Just a quick question about invariance of light: We assume the following as far as I know but maybe there are other qualities that are invariant as well. 1) velocity 2) Temperature 3) Intensity 4) Direction? Are there any other or have I got some wrong? Care to discuss?
David F- A question regarding #4. What do you use to base your staement on? Also, have you any indoermation regarding the motion of a light beam emitted transvese to the direction of the moving frame?
Invariance is only a mathematical term for a quantity that does not change under a transform. The point to realise is that the Lorentz-Fitzgerald transform is an equation that acts on sets of numbers. Only speed is known to be invariant. There is no reason to suspect that the laws of physics are different elsewhere in the Universe. Granted that is an assumption but wierd things happen if it was not true. There have been claims that solar eclipses effect pendulums behaviour but I've never heard of light slowing down. Care to expand on this?
I caution you on the use of your words. It seems that by this statement you have redefined "invariance" soley for the possessin and ownership of SR. Einstein used the word in a physical sense when discussing the attributes of light motion. I use the term in a nonSR context and so do others. SR ain't the author of scientific dictionaries. When you say that, " Only speed is known to be invariant.", who is this known by and how do they know it? Is it known from the unambiguous results of experiment, or is it known by assumption? Your statements ae generally, statements of conclusion and in a scientiic doscussion it is dofficult to maintaibn coherence. I suspect that you have never has a period of time when you analyzed the attributes of the universe through any but the rose tainted glasses of SR. If, as you say, only speed is "invaiant" are you telling us that SR predicts variance in he temerature, direction and intensity? I understand the use of the word related relative to the law of inertia, which does not prevent any variations, including speed. The law of inertia is a statement defining a state of equilibrium of matter at rest, or moving in a uniform motion. The law merely states that the object will not vary of its own internal spontaneous attributes. You are saying soemthing different from the law of inertia, not necessarily contradictory, or even erroneous, you are saying thgt no outside force can vary the speed of light. This is what I understand you are saying. If you are correct then, when the light direction is varied the speed remains constant, no matter how drastic the direction turning rate the speed is invariant. This also says to me that a reflected beam from a mirror surface undergoes an inon-zero delta T in changeof direction process that does not vary the speed. Why do I conclude thus? Mother Nature told me that no local activity occurs instantaneously, where local is meant to include all observable activity, nonlocal activity means all other activity essential to the exitence of he object under scrutiny, but is not observable directly, i.e.the nonlocal activithy is determined by inference only. Are you telling us that there is no break in the speed of the light in the time span between the forward and reflected direction of the light? You are probably correct here, but, when one asssmes their understanding of the laws of physics are the laws of the universe, any apparent anomoly gets interpreted as a unique phenomenon , when the observation may simply be the manifestation of signalling an error in the assumptions inherent in the structure of the theory exprssing the "law'". My research into the 1919 exclipse experiments do not indicate any variation in the direction of the motion of light, for any physical reason, Newtionian or SR. This means only that the particular experimental arrangements did not provide suffcient resolution of the measurements that would provide a result with any reasonable level of confidence.
As I said, it is a mathematical term relating to transforms. Mostly used in set theories. In the context of the OP the use of speed only being invariant was quite obvious. As other properties (of light) are not addressed by the transforms it is a moot point. I'll remind you of your admonishment to mind what you are saying. You might be very surprised. No prizes for guessing what my degree is in though. I neither said nor implied any such thing, as I am sure you know. As we are being picky about wordage; Light has no temperature, energy yes, no temperature. SR has nothing to say about temperature. That is a thermodynamic property. What do you mean by 'direction'? That is a very loose term to use in this context. In GR the metric is a straight line in 4D, in SR the modulus of the 4-vector is invariant. That is, the 'direction' is not invariant in all possible cases, especially our 3 dimensional world. Intensity is also not addressed by SR as that is another physical property. You appear to be trying to trip me up by implying other properties are invariant/not invariant. If so, then you are misunderstanding/deliberately misconstruing what invariant means. This has nothing to do with invariance. Nope, didn't even imply that, within the context of the invariance of light speed. Invariance has a very specific meaning in SR. Though it is true that no outside force can vary light speed. Not to say that light speed does not vary due to differing mediums, say. None of which implies a failure of invariance.
Thed, Thank you for clarifying the SR position on invariance [as per your understanding] In reference to my original question I could be said to be correct if I state that lights "brightness" is also invariant under a more common and less specific definition of the word "invariant". "no matter what velocity you are traveling brightness is the same for all observers at a given space time-co-ordinate." The reason I have raised this issue is that I am attempting to dtermine whether bightness can be used to determine distance. I woudl intuitively think that this is the case. And if brightness is a valid "yard stick" then velocity or speed of light is no longer an issue when attempting to find an absolute time reference. fro ships in flight at relativistic speeds. [light clocks]
” My research into the 1919 exclipse experiments do not indicate any variation in the direction of the motion of light, for any physical reason, Newtionian or SR. This means only that the particular experimental arrangements did not provide suffcient resolution of the measurements that would provide a result with any reasonable level of confidence. I understand. Your use of the terms "speed" and "variance" are confined to the nonphysical world of mahematics So, if other properties of light are not addressesd by the transforms then mathematical analysis ignores any contribution of any attributes of light to the speed of light. I could care less what your degrees are in. I was asking you a question. The mass of a photon has no temperature? Oh, yes, in SR photons/light have no mass. Newtonian physics assigns temperature to the speed of particles and also equates speed and temperature, with the proper constants of proportionality. Then photons located in the mass center of a nuclear blast have the same temperaure as the light coming from the neon tube over head? You are saying here that SR is niot equipped to scrutinize the internal attributes of light itself and is concerned only with speed. This I understand from you. Do I understand you correctly? In the context of light moving in free space direction is the arrow of the light trajectory. As SR is concerned with speed only, as you say, then is a change of direction of the light, absent the intrusion of an ouside force, outside with respect to the "volume geomentry" of the light, permissible? Again, this is another question. No, you are just overly sensitive. I am enquiring about the descriptive limits of SR. If the challenge to SR, as you see it, is taken as an attempt to trick you, then so what? I could care less what your reaction is to being tricked, as you perceive the exchanges here. I am scrutinizing SR through you , the lens. I was also infoirming you that the word, invariance, is used by others in contexts external to SR. You do see , do you not that there are other uses of he word "variance'? Light speed varies in different media? I was under the impression that it was the medium that absorbed and reradiated light that produced the illusion of a mediated light speed that is attributable to the delay in reradiation process. You are saying then that in the processes of the reflection of light SR must be discarded as a model in determining the attributes of motion of he light? Likewise, I read from your statement, which needs some intellectual tuning up, that in the study of all the dynamics of the interaction of light and external media, even light external to a "known" beam of light, that SR is useless. The reflection of light implies the reflection of light. tautologically speaking. Why do I conclude thus? Mother Nature told me that no local activity occurs instantaneously, where local is meant to include all observable activity, nonlocal activity means all other activity essential to the exitence of the object under scrutiny, but is not observable directly, i.e.the nonlocal activity is determined by inference. . It would be much simpler for the sake of the discussion that you find an exception. to the claim. I will even accept as an answer your claim that processes are instantaneous. That nonlocal activity may be instantaneous in the nonlocal force world and inferred from observation, the processes in which the nonlocal activity is inferred is certainly not instantaneous We were discussiing the speed iof light in the context of SR. I did not infer, nor state, imply or deduce, surmise or assume, hint nor think, that the laws of physics weren't universal. The statement I made was: "You are probably correct here, but, when one asssmes their understanding of the laws of physics are the laws of the universe, any apparent anomoly gets interpreted as a unique phenomenon , when the observation may simply be the manifestation of signalling an error in the assumptions inherent in the structure of the theory expressing the "law'". Lethe's statement that the Eddington experiment was "not highly accurate" should have been stated as the "experiment was highly inaccurate". I have head of light varying over time, as measured. You haven't heard about this?
Geist, I also have heard that 'c' has been slowly getting smaller in value over the last 100 years or so, but the reduction is so small that it could be simly be attributed to the methods used in the measuring. But if we assume the observation is correct and light speed is slowing, in space time terms this is rather an interesting development. The only way I can account for it is that the furture and past is balancing out. Which you will probably think is a ludicrous suggestion.....
Brightness cn be used as a measure of distance, but it ha nothing to do with Relativity. Astronomers routinely use Absolute (total intensity of light emitted from a star) and Relative (intensity measured on Earth) magnitudes to determine distance. This works as intensity drops as an inverse squre law. Short answer, not at all. Intensity of light does not work around Relativity. Long answer, Geistkiesel raised a point about this in another thread I want to address. First I need to get my kids out for dancing lessons. Then tackle the very mundane tasks of putting in new skirting boards, architraves and dado rails in my dining room. When finished I have a load of shelves to put up, then I need to configure a LDAP server/get DNS working at home. Could be rather busy here today.
That statement is false, as far as I can tell. The only meaningful quantifications that I can think of for "brightness" all come down to an energy-time relationship, and neither energy nor time are invariant under transforms in Einstein's relativity.
'tis interesting that brightness is quaified by time.....over time.....hmmmmmm....I am sure relativity doesn't deem brightness to be invariant yet it deemes the source of the brightness to be so.... maybe from a philosophical perspective relativity uses absolute time as a reference to determining dilated times...I see no problem with that.... how can you calculate dilations with out absolute reference even if it is generally earth time used?
for example the v=c is always used and this is an implied absolute time reference. 1 second = 299792kms..of light travel. Is this not a universal constant of earth time?
