# Would it be possible with a light-speed ship to reach intergalactic space in a human lifetime?

I have one issue coming out of one conversation between me and my roommates (none of us professional in the subject of space)!

If one had a ship which could approach light speed, could one reach intergalactic space? (Suppose there are no Food, Water and Oxygen issues!)

Suppose this person leaves the earth at his 20s and lives an average life time.

• I have altered your question substantially to focus it on your question about exiting the galaxy in a human lifetime. Let me know if I have changed your intent in any way. Nov 21, 2013 at 14:19
• It all depends on just how fast your ship is. If your engines can produce 1g forever you can not only reach intergalactic space but go anywhere in the observable universe. (You can't, however, get to the really distant locations and stop within a human lifespan, though.) Nov 21, 2013 at 20:19
• @LorenPechtel: I vaguely recall reading that a continuous 1g acceleration gets you to M31 in something like 75 shipboard years (about 2.5 million years to an outside observer). Update: More information here. Apr 18, 2014 at 18:56

With current technology: no.
The Milky Way is about 1000 light years thick, and we're near the center plane so you'd need to travel at least 500 light years. The fastest spacecraft, Voyager 1, needs ca. 17,000 years to travel 1 light year, so you'd need 8.5 million years at that speed to reach the nearest edge.
(note: answer was given before the question was edited to add the 'light speed' condition)

• Thanks for your reply; So according to these numbers we should build a machine that runs at a speed of around 10^11 km/h. If we don't consider the technological problems is that possible according to the universe rules ? Nov 21, 2013 at 10:35
• Everything we know indicates that it's physically impossible to travel faster than the speed of light. It's not a technology problem, we'd have to find entirely new physics to solve this. Nov 21, 2013 at 10:40

Yes, kind-of.

As you move faster, according to special relativity, time actually slows down. Let's take the 500 light year number mentioned by Hobbes answer, and work with that. So let's assume you have a 60 year lifetime. That would require a time dilation factor of about 500/60, or 8.333. I found an online calculator that states you would have to go 0.99277c to achieve that dilation factor. For a smaller lifetime, the speed would have to increase, but it is possible, if you can achieve near light speed somehow, that you could reach any distance. Of course, anyone on Earth would have the full 500 years pass (Well, 500/speed, but close enough)

Practically speaking, achieving such speeds is virtually impossible, and then there's the chance of an impact, which would be quite serious. Still, it is possible.

• Well, at velocities close to c, interaction with any baryonic matter would be devastating, even a speck of dust, but yes, I was waiting for someone to mention time dilation here. +1 and one more link in my favorites for that page with relativity calculators. :) Nov 21, 2013 at 15:51
• @TildalWave: Yeah, but if one can entertain the fantasy that one can go almost light speed, let's entertain the fantasy that somehow we can deal with specks of dust. Nov 21, 2013 at 15:53
• That's what deflector shields are for. Nov 21, 2013 at 16:21
• Note, $E=mc^2$ so to achieve that speed you'd need to literally annihilate 8x the payload weight to accelerate that payload to that speed (that says nothing about what you'd need to burn to accelerate the fuel...) - essentially this is for mass of antimatter as fuel. Nuclear is about 2% of its efficiency. Hydrogen or Ion drives - far, far beyond.
– SF.
Nov 22, 2013 at 12:47
• @Philipp: Yes. Subjectively (from the traveler's point of view) acceleration of 1g yields roughly 1 c / year. 1g acceleration would be perfectly sufficient, the problem is energy.
– SF.
Nov 22, 2013 at 12:52

Hypothetically, if you could travel sufficiently close to the speed of light, you could not only exit the galaxy, but circumnavigate the observable universe in what would be less than a human lifespan in ship-time, due to time dilation. Since you'd be travelling no faster than light, and the observable universe is billions of light-years across, it would take you billions of years (Earth time) to complete such a voyage.

In practical terms, accelerating the required mass of ship, payload, and all to a such a large fraction of the speed of light, and then decelerating it at the end of a voyage would be practically impossible by any known means.

Because of near light speed, and the nearest "intergalactic" space being over 1000 light years, no one on Earth would still be alive by the time the ship reached it.

Those on the ship, however, could survive it if the velocity was in excess of 0.9999 C. If I do the math correctly, at that point, the Lorentz factor exceeds 100, putting the perceived time to between 10 and 50 years to the edge of the galactic disk.