A long time ago, in a galaxy far, far away...
Who knows what the future will bring?
Well, it's about time.
We use time references everyday of our lives. We can't avoid it. It is the great leveller. Everything grows older. Time passes on like clockwork.
Or, at least, that is the way physicists once regarded time. To quote Newton, the universe was based on "absolute, true, and mathematical time, which of itself, and its own nature, flows equatably without relation to anything external". Time passes regardless of anything else. To Newton, it was the one solid fact of the universe.
In the late 1800s, scientists began to question this idea. To have an eternal time implied that everything in the Universe was set against a static backdrop which scientists called the "aether". But when experiments were devised to look for the aether, nobody could find it.
The most famous of these was the Michelson-Morley experiment which tried to measure the difference in the speed of light when it was travelling with or against the aether as opposed to across it.
They didn't find any difference. Moving with or against or across the flow of aether had no effect on the speed measured for light.
The explanation of this was offered by two other scientists, Lorentz and FitzGerald, who postulated that maybe length and mass were affected by velocity. Their equations suggested that there is a contraction in the distance that the light beam had to travel that just offset the time delay that should have been there.
The final blow to "absolute" time was struck by Albert Einstein who argued that if mass and length were variables, then maybe time itself was also variable. This is the basis of Einstein's "Special Theory of Relativity".
Is time a variable? The answer had to wait until some better clocks could be made since the speeds that we can achieve on Earth are minuscule relative to the speed of light. But in 1971, with the aid of four atomic clocks, two scientists, J.C.Hafele and R. Keating, set out to test Einstein's equations.
They load up the four clocks on a commercial airliner heading east and flew all the way around the world. And sure enough, when they got back to the U.S. Naval Observatory, the four clocks were, on average, 59 nanoseconds or 59 billionths of a second slow relative to the clocks that had remained at the Observatory. They then loaded the clocks on west bound flights and flew once more around the world. When they got back, the clocks were, on average, 273 nanoseconds fast.
The reason for the difference is that, as Einstein noted, the rotation of the Earth produces a time dilation effect. When this is taken into account, the time dilation, or the slowing down of time because of the speed of the airplane, is exactly what Einstein predicted.
The results have been repeated using sub-atomic particles and large cyclotrons where truly relativistic speeds can be obtained. All of the experiments that have been performed so far lead to the same conclusion. Time is a variable.
Of course, Einstein's theory was predated by science fiction writer, H.G. Wells, who, in "The Time Traveller", wrote: "There is no difference between Time and any of the three dimensions of Space except that our consciousness moves along it."
The notion that time is a variable and linked with the dimensions of space naturally leads to the question of time travel. Is it possible? For Wells, it was a literary trick that allowed him to write a classic story. For Einstein and every other physicist, it is a matter of speculation, possibilities, and concern.
Speculation because of the implications of being able to move freely in time. We are all "time travellers" but locked into a one way trip with no chance to change direction or speed. But what if this wasn't the case? What if time was not linear?
Black holes and tunnels in space time offer the possibility of being released from linear time. Step outside of the Universe and time suddenly becomes a variable that can be manipulated. Theory doesn't prevent it but theory also doesn't explain how to make it happen.
The possibilities are endless and that causes concern. What if a time trip was to alter the time line such that Albert Einstein was never born? If he was never born, then he could never have come up with his theories and time travel could never have been invented, so the time line could not have been altered.... Such paradoxes present the possibility that time travel may not be something that we want to pursue.
In any case, it is all about time... as in, it is time to stop.
