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All electromagnetic waves travel at the same speed through a vacuum, a value somthing around 300,000 km / s. Einstein says in his theory of relativity that the speed of light is always the same, no matter how fast its source is traveling. Speed of an electromag. wave is just freq. times wavelength. Given this, how is Red Shift possible? Even if the source of light is traveling away from us, the light is still traveling at a constant speed. Does the freq. change as well? Thank you
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Yes, the frequency changes as well.Originally Posted by earthman2110
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But what causes the freq. to change and why does it only happen over such a huge distance?
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Surprisingly, "space" is expanding (Big Bang Theory) and the light gets stretched. This increases the wavelength and, therefore, lowers the frequency (red-shifting) but travels at c regardless of the stretch.
If an object itself is traveling away from us at the time the light is emmited, then light is also red shifted by this "proper" motion in addition to the expansion of the universe.
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I thought the later effect was more prominant than the former? I could be wrong, though.
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Einstein said in 1911 that light speed slows down in a gravity field the rate of:
c= c0 (1 - Φ/c^2)
This means that gravity fields act something like a “local ether” or a local light speed regulator. Light slows down in a strong gravity field and speeds up in a weak one.
For a modern version of this theory, see:
LINK
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Hmm. I knew that by quantum mechanics, light could be slowed down when passing through a medium (water, glass, etc.), but I thought that gravitational fields only altered the spacetime around them, not the speed of light. Perhaps it's the alteration of time that leads to the appearance of c being slowed?
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Well, it can be explained in a complicated modern way or in an easy classical way. I prefer the easy classical way. You can see it explained in calculus terms at the end of this 1916 General Relativity paper. Or you can read his vague mentions of it in his 1916 book and the 1952 Appendix V.
Essentially, in 1911 he changed his 1905 “constancy” postulate to be more like this (these are my words): “An atomic clock located inside a gravity field will always measure ‘c’ as the local speed of light when the light is passing the place where the atomic clock is located.”
Seems that atomic clocks slow down inside a gravity field at the same rate light speed slows down inside a gravity field.
But if we use just one atomic clock, located in one place, to measure the speed of light traveling through several different gravity fields of different strengths, then we will measure a variable speed of light.
The gravity field might not be a true “propagating medium” of light or a true “ether”, but it is a local speed regulator for light. I.E., a strong local gravity field slows down the local speed of light. A gravity field acts something like a “medium” for light, in that it slows down the speed of light, and the stronger the field is, the more it slows down the speed of light.
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OK. So gravity slows the speed of light because gravity slows time, and since speed is just distance / time, anything which makes time slow down (that is, get "bigger") will make the speed get "smaller." Gotcha.
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I don’t like that way of explaining it. I prefer the classical way: Light speed slows down in a gravity field and atomic clocks slow down in the same gravity field at the same rate.
Remember, atoms are what emit light. Light comes from atoms. So that is most likely why their rates are tied together.
But an atomic clock does NOT represent all of “time”. It only represents the atomic time, the tick rate of the atom, the internal harmonic oscillation rates of the atoms in the gravity field. This is a function of quantum mechanics law. That law is an “electrodynamics” law, which is different from a large-mass mechanical law. For example, a pendulum clock speeds up in a gravity field where an atomic clock slows down. Why? Two different laws at work. One is a large-size mechanical law and the other one is a small-size electrodynamical law.
So, an atom’s vibration rate doesn’t represent our own human “biological time” any more than a pendulum vibration rate does. Our biological time is based mainly on molecular vibration rates, i.e. thermodynamic time.
Physicists like to go by atomic and light-speed time, while biologists like to go by thermodynamic time.
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Hmm. Clearly, a pendulum changes ticks differently near a black hole, but that's because a pendulum's motion depends on an external force. Neither an atomic clock, a light clock, or a biological clock directly rely on external forces to control them. I'm pretty sure that those three clocks correspond to one another almost perfectly.
As far as the view of whether gravity slows light or time, it probably is just a matter of point of view. If gravity slows light, then it slows the motion of light clocks, and any observer in a different frame looking at that light clock will think time is being slowed. If gravity slows time, then since speed is dependent on time, light-speed is also slowed. Must be another one of those things that can be interpreted two different ways, but which are both the same physical event.
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Yes.
I think I'm right here...
If the light is from a nearby star, it's redshift will be more from the star’s proper motion than from space expansion. Some stars are close enough to show slight blueshifts since they are traveling more towards us than away. However, over long distances/time, light is more stretched by the expansion of space.
Imagine being outside in the wind and throwing a Nerf ball to someone. If they are close to you, the speed of your throwing hand (proper motion) determines what the receiver catches. However, if they are far away and it is windy (space expansion)....yep, it’s the wind that dominates the event.
There is also rotational redshift. As stars rotate, one side is redshifted and the other side is blue shifted relative to its center. This will reveal the star’s rotational speed.
Hopefully, someone will confirm this or nit it.
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BTW, Earthman....Welcome to the board! =D> =D>
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No, biological time is heat time, thermodynamic time. That's different from atomic time.
An atom can both speed up and slow down at the same time, i.e. it's molecular vibration rate can speed up while its internal harmonic oscillation rate can slow down. It happens in stars all the time. These are two different kinds of time, thermodynamic time and atomic time.
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Ha, ether.
Apparently the gravitational fields act as light "ether", as light speed regulators. Einstein deduced this from his 1911 theory, but he hated calling a gravitational field an "ether". Why? Because he had already gone on record in 1905 saying there was "no ether". He hated to admit he was wrong about anything.
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Earthman (and apparently rwald as well), as you are new, I'll put this rather succinctly for you: Sam5 is pushing his own personal version of Relativity at odds with Einstein's and the scientific community's understanding. He's going to hijack your thread and turn it into a debate on Relativity. Its unclear if he doesn't understand it or if he's just purposely misrepresenting it, but either way: he's wrong.
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No, Russ is wrong. I back up my new information with the latest physics papers on the subject.
Russ is a, “Einstein Was Never Wrong”, kind of guy, and he hates to admit that the 1905 SR paper had flaws, but, that’s just too bad, because non-American physicists are finally admitting that the 1905 paper contained flaws.
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I agree. But I would say that gravity slows atomic clocks. That's a function of nature. It's a quantum mechanics and "electrodynamics" function. But atomic time doesn't represent all of time inside any "frame of reference". Ask any biologist.
When you go to a doctor, what is the first thing a nurse does? Measure your internal harmonic oscillation rates? Your body’s “atomic clock”? No. She measures your average thermodynamic time rate with a thermometer.
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I'm quite sure she measures your temperature with a thermometer.
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Right.I'm quite sure she measures your temperature with a thermometer.
Here, read this. A clock man should know about this:
"TIME IN BIOLOGY AND PHYSICS"
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The rate that thermodynamic reactions happen at is dependent on atomic time. If I sat near a black hole, my light clock, atomic clock, and biological clock would all be dialated by the same factor. If I would have lived for 70 years on Earth as measured by an Earth clock, I would live for 70 years near the black hole as measured by my black hole clocks. If there were any difference, I could use that to determine whether I was truly at rest or not, and that would violate the principle of relativity.
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Are you saying you would freeze to absolute zero at a black hole? Can you provide some science papers that support your point of view?
What about the crushing factor? Wouldn't you be dead if you received more than 10 or 20 gs of pressure?
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Well, listen to Russ. Sam may or may not understand relativity, but he thinks there is some American conspiracy to protect Einstein or something. Just be careful about taking Sams word on the way things work.
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(Sorry Russ, but I'm a sucker for trolls.)
As viewed from the outside, you would never reach the event horizon. As you got closer and closer to it, from the outside view your time would dialate infinitely. You would appear to be forever falling closer, never actually reaching the horizon. So yes, from an outside perspective, you would appear to be at absolute zero.
However, from your own perspective, this is not what would happen. Barring tidal effects temporarily (and looking around, etc.; I mean based on your clocks and meter sticks), you wouldn't know that you were approaching a black hole. You would think your clock was running normally, etc. The crushing would happen when tidal forces became strong enough to squish you infinitely thin along one direction while streaching you infinitely long along the other. Whether this happens before or after the event horizon depends on the mass of the black hole; counterintuitively, the more massive the black hole is, the closer you can get to the event horizon before tidal forces rip you apart (for the really massive ones, you would be ripped apart after you passed the event horizon, though that wouldn't do you much good in the long run.)
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Well, if you are at absolute zero, you are dead. Now how is someone going to see you “appear” to be at absolute zero, but you feel yourself still warm?
Some of these kinds of thought experiments become so ridiculous, they are totally useless, except to amaze a few junior-high kids.
I could just as easily sit here and say, “Imagine you have invented a time machine, and you go back to caveman days, then you get chased all over the place by angry cavemen, but all your friends see you frozen in time on their TV monitor down at the time machine lab. And Einstein predicted all this stuff.”
See, I can make up fantasy stuff too.
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The point of the example I gave is that not all observers need to observe the same events at the same times. Have you heard of the barn example? If not, I'll go into more detail in a later post, but the gist of it is that in one reference frame, a 5 foot long pole is completely enclosed within a 10 foot long barn for a period of time, while in another frame a 20 foot long pole is at no time enclosed in a 2.5 foot long barn. Both perspectives are right; synchronicity at a distance doesn't exist in a relativistic universe. No one said that everyone has to observer the same things happening at the same time in all places; if that were the case, then the whole time dialation thing wouldn't work.
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And you think we needed Einstein to tell us that??
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Yeah, so?
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Wow Sam. I ask you for this so many times in the relativity thread, and here you are claiming to have it. Like I've said before, if you have evidence that the speed of light can go faster than c, or even is affected by gravity, please share it. No opinions, nothing else, just a link to an experiment verifying this. If you post anything other than that, I will assume you don't have it.
Order of Kilopi
Sam is busy, I will post in his stead:
Normandy, can you answer my question? If two people pass each other, and one person sees the other has a temperature of a few degrees Kelvin, how come the other person is still alive?
Do you have a solution for the Twins paradox? You should call NASA and share! LOL!
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