For centuries Time-Travel has been an ever stirring thought in the mind of the intellectual. From the midevil alchemist to the twenty-first century physicist, people have wanted to travel through time. To visit the future, and explore the past, to see history for what it was, and to see what we will become.
This thought only started to really take over a few decades after the industrial revolution, specifically around world war one during Albert Einstein’s annus mirabilis. Before then, was the time of newton (No pun intended). In newtons universe, time was absolute; just as most of us perceive it to be. We think the ‘Flow’ of time is constant, that there is nothing we can do to effect it; it is a huge wave crashing in our ocean of life, and there is no force that will stop it from pushing forward.
However in 1905 Einstein proved Newtons absolute view of space and time wrong; After formulating his special theory of relativity (Or at the time; The electrodynamics of moving bodies) which he derived from basic laws of Newton and Galileo, and the results of the Michaelson-Morley experiment ( ie: the claim that the speed of light is constant no matter what your relative velocity is). From his paper, it was concluded that space, and more importantly time, are not constant. They are like a malleable substance, dependant on the observers velocity.
For example, if you are moving at near the speed of light, if you measure a rod that is supposed to be a meter long; in your reference frame, it may be only 43 cm! And even more; your time would slow down relative to an outside observer. so while an hour may have passed by for you, a few days may have passed in the observers reference frame!
Okay so now you’re all “Okay I get it Einstein was cool guy who did a lot of smart things but you said this was a time travel article!” and indeed it is, so without further ado lets proceed!
How to time travel:
- Do nothing! You’re already travelling through time! (Unless of course you’re a gauge boson, but that’s a different article) Okay I know this isn’t what you came here for so ill get to the interesting parts, time travel relative to other things.
- Stand up. I should have mentioned this earlier in the Einstein paragraph, but gravity dilates time as well! So just standing up means your head will age slightly less than your feet!
- Go for a walk; As I mentioned above, the faster you move, the slower time will flow for you (relative to an observer) so taking a walk around the block can make you about 10 femtoseconds younger than your lazy friend who sat at home.
Okay those were boring lets get into the Science Non-fiction of time travel.
- A rotating universe. If the universe were rotating, Einstein’s general theory of relativity predicts that there would be ‘Time loops’ or Closed time like curves, scattered throughout the universe. Moving along one of theses loops, you would feel as though you were moving forwards through time, but you would always end up back when you started, similar to running in a circular track. However, current evidence predicts the universe is not moving, so lets (sadly) move on.
- Another idea, is to create an infinitely long, super dense spinning cylinder. According to theory, this would create closed time like curves around the cylinder,which a spaceship could circle around and arrive before he entered the curve. However you may have noticed this cylinder needs to be infinite, ie it requires an never ending amount of resources, which we don’t have. Also to create a finite cylinder would require a ‘negative energy’, something physicists aren’t even sure exists!
- Okay, so how about the notorious worm hole? ah here we go finally making some progress. A wormhole, although only hypothetical, but not impossible, is a bridge between two points in space-time. This could hypothetically connect one place at two different times, possibly allowing us to visit the past. The problem is no one knows how to build a wormhole. Even the best of the best say if it were made, it would probably be very unstable. Then with stable wormholes we also run into the negative energy problem. To make a stable wormhole you need some form of negative energy, which no one knows how to make!
UGH! So it seems for the time being, we are stuck in moving at a few femtoseconds relative to each other.
On the topic if time travel; remember that thing you did a while back? You know; the hilarious joke that was taken in bad taste at the job interview? The waste of hundreds to get the newest iProduct? Embarrassing yourself in front of your dream girl? These examples I’m sure have happened to many, along with all the other things you painfully regret doing. I know the feeling, you just wish it hadn’t happened, that you could go back and stop it. So just for fun, lets say you manage to get a hold of negative energy, and you invest in (instead of taking over the world) a time machine. You travel back to to the early 1900’s to shoot your grandfather before you are born. What happens?
Luckily, Physicists have two possible answers, both as crazy as the other. The first, is considered the ‘Many worlds interpretation of quantum mechanics’. Don’t worry, you don’t have to know what that means, it basically says that every time a choice is made, or in this case, someone travels time, a new universe is made, one where the choice went one way, and another where the opposing choice was made. This is where the idea of parallel universes comes from. I personally am not a fan of this choice, but to each their own.
The second possible answer is that there is NOTHING you could do to change the course of history. The gun would lock up, you would always miss, in any event, it would be impossible. This claim is backed up by the research done by Seth Lloyd, a quantum physicist at MIT. However, there is one massive massive problem with this view. It gets rid of causality! Information just comes from nothing. At first i figured it was a failed attempt to get rid of the many worlds hypothesis. What i didn’t know at first was that THEY’VE ACTUALLY DONE THE EXPERIMENT! Okay, well, they didn’t go back in time to see if you could kill your grandfather, but they used photons (Particles or quanta of light).
Essentially, photons can be polarised a couple of ways, (Their quantum spin) and they’ll only go through screens that are oriented with their polarization. That’s why Polaroid sun-glasses work – they block all the photons that are polarised the wrong way, so only some light is let through.
Now, until something detects it, a photon isn’t in any particular polarisation; it’s in all of the possible polarisations at once (Called quantum superposition). But once something has detected what kind of polarisation a photon is in, it’s always been in that state. Essentially quantum causality works both ways in time. So you can set up an experiment that only detects photons of one polarisation, and that way you can send a message back to the past, to the photon emitter (light source) saying “Only send photons of this type”. If you do this the right way, you can send a photon back in time (but you can’t look at the photon that’s been sent back in time until it’s come back to the time you sent it from, or the experiment can’t work). This might sound incredulous, but it’s the way things are.
By doing the above, you can set up a kind of quantum ‘gun’ – set it up so that the photon going back in time tries to cancel out itself coming forward in time – all you do is put something in the middle that tries to change the polarisation of the backwards-in-time photon to the opposite of the forwards-in-time one. Changing polarisation is easy, and works about 96% of the time.
BUT IT NEVER WORKED ON THE BACKWARDS IN TIME PHOTONS
Now, assuming their experimental design wasn’t flawed and their maths works – and it looks OK to me, but I’m not a quantum physicist.. .yet; then this means a few things:
- Firstly, it means the universe is completely deterministic. There’s no such thing as chance.
- Secondly, it’s strong evidence against the many-worlds hypothesis; the first evidence I’ve ever heard of. It almost certainly means there’s a single universe.
So it appears we live in a very Bill and Ted universe, and not a back to the future one.
Either way, if its any consolation you’re about 5 minutes into the future, and we now have personal JetPacks!*