possibility of time travel

[gnarledreaper]

Before i start i would like to say i am not a scientist and have no qualifications, what i will type is speculation i had after reading an article by Stephen hawking (http://www.dailymail...me-machine.html)

 

In that article he mentions he did an experiment where he made a party invitation and only planned to tell people about it afterwards, no one turned up as expected which means either travelling through time is impossible or the visit to his party was not worth the effort (which may be considerable)

 

This provoked me into thinking about time travel myself, i dismissed the idea of actually travelling back or forward in time because it seems impractical, what i did think about is would it be possible to communicate with the future, or the past.

 

In that article Stephen hawking suggests that everything has wrinkles and holes in it as a basic natural fact, even the fabric of space and time so if he is right it stands to reason that something could pass through these holes and appear in the future, or the past (maybe a signal of some kind)

 

I don't know if anyone has ever bothered with this and probably dismissed it as implausible if they have but i propose an ongoing experiment, listen in and see if we might be able to talk to ourselves from the future.

 

You take a frequency, a set period of time and a date, you ask a question and then you listen to the frequency, and only release the information after the time has passed, preferably onto the internet and in places where the information will be around for a long time, if we are able at some point in the future to communicate with the past there is probably no motive to do so as unless someone has anticipated this and is actually listening at a certain time the effort would be wasted.

 

Feel free to call me nuts and throw this in the trash, or point me in the direction of someone actually trying this if there is someone (i doubt it)

[Edtharan]

Interesting article.

 

I admit that I too have been facinated by time travel and do spend time think about whether it is posible or not.

 

The experiment that Hawking suggested, I think (although I am not a scientiest either), was never going to work. As he explained a wormhole type time machine will self destruct through feedback. However there are other proposed time machines, and all of them (including the wormhole type) can't send information (or time travelers) back before the machine is started. As no known time machines exist (yet ), then it would be imposible for any time traveler to return to the time of Hawking's party.

 

One of the more plauseable time machines use what is called frame draging (which has now been confirmed AFAIK). This where you have a massive object rotating (yes the Earth qualifies for frame draggin, but the effect is very small, but this is where it has been detected).

 

To turn this into a time machine, the rotation of the massive object has to be very fast (surface velocity close to the speed of light). This will then cause large frame draging (a bit like sphagetti around a fork). Orbiting this object in one way will allow you to go backwards in time, and orbiting the other way will take you forwards in time - but only for as long as the machine is operating. So you can't go back beyond when it was started, and can't go forwards beyond when it is eventually switched off (so going to Hawking's party is not possible either ).

 

As for paradoxes of time travel, I too believe that Hawking is right in that "somthing" will prevent the paradox from occuring. For an explaination of how this might occur is look at interference. According to Quantum Mechanics, all matter can behave as a wave and that a collection of matter can have a wave that describes the whole collection (although the wave would be a very complex wave). So, if you extend this to the entire universe (or just the matter directly affected by the paradox), then the state of the universe can be described by one such massive wave.

 

Now, waves have the property that they can interfer with each other, and waves that postivly interfer re-enforce each other giveing a stronger wave amplitude, where as if waves negatively interfer with each other they cancel out.

 

A paradox, in effect, acts like a negative interferance event with the time traveler cauings the paradox as the interfering wave. This causes the "loop" to cancel out and not exist, preventing the paradox from happening.

 

Think of this in terms of "Sum over Histories" ( http://en.wikipedia.org/wiki/Path_integral_formulation ) as used by physicists when looking at quantum physics.

 

It means that anything is allowed, as long as the two events (when the time traveler gos back and when they arrive) occur. Anything that prevents these two events occuring cancels out and can not exist.

[ajb]

Time travel is fascinating. Our current understanding of physics has no complete answer to why it should not be allowed.

 

In classical general relativity space-times that allow time travel can be found. They typically involve either exotic matter or rotation "mixing an angular coordinate with a temporal one". From the classical perspective (allowing exotic matter) it is not obvious that time machines are not a natural feature of our universe.

 

The tricky part come when adding quantum mechanics to the mix. There is the Hawking chronology protection conjecture that states that time machines are not allowed. I don't think there is any full proof of this, i.e. it is not promoted to a theorem, but is based on observation of semiclassical gravity.

 

So, semiclassical gravity is the theory of quantum fields on a classical fixed curved space-time as the background. You should think of this as quantising matter and the forces except gravity which remains classical. People study such theories on space-times that allow time machines, or Closed Time-like Curves as people prefer to call them. It appears that near the CTC's the quantum field theories are not well-behaved. Technically, the renormalised energy-momentum tensor diverges near a CTC.

 

This evidence is provided by examples. I must say I am not aware of any full general proof that QFT near a CTC is always sick.

 

The full answer to the problem of time machines will be found in a full quantum theory of gravity. Semiclassical analysis may not truly be enough.

[Spyman]

In that article Stephen hawking suggests that everything has wrinkles and holes in it as a basic natural fact, even the fabric of space and time so if he is right it stands to reason that something could pass through these holes and appear in the future, or the past (maybe a signal of some kind)

I think if these holes do exists then they are probably not only very small in size they are likely also very short in time, any signal passing through would therefor come from such a close future or past that they wouldn't be distinguable from normal signals.

 

 

point me in the direction of someone actually trying

Check out Professor Ronald Mallett, he is trying to build a time machine with circulating laser beams that he thinks could be used to receive messages from the future.

 

One of many newsarticles: http://www.physorg.com/news63371210.html

 

Home Page of Ronald L. Mallet: http://www.phys.uconn.edu/~mallett/main/main.htm

 

Wikipedia article: http://en.wikipedia.org/wiki/Ronald_Mallett

Edited October 20, 2010 by Spyman

[Incendia]

Sorry to tell you but...

Someone beat you to the idea ages ago:

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

http://www.daviddarling.info/encyclopedia/T/tachyon.html

 

 

In 1917 to be exact...

[gnarledreaper]

Thanks for replying to all of you, i have had the idea i described on my mind for a while now and wanted to express it without being called nuts, i figured a physics forum was the place for it.

 

The antitelephone isn't quite what i had in mind but thanks for the link, i had a look at it.

 

I will be following ronald mallet as well, so thank you for that link also.

[ajb]

I will be following ronald mallet as well, so thank you for that link also.

 

I have not heard much from Ronald Mallett the past few years. I guess we can take that as the experiments are not going as planned?

[gnarledreaper]

I believe he is seeking funding to build a machine he designed, read about him in a newscientist article and it implied he hasn't tried it yet.

[ajb]

I believe he is seeking funding to build a machine he designed, read about him in a newscientist article and it implied he hasn't tried it yet.

 

so the funding is not going quite as he planned...