The Speed Of Light

Davini994 · 266906. Mon Jan 28, 2008 1:42 pm

Hi Hugo, if you go to http://imageshack.us/ you don't have to enter an email address so I think you are pretty safe:)

I'm intrigued to see this theory, sounds QI:)

Hugo Rune · 266970. Mon Jan 28, 2008 3:08 pm

Hugo Rune · 266974. Mon Jan 28, 2008 3:15 pm

[First published in ELECTRONICS WORLD September 2000, by Al Kelly]

SPECIAL RELATIVITY – right or wrong?

In telecomms, synchronising clocks around the Earth is an important issue. Al Kelly believes that the correction applied to such clocks is not explained properly by existing theories because they rely on the notion that light has a constant velocity.

Light travels around the Earth faster eastward than westward. Does not the Special Theory of Relativity claim that the speed of light is a constant?
The standard answer to this conundrum is that the Special Relativity applies solely to uniform straight line motion. It is claimed that, no matter how big the circle, motion along its periphery cannot be said to approach straight line motion. This is said to be so even if the best measuring instruments devised cannot pick up the divergence from straight line motion over the portion of circumference being used.
In his paper launching the theory in 1905, having applied his theory to straight line motion, Einstein then applied it to a closed curve of any shape. This rather undermines the popular explanation!
The circuit does not have to be as large as the cross section of the Earth to detect this effect. A Frenchman, Sagnac, found in 1914 that light signals go around a disc of 1m diameter faster against the spin of the disc than in the direction of spin, Fig. 1.

By a measurement made solely upon the spinning disc, he recorded the difference in time of the signals sent in the opposing directions. As shown in the diagram, the time for the signal to traverse from the light source at A via C-D-E-F-C is less than the time in the opposite direction A-C-F-E-D-C.
The light source was fixed to the spinning disc; the measurement of the time difference was at an interferometer at C also fixed to the spinning disc. Sagnac produced a formula that exactly matches the difference in the times taken in opposing directions.
This formula can be derived, by assuming that the light travels in relation to the fixed laboratory. But, the measurement of the time difference is done solely aboard the spinning disc. What can this mean? The only explanation possible is that the time aboard the spinning disc and in the fixed laboratory is the very same. This is not in accord with Special Relativity.
Another defence of Relativity theory is the claim that the light path upon the disc is longer in one direction than the other. But, the circumference of the disc, as measured by someone upon it, is surely the very same in both directions.
In a test in which signals are sent around the Earth from a fixed position, the light signal is emitted upon the spinning Earth, and the record of the time difference taken by the opposing light paths is solely upon the Earth. To claim, in this case, that the circumferential distances east and west are different is bizarre.
A test done in 1926, by Michelson & Gale, first showed that the speed of light was not the same eastward and westward around the Earth. They constructed a rectangular circuit of over a mile in periphery. This was a Sagnac test on a disc of diameter 9 500 000m diameter - the diameter of the Earth at that latitude.
In the case of the Earth at the equator, the difference between the times taken in opposing directions is 414.8ns. This result is enormous when considered against the accuracy – one million times better than that – required today of standard clock stations. The difference between the times going northward and southward around the globe is zero.

The International Telecommunications Union (ITU) sets the rules for synchronising clock stations. A signal sent eastward around the globe has to allow for the fact that it travels at the speed of light c plus the rotational speed of the Earth at that latitude v, giving c+v.
A signal sent westward has to allow for the fact that the speed of the signal is c–v. According to Special Relativity the speed of light is a constant. Not only that, but the direction is not supposed to matter to Special Relativity; going east, west or north should have the very same speed.

As shown in Fig. 2, a ground clock station at A is to be synchronised with a ground station at B, via a satellite S. The signal sent from A to B travelling in the same direction as the spin of the Earth takes more time than in the reverse direction.

A third defence that is used is that the c+v and c–v are only average figures and that the instantaneous velocity of the light signal is always equal to c. On a perfectly circular circuit the c+v in one direction is the velocity that would be measured at a million spots on the circumference; how then can the average become c?
Take v as 250 000km/s. In a million measurements the speed of the signal is 550 000km/s while the claim is that the instantaneous speed is 300 000km/s. Bunkum.
The ITU apply the necessary correction and call it ‘a relativistic correction for the rotation of the Earth’. But it is not a relativistic correction. A person at a fixed position sends signals eastward and westward around the globe. There is no relative motion concerned. How then is it that the signals arrive back at different times?
There is only one sensible explanation. The signals are travelling at different speeds around the globe. Taking the speeds to be cv in the opposing directions agrees exactly with the experimental result.
A test was done in 1976 in which an atomic clock was transported on a aeroplane from Washington (USA) to Tokyo. Also, a signal was sent between the two clock-stations. A correction had to be applied to the signal exactly as described above, while the transported clock needed no correction.
Despite this, the ITU claims that a correction of 207.4 nanoseconds has to be applied to the time on a clock brought around the Earth at zero height and very slowly; these stipulations ensure that there can be no correction due to General Relativity (height over sea level) or to Special Relativity (speed). This correction is nonsense.

The President of the organisation in Paris which oversees these rules wrote to the author
‘you are right stating that the Sagnac effect is not relativistic’.
That is an honest answer.

For the sending of signals from one site to another, their rules work fine. Saying the correction is ‘relativistic’ is a misnomer. The rules are wrong in the case of physical transportation of a clock from one site to another, but that is very rarely done, and can conveniently be overlooked.
There is also a correction applied to the clocks that ride on a satellite, to keep them in synchronisation with clocks on the ground. This is also supposed to be a relativistic correction. But, there is virtually no relative motion between the satellite clock and the ground station; the only relative motion is caused by the slight variation in the orbit of the satellite from an ideal orbit.
The correction applied is huge; it can amount to as much as 7500ns per day in a typical case; the clock is preset to alter by this amount each day, so that it will keep the same time as the clock fixed to the ground. It is calculated from the absolute velocity of the satellite compared with the absolute velocity of the ground station clock, in relation to the centre of the Earth, as it orbits around the Sun.
This correction is due to this absolute velocity, and not to the relative velocities of the satellite clock and the ground clock.

A very simple assumption would fit all of these necessary corrections. If we assume that the signals travel with the Earth, on its orbit around the Sun, but do not adapt to the daily spin of the Earth, this fits the facts. In this case, the absolute velocity of the satellite versus the ground station accounts for the correction applied to the satellite clock; the c+v of the signals sent around the Earth is explained simply by the spin of the Earth affecting the speed of the signal.
What could cause the signals to behave in this fashion? If light and gravity went together, on the Earth’s orbit around the Sun, then the result would be fully explained.
We must then take it that the Special Theory of Relativity is not correct and that time and space are absolute, not relative. The speed of light is no longer sacrosanct.
But, what about the many many experiments that fit Relativity theory? A thousand things may fit a theory but, if one fact does not, the theory fails. In the words of Huxley ‘the great tragedy of science – the slaying of a beautiful hypothesis by an ugly fact’.

Davini994 · 267190. Mon Jan 28, 2008 9:58 pm

Blimey, that's a long post. I'll answer it as simply as I can, which isn't very simply.

The claim is for The Ballstic Theory, which is simply that the speed of light observed is the speed of the emitter + c.

The basis for this relates to a misunderstanding of something called the Sagnac effect, which is very interesting. It's interesting because it's a situation where the ballistic theory and special relativistic results coincide.

The reason for this is none of the straw man arguments put forward in the article, but something odder on first glance: in the SR consideration, the different elements of the apparatus are not fixed relative to each other.

This is because the motion is not inertial, as the various points are accelerating in order to rotate. If one mirror on the rim is traveling at v in one direction, the mirror opposite is traveling at v in the opposite direction. i.e. a total classical relative velocity of v; but you then need to factor in length contraction. This creates anisotropy in the two different paths, which, in the same way as with the twin paradox, results in different transit times for the light on each path.

If you calculate this difference, it comes out identical to the classical method.

There's a lot more detail on these pages if you are interested enough:

http://www.mathpages.com/rr/s2-07/2-07.htm
(classical derivation then SR derivation, followed by notes)
http://renshaw.teleinc.com/papers/fizeau/fizeau.stm
(everything on everything to do with doubts about SR,; see (12))

It is true that the time difference measured is nonrelativistic, but this is because...

KieronCreagh · 267725. Tue Jan 29, 2008 6:21 pm

So it is possible to Travel faster than the speed of light relative to an observer travelling in the opposite direction?

Davini994 · 267763. Tue Jan 29, 2008 7:10 pm

...

[double post]

Davini994 · 267766. Tue Jan 29, 2008 7:12 pm

Depends what you mean. But no.

You can measure A to be traveling at say 0.9c in one direction, and B to be traveling at 0.9c in the other; but A won't measure B's speed to be 1.8, you have to use relativistic velocity addition.

Is that what you meant?

KieronCreagh · 267780. Tue Jan 29, 2008 7:44 pm

Davini994 · 267781. Tue Jan 29, 2008 7:47 pm

It?

;)

The answer to that is wrapped up in time dilation and the concept of simultaneity.

A simple bit on the non linearity of time!

post 49225 concerns a similar question and might be of interest.

Tas · 267901. Wed Jan 30, 2008 5:34 am

Nick James · 268063. Wed Jan 30, 2008 7:39 am

I read in the latest compilation of New Scientist articles - "How to fossilise your hamster" - that you can measure the speed of light using a chocolate bar and a microwave. The technique needed is described in the book, but still, how is this possible?

dr.bob · 268156. Wed Jan 30, 2008 10:06 am

'Cos speed = wavelength X frequency

(which makes sense, if you think about it. The distance across one wave multiplied by the number of waves that go past in one second gives you the distance per second, or the speed as it's otherwise known).

The microwave + chocolate* experiment allows you to measure the wavelength of the light** by setting up a standing wave. It then tells you to check the frequency by looking on the back of the microwave (which is a bit of a cheat if you ask me), and then you just need to multiply them together using that complicated formula I produced at the start of these crazed ramblings.

*or marshmallows or cheese or whatever

**For some value of "light" to mean "electromagnetic radiation", in this case microwaves

Flash · 268166. Wed Jan 30, 2008 10:30 am

KieronCreagh · 268190. Wed Jan 30, 2008 11:13 am

Davini994 · 268324. Wed Jan 30, 2008 4:52 pm

[quote="Tas"]