With a spacecraft big enough to live in, we are talking of a time frame not too different from the one from the age of exploration by sea. I have no doubt many people would want to take such a trip even if it takes 10 years to get back to earth.

Unmanned spacecrafts would be able to go much faster, sustaining more dramatic accelerations. So getting cargo and robots there for support would be way faster.

This takes you to 0.99C, how feasible is that (thinking materials more than anything)

Only 0.95 per the source linked above. I don't know.

Speculating you'll substantially blue shift the light coming from in front of you, and I suppose that can't be good for materials (or people), but I'm not sure if there is enough to matter. Any dust you collide with is also going to have ridiculous amounts of energy, but you'll be in interstellar space when you're at high speeds so there shouldn't be much of it (even for space) either.

Yeah well, we don't really know what happens at high speeds. Probably biochemistry stops working at 0.3c? It doesn't seem structural materials would remain solid at 0.95c... who knows.

High speeds relative to what? The earth orbits at 30 km/s, our galaxy arm is at over 200 km/s (say 0.1% c), I'm not sure relative speed matters at all

I am not a physicist but I suspect that we are already moving at significant speed relative to other bodies. We have no special frame of reference that defines our "real" speed.

That's not quite right. There's the cosmic background radiation "rest" frame, which can reasonably be taken as 0 velocity.

The laws of physics don't change in different frames (Einstein's assumption), but that doesn't mean that all frames are equivalent in other respects.

> cosmic background radiation "rest" frame, which can reasonably be taken as 0 velocity

What does this mean? The CMB is radiation travelling at the speed of light in every direction.

There's a rest frame where the CMB is (nearly) isotropic, and in every other frame there's a larger anisotropy, see the first comment here

https://www.reddit.com/r/AskPhysics/comments/2va4t6/does_no_...

> You are absolutely right in that the CMB becomes Doppler shifted when you have some relative velocity. But Earth is not in the CMB rest frame: when we observe the CMB from Earth, we observe a dipole component to the CMB caused by the Earth's motion orbiting the Sun, the Sun's orbit around the Milky Way, and any velocity the Milky Way as a whole has. I was at a talk about the new Planck results last week, and saw a plot in which you can clearly see the dipole component in the raw data. You need to correct for this motion before you can even remotely see the anisotropies that are the interesting science goals of Planck.

> There is a rest frame in which the CMB is closest to isotropic (no dipole component), and this rest frame is special but not 'absolute'. This frame is effectively the 'center-of-momentum' frame of the observable universe, in which we expect the total momentum to be zero. We know from classical mechanics that for any system of objects, we can construct such a frame, and that it sometimes has useful properties for solving certain types of problems. But there is nothing 'absolute' about this rest frame, the laws of physics operate entirely the same.

> And so this is fine, because ultimately what relativity requires is that the laws of physics operate the same in every rest frame, not that every rest frame looks the same. Because the CMB is itself physical (made of photons) and was emitted by matter, it is entirely natural that it should be affected by frame transformations, and should look different if you shift to a frame that is moving differently than the emitting medium.

The frequency of light changes depending on how fast you are moving relative to it. Move away from a light source and the light still approaches you from the same speed, but is lower frequency. Rest here is where the frequency becomes "uniform" (ish) regardless of direction.

The speed of light is the frame of reference. It remains constant for any observer no matter at which speed is moving.

It's not feasible. It would require more fuel than the Earth is heavy, even if we had nuclear propulsion.

It depends on the mass of the ship, but yes; quite a bit.

https://www.quora.com/How-much-energy-does-it-take-to-accele...

I don't think that means is unfeasible if the energy source allows for that.

No, actually it does not depend.

The rocket equation says that the fuel mass of a rocketship is higher than the cargo mass by exp(delta_v/v_exhaust).

When the final velocity is relativistic, delta_v should be replaced with delta_rapidity. In our case this would introduce a factor of 2.65, but the results are so ridiculous that we can ignore that.

So, let's simply say that delta_v is the speed of light, or 300000 km/s.

The exhaust velocity for a nuclear thermal rocket is about 9 km/s.

The ratio between delta_v and the exhaust velocity is about 33000. The exponential of that is roughly speaking 1 followed by 15000 zeros.

There are less than 10^100 atoms in the known universe.

So, even if you want to accelerate just one single atom to 99% of the speed of light, you would need more fuel than the entire universe. Many, many, many times more.

Sadly, not very feasible because of the hydrogen atoms floating around in the empty space, about 1 per cubic meter.

At speeds about 0.5C a collision with such an atom produces X-rays, and harder gamma rays at higher speeds. They are pretty hard to insulate against, and are actively harmful. For a spaceship of a considerable size, enough collisions would occur to be dangerous. The paper: https://www.scirp.org/journal/PaperInformation.aspx?paperID=...

To make it even worse, that's based on an average density 1.8 atoms/c3. The real values would probably vary wildly, and you won't be able to "break" in advance in order to go through a high density area.

And then there's the problem of hitting an interstellar grain of sand at 0.5c.

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