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Post by Progenitor A on Nov 30, 2010 18:23:31 GMT 1
The Mantra Speed of light = 3x 109 m/s! The dogma Speed of light is constant
Oddities 1. Black holes Light travels outward from a black hole at constant speed but doesn't get out! Why? Is it decelerated (to a lower speed)by the intense (infinte??) gravitational field? Or is its wavelength so stretched that we cannot see (or indeed measured)it?
But if its wavelength is so stretched by an (infinite?) gravitational field ,then what is its wavelength? Is it so long that we cannot measure it? Do we have em energy escaping at a really longwavelength, like at the LW of Radio Luxembourg?
Or is the light energy trapped by the intense gravity field?
(Of course if it is trapped it cannot be moving at a velocity of 3x109 m/s can it now?) [Don't worry, no-one (I think) has a clue when they are talking of black holes - all those infinities!]
Oddities 2. Expansion of the Universe Measurement of the universe show matter hurtling away from us at nearly the speed of light. Theory (naturally it cannot be other than theory) tells us that galaxies are hurtling away from us at 3c! Puzzled? Nah! Wheel on the mantra!
They are not hurtling away from us at >c, because (wait for it!) they are motionless and it is the space between them that is expanding!
But goodness me. velocity (of light) is defined as d(d)/d(t) (does anyone have another definition?), so even if it is expanding space then by that definition, galaxies are receding from one another at v > c!
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Post by speakertoanimals on Nov 30, 2010 19:11:37 GMT 1
What you have got wrong is in your assumption of what the speed of light of light MEANS. TO be precise, it means the speed measured by some observer sat right next to the light, NOT some distance divided by time being inferred by some distant observer.
Take the black hole. If light was emitted right at the event horizon, directed radially outwards, then it would hover there. So why does someone not measure this 'stopped light'? Because we can't hover just at the event horizon without using an infinite acceleration!
It is no more mysterious than saying -- if I travelled at light speed next to a light beam, then wouldn't that light be stationary relative to me (actually, one of the original concepts that led Einstein tio relativity, that a stationary but oscilatting em field made no sense!). Except tha answer is, no physical observer can be boosted to lightspeed, hence this measurement can never be made. For all observers at finite speed, they still measure the light as moving at c, even if I say that they are moving at 0.99999999.... of c.
Same goes for the hovering light at the event horizon of a balck hole -- anyone falling in, however hard they try to hover, will see the light as moving at c.
Its the same problem -- you think speed is just the derivative of distance, but whose distance and whose time?
The point about distant galaxies supposedly receeding at greater than c is that for all inertial frames IN THEIR VICINITY, they are always moving at less than c, and all light near then moves at c.
I don't know why you've started yet another thread trying to show that expanding spacfe is illogical, what was wrong with continuing the previous thread? Why repeat questions that have already been answered and explained?
It's your definition of speed and distance that is flawed. The meaning of distance is non-trivial in relativity, that is the point. Because what do we mean by distance? We mean the distance from one end of this rod to another AT THE SAME TIME. But since what 'at the same time' means depends on your state of motion (relativity of simultaneity), it is already getting complicated. I refer you again to the pole in the bran (Barn not bran!) thought experiment, you need to understand the basic in special relativity before trying to understand distance in general relativity.......................
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Post by Progenitor A on Nov 30, 2010 19:35:38 GMT 1
What you have got wrong is in your assumption of what the speed of light of light MEANS. TO be precise, it means the speed measured by some observer sat right next to the light, NOT some distance divided by time being inferred by some distant observer. Just how far does 'right next' extend to? One metre? 100m? 10 light years? Are you saying the speed of light changes the greater the distance that it is measure over? That is interesting indeed! Take the black hole. If light was emitted right at the event horizon, directed radially outwards, then it would hover there. My this is difficult! If light 'hovers' it has zero velocity! Same goes for the hovering light at the event horizon of a balck hole -- anyone falling in, however hard they try to hover, will see the light as moving at c. So goes the (unverifiable) mantra Its the same problem -- you think speed is just the derivative of distance, but whose distance and whose time? The distance over which c is meaured of course! The point about distant galaxies supposedly receeding at greater than c is that for all inertial frames IN THEIR VICINITY, they are always moving at less than c, and all light near then moves at c. Have there been experiments that verify this statement? Why repeat questions that have already been answered and explained? Simple. They have not. Except through teh repetition of dogma and mantra It's your definition of speed and distance that is flawed. Not my definition! Is there another one that someone has not told me about? The meaning of distance is non-trivial in relativity, that is the point. Because what do we mean by distance? We mean the distance from one end of this rod to another AT THE SAME TIME. No we do not - at least no I do not. I mean the distance travelled by a calibrated wheel traversing an element of space.
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Post by speakertoanimals on Nov 30, 2010 20:16:14 GMT 1
Sorry, if you keep using a kindergarten definition of velocity, then you'll keep getting daft answers (since most kindergartens aren't up to doing relativity).
'Close to' means in your inertial frame, and the point is that although in special relativity, an inertail frame can be extended across the universe, the same is not true in a curved spacetime.
Lets go back to the light hovering at the event horizon. How can you MEASURE its speed if you're not there? You can't SEE it can you? Hence the only way you can measure it's speed is by instruments in its vicinity -- so we could imagine a laser beam emitting light, a detector recording that the light was received, and a way of comparing times at the two places (when did the light start, and when was it detected), and a way of measuring the distance between the laser and the detector. Except the distance between them only makes sense if they are not moving relative to each other, hence we have to bolt them to a rigid frame. This is a bit difficult near a balck hole, since the tidal forces are so great that any frame we could build would be stretched (and since infinitely-strong materials are prohibited by relativity). Hence we have to take the limit of a very small frame, which is precisely the only local inertial frame of reference I referred to earlier.
The question about whether or notn this has been verified doesn't apply, since the objection you were trying to raise was that the theory itself was inconsistent or nonsensical, which is a DIFFERENT question to whether or not it is true, so lets stick to one question at a time shall we!
I never said relativity was easy! And you've still missed the point that relativity just concerns itself with what can be measured by observers -- which excludes the hovering light from being measured as hovering, just as it excludes the stationary light being measured as stationary by someone moving at lightspeed. There isn't a meaning to what is 'really' going on, as opposed to what is capable of being measured. Or rather, you can view relativity as its just all relative, and relativity tells us how to relate what can be measured by two different observers. So, as I said before, ANY two physical observers falling past the supposedly hovering light will always measure the speed of the light as c, and that is what relativity STATES, that all observers always MEASURE the speed of light as being c.
Asking what the speed of light 'really is' totally misses the point, because relativity says that such a thing has no meaning -- different observers measure different things (times, distances, and speeds), and have different opinions as to what occurred at the same time. Hence asking whether things really occured at the same time or not is daft -- the only question that can be assigned a unique answer is what events occured before others, that all agree on that when the events are causally related. No one will say that the window broke before the bullet was fired, hence all observers agree on the causal sequence of related events. Just as all observers agree that when they measure the speed of light, it comes out the same.
Except different observers disagree about distance! And don't forget, what you mean by the distance between the ends of a measuring rod implies that the measuring rod is stationary relative to you! Hence its that local inertial frame again. I have to have the measuring riod strapped to me as I fall through the event horizon, as I time how long the hovering light takes to pass from one end to the other.
Or that you mean the separation of the two ends measured at the SAME time (except again, what the same time means depends on your state of motion). So measuring a simple velcoity is far from simple
O stop being an arse! YOU were trying to imply that relativity AS A THEORY made no sense, which is a DIFFERENT question as to whether or not that is the way the real world works. If you meant, what is the experimental evidence to support relativity, that is a different question, and I'm still answering your implication that relativity as a physical theory makes no sense or gives contradictory answers. It's called moving the goalposts, a favourite tactic of various sorts of time wasters! Just replace 'will measure that' with 'it is predicted that they will measure that', and that does the job.
And please don't fall for the simple (and obvious) time-wasters trick of referring to current physical theories as dogma and mantra, when the very question you posed was in effect -- explain to me why the predictions of these theories aren't a pile of nonsense. You implied they were obvious nonsense, I can show they are not, calling it dogma just reduces to -- I can't understand the maths, hence when anyone tells me what the result of the maths is, I'll refuse to believe it, and just call it dogma.
I'm afraid you are very, very transparent, and your supposedly insurmountable problems are just the same ole questions answered on every physics and cosmology FAQ, the same questions that everyone who doesn't actually understand the theory comes up with -- just that most people aren't daft enough to assume that their inability to understand equates to a glaring problem with the theory.
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Post by mak2 on Nov 30, 2010 20:19:16 GMT 1
c is actually 300,000,000 m/s , that is, three times ten to the eighth metres per second.
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Post by speakertoanimals on Nov 30, 2010 20:23:39 GMT 1
If you can't even understand exponential notation (I think you'll find the speed of light is actually 3 x 10^8 ms^-1, approximately).
But what's an order of magnitude between disputants.............
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Post by Progenitor A on Nov 30, 2010 22:35:08 GMT 1
c is actually 300,000,000 m/s , that is, three times ten to the eighth metres per second. Thanks Mak, miscounted 3x10 8
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Post by Progenitor A on Dec 1, 2010 8:49:02 GMT 1
Sorry, if you keep using a kindergarten definition of velocity, then you'll keep getting daft answers (since most kindergartens aren't up to doing relativity). ;DKindergarten eh? I wonder what 'grown up' definition of velocity you work with? Oddly my fellow playground playmate 'ubble, uses the same definition of velocity as do I - he gives the rate of expansion of the universe as about 60 km/sec per million-light-years. Note that eh? 60km/sec per.....! ;D Lets go back to the light hovering at the event horizon. How can you MEASURE its speed if you're not there? What an odd statement. Cosmologists are continually measuring the speed of galaxies without 'being there' You can't SEE it can you? No we cannot see it. Because as you say it is 'hovering' -i.e stationary Hence the only way you can measure it's speed is by instruments in its vicinity -- so we could imagine a laser beam emitting light, a detector recording that the light was received, and a way of comparing times at the two places (when did the light start, and when was it detected), and a way of measuring the distance between the laser and the detector. Except the distance between them only makes sense if they are not moving relative to each other, hence we have to bolt them to a rigid frame. This is a bit difficult near a black hole, since the tidal forces are so great that any frame we could build would be stretched (and since infinitely-strong materials are prohibited by relativity). Hence we have to take the limit of a very small frame, which is precisely the only local inertial frame of reference I referred to earlier. You seem to be missing something. You have already told me that light is 'hovering' (stationary) at the event threshold. So I assume that you have done all this measurement stuff and confirmed what I have been saying! I never said relativity was easy! And you've still missed the point that relativity just concerns itself with what can be measured by observers This statement is arrant nonsense! Relativity was devised by Einstein as a purely intellectual exercise. Measurements simply confirm(or otherwise) his intellectual theory. relativity just concerns itself with what can be measured by observers-- which excludes the hovering light from being measured as hovering, Hmm.. you seem to be saying here that black holes fall outside the realm of relativity, but I am more inclined to think that you are getting a little mixed up There isn't a meaning to what is 'really' going on, as opposed to what is capable of being measured. What an astonishing statement! There is no real 'meaning' to relativity unless we are measuring something! So, as I said before, ANY two physical observers falling past the supposedly hovering light will always measure the speed of the light as c, and that is what relativity STATES, that all observers always MEASURE the speed of light as being c. I know what relativity states but you contradict relativity (and I agree with you) by saying that light is stationary at the event threshold Asking what the speed of light 'really is' totally misses the point, because relativity says that such a thing (the speed of light?) has no meaning So relativity is telling us that c=3x 10 8 has no meaning? Hahaha! Just as all observers agree that when they measure the speed of light, it comes out the same. But that speed of light has no meaning (see your quote above). How can something physical that has no meaning always be the same? O stop being an arse! YOU were trying to imply that relativity AS A THEORY made no sense, No relativity makes a lot of sense. I simply point out oddities that you cannot satisfactorily explain If you meant, what is the experimental evidence to support relativity, that is a different question That is not what I meant and I have not asked that question And please don't fall for the simple (and obvious) time-wasters trick of referring to current physical theories as dogma and mantra, You mistake me. What I am saying is that there is a great intellectual underpinning to the outstanding theories of physics (and also massive limitations in the applicability of those theories), but most people do not understand that intellectual underpinning (and ignore the limitations) That does not stop some from repeating the axioms of these great intellectual undertakings as though they are religious principles. That is dogma. The repetition of stock phrases without understanding. the simple (and obvious) time-wasters trick ... I must say that you do appear to have a lot of time to waste! The test of whether anyone is simply reciting a mantra is how they respond to apparent inconsistencies in these theories Quite when the very question you posed was in effect -- explain to me why the predictions of these theories aren't a pile of nonsense. You implied they were obvious nonsense, You inferred that I thought them nonsense. I have no such presumption Well, if you can show me, you have failed this time. Perhaps because you find difficulty in expressing yours science adequately in English - for example if something is 'hovering' - your phrase -then it is normally taken to be stationary. I'm afraid you are very, very transparent Why thank you very much. I do attempt to keep my English clear and understandable. I just wish that you had the same facility! Now consider this: We all agree, don't we, that light can be accelerated by gravity (Einstein predicted that and it has been verified) Deceleration is simply negative acceleration, so it is quite logical that light can be decelerated by gravity. Isn't it? Deceleration = slowing down!
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Post by carnyx on Dec 1, 2010 9:42:10 GMT 1
If light (i.e. em waves) can be slowed by gravity, then can it be accelerated by gravity? And magnetic fields, and electric fields?
And by transmission through media such as diamond to the tune of ~ 50%?
So over such huge distances of 'space' which is really full of 'stuff' such as all kinds of atoms, molecules, particles and fields of all types and strengths, inculding hydrogen which supposedly pops in and out of existence ....... won't the characteristics of light be changed ?
A question for STA ...... what extra 'something' would be needed to accound for 'red-shift'.. other than inflation?
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Post by speakertoanimals on Dec 7, 2010 14:03:30 GMT 1
Why don't you try paying attention occassionally, you might learn something?
Relativity predicts that in a certain coordinate frame, light will be stationary, hovering above eevent horizon. This is no more surprising than the statement that if I choose coordinates moving with a beam of light, that the light will be stationary with respect to those coordinates.
So, we have to distinguish between stationary in the sense above, and stationary in the sense that someone can measure it as being stationary -- ie that the system of coordinates you have chosen correspond to the possible reference frame of an observer.
Just as an observer can't travel at lightpseed and hence 'see' light as stationary, so an observer can't hover above the event horizon and see the hovering light as stationary.
And you don't seem to have any interest at all in the actual physics of relativity (NOT just an intellectual exercise, Einstein, whatever else he was, was interested in doing PHYSICS), just playing silly, childish word-games. Or perhaps you really are as daft as you make out...................
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Post by Progenitor A on Dec 7, 2010 14:25:13 GMT 1
Why don't you try paying attention occassionally, you might learn something? Relativity predicts that in a certain coordinate frame, light will be stationary, hovering above eevent horizon. This is no more surprising than the statement that if I choose coordinates moving with a beam of light, that the light will be stationary with respect to those coordinates. So, we have to distinguish between stationary in the sense above, and stationary in the sense that someone can measure it as being stationary -- ie that the system of coordinates you have chosen correspond to the possible reference frame of an observer. Just as an observer can't travel at lightpseed and hence 'see' light as stationary, so an observer can't hover above the event horizon and see the hovering light as stationary. ;D Gobbledygook corner here I am afraid If you really do understand physics you must find it terribly frustrating not being able to communicate it! And you don't seem to have any interest at all in the actual physics of relativity (NOT just an intellectual exercise, Einstein, whatever else he was, was interested in doing PHYSICS), just playing silly, childish word-games. Or perhaps you really are as daft as you make out................... Go on..go on...go on go.o..o...o...o..n, go-ongo-ongo-ongo-on, vent that frustration!
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Post by speakertoanimals on Dec 7, 2010 14:36:45 GMT 1
The evidence seems to show that he really is as daft as he pretends to be.
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Post by carnyx on Dec 9, 2010 15:36:20 GMT 1
A set of dim questions to do with the relationship between frequency and speed of propagation.
- If light is slowed down by gravity, will the frequency change?
- can light be accelerated by gravity? and so does the frequency change?
Does the frequency of light change when it passes through , say, a diamond, which will slow the speed of light by around 40%?
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Post by Progenitor A on Dec 9, 2010 17:47:21 GMT 1
A set of dim questions to do with the relationship between frequency and speed of propagation. - If light is slowed down by gravity, will the frequency change? - can light be accelerated by gravity? and so does the frequency change? Does the frequency of light change when it passes through , say, a diamond, which will slow the speed of light by around 40%? Interesting Lets see STA on this one. I have never seen her doing sums in physics and indeed I believe that she is incapable Oh the answer to your second question is yes, light is accelerated by gravity I will leave it to STA to answer the frequency change part
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Post by speakertoanimals on Dec 9, 2010 18:37:29 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.
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