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Post by speakertoanimals on Nov 18, 2010 14:12:35 GMT 1
Nope. In terms of the physics, there are two different effects. The recession of he source is insufficient, as we can see if we consider a case where the rate of expansion varies as the light signal travels. SO what source velocity should we use, if it varies over the journey of the photon. And why should the velocity of the source at a time after the light was emitted alter what happens to the light? This just shows us that we need to keep clear in our minds two effects.
So in flat, non-expanding space, we have a frame of reference that encompasses both the target and the source. We then have a simple shift of reference frame from the frame in which the source is stationary, to one in which the source is moving, which just gives us the usual Doppler shift.
Expanding space is different -- now we have to consider not what happens to the source (whose apparent recession speed may vary after the light has been emitted), but what happens to the photon as it travels. Then the varying recession speed of the source (which logically should have no effect on light that has already been emitted) is instead looked at as the space through which the photon is moving expanding as the photon moves through it. Yes, this can be written down as an effective recession speed for the source, but that isn't the physical cause of the effect, its space stretching as the light moves through it. Hence we have a DIFFERENT source of redshift, the cosmological redshift.
Which is why the statement about the source of the CMB receeding at 0.99 lightspeed is wrong -- its just equating the effects of cosmological redshift with a DIFFERENT physical effect (Doppler shift), and finding the speed for one that would give the same size effect. That is NOT saying that the velocity we get actually refers to anything physical, since that is not the actual physics causing the effect.
Its not just arguing about words, it is two different bits of physics, and since you failed to see that, no wonder you keep coming out with nonsense.
Nope, you got it wrong again!
Convoluted, perhaps, but blame the physics, not me. Presumptuous? Have you been mining your thesaurus again? Perhaps you should use a dictionary as well, I think you'll find it is impenetrable....................
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Post by Progenitor A on Nov 18, 2010 15:15:01 GMT 1
Nope. In terms of the physics, there are two different effects. No. Recession means moving away - whether through the relative movement of two separate bodies or the 'expansion of space' between them. The effect is exactly the same. They recede (move away)from one another .... And why should the velocity of the source at a time after the light was emitted alter what happens to the light? Amazing! If the source moves after the light is emitted the wavelength of the light changes - this is called the DOPPLER effect! This just shows us that we need to keep clear in our minds two effects. It shows nothing of the kind my dear. It DOES show befuddlement on your part Expanding space is different ..... Then the varying recession speed of the source (which logically should have no effect on light that has already been emitted) Nonsense! The receding source will cause red-shift of its emitted light. Yes, this can be written down as an effective recession speed for the source, Contradicting yourself again my dear - this time you are agreeing that expansion of space causes recession! .....but that isn't the physical cause of the effect, its space stretching as the light moves through it. Hence we have a DIFFERENT source of redshift, the cosmological redshift. I do not disagree. I am simply saying that it is due to the recession speed of the two bodies (no matter whether due to relative movement or 'expansion of space') Which is why the statement about the source of the CMB receeding at 0.99 lightspeed is wrong -- its just equating the effects of cosmological redshift with a DIFFERENT physical effect (Doppler shift), and finding the speed for one that would give the same size effect. You say it is WRONG then in the same sentence say it gives the same effect, which is what I said at the beginning. Madness! That is NOT saying that the velocity we get actually refers to anything physical, since that is not the actual physics causing the effect. Gosh you are getting your knickers in a twist. Its not just arguing about words, it is two different bits of physics, and since you failed to see that, no wonder you keep coming out with nonsense. Hahahah! Nope, you got it wrong again! No you are simply an argumenative fool determined to 'do down' other people disregarding any contradictions that you come up with as so often Gosh I wish there were a reliable physicist on this board rather than a dogma-filled inarticulate who claims to be a physicist.
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Post by speakertoanimals on Nov 18, 2010 17:14:16 GMT 1
Wrong. If the source is moving as the light is emitted, that is the doppler effect. If it moves after the light is emitted, that can be due to two things -- either the source really moves (i.e. someone sat on the source would feel an acceleration), which DOESN'T effect the light vthat has already been emitted. OR: The source moves (but no acceleration is felt), because what is really going on is the space between us and the source expands. ANd the light already on its way is effected by that, and it isn't the doppler effect, but the cosmological redshift. It gives the SAMe effect in terms of the redshift you measure, but that isn't to say it is the same physical cause. Just as you can boil a pan of water by heating it in a microwave, or by putting it on a gas stove. The effect you measure (the temperature of the water) may be the same in both cases (hence they have had the same effect on the water in terms of the measured temperature rise), but the means by which that effect was cauised is not the same. You're still wrong,,and don't seem willing to listen, so who is being dogmatic? www.astro.virginia.edu/~jh8h/glossary/redshift.htmAnd you'll find the same things stated on any decent physics website -- even if some gloss over the difference between the doppler and cosmological shifts -- mainly because people are used to the Doppler shift from ambulance sirens, and might not find it so easy to see that expanding space stretches light moving through it. Subtle but important, and you've muffed it.................
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Post by Progenitor A on Nov 18, 2010 17:59:46 GMT 1
Wrong. If the source is moving as the light is emitted, that is the doppler effect. If it moves after the light is emitted, that can be due to two things -- either the source really moves (i.e. someone sat on the source would feel an acceleration), which DOESN'T effect the light vthat has already been emitted. AS the light is emitted is much the same as AFTER the light is emitted because the wave is moving outward AFTER it has left the source and if the source then moves the wave is stretched. Why on eath do you raise these idiot objections? Attempting to point score I suppose. It gives the SAMe effect in terms of the redshift you measure, but that isn't to say it is the same physical cause. I agree but haven't a clue why you are repeating yourself Just as you can boil a pan of water by heating it in a microwave, or by putting it on a gas stove. The effect you measure (the temperature of the water) may be the same in both cases (hence they have had the same effect on the water in terms of the measured temperature rise), but the means by which that effect was cauised is not the same. Idiotic analogies to illustrate a point that I have already told you I agree with in a prior posting! You're still wrong,,and don't seem willing to listen, so who is being dogmatic? Silly little point- scorer! And you'll find the same things stated on any decent physics website -- even if some gloss over the difference between the doppler and cosmological shifts -- mainly because people are used to the Doppler shift from ambulance sirens, and might not find it so easy to see that expanding space stretches light moving through it. You mean illustrations I have already agreed with in a previous posting? More lack of clarity in your thought process Subtle but important, and you've muffed it................. IDIOT!
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Post by speakertoanimals on Nov 18, 2010 18:52:35 GMT 1
Because what you are saying is bollocks! If the source accelerates away after the light has left, it has NO EFFECT on the light. If the source 'moves' after the light has left, because space has expanded, then it will effect the light, but NOT because the source has moved, but because the light has moved through expanding space.
I don't care what you now claim you previously agreed with, not when you come out with bollocks such as the first part of your post.
So take this case. Suppose we have done some fancy spacetime engineering, so that after the light has been emitted, we cause the space in front of the light to expand, whilst the space behind the light contracts, in such a way that the net distance to the source remains the same. Hence the source is not moving, given YOUR definition of distance.
Yet the light will be redshifted as it moves through the expanding space.
QED, the cosmological redshift is a different physical effect to the Doppler shift.
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Post by nickcosmosonde on Nov 18, 2010 19:02:05 GMT 1
Yes, but are you a woman? I ask simply in a spirit of disinterested enquiry, of course. Nothing odd about it, either way.
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Post by speakertoanimals on Nov 18, 2010 19:25:50 GMT 1
Yes. And my wife can confirm that.............
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Post by Progenitor A on Nov 19, 2010 9:05:44 GMT 1
I don't care what you now claim you previously agreed with..... Of course you do not , you are simply a blindly argumentative fool So take this case. Suppose we have done some fancy spacetime engineering, so that after the light has been emitted, we cause the space in front of the light to expand, whilst the space behind the light contracts, in such a way that the net distance to the source remains the same. Hence the source is not moving, given YOUR definition of distance. Ok, tell me how you going to 'engineer' this.
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Post by speakertoanimals on Nov 19, 2010 14:17:47 GMT 1
It doesn't MATTER, don't you know what a gedanken experiment is?
It shows quite explicitly that we can think up a case where we have expansion for travelling light, but no recession for the source. What answer do you give to that, that's the point!
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Post by Progenitor A on Nov 19, 2010 14:21:48 GMT 1
It doesn't MATTER, don't you know what a gedanken experiment is? It shows quite explicitly that we can think up a case where we have expansion for travelling light, but no recession for the source. What answer do you give to that, that's the point! Some thought experiments are valid, other, such as yours in this case, eminently silly
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Post by speakertoanimals on Nov 19, 2010 16:09:34 GMT 1
Nope, you're just trying to evade answering the question. I have given you a case where there is no recession, hence no recession speed for the source, yet the light moves through expanding space. What do you think is the effect on the light, given that you have previously stated that the whole effect can be explained by considering the recession of the source...............................
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Post by Progenitor A on Nov 19, 2010 20:50:41 GMT 1
Nope, you're just trying to evade answering the question. I have given you a case where there is no recession, hence no recession speed for the source, yet the light moves through expanding space. What do you think is the effect on the light, given that you have previously stated that the whole effect can be explained by considering the recession of the source............................... Your 'thought' expriment is invalid because the conditions that you stipulate are impossible Unlike Enisten's 'thought experiments' that propose 'experiments' within the bounds of what is theoretically possible, your 'thought experiment' demands both the compression and expansion of ST. Of Expansion of ST there are multitudinous examples (although to be viewed with scpticism) ; 'compression' of ST is unkown and an invention of your imagination. So you do not make sense my dear
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Post by speakertoanimals on Nov 22, 2010 13:39:40 GMT 1
Well, given that the same theory which predicts that spacetime can expand also predicts that spacetime can contract.............
As regards expansion, we have one example, the cosmological one. Why youn think this should be viewed with scepticism is another matter..........
But doesn't alter the fact that you can't answer the question, and the only one not making sense is yourself.
Let's take this one then, that by your own reasoning is allowed -- suppose the rate of expansion changes over the course of the journey for light. According to you, the changing recession speed of the source should still effect the redshift, even though the light has already left. Please explain how this marvellous non-local effect is achieved....................
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Post by Progenitor A on Nov 22, 2010 13:59:08 GMT 1
Well, given that the same theory which predicts that spacetime can expand also predicts that spacetime can contract............. As regards expansion, we have one example, the cosmological one. Why youn think this should be viewed with scepticism is another matter.......... But doesn't alter the fact that you can't answer the question, and the only one not making sense is yourself. Let's take this one then, that by your own reasoning is allowed -- suppose the rate of expansion changes over the course of the journey for light. According to you, the changing recession speed of the source should still effect the redshift, even though the light has already left. Please explain how this marvellous non-local effect is achieved.................... Well, if the 'rate of expansion' changes then in terms of recession, we have accelaration or deceleration of the distant object. If the object accelerates then , when the from light from the accelerating star reaches the oberver, the red shift will be changing to reflect the changing velocity.
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Post by alanseago on Nov 22, 2010 15:22:55 GMT 1
"Well, if the 'rate of expansion' changes then in terms of recession, we have accelaration or deceleration of the distant object. If the object accelerates then , when the from light from the accelerating star reaches the oberver, the red shift will be changing to reflect the changing velocity." This is the cretin who attacks other poster's English!
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