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As Einstein’s theories gained foothold with the younger generation of believers in the “new physics”, Einsteinian fame increased steadily and the ether scientists seemed to die out accordingly. But in 1913 French scientist Georges Sagnac took Einstein’s second postulate to the slaughter bench by mounting an interferometer on a spinning disk and proving that there was a definite difference between light going with or against the direction of rotation. This difference could be easily explained by using old-time Newtonian arguments that speed of light changes according to direction rotation....
....Later when he made his famous theories of the universe after publishing his General Theory of Relativity in 1916, Einstein still refused to accept that galaxies were spinning. He claimed it counteracted his second postulate in the STR. Sadly for common sense all astronomers by 1916 knew that galaxies were spinning (14).
Years after Einstein’s death, decision is still in favour of Sagnac and the absolute nature of rotation. When satellite clocks are synchronized, corrections are made using speed of light either greater or less than c. And today spaceships, satellites and airplanes all carry Laser-ring-gyroscopes that use the non-relativistic Sagnac effect to tell the speed between the plane and the rotating Earth, with accuracies down to nanoseconds
Originally posted by Motion-Man
If light can't escape a black hole, then maybe at a certain distance the gravity bends the light in another direction.
Think about how fast a shadow can move. If you project a shadow of your finger using a nearby lamp onto a far away wall and then wag your finger, the shadow will move much faster than your finger. If your finger moves parallel to the wall, the speed will be multiplied by a factor D/d where d is the distance from the lamp to your finger and D is the distance from the lamp to the wall. It can actually be much faster than this if the wall is at some oblique angle. If the wall is very far away the movement of the shadow will be delayed because of the time it takes light to get there but its speed is still amplified by the same ratio. The speed of a shadow is therefore not restricted to be less than the speed of light.
Others things which can go faster than the speed of light include the spot of a laser which is pointed at the surface of the moon. Given that the distance to the moon is 385,000 km try working out the speed of the spot if you wave the laser at a gentle speed. You might also like to think about a wave arriving obliquely at a long straight beach. How fast can the point at which the wave is breaking travel along the beach?
This sort of thing can turn up in nature. For example the beam of light from a pulsar can sweep across a dust cloud. A bright explosion emits an expanding spherical shell of light or other radiation. When it intersects a surface it creates a circle of light which expands faster than light. A natural example of this has been observed when an electromagnetic pulse from a lightning flash hits an upper layer of the atmosphere.
These are all examples of things which can go faster than light, but which are not physical objects. It is not possible to send information faster than light on a shadow or light spot so FTL communication is not possible in this way. This is not what we mean by faster than light travel although it shows how difficult it is to define what we really do mean by faster than light travel.
Tachyons are hypothetical particles which travel faster than light locally. They must have imaginary valued mass to be able to do so, but they have real valued energy and momentum. Sometimes people imagine that such FTL particles would be impossible to detect but there is no reason to think so. The shadows and spotlights suffice to show that there is no logic in the suggestion because they can go FTL and still be seen.
No tachyons have been definitely found and most physicists would doubt their existence. There was a claim that experiments to measure neutrino mass in Tritium beta decay indicated that they were tachyonic. It is very doubtful but not entirely ruled out. Tachyon theories have problems because, apart from the possibility of causality violations, they destabilise the vacuum. It may be possible to get round such difficulties but then we would not be able to use tachyons for the kind of FTL communication that we would like.
The truth is that most physicists consider tachyons to be a sign of pathological behaviour in field theories, and the interest in them among the wider public stems mostly from the fact that they are used so often in science fiction
THE MOON REVOLVES ROUND MY HEAD FASTER THAN LIGHT!
Stand up in a clear space and spin round. It is not too difficult to turn at one revolution each two seconds. Suppose the moon is on the horizon. How fast is it spinning round your head? It is about 385,000 km away so the answer is 1.21 million km/s, which is more than four times the speed of light! It sounds ridiculous to say that the moon is going round your head when really it is you who is turning, but according to general relativity all co-ordinate systems are equally valid including revolving ones. So isn't the moon going faster than the speed of light? This is quite difficult to account for.
What it comes down to, is the fact that velocities in different places cannot be directly compared in general relativity. Notice that the moon is not overtaking the light in its own locality. The velocity of the moon can only be compared to the velocity relative to other objects in its own local inertial frame. Indeed, the concept of velocity is not a very useful one in general relativity and this makes it difficult to define what "faster than light" means. Even the statement that "the speed of light is constant" is open to interpretation in general relativity. Einstein himself in his book "Relativity: the special and the general theory" said that the statement cannot claim unlimited validity (pg 76). When there is no absolute definition of time and distance it is not so clear how speeds should be determined.
Some of us suspect that the ostensible decay of c, the slowing velocity of light, was one of the results of the upheavals of Genesis Chapter 3.
The possibility that the speed of light is not a "constant" after all and has been slowing down is highly controversial and conjectural. Yet, some of the most dramatic changes in scientific perspective come only after much debate, vigorous opposition, and the like.
The entire field of physics is presently in a state of upheaval. The particle physicists have decided there is no causality, and that the universe has at least 10 dimensions. The redshift has been discovered to be quantized and that may shatter previous conceptions of our universe. Particle physics has totally altered our concepts of reality.
Many of today's scientific orthodoxies, however, originated from yesterday's unpopular heresies. The apparent decay in the velocity of light may be another of these controversial "heresies" looming on the horizon of modern physics. Only time will tell.
But the Bible changes not. It doesn't need to!
Originally posted by Motion-Man
...Stars could even be in different positions because the light could be bent and curved to fly in another direction, by obstacles or even gravity.
As far as we know, all the light coming from the heavens could be part of one giant light "source" that is being fragmented by "environmental conditions". So tell me, do you agree that we may be wrong about many, if not all, distances between us and other heavenly bodies, and using the distance of stars (according to the speed of light) to prove theories is wrong?
If a wave solution has a frequency dispersion it will take the form of a wave packet which travels at the group velocity which is less than c. Only its wave trains travel at the phase velocity. It is only possible to send information with such a wave equation at the group velocity so the phase velocity is yet another example of a speed faster than light which cannot carry a message