Tim88

Emphasis mine: Obviously that's a contradiction: at best one can be right (except of course that they can be both right about their experience; but I doubt that you mean that). I agree with your reasoning (and so do many others); however the point of SR is that we cannot determine which one.

Readily available indeed - did you notice from where you linked that paper?

OOPS I wasn't co-mingling anything and we had a mutual misunderstanding about Doppler, but you are right that I overlooked the main reason why there is no Doppler effect involved in MMX. As a matter of fact, MMX doesn't even compare the frequency of the emitter with the frequency of the detector.

Nonsense - what matters is the velocity at time of emission compared with the velocity at time of detection, and in case of acceleration there IS relative motion between those events. As a matter of fact, GR originated from a study of the Doppler effect from acceleration. But in MMX acceleration is negligible; during a measurement the velocity is assumed to be constant.

It may be useful to clarify the other answers. Basically, the Doppler effect is the change in frequency of a wave for a detector that is moving relative to the source - see for example https://en.wikipedia.org/wiki/Doppler_effect Addendum: that article ignores acceleration effects - a Doppler effect can be produced when the system as a whole accelerates. In MMX, source and detector are at rest with respect to each other; effects of acceleration are assumed to be negligible. MMX has therefore no significant Doppler effect; your statement here above is fundamentally wrong. Note that you can of course apply Doppler calculations for theoretical analysis, for example by calculating the frequency in the solar rest frame upon light emission, and then again back to the instrument's rest frame upon detection (I don't know if you did, as the link doesn't work for me). A correct calculation must result in zero frequency shift, as the second transformation is the inverse of the first. That's the most basic consideration of Doppler: no wave cycles crests are created or destroyed "in flight".

That won't work; I have the impression that you forgot about the "classical" Doppler effect. - https://en.wikipedia.org/wiki/Doppler_effect What is done in practice, is assuming that the redshift is fully due to velocity, and the velocity is estimated from characteristic emission wavelengths in the spectrum.

To add to mistermack's reply: usually daylight is relatively strong, and people are only interested to switch off the LED light when the room is well lit by the Sun. It may be good enough to detect on the outside of the LED lamp, with the sensor area on the outside, if the environmental light strength is above a certain threshold.

As others already mentioned, there is not Doppler effect involved in MMX. MMX type experiments did not support the ether theory of that time, which was an inconsistent mixture of Maxwell's theory and Newton's mechanics. Inversely MMX type experiments cannot tell us that an ether does not exist - compare https://en.wikipedia.org/wiki/Affirming_the_consequent . Note that this fallacy of the converse is often encountered, even in scientific discussions.

The delayed choice quantum eraser merely makes a selection of received information; there is no reason to assume "reverse causality".

That still looks not quite ok, I think that something went wrong there: for the Earth's radius isn't 279-275=4 miles...

That's fine, you are receiving many replies and it's not always clear which are real answers. If you like, I can scan and send you an old paper in which this was done.

First of all, their translation may make you read something in there that wasn't intended. The German word "bestimmten" merely means "certain" or "definite", as also so translated here: http://fourmilab.ch/etexts/einstein/specrel/www/ (in the intro) Further, as you can also see in the intro of Einstein's paper, that whole phrase is the second postulate; it simply characterizes light as a wave. A wave has a certain or constant speed c, as it is independent of the speed of the source. Nevertheless you are right that the "speed of light" as defined in SR, following Einstein's lead, is a "determined" speed based on a measurement convention - as specified in §1. And according to the theory, even accurate clocks cannot help to change that.

No, it's not a feature in Maxwell's equations. The fact of the matter is that he had not done what I mentioned in post #21. Instead, he expected a positive result of MMX type measurements (he originally proposed such a measurement). PS: the very neat video to which Strange linked, shows how the speed of light as a *wave speed constant* "jumps out" of the Maxwell equations. Thus a disambiguation may be at its place here... You emphasized that you are not asking here about the constancy of the speed of light (as in the second postulate), but about the invariance (as in the first postulate).

p.43 is not visible for me in your link. Anyway, it has been shown that if you assume the validity of Maxwell's equations for a single reference system as well as the validity of the conservation laws (energy, momentum), the relativity principle follows - which implies invariance and limit speed.

Yes, exactly! PS. did you notice that, apparently, for saying exactly the same things in perfect agreement, some forum participant gave me -1 point of appreciation and you +1 point? ... and I bet that that same individual will want to give me -2 points for exposing it!

It's a big mistake to confound science (a discipline) with scientific circles (groups of people who are subject to all kinds of pressures, including highly unscientific ones); it's even an important topic of discussion. My estimation that Tesla is not underrated in scientific circles is therefore a matter of opinion but it's not superfluous. Apart of the shaky theoretical basis, the claim that Tesla's inventions allow free, unlimited energy is extremely doubtful to me for the simple reason that no "allowance of the system" is required for a few electrical engineers to build such a magical machine. It's a hilarious conspiracy theory. Wikipedia labels him as an inventor, engineer and physicist. Tesla had a similar education as Einstein (polytechnic university in Austria + university in Czechoslovakia, vs one in Switzerland) but due to personal (gambling!) issues he never graduated.

A nice and perhaps fair overview is given in Wikipedia: https://en.wikipedia.org/wiki/Nikola_Tesla He is probably overrated in crank circles; I don't think that he is underrated in scientific circles. The fact that magnetic fields are measured in his name shows appropriate appreciation.

Good. Newton and Tesla were cranks you say? Hmm, maybe - but how poor science would have been without them!

Hi Madmac probably you arrived when I took an extended holiday. That issue was elaborated in the following threads: http://www.scienceforums.net/topic/97105-is-space-time-a-physical-entity-or-a-mathematical-model/page-11#entry943184 http://www.scienceforums.net/topic/98845-models-for-making-sense-of-relativity-physical-space-vs-physical-spacetime/ In a nutshell, the experimental support for theory (SR, GR, QM) apparently obliges us to accept that Space is not merely a mathematical concept that relates to nothingness. But what is it made of? I'm afraid that the definite answer to that question may always be beyond our reach. Currently, the only thing we can do is to invent models. A promising looking route was that of unifying field theories, but as far as I know, a well developed and satisfying theory is still wanting (although there are some around that seem to have potential).

While the phrasing there could be better, I disagree that the physics FAQ there is "very poorly phrased". This concerns a fundamental point of SR, directly related with the topic at hand. The simultaneity convention is just that, a convention. Choose another convention and you "make" the speed of light anisotropic in your rest frame. You do not need to assume the light speed to be isotropic wrt your system of reference; it's merely convenient to do so. Therefore, Einstein rephrased the second postulate as follows in 1907 (emphasis mine): "We [...] assume that the clocks can be adjusted in such a way that the propagation velocity of every light ray in vacuum - measured by means of these clocks - becomes everywhere equal to a universal constant c, provided that the coordinate system is not accelerated." - http://www.soso.ch/wissen/hist/SRT/E-1907.pdf

With emphasis mine: Not just "mainstream" but a simple fact: experiments that clearly use a one-way light path and find isotropy are inherently unable to rule out a large class of theories in which the one-way speed of light is anisotropic - http://math.ucr.edu/home/baez/physics/Relativity/SR/experiments.html#one-way_tests ( Yes I'm back ) While that may be true, it's up to us to demonstrate that by means of scientific arguments. Mud throwing is particularly unscientific. PS I read: "In 2010 the Telesio - Galilei Academy of Science awarded Professor Reg Cahill a Gold Medal for the development of Process Physics. The ceremony was held at the University of Pecs, Hungary." - http://www.flinders.edu.au/science_engineering/caps/staff-postgrads/info/cahill-r/process-physics/ Not bad for a "crank"!

Of course not - do you proclaim a theory that disproves Einstein's field theory? If so, please present it. Right. However, it's it's not an entity but a property. Would you similarly reason that if elasticity is a real property, that the entity to which you ascribe that property must be real as well? In other words, that it may be called, as the OP phrased it, a "physical entity"? Thus: Elasticity is a property, it's not an entity and therefore it cannot be a "thing". However I agree with you that if something has a real property in the sense that it can affect physical measurements, then it's normal to call that something a physical entity.

That's right; how would you define reality? I'm not a dictionary. In the end, words are defined by their usage and context. And what do those "fields" consist of? Are those fields just made of mathematics, merely imaginations of our minds, or are they something substantial of nature according to you? And where did I misquote any post of yours?? Anyway, it's a huge misconception to call Lorentz Ether a "mathematical model". Except if it's a mis-definition of the word "mathematical". Maybe you call radio waves and air molecules "mathematical models"?? Exactly! Not sure if it is what you meant, but physical realty doesn't depend on our mathematical approximations. You mean, a (meta)physical entity such as an ether? Einstein tried to get rid of that concept by means of Mach's principle, but that didn't work as he explained. Others replaced "ether" by other words such as "fields" and "the vacuum", which are conceptually slightly different; but mere empty nothingness fails to explain inertia and related things such as clock retardation. Maybe you have an idea? No, mathematical models are not metaphysics in my book.

Don't you know Polaroid sunglasses? They mostly absorb the light that is blocked.

I find the drawings a bit difficult to read, but it looks to me that the mirror is placed somewhat next to the channel rays. Alternatively it could be a mirror with a hole to let the rays through. Essential is to understand, once more (both Swanson T and I mentioned this) that the channel rays are hydrogen ions. They emit light in all directions. These ions are treated as microscopic clocks, as they emit light at precise frequencies (wavelengths). It's the light from the moving ions that is measured, and it's necessary to let them pass the mirror so that one can reflect the backward sent light forward. For spectroscopy, see: https://en.wikipedia.org/wiki/Spectrometer#Optical_spectrometer and the link from there: https://en.wikipedia.org/wiki/Diffraction_grating