the human body will encounter complications in low and zero gravity
ftl will never happen
space stations are a scam that rich tech ceo's promise
mars cannot be terraformed
life is probably unexceptional and we will never make contact with others
you will all die on earth
FTL is unnecessary. But not because of generational ships like @Shmyt said, but because there's no speed limit in the universe. Yes, you read that right, relativity does not actually impose a limit on how fast you can go, only in how long it will take the information to get back to Earth. Not only that, relativity actually helps you: the faster you travel the more space squishes in your direction of travel.
The squishiness is given by the "Lorentz factor"
γ = 1/√(1 - v²/c²)
where c is the speed of light, 299,792,458 m/s, and v is the relative velocity between you and whoever is measuring your speed, Earth probably. So for example if your velocity is v=0.99995c, γ ≈ 100, and from the point of view of the spaceship all distances are 100× shorter, while from the point of view of Earth everything inside the spaceship moves 100× slower than normal.
So let's say you want to travel to the other end of the Milky Way, which is about 100,000 light years away. Let's brute force the problem and attach a massive rocket to the spaceship that accelerates at 9.8 m/s², and when we're midway through we rotate the ship 180° and decelerate at 9.8m/s². This is convenient because the ship can be organised as a tall building with gravity equivalent to the Earth's.
The Lorentz factor we reach at the midway point is[1]:
γ = ad/c² + 1
Plugging in a = 9.8m/s² (1.032 light-years/year²) and d = 50,000 ly, we get γ ≈ 50000. So suddenly our eternal 100,000 light year journey is squished to 2 light years, and we're travelling at 0.9999999998c from the point of view of the Earth.
Calculating the total time from the point of view of the spaceship, including the time to accelerate to almost the speed of light, is involved so I'll just drop the formula from [1]:
T = 2c/a acosh[ad/(2c²) + 1]
And the table of how long it will take to reach certain landmarks:
So we can reach the other end of our galaxy within a single person's lifetime without any speculative technology like wormholes or whatever.
The problem: fuel
I said this was a brute force solution. Accelerating constantly a 9.8m/s² takes an absurd amount of energy. More precisely, if we're carrying the fuel with us and we have a 100% efficient antimatter engine that annihilates all its fuel using the good-old E=mc², we need:
M = exp(aT/c) − 1
to accelerate at a for time T from the point of view of the spaceship. We can then substitute how much matter-fuel we need to carry along with a tiny 1000 kg spaceship to these landmarks:
It gets much better if we don't need to carry the fuel with us. In this case we only need:
E/c² = 2 m (γ - 1),
twice the relativistic kinetic energy of our vessel. We could build galactic highways that push spaceships with lasers, the energy requirements would be quite modest because of how the energy of the lasers gets multiplied by the γ factor.
The other problem: Heat
You usually think of the universe as a cold place, and hear that its temperature is 2.725 K. This is the temperature of the cosmic background radiation, which is essentially the Big Bang, as we can see it still occurring in the edges of the observable universe. The Big Bang was originally very very hot, but as the universe expands it is stretched and "redshifted" into cooler radiation. When you accelerate to almost the speed of light you undo this, and the Universe starts feeling hotter and hotter, linearly with the Lorentz factor[2].
So at γ = 110 the Universe feels like a comfy 300 K (27 °C, 80 °F), but at the γ=15500 you'd reach travelling to the centre of the galaxy the Universe in front of your spaceship is a bright, 50000 degree hell that vaporises any known material. You may see it as "space friction". Maybe somebody will come up with a "cosmodynamic" design that deflects the heat from the front into the 0 K cold of the back.
And what does this have to do with communism?
I think the obsession with FTL travel in fiction is bourgeois ideology. It is only really necessary to build a sort of centralised galactic empire. The physicists that figured out relativity saw it as enabling space travel, not as an impediment: A loosely coupled "fully automated" galactic federation sees no real problem with communication delays of thousands of years.
This is great stuff.
Ian Banks and many others have come to the same conclusion, that even with life extension interstellar imperialism is basically impossible at STL speeds. Even with FTL it is difficult, The Culture is certainly a (somewhat diverse) cultural union, but states proper don't exist and it's pretty much impossible to stop secession.
The Player of Games establishes that the (rather small) Empire they found is the second centralised interstellar state ever discovered in Galactic History (and Culture history alone goes back 6000 years). And it uses 99.9 percent of its resources keeping itself together
Karl Schroder does make one that exists by forcing people on the colonies into increasing amounts of cold sleep to sync travel times.
Damn, this is some gourmet shit.
Seriously though, really nice calculation and an interesting perspective on FALGSC.
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v>c is not allowed, but v here is the speed of anything from the point of view of something else in an inertial frame of reference. And "speed" is defined something like "if this thing was a mirror, and I sent two light pulses towards it 1s apart, how far apart would I see reflections of it". In a similar way "time" is defined as "if this thing was two mirrors 1 light-second apart, with light bouncing between them, how long does it take a photon to bounce from one mirror to the other and back". You can picture why there is time dilation if you imagine the two mirrors moving, and the light bouncing diagonally between them. Because of geometry the diagonal path is longer than a straight path—this is where all the square roots in the formulae come from—, but the speed of light is fixed, so "time" stretches out. These geometric definitions sound pedantic but they are actually useful and accurate with respect to the more formal definition that uses a non-euclidean metric space.
If you instead define "fast" from your own point of view, as in "how far away it is / how long it would take you to reach it", then you can be arbitrarily "fast".
The loophole is space contraction / time dilation: you will never see the speed of your destination be higher than c as long as you are in an inertial frame of reference, that is, not accelerating. But as you accelerate you'll find all distances between all objects become less than they used to be before you started accelerating. So the apparent speed of your destination will be
v_apparent = v_inertial + Δγ/Δt * d.
Since Δγ/Δt depends only on your rocket, v_apparent can be arbitrarily large.
So in the middle of your trip towards Andromeda, 14 years after you departed, from the point of view of the Earth you will look like a compressed, redshifted blob moving at almost the speed of light, that left 100000 years ago and still has 100000 years to go.
From your point of view, the Earth below looks like a compressed, redshifted blob approximately 1 lightyear away. It is vertically mushed together along with most of the Milky Way. Andromeda is also approximately 1 light year away and looks compressed and blueshifted.
From the point of view of your destination in Andromeda, 14 years ago a relatively bright, blueshifted thing came out of the Milky way and has already moved halfway across. In 14 more years it will arrive. If you defined speed as apparent distance / apparent time it'd look like you're moving faster than light, but if Andromedans know about the speed of light, they'd know you're not actually moving faster than light.
You can't actually see coming something that moves faster than light. If you were, when you arrived you could look behind you and see yourself from the past, moving backwards as the light from your ship arrives after you did.