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dwellexity
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Do we have any understanding as to why em waves have same speed in all inertial frames?
If we did, would you want a theory to explain that theory?dwellexity said:don't we have any separate theory to explain this postulate?
dwellexity said:Do we have any understanding as to why em waves have same speed in all inertial frames?
Historically this was Maxwell's theory of electromagnetism from which unique and invariant c follows. But today we understand this theory as one field theory build on top of SR and therefore being Lorentz covariant by construction.dwellexity said:yes, i know that but what i am asking is that now this postulate has been confirmed by experiments, so don't we have any separate theory to explain this postulate?
dwellexity said:now this postulate has been confirmed by experiments
Here you confound two different things; perhaps this is due to even some textbooks confounding them.dwellexity said:Do we have any understanding as to why em waves have same speed in all inertial frames?
He certainly knew Poincare's "La Science et l'hypothèse" of 1902 which he appears to paraphrase there. In that book Michelson's experiment is not mentioned by name, as far as I can see; however the theoretical consequences of that type of experiments that failed to determine the motion of the Earth are discussed in detail. And in particular he mentions Fitzgerald's hypothesis, which as we know related to Michelson-Morley.vanhees71 said:[..] in the next sentence he says:
"Examples like this, and the failed attempts to measure the motion of the Earth relative to the "light medium", lead to the conjecture that there are no phenomena related to the notion of absolute rest not only applies to mechanical but also to electromagnetic phenomena." (highlighting mine)
Unfortunately Einstein doesn't give a reference (BTW there are no references at all in that whole paper!) for such attempts to measure the relative motion to the ether. So we cannot say with certainty which "failed experiments" he had in mind.
His study by means of Lorentz's papers was archived in an exposition in Bern: his teacher could not find a good textbook that included the latest developments, therefore he told Einstein to use Lorentz's papers instead. His reading and discussing of Poincare's work is mentioned by Pais ("Subtle is the Lord"), based on the declarations of one of the members of the Olympia Academy. See also http://en.wikipedia.org/wiki/Olympia_Academyvanhees71 said:Yes, as far as I remember right, reading Einstein's contribution to Schilpp's "Einstein, philosopher scientist" book, he mentions that he studied Lorentz. I'm not sure whether he mentioned Poincare. I have to get this book again and check.
vanhees71 said:Unfortunately Einstein doesn't give a reference (BTW there are no references at all in that whole paper!) for such attempts to measure the relative motion to the ether. So we cannot say with certainty which "failed experiments" he had in mind.
dwellexity said:yes, i know that but what i am asking is that now this postulate has been confirmed by experiments, so don't we have any separate theory to explain this postulate?
Please explain how the principle of relativity and/or causality are broken by Newton's mechanics.nix00 said:In fact, we have a theory to explain this postulate, special relativity simply. The second postulate of Einstein for special relativity is a natural consequence of the others postulates (principle of relativity and causality) when considering an homogeneous and isotropic space-time : it can be shown that under these assumptions, a speed limit exists and is generally taken as c the speed of light in vacuum. I just know a book in French which shows it "relativité restreinte ; bases et applications ; cours et exercices corrigés (2e édition) Bernard Semay, Claude Silvestre-Brac".
You talk about Maxwell's equations. Maxwell's theory is wave theory and as such it includes the second postulate as basic assumption; together with the PoR that leads to c as the limit speed. With only the PoR and causality, Newton's mechanics and ballistic light theory do not predict a limit speed. As this is definitely off topic here, I won't say more; there have been threads that explain that issue in more detail.nix00 said:they are not broken, they are considered also in Newton's mechanics, in a weak form.
The fact is that when you consider Newton's equations, in an absolute referential, they are invariant under the Galilean transformations, which is fine. But Maxwell's equations are invariant under Poincare transformations, from which the Galilean ones are a limit case, when you consider small velocities. [..].
That looks fine to me, as you now included the words "wave" and "Maxwell".nix00 said:I am not sure to understand your point harrylin.
I was trying to answer the question by saying that naturally in an homogeneous and isotropic space-time, under the principles, it exists a maximal speed, and you get the Poincare transformations which relate two inertial frames, moving in an uniform and linear way with respect to each other.
Maxwell's equations which define the propagation of an electromagnetic wave [..] yes it was a postulate, but it can be explained by special relativity. [..]
It's this contradiction between Newton and Maxwell's laws and their laws of transformation (symmetry) which leads people as Einstein and Poincare to think about special relativity, which explains again, why the speed of light can be constant in each referential.
I disagree with this as stated. The speed of light is a result of Maxwells equations, not an assumption. You seem to like historical accounts so I would think that would be clear to you from Hertz's work.harrylin said:Maxwell's theory is wave theory and as such it includes the second postulate as basic assumption
Yes of course! [edit:] although... do you claim that Maxwell's theory that his equations apply to EM first of all, and even to light, was not an assumption?? But no need to answer, as this phrasing issue has nothing to do with the topic.DaleSpam said:I disagree with this as stated. The speed of light is a result of Maxwells equations, not an assumption. [..]
The speed of electromagnetic waves, also known as the speed of light, is approximately 299,792,458 meters per second in a vacuum.
The speed of electromagnetic waves is constant because it is a fundamental property of the universe. According to Einstein's theory of relativity, the speed of light is the maximum speed at which all energy, matter, and information can travel.
The speed of electromagnetic waves is directly proportional to frequency and inversely proportional to wavelength. This means that as the frequency increases, the wavelength decreases, and vice versa.
No, the speed of electromagnetic waves is constant and cannot be altered. It is a fundamental constant of the universe and is not affected by external factors such as medium or observer velocity.
The speed of electromagnetic waves changes when traveling through different mediums, such as air, water, or glass. This is due to the interaction of the waves with the particles in the medium, which can slow down or speed up the waves. However, in a vacuum, the speed of electromagnetic waves remains constant.