None. They just go back in time until it doesn’t need changing.
Last week, some scientists conducted an experiment where they got some neutrinos to, apparently, move faster than light. It wasn’t the first time this apparently happened, either. They fired the neutrinos out of some kind of big slingshot, sent them through the earth’s crust, and caught them in a second location 450 miles away. The neutrinos hit the finish line 60 billionths of a second before light would have (if light could travel through the earth’s crust which is, after all, opaque).
How do they know its the same neutrinos? Those things all look alike to me.
Here’s my hypothesis: a hidden underground race of
mole men superintelligent earthworms (mole men are so cliche) is trapping our neutrinos, while simultaneously firing off others from a few feet to the left, making it appear that the neutrinos are FTL when in fact they didn’t traverse the entire distance. Just to mess with us.
Experiments show that as one approaches the speed of light, time slows down relative to slower-moving objects. If you spent a year traveling at (say) half of light speed, when you returned you would find that what seemed like a year to you was a much longer time for the earth-bound.
In theory, any object reaching the speed of light would experience zero time. A trip taken at light speed would seem instantaneous to the traveler, no matter how long it was*.
The linked Economist article states that going faster than the speed of light would therefore cause time to reverse. This is a nonsensical statement. Would the traveler actually become younger? What would his perception of the trip be like? ‘Reverse time’ in this context is similar to ‘negative length’. You can say it, you can think it, but you can’t explain it. It has no meaning.
More importantly, it’s nonsensical because experiment also shows that as an object accelerates, it’s mass increases. In theory, the mass of an object becomes infinite once the object reaches the speed of light. Infinite (or just near-infinite) mass would mean an infinitely strong gravity field, which would immediately pull in and destroy all other matter in the universe. So who cares about ‘reverse time’?
“Don’t destroy the universe” is one of those little rules I try to live my life by. Unfortunately, it makes faster-than-light travel a lot harder. That’s why they use massless particles like neutrinos in these experiments; because a 1000% increase in zero is still zero.
So if you ever want to travel faster than light, better get started on that diet, lardbutt. What, you didn’t think all those chins could affect anybody but you?
*It occurs to me that not only would the trip seem instantaneous to the traveler, but also to his vehicle. Which means it wouldn’t require much fuel at all, once it reached light speed. Think how much you could save in gas money if you could drive at relativistic speeds!
Yes, there are many, many things wrong with that assertion.
UPDATE: “We don’t allow faster-than-light neutrinos in here,” says the bartender. A neutrino walks into a bar.