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Comment by SketchySeaBeast | Hacker News Reader

Quote from the original claim:

> 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.

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You move at a constant vector, the speed of light, through both space and time. Since you go from basically 0 magnitude in space (anything us humans do on earth) to approaching the speed of light, that robs direction from the time magnitude. Therefore, going that quickly means you experience substantially less time. Taken to the extreme, when you move at the speed of light, you experience no time; you would simply from a human perspective teleport to the place where you start decelerating (given that's possible lol).

No, you're misunderstanding.

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.

Thanks - yeah, I realize now that the length actually shortens.

When you go fast, subjective experience slows down.

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.

It's not about time dilation, I realize now it's possible due to the length actually contracting. https://courses.lumenlearning.com/physics/chapter/28-3-lengt...

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.

They are different sides of the same coin.

This is the realization that really made SR click for me. The fact that "in the traveller's frame of reference, the universe becomes smaller in the direction of travel" is the same thing as "in the traveller's frame of reference, time becomes dilated".

As an example, from the perspective of a photon, the trip takes 0 seconds, the photon is emitted and absorbed at its destination with no (subjective) travel time

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