Latest developments on the variable speed of light theory? Any experiments devised to test it yet?

Answer 1

The speed at which light APPEARS to travel depends on the medium it is traveling through. In a vacuum, light travels at c (299,792,458 meters per second). In any other medium, light appears to travel at a speed less than c. This characteristic of light is what allows such things as lenses to function. All evidence I'm aware of still supports special relativity, indicating it is not possible for light (or anything else) to travel faster than c.

There have been several experiments in the past couple of years that have attempted to slow light down. The most recent one I'm aware of was reported in the Washington Post last month, which I've linked below. (Bear in mind it's a newspaper and not a scientific journal, so it's pretty slim on the specifics and might even be inaccurate in some areas.)

You may also want to check out Lene Hau's experiments with light passing through a Bose-Einstein condensate, which was discussed in the Harvard University Gazette (also linked below). In those experiments, light was "slowed" to around 17 meters per second.

When light interacts with a medium, it doesn't technically slow down as most people would think, but rather travels in one linear direction at that speed and only appears to slow due to the absorption and reemission of photons by the medium. This is explained in more detail in an article at Physlink, which I've also linked below. The discussion there may also answer some other questions you might have on the issue.


*edit* - took out the word "roughly" since it's both unnecessary and misleading. thanks Jano. silly of me! :)

Answer 2

Just a NOTE (for DavidGC said roughly about c):

In metric units, c is EXACTLY 299,792,458 metres per second (1,079,252,848.8 km/h). Note that this speed is a definition, not a measurement. Since the fundamental SI unit of length, the metre, has been defined since October 21, 1983 in terms of the speed of light; one metre is the distance light travels in a vacuum in 1/299,792,458 of a second. Converted to imperial units, the speed of light is approximately 186,282.397 miles per second, or 670,616,629.384 miles per hour, or almost one foot per nanosecond.

Answer 3

I haven't heard more than the theory yet, but as light is "known" to have mass, and is "bent" by gravitational forces, it should have been postulated well before this that this effect could alter velocity as well as direction. I wonder about scientists sometimes.

Answer 4

the "bending" of light in a gravitational field is caused by the distortion of the space-time continuum predicted by Einstein.

As a side note, speed of light is ~11.8029 in/ns

Answer 5

That idea died about 15 years ago although on or two still hang on to it. To comment on one of the answers, light does not have mass. Only energy and momentum.

http://math.ucr.edu/home/baez/physics/Relativity/SR/light_mass.html

Answer 6

once it leaves a medium of higher optical density it speeds up to"C" and stays there.