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> Spacecrafts can traverse the Solar System to reach nearby stars in span of days to weeks Is there something I'm missing here? Proxima Centauri is 4+ light-ye

> Spacecrafts can traverse the Solar System to reach nearby stars in span of days to weeks Is there something I'm missing here? Proxima Centauri is 4+ light-years from us and firmly out of the solar system.

sedatk 2y ago
Relativity?
- prox 2y ago
  At the actual speed of light, that’s still 4 lightyears. If you mean how much time will pass for the traveler, that might be it yeah.
  - sedatk 2y ago
    Yes, that’s what I mean.
bboygravity 2y ago
Traverse the solar system to reach the nearby star (the sun) maybe?
m463 2y ago
That is just sort of an ambiguous sentence. How about this one though: At a constant acceleration of 1 g, a rocket could travel the diameter of our galaxy in about 12 years ship time, and about 113,000 years planetary time. If the last half of the trip involves deceleration at 1 g, the trip would take about 24 years. If the trip is merely to the nearest star, with deceleration the last half of the way, it would take 3.6 years. https://en.wikipedia.org/wiki/Space_travel_under_constant_acceleration https://en.wikipedia.org/wiki/Space_travel_under_constant_ac...
sethev 2y ago
From the perspective of someone on the spaceship, this is absolutely possible by the laws of physics. It's a common misunderstanding that the speed of light is like a highway speed limit that's enforced by the universe. In reality, it means that light always travels at the speed of light and that you can never observe an object traveling faster than that. However, a key part of relativity is that the laws of physics are the same in every reference frame. If you're on a ship with sufficient fuel, you can keep accelerating forever and cover vast distances. You'll never reach a point where the universe prevents you from accelerating. If it were otherwise, then relativity wouldn't be true - because there would be special rules that apply to people traveling at a certain speed. That's the whole point of relativity is there can't be such laws because there isn't a preferred reference frame in the universe! However, the more you accelerate away from the earth the longer time will have passed on earth if you turn around and come back. Here's a calculator you can play with: https://spacetravel.simhub.online https://spacetravel.simhub.online As an example, if you could accelerate at 9.8 m/s (same as gravity - so you could walk around the 'back' of the ship as if in earth gravity), then you could travel 50 light years in 7.7 'ship years'. However, if you turned around and went back to earth 102 years would have passed there, even though you would only be ~15 years older.
- api 2y ago
  There’s a classic sci fi novel called Tau Zero about a Bussard ramjet breaking so they can’t turn it off, so they keep asymptotically accelerating toward c and experiencing more and more time dilation. Won’t spoil the rest.
  - dannyfreeman 2y ago
    I read this book after seeing this comment. It was a fun book, thank you!
- thrance 2y ago
  Everything you said is true, but I think reaching Proxima Centauri in a matter of days would require an acceleration that would crush the most well trained of astronauts into a thin meat pancake. I do think the article meant planets instead of stars.
  - ben-schaaf 2y ago
    Here's some further calculations for a 1G space ship: https://math.ucr.edu/home/baez/physics/Relativity/SR/Rocket/rocket.html https://math.ucr.edu/home/baez/physics/Relativity/SR/Rocket/.... 3.6 years to Proxima Centauri if you want to stop.
- alextingle 2y ago
  > this is absolutely possible by the laws of physics Not with antimatter rockets, it's not. Even though antimatter is extremely energy dense, the rocket equation still applies. You need reaction mass. If you use laser beams as your rocket exhaust, then you get maximal efficiency (exhaust velocity is C), but very low thrust. That's not going to get you anywhere in days or weeks. If you use stored matter (hydrogen, say) as your rocket exhaust, then you'd get better thrust, but all sorts of other issues come into play. Radiating all that waste heat. Running out of reaction mass. Again, there's not a practical design that could get you anywhere near a nearby star in "days or weeks", even if you assume "perfect" materials, efficiency, etc. > If you're on a ship with sufficient fuel, you can keep accelerating forever Um, no.

sedatk 2y ago

Relativity?

prox 2y ago
At the actual speed of light, that’s still 4 lightyears. If you mean how much time will pass for the traveler, that might be it yeah.
- sedatk 2y ago
  Yes, that’s what I mean.

bboygravity 2y ago

Traverse the solar system to reach the nearby star (the sun) maybe?

m463 2y ago

That is just sort of an ambiguous sentence. How about this one though: At a constant acceleration of 1 g, a rocket could travel the diameter of our galaxy in about 12 years ship time, and about 113,000 years planetary time. If the last half of the trip involves deceleration at 1 g, the trip would take about 24 years. If the trip is merely to the nearest star, with deceleration the last half of the way, it would take 3.6 years. https://en.wikipedia.org/wiki/Space_travel_under_constant_acceleration https://en.wikipedia.org/wiki/Space_travel_under_constant_ac...

sethev 2y ago

From the perspective of someone on the spaceship, this is absolutely possible by the laws of physics. It's a common misunderstanding that the speed of light is like a highway speed limit that's enforced by the universe. In reality, it means that light always travels at the speed of light and that you can never observe an object traveling faster than that. However, a key part of relativity is that the laws of physics are the same in every reference frame. If you're on a ship with sufficient fuel, you can keep accelerating forever and cover vast distances. You'll never reach a point where the universe prevents you from accelerating. If it were otherwise, then relativity wouldn't be true - because there would be special rules that apply to people traveling at a certain speed. That's the whole point of relativity is there can't be such laws because there isn't a preferred reference frame in the universe! However, the more you accelerate away from the earth the longer time will have passed on earth if you turn around and come back. Here's a calculator you can play with: https://spacetravel.simhub.online https://spacetravel.simhub.online As an example, if you could accelerate at 9.8 m/s (same as gravity - so you could walk around the 'back' of the ship as if in earth gravity), then you could travel 50 light years in 7.7 'ship years'. However, if you turned around and went back to earth 102 years would have passed there, even though you would only be ~15 years older.

api 2y ago
There’s a classic sci fi novel called Tau Zero about a Bussard ramjet breaking so they can’t turn it off, so they keep asymptotically accelerating toward c and experiencing more and more time dilation. Won’t spoil the rest.
- dannyfreeman 2y ago
  I read this book after seeing this comment. It was a fun book, thank you!
thrance 2y ago
Everything you said is true, but I think reaching Proxima Centauri in a matter of days would require an acceleration that would crush the most well trained of astronauts into a thin meat pancake. I do think the article meant planets instead of stars.
- ben-schaaf 2y ago
  Here's some further calculations for a 1G space ship: https://math.ucr.edu/home/baez/physics/Relativity/SR/Rocket/rocket.html https://math.ucr.edu/home/baez/physics/Relativity/SR/Rocket/.... 3.6 years to Proxima Centauri if you want to stop.
alextingle 2y ago
> this is absolutely possible by the laws of physics Not with antimatter rockets, it's not. Even though antimatter is extremely energy dense, the rocket equation still applies. You need reaction mass. If you use laser beams as your rocket exhaust, then you get maximal efficiency (exhaust velocity is C), but very low thrust. That's not going to get you anywhere in days or weeks. If you use stored matter (hydrogen, say) as your rocket exhaust, then you'd get better thrust, but all sorts of other issues come into play. Radiating all that waste heat. Running out of reaction mass. Again, there's not a practical design that could get you anywhere near a nearby star in "days or weeks", even if you assume "perfect" materials, efficiency, etc. > If you're on a ship with sufficient fuel, you can keep accelerating forever Um, no.