> 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.
Is there something I'm missing here? Proxima Centauri is 4+ light-years from us and firmly out of the solar system.
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
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.
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.
That's pretty mind boggling and quite different from "you can never reach the speed of light therefore you could never travel across the Milky Way in a human lifetime".
If you could carry sufficient fuel to accelerate at 9.8 m/s for 12 years you could travel across the Milky Way galaxy (112000 light years). You would be 12 years older but 112000 light years away from where you started. That's amazing to me.
It's a given that this is impractical.
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_ac...