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[Darvi]

He was talking about 0.5c, not 2c. Hence there's only half as much energy invested, not twice.

[kaijyuu]

Ah I see.

[MetalSlimeHunt]

Yes, but the closer you get to 1c the more exaggerated the time dilation of the accelerating entity becomes for any additional acceleration, even if you're only going from .90 to .99c.

[Darvi]

You still can't make 4.5 lightyears in two years with less-than-light speed

[10ebbor10]

Wait... isn't Alpha Centauri like 4 and a half lightyears from the Sun? Even at half the speed of light, it would take you less than 3 years to get there.

My brain just broke.

It's really not that complicated. Acceleration is (effectively) linear from the POV of the entity accelerating. If you double the energy pushing you forward, you reach your destination in half the time.

The speed of light and associated time dilation affects your travel time from other's POV. Your origin and destination will see you as limited by the speed of light, as far as travel time is concerned.

It's relative. Hence, "relativity."

It doesn't work like that for near relativistic speeds though. The faster you go, the more energy you need to invest, since increasing in speed increases your mass(So standing still is indeed a way of losing weight). Hence why you can't reach or pass lightspeed, as then your mass and the energy to arcelerate would be infinitif.

Also, time dilation always works from your point of view. If you were to fly to Alpha Centauri and back at light speed, almost no time would pass in your craft. On Earth, 8 years would pass.

You still can't make 4.5 lightyears in two years with less-than-light speed

In your ship it can take 2 years, but outside normal rules apply.

[Darvi]

In your ship it isn't 4.5 ly either. But eh.

And I studied relativity at high school, I know how it works, thank you very much.

[ChairmanPoo]

Is "travelling to before the Big Bang" an option?

[Sergius]

Yeah, I had a bit of a brainfart there (I halved time, instead of doubling it )

Anyway, far end of milky way, let's say, that's about 75,000 years at light speed.

For the traveller, it would be effectively instantaneous.

At 0.9c, the "objective" time would still be in the same ballpark (around 83k years), but the traveller would feel about HALF of that, so about 36,000 years (according to this calculator).

At 0.9999999999c the voyager would only take about 1 "subjective" year to get there. To everyone else, it's still about 75,000 years.

[Darvi]

Is "travelling to before the Big Bang" an option?

Weeeell, we could get beyond the background radiation, I guess that'd be sort of the same?

[MetalSlimeHunt]

You still can't make 4.5 lightyears in two years with less-than-light speed

It depends on who we're talking about. The traveler can make that and more, but the observer can't.

[Darvi]

Fuckin' time travel, how does it work.

No seriously, I'd like to know that.

[Sergius]

Fuckin' time travel, how does it work.

No seriously, I'd like to know that.

It depends on whether you're a main character or not.

[Vorthon]

Fuckin' time travel, how does it work.

No seriously, I'd like to know that.

All I needed to now about time travel I learned from Homestuck (It's confusing as fuck) and Doctor Who (It is also fucking awesome).

[Darvi]

...ditto, plus Chrono Trigger.

[kaijyuu]

It doesn't work like that for near relativistic speeds though. The faster you go, the more energy you need to invest, since increasing in speed increases your mass(So standing still is indeed a way of losing weight). Hence why you can't reach or pass lightspeed, as then your mass and the energy to arcelerate would be infinitif.

This is false. Increasing your speed does increase your mass... but only from other's perspectives. Mass (from speed) is also relative. Remember, your speed from your own perspective is always 0.

It still takes infinite energy to "reach" c though. If you do, your time to reach your destination from any origin is literally 0. Your origin and destination will see you going c, you'll look damn similar to a singularity, and will be infinitely heavy. Fun stuff.

Is "travelling to before the Big Bang" an option?

It's impossible to go back in time. If you somehow go past the speed of light, you don't go backwards in time; you go into imaginary time (as in, square root of negative 1).