Is FTL Travel Within a Light Cone Possible for Time Travel?

[Gamish]

FTL travel in a light cone?

I read in several places there there is one condition in GR, that will allow you to travel faster than light, and allow time travel to the past. Can someone explain this further, without getting too mathamatical (Ok, maybe a little math).

Thanks in advance

 

[Garth]

I think you are referring to one of two outcomes of GR. First it is not possible for a massive body to reach light speed measured locally, i.e. relative to local frames of reference.

Note: Depending on how you measure distance and time at events far from home it is possible to both have and observe distant bodies that are receding faster than light because of cosmological expansion, but this is not what you are talking about.

However there are at least two occasions when GR suggests time travel into the past is possible.

The first is when solutions are found with closed world-lines. i.e. like in "Groundhog Day" you keep revisiting the same place and time that you were at before. These solutions generally require some pathological combination of multiple spinning black holes and a spaceship doing a figure of eight around them or so - I wouldn't like to try it - apart from the inherent danger I would not want to be stuck in a closed time loop!

The second involves an Einstein-Rosen Bridge, a worm-hole or tube, connecting the annular singularities at the centres of two spinning black holes. You go in one and pop out the other - at least that’s the idea! You may well pop out within your own past light cone and therefore able to revisit yourself before you went in! Again I wouldn't like to try it - there's no guarantee the theory, having been extrapolated to extreme and untested regimes is correct – and you could pop out anywhere even in a different universe!

I hope this helps.

Garth

 

[R0man]

FTL (faster-than-light) travel within a light cone is a concept in theoretical physics that suggests the possibility of traveling faster than the speed of light within the boundaries of a light cone. A light cone is a geometric shape that represents the path of light in space-time, with the tip of the cone representing the present moment and the base representing all possible points in the future and past.

According to the theory of general relativity, time and space are interconnected and can be affected by gravity and the movement of objects. This means that the shape of the light cone can be altered by the presence of massive objects, such as planets or stars. As a result, if an object were to move faster than the speed of light within the boundaries of the light cone, it could potentially travel backwards in time.

However, this concept is still purely theoretical and has not been proven or observed in reality. The equations and theories that suggest the possibility of FTL travel within a light cone also come with many limitations and paradoxes, making it a highly debated topic among physicists.

In order to fully understand this concept, some level of mathematical understanding is necessary. But in simple terms, it suggests that under certain conditions, it may be possible to travel faster than light and potentially travel through time. However, the feasibility and practicality of such travel is still uncertain and requires further research and understanding of the laws of physics.