Time Travel Is Possible, Says Stephen Hawking

[iamwhoiam]

Now we have plenty of scientific evidence supporting the idea that ftl travel is impossible, and that even nearing the speed of light would be fatal for humans.

It's impossible with the knowledge and understanding that we have today.

[Phenom II]

If I could travel backwards in time, I would have already traveled backwards in time to explain to myself how I did it.

+1 !!!

Yea if time backwards travel was EVER going to be possible, we would have known about it a long time ago because someone from the future would have traveled back in time and given us the know how to do it.

Which means one of two things,

1. Backwards time travel will NEVER be possible

2. There is no future, it hasn't happened yet.

Personally I believe there is only NOW, the past is gone, and the future has not happened yet

EDIT - If backwards time travel was one day possible and there is a future before we get to it, then I am sure someone would have gone back to the stone age and given them some tools and diagrams and tought them english etc etc so that we would be 100x more advanced now

[JoeyF]

It's mind-boggling. Even if we get the technology which can enable us to travel at such speeds, waiting for feedback from such a ship will still take a hell of a time here on Earth. Forget about ever seeing it come back in your lifetime. :)

If you managed to do this, and each day at light speed was a year on earth - by the time you got home, there would be no-one left alive that knew you were up there in the first place, except kids with nursery rhymes about the fairy tale spacemen flying around the earth and the speed of light.

I'm not saying I agree with his concepts, but going by his argument, you two are incorrect:

He says it takes six years for the ship to accelerate to the speeds required. If it was possible to build a ship able to withstand those forces while keeping the humans on board alive, it would be reasonable to assume that the ship could withstand centrifugal force as well. If the ship flew with a slightly curved path, it can rotate around until it is relatively close to earth by the time it reaches this speed. If the ship were three light-days away from earth, it can travel at light speed for two of those days, and then begin deceleration on the third day. Since the ship would no longer be traveling close to the speed of light, one day on board will still equal one day on earth, yet the ship will still be traveling fast enough to bridge the remaining distance through deceleration. At that point, the ship will return roughly 8-9 years after departure, and it would be reasonable (at this current time) to assume that a good percentage who were on earth upon the ship's departure would still be alive at that time.

Even if flying at a curve is not possible, the ship will simply have to accelerate for six years, fly for ten days or so (ten years), turn around, and do it again. That will mean the ship arrives ~32 years later, still reasonable to assume that at least 50% of the people alive when you departed would still be living pending no global wars/epidemics.

[giantpotato]

Haven't we know about this for ages? Twin Paradox. I'm pretty sure they've even tested that two atomic clocks will become out of synch if one is travelling through space faster than the other. I don't see why the human body wouldn't be able to withstand near-light speeds, as long as you don't accelerate abnormally fast. If you think about it, we're traveling thousands of mile per hour, if not more, right now through the galaxy, relatively speaking.

[Steven P. Administrators]

I cant fathom the theory!

It takes 8 minutes for the light of the sun to travel to the Earth, and the most distant stars even longer (up to millions of years)

..but if we consider that 200 years ago, to travel across the entire USA (East to West) it would have taken weeks, when it now takes just mere hours, the speed has increased for the traveler, but the person waiting on the west coast didn't age anymore than I would have now, or 200 years ago with the same journey, so why would that change any if the speeds were increased (even to light speed, and possibly beyond?)

So are scientists saying that when approaching light speed, somehow the current norm suddenly becomes something else?

[.Markus]

+1 !!!

Yea if time backwards travel was EVER going to be possible, we would have known about it a long time ago because someone from the future would have traveled back in time and given us the know how to do it.

Which means one of two things,

1. Backwards time travel will NEVER be possible

2. There is no future, it hasn't happened yet.

Personally I believe there is only NOW, the past is gone, and the future has not happened yet

EDIT - If backwards time travel was one day possible and there is a future before we get to it, then I am sure someone would have gone back to the stone age and given them some tools and diagrams and tought them english etc etc so that we would be 100x more advanced now

I can see where you're coming from, however ponder this;

If the time machine hasn't been invented yet - how can they in that case travel backwards in time..?

Perhaps one day some scientists will have come up with a way to travel backwards in time and the next moment we know the whole place is perhaps crowded with 'time tourists' to witness how the time machine was invented...

[MrChainsaw]

[Guest]

I cant fathom the theory!

It takes 8 minutes for the light of the sun to travel to the Earth, and the most distant stars even longer (up to millions of years)

..but if we consider that 200 years ago, to travel across the entire USA (East to West) it would have taken weeks, when it now takes just mere hours, the speed has increased for the traveler, but the person waiting on the west coast didn't age anymore than I would have now, or 200 years ago with the same journey, so why would that change any if the speeds were increased (even to light speed, and possibly beyond?)

So are scientists saying that when approaching light speed, somehow the current norm suddenly becomes something else?

Try reading the article over on the Daily Mail:

http://www.dailymail.co.uk/home/moslive/article-1269288/STEPHEN-HAWKING-How-build-time-machine.html

It's much longer and I think you get better explanations. The train analogy will explain what you're stuck with (it starts on the 4th paragraph below the LHC pic).

But yes, when you get to near-light speed time slows down for you.

Personally I believe there is only NOW, the past is gone, and the future has not happened yet

I agree but personally I like to live for the future.

[Phenom II]

I can see where you're coming from, however ponder this;

If the time machine hasn't been invented yet - how can they in that case travel backwards in time..?

Perhaps one day some scientists will have come up with a way to travel backwards in time and the next moment we know the whole place is perhaps crowded with 'time tourists' to witness how the time machine was invented...

Hmmm... if they invented a time machine to go back in time, surely they would only be able to travel as far back as to when the machine was switched on, any time before that and time travel was impossible....

And yea... just imagine, the country suddenly full of people who dont belong here...... surely that could never happen.... right ? .. O.o

I cant fathom the theory!

It takes 8 minutes for the light of the sun to travel to the Earth, and the most distant stars even longer (up to millions of years)

..but if we consider that 200 years ago, to travel across the entire USA (East to West) it would have taken weeks, when it now takes just mere hours, the speed has increased for the traveler, but the person waiting on the west coast didn't age anymore than I would have now, or 200 years ago with the same journey, so why would that change any if the speeds were increased (even to light speed, and possibly beyond?)

So are scientists saying that when approaching light speed, somehow the current norm suddenly becomes something else?

Yea thats what I keep wondering, why would anything change

When a Jet goes faster than sound, OK, he can no longer hear the sound, but apart from that nothing changes, so with that theory, when people hit the speed of light, they would just not be able to see anything, right?

Except now you have the issue of particles colliding at light speed, ie. the ship and dust, space crap - are they not saying with the Large Hadron Collider it could potentially create a black hole with only 2 particles, let alone a space ship ?

[iamwhoiam]

And yea... just imagine, the country suddenly full of people who dont belong here...... surely that could never happen.... right ? .. O.o

:whistle:

[Phenom II]

Try reading the article over on the Daily Mail:

http://www.dailymail.co.uk/home/moslive/article-1269288/STEPHEN-HAWKING-How-build-time-machine.html

It's much longer and I think you get better explanations. The train analogy will explain what you're stuck with (it starts on the 4th paragraph below the LHC pic).

But yes, when you get to near-light speed time slows down for you.

I agree but personally I like to live for the future.

From that article, I read this paragraph---

---

Through the wormhole, the scientist can see himself as he was one minute ago. But what if our scientist uses the wormhole to shoot his earlier self? He's now dead. So who fired the shot? It's a paradox. It just doesn't make sense. It's the sort of situation that gives cosmologists nightmares.

Now.. In my mind, as soon as the scientist decided that he was in fact going to do this, he would be dead.

[benplace]

You dont even have to travel anywhere near the speed of light to alter your time. Satellites in orbit that we use for gps have to have their on board clocks altered because time travels at a different speed when they are whizzing around the earth. If they didnt alter the clocks our gps system would move off course by something like 6 miles a day. I liked Hawkings explanation of why a wormhole couldnt allow travel back in time, because of the feedback, similar to the feedback you get when you move a microphone close to an amplifier.

[spenser.d]

If you watched the Discovery channel special, his theory is explained quite a bit more in depth and sounds quite a bit more legitimate. Its explained as analogous to the GPS grid and how GPS satellites have to correct for the billionths of a second they "travel ahead" in time every day just so our GPS devices work properly. Its not the same as traditional sci-fi time travel.

Its an interesting show and an interesting theory, but all fairly irrelevant :p

[Growled Member]

When a Jet goes faster than sound, OK, he can no longer hear the sound, but apart from that nothing changes, so with that theory, when people hit the speed of light, they would just not be able to see anything, right?

At this point it's just theory. We won't know for sure until we have much faster travel than we do now.

[Phenom II]

You dont even have to travel anywhere near the speed of light to alter your time. Satellites in orbit that we use for gps have to have their on board clocks altered because time travels at a different speed when they are whizzing around the earth. If they didnt alter the clocks our gps system would move off course by something like 6 miles a day. I liked Hawkings explanation of why a wormhole couldnt allow travel back in time, because of the feedback, similar to the feedback you get when you move a microphone close to an amplifier.

Its nothing to do with speed that makes them "Time travel" it is the mass of earth which slows our time down, in space there is no mass to drag time

[micro]

Famed astrophysicist Stephen Hawking believes humans are capable of time travel -- and he's not afraid to let everyone know.

Claiming he is not as concerned about being labelled crazy as he once was, Hawking has publicly aired his second startling theory in two weeks.

Hawking said he believed humans could travel millions of years into the future and repopulate their devastated planet.

Hawking said once spaceships were built that could fly faster than the speed of light, a day on board would be equivalent to a year on Earth. That's because -- according to Einstein -- as objects accelerate through space, time slows down around

them.

Which also means that Hawking's theory only applies to moving forwards through time.

Moving backwards is impossible, Hawking says, because it "violates a fundamental rule that cause comes before effect."

If moving backwards through time was possible, a person could shoot their former selves.

?I believe things cannot make themselves impossible,? Hawking said.

However, once spaceships approached the speed of light, their crew would start skipping through Earth years on a daily basis, giving the human race a chance to start again.

?It would take six years at full power just to reach these speeds," Hawking said. "After the first two years, it would reach half light speed and be far outside the solar system. After another two years, it would be traveling at 90 per cent of the speed of light."

?After another two years of full thrust, the ship would reach full speed, 98 per cent of the speed of light, and each day on the ship would be a year on Earth. At such speeds, a trip to the edge of the galaxy would take just 80 years for those on board.?

full story

He didn't say TRAVEL FASTER than the speed of light (since its not possible) he said 99.9999% of the speed of light.

In-fact time slows down to prevent anything from traveling faster than the speed of light.

The example given is this:

A little girl is aboard a train that is traveling 99.999% the speed of light. Now if this girl were to leave her seat and begin to run up the isle she would potentially be able to surpass the speed of light, however quantum physics does not allow this.

The moment the little girl would begin moving forward time for her would begin to run slower and slower, thus preventing her from ever running past the speed of light.

[Phenom II]

So why is light allowed to move at the speed of light without slowing down ?

What makes IT so special ? :laugh:

And if that little girl turned her torch on, whilst travelling 99.9999% the speed of light, would the torches light suddenly travel Faster than light ?

[Nayos]

Reminded me of

[JoeyF]

^ reminded me of:

[Nihilus]

It's impossible with the knowledge and understanding that we have today.

But with the knowledge we have today we can predict that it will probably remain impossible :p When people said that space flight/other recent technological achievements were impossible they did not say so because those accomplishments would violate the fundamental laws of physics. You can't compare their predictions to ours because we understand why these far fetched concepts probably won't happen.

Still, I won't say it's a definite no, but when it comes to probability I'd put managing ftl/time travel up there with proving there is/isn't a god.

I mean hawking is just talking about reaching an appreciable fraction of the speed of light, and even that would kill any humans on board. Traveling at superluminal velocities would give rise to even more numerous problems. If you're interested there was a thread on here a while ago where a well known physicist listed some of the problems, and explained why he thought it wasn't possible.

I cant fathom the theory!

It takes 8 minutes for the light of the sun to travel to the Earth, and the most distant stars even longer (up to millions of years)

..but if we consider that 200 years ago, to travel across the entire USA (East to West) it would have taken weeks, when it now takes just mere hours, the speed has increased for the traveler, but the person waiting on the west coast didn't age anymore than I would have now, or 200 years ago with the same journey, so why would that change any if the speeds were increased (even to light speed, and possibly beyond?)

So are scientists saying that when approaching light speed, somehow the current norm suddenly becomes something else?

Yarr, tiz the theory of special relativity :) And technically you do age slightly differently traveling across the USA relative to someone who didn't. The difference is just so inconsequential I'm not sure it could be measured even if you wanted to.

They did an experiment with a few atomic clocks a while back though, one flown around the earth at supersonic speeds and one left stationary on the ground. The one in flight aged more slowly :) You go faster, you age more slowly relative to the stationary observer. Traveling at 98% of the speed of light you age very, very slowly :p

Hmmm... if they invented a time machine to go back in time, surely they would only be able to travel as far back as to when the machine was switched on, any time before that and time travel was impossible....

And yea... just imagine, the country suddenly full of people who dont belong here...... surely that could never happen.... right ? .. O.o

Yea thats what I keep wondering, why would anything change

Heh, I think Hawking once said that the fact we aren't inundated with time tourists is the surest evidence that time travel is not possible :D

When a Jet goes faster than sound, OK, he can no longer hear the sound, but apart from that nothing changes, so with that theory, when people hit the speed of light, they would just not be able to see anything, right?

Except now you have the issue of particles colliding at light speed, ie. the ship and dust, space crap - are they not saying with the Large Hadron Collider it could potentially create a black hole with only 2 particles, let alone a space ship ?

Nothing "hits" the speed of light :p time slows down to prevent it, even in your jet example time slows down for the jet.

The LHC won't create a black hole, even if it does create micro black holes they wouldn't be stable. A more pressing problem for a ship traveling at 98% of the speed of light would be those particles killing the crew. I'm not sure what effect they'd have on the hull, black holes or no, but I don't think that would be good either :p

So why is light allowed to move at the speed of light without slowing down ?

What makes IT so special ? :laugh:

And if that little girl turned her torch on, whilst travelling 99.9999% the speed of light, would the torches light suddenly travel Faster than light ?

No... time would slow down for the girl relative to everything else. Preventing her from traveling faster than light, and keeping the speed of the light coming out of her torch a constant :)

[+Mirumir Subscriber¹]

I'm not saying I agree with his concepts, but going by his argument, you two are incorrect:

...

At that point, the ship will return roughly 8-9 years after departure, and it would be reasonable (at this current time) to assume that a good percentage who were on earth upon the ship's departure would still be alive at that time.

And how far would you go? ;) Merely outside of the Sun System and back? This ain't fun :)

The nearest to the Sun star is Proxima Centauri; it's 4 light years away...let's do the math :)

So you need to travel for 4 years at the speed of light to reach the star.

4*365 = 1460

a day on board would be equivalent to a year on Earth

Without accounting for the acceleration:

1460 years will go by on Earth when you reach it after having travelled for 1460 days at the speed of light! :cool:

[+Anarkii Subscriber²]

As smart as Hawking is, this is information that has been around for decades now. Just because he says it can happen doesn't really make it 'new'.

[Mordkanin]

Sounds like Hawking has officially lost his marbles. While time travel on a particle/wave level is theoretically possible, to suggest that a human could withstand it is ludicrous. And all of our popular notions of time travel assume that there's an absolute time scale, which of course doesn't exist. Everything is relative.

And that's exactly the problem: you're fantasizing by anthropomorphizing a quantum observer.

What? This is simple special relativity. We've done the experiment with clocks and airplanes. Time dilation is a real phenomenon, and exploiting it would only mean that we need to accelerate a vessel to an appreciable fraction of the speed of light, relative to the earth. Why wouldn't a human be able to withstand that?

When a Jet goes faster than sound, OK, he can no longer hear the sound, but apart from that nothing changes, so with that theory, when people hit the speed of light, they would just not be able to see anything, right?

No. You can't ever hit the speed of light. As you approach the speed of light, you get diminishing returns on how much you get out of each unit of energy you put into the acceleration. You'd essentially need infinite energy to accelerate a particle with non-zero mass to the speed of light. (Real infinity, like, more energy than there is in the universe) This falls out of the Lorentz Transform, basically.

For the most part (There are a few experiments which show superluminal movement of a photon is possible in certain scenarios), the speed of light is a hard barrier.

[+M2Ys4U Subscriber¹]

So why is light allowed to move at the speed of light without slowing down ?

What makes IT so special ? :laugh:

Photons don't have any mass, which is what stops other particles from reaching the speed of light.

As you accelerate a particle with mass, the amount of energy needed to keep accelerating it increases, so that as it approaches the speed of light the energy needed to continue accelerating it approaches infinity.

[Tekkerson]

Actually, photons DO have mass (proved by Einstein's eclipse experiment).