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Comment by melling | Hacker News Reader

Unfortunately every single one of them is unreachable within several lifetimes. We're going to be pretty much trapped in our solar system until we try to solve some of the more difficult problems.

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We're (other people, not me) at least working on it.

http://www.nasa.gov/centers/glenn/technology/warp/warp.html

http://en.wikipedia.org/wiki/100_Year_Starship

http://en.wikipedia.org/wiki/Faster-than-light

If they're successful and you warp to a planet that's 100 light years away then warp back, I don't know how much time would have passed on Earth though.

Depends on their velocity. Assuming a warp of 95% the speed of light, then ~640 years (~320 years one direction). See:

http://www.fourmilab.ch/cship/timedial.html

http://physics.stackexchange.com/questions/31105/how-to-calc...

http://www.phy.olemiss.edu/HEP/QuarkNet/time.html

t / 2 = 100 / (1 - (0.95 * c)^2 / c^2)^(1/2)

Where t is the time for a one-way trip and c is the speed of light.

A lot sure will have changed. Imagine going back to the year 1370 and arriving today. Before Kepler, Galileo, before the discovery of America, or the printing press. Heck, a lot can go wrong in 640 years too.

That's not how Alcubierre-derived warp fields work. The time inside a warp bubble is predicted to remain synchronized with the time in the originating frame. Thus, if your warp bubble goes at .95c, it'll take you 105.26 years one way, 210.52 going there and back.

And I'm sceptical of your calculation, anyway. From Earth's unchanging perspective, if your are going at .95c in a conventional manner relative to Earth, Earthlings will see your trip as taking the same 210.52 years. Time dilation will only affect the time that passes for the people on board, which will make it seem shorter, not longer. So, really, if your warp drive can't break c, it's better from the passengers' perspective not to use one. This is explained in the StackExchange article you linked to- you put the factor of gamma in the wrong spot (http://physics.stackexchange.com/questions/31105/how-to-calc...).

I was assuming conventional propulsion at 95% c. An Alcubierre warp field would be ideal, assuming the problems can be overcome:

http://en.wikipedia.org/wiki/Alcubierre_drive#Difficulties

http://arxiv.org/abs/1001.4960

http://arxiv.org/abs/1202.5708

I'd enjoy seeing your calculation of the number of years that would have passed on Earth for a round-trip of 100 light-years out.

You've seen it. 210.52 years. The passengers on the ship should only experience 65.7 years- (210.52)sqrt(1-.95^2). Hence the famous twin paradox- the twin who goes on a relativistic trip comes back younger than the one who stayed behind. What you calculated was how much time would pass on Earth for a trip that took 100 years and 100 light-years from the perspective of the people on the ship, which is not generally what people mean when they say that a star is 100ly away.

I found the source of my confusion.

The post I replied to stated, "I don't know how much time would have passed on Earth though." You stated I calculated "how much time would pass on Earth."

The OP was wondering, "if a person on a ship visited a star 100ly away, how much time would have passed on Earth when they returned?"

However, the OP was wondering about time frames in terms of a warp drive, rather than a conventional almost-light-speed drive. Take my upvotes. :-)

I wonder how much of a perception you have of this trip though... if you're just radiation floating through space you might just was well think you just "instantly jumped" as soon as you arrive and "assemble" (whatever that process may consist of)

We can visit up to a few tens of solar systems in a few hundred years, if we could develop a space-ship powered by a black hole, antimatter, or some advanced or innovative hybrid fusion engine (there were talks about one from the 60's around here).

Colonizing a few solar systems out of the 100 or so we can visit with such a ship that reaches a large fraction of the speed of light, should be "enough" for the next 1,000 years or so.

By year 3,000, we'll probably figure out something faster than that, to really begin exploring the whole galaxy.

Black holes naively look like a great way to get 100% mass-to-energy conversion, but when you really look into it, things aren't that great. To get more energy output, you want the black hole to be small (to have a high curvature in the event horizon); but, black holes that are small enough to give reasonable output are also too small (smaller than an atom) to reasonably feed new matter into.

Meanwhile, black holes big enough to feed fuel into have an incredibly terrible power-to-weight ratio.

And that's assuming that black holes even work the same way when they get that small. Quantum gravity could easily screw things up even more (or make them more convenient; who knows?)

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