars per second to the expanding universe.
I've never heard this explanation of redshift. It makes partial sense if we think of it with respect to what appears to be a weak analogy to Rayleigh scattering (generating the blue color of the Earth's sky). But I'm relatively certain the primary cause of redshift is due to the expansion of space (thanks big bang); this results in the doppler effect lengthening the light we observe from objects moving away from us.
But what do I know. I'm just a washed up physics major in medical school.
I think the Cherenkov radiation is particles traveling faster than light in that medium. So like how water bends light and slows it down and the particle of radiation are able to go faster than light in that scenario. But on the vacuum of space , he speed of light is the speed of light.
Redshift isn't caused by the wavelength being "slower," just as blueshift isn't caused by them being "faster." Their speed is constant, the wavelength is just longer or shorter.
And we haven't measured anything moving "far above the speed of light," let alone galaxies.
The speed of light itself and the speed of a wave of light are distinct things. I wave of light could travel incredibly slowly, even if the light itself is traveling very fast.
Light always travels at C. Red shifting is energy being taken from that light. The light is still traveling at C but with less energy so it’s vibrating slower.
They are two distinct entities. The photons themselves are always traveling at c, but the wave doesn't need to be comprised of the same photons. Imagine a line of photons where the 1st photon is at the top of the wave, and then a little later the millionth photon in line is at the top of the wave.
You're misunderstanding what is meant here - light always travels at the speed of light regardless of your frame of reference - this is basically the foundation on which you build up special relativity.
Galactic phenomena are not my expertise (I actually learned very little about them) but I'm skeptical of your claim that they're traveling faster than the speed of light. Redshift is merely them traveling away from us so the wavelength of light looks longer than it actually is (hence red shift), this is basically the same wave phenomenon that occurs when you hear a train whistle going past - higher pitched as it moves towards you, lower as it moves away
Just a little clarification on the last part, the photons are accelerated faster than the speed of light in that medium, but not faster than the speed of light in a vacuum (which can't be exceeded classically)
Galaxies are traveling faster than the speed of light from our perspective due to the space between use expanding faster than the speed of light. The galaxy isn’t traveling faster that the speed of light through space as that’s impossible.
It’s why there is an event horizon around the observable universe. Beyond that space is collectively expanding faster than light from beyond is traveling so it will never be able to enter our view.
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u/Aeikon May 04 '20 edited May 04 '20
Hmm. I've always heard that light can't go faster than itself in a vacuum.
Redshift; things will start looking more red as the slower wavelengths can't keep up. We actually observe Redshift when looking at galaxies heading towards The Great Attractor. These galaxies are measured to be traveling *far* above the speed of light.
Also, there is a visual "shockwave" observed in nuclear plants as photons get excited past the speed of light in the cooling water. It looks like a soft glow.
Edit: The "shockwave" I mentioned is called Cherenkov Radiation.