This is one of a few interesting articles concerning the speed of light in the last couple of years. They have slowed light down, sped light up, and now they say the overall speed changes naturally.
This doesn’t make it any easier to convince creationists the universe is billions of years old!!! I have seen the following argument used: “The speed of light may change, so we ARE living in a 6000 year old Universe.” Doh!!!
Speed of light changes with the medium. For a material with refractive index n the speed of light, which is c in vacuum, bacomes c/n.
Then there’s weird stuff like Self Induced Transparency, where the speed of light is effectively reduced by several orders of magnitude, and the recent experiments in suspended matter where it’s reduced even further.
The thing you can’t do is propagate things faster than the speed of light. There are various loopholes (you can get “phase velocities” that exceed c), but you still can’t propagate information faster than the speed of light in vacuum.
Forgive me if my question misses the point. I always have trouble with equations. I am more interested in the practical and ethical ramifications of discoveries then with the mathmatical/technical ends. I would however, like to understand. That said:
But if the speed of light in a vacuum changes over time, then todays light can be faster/slower than yesterdays light, right? So can I say (assuming the observations turn out to be correct) that the maximum speed you can propagate information changes with the strength of electromagnetic force? If we can control the electromagnetic force we can control the speed of light?
c in vaccuum, absent other electromag forces, is a theoretical limit. For matter as we know it, it is an upper limit, and is asymptotic–we can get infinitely close without reaching it.
Not quite. The article you posted a link to in the OP says:
“The team found that the fine structure constant - a number that determines the strength of electromagnetic force and thus the speed of light - may have been ever so slightly smaller billions of years ago. If true, then current theories are incorrect because they maintain that light’s speed and other fundamental properties do not change in either space or time.”
By “the strength of electromagnetic force,” the article does not mean that if you crank up the local electric or magnetic field strength, the speed of light passing through it will change. It means that a couple of the fundamental constants of the universe which determine the strengths of a given electric or magnetic field – probably the vacuum-permittivity constant (epsilon-nought) and the vacuum-permeability constant (mu-nought) – may have changed a teeny weeny bit over the universe’s history. We mere mortals can control the strength of an electromagnetic field by introducing more charged particles, for example, but we haven’t a snowball’s chance in Hell of being able to alter these fundamental constants ourselves.
So, no, even if the speed of light in a vacuum has changed a little bit over the course of the universe’s history, as this article suggests it may have, we cannot change the speed of light in a vacuum.
Y’all do realize that the fine structure constant is composed of more than just the speed of light, right? Basically, it tells you how strongly light interacts with matter. So a slight change in alpha could be due to:
a change in the speed of light
a change in the vacuum permittivity (or permeability; the two are related through c)
a change in the electron charge
a change in Planck’s constant
Also, it’s a little misleading to speak of the fine structure CONSTANT, because it’s one of those “constants” that changes depending on how intense a field is anyway.
In other words, what you might be seeing from Reuters is an interesting and perhaps important experiment that may or may not be correct but which the press thought was worth mentioning. As is their usual habit, I’m willing to bet that in order to make it more comprehensible to the layman, they butchered the science.