We take great comfort in knowing that some things never change. The sun always rises in the morning and sets in the evening (except at the North Pole in June). Water always flows downhill (unless you are a scientist at the University of Rochester). And every week the Internet will have a new party-photo of Johnny Football (until it doesn’t). This sort of difficulty with identifying things that are truly dependable led to Ben Franklin’s pithy remark, “In this world nothing can be said to be certain, except death and taxes.”
Over a century later, Albert Einstein noticed that many contemporary physics observations and calculations were based on the assumption that light speed was instantaneous. By assigning an actual constant value to the speed of light in a vacuum (c = 299,792,458 meters / sec), he was able to develop the theory of Special Relativity (which was certain until gravity spoiled things).
Either way, light is still way faster than even a Tesla P85D, which is all that matters for most of us. Physicists, on the other hand, have lots of complicated mathematics that hinge on the unwavering speed of light. The fact that it’s constant in a vacuum has been a certain and reassuring truth since the early part of the 20th century (until now).
Miles Padgett and his colleagues at the University of Glasgow have shown that photons shaped by different filters travel at different speeds by about a thousandth of a percent. The layman’s explanation is that part of the slower beam is moving sideways rather than forwards some of the time, thus slowing it down. Physicists may cringe at this explanation, but it works for me.
The U of G researchers are playing this down for now, still unwilling to challenge Einstein. Whether variable speed light is a footnote for future physics texts or a breakthrough discovery is not yet certain, but a timely resolution is needed. The PhD dissertations of thousands of physics grad students hang in the balance.