Friday, November 17, 2017

Time Travel is Possible

Now, to be fair, possible doesn't mean easy, but still. The energy requirements are so far beyond what our civilization can produce that they're hard to imagine, but the point is that the laws of physics don't explicitly prevent it from happening. According to astrophysicist Ethan Siegal, what you need is a pair of entangled wormholes and a way to accelerate one end to the speed of light. Then someone in the future could pass through the wormhole and arrive in the past. The only issue is that it's a one-way trip, at least through the wormhole.

Time travel has been the holy grail of science for centuries but it could finally be within our grasp. There is just one problem, we might not be able to return to the present from the past.

Astrophysicist Ethan Siegel has outlined in his blog Starts With a Bang how the theoretical rules of physics might allow a way to use wormholes to travel back in time. A wormhole which is still at one end and as fast as the speed of light at the other could provide the basis for humans to step back into another era. This will not be easy, and considering how many people get confused when the clocks go forward or back the chances of successfully pulling off the creation of time travelling wormholes could be tough.

Siegal said: ‘If, 40 years ago, someone had created such a pair of entangled wormholes and sent them off on this journey, it would be possible to step into one of them today, in 2017, and wind up back in time at the mouth of the other one back in 1978. ‘The only issue is that you yourself couldn’t also have been at that location back in 1978; you needed to be with the other end of the wormhole, or traveling through space to try and catch up with.’

As far as returning to the present, that actually is so easy (relative to going through everything that you would have to do to create and accelerate time-entangled wormholes, of course) it doesn't even get a mention in the article. We already know how to do that, and it's a mainstay of every introduction to relativity theory. You just go really, really fast. That's how the "twins paradox" works. The fast-moving twin who doesn't age isn't rendered ageless, he or she experiences dilated time - in effect, the same thing as jumping forward in time.

So if you jump into the past via a wormhole, it's entirely possible for you to get back. Just fly through space at very close to the speed of light and make a really big loop that starts and ends at the earth. When you finish your journey, hardly any time will have passed for you but many years will have passed on earth and you will have traveled in time in the other direction.

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Rodav said...

Hi Scott,
it's the big question, can we travel through time. Physicist Paul Davies wrote a book in 2001, called How to build a time machine. I bought it, but no longer have it. He proposed in the book that two way travel is possible. He asserts that if we built a wormhole today, it would need a "stargate" like the TV series, and we would be able to travel to any point in the future (as long as the stargate at the other end still exists), to the other end of the wormhole and return. But you could not travel further back than today, since the stargate didn't exist before today.
According to current physics, travelling at 99.9% of the speed of light for two weeks would see 4 years on earth passed. However, current physics says that, at the speed of light, your mass would become infinite and time for you, would stop, hence it is believed that travel at the speed of light is impossible. What never seems to have been spoken about is whether it's possible to travel at 99.9% of the speed of light. If our mass would become infinite at 100%, does that mean it would be expanded by 1 billion at 99% ? What is the limit of the speed of travel ? Incidentally, astronauts on the International Space Station, which travels at about 25,000 mph for six months, have aged 0.007 seconds less !

Scott Stenwick said...

Right, if you could link each end of your wormhole to a gate-like device and then accelerate one end close to the speed of light, time dilation would result in each end being at a different location in time. It's not clear how easy it is to link a wormhole like that, though.

It is possible to get arbitrarily close to the speed of light from the perspective of the outside universe. It's important to to understand, though, that when you're standing on board a spaceship the universe appears to be entirely Newtonian. That is, from your perspective it's as if you can fly many times the speed of light easily.

The bug there - or maybe it's a feature - is that time in the outside universe always passes as if you were traveling arbitrarily close to light speed. Time dilation is the difference between the time it took for you to reach your destination and the time it took from the perspective of the rest of the universe.

Mass dilation has to do with relative momentum. Again, from your perspective, your mass doesn't change at all. However, if you collide with something in your path the momentum will be as if you were going however many times the speed of light you are experiencing from your perspective.

So, in effect, your mass dilates because momentum equals mass times velocity. Your velocity to the outside universe is still apparently around light speed no matter how fast you go, but as you put more and more energy into accelerating what increases from an outside perspective is your mass.

It's not clear that any material object can move at the speed of light without transforming into energy - that is, photons. In practice, as you accelerate you get closer and closer but from the perspective of the outside universe you never get there.