Long story short: to travel to Alpha Centauri it would take for the traveller still about 4 years, and when back at home, people would have aged only some months more than the astronauts.
Crazy things happen if you decide to go on galaxy-wide trips though, to the astronauts because space contraction they perceive their own trip as happening still rather quick, a 100 000 ly trip (the size of our galaxy, for reference) takes 22 years for someone inside a spaceship with 1g acceleration, perfectly doable. But people outside still see it taking 100 000 years... (meaning they will be 100 000 years "older" from the point of view of the astronauts)
After I found all this out, I concluded space travel isn't THAT hard, assuming you have a way to accelerate constantly at 1g for 22 years (that is the hardest part actually), you can get anywhere in the galaxy in a human lifetime, no need for generation ships, cryogenics or other crazy tech.
In fact even going to other galaxies is easy, a trip to Andromeda takes 28 years!
Mind you, all those calculations were done assuming you will burn at 1g until half the distance, and then burn at 1g to brake, if you don't brake you can get even faster to places (although that wouldn't be very useful I guess).
According to google the universe is 93 billion ly wide. If you accelerate (and decelerate later) at constant 1g, this trip takes 49 years for the astronaut!
Edit: Ah, wasn't aware of length contraction. https://courses.lumenlearning.com/physics/chapter/28-3-lengt...
> After I found all this out, I concluded space travel isn't THAT hard, assuming you have a way to accelerate constantly at 1g for 22 years (that is the hardest part actually), you can get anywhere in the galaxy in a human lifetime, no need for generation ships, cryogenics or other crazy tech.
They are saying add a constant 1g acceleration and you can get anywhere relatively quickly, no warp bubble required. That's what I'm taking exception to. If we add a warp bubble, sure, but a constant 1g acceleration shouldn't ever see you having an experience of moving faster than the speed of light, and that 10,000 ly trip should still take > 10,000 ly.
From your frame of reference, the universe is much flatter in the direction of travel, and getting flatter and flatter the more time you spend. The distance between Earth and the edge of the galaxy will get smaller and smaller in your direction of travel.
You'd have 22 years of thoughts, for example, even though 10,000 years of stuff happened elsewhere.
From the perspective of an observer on earth, the trip takes a long time. The people on the spaceship experience 22 years.
If it didn't you'd still need to pass through 10,000 ly of space and if you were going at slower than the speed of light it would still appear in your frame of reference to be > 10,000 years. But contraction removes that limit and shortens the distance.
If you somehow DO achieve lightspeed, time stops for you, completely, so from your point of view you are teleporting, but since time is stopped no machine or chemical reaction can happen, thus why we believe lightspeed machinery is impossible.
By the way, achieving near lightspeed with 1g acceleration is in a way, hard, for example the trip to alpha centauri at 1g results in you achieving "only" 94% of light speed... to do that same trip peaking at 99.0% of light speed it would take 3g of acceleration, and it would result in the trip being roughly 1/3 shorter (taking 1.7 years more or less, instead of 5)
But from your frame of reference wouldn't you be moving much faster than the speed of light? If you're taking 22 years to travel 10,000 ly, that means you're moving faster than light in your perception, doesn't it? Isn't that forbidden in any frame of reference?
Unfortunately, there is also a kind of rocket equation for constant 1g acceleration, and if I remember correctly it's not really doable for any realistic amount of time, even with matter/antimatter reaction drives.
Technically they wouldn’t be older, you’d be younger.