Hawking Says Time Travel Possible

Why is this making headlines now? It has been known for decades that the closer to light speed you go, the slower time moves for you.
 
Say you had a really really long string. You left one end stationary, and tied the other end to the really fast spaceship.

Said spaceship accelerates for 6 years, reaches the speed of light, etc.

Now the spaceship slows down and returns back to where the beginning of the string is.

Does that mean the ends of the string would be in multiple time periods simultaneously?
 
quixotic said:
Instead of explaining it from the ground up, it's easier to think of it this way: Because everything else is defined using it, including time and space. Physicists slow and speed up time itself and add more dimensions to space to fit c, not the other way.
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Was the selection of light as the master reference completely arbitrary, or is there a logical argument to be made that light is the "natural" reference? Perhaps the math works out much more cleanly that way?

I always thought c being constant was a result of us measuring it - but measuring velocity requires measuring time, and our measurement of time depends on a constant speed of light, so I guess you have a point. But your post implies that physicists are changing reality to fit their models, and I don't think that is true.*

Is it similar to the reason why we use Euclidean geometry, even though elliptic and hyperbolic geometries are equally "correct" - because its the simplest way for us to look at things?

*Of course, going into the depths of quantum theory, there is no difference between what a scientist perceives as true and what "is" true, so...
 
collegeboy69us said:
Michio Kaku - he's quite famous, funny, I even have several of his books. He's a player on all these History and Discovery channel physics and astronomy shows.

Seems like you are the only one fixated on his disability. I know he's brilliant, and handicapped... I've heard things though about how he's kind of an ass once you get to know him. *shrugs*
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There's also that Tyson DeGrasse something or other guy; I guess he's personable, but I've always found him cheesy and annoying on those shows.
 
radioactivez0r said:
There's also that Tyson DeGrasse something or other guy; I guess he's personable, but I've always found him cheesy and annoying on those shows.
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He's actually really fun and nice if you talk to him though, less of a hand-puppet astronomy teacher... which I've noticed I'm also guilty of, and here I thought it was simply my Italian genes kicking in :D
 
Theoretically, such a space ship would allow the crew to repopulate the earth if they found our species had become extinct during their flight.
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Sounds like the backstory for a Fallout-like video game.
 
quixotic said:
Instead of explaining it from the ground up, it's easier to think of it this way: Because everything else is defined using it, including time and space. Physicists slow and speed up time itself and add more dimensions to space to fit c, not the other way.
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Interesting, I'm curious along the lines of what HOCP4ME stated as well. Is it the sort of thing where we sort of assume it's constant for the sake of our mathematical calculations and so far it has not yet (to our knowledge) gotten us in trouble yet?
 
My problem with time travel into the past is that we would have to assume that the past exists at the same time as the present. Forward time travel does make much more sense.
 
RangerXML said:
For me the whole traveling at the speed of light thing and time traveling things has always been a funky subject, namely because photons traveling from the subjects traveling at or near the speed of light would be like a slide show. Say a baseball pitcher can throw a baseball at 101mph and picture he is traveling at 101mph and throws the ball out of the back of the car, how fast is the ball traveling? To me, this is all relative, pun intended.
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NO. ALL inertial observers will measure the SAME value of c. That means that if you're on a ship going 99.9999999% of c you do NOT see the light moving at 0.0000001% of c - it still races away from you at 3x10^8 m/s. THIS is the core of special relativity - that all inertial observers experience the same laws of physics, and hence will measure the same value for the speed of light.
 
Sgraffite said:
Say you had a really really long string. You left one end stationary, and tied the other end to the really fast spaceship.

Said spaceship accelerates for 6 years, reaches the speed of light, etc.

Now the spaceship slows down and returns back to where the beginning of the string is.

Does that mean the ends of the string would be in multiple time periods simultaneously?
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Yes. Now think of the crazy implications of that:

Say the spaceship travels at a speed such that it takes 10 years, from the perspective of the ship, for the craft to return to Earth. From Earth's perspective, however, it takes 100 years (due to the time dilation thing). Ride on the spaceship, and you'll get back to Earth in 10 years; stay home, and you'll see the ship land in 100 years. Therefore, a person riding on the ship will have effectively traveled 90 years into the future.

Now, replace that string with a really long fiber optic cable. Wait 10 years. The other end has landed. You don't see it yet - you won't for another 90 years - but take a look through the cable: you'll see the landing site, 90 years into the future. You have now established a communication link through time. Citizens of the +100 years Earth can communicate with citizens of the +10 year Earth, and vice versa.

Of course, that won't actually work. The reason why is that communication still requires you to send information - at the speed of light, maximum - through that cable. And because of the time dilation, it will take precisely 90 years for your signal to reach the other end. Not a very useful communication link. Do the same thing with a wormhole, however, and you'll be rocking. It's too bad we don't know how to make those yet. :(
 
Sgraffite said:
Say you had a really really long string. You left one end stationary, and tied the other end to the really fast spaceship.

Said spaceship accelerates for 6 years, reaches the speed of light, etc.

Now the spaceship slows down and returns back to where the beginning of the string is.

Does that mean the ends of the string would be in multiple time periods simultaneously?
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No, that is not the correct interpretation. The two ends of the string will exist at the same point in space time, but will have taken different paths to get there.
 
HOCP4ME said:
Of course, that won't actually work. The reason why is that communication still requires you to send information - at the speed of light, maximum - through that cable. And because of the time dilation, it will take precisely 90 years for your signal to reach the other end. Not a very useful communication link. Do the same thing with a wormhole, however, and you'll be rocking. It's too bad we don't know how to make those yet. :(
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you mean we don't know how to make something for which we have no evidence of its existence? Simply because it's an allowed solution to an equation doesn't mean that it's reflective of reality.
 
Bobthecoolguy said:
I don't get it, how can you travel back in time (Technically reversing time to a point, while keeping yourself from being reversed.) then shoot another you? You would just shoot yourself, like not a younger version of yourself, just you. You wouldn't leave a copy to reverse in your place.
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I think that's the key argument to traveling in reverse. A more plausible theory is multiple universes in which one of them exists a younger you from the theoretical past.

I'm not the one to ask though, just some thoughts I'm throwing out there. This is totally out of my knowledge grade.
 
toy4x4 said:
I listened to a Discovery Channel show on black holes and how we might be able to travel through time via them. I can't name a person from that show. Would anyone be able to name Stephen Hawking is he was not disabled?

Don't get me wrong, he is one smart person. But would he be as renown if he was not disabled?
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Haven't gotten all the way through the thread yet but I just wanted to chime in and say I could probably name 5 - 8 people who were on on that show and another 10 who weren't who could have added to it.
 
JL6speed said:
Well then technically speaking, space exploration at great distances would be rather useless since it would require the people exploring to travel at the speed of light to even make any useful distances around even just within the galaxy. Then having them travel at that speed to return home to deliver the data, too much time would have gone by for the people at home.
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Exactly

So if you, travelling at 98% the speed of light, endured a day at the same time people on earth endured a year, and say you travelled 30 years worth away and 30 years worth back, earth would have endured 21,900 years. By then, people would be much much more advanced or not even around.
 
This is news?
The science behind this has been explored in numerous SiFi books, one of my favorites is Tau Zero.
 
spintroniX said:
Simply because it's an allowed solution to an equation doesn't mean that it's reflective of reality.
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Very important words. I'm not speaking against HOCP4ME's post. But in general people and their fantasies all to often seem to forget this important principle. There is a difference between what's logically possible and what's actually possible.
 
spintroniX said:
No, that is not the correct interpretation. The two ends of the string will exist at the same point in space time, but will have taken different paths to get there.
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This is actually a better description of what's going on than what I said earlier. Come to think of it, the original question - "existing in multiple time periods simultaneously" - doesn't really make much sense. There's that stupid time-based language again. :p

spintroniX said:
you mean we don't know how to make something for which we have no evidence of its existence? Simply because it's an allowed solution to an equation doesn't mean that it's reflective of reality.
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Parmenides said:
Very important words. I'm not speaking against HOCP4ME's post. But in general people and their fantasies all to often seem to forget this important principle. There is a difference between what's logically possible and what's actually possible.
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We have evidence that black holes exist, and according to the equations governing black holes, some of them should produce wormholes. Whether any of these are traversable, exist for more than a fraction of a second, or even work within the laws of general relativity, however, is unknown.

I look at the existence of wormholes the same as the existence of other intelligent civilizations: we've never actually seen them, but according to what we have seen, they should almost certainly exist (even if they will never be more than a curiosity from our perspective).
 
spintroniX said:
you mean we don't know how to make something for which we have no evidence of its existence? Simply because it's an allowed solution to an equation doesn't mean that it's reflective of reality.
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Reality is, he is correct.

Reality is, there is no engine currently even close to capable of propelling a craft up to 98% the speed of light. Energy req. for that speed increases exponentially as your speed increases. Not even close. Theres also the problem of space debris, slamming into anything at however many million (650) miles per hour would be fatal with anything we have today. The energy realeased would be tremendous.

Same idea bedind kinetic energy weapons (essentially a large several ton rod dropped from space) that will release as much or more energy as a nuclear weapon, depending on the speed it collides with earth.

Yes it Could happen, but it wont anytime soon.
 
HOCP4ME said:
We have evidence that black holes exist, and according to the equations governing black holes, some of them should produce wormholes. Whether any of these are traversable, exist for more than a fraction of a second, or even work within the laws of general relativity, however, is unknown.

I look at the existence of wormholes the same as the existence of other intelligent civilizations: we've never actually seen them, but according to what we have seen, they should almost certainly exist (even if they will never be more than a curiosity from our perspective).
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Hey man, my post wasn't directed at you. What I think gets a little too fruity is where there people imagine alternate universes where I chose not to post in HardForum, rather than to post in HardForum.
 
Parmenides said:
Hey man, my post wasn't directed at you. What I think gets a little too fruity is where there people imagine alternate universes where I chose not to post in HardForum, rather than to post in HardForum.
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I know it wasn't directed at me. No offense taken.

And ah yes...the many worlds theory. That's another whole can of worms. Although its main purpose is as one of the many explanations of time and time travel paradoxes. One off the (few) things physicists still don't understand hardly at all is why we experience time in such a linear, directional fashion. According to classical and relative theories, time should be just like any of the spacial dimensions, and the difference between past and future should be no greater than the difference between left and right. But it's obvious that's not the case, for unknown reasons.
 
He missed the fact that if a ship were to travel the speed of light or 98% you would need some kind of dampening field so the crew are not turned into a pile of mush.
And to avoid debris from smashing up the ship, some kind of shield would have to be invented.

Ok I'm watching too much star trek at this point, but theoretically it's all possible :)
 
Perhaps time is taken too seriously. I'd be inclined to say that it is just a measurement of sequence of events.
 
spintroniX said:
you mean we don't know how to make something for which we have no evidence of its existence? Simply because it's an allowed solution to an equation doesn't mean that it's reflective of reality.
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People said the same thing about black holes until we started seeing one in every galaxy...
 
HOCP4ME said:
I know it wasn't directed at me. No offense taken.

And ah yes...the many worlds theory. That's another whole can of worms. Although its main purpose is as one of the many explanations of time and time travel paradoxes. One off the (few) things physicists still don't understand hardly at all is why we experience time in such a linear, directional fashion. According to classical and relative theories, time should be just like any of the spacial dimensions, and the difference between past and future should be no greater than the difference between left and right. But it's obvious that's not the case, for unknown reasons.
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I hate to seem that I'm picking on you, but I'd like to correct some things in your post (sue me, I'm anal). Many worlds is an interpretation of the quantum mechanical process of measuring an observable; it wasn't developed to deal with time travel and the paradoxes it brings. If you'd like to read on the topic, go ahead and google it, as well as the Copenhagen interpretation - as they are competing view points.

Also, it's not quite true that we don't have an explanation for the arrow of times. It's true that many physical phenomenon are invariant under time reversal, but as you've pointed out there is a definite arrow to time. The reason is pretty simple, as it turns out: entropy. It appears as if the universe prefers to maximize its entropy, and this gives time a definite direction. If we reversed the arrow of time, we would be reducing the entropy of the universe - which is mathematically forbidden.

Think about it. Say you walk across the room and in so doing you radiate heat into the environment. If we reversed this process we would have to take all that energy and put it back into your body - which can't be done as that heat has been lost (otherwise perpetual motion machines would be commonplace).
 
delahaya said:
Would this ship be going to meet the aliens that Hawking believes in?
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Not many respected scientists doubt the existence of alien civilizations.

For a while I thought that if something was out there, we would have found it by now, but here's an xkcd comic that changed my mind (literally).
 
spintroniX said:
I hate to seem that I'm picking on you, but I'd like to correct some things in your post (sue me, I'm anal). Many worlds is an interpretation of the quantum mechanical process of measuring an observable; it wasn't developed to deal with time travel and the paradoxes it brings. If you'd like to read on the topic, go ahead and google it, as well as the Copenhagen interpretation - as they are competing view points.

Also, it's not quite true that we don't have an explanation for the arrow of times. It's true that many physical phenomenon are invariant under time reversal, but as you've pointed out there is a definite arrow to time. The reason is pretty simple, as it turns out: entropy. It appears as if the universe prefers to maximize its entropy, and this gives time a definite direction. If we reversed the arrow of time, we would be reducing the entropy of the universe - which is mathematically forbidden.

Think about it. Say you walk across the room and in so doing you radiate heat into the environment. If we reversed this process we would have to take all that energy and put it back into your body - which can't be done as that heat has been lost (otherwise perpetual motion machines would be commonplace).
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No problem. Please do let me know if I say something inaccurate. As a physics major (see sig) I will be studying these things very deeply over the next few years, although my understanding of them right now is mostly out of hobby reading.

I do understand the concept of entropy and how it gives time a direction. I'm not sure why I wasn't thinking of that when I posted. The way I understand it, entropy is not only why time has direction, but how we define that direction: given state A and state B, whichever state was lower entropy existed "after" the higher entropy state, correct?

I don't quite understand how many worlds explains the quantum effects of observation...care to elaborate on that? Is it that every observer exists in his own universe, which consists of everything he has observed up to that point?
 
For someone who can't talk he sure does talk alot, he is lame.


2 jokes in 1.


Time for theory is over, time to try to reach the speed of light.....which is unlikely possible.
 
Chombo said:
My problem with time travel into the past is that we would have to assume that the past exists at the same time as the present. Forward time travel does make much more sense.
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well by time travel I dont think he's referring to the fictional depiction where you can go through time and meet up with with yourself from 10 years in the past or future
 
stevedave said:
For someone who can't talk he sure does talk alot, he is lame.


2 jokes in 1.


Time for theory is over, time to try to reach the speed of light.....which is unlikely possible.
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IIRC, the current theory suggests that you cannot reach the speed of light; you can go slower or faster than light, but not the speed of light. I'm not sure if that is correct though...I remember learning something similar in one of my undergrad physics courses (only took a few, biology major and whatnot lol)
 
That's pretty much right. You can go 99.9999%..etc the speed of light, but not 100%. In order to get that last fraction of a percent would require more energy than there is in the universe.
 
Samson4EiT said:
That's pretty much right. You can go 99.9999%..etc the speed of light, but not 100%. In order to get that last fraction of a percent would require more energy than there is in the universe.
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there is a thoery that says you can go faster then light, but basically you warp the space around your ship. you are basically stationary but the space around you is going faster than light.

basically what star trek does. contract/expanding space, and it does not violate thermal dynamics, and there is not dialation effects as the space where your ship is is not moving.

Its all very theoredical, and would still require a massive ammount of energy but it is possible.

So if anyone has a machine capable of warping space-time let me know :D
 
HOCP4ME said:
I do understand the concept of entropy and how it gives time a direction. I'm not sure why I wasn't thinking of that when I posted. The way I understand it, entropy is not only why time has direction, but how we define that direction: given state A and state B, whichever state was lower entropy existed "after" the higher entropy state, correct?

I don't quite understand how many worlds explains the quantum effects of observation...care to elaborate on that? Is it that every observer exists in his own universe, which consists of everything he has observed up to that point?
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Well, you have to be careful. On a local scale, entropy can decrease - it's just that the total entropy of the universe has to increase. So if you lower it in one system, it increases in another. Therefore, your statement isn't entirely correct.

WRT the many worlds interpretation: suppose you have a system who has only two eigenvalues (possible outcomes of a measurement). For the sake of argument, let's say you're measuring the spin of an electron. Its projection along the z-axis can only have two possible values, +/- a constant. If you measure +constant, is there a universe in which an observer measured -constant? In essence, it ascribes a physical reality to all possible outcomes of a measurement.

If you want to truly be a physicist, best advice I can give is the following:
1) absolutely be prepared to work 60+ hours a week for the next few decades. Not everybody is capable of this, or does it, but they are not successful in the field in any meaningful sense of the word.
2) work in a lab as an undergrad and learn all that you can about instrumentation. You won't really learn physics until graduate school anyway.
3) start reading scientific papers now and learn how it is done.
4) ask questions in class and do your best to drive the discussion.
5) The most important quality is curiosity. Research begins with a question.
 
Why are you guys being so hard on Mr.Hawking? The new show on Discovery Channel is pretty good, and it gets people thinking and talking about this stuff. He won't be around forever and we'll need a new generation of physicists to solve these problems. A good start would be getting the masses interested in this and a little educated about it, which is what the TV show does.
 
say you build a ferris wheel the size of the planet that can make 8 revolutions a second. its possible yes? granted the enursha would kill you probably. that could travel faster then light!
 
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