4 ms·

constant 1g acceleration gets you to speed of light pretty quickly (around 1 year), so still around 12 years.

deleted 7y ago
[deleted]
Someone 7y ago
If our current ideas about physics are correct, acceleration _never_ gets you to speed of light. The faster you go, the higher your relativistic mass, so if you accelerate by constant force, the lower your acceleration. Conversely, to keep acceleration constant, you would need larger and larger forces, in the limit ‘infinite force’. For more and better info, see https://en.wikipedia.org/wiki/Space_travel_using_constant_acceleration https://en.wikipedia.org/wiki/Space_travel_using_constant_ac....
- pdonis 7y ago
  > The faster you go, the higher your relativistic mass, so if you accelerate by constant force, the lower your acceleration. The Wikipedia article you linked to calls this (rightly) a "half-myth". It depends on your reference frame.
  - 4bpp 7y ago
    As far as I understand, viewed from Earth's reference frame, a spaceship accelerating by constant force will get heavier and heavier as it gets faster, and thus get less and less speed out of it, asymptotically approaching the speed of light but never exceeding it. Moreover, crucially, any pingbacks from clocks on the spaceship we observe will appear to be progressively going slower than they should. (Time dilation) The spaceship's own reference frame will be a whole different story. If I understand correctly, it will perceive its own mass to be constant, the rest of the universe's relative speed to asymptotically approach the speed of light, but also the rest of the universe to get progressively squashed in the direction of travel (length contraction dual to time dilation), with the two effects multiplying up in such a fashion that the Newtonian relation between the integral of your acceleration and the time it takes to the destination seems to hold throughout. In other words, for the spacefarer's schedule, it's as if the speed of light does not actually play a role: they can always accelerate more/go arbitrarily faster to get to their destination faster. However, from their point of view, it is as if the universe around them will deform in the process to accommodate this, and from the stationary observer's point of view, it is as if they are actually still moving slowly but tricking themselves into thinking otherwise by accelerating their passage of time.
nine_k 7y ago
Unfortunately, radiation from hitting hydrogen atoms in interstellar space starts to become deadly around 0.25c or so, IIRC.
Eupolemos 7y ago
No, it will be much less as seen from the ship. Seen from Earth, it'll be around 13 years (takes a year to got close to c and another to decelerate - that is two years to travel roughly a lightyear, then 11 to travel 11).
8bitsrule 7y ago
Course, assuming you want to orbit your destination when you arrive ... at some point you'd need to turn that 1g in the opposite direction to decelerate. (And I'm mighty impressed by the energy source that provides two years of continuous thrust.)

deleted 7y ago

[deleted]

If our current ideas about physics are correct, acceleration _never_ gets you to speed of light. The faster you go, the higher your relativistic mass, so if you accelerate by constant force, the lower your acceleration. Conversely, to keep acceleration constant, you would need larger and larger forces, in the limit ‘infinite force’. For more and better info, see https://en.wikipedia.org/wiki/Space_travel_using_constant_acceleration https://en.wikipedia.org/wiki/Space_travel_using_constant_ac....

pdonis 7y ago
> The faster you go, the higher your relativistic mass, so if you accelerate by constant force, the lower your acceleration. The Wikipedia article you linked to calls this (rightly) a "half-myth". It depends on your reference frame.
- 4bpp 7y ago
  As far as I understand, viewed from Earth's reference frame, a spaceship accelerating by constant force will get heavier and heavier as it gets faster, and thus get less and less speed out of it, asymptotically approaching the speed of light but never exceeding it. Moreover, crucially, any pingbacks from clocks on the spaceship we observe will appear to be progressively going slower than they should. (Time dilation) The spaceship's own reference frame will be a whole different story. If I understand correctly, it will perceive its own mass to be constant, the rest of the universe's relative speed to asymptotically approach the speed of light, but also the rest of the universe to get progressively squashed in the direction of travel (length contraction dual to time dilation), with the two effects multiplying up in such a fashion that the Newtonian relation between the integral of your acceleration and the time it takes to the destination seems to hold throughout. In other words, for the spacefarer's schedule, it's as if the speed of light does not actually play a role: they can always accelerate more/go arbitrarily faster to get to their destination faster. However, from their point of view, it is as if the universe around them will deform in the process to accommodate this, and from the stationary observer's point of view, it is as if they are actually still moving slowly but tricking themselves into thinking otherwise by accelerating their passage of time.

nine_k 7y ago

Unfortunately, radiation from hitting hydrogen atoms in interstellar space starts to become deadly around 0.25c or so, IIRC.

Eupolemos 7y ago

No, it will be much less as seen from the ship. Seen from Earth, it'll be around 13 years (takes a year to got close to c and another to decelerate - that is two years to travel roughly a lightyear, then 11 to travel 11).

8bitsrule 7y ago

Course, assuming you want to orbit your destination when you arrive ... at some point you'd need to turn that 1g in the opposite direction to decelerate. (And I'm mighty impressed by the energy source that provides two years of continuous thrust.)