So, to review, the speed of light in a vacuum is the constant c. The constant crepresents 299,792,458 meter per second. James Franson of the University of Maryland, Baltimore County says no, light actually travels much slower and he says he has proof.
What is that proof? Recently there was a supernova, supernova SN 1987A which exploded in February of 1987. How does that offer proof? Well, measurements here on Earth recorded the light as having arrived later than expected – 4.7 hours later. There are many others that say that the photons that arrived at that time weren’t actually from the supernova. Interesting.
What Franson is saying is that due to a property called vacuum polarization (when a photon splits to become a positron and electron for a bit before rejoining) there is an impact on them, a slowdown that would mean that every single light measurement is a bit off – just a little unless you enter into to the 175 light year distance, than perhaps a tad slower than expected.
So then does the speed of light have to worry about time? Photons know little of time. A photon is emitted and then it travels and travels and travels and next thing it knows somebody is clocking it claiming it isn’t as fast as it used to be.
Let's do a quick review. If we want to travel to some distant point in space, and we travel faster and faster, approaching the speed of light our clocks slow down relative to an observer back on Earth. And yet, we reach our destination more quickly than we would expect. Sure, our mass goes up and there are enormous amounts of energy required, but for this example, we'll just ignore all that.
If you could travel at a constant acceleration of 1 g, you could cross billions of light years in a single human generation. Of course, your friends back home would have experienced billions of years in your absence, but much like the mass increase and energy required, we won't worry about them.
The closer you get to light speed, the less time you experience and the shorter a distance you experience. You may recall that these numbers begin to approach zero. According to relativity, mass can never move through the Universe at light speed. Mass will increase to infinity, and the amount of energy required to move it any faster will also be infinite. But for light itself, which is already moving at light speed… You guessed it, the photons reach zero distance and zero time.
Photons can take hundreds of thousands of years to travel from the core of the Sun until they reach the surface and fly off into space. And yet, that final journey, that could take it billions of light years across space, was no different from jumping from atom to atom.