Scientists claim warp drive is possible

[Zeropoint]

Re: Scientists claim warp drive is possible

 

Nyrath, I don't see where the (1-V) factor comes from in that equation.

 

Megaplayboy, a big part of the problem here is that, contrary to our expectations and intuitive understanding of the universe, simultaneaity is relative. Let me say that again: whether two events separated in space are simultaneous or not . . . is NOT absolute. It depends on the motion of the observer. I don't understand all the math completely, but I have learned enough to know that our experiences here in the low-speed world of human activity do NOT prepare us to grasp the nuances of relativistic effects.

 

I don't have time to get into this now; later this evening I can provide a relatively (hah!) simple example of observer-dependent simultaneaity involving a train with a light in the middle.

[Nyrath]

Re: Scientists claim warp drive is possible

 

Is the only way to have an FTL drive that doesn't violate causality to have one that somehow leaves 3-dimensional space entirely (via wormhole' date=' "hyperspace" or whatever) and returns at another point in space without having travelled across the space between the two points, provided such travel does not move the ship backwards in time?[/quote']

If the ship leaves 3-dimensional space and returns to another point in space without having traveled across the space between the two points, and not having the ship move backwards in time, it means the ship will emerge from the wormhole no earlier than the time it would take a ray of light to make the thrip through normal space.

 

In other words, the only way to prevent the ship from moving backwards in time is to make the trip effectively slower-than-light.

[Nyrath]

Re: Scientists claim warp drive is possible

 

Nyrath' date=' I don't see where the (1-V) factor comes from in that equation.[/quote']

ummmmm, let me go check my notes

[megaplayboy]

Re: Scientists claim warp drive is possible

 

If the ship leaves 3-dimensional space and returns to another point in space without having traveled across the space between the two points, and not having the ship move backwards in time, it means the ship will emerge from the wormhole no earlier than the time it would take a ray of light to make the thrip through normal space.

 

In other words, the only way to prevent the ship from moving backwards in time is to make the trip effectively slower-than-light.

 

Yeah, that doesn't make any sense to me--the ship in this scenario is effectively leaving the physical universe for a period of time, then returning to the physical universe at a different point in space. How is that time traveling?

 

I don't see how relativity would be applicable to some theoretical "hyperspace wormhole".

[Zeropoint]

Re: Scientists claim warp drive is possible

 

Okay, as promised, here's a look at how and why "at the same time" depends on where you're standing.

 

Imagine, if you will, a train with a lot of passenger cars, all of which have their doors at the ends open, so you can see from one end of the train to the other. In the middle of the middle car there is a lamp which can be turned on and off. When the lamp is turned on, it propagates both forward and backward at the same speed. After all, the speed of light (relative to the observer) is constant. Since the light travels exactly the same distance to the front of the train as it does to the back, the light hits the front of the train at the same time as the back of the train, right? Of course. Those two events--light hitting the front of the train and light hitting the back of the train--are simultaneous.

 

From the perspective of the people on the train, anyway.

 

Let's see how things look to an observer on the ground.

 

The speed of light, relative to the observer, is constant, as we already acknowledged. That means that the stationary observer sees the light coming off of the lamp in the middle of the train moving both forward and backward at the same 3x10^8 m/s.

 

This is imporant--the light is NOT moving faster in the forward direction and slower in the backward direction because of the train's motion. The speed of light relative to the observer is a constant 3x10^8 m/s under ALL circumstances.

 

So, the stationary observer sees the light moving in both directions when the light is turned on. Eventually, it reaches the ends of the train. But wait! The train has been moving while the light was in transit. At the back, the end of the train has been moving TOWARD the lamp, and the light therefore doesn't have to go quite as far. At the front, the end of the train has been moving AWAY FROM the lamp, and the light has to go farther before it gets there.

 

You should be able to see where this is going--the observer on the ground sees the light hit the back end of the train some finite amount of time before it reaches the front end.

 

The part that's hard to wrap your head around is that you can't say "oh, the stationary observer didn't see it how it really happened." BOTH observers are RIGHT. Whether two things happen at the same time or not is relative to the observer, not a fixed property of the events.

 

 

So, why is instant travel a trip through time? Imagine someone instantly teleporting from the front of the train to the back of the train, at the moment the light gets there. To the observer on the train, this presents no real problems, the teleportee vanishes and then instantly reappears at the other end.

 

But, we've already seen that from the perspective of the stationary observer, the light hits the back end of the train some time before it gets to the front. That means that in this case of instant travel, he sees the teleportee arrive before he leaves!

 

And again, the perspective of the stationary observer is just as valid as that of the moving observer; one of the things that relativity tells us is that there are no "privileged observers"; no one gets to say "my perspective is correct, and if you see something funny, it's because you're not looking right."

[megaplayboy]

Re: Scientists claim warp drive is possible

 

But it isn't "instant" travel, it's just travel via some hypothetical extraspatial means that takes you from point A to point Z without actually travelling across the points in between. One would see the ship prior to seeing the light from where the ship was, true, but that still doesn't sound like time travel under this particular means of travel.

[Comic]

Re: Scientists claim warp drive is possible

 

Saying 'hypothetical medium' or 'shortcut' introduce more complicated math, and moves the problem around a bit, but doesn't get rid of the problem.

 

All of these 'bent space' modes of travel require that something equivalent to FTL be happening at some bend, somewhere. They're a shell game, and inevitably collapse on close examination.

[megaplayboy]

Re: Scientists claim warp drive is possible

 

What about entering a parallel universe and re-entering our universe at a different point in space? There's no rule that says the laws of physics outside of our universe(should "outside" actually exist) have to be identical to the laws of our universe.

[Nyrath]

Re: Scientists claim warp drive is possible

 

What about entering a parallel universe and re-entering our universe at a different point in space? There's no rule that says the laws of physics outside of our universe(should "outside" actually exist) have to be identical to the laws of our universe.

I'm afraid that the laws of physics in the other universe doesn't matter.

 

Under Einstein's Relativity, the fact that the ship appears at point B at a point in time earlier than a ray of light that left point A at the same time the ship started, this makes the ship both an FTL traveller and a time machine. It doesn't matter if the ship uses hyperspace, folds space, passes through a wormhole, is pulled by teams of fairies covered in magic pixie dust, or uses the Holly Hop drive. If you have Relativity, FTL = Time Travel.

[Nyrath]

Re: Scientists claim warp drive is possible

 

Nyrath' date=' I don't see where the (1-V) factor comes from in that equation.[/quote']

I think I was trying to simply the equation, and inadvertently factored out the Lorentz Boost. I'm still trying to recover the original.

[Cancer]

Re: Scientists claim warp drive is possible

 

I think the (1 - V) is (c - V) -- with c the speed of light; in the diagram you mention, the units are always cast so c is 1.

[SSgt Baloo]

Re: Scientists claim warp drive is possible

 

All these arguments against FTL travel seem to boil down to "it doesn't make sense if that's what really happens!" I suspect that if FTL travel is actually possible, our understanding of causality is flawed when it is used to describe special cases (such as time travel and FTL travel).

 

Just as Newtonian physics is perfectly adequate for describing and predicting most events that do not approach the speed of light, so is Einsteinian physics for describing the universe more accurately in both the mundane observable world and the near-lightspeed regime. Newtonian physics does not account for relativistic effects at high velocities. Einsteinian physics breaks down when asked to predict results where Velocity > C. Just as Newtonian physics breaking down when applied to extreme cases did not render Einsteinian physics invalid, perhaps some unexplained (thus far) aspect of the physical universe allows for events to appear pre-cause for some observers and not others, just as the stationary trainwatcher sees events aboard the train in a different order than the train passengers do?

[Maur]

Re: Scientists claim warp drive is possible

 

Relativity also breaks down under other extreme conditions. Think about all the problems physicists are having in trying to merge Quantum Mechanics (the realm of the small) with Relativity (the realm of the massive/fast). As far as I'm aware the two haven't been successfully integrated into each other (solutions with probability greater than 100%...). Creates interesting problems when studying things like blackholes.

[Cancer]

Re: Scientists claim warp drive is possible

 

When you say "relativity breaks down", it's important to acknowledge that the "breakdown" is in our ability to put together a formalism that lets us compute and predict what goes on in conditions of very high energy. Every observational test of relativity that we have been able to make so far has been successfully passed. The problem is that we cannot produce in an experiment the conditions where relativistic quantum mechanics has problems, and the few places where such conditions exist in the Universe now are intermittent, unpredictable, and shielded from our view. Lacking hard experimental/observational data to guide us, theory is very hard to concoct.

 

That's very different from the breakdown suffered by pre-relativistic physics, which makes predictions which are absolutely at odds with observation.

 

So far there have been no clear, confirmed observations of phenomena that require a revision or abandoning of relativity. That is really more a statement about the phenomena we have seen in the last 120 year or so than the correctness of relativity, because it has to break down at some level. But we haven't seen any cases of that, and without that data, we can't make a lot of progress.

 

 

If simple perfect laws uniquely rule the universe, should not pure thought be capable of uncovering this perfect set of laws without having to lean on the crutches of tediously assembled observations? True, the laws to be discovered may be perfect, but the human brain is not. Left on its own, it is prone to stray, as many past examples sadly prove. Thus pillars rather than crutches are the observations on which we base our theories: and ... these pillars must be there before we can get far on the right track.

[megaplayboy]

Re: Scientists claim warp drive is possible

 

I'm afraid that the laws of physics in the other universe doesn't matter.

 

Under Einstein's Relativity, the fact that the ship appears at point B at a point in time earlier than a ray of light that left point A at the same time the ship started, this makes the ship both an FTL traveller and a time machine. It doesn't matter if the ship uses hyperspace, folds space, passes through a wormhole, is pulled by teams of fairies covered in magic pixie dust, or uses the Holly Hop drive. If you have Relativity, FTL = Time Travel.

 

So, time is tied to the speed of light? It is arriving faster than light is, true, but I don't see where that of necessity implies that it is engaging in "time travel" as we popularly understand the term.

[Zeropoint]

Re: Scientists claim warp drive is possible

 

"Common sense" is not a reliable guide to relativistic physics. Or quantum mechanical physics, for that matter.

[Nyrath]

Re: Scientists claim warp drive is possible

 

So' date=' time is tied to the speed of light?[/quote']

Yes. Time is not absolute.

Relativity of simultaneity

 

Under relativity, if you have two events A and B which are separated at some distance from one another, different observers will have different opinions on whether A happened first or B happened first. This is tied to the fact that the speed of light is the only constant.

 

Everything else is relative. Which is why it is called the theory of relativity.

[megaplayboy]

Re: Scientists claim warp drive is possible

 

Yes. Time is not absolute.

Relativity of simultaneity

 

Under relativity, if you have two events A and B which are separated at some distance from one another, different observers will have different opinions on whether A happened first or B happened first. This is tied to the fact that the speed of light is the only constant.

 

Everything else is relative. Which is why it is called the theory of relativity.

 

But if some wormhole-type loophole existed, we could toss the theory of relativity and keep causality?

[Kristopher]

Re: Scientists claim warp drive is possible

 

I'm afraid that the laws of physics in the other universe doesn't matter.

 

Under Einstein's Relativity, the fact that the ship appears at point B at a point in time earlier than a ray of light that left point A at the same time the ship started, this makes the ship both an FTL traveller and a time machine. It doesn't matter if the ship uses hyperspace, folds space, passes through a wormhole, is pulled by teams of fairies covered in magic pixie dust, or uses the Holly Hop drive. If you have Relativity, FTL = Time Travel.

 

OK, so basically, getting there before the light is defined as time travel?

[Comic]

Re: Scientists claim warp drive is possible

 

So you know, university Physics is essentially three years of this discussion among like-minded enthusiasts.

 

Done with supercomputers, access to the textbook collections of five continents and thirty languages.

 

On four hours sleep a night.

 

With no sex.

 

You're not going to find the loophole these guys missed.

[megaplayboy]

Re: Scientists claim warp drive is possible

 

Not YET, anyway.

[Nyrath]

Re: Scientists claim warp drive is possible

 

But if some wormhole-type loophole existed' date=' we could toss the theory of relativity and keep causality?[/quote']

Yes.

 

Unfortunately, if you toss relativity, you now have to deal with the problems Cancer mentioned.

[Nyrath]

Re: Scientists claim warp drive is possible

 

OK' date=' so basically, getting there before the light is [i']defined as[/i] time travel?

Yes.

[megaplayboy]

Re: Scientists claim warp drive is possible

 

If you converted all the mass of the universe to energy and converted it with 100% efficiency, into an accelerative force propelling one atom, would it still be limited to light speed, or would the fact that the rest of the mass of the universe no longer exists "break" our system of physical constants?

[SSgt Baloo]

Re: Scientists claim warp drive is possible

 

If you converted all the mass of the universe to energy and converted it with 100% efficiency' date=' into an accelerative force propelling one atom, would it still be limited to light speed, or would the fact that the rest of the mass of the universe no longer exists "break" our system of physical constants?[/quote']

 

Unless the space disappeared also (rendering "speed" a meaningless term), you would only accelerate the atom to a very high sub-light velocity. It takes (literally) infinite energy to accellerate an object to the speed of light. You would have to use some value greater than infinity and "infinity" doesn't work that way. If you can add to it, it either wasn't infinite to begin with or it was a type of infinity that is (by definition only) a "smaller" sort of infinity.

 

Example: All even integers is an infinite set. All integers is also an infinite set, but includes "more" integers (the odd ones) than the previous set. Both sets are still infinite and therefore (technically) equal.