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[Furtuka]

It makes good universe building if they just call them midichlorians or something and admit that they are magic and fictional particles which do not and cannot really exist. Trying to explain the impossible in terms of science cannot work.

Ah alright that explains our disagreement in the other thread. You didn't mean literal magic, you meant just coming up with something distinct from the known science of our universe. That's a bit better. When you said to just call them magic without context you made it sound like you wanted them to literally be classified as magic no matter the situation which would be rather silly and came off as a little insulting.

[~Neri]

How do particles with imaginary mass behave? I am very unfamiliar with them.

Spoiler (click to show/hide)

Late. But I had to.

[10ebbor10]

Indeed; speed of light is only a local limit.

[LordBucket]

Nov 2014 NASA presentation on advanced and theoretical propulsion systems

Summary: Alcubierre drive is not looking good. Experiments to test whether the concept is even physically valid are still in the "eliminating false positives" stage, and even if it is you might need to do something like use Jupiter for fuel. Also, even if everything works, we still don't know how to make matter with negative mass. EM Drive is looking good. They're still only doing low energy testing, but it appears to work and they're seeing results on the order of .4 to .9 newtons per kilowatt. So possibly not a good solution for escaping planetary gravity, but good for long term missions that don't require you to get anywhere in a hurry.

[Sergarr]

Any faster than light movement/teleportation method allows time travel (http://en.wikipedia.org/wiki/Time_travel#Via_faster-than-light_.28FTL.29_travel).

Time travel is impossible, or else somebody would have arrived at that party Hawking threw for time travelers. (or human civilization dies before it can discover time travel, but that variant is too depressing to consider)

Therefore, faster-than-light movement is impossible, at least for normal objects.

If I recall, Alcubierre drives travel faster than light by not traveling at all- they manipulate space itself, changing velocity without accelerating in their frame of reference. This, of course, bypasses relativity (since space can expand and contract without restriction to how fast), and therefore bypasses any changes of time.

No, it doesn't.

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

Any way to move faster-than-light, be it simple movement, or teleportation, or anything else fancy, it will cause time travel to happen. No exceptions!

[Sergarr]

Well all theories of physics postulate that all physical laws work the same in all dimensions.

So using a fourth, fifth, and so on - dimensions will not shorten the path.

You should accept that there is no easy method of interstellar movement. If there was, aliens would've already discovered it. And, coupled with the fact that easy interstellar movement = faster-than-light = time travel, we wouldn't exist since our planet would've been consumed for resources needed to fuel a gigantic faster-than-light time travelling alien empire.

Do you want to get our planet consumed for resources by aliens? Then don't wish for easy interstellar travel.

[~Neri]

A FTL Alien Civ likely would enslave humanity for free labor.

They probably have a market for pets.

I just need to be freaking adorable and I'm set.

[Sergarr]

Anything we do to the planet is reversible as long as the Sun continues to shine upon us.

A wasteland it'll never be.

[Sergarr]

Humanity is ridiculously durable. Unless somebody drops the bomb on half the cities on Earth, humanity will survive.

It's what we do the best, after all. Surviving.

[Urist Tilaturist]

Easy interstellar travel? Not happening for me (not an expert physicist by any measure, but still know a damn lot more than those jackass writers).

Particles cannot go faster than light because as something accelerates close to light speed its mass increases so much that it can accelerate no longer. All plans for fast interstellar travel work around this rather than doubting it - Alcubierre drives warp space around the craft, while wormholes connect different parts of space-time to each other. The Alcubierre drive looks very unlikely to me, since it needs particles with negative mass, which I do not believe exist. Even antimatter seems to have positive mass.

Time travel of a sort, accelerating time to go faster into the future, is possible and people do it all the time just by moving at higher velocity. Going back in time looks impossible, because of the relativistic reasons which I gave earlier. Some wormhole trickery may be possible, but since the crew would have to survive essentially going through a sort of black hole, it still seems unlikely even if it is possible in theory.

My fuss about the "tachyons" was because tachyon is a real scientific word for a particle which exists. Any explanations of magical phenomena should not misuse any real scientific terms. This keeps the divide between truth and fiction clear. I did not mean that all fantasy had to be like Tolkien, only that it should not misuse any real science.

[i2amroy]

My fuss about the "tachyons" was because tachyon is a real scientific word for a particle which exists. Any explanations of magical phenomena should not misuse any real scientific terms. This keeps the divide between truth and fiction clear. I did not mean that all fantasy had to be like Tolkien, only that it should not misuse any real science.

Thats... pretty much exactly what most of the "harder" half of Science Fiction is designed to do, i.e. to take partial explanations of science, extrapolate things to fill in the gaps, and then give them as explanations. Mohs Scale of Science Fiction Hardness exists specifically to differentiate the "softer" works that basically boil down to "magic, but dressed up as technology", to more "medium" works that give some sort of explanation (be it logical or not), to "harder" ones that actual follow totally real science of the point when they were written.

Which brings up another point, in that there is tons of stories out there who's explanations were totally consistent when they were written, but have been shown to be impossible since that date. Are we proposing to suddenly ban all the books that fall into that category if science ever evolves to the point where it shows their explanations are impossible and they are now "misusing [...] real scientific terms"? You state that you want to "keep the divide between truth and fiction clear", but the a major "point" of science fiction, is to do exactly the opposite, and to ask "what if" questions that specifically blur the boundaries.

[10ebbor10]

On a side note, wormholes also require exotic mass, otherwise they wouldn't be stable and would collapse before anything could go through.

[~Neri]

What if we raise the speed of light?

[Sergarr]

What if we raise the speed of light?

Not possible without another Big Bang, I'm afraid.

[Graknorke]

What if we raise the speed of light?

Not possible without another Big Bang, I'm afraid.

Nothing is impossible. Not if you can imagine it. That's what being is a scientist is all about.