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Comment by konschubert | Hacker News Reader

If you have enough acceleration , you can travel 1000 light years in a human lifetime.

It’s just that when you return, at least 2000 years will have passed on earth.

1g constant acceleration is enough. But we don't have the technology yet.

so you're implying speed atleast 10x the speed of light? i think you'll have better luck increasing the human lifespan instead.

Not that's not what he is implying. He is talking about time dilation.

How does one travel 1000 light years in a span of human lifetime (~80 yrs) if you’re not going faster than the speed of light?

Time dilation! Time is relative. For an outside observer, over 1000 years pass, but aboard the ship, much less time passes. There are calculators for this, e.g. at [0]. If you constantly accelerate at 1g, flip around at the halfway point and accelerate in the opposite direction for the rest of the journey, roughly 13 years would pass from the traveler's perspective.

This site also has a "Newton's universe" mode, which pretends that relativity doesn't exist. Interestingly, in that case you would take over 44 years!

[0]: https://www.omnicalculator.com/physics/space-travel?c=EUR&v=...

I am pretty rusty in special relativity, but IIRC, in the ship it basically seems like the distance is contracting as you accelerate. And from earth, it seems like time is going slower inside the moving spaceship.

With relativistic time dilation. 1000 years will pass on Earth, but on tge ship, it will be only a couple of decades, assuming they're close enough to the speed of light.

""" Time dilation is the difference in elapsed time as measured by two clocks, either due to a relative velocity between them (special relativity) or due to a difference in gravitational potential between their locations (general relativity). When unspecified, "time dilation" usually refers to the effect due to velocity. """

https://en.wikipedia.org/wiki/Time_dilation

wow thanks! this was super fun, do you happen to have some souce about the calculations that go into determining the time dilation based on different velocity? i'm aware about black holes being capable of well, doing time dilation thingy due to their massive gravitational force but nothing else.

edit: souce as in something a regular average joe can make sense of haha

Well, depending on your preferred format there's a great book called A Brief History of Time - https://en.wikipedia.org/wiki/A_Brief_History_of_Time , or lots of videos about it at https://www.youtube.com/results?search_query=time+dilation

More broadly, the series Cosmos with Carl Sagan was excellent, and is worth a view. The bit about time dilation is at https://www.youtube.com/watch?v=kWgEzxi_A0w . The more recent one with Neil Degrasse Tyson is also good (but while I enjoy both, I think I prefer the older one)

The time dilation equation from special relativity only needs basic maths: https://www.omnicalculator.com/physics/time-dilation

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