OF GEORGES SAGNAC, RING LASERS, AND TIME MACHINES

This story was spotted by M.H., and it's a lot of fun, and I knew when I saw it I'd be blogging about it; it went straight from "inbox" to this week's "finals folder" right off the bat.

But you might be asking yourself "who the heck is Georges Sagnac"? To answer that question we have to take a little stroll around Harvey's Barn, as my mother used to say. I've written a great deal of high octane speculation in my books concerning the famous Michelson-Morley experiment in physics. It's one of the most famous, if not the most famous, experiments in modern physics. In 19th century physics thinking, it was known that light traveled in waves. Physicists drew an interesting conclusion from this: all waves had to have a medium upon which to "wave" as it were. So how did electromagnetic phenomena like light propagate through "empty" space? Their conclusion was a logical one: there had to be some sort of medium permeating all "empty" space that was so "fine"  that it was not detectable to ordinary techniques of measurement and observation. Physicists named this ultra-fine medium the aether (or ether) lumeniferous, or literally, "light-carrying stuff," or even better, "light-carrying air." Obviously, the Latin sounded so much more sophisticated and academic than the English that the term stuck.

Well, the American physicists Michelson and Morley set out the measure and observe that light-carrying stuff second hand, as it were. They reasoned that as the Earth rushed through space, that it would create an "aether wind" and blow against light propagating in the opposite direction. But how to detect it? They reasoned that if the aether hypothesis was true, then it could be detected by splitting a beam of light, running one beam against the direction of the Earth's rotation, and another perpendicular to it, and then combining the beams on an interferometer. If there was an aether wind, the beam of light traveling against the Earth rotation would be slowed down, and this would show up against the other beam as an interference pattern as the two waveforms mixed. The interferometer would show a kind of checkered "ripple effect", like tossing several stones into a pound and watching the waves crisscross.

Their reasoning may be more readily appreciated by drawing an analogy to sound (and indeed, this analogy was actually used in different publications by Albert Einstein to explain their reasoning). If one stands by a railroad track as an approaching train is blowing its horn, the waves of sound will be compressed, and thus be of higher phase, and the tone of the horn will be high. As the train passes, the sound waves appear to stretch, and the tone falls.  Now take a sound sample of the same horn blowing as the train is stationary, then combine the two: one will hear a steady tone, and in addition, a high-pitched and then a falling tone. You will hear the mixing of waveforms. The only difference in Michelson and Morley's case, was that they were trying to see the two different waveforms, to take a picture of it.

But when they performed their experiment (over and over in fact), the detected no difference of wave forms from the split beam of light.

This threw such a monkey wrench into the physics of the period that we know the rest of the story: Albert Einstein stepped into the picture in 1905 to offer an explanation for the result of the experiment with Special Relativity, maintaining that the experiment showed that the speed of light was an "upper speed limit" regardless of the frame of reference. The aether wind was not detected because there was no aether, at least, not in the sense that it had been understood up to that time.

But in 1913, French physicist Georges Sagnac had a different take, and decided to reperform the Michelson-Morley experiment, but with certain modifications. He reasoned that since all major physical systems were in some state of rotation, then the Michelson-Morley experiment's interferometer had not been constructed properly, since it wasn't rotating. He therefore decided to test if there was an "aether drag" or "aether wind" that could be detected by an interferometer in rotation. Setting up his apparatus on a modified phonograph turntable in a high speed of rotation, he split a beam of light to run with the rotation and against it, and then recombined the beams to take a picture. Sure enough, this time, there was a detectable interference pattern. His experiment has since been reperformed using ring lasers in a rotating system. To borrow our sound analogy once again, imagine two trains racing in opposite directions on a rotating system of parallel tracks, blowing their horns. One sound will be modified to a particular pitch going in the same direction as the rotation, and another will have its sound dropped running in the opposite direction. The upshot is that a rotating system gave harmonic properties to wave forms propagating within it depending upon the direction of propagation.

So with that rather long trip around Harvey's Barn in mind, consider this story:

Astrophysicist Says He Knows How to Build a Time Machine But his peers are far from convinced that it'll work.

Now remember that little bit about rotating systems, light, and harmonic properties, and ponder  this from the article:

“If you can bend space, there’s a possibility of you twisting space,” Mallett told CNN. “In Einstein’s theory, what we call space also involves time — that’s why it’s called space time, whatever it is you do to space also happens to time.”

He believes it’s theoretically possible to twist time into a loop that would allow for time travel into the past. He’s even built a prototype showing how lasers might help achieve this goal.

“By studying the type of gravitational field that was produced by a ring laser,” Mallett told CNN, “this could lead to a new way of looking at the possibility of a time machine based on a circulating beam of light.”

As optimistic as Mallet might be about his work, though, his peers are skeptical that he’s on the path to a working time machine.

“I don’t think [his work is] necessarily going to be fruitful,” astrophysicist Paul Sutter told CNN, “because I do think that there are deep flaws in his mathematics and his theory, and so a practical device seems unattainable.”

Even Mallet concedes that his idea is wholly theoretical at this point. And that even if his time machine does work, he admits, it would have a severe limitation that would prevent anyone from, say, traveling back in time to kill baby Adolf Hitler.

“You can send information back,” he told CNN, “but you can only send it back to the point at which you turn the machine on.” (Emphasis added)

But for the sake of a bit of fun high octane off-the-end-of-the-twig speculation, let's assume that there has already been a large ring system of electromagnetic propagating beams in opposite directions and that it's been around and operating for a while. And let's say that you mix those streams or cause them to collide at a certain point. (CERN, anyone?) One wonders what sorts of time dilation or gravitational effects might result. One wonders, too, if we'd ever be told about it.

And for that matter, why not build a great big huge gigantic ring laser?

And while we're speculating, why not find a way to tap into large, naturally occurring rotating systems that have some sort of differential rotation within them, like, say, the Sun? Might it be possible, then, that in addition to massive objects bending space-time, one might discover eddies and currents within that overall bending? Might, indeed, the eddies and currents in the Sun's plasma be a manifestation of those deeper temporal eddies and currents? And might one be able to find a method to tap into them and "read that information" from when those systems were "turned on"? (And while I'm off the end of the twig in fantasy land, just for the record, I'm thinking of ring lasers arranged in hexagonal formation with phase conjugate mirrors on the beams, and of rotating Kohler coils, and all sorts of abstruse stuff).

Well anyway, maybe. Maybe not. Time - to coin a pun - will tell; it remains to be seen whether the public will be told. In any case, it's fun to speculate and let the imagination run wild from time to time.

See you on the flip side...