Funny the first time I see about speed of lights mesure errors was in Walter SHEWART's book "Statistical Method from the Viewpoint of Quality Control" where he shows that even mesures supposed to be very precise are sometimes doubtful and he questioned if the mesure of light was indeed from a Normal Law . Then a notorius Nobel Prize Maurice Allais - who was in fact a theorical Physician but also an Economist and funny he receives his Nobel Prize for Economy - questioned also about the mesures of light http://allais.maurice.free.fr/English/Science.htm: All the scientific work of Maurice Allais relates to the field of the gravitation, the velocity of the light and the anisotropy of space. Maurice Allais, initially, carried out his own experiments which led him to observe the existence of phenomena incompatible with the commonly accepted theories. He drew from them his own conclusions according to which the velocity of the light does not have a constant value but varies (slightly) according to the direction. What led him to show the existence of " ether " and of the anisotropy of space. In a second time and to consolidate his own results, Maurice Allais was brought to reexamine the detail of the results of the experiments which had been carried out in the past on the same subject in the U.S.A. by Michelson and Morley in 1887, by Morley and Miller in 1902, 1904 and 1905, and by Miller in 1925, 1926 and 1930. He then could observe that these results contain the same anomalies which were not noticed at the time by the experimenters or were neglected. Maurice Allais affirms today with force that these anomalies are real and indisputable and that they call into question the general theory of relativity of Einstein.

And now SuperString Theory also questioned about the constant of light http://superstringtheory.com/cosmo/cosmo5.html The problem with acceleration There is a problem with an accelerating Universe that is fundamentally challenging to string theory, and even to traditional particle theory. In eternal inflation models and most quintessence models, the expansion of the Universe accelerates indefinitely. This indefinite acceleration leads to situation where a hypothetical observer traveling forever through the Universe will be eternally blocked from seeing any evidence of most of the Universe. The boundary of the region beyond which an observer can never see is called that observer's event horizon. In cosmology, the event horizon is like the particle horizon, except that it is in the future and not in the past. From the point of view of human philosophy or the internal consistency of Einstein's theory of relativity, there is no problem with a cosmological event horizon. So what if we can't ever see some parts of the Universe, even if we were to live forever? But a cosmological event horizon is a major technical problem in high energy physics, because of the definition of relativistic quantum theory in terms of the collection of scattering amplitudes called the S Matrix. One of the fundamental assumptions of quantum relativistic theories of particles and strings is that when incoming and outgoing states are infinitely separated in time, they behave as free noninteracting states. But the presence of an event horizon implies a finite Hawking temperature and the conditions for defining the S Matrix cannot be fulfilled. This lack of an S Matrix is a formal mathematical problem not only in string theory but also in particle theories. One recent attempt to address this problem invokes quantum geometry and a varying speed of light. This remains, as they say, an active area of research. But most experts doubt that anything so radical is required.

The maximum value from an observer standpoint is approximately 186,282 miles per second. However, if you are the one doing the traveling, you are essentially covering any amount of distance instantly. If you are in a spaceship that is going the speed of light, you would reach another star that was 10 light years away instantly, but people on Earth observing your trip would notice it took you 10 years to make the trip. Since there is no universal time, it depends on the reference point of the observer.

The speed of light is constant and independent of the velocity of the source and the observer: Special theory of relativity.

Aphie I don't understand your logic here. It seems that you are saying observed speed and actual speed are two different things. A light-year is an actual measure of distance that assumes a constant speed. The distance is not covered instantly. It is covered in a year. If I am cruising at the speed of light, it will take me a year to get to something one light year away. And it will feel like a year, not an instant.

aphexcoil. In school I always questioned my physics professors about the concept that two spaceships travelling at 99C shine a light at each other and the light still moves at C. No one ever answered my questions satisfactorily. Is that because as you state an observer only sees one C but for light it gets there instantly. Perhaps none of my professors knew enough to explain the observation vs getting there instantly thing. Are you sure about light can travel a distance of 10 light years instantly? Two, if light is not a constant does that effect time. Would the earth be older or younger if light is slowing down? I just saw the other posts perhaps my professors were correct. Nevertheless I would like to find out the question about if light is slowing down do we have to recalculate things like the age of the earth, and the size of the universe.

If the speed of light is not a constant and independent of the velocity of the source and the observer then the Michaelson Morley experiment is not explained and E does not equal MC square.

Nitro responded to a thread of mine about some of this already. There's a physicist that is challenging c whose book you can find in the second post of the link below. I haven't read it yet and want to. What doesn't make sense to me is that astronomers can calculate the speed of light by using spectroscopy and observing the hyperfine split spectral line of hydrogen. And from what they have observed, everywhere they look in the universe, the speed of light is constant for this line. But I haven't read the book, so I don't know exactly what he's claiming. http://www.elitetrader.com/vb/showt...rpage=6&highlight=speed of light&pagenumber=1

And, by the way, relativity has been verified with many significant places of the decimal as the decades have gone on. For example, "By 1976 an echo delay experiment placed on the moon by Apolla astronauts reduced the uncertainty down to 0.5%. In 1979 measurements of the gravitational effects on radio signals further reduced the uncertainty to just 0.1%. In 1980 a hydrogen maser clock (based on the laser principle and nearly a hundred times more accurate than the best atomic clock) aboard a NASA rocket confirmed general relativity to the fifth place of the decimal." In other words, relativity has been confirmed to many places of the decimal in repeated experiments. Of course, relativity applies to large scale structures. By the way, here's an interesting article that shows the speed of gravity has actually been shown to be near the speed of light, another interesting verification of relativity. (The accuracy of this is still not there: +-20%.) http://www.space.com/scienceastronomy/gravity_speed_030107.html