Time Travel and Paradoxes

[blike]

Assuming time travel was feasable, the production of a time machine could open a whole box of casual paradoxes. For example, the girl who traveled back in time to kill her mother. If the mother dies while she was a young girl, her daughter would never travel back in time to kill her. How do we make sense of this?

 

Or consider the time traveler who leaps ahead and learns of a new mathematical theorem in a leading journal. Suppose he returns to his own time and publishes the article in a journal. The article is the same one he read in the future. Where did the information come from? The information seemingly came into existence from nowhere.

 

Are there laws of physics that will prevent these kinds of paradoxes from occuring? Stephen Hawking proposed a "chronology protection conjecture" which would outlaw casual loops. Because the theory of relativity is known to permit causal loops, chrnology protection would require some other factor to intercede to prevent travel into the past. What might this factor be?

[Adrian]

you wouldnt be able to travel back in time before the time-machine was created. its easy once you think about it. michu kaku explained this in detail in an interview.

[Radical Edward]

I doubt there will be ant protection as such. I think that either there will be casual loops, or that current thinking is actually wrong, and the universe won't allow time travel in the first place. failing that we can always fall back on one of the more exotic theories, such as multiple universes.

[aman]

The past is recorded in space. 2000 light years from here is our Earth 2000 years ago. If the past is recorded than the best we will ever do is visit a recording and observe. I don't think this will cause a paradox.

Just aman

[blike]

The past is recorded in space. 2000 light years from here is our Earth 2000 years ago. If the past is recorded than the best we will ever do is visit a recording and observe.

 

So if we visted, we could look, but not touch?

 

 

--

 

Paul Davies presented a view I'm not too familiar with in scientific american. I always envisioned us flowing through time in a specified direction. He says this is due to unidirectional sequence, for example dropping an egg will smash it to pieces, but you'll never seen a broken egg fix itself. Roughly, this is the second law of the thermodynamics.

 

He goes on to say

 

"Because nature abounds with irreversible processs, the second law of thermodynamics plays a key role in imprinting on the world a conspicuous asymmetry between past and future directions along the time axis. By convention, the arrow of time points toward the future. This does not imply, however, that the arrow is moving toward the future, anymore than a compass needle pointing north indicates that the compass is traveling north. Both arrows symbolize an asymmetry, not a movement. The arrow of time denotes an asymmetry of the world in time, not an asymmetry or flux of time. The labels "past" and "future" may legitimately be applied to temporal directions, but talk of the past or the futre is as meaningless as referring to the up or the down."

[jvanhalderen]

First off al, I do not think it is possible to "TRAVEL" back or forwards in time. I do think it could be possible to watch back into time. As each object reflects light and light is continuous.. "Simply" travel faster than the speed of light in the same direction to collect "history". Quite logical because the same thing is happening when we look at for example: galaxy M87. This galaxy is 65 miliion lightyears away. If we observe today we will get a reflection of how it was 65 million yrs ago.

 

But lets assume it is possible to actually go back in time. How could you be sure that at that point in time, time is contineus. For all you know you are stuck in that fraction of time. And without time there can not be movement, without movement there is no energy. What will remain??? Nothing if you ask me.

 

Time travel: I still think its impossible

[blike]

First off al, I do not think it is possible to "TRAVEL" back or forwards in time.

 

Say for example I travel very close to the speed of light, quite simply put, I would travel forward in your time. You would live and die while I age a few minutes. Essentially, I travel forward in time

 

Traveling back in time is a bit trickier, though.

[jvanhalderen]

You would live and die while I age a few minutes.

 

If heard of this before but never actually completly understood it, would you mind explaining this to me?

[fafalone]

I believe it's fully possible to travel forwards in time due to time dilation, at least in a way. If you could stay just beyond the event horizon to a black hole, a day for you would be a year for everyone in normal spacetime. Same with travelling close to the speed of light. In this sense, it's possible to "travel" into the future.

[quantumdream]

The question might be, [how] does eliminating information paradoxes restrict the topology of spacetime? If there are no spacetime singularities allowed, anomalies involving an intersection from joining two separate timelines might be eliminated. Then again, branes or strings could smoothly connect disparate paths. In this latter case, uncertainty may justify the "coexistance" of many parallel, indistinguisable events.

[aman]

Originally posted by quantumdream In this latter case, uncertainty may justify the "coexistance" of many parallel, indistinguisable events. [/b]

 

If time was not a flow but divisions of time, say 10^80 slices per second for example. Then in between each of those slices it is possible for 10^80 smaller slices slightly out of phase but imperceptable to any other phase. Is that what you mean by coexistance? At the same time but out of phase?

Just aman

[quantumdream]

Close enough. It seems like you are near the definition of a brane, where gravity is always "in phase," and parallel E-M "out of phase" with parallel dimensions of compactified/extradimensional space. It would take years for a light signal to travel the distance which for gravity would take a moment.

[aman]

That suggests there is no unified field theory possible if gravity "is always" and E-M or QM can do independant and irrelevant things. I would like to believe there is some kind of fundamental relationship. We'll figure it out.

Just aman

[quantumdream]

"In phase" suggests that gravity has a dimensionality with wavelengths on cosmological order, and "out of phase" that E-M has this dimensionality with wavelengths on the order of a millimeter (from extradimensionality models of spacetime and lower limit on measured gravitational effect). Long wavelengths tend to stay in phase over a given distance, whereas short ones would tend to interfere over that same distance. Coherent-phase extradimensional waves enable the efficient transfer of gravitational information through vast spacetime, but only narrowly for light.

[Radical Edward]

Originally posted by quantumdream

"In phase" suggests that gravity has a dimensionality with wavelengths on cosmological order, and "out of phase" that E-M has this dimensionality with wavelengths on the order of a millimeter (from extradimensionality models of spacetime and lower limit on measured gravitational effect). Long wavelengths tend to stay in phase over a given distance, whereas short ones would tend to interfere over that same distance. Coherent-phase extradimensional waves enable the efficient transfer of gravitational information through vast spacetime, but only narrowly for light.

 

maybe I'm getting you wrong somewhere, but wouldn't this imply that light of different wavelengths travels at different speeds?

[quantumdream]

I'm not referring to conventional dimensions like those of ordinary spacetime. I'm speculating, using harmonics of compactified string or extra brane dimensions.

[Radical Edward]

not knowing anything about M-Theory, I'm just using the meanings of the words as I understand them. If you can explain yourself a bit more clearly, that would be nice.

[quantumdream]

I'm in the same boat, so here it goes, by the seat of my pants:

 

Branes involve extradimensional (parallel) dimensions. I'm thinking that at least one of those (spacetime) dimensions' resonances interferes less destructively (if at all) for gravity than for E-M waves (restricted to conventional spacetime). The brane extraspacetime may then be seen through gravity as traversing the cosmos, "short-circuiting" our accustomed four dimensions, as it were. We see light confined to our spacetime and travelling circuitously compared to gravity cutting across its E-M paths.

[Sayonara]

Originally posted by quantumdream

I'm in the same boat, so here it goes, by the seat of my pants:

You mean, putting it in the simplest possible terms, this brane dimension is a 'short cut' which gravity may traverse but which EM may not?

[aman]

We have a neutrino dimension that exists all around us but just barely interacts with our existance. This is because of unmeasurability. Are branes proposed as just on the edge of our measurability or are they synchronous to our existance with masses equal but out of phase?

I can understand propositions of the former. There can be an infinite number of four dimensions of things too small to measure or too big at the same time. Could you clarify? Thanks.

Just aman

[fafalone]

26 dimensions

[aman]

I still have trouble with dimensions. I know the example of the point dimension that couldn't understand the line dimension that couldn't understand the plane dimension that couldn,t understand the cube dimension. I can see the four dimensions wee experience. I can see the smaller dimension and faster dimension and larger dimension than we can experience. The past, present, and future could be three dimensions instead of the one, just time. I can't imagine 26?

Just aman

[Sayonara]

Using rationality in a thread where the other participants are citing conjecture as fact and regurgitating 'Daily Mail' science is fun.

 

>here<

[Ragnarak]

Originally posted by fafalone

26 dimensions

 

A search on 'metric tensor' might be useful but from memory due to symmetry or some similar concept these 26 dimensions can be thought of as 10 dimensions which seems to be the accepted (?) number given by superstring theory

[Guest timetraveller]

Some one said on here therer are 26 dimensions. I saw on a TV science Prog that said there were 11 dimensions so Who is correct?