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Question: Time travel... could it exist, and would it involve the speed of light? Could you actually travel backwards or forwards in time while staying still?
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anon answered on 28 Apr 2020: last edited 28 Apr 2020 10:28 am
Hey! So backwards time travel, unfortunately, isn’t allowed by our current understanding of physics. I’d love for that to change, but at the same time I really don’t think it’s likely.
Forwards on the other hand, that’s very different. I mean, we’re already travelling forwards in time, just all at pretty much the same rate, which is a bit boring. If you want to get a head start on everyone else though, you just need to travel really fast, which is where the speed of light comes in. The closer you get to the speed of light, the faster everything behind you seems to progress. If you want to see how whacky this can get, have a look at the Twin Paradox.
Now unfortunately we’re not very good at travelling that fast. But there is one other way you can cheat time and travel differently to everyone else, and that’s to stand next to something really heavy. REALLY REALLY heavy, like a black hole, or a star. The closer you are to something heavy, the slower time runs for you. What that will look like though is everyone else zipping around really fast. You won’t notice anything unusual yourself, until you look at someone that isn’t stood next to the heavy thing.
We know this because it’s happening to us right now. The Earth is pretty heavy, and we have people spending time up in orbit, further away from Earth than us. We’ve been able to measure, using really precise clocks, that time runs slightly slower for us on Earth compared to the people in orbit. In fact, the core of the planet is ever so slightly younger than the surface of the planet, by about 2 years.
So to summarize, backwards time travel currently doesn’t look possible. Forwards time travel certainly is, but it’s really hard to do, and wouldn’t really look like it does in sci-fi. You wouldn’t even notice it happening until you carefully measured time somewhere else.
Disappointing, I know…
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anon answered on 28 Apr 2020:
So, seeing as the others already covered this, just to “troll” you a bit:
The speed of light is a postulated limit. As in, Einstein just put it out there and the rest nodded (eventually) and said “makes sense”. But we still have no direct evidence that it is indeed a limit – but our experiments and observations sure suggest that it is. There was very recently a huge hype about experiment that supposedly detected a particle moving faster than the speed of light – this turned out to be a measurement error, but inspiring!
A lot of things have been taken for granted before because “it must be so” or because anything else was inconceivable. Take Newton’s law of motion for instance – completely revolutionary in its time, but two centuries later, turns out it’s an approximation! Very useful yes, but an approximation nevertheless.But what IS “time travel”? Get in a blue box and whoosh? One could say we go back each time we remember something. But memory is a fickle thing, we actually modify it slightly each recollection.
We could set up a VR experience that would be realistic to the extent of our knowledge. There is a bus in Washington DC that can take you for a ride on Mars for instance – so a travel to the “not-so distant future”, if you will. Then there is geology and archaeology – looking at tangible objects that have “memories” of the past. Extending this to space, each meteorite is a very physical “record” of the formation of the solar system.My point is, since we effectively hallucinate our reality (yes, really! there’s a great TED talk on this – have a look) – being somewhere physically and mentally can overlap enough to count as actual experience.
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anon-251974 commented on :
Thanks so much everyone for all your answers, this is really interesting!