Faster than speed of light = time travel ?

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Discussion Overview

The discussion revolves around the concept of faster-than-light (FTL) travel and its potential implications for time travel. Participants explore the relationship between FTL travel and time perception from different reference frames, as well as the theoretical consequences of such travel within the framework of special relativity.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • One participant questions the connection between FTL travel and time travel, expressing confusion about the implications of traveling faster than light.
  • Another participant suggests that traveling faster than light in one reference frame allows for a different reference frame where the journey appears to go backwards in time.
  • It is proposed that all observers would see the arrival of an FTL traveler before their departure, raising questions about the nature of time and observation.
  • A hypothetical scenario is presented involving a line of stationary observers and an FTL spaceship, questioning what those observers would perceive during the journey.
  • Some participants express skepticism about the conclusion that FTL travel would enable time travel, suggesting that the outcomes of such travel are currently unknown and may challenge causality.
  • Discussion includes the idea that FTL travel could be analyzed within the context of Minkowski spacetime, indicating a theoretical approach to understanding the implications.

Areas of Agreement / Disagreement

Participants express differing views on the implications of FTL travel for time travel, with no consensus reached on whether FTL travel necessarily leads to time travel or what the observable effects would be.

Contextual Notes

The discussion highlights uncertainties regarding the assumptions underlying FTL travel and its effects on causality and time perception, which remain unresolved.

collector
This is my first post so let me know if I'm posting this in the wrong section.

I read somewhere that if we are ever able to travel faster than the speed of light that fact would automatically enable us to travel back in time. I don't see how those two things are connected. Even if we travel faster than the speed of light, say 1.5c, we would still be traveling at a finite speed.
Is this true, or did I misunderstand it when I read it? How does it work?

Thanks.
 
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If you can travel faster than the speed of light in some reference frame (like the earth), there is always a different reference frame where this journey goes backwards in time.
You would go backwards in time for some, not for all observers. If you turn around and go backwards (again faster than the speed of light, for some reference frame), you can get back to Earth before you started. That is time travel for all observers.

I am sure we have a detailed description somewhere in the forum.
 
Does the observer on Earth also see the person arrive before he leaves?
 
All reference frames will see the arrival before the departure.
 
This is like an FTL guy who checks into a hotel and the clerk says I'm sorry you don't have a reservation and then checks again oh there you it just came in.
 
So say you had a line of people (all stationary with respect to the planets) between Earth and some other planet and you let a faster-than-light spaceship fly next to the line. It would go from Earth to the other planet and then back again. What would the people observe? Let's say that the spaceship takes some time accelerate to it's top speed.
 
collector said:
I read somewhere that if we are ever able to travel faster than the speed of light that fact would automatically enable us to travel back in time.

I think that's a hasty conclusion. We don't really know what would happen, but we will find out when the first FTL travel is observed.
 
collector said:
So say you had a line of people (all stationary with respect to the planets) between Earth and some other planet and you let a faster-than-light spaceship fly next to the line. It would go from Earth to the other planet and then back again. What would the people observe? Let's say that the spaceship takes some time accelerate to it's top speed.
That depends on details of the journey, but a backwards-moving spaceship would be a possible observation.

Ookke said:
I think that's a hasty conclusion. We don't really know what would happen, but we will find out when the first FTL travel is observed.
Well, we can give up causality, and ask how FTL travel in a Minkowski spacetime (=the framework of special relativity) would look like.
 

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