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[Eagleon]

It works because if something is travelling faster than light, it actually moves backwards through time. If you send something at 2c, then it moves with a 1/1 correlation with real time - i.e, for every minute that it moves, it goes 'backwards' one minute. You'd need to resend your signal exactly half a light-minute away from the transmitter in order to get it back instantly (plus the time it actually physically takes to resend it) If you send the signal "long" enough (which is weird to think about with negative time), you run into a situation where you can get something back earlier than it was sent off. It didn't happen here because the distance was so short, but if you magnified the distance enough it would.

And yes, I realize that with the speeds (and therefore distances) involved the idea is ridiculous That's why it's an idea and not an "Oh hey, I've just invented a cool thing we should do."

[RedKing]

Except that it doesn't. If the neutrinos went backwards in time, they should have arrived at the detector before they were sent. Which they didn't.

[Bohandas]

It works because if something is travelling faster than light, it actually moves backwards through time.

Only from certain perspectives; perspective is everything; that's why its called relativity.

It may be moving backwards in time from the prespective of the receiver but not the emitter.

[Eagleon]

Except that it doesn't. If the neutrinos went backwards in time, they should have arrived at the detector before they were sent. Which they didn't.

Except that it does. It takes a finite amount of time (even if it is a negative value) for the neutrinos to move across the distance involved, and that is less than but not even approaching negative values for how long it would normally take for the detector to find a neutrino from the collision, if it had sent out normal neutrinos. Basically, if it really did happen, we've already violated causality, but the violation is so minute that it's non-useful. Time is still going for the detector and the origin of the neutrinos, remember.

Only from certain perspectives; perspective is everything; that's why its called relativity.

It may be moving backwards in time from the prespective of the receiver but not the emitter.

Does it matter? Past a critical point, you can use the same process at the receiver to distort the perspective of the origin such that it precedes the original signal by sending it back again. That's what I'm saying.

[Bohandas]

Could somebody draw a lightcone diagram of this or something so we can follow easier?

[Aqizzar]

Except that it doesn't. If the neutrinos went backwards in time, they should have arrived at the detector before they were sent. Which they didn't.

Except that it does. It takes a finite amount of time (even if it is a negative value) for the neutrinos to move across the distance involved, and that is less than but not even approaching negative values for how long it would normally take for the detector to find a neutrino from the collision, if it had sent out normal neutrinos. Basically, if it really did happen, we've already violated causality, but the violation is so minute that it's non-useful. Time is still going for the detector and the origin of the neutrinos, remember.

This was always a sticking point with me, about relativity.  Science just stuck up this big notice seventy years ago saying "nothing can travel faster than light, if it does, time is broken", and all of science has said welp, gotta make sure everything we ever learn about physics conforms with that from now on.  Now, I don't really know anything about how this stuff works, but what I'm hearing is that something was observed that doesn't fit the theory.  Does that not mean that maybe, just maybe, everything you just said is actually wrong?

[Virex]

Except that it doesn't. If the neutrinos went backwards in time, they should have arrived at the detector before they were sent. Which they didn't.

Except that it does. It takes a finite amount of time (even if it is a negative value) for the neutrinos to move across the distance involved, and that is less than but not even approaching negative values for how long it would normally take for the detector to find a neutrino from the collision, if it had sent out normal neutrinos. Basically, if it really did happen, we've already violated causality, but the violation is so minute that it's non-useful. Time is still going for the detector and the origin of the neutrinos, remember.

This was always a sticking point with me, about relativity.  Science just stuck up this big notice seventy years ago saying "nothing can travel faster than light, if it does, time is broken", and all of science has said welp, gotta make sure everything we ever learn about physics conforms with that from now on.  Now, I don't really know anything about how this stuff works, but what I'm hearing is that something was observed that doesn't fit the theory.  Does that not mean that maybe, just maybe, everything you just said is actually wrong?

The question is of course, is what we know actually wrong? If the measurements can be described using a minor modification of existing theories (or even a reinterpretation of a theory without changing it), why assume that everything we know is wrong and that we need a radically new theory? Why are people so eager to call science wrong anyway?

[G-Flex]

This was always a sticking point with me, about relativity.  Science just stuck up this big notice seventy years ago saying "nothing can travel faster than light, if it does, time is broken", and all of science has said welp, gotta make sure everything we ever learn about physics conforms with that from now on.  Now, I don't really know anything about how this stuff works, but what I'm hearing is that something was observed that doesn't fit the theory.  Does that not mean that maybe, just maybe, everything you just said is actually wrong?

Or that, much more likely, what they observed is wrong, or something else is going on entirely.

I don't know why any of that has been a "sticking point" with you anyway. Yes, science has that "big notice" and it has worked. The only reason they still have that "big notice" is because everything has been consistent with it so far.

[Bohandas]

Except that it doesn't. If the neutrinos went backwards in time, they should have arrived at the detector before they were sent. Which they didn't.

Except that it does. It takes a finite amount of time (even if it is a negative value) for the neutrinos to move across the distance involved, and that is less than but not even approaching negative values for how long it would normally take for the detector to find a neutrino from the collision, if it had sent out normal neutrinos. Basically, if it really did happen, we've already violated causality, but the violation is so minute that it's non-useful. Time is still going for the detector and the origin of the neutrinos, remember.

This was always a sticking point with me, about relativity.  Science just stuck up this big notice seventy years ago saying "nothing can travel faster than light, if it does, time is broken", and all of science has said welp, gotta make sure everything we ever learn about physics conforms with that from now on.  Now, I don't really know anything about how this stuff works, but what I'm hearing is that something was observed that doesn't fit the theory.  Does that not mean that maybe, just maybe, everything you just said is actually wrong?

And like I said, the theory of relativity doesn't ACTUALLY limit velocities to being lower than the speed of light, it just says that it requires an infinite amount of energy (or even more  technically, an amount of energy equivalent to infinity times the resting mass of the particle or object) to ACCELERATE TO the speed of light*. If you can find a way to get an object to superluminal speeds without moving at the speed of light in the interim (or if you somehow can completely negate its rest mass, even briefly) that's perfectly in accordence with relativity.

*as speeds approach the speed of light, energy applied to increase momentum is increasingly applied to mass rather than to velocity.

[Aqizzar]

Because when you get experimental results that don't fit your theory, you change your theory.  The theoretical structure that science approaches the speed of light from was written before we even had atomic clocks or orbital telescopes.  Is it really so shocking that it might be wrong?

Of course, I'm perfectly aware that the far more likely explanation that there was an error in the experiment itself.  But if not, and they get a consistent result, then it might just be time to accept that yes, science was wrong, and now it gets to be less wrong.

[Bohandas]

Because when you get experimental results that don't fit your theory, you change your theory.  The theoretical structure that science approaches the speed of light from was written before we even had atomic clocks or orbital telescopes.  Is it really so shocking that it might be wrong?

Of course, I'm perfectly aware that the far more likely explanation that there was an error in the experiment itself.  But if not, and they get a consistent result, then it might just be time to accept that yes, science was wrong, and now it gets to be less wrong.

That's what they'll have to do if the result is independently duplicated elsewhere. If it isn't duplicated elsewhere then the simplest explanation for the result is that the extremely delicate, fragile, and finely calibrated equipment used in the experiment has broken or is defective.

[Virex]

Because when you get experimental results that don't fit your theory, you change your theory.  The theoretical structure that science approaches the speed of light from was written before we even had atomic clocks or orbital telescopes.  Is it really so shocking that it might be wrong?

Yes, you adjust your theory unless and until you can't do with that theory anymore. Then, you keep working with the old theory and a provisional adjustment to account for the discrepancy until someone has found a unifying theory that reduces to the old theory under certain circumstances. If these results really cannot be explained with relativity, and that is still something that hasn't been established yet, then relativity is still true, because it still describes all experiments that adhere to it, just as Newtonian mechanics is still true, for low velocities in Euclidian space. If these measurements really cannot be explained by our current theories (and remember, the Scharnhorst effect is another case of superluminal velocities that does not invalidate relativity), our current theories aren't wrong, but incomplete. But we already knew our theories are incomplete, that's where all the fuzz with string theory, M-theory et cetera is about.


A wrong theory is a theory that is incapable of predicting anything correctly, or one that invokes demonstratively false phenomena (think phloggistons). An incomplete theory is a theory that only does valid predictions in a limited number of cases (think Newtonian dynamics). A non-theory is a theory that predicts proper behavior but cannot be used to predict or extrapolate anything (such as intelligent design). A worthless theory is a theory that, while being able to predict, is neither simpler nor broader then another theory (for a long time, the matrix explanation of quantum mechanics was this, though I think recently it has gotten some more attention).
Claiming a theory is wrong is claiming that it makes false predictions all of the time, which is obviously not true for relativity.

[Starver]

Nine new replies?  I must type quicker.  Or less of it at a time...
edit: Typos corrected, e.g. "14 seconds" instead of "15 seconds", which I can't leave without looking like I'm innumerate

Yes, I see the confusion.  And regardless of how far ahead of the lightspeed-signal you get (thus "information from the future") it won't ever make a round-trip in negative time, because it will always have spent a positive time amount travelling, and will reach its origin/destination after it was sent.  Really, when I wrote up that travelling salesman example, I was being a bit flippant and didn't think that was what was meant, but was extending things out to perhaps slightly more ridiculous lengths than I should have allowed myself.

A signal going at 2c to a location half a light minute away will take (assuming, for now, the same inertial frame of reference for both ends) 15 seconds to get there.  If the sender flashes a "sending" signal with a standard signalling light, it will have arrived 15 seconds before the flash is seen by the recipient, but it's still not instantaneous, just less delay.  If the receiver flashes a "receiving" signal back (by standard means), the transmitters will see a response in 45 seconds (rather than 1 minute, if it had been a standard light-only signal sent out.)  If the outward transceiver is bouncing the signal back, it will again take an additional 15 seconds of transit time.  To the sender, that would be 15 seconds before the RCV-signal light, but it will still have been a 30 second round-trip time.  Positive 30 seconds later.

Even sending a signal at ∞c will mean that the 0.5lmin distant receive will get the signal 30 seconds ahead of conventional traffic.  If bounced, it will get back home 30 seconds ahead of the standard-type receipt acknowledgement.  Woohoo, that's a full 60 seconds of travel time saved, surely putting us into "voice from the future" territory, compared to....  oh, 60 seconds of normal transit.  What you're getting back is your signal, instantaneously (plus overhead).  Which is no better than just using your information locally and not sending it outwards in the first place.  No real time-travel here.



I am reminded of a story (I think a short story in a collection, I don't think it was the basis of a whole book, but if someone can recognise it it would interesting to reacquaint myself with those details) set in a future where there is galaxy-wide settlement, and communication is by an insta-transit coms-device that meant that we at least could talk to people hundreds of thousands of light-years away without having to wait (two times) hundreds of thousands of years.  But part of the plot of this piece was about the annoying "beeeeep" or screech or somesuch that started each communication.  It seems that somebody had worked out that this anomaly was actually a highly compressed signal consisting of the contents of absolutely every message that had been sent or would be.  And so there was an organisation that (protecting the secret) had set about to extracting all the messages it could, in order that news of assassination attempts or natural disasters was (wherever possible) used to pre-empt events in whatever allowable way they could[1] to help avert the dire results that might have arisen without the foreknowledge.

However, while a good plot device (at least if wielded in the right hands) not relevant to our discussion, I believe.  Just something that was dredged out of my memory from at least three decades back.


[1] I can't recall that they could change events, which meant that successful assassinations and actual casualty reports could not be done anything about, but I could be misremembering.  As I've always been a believer in time-travelling information being of the self-fulfilling variety, I much prefer a clever story where "what was sent back and was done had already been back and done" to any number of plots where history gets overturned or (at the extreme silly end) you get "Fading Marty McFly Syndrome".

[G-Flex]

And like I said, the theory of relativity doesn't ACTUALLY limit velocities to being lower than the speed of light, it just says that it requires an infinite amount of energy (or even more  technically, an amount of energy equivalent to infinity times the resting mass of the particle or object) to ACCELERATE TO the speed of light*. If you can find a way to get an object to superluminal speeds without moving at the speed of light in the interim (or if you somehow can completely negate its rest mass, even briefly) that's perfectly in accordence with relativity.

*as speeds approach the speed of light, energy applied to increase momentum is increasingly applied to mass rather than to velocity.

I feel like you're going to need to provide sources for what you're saying here. According to the equations involved, it seems to me that, yes, an object with positive rest mass going over the speed of light would either require infinite energy or be strictly impossible even with it. As kinetic energy increases, speed asymptotically approaches c. Going faster than c violates this.

[Bohandas]

And like I said, the theory of relativity doesn't ACTUALLY limit velocities to being lower than the speed of light, it just says that it requires an infinite amount of energy (or even more  technically, an amount of energy equivalent to infinity times the resting mass of the particle or object) to ACCELERATE TO the speed of light*. If you can find a way to get an object to superluminal speeds without moving at the speed of light in the interim (or if you somehow can completely negate its rest mass, even briefly) that's perfectly in accordence with relativity.

*as speeds approach the speed of light, energy applied to increase momentum is increasingly applied to mass rather than to velocity.

I feel like you're going to need to provide sources for what you're saying here. According to the equations involved, it seems to me that, yes, an object with positive rest mass going over the speed of light would either require infinite energy or be strictly impossible even with it. As kinetic energy increases, speed asymptotically approaches c. Going faster than c violates this.

What if you re-plot the chart sideways, showing kinetic energy as speed increases? I haven't actually worked this problem out myself, but if I understand asymptotes correctly, kinetic energy should only have an infinite/undefined value at the one point when speed is exactly equal to c.