Sci-fi lines that just hurt to listen to

[keen320]

In slingshoting (is that actually a verb?)

Just say "When you slingshot." Why am I saying this. I feel an obnoxious OCD impulse. Even though I'm not OCD.


And about what somebody said waaayy back about it all being magic anyway, IIRC some physicists think Warp Drive might be theoretically possible. They just have no idea how you'd do it, and you'd almost certainly need ridiculous power levels to carry it out.
I heard it on TV, so it must be true!

[Marcus Aurelius]

And about what somebody said waaayy back about it all being magic anyway, IIRC some physicists think Warp Drive might be theoretically possible. They just have no idea how you'd do it, and you'd almost certainly need ridiculous power levels to carry it out.
I heard it on TV, so it must be true!

Not power levels exactly, but something even more difficult to obtain. Wikipedias article is, as far as I can tell, a good popular science explanation, although I am not a physicist:

http://en.wikipedia.org/wiki/Alcubierre_drive

[Edi]

Stark's trolling and Eternal_Freedom's responses split to a more deserving place.

[Eternal_Freedom]

If I correctly recall the article I read about the "warp drive," you need something like a good sized asteroid mass in front of your ship and an equal but negative mass behind it. Then you make the masses move or something...

So, yeah, possible theoretically but nigh-impossible to do in reality

[Guardsman Bass]

If I correctly recall the article I read about the "warp drive," you need something like a good sized asteroid mass in front of your ship and an equal but negative mass behind it. Then you make the masses move or something...

So, yeah, possible theoretically but nigh-impossible to do in reality

That's better than wormholes. If I remember right, a fairly small wormhole (1 meter across) required Jupiter-scale masses of negative matter-energy to hold it open.

[Eternal_Freedom]

Yeah I read that. And then if you try and pass through it, it snaps shut and makes you go "ow" very loudly

[starslayer]

Alcubierre drives used in the manner described in the original paper require some 1E70 kg of negative matter, as I recall. This is more material than is present in the entire observable universe. If you're sneaky, you can make a really, really tiny Alcubierre "path" (like, a few Planck lengths wide tiny), and then stick a wormhole mouth inside that which contains your ship. This cuts your requirements down to a couple of solar masses worth.

Even so, there are additional difficulties with the concept, even presuming you have negative matter. If you look at a light cone diagram of an Alcubierre bubble surrounded by normal Minkowski spacetime, you'll find that no signal launched at the ship will ever reach it from the front quarter. This works both ways, so if you're on a ship inside the bubble, you can't get out of it or send any signal outside of it either. So presuming you have several solar masses of negative matter lying around, you would have to string up warp tunnels almost like bridges between systems; permanent stations would be strung along the warp path and form a bubble around a ship, transport it to the destination, and then destroy the bubble upon its arrival.

Yeah I read that. And then if you try and pass through it, it snaps shut and makes you go "ow" very loudly

If you have the negative matter, no it does not. A wormhole only closes before you can cross it if you are restricted to positive energy densities.

With a black hole's event horizon, it isn't just that gravity is pulling so strongly you can't tug free. It is that space is actually so fucked up that all paths lead inward. (i guess this is saying the same thing in different words but whatevs yo)

All timelike paths lead inward. FTL worldlines are all spacelike, and they can easily lead you out of a black hole. Remember that nothing at all special happens when you cross the event horizon, except that all timelike paths now lead to the singularity; you still see the horizon below you when you cross it, and then it actually splits in two, but you can't tell (it's purely a coordinate effect). See this site for some simulations of what it's like to fall into a black hole.

A good way to think about a black hole and the event horizon is described on the site I linked to above; imagine space being like a river. Gravity is the river's current, pulling you along with it; the curvature of space does the same thing, really. A black hole is something like a waterfall in the space river; the current is flowing so quickly that nothing can resist it, and everything goes over the edge into the abyss. But if you have rocket boots or something, it's easy to go back up the waterfall, even when you're in it; the stronger the rocket boots, the farther you can fall down the waterfall and still get back up. The rocket boots are our FTL drive; it allows us to cheat and resist the current of spacetime flowing to the singularity. It's just that, to build this FTL drive, you need negative energy/matter. Whether this exists is something of an open question, but it probably doesn't.

Quantum mechanics allows for negative energy densities and such, and GR says nothing one way or the other. Classically, they make no sense - except when dealing with potential energy - but that's not necessarily a real barrier. In decision that often gets bandied about of "relativity, causality, FTL: pick two," it is perfectly reasonable physically to pick relativity and FTL (hell, if negative matter really does exist, our universe has done it), as long as you stay consistent with what this means. Closed timelike curves (time machines), faster than light travel, and wormholes/travel to other universes go hand in hand.

[Wyrm]

The problem with taking the escape velocity as simply being greater than the speed of light is that's the classical look at it, and the classical equations break down in extreme situations like a black hole.

No. Escape velocities are quite well defined in GR, as they are simply the specific kinetic energy needed to be gravitationally unbound to an attracting body. Short of the event horizon, give a body sufficient kinetic energy to equal or exceed the gravitational potential at that point, and it will escape, and that kinetic energy will correspond to a speed.

As to the breakdown of classical mechanics at this point... well... let me show you something interesting:

Identify escape velocity, v₀, as the speed of light, c, in the classical escape velocity equation

v₀ = c = √[2GM/R]

c² = 2GM/R

R = 2GM/c²

which is the Schwarzchild radius as derived from GR. While this is not a rigorous proof that the classical escape velocity applies in the Schwarzchild metric at all radii greater than the Schwarzchild radius, it is a quite the peculiar coincidence.

It is also justified to characterize the escape velocity at the event horizon, and as c. For any observer accelerated such that she remains exterior to the event horizon, the gravitational redshift between an event on the horizon and her is infinite, just as it would take an infinite amount of energy for a massive object to accelerate to the speed of light. No matter how high the energy of the photon trapped at the event horizon, it will be redshifted to zero energy were it to make it out. (If the observer free-falls into the black hole, the redshift is not infinite.)

With a black hole's event horizon, it isn't just that gravity is pulling so strongly you can't tug free. It is that space is actually so fucked up that all paths lead inward. (i guess this is saying the same thing in different words but whatevs yo)

All timelike paths lead inward, to be precise. It's an important distinction, because FTL by definition takes you along spacelike paths.

Depending on how the space is arranged, and the details on how the FTL works, it is possible to escape from a black hole using an FTL drive... provided you can turn it on fast enough — see below.

If other races have no FTL but you do, the interior of a black hole is a safe place to hide.

Well, no. Thing is, all timelike paths lead to the singularity of the black hole, where you will be destroyed with certainty. Also, for black holes on the order of a solar mass, the time you have before you hit the singularity is measured in miliseconds. Speeding away doesn't help because your time slows down as your engines push harder — the 'coordinate time' you gain (however you're measuring it) doesn't win you any more proper time.

It doesn't matter where you go or how hard you try, the universe itself is a sadistic, twisted fuck out to ruin you. It's like in video games if you get stuck in an endless looping map. Punch in all the cheat codes you want for full speed, it won't help.

I agree fully with the sentiment of this statement. The universe is out to kill us.

[Stark]

What about FTL systems like warp drive that compress space to go faster? Is that relevant?