J Richard Gott describes how two cosmic strings, passing close to each other at close to c, could be used to achieve past directed time travel.

One prerequisite is that the strings must be of infinite length. The process would be extremely expensive, difficult, dangerous and almost certainly impossible. It seems unlikely that anyone would undertake this without being sure they had the right sort of strings. How could they know the strings were of infinite length?

Wave = ENERGY




ARE YOU ABLE SHOW ME Si units for (piece of) string ?

What is STRING theory ?

sometimes mathematica is showing many WAYS how to solve Equation
BUT only one solution is optimal real and TRUE ( this what we can observe not this what we are able imagine and evaluate ) !


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physics = ENERGY and many process energy changing form !

NOT EXIST PERPETUAL MOTION !

each process has got some efficiency never equal 100 %

BACK in TIME it is process ?

if You are able back in time You are able recoup energy that WE lost
in process that had place in past ?

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for example 5 minutes You giving HOT to Water ( TEA)
1 kW / efficiency 70%

You backing in time 5 minutes and WHAT ?
YOU HAVE COLD WATER ????

efficiency to make water cold 90%

ENERGY BILANS ???

PLEASE WRITE YOUR POST IN SCIENCE FICTION SECTION !
PLEASE STUDY CLASSICA ( on FORUM I showing YOU many nice problems)
STUDY HOW ENERGY IS CHANGING FORM THIS IS PHYSICS YOU WILL NOT WASTE TIME !

NONSENSE / IDIOTISM / STUPID ....I CAN NOT UNDERSTAND PEOPLE WHO NOT RESPECT ENERGY BILANS !

Well, that brings up a quick point. Does it really require that the strings be infinite in length? Is that just a simplification to make it easier to do the calculations? Maybe they could just be very long with respect to the frame of reference.

And how do cosmic strings move? They are extremely long and I believe massive. What would cause them to move at close to the speed of light? Also if they were moving at that high a speed they would probably create a significant disturbance in space and a distortion of our view. We should be able to spot them by the trails they would leave behind.

Bill Gill

Gott says they do; but as you know, I tend to suspect interpretations of infinity, even by experts.

I believe the estimated mass of a cosmic string is about 4 x 10^16 tons per inch. Initially I had difficulty imagining how two such massive objects could pass close to eachother, because of their enormous gravity. However, Gott is of the opinion that their gravity would be cancelled out by their tension.

This leaves me wondering how a string could be responsible for gravitational lensing.

Shouldn't this be in the NQS forum.

or perhaps general science , I just don't think it
belongs in the Physics forum pointing to the definition of Physics.



you cant do a study using imagined non physical objects
and we dont have a philosophy forum.

You are probably right there, Paul, but bowing to "convention" one has to accept that cosmic strings are included in astro-physics; there's a lot of fantasy physics out there.

Keeping in mind that Cosmic Strings are hypothetical. There is no evidence for them, and as far as I know there isn't any way to look for them, at least not yet.

Bill

There is, indeed, no physical evidence for them, but I suppose their interest lies largely in the proposed symmetry breaking in the early Universe which would have given rise to them. I understand there are people looking for unexplained gravitational lensing, which might the result of their presence.

My particular interest in them is that Gott and others argue for their possible use in achieving past directed time travel, which I enjoy arguing against.

Well, I don't know about past directed time travel. It does seem unlikely. Of course I do remember in some science fiction story I read some time or other that it was argued that if time travel is possible it will never be discovered. Because if it is discovered somebody will travel back in time and change something that will keep it from being discovered. One of those problems with the grandfather paradox.

Bill Gill