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[Osmosis Jones]

Yeah, I can dig that. Einstein hated the idea of a probabilistic universe, and there are still quite a few scientists looking for a way around it. Guy named Bohm, who carked it back in the 90s, did a lot of work on the topic too. That said, if you take it to its extremes, you have to realise that a deterministic universe means that there is only one possible future, and our every future action is already fixed. Mind you, I'm not saying that QM gives us free choice, just that we're at the mercy of the dice instead.

[Starver]

If you could, however, reach a star 4 light years away from the Earth in a second, theoretically you would be able to view Earth as it was 4 years before.

Bears repeating.

However, to an outside observer it might appear this way.

Take the example of one object moving towards the observer faster than the speed of light. Essentially, it would look like it was in two places at once.

Which does nothing 'interesting'.  The guys on Alpha Centauri use their telescopes to see the USS Picard Manoeuvre being built for four whole years even while the completed ship is now sitting in orbit and telling them about the other events they are yet to see through their telescopes.  But it's no better or worse for them than if they'd been sent a radio signal telling them what they'd eventually get to see on the video-tapes being sent to them at 0.5c.

It might be a curiosity, but the information does not in that way break any particular laws of physics.  We all see the causes of effects after their actual occurrences (whether they have occurred three feet away or are in the furthest observable galaxies.  Merely seeing the effect before the cause is akin to archaeology, as long as you aren't at the location of the cause and not observing an echo.

Now remembering that gravity travels at the speed of light...

Hmmm...  So, I suppose what's interesting with this is that sending the USS Heart Of Gold very quickly to every single point in the universe means that the everywhere is immediately given the gravitational potential of the HoG.  Which wouldn't cause any problems, at first, given that being inside any mass effectively cancels that out...  But then, as time continued, you'd start feeling gravitational pull from all directions.  From further and further away but (an inverse square of influence) but more and more examples (squared, in its influence), thus piling a constant gravitational field which... what?  Well, within the topology of the Universe could it tip the balance between expansion and providing enough force to halt the advance and send us (eventually) into the Big Crunch?  That very much depends upon the topology, but it could cause localised structural changes in the way matter accumulates.  (Or hold it off from doing so?)

But the while there'd be a similar "There's two of 'em" effect as far as the gravity from the mass of the USS Picard Manoeuvre, I don't see that causing any complications, either.  When the ripples of the effect spread as far out as the rim of the galaxy then would the mass of a single space-ship count towards any significance[1] in the Grand Scheme Of Things?


Even FTL travel in opposition to another FTL ship (choosing the most extreme difference frames of references) don't get you actually telling something that it's about to be poked before the poke occurs that sets up the chain of events that (through superluminal information systems) that informs the poke-informer to tell the poke-informee...  That is, IYSWIM.  And does not apply if you also have to apply "imaginary time" to the travellers (root one minus v-squared over c-squared giving an imaginary factor), which is (along with the like factoring of mass, length, etc) the big problem with FTLness.


[1] My previous post notwithstanding.  Although if it was deterministic that the ship should do this, then it is deterministic that this effect should be felt, so no problem there.

[Virex]

Proof is here. It looks scary, and it is kind of mind bending, but it's possible to work your way through it with first year uni maths and physics.

I'm going to keep quoting this post until people understand why breaking C is going to break stuff in more ways than just being super-duper-fast.

[Dsarker]

What about for those who have done neither?

[Starver]

In short, for any signal sent FTL in one frame of reference, another frame of reference can be found in which that signal actually traveled backwards in time, thus violating causality in that frame.

That means that if we shoot a couple of neutron sources and recievers off into space at an appreciable fraction of c (possible with project orion style rockets) and pass messages from us to one source to the next source and then back to us, we actually could send messages back in time. NOTE: We ourselves are not going back in time; only our messages are.

I'm not convinced by that.  As I think my immediately prior message hinted at (without having read this first, sorry)...


Messages that "travelled back in time" are only 'seen' from frames of reference in which there are further SoL delays.  i.e. you can see a 'further away' destination receive a message before it should have done (by your frame of reference), but the time taken to be notified of that reception completely lags the message behind that which would have come directly from the initial sender.

And those sent from further to nearer could just have been sent straight to you, rather than stopping off at the nearer.  Rotating frames add other complications, of course, but a similar lack of advantage in all the variations I'm contemplating.

(BTW: "neutron sources"->"neutrino sources", yes?)


edit: In a classic "message takes time to get somewhere" example, I think I've been replied to on a previous version of this point.  I'll look at the link in a moment, but I'm entitled to make myself look like a fool for the courage of my convictions, so I'll post anyway and recant at leisure if need be.

[Loud Whispers]

*Sigh*

If this is to be true, and Neutrino's can travel faster than the speed of light (without changing velocity thus not violating Einstein's law) then I am yet to learn all I need to know about the universe. Well, if Physics for that matter are rewritten considerably.

Dammit CERN, Y U NO HAZ GORDON FREEMAN?

DAMMIT LIFE, Y U NO MAEK SENZE?

[Darvi]

From: Life
To: LW
Subject: Re:No Sense

Lol, U mad?

[Virex]

If this is to be true, and Neutrino's can travel faster than the speed of light (without changing velocity thus not violating Einstein's law) then I am yet to learn all I need to know about the universe. Well, if Physics for that matter are rewritten considerably.

Get used to the feeling

[thobal]

If we can harness it, possibly a way to send messages backwards in time

It doesn't work that way. Approaching faster-than-light speed wouldn't allow you to travel backward in time.

If you could, however, reach a star 4 light years away from the Earth in a second, theoretically you would be able to view Earth as it was 4 years before.

Actually, yes it does;

In short, for any signal sent FTL in one frame of reference, another frame of reference can be found in which that signal actually traveled backwards in time, thus violating causality in that frame.

That means that if we shoot a couple of neutron sources and recievers off into space at an appreciable fraction of c (possible with project orion style rockets) and pass messages from us to one source to the next source and then back to us, we actually could send messages back in time. NOTE: We ourselves are not going back in time; only our messages are.

I should also point out, it would be insanely difficult if the best signal speed we can get is only 1.00002c. If we can get faster than that, then it gets a lot easier.

Trust me, I'm a scientist 

Quick question, how does light get moving? I flick a switch and light come flooding out at some ungodly pace. But how does it get moving? Is the flashlight being impulsed backwards ever so slightly? Do the batteries lose mass over time?


Also, re. what Starver said: I am also unsold on the idea that somehow going faster than light breaks causality.

edited for possible stupidity.

[Loud Whispers]

From: Life
To: LW
Subject: Re:No Sense

Lol, U mad?

Spoiler (click to show/hide)

RUUUUUUUUUUUUUUUUUUUUUUAUUUUAuAUAUAAAAUAAAAAAAAAAAAAAAAGHHHHHHHHH!!!!

[Virex]

Yes and yes. Light has an amount of impulse and absorbing, reflecting or producing a photon will affect the impulse of whatever interacted with the photon. That's how radiation pressure and solar sails work. In addition to that, light is energy and energy is mass, so a battery will lose a tiny amount of mass when it's energy is used to produce light. However, in general the amount of mass lost is, if I recall correctly, less than a part per trillion (long scale), so you won't notice it even with an implausibly precise scale.


However, one thing you need to remember is that light is not accelerated. Photons are created at the speed of light and never change velocity, only direction and energy. The reason behind this is that light, as per Maxwel's equations, is a coupled electrical and magnetic field that oscillate at a certain energy-dependent frequency but moves at a constant velocity. Adding or removing energy will affect the frequency, but not the speed of the photon, so 'slowing down' a photon will actually redshift it instead of making it slower and 'speeding one up' will cause it to be blueshifted.

[Starver]

That said, if you take it to its extremes, you have to realise that a deterministic universe means that there is only one possible future, and our every future action is already fixed.

Yes.  Indeed.  That's not its extreme, that's just inevitable.  (As in "it's inevitable that I would think that".)

One universe, one future.  I also tend to believe that if (true!) time-travel is possible, "what you go back and do is what you went back and did", and thus the Universe suffers no paradox.  Other alternatives exist, as I have already mentioned in past threads on this forum[1], and apply to conveyed information as much as full-bodied time-travellers.  "Self-fulfilling predictions", et al.  Think something like the Twelve Monkeys situation, rather than the Timecop series (where things change, despite the cops) or the Back To The Future franchise where you can "fade out".  Only a universe which does not paradox itself can possibly exist.  Again, those are my aesthetic sensibilities applied to the issue, and there are alternatives.

Proof is here. It looks scary, and it is kind of mind bending, but it's possible to work your way through it with first year uni maths and physics.

I'm going to keep quoting this post until people understand why breaking C is going to break stuff in more ways than just being super-duper-fast.

I may have read this far too quickly, but as far as I can see he's saying "time-travel breaks out of the light-cone" and... well, that's it.  Breaking out of the light-cone does not imply going backwards out of the light-cone, and even if I angle two light-cones (unless I angle the cones so that their extremities do not intersect, which implies each frame is already considered to be FTL compared with the other) I can't seem to get such an exit angle coming into the other light-cone 'backwards' and thus back in time.

I'll go back to this later (it's too late at night, now, given I'd rather not be late in to work later this morning), and maybe I'll get my head around the concept while I'm dreaming.  (I say 'maybe', but surely it is predetermined whether I will or not? )



[1] But, to summarise the main one: Arrival 'back in time' sparks off a new branch which has you arriving back in time in, while the one that leads up to you travelling back in time survives without your incursion (in order for you to leave it).  If the new-branch universe needs to be created from 'something' (and is not somehow a zero-sum of matter and energy) the branch of the "original timeline" beyond the departure-point of the time-traveller is deconstructed in order to construct the new branch.  Bad summary, but it covers most of the issues.

[Loud Whispers]

Yes and yes. Light has an amount of impulse and absorbing, reflecting or producing a photon will affect the impulse of whatever interacted with the photon. That's how radiation pressure and solar sails work. In addition to that, light is energy and energy is mass, so a battery will lose a tiny amount of mass when it's energy is used to produce light. However, in general the amount of mass lost is, if I recall correctly, less than a part per trillion (long scale), so you won't notice it even with an implausibly precise scale.


However, one thing you need to remember is that light is not accelerated. Photons are created at the speed of light and never change velocity, only direction and energy. The reason behind this is that light, as per Maxwel's equations, is a coupled electrical and magnetic field that oscillate at a certain energy-dependent frequency but moves at a constant velocity. Adding or removing energy will affect the frequency, but not the speed of the photon, so 'slowing down' a photon will actually redshift it instead of making it slower and 'speeding one up' will cause it to be blueshifted.

And so Einstein's laws are not broken. Hopefully this stays constant, and if anything at all, at worst we'll be having to add things to our already cluttered minds. Well, time to end all sentient life with a super-massive black hole!
>Serious face<

What next, you'll be saying that scientists are going to rip holes through the universe and ....

...

...

...

Spoiler: ... (click to show/hide)

WELL SCREW YOU LIFE

[Bremen]

What about for those who have done neither?

The basics, as I understand it, are these:

According to special relativity, there is no "one" measurement of space/time that is correct. Instead, there are any number of reference frames.
Most importantly for this discussion, time is not universal in all reference frames; hence the phenomena of time dilation you've probably heard of.
However, time flows normally for each reference frame; if you fly away from Earth at relativistic speeds, to you its Earth's time that is slowing down. From your frame of reference, there's no distinction between you moving one way and the Earth moving the other way.
All of these reference frames are correct.

Then comes the problem:
 
FTL travel, alone, does not violate causality; IE you could fly to alpha centauri with your hyperdrive and fly back, but you wouldn't arrive before you left.
A combination of FTL and STL travel, however, can result in an arrangement of reference frames so where a signal (or, in the case of an ftl ship), arrives before it left.
Imagine you fly away from Earth at relativistic speed. To you, time is passing slower for Earth than for you. After a day, you use your neutrino ftl communications to tell them you forgot to turn the oven off. Since (from your reference frame) time is passing slower for Earth, they receive it in 12 hours. They turn the oven off, then send back a message that they have done so. However, from their frame of reference time is moving slower for you than it is for them, so you receive the reply 6 hours after you left; 18 hours before you send the original message.

There's a more in depth (and probably better informed) explanation to be found here

Edit: Or as it was once explained to me: "The Universe works like this: Special Relativity, Causality, and FTL travel: pick two"

[MaximumZero]

Has anyone figured out a way to harvest vacuum energy yet, so we can use it as a fuel source? You guys are all freakin' brilliant, it shouldn't take too long.