possible time travel

[dieferbiefer]

Could someone plz help me answer this, albert einstein said that if you went faster than the speed of light you would go forword in time because the faster you go the slower you age, so if you were in the space shuttle moving at about 12000 mph (nowhere near the speed of light) would you still age a little slower at all?

[iNow]

Could someone plz help me answer this, albert einstein said that if you went faster than the speed of light you would go forword in time because the faster you go the slower you age, so if you were in the space shuttle moving at about 12000 mph (nowhere near the speed of light) would you still age a little slower at all?

 

The short answer is, yes. Relative to a stationary observer, the person on the space shuttle traveling at 12,000mph (relative to that stationary observer) *would* age a bit more slowly.

 

The cool thing is, one can calculate by how much using the Lorenz Factor:

 

http://en.wikipedia.org/wiki/Lorentz_factor

 

12,000mph is 0.000017893979c (since c = 670 616 629 mph).

 

[math]

\tau = \sqrt{1 - . 000017893979^2} \cdot= 0.999999999839903

[/math]

 

That last number is what you would multiply Earth seconds by to get shuttle seconds. As you can see, for every one Earth second, the shuttle crew gains about 0.00000000016 seconds.

 

In other words, you can see that those in the shuttle actually aged less than those on Earth (or stationary observer), but only by a tiny fraction of a second.

 

 

Actually, check my work. I'm not sure if I did the conversions correctly, but the point is that the difference in elapsed relative time is extremely super tiny until one gets close to the speed of light.

[kevin55521]

relative to this, if you do travel that fast and age slower do you actually stay in the same state of time as an observer? or would say a year to the observer be like a second to you (with whatever speed is needed).

 

 

also, id like to clear up that traveling backwards in time is impossible, my reason for this being the fact that if some1 DID invent a time capsle or whatever they could have come bak in time and told us that they invented it, and considering time is endless either the human race dies out before one can be invented or, some1 who did invent one would find a way to keep it nder wraps the entire time which does seem highly unlikely.

 

travelling forward in time does seem very interesting, do you know what it would do if you were instead of "moving" fast, spinning around fast?

[Fred56]

Traveling in time is not possible because time isn't like a line you can walk along or like a plane or like a 3d space you can move through. It has no dimensions, like space does. Traveling back to a previous time assumes that the "previous time" is "back" there, maybe it's recorded on some big universal recording mechanism, or something. Or maybe it's not there because there is no "there" for it to be.

 

The relativistic time dilation issue is due to traveling at a reasonable fraction of c. So, as the previous post to yours indicates, someone traveling at high speed would age slower, at very high speed, even slower, and so on. Even the guys on the space shuttle (and airline passengers) do this.

[Spyman]

Traveling back to a previous time assumes that the "previous time" is "back" there, maybe it's recorded on some big universal recording mechanism, or something. Or maybe it's not there because there is no "there" for it to be.

I think the spacetime coordinates for the past exists just like the coordinates for the now and the future.

 

So there is a "there" for it to be, but the "there" is likely empty now since objects is moving forward in time.

(The previous time is back "there", but the objects are here now.)

[Fred56]

Entropy is like having a one-way ticket. When you arrive, you see that not only are there no return tickets available, but where you came from doesn't exist any more.

 

I think the spacetime coordinates for the past exists just like the coordinates for the now and the future.

 

Exists where?

[Sisyphus]

Exists where?

 

You're asking where coordinates are? How would one answer such a question?

[ydoaPs]

Entropy is like having a one-way ticket. When you arrive, you see that not only are there no return tickets available, but where you came from doesn't exist any more.

 

Not really. In fact, for heat engines to exist, your statement must necessarily be false. Heat transfer out of a system will reduce that system's entropy.

[Fred56]

You're referring to a so-called "reversible" process. When these occur, entropy (heat) is transferred (to do work) but the overall entropy of the system is still >=0. Check it out.

[Edtharan]

albert einstein said that if you went faster than the speed of light you would go forword in time

Actually you don't need to go faster than the speed of light to go forward in time. When ever you are moving relative to another object then you local Time will be "stretched" out and you will appear to travel faster in Time.

 

This has been experimentally confirmed by flying an atomic clock in an aircraft around the World. They put 1 clock in the plane and another stayed at the take off point. When the plane came back around to the take off point, they compared the two clocks and the clock on the plane had recorded less time than the one of the ground. This means that more time had passed for the clock on the ground than the clock on the plane, the clock on the plane had travelled forwards in time.

 

Of course this Time travel in not like the time travel depicted in movies like "Back TO The Future". The plane didn't disappear "leaving trails of Fire" and reappear in a similar manner. The plane existed continuously through the journey, it's just that to observers not on the plane, they would have seen things (like clocks) running slower (a bit like a slow motion movie), where as on the plane they would have seen the rest of the world sped up (like fast forwarding a movie).

 

Because the plane exists at all points along the time line as observed from the ground, anything from the ground can interact with the plane and anything from the plane could interact with things from out side it (like radio signals, or a ball even - if you could throw fast enough to hit a flying jet ).

 

So, yes. In this situation we can have time travel. But so far we have no practical method to go backwards in time.

 

Relativity does not say that we can't go backwards in time, but the methods scientists have (mathematically) explored so far are very impractical (like infinitely long cylinders, moving faster than light, and so forth).

 

But what would someone going backwards in time look like to an outside observer? Well, again, they wouldn't just disappear from our time and reappear in the past in a flash of light. As an outside observer, we would see them throughout their journey as they travelled backwards in Time.

 

We would see one "copy" of them going forwards in time as they prepared to go backwards, and then we would also see then as they travelled backwards, however it would appear that their motion was Time reversed (like a movie in rewind).

 

We could interact with the backwards time traveller just as we could interact with the forwards time traveller (the plane). However, every thing from both our perspectives would be reversed, including what appears to be cause and effect.

 

This is what would be the most bizarre part of backwards in time travel. A Reverse Time traveller (according to our perspective) would be able to answer a question that we have yet to ask. However, from their perspective, they would be answering the question after we asked it.

 

The same is true if they were to ask a question. We would appear to answer it before they asked it, but according to our perspective we would be answering the question after they asked it.

[Spyman]

Exists where?

Where is the spacetime coordinates for "now" ?

[foodchain]

Where is the spacetime coordinates for "now" ?

 

Well I would think that such would be the entirety of the universe right now if it could be instantly frozen or taken a snapshot of. I think a second into the future would be all that as one second passes, universe time:eek: would be the coordinates for that future. I thusly think the past would be the coordinates of everything in the universe, again universe time one second ago. Universe time I know does not exist I am just thinking of one clock for the whole universe to compare to.

[Spyman]

We could interact with the backwards time traveller just as we could interact with the forwards time traveller.

I don't think we could see or interact with a time traveller, he would not be inside our light cone.

(Both the past and the future part.)

 

The plane in your example never left our light cone, but a "real" time traveller would have to.

 

In general relativity, the future light cone is the boundary of the causal future of a point and the past light cone is the boundary of its causal past.

http://en.wikipedia.org/wiki/Light_cone

 

 

@foodchain: My reply was for Fred56, who was asking me where the past spacetime coordinates exists.

(If I interpret your post correctly, I think I agree.)

[Fred56]

Actually you initially said that you think the spacetime coordinates for "the past" are just as real or exist like the coordinates do for "now and "the future". So I asked where they are, or where you think these coordinates exist. If you are implying that the past and future coordinates (of everything) are the same this would only be true in a motionless (no change) universe (or maybe a universe with no objects, that would be odd, empty space with no motion or interaction, would it qualify as a universe?). I am also assuming that by coordinates you mean something like "all points in space", which isn't the same thing as the location of some event. I first thought you were talking about the coordinates of past events, but you seem to be talking about all coordinates, i.e. every point in space, which must be an infinite set. Can you see the point of my question now?

[ydoaPs]

You're referring to a so-called "reversible" process. When these occur, entropy (heat) is transferred (to do work) but the overall entropy of the system is still >=0. Check it out.

 

It depends on how you define the system. For a heat engine to work, all properties of the system must return to the original value. Entropy of the system is still >0, but the entropy of the system still decreases with heat transfer out of said system.

[Edtharan]

I don't think we could see or interact with a time traveller, he would not be inside our light cone.

(Both the past and the future part.)

Yes, from the point/time of departure, but remember they will be travelling backwards in time. If light is emitted from them, then would it be travelling backwards or forwards in time? I think it makes no difference.

 

From lights point of view, time is not happening, so whether or not it is emitted backwards of forwards is irrelevant form the lights point of view. All events along the world line of a photon occur simultaneously.

 

So the photons emitted from a time traveller could interact with a normal point of view because the light emitted by the time traveller and the non traveller are to all intents and purposes the same.

 

According to QM, however, interactions between matter is conducted through bosons (and light is a boson). Normal matter (I'm not considering dark matter here) interacts through the EM boson (light). If we can therefore interact with light emitted from a time traveller, then we can interact with them (even at the very least use flashes of light to ask them a question).

[Fred56]

For a heat engine to work, all properties of the system must return to the original value.

 

But if the entropy returned to its original value wouldn't that mean the engine had not done any work? Doesn't a reversible system return to its original state only if the entropy change is =0 (a perfect reversal), and this means no work is done?

[Spyman]

Actually you initially said that you think the spacetime coordinates for "the past" are just as real or exist like the coordinates do for "now and "the future". So I asked where they are, or where you think these coordinates exist. If you are implying that the past and future coordinates (of everything) are the same this would only be true in a motionless (no change) universe (or maybe a universe with no objects, that would be odd, empty space with no motion or interaction, would it qualify as a universe?). I am also assuming that by coordinates you mean something like "all points in space", which isn't the same thing as the location of some event. I first thought you were talking about the coordinates of past events, but you seem to be talking about all coordinates, i.e. every point in space, which must be an infinite set. Can you see the point of my question now?

The past, now and future coordinates are of the same cind, placed in the same spacetime continuum, the Universe.

 

The space coordinate (x,y,z) in the past is the same as space coordinate (x,y,z) in the future. Motion is when objects is changing coordinates, not when the coordinates is changing. An event is a specified change at a specified spacetime coordinate. Any change could qualify as an event, at any position, (both space and time).

 

I think that the spacetime coordinate (x,y,z,now) is as real as (x,y,z,now-3days) or (x,y,z,now+3days).

 

Where they exists ? - That would be relative where you are, wouldn't it ?

 

The coordinate -3days is three days back in the past relative now, tomorrow it will be four days back, relative me because I will have moved 1 day forward into the future. It's not very far from saying that a position three meters away will be four meters away if I move one meter. The position where I stand now doesn't vanish because I move one step, it's still there but at a different position relative me.

 

I view Time like a line and we are moving along it, our past and future positions on the line exists too.

 

The question if it is possible to "jump" backwards or forward is still unsettled by science, but we have already proved that we have the ability to slow down or speed up our relative speed in time, (like Edtharans example).

 

Maybe it turns out that "it's recorded on some big universal recording mechanism" so you can visit your grandfather. But then it's likely that you would create a paradox with a major malfunction as a result.

 

In my opinion a time traveller jumping backwards or forward in time will only find empty space, unless there are other time travelling objects or persons out there. The particles that your grandfather was made of has moved and is here now, and they have not moved to the future jet. Unless you don't bring the particles with you, you are not going to be able to interact with them.

(And the particles won't reverse their actions and become your grandfather if you bring them back with you either.)

 

I don't see any problems with a infinite set of spacetime coordinates...

 

 

Yes, from the point/time of departure, but remember they will be travelling backwards in time. If light is emitted from them, then would it be travelling backwards or forwards in time? I think it makes no difference.

 

From lights point of view, time is not happening, so whether or not it is emitted backwards of forwards is irrelevant form the lights point of view. All events along the world line of a photon occur simultaneously.

 

So the photons emitted from a time traveller could interact with a normal point of view because the light emitted by the time traveller and the non traveller are to all intents and purposes the same.

 

According to QM, however, interactions between matter is conducted through bosons (and light is a boson). Normal matter (I'm not considering dark matter here) interacts through the EM boson (light). If we can therefore interact with light emitted from a time traveller, then we can interact with them (even at the very least use flashes of light to ask them a question).

Everything seems to be moving forward in time, or at least everything we observe, they only photons we can see is the ones emitted in the past and reaching us now, those photons must be moving forward in time too.

 

The photons point of view is irrelevant, if the photon and the observer is moving through time with the same pace then the photon is not able to catch up with the observer. The observer is no longer in the photons world line.

The photon might belive it is a time traveller but from our POV it still takes time for a photon to move.

 

If you new beforhand when and where they would pass, you could flash a picture which they could see, but the pass would be instant so they can't reply. Likewise they could flash an image, but they would be gone before you could reply. Any light from our time would reflect of them in the past, outside our light cone.

 

A think a "real" time traveller would be beyond our event horizon, anything else would be something moving forward in time together with us, inside our light cone.

 

Ability to reply to questions not yet asked, implies Fred56s machinery with an infinite row of Edtharans...

[stormwarrior]

I love the whole Idea of time travel. If it twere possible, I think that people would be amazed.

much the same way that the first fire started was startled by fire.

Or when watching televisions Star trek sparked cell phones from the ever so popular communicator!

 

Or even the horseless carriage....

 

All things are possible, the only thing that is impossible is human ignorance from marvels that have yet to be discovered. Funny as it sounds though you can be pessamistic or optimistic.

 

When asked if he thought he was dishearted about it taking 1000 failures to create the lightbulb Edison said. "I never failed in my attempt to create light in a filiment. Simply put I found 1 way to create light in a filiment and 999 ways to not create light in a filiment. I never failed, I simply didnt give up in my pursuit."

[Fred56]

Where they exists ? - That would be relative where you are, wouldn't it ?

 

You are still confusing position in space with position in time. They are not the same thing. If the (x,y,z) coordinates of a past event are known, i.e. where it occured that is different from when it occured.

 

I view Time like a line and we are moving along it, our past and future positions on the line exists too.

 

Lots of people do this. I do it too because it's a "simple" model of time. But that doesn't mean it's correct. If time is like a line, why isn't it also like a 2d plane, or a 3d space? If "our past ... positions on the line" existed we would be able to see them or move to them, but we can't do either of these things.

 

I don't see any problems with a infinite set of spacetime coordinates...

 

Nor do I, unless you are trying to find one of them, in which case an infinite number of them would make the job pretty tedious (just kidding).

[DZane]

Maybe someone has already invented a time machine that takes everything back in time and we just keep repeating the same things over and over again! That is why we dont know about it.

 

Edit: The could explain De Ja Vu !

[Spyman]

You are still confusing position in space with position in time. They are not the same thing. If the (x,y,z) coordinates of a past event are known, i.e. where it occured that is different from when it occured.

No, I am not, read my post again, please.

 

I said that (x,y,z,t1) coordinate is not the same as (x,y,z,t2) but the (x,y,z) part is, the position in space.

 

And that the difference between (x1,y,z,t) and (x2,y,z,t) is similar to (x,y,z,t1) and (x,y,z,t2).

 

Lots of people do this. I do it too because it's a "simple" model of time. But that doesn't mean it's correct.

I don't think General Relativity is a "simple" model of spacetime, and it is the best model we have.

 

If time is like a line, why isn't it also like a 2d plane, or a 3d space?

Yeah, and why don't space have 4d or even 5d ? - Knock it off, I don't know WHY nature is like it is.

 

Such questions won't aid your opinion or shot down mine...

 

If "our past ... positions on the line" existed we would be able to see them or move to them, but we can't do either of these things.

Everything we see is from past positions, you are in fact not able to see the actual "now"...

(So with your own argument the only real positions is in the past and "now" doesn't exist.)

 

AFAIK, The lack of ability to see or move to positions don't make them less real.

[stormwarrior]

trying to rationalize things that you dont understand can be interesting but in no way does it make it less real

[ydoaPs]

But if the entropy returned to its original value wouldn't that mean the engine had not done any work? Doesn't a reversible system return to its original state only if the entropy change is =0 (a perfect reversal), and this means no work is done?

 

No. All heat engines do work. There must be work on the system, work by the system, heat transfered into the system, and heat transfered out of the system. I'm tired of arguing, so this will be my last post about it. You can either trust me (there's no real reason for you to, but I am a nuclear mechanic, so I know a thing or two about heat engines) or you can research it yourself. I'll even give you the link to wikipedia.

 

http://en.wikipedia.org/wiki/Heat_engine

[Fred56]

There must be work on the system, work by the system, heat transfered into the system, and heat transfered out of the system.

 

Sure, but what happens to the entropy (the heat energy)? Doesn't work being done mean a change in entropy? I must have completely misunderstood my Physics on this.

 

I said that (x,y,z,t1) coordinate is not the same as (x,y,z,t2) but the (x,y,z) part is, the position in space.

 

And I said this is incorrect. I still say it. (x,y,z,t1) certainly is not the same as (x,y,z,t2), and the (x,y,z) bit will only also be the same if there has been no motion, no movement or change in any of x, y, or z.

(x1,y1,z1) will only be equal to (x2,y2,z2) at another time if and only if they haven't changed. A no-change universe means a no-time universe.