Gun with a tachyon bullet paradox

[amorphos_b]

Gun with a tachyon bullet paradox

if you had a device akin to some kind of ‘gun’, which created tachyons and the fired them, perhaps in a beam or some kind of ‘packet’, when they go faster than the speed of light would go back in time. Lets say the ‘bullet’ or beam, went out into the universe and due to the curvature of space, it would eventually arrive at its original point, but before it was launched or even created?

Having no mass the tachyon bullet or beam would not kill you? Although light has no mass but a laser could. if we could go back in time and fire a gun at ourselves, it would kill us before we fired the gun!

Is there an upper limit to time and speed, which would stop such things occurring, and does the closed universe model have limits?

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[anuttarasammyak]

If there exist tachyon, which go faster than light, what you say would make a paradox as you expect. But we have not found tachyon yet.

 

[Ibix]

There are definitely real paradoxes in relativity if you can exceed the speed of light. The "tachyonic anti-telephone" is a standard one, and doesn't require a closed universe. That it doesn't make sense may be a reason why we've never seen any evidence of it.