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Post by Progenitor A on Dec 9, 2010 18:49:18 GMT 1
First off, light is neither slowed down nor accelerated by gravity, in the sense that the speed of light according to local observers is ALWAYS lightspeed. Light is bent by gravity, but that is because space is bent (that is what gravity is). The frequency changes when light moves into a gravity well, or moves out of one -- that ia gravitational redshift, and h as been tested over height differences of (at first) the height of a tower, and more recenly, over height differences of (I think) about 30cm. When light passes through diamond, the speed changes, but the frequency does not, it is the wavelength that changes. So, our little friend gets it wrong again, surprise, surprise......... The problem when talking about what happens to light is that you have to ditch Newtonian ideas, because to understand what gravity does to light, you have to switch over to relativity, where space bends, and so does time. And to back to the black hole -- even though light emitted radialy outward at the event horizon hovers, that DOESN'T mean that its speed is reduced, because according to anyone locally measuring the speed, it still moves at c, because any observer cannot hover above the event horizon (that would take infinite acceleration), but must keep falling. Hence relative to them, the light moves past at c, even though if we take a special set of coordinates, the light seems not to move. ANd as I said before, this is really no more mysterious than the fact that it you take coordinates travelling with a lightbeam, the light doesn't seem to move in that coordinate system, yet no one can measure light as being stationary, because no observer can travel with the light. Rather than just saying -- light always travels at lightspeed, a more PRECISE statement would be -- according to any possible physical observer (i.e., you with a stop-watch and a ruler), the speed of light is always MEASURED to be c. See that Carnyx? All without sums! She has fallen straight into your trap! Hahahahah! Sheer unadulterated waffle, She has even managed to (unknowingly) contradict herslf I do not know what this woman is but a physicist she is not!
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Post by speakertoanimals on Dec 9, 2010 18:51:45 GMT 1
Why would anyone think that you need a sum to answer a non-numerical question?
Does gravity accelerate light? Well, possible answers are surely just yes/no/sometimes. DO you really need to do a SUM to work that out?
Plus for someone who claims to have an engineering background, your use of supposedly technical language is definitely infantile................
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Post by carnyx on Dec 9, 2010 19:44:36 GMT 1
Sorry STA, but you answer makes no sense. Try again, if you would.
I sit in my deckchair, observing the night sky. Galaxies far away are red-shifted; i.e their frequency has dropped. There are two possible answers; either they are all speeding away from me,the observer, or that the light is somehow being affected on it's way over these considerable distances.
Space is not a void, and over such huge distances the light passes through gravitational, electrical, magnetic fields of varying strengths, and will also encounter fields of particles of all kinds.
So, it ought to be possible to estimate the amount of mass, and the electric and magnetic fields that would produce the equivalent 'redshift' that I see. Does this estimate of mass fall with the 'accepted' range of values?
(PS, a supplementary question; if you were an observer within a diamond, what would your measurement of 'c' come out to be?)
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Post by speakertoanimals on Dec 9, 2010 20:28:53 GMT 1
Correct, and what has effected it is the fact that the space it has traversed has been stretching as it traversed it, shifting the light to longer wavelengths.
Other stuff it encounters (like mass) doesn't have a net effect, because if it gets blueshifted falling down a gravity well, it gets redshifted back again when it comes out the other side.
The only way to get a net redshift from mass is if, for some strange reason, we are uphill of the rest of the universe.
The point about expansion is that it explains why ALL galaxies are redshifted, whatever direction we look, and why the further, the more redshifted.
Less than c, but that is becasue the full statement should be -- in vacuum, because its fairly obvious that if you're going to stick matter in the way, then things can get slowed down. You're going from a situation where you have a free photon, effected only by what happens to the space it is traversing, to one where you have a photon intercating with all the particles that make up the matter that it is trying to pass through -- a totally different case, and no wonder it can slow down! I should add, the point about effects due to space is that they don't depend on the wavelength/frequency of the light, whereas when passing through matter they do, and now different frequencies travel at different speeds.
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Post by carnyx on Dec 9, 2010 20:50:43 GMT 1
STA,
I have given you a case where you agree that light will interact with matter, which slows it down.
And you appear to agree that the interaction with matter will cause different frequencies to travel at different speeds.
As I have pointed out, 'space' is not empty by any means, and so it must be possible to estimate the anount of matter that would cause such a 'red-shift'.
And here is a supplementary question; how do astronomers know the speed of the light from distant galaxies when it arrives here ? Have they measured it?
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Post by Progenitor A on Dec 9, 2010 20:53:53 GMT 1
Does gravity accelerate light? Well, possible answers are surely just yes/no/sometimes. Well, I did ask you to be reasonable in discussion but you simply responded that I was an idiot Well my dear you are an ignorant imbecile! Of course the possible answers are yes/no/sometimes and they are all right so what an idiotic position you take The answer is YES if it is accelearting No if it is not accelerating Sometimes at the times it is accelerating in comparison to when it is not accelerating You really have no idea how to use the English language To the question 'Does gravity accelerate light' the answer is YES You really are exposing your ignorance. You are not a physicist, just someone who bumbles what you have read without understanding it. Here for your education are some simple sums Velocity = ds/dt Frequency = d(phi)/dt Wavelength,Lambda = s per Herz c = Lamda x f From these simple equations it is seen that the frequency does not vary with velocity It also seen that Lamda does vary with velocity The acceleration of light has been experimentally observed You really are useless
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Post by speakertoanimals on Dec 10, 2010 12:20:03 GMT 1
Wrong, if by acceleration you mean change in speed (ie magnitude of velocity), as opposed to the slightly more general change in velocity (ie change of direction but without change of magnitude). It was quite clear from the context that what was being asked was in the first context.
More nonsense, in that you are mistakenly trying to equate a velocity defined in terms of ds/dt, with a different distance, which is wavelength. Your wavelength is s per hertz is really rather odd, as is frequency is d(phi)/dt, since you've not bothered to define phi...................
In short, your usual bollocks!
Well, that isn't derivable from your nonsensical set of equations! The fact that frequency doesn't vary with velocity, in the sense of what happens as light crosses a boundary between two different media, can't be seen from your nonsense, but from the boundary conditions of the problem -- basically, what happens on side has to keep in step with what happens on the other (ie same temporal variation, which is frequency). So, from v = f lambda, if f constant and v varies (refractive index), so must lambda.
Back to empty space.
1) On average, space is very empty, you have to consider space between galaxies, not just what happens within galaxies.
2) WHY should anyone think that passing through matter would give a consistent redshift? Especially since FREQUENCY unchanged as we pass through matter, but frequency DOES change in the cosmological case Plus we have the time-shift in supernovae decay curves as well.
Different frequencies travelling at different speeds is NOT the same as red-shift.................
3) Yes, the speed of light from cosmological sources has recently been directly measured, and agrees with the speed of recent light.
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Post by Progenitor A on Dec 10, 2010 13:37:21 GMT 1
Wrong, if by acceleration you mean change in speed (ie magnitude of velocity), as opposed to the slightly more general change in velocity (ie change of direction but without change of magnitude). It was quite clear from the context that what was being asked was in the first context. Nonsense . Acceleration has always been defined in that way. Acceleration is the effect of a force acting upon a mass. that results in change in velocity. As the light is accelerated by the gravitational filed it loses (or gains)energy Additionally you are self-contradictory , variations in the speed of light have been discussed,. You really have fallen headlong into the trap that Carnyx set for you More nonsense, in that you are mistakenly trying to equate a velocity defined in terms of ds/dt, with a different distance, which is wavelength. Amazing! Sheer gobbledygook. They are not different distances - you really do not have a clue do you! You are really exposing your ignorance. Perhaps you would like to explain how they are different distances? Your wavelength is s per hertz is really rather odd, as is frequency is d(phi)/dt, since you've not bothered to define phi................... Oh my God! Everyone, every physicist, every engineer knows that d(phi)/dt in the context of frequency is the rate of change of angle! When d(phi)/dt=k a constant we have a constant frequency; if d(phi)/dt (not)= k then we have a varying frequency I can hardly believe this - from someone who purports to be a physicist and understands the mathematics of QM! Wavelength is defined as s per Hz! Physicist! You most certainly are not! I will not bother further with the wavelength bit as you evidently do not have a clue - if anyone else that might understand is interested I will explain Well, that isn't derivable from your nonsensical set of equations! This is incredible! You apparently have no idea of basic Newtonian physics! You cannot do maths can you! The nonsensical set of equations are standard equations from any A level text book! It is self evident (to a phycisist, engineer, technician, Mathematician ) from the standard equations that I have given you that frequency does not vary with velocity, you simply do not understand them This tomfoolery, combined with you making a total ass of yourself in the Path Losses thread(I have has technicians find the right answers there), confirms what some people think, you are not a phycisist at all but someone that simply parrots the various books you read - in fact some of the phraseology you used is directly traceable to popular science books You are like the fabled naked singularity your ignorance is exposed for all to see.
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Post by carnyx on Dec 10, 2010 14:55:01 GMT 1
@sta
You say space is empty .. I find an average estimate of around 1 atom per cubic centimetre
Taking the Galaxy Abell 1835 IR1916, it is ~ 1.0 ^10 light years away
There are approximately 1.0^19 centimetres in a lightyear ...
So, a stream of photons of cross-section 1 cm^2 from this galaxy will have traversed 10^28 centimetres.. and would on average have encountered 10^ 28 atoms .....
.... this is similar to the passage through 10km of diamond.
If we then add the effects of all of the gravitational, electrical, and magnetic fields that criss-cross 'space, and which these photons would have encountered .. I reckon that there will be considerable effects on the frequency and the speed of this light, before we need to talk about 'iinflation' as an explanation.
As I asked you previously; what matter, gravity, electric, magnetic fields would be needed in space, in order to 'simulate' redshift?
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Post by nickcosmosonde on Dec 10, 2010 18:55:20 GMT 1
It's hard to tell whether you're saying here that a naive person ignorant of what either SR or GR asserts would be surprised by the actual implications of the theories, or whether this is what you yourself believe. As you have previously shown yourself to be seriously deficient about what SR and GR imply, I suspect it's the latter. The simple fact is you're incorrect. There is no possible coordinate frame that you could choose from which you would measure c as stationary - or in fact at any other speed than c.
As for a prediction from GR that light will be stationary, "hovering" above event horizon, it doesn't say this either. Light will still be measured as travelling at c, from whatever coordinate frame you choose. Light hasn't stopped moving; rather, time has dilated to a near infinite extent.
You appear to believe, in the above statement and elsewhere where you've discussed this issue, that Einstein's original gedankenen, where he imagines himself travelling at c alongside a beam of light, would result in him observing the beam alongside him as stationary. This is quite incorrect. He realised that he would still observe it moving at c - always, at whatever speed he travelled, even at c himself.
Are you as abusive as this to anyone you happen to disagree with? Do you find that it helps you in life much, this attitude?
From my experience of your knowledge of the actual physics of relativity, Nay would do well to pursue his obvious interest elsewhere, in discussions with someone who actually knows what they're talking about.
The source of light is of course irrelevant to any measurement of its speed. But I've seen this bizarre claim elsewhere in recent months, even in Nature a few weeks ago. As I've said, it's really quite astonishing at how uneducated many theoretical physicists are - seemingly unaware of the history of science, or of what the theories that they use on a daily basis do or do not mean. In this case there's an unspoken unanalysed assumption that if c had been different in the past, or in a different part of the universe, we would be able to measure it from here, now. Ergo, the fact that we don't demonstrates it was always the same. It doesn't seem to occur to any of them that if c is a function of the tension in the universal field, determined by its total size and energy, then c will always be measured as c, whatever its source, wherever you are. It may well have had a different speed starting out, it may have a different speed in a distant galaxy, but we'd never be able to tell. This was, incidentally, Einstein's own opinion about the meaning of c.
Also incidentally, there seems to be an odd confusion...the term acceleration in relativity - and in dynamics generally - refers to any change in velocity, not to an increase.
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Post by nickcosmosonde on Dec 10, 2010 19:04:47 GMT 1
I presume you mean spacetime. The question as to whether your parenthetical assertion is correct is interesting.You're saying that gravity is caused by the curvature of spacetime? Or vice versa? Or are they equivalent? Do you know what Einstein's view of the matter was?
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Post by Progenitor A on Dec 11, 2010 10:13:07 GMT 1
Light will still be measured as travelling at c, from whatever coordinate frame you choose. Light hasn't stopped moving; rather, time has dilated to a near infinite extent. Of course that is the axiom of the Special Theory Of Relativity. And it makes sense. If time is dilated so that 1 s at the event horizon is dilated to 100 years, then the apparent speed of light (apparent to whom? - well us looking into this blacknes) will be about 10cm/s; in other words it is going to take quite a while to reach us!. But how does SR explain this apparent (in fact it is very real to us - because of it we see FA!) slowing down of c from our point of view? And from our frame of reference has it not slowed down?
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Post by Progenitor A on Dec 11, 2010 10:22:46 GMT 1
@sta You say space is empty .. I find an average estimate of around 1 atom per cubic centimetre Taking the Galaxy Abell 1835 IR1916, it is ~ 1.0 ^10 light years away There are approximately 1.0^19 centimetres in a lightyear ... So, a stream of photons of cross-section 1 cm^2 from this galaxy will have traversed 10^28 centimetres.. and would on average have encountered 10^ 28 atoms ..... .... this is similar to the passage through 10km of diamond. If we then add the effects of all of the gravitational, electrical, and magnetic fields that criss-cross 'space, and which these photons would have encountered .. I reckon that there will be considerable effects on the frequency and the speed of this light, before we need to talk about 'iinflation' as an explanation. As I asked you previously; what matter, gravity, electric, magnetic fields would be needed in space, in order to 'simulate' redshift? Some good points here Carnyx. You do not really expect STA to answer them though? What is your take? (I know that you are just asking awkward questions (in fact awkward indeed!) - as should be asked unless we regard science as a religion)
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Post by eamonnshute on Dec 11, 2010 11:21:45 GMT 1
@sta You say space is empty .. I find an average estimate of around 1 atom per cubic centimetre The density of inter-galactic space is nearer to 1 atom per cubic metre, so you can reduce your estimates by a factor of a million. The speed of light depends on the density of the medium, not how far it has travelled, or anything else. When light enters water it immediately slows down, but then continues at the same reduced speed. The density of matter in space is negligible, so the effect on the speed is also negligible.
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Post by carnyx on Dec 11, 2010 11:38:55 GMT 1
Eammon
Even if I revise the estimate to your very low density number (btw any references?).... it still comes out to the equivalent of 1km of diamond (which as you know is very, very, dense)
And now, could you have a go at answering the whole question as put?
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