A quick one on time travel

Time travel, it happens in movies and Uri Geller can probably do it. (Actually he can’t).

In a previous post I mentioned that physicists believe it could be possible to travel forwards in time, but not into the past. Why did I make this bold claim?

Well I’ll explain, and I’ll also prove that there are time travelers from our past living among us right now!

First of all you may need to challenge your thinking about time. A lot of people think of time as a phenomenon which humans have invented; it’s a human concept for a whole host of things which happen in nature, like aging, the conscious human mind just experiences these things as something we call time, but there’s no actual thing or force involved which is external to us. There’s nothing for scientists to measure and triumphantly shout, “aha, I have found some time!

But that’s not actually the case. Time does exist as an external phenomenon. It’s not merely a human experience or a product of our consciousness. Isaac Newton was the first scientist to demonstrate this in his revolutionary physical depiction of our Universe. Newton’s portrayal of time was as a force that flowed everywhere at exactly the same speed, in one direction, from the past into the future. It didn’t matter where you were in the Universe, in Geneva or on the Moon; it was the same time everywhere. Yesterday was in the past and tomorrow would be in the future. This makes sense, and it’s probably what most people believe about time.

Einstein utterly destroyed this view of time though. He obliterated it with the metaphorical hammer that was his brain. He introduced the idea of relativity to time, and made it the same thing as space. Einstein said that time and space were the same thing, different sides of the same coin if you will. A tough concept to grasp? Well let’s break-it-down. Einstein said that at any given time, like right now, all of space exists. A bit like at any given time all of America exits. That makes sense. Well Einstein also said that at any given time, all of time exists, it’s all out there. Your younger self? Somewhere out there. Your unborn kids? Somewhere out there as well. Even dinosaurs are out there somewhere. So if every bit of time is out there, could we travel to it?

Well Einstein said the secret of traveling in time was speed. He worked out that the faster you moved the slower time flowed. If you took two identical twins and put them in space ships, and if one ship traveled at a faster speed, then the twin in that spaceship would experience time more slowly and would age more slowly than his brother (I’ve misogynistically assumed they were male). This is what is meant by relativity. Time is relative to your speed, and thus flows at different rates under different conditions; there is no universal time as Newton conceived of it.

Relativity can be used to travel into the future. If you got into a spaceship and traveled at an immense speed in a big loop then it may take you ten years until you get back to Earth. You would experience those ten years normally; you wouldn’t notice time slowing down. But the faster you flew the slower time would have passed for you. You may have been away for ten years, but time will have passed more quickly on the Earth, so it may be 100 years later on the Earth. By travelling at a faster speed, you have arrived 90 years in your future. This sounds mad right? Surely it’s just a crazy physics theory that will be overturned in a few years?

Remember earlier I claimed there are time travellers living among us today? Time travellers from our past. Well its true, they’re astronauts. When astronauts are in space they travel faster than the rest of us back on Earth, so time travels more slowly for them. When they return to Earth they are actually returning to a future Earth in which more time has passed, although only a few millionths of a second. Still not convinced that this actually happens? Well people who manage satellites, such as GPS satellites, have to account for effects of time relativity in their software, as time flows more slowly for the satellites. Satellite technology has allowed scientists to record the incredible affects of time relativity.

Unfortunately Einstein said it was impossible to travel back in time. His theories did say that if you travelled really fast time could stand-still and eventually could actually begin to move backwards. But there was one big problem; you’d need to travel faster than light to make this happen, and Einstein’s equations showed nothing could travel faster than the speed of light, at least not by conventional means, as it would need infinite energy. There have been solutions proposed to circumvent this problem, like warping space; maybe I’ll post about this some other time.

So astronauts travel into the future, but we’ll never go back to see the dinosaurs, probably. I guess we’ll have to make that simulation I was wittering about earlier.

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1 Response to “A quick one on time travel”


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