Physicists Theorize New Method for FTL Travel

[Mr. Paradox]

Exactly. But such a solution is self-consistent, which is the only requirement.
Of course, your spiralling solutions are also self-consistent. Moreover, your spiralling solutions may be more interesting from the physical point of view. Still, O-solutions are possible as well.

How exactly would it be possible?

 

[spock0149]

... Any FTL craft is a time machine in an appropriate frame OR you are breaking Lorentz covariance...

The basic idea of FTL travel is that you jump in a ship at point A and arrive at point B faster than light could travel by a direct path. Specifically you get ahead of the sphere of light emitted by the television coverage of your departure.

Saying one travels there via some modification of local space-time around the craft doesn't matter. If the arrival event at B is outside the future light cone of the departure event at point A then you can boost the whole mechanism of travel (assuming local Lorentz covariance) so that the arrival event is prior to the departure event and then reverse the boost and reverse the trip so as to arrive at A prior to the original departure.

Does anybody know if wormholes suffer from similar problems?

 

[Demystifier]

How exactly would it be possible?

You mean in practice, by acts of an advanced civilization? I am not saying that it is possible in that sense. All I'm saying is that such solutions of the equations of motion exist, so nature may (or may not) realize such solutions in reality. If you want, I can write such solutions explicitly. But if you are familiar with Fourier expansions of periodic functions, you can also do it by yourself.

 

[Dmitry67]

I add Dmitry67 conjecture :)
I state: There are no macroscopic objects without a history

An object without a history is an object, which exists exclusively inside a time loop. So it had been never created and its entropy does not always increase.

Remember my exaple with spiraling inside the time loop? I arrive inside a time loop and see a future copy of my ship. We fly close to each other, and someone arrives to my ship from a future ship. It is a guy called John Doe. he says "Hi, it is really cool here! I will never die, I am immortal! But don't forget to let me go after a full cycle, otherwise we create a causality paradox!"

I drink beer with him, and then I see my own ship - now it is a "past" copy of my ship. I let John Doe jump into that ship, saying farewell to him, then I hit a pedal to the metal and leave the time loop.

So who was that John Doe? He had no mother, father... How could he appear there in a first place? While it might be consistent with the Novikov's principle it sounds impossible.

So while world line of individual particles can be short cut, world lines of macroscopic objects never intersect and never form loops.

 

[Vals509]

i read this article somewhere too but its application will be unlikely as to travel FTL for 1 meter you need to have a size or mass (can't remember which one) the size of jupiter. obviously not feasible

 

[Demystifier]

While it might be consistent with the Novikov's principle it sounds impossible.

If something sounds impossible, it doesn't mean that it IS impossible.
It sounds impossible to you because you are used to think that all events have their cause in the past. But this is only an illusion, caused by the fact that we live in a very UNTYPICAL universe in which entropy increases with time. In reality, there are no causes and consequences. There are only solutions of the equations of motion.

 

[Dmitry67]

It sounds impossible to you because you are used to think that all events have their cause in the past. But this is only an illusion, caused by the fact that we live in a very UNTYPICAL universe in which entropy increases with time. In reality, there are no causes and consequences. There are only solutions of the equations of motion.

I agree with you regarding the nature of time.
However, I still don't believe in that John Doe.

The solution where during my spiraling I meet John Doe is mathematically possible, but the probability of it is not higher then the probability that a human being condense from atoms somehwere due to very lucky coincidence.

 

[Demystifier]

I agree with you regarding the nature of time.
However, I still don't believe in that John Doe.

The solution where during my spiraling I meet John Doe is mathematically possible, but the probability of it is not higher then the probability that a human being condense from atoms somehwere due to very lucky coincidence.

But humans DO exist due to a lucky coincidence (irrespective of the time-travel issue), don't they? Unless God created them, in which case She can also create them in a loop.
So, in a loop, either there will be no humans at all (neither John Doe nor yourself), which indeed is the most probable option, or there will be many "copies" of them.

 

[Dmitry67]

But humans DO exist due to a lucky coincidence (irrespective of the time-travel issue), don't they?

Correct, but there was 13 billions years to filter out 'useful' coincidences
Time loops (around Kerr singularities) are very short.

P.S.
I've just realized, what if the Big Bang is actually an END of the Universe - we live in the epoque when the entropy decreases? :)

 

[Demystifier]

Correct, but there was 13 billions years to filter out 'useful' coincidences
Time loops (around Kerr singularities) are very short.

Correct! So probably the loop will not contain any humans at all.

 

[Dmitry67]

Correct! So probably the loop will not contain any humans at all.

Except the ones coming there from outside
You CAN enter the time loop, even it is a loop.

 

[Demystifier]

You CAN enter the time loop, even it is a loop.

How?
Can you describe the topology of such a universe?

 

[Dmitry67]

How?
Can you describe the topology of such a universe?

Sure. Check the image attached. yes, I know, my drawings are really bad.
But I did it in Paint using a mouse...

So, you see a naked ring singularity. When you approach it due to frame dragging the 'hourglass' rotate finally forming a closed timelike loop (red). Still, you can enter it approaching to it from outside (green line)

In other words, the timelike loop region can be absolutely "naked", there is no horizon preventing from going inside or outside from it.

 

[Demystifier]

Hm!
If I understood you correctly, the trajectory of a traveller is described by both the green and the red curve. However, there is something inconsistent with it. The problematic point is the point at which the two lines (green and red) meet. At that point, the traveller has TWO different 4-velocities, which means that this "solution" is not self-consistent. How do you comment on this?

 

[Dmitry67]

No, red line just shows 1 example of a timelike loop. Timelike loop region contains infinitely many different timelike loop trajectories, including intersecting trajectories.

So red like is just an example of one of them.

Green line shows that he entered that area, then it depends on his decision what to do (so it did not show what happened next to him).

 

[Demystifier]

No, red line just shows 1 example of a timelike loop. Timelike loop region contains infinitely many different timelike loop trajectories, including intersecting trajectories.

So red like is just an example of one of them.

Green line shows that he entered that area, then it depends on his decision what to do (so it did not show what happened next to him).

Show me the whole green line (or at least a much larger part of it) because otherwise I cannot see that there exists any consistent green line at all! I want to see that the green line can make a loop (or something like that) in a consistent way.

 

[Dmitry67]

Ok, so the spaceship finishes a loop, sees his own 'old' copy and commits suicide hitting the singularity.

 

[Demystifier]

Fine, that's consistent!

 

[Mr. Paradox]

Wait so if you are in a time loop than how can you leave the loop if time repeats itself?

 

[Dmitry67]

Check the diagram
After you complete a loop, you end at the same time, but slighlty different position in space. Hence you don't need to repeat all you did before, you can do something different

 

[Demystifier]

Check the diagram
After you complete a loop, you end at the same time, but slighlty different position in space. Hence you don't need to repeat all you did before, you can do something different

This can also be rephrased as follows. You do two different things at the same time, but you also do them at two different positions in space, which makes it consistent.

 

[Dmitry67]

I've realized (and now I remember, I read somewhere about it before) that if there is a closed time-like loop (like the one I drew) then it is possible to go back in time just orbiting around the naked singularity (that is why physicists are so afraid of naked kerr rings?) - at least to the moment of the formation of the naked singularity.

In other words, if there is a closed time-like loop, the causality paradoxes (even we agree with the Demistifier that these paradoxes are not real) "leak" outside of that loop to the whole Universe.