Ok, this may depress some of you, but, sadly, the basic fact is that John can never return to earth, even if he is, relatively speaking, quite close to it. And, being a theoretical physicist, he should have already thought about this.

Einstein's "Theory of Special Relativity" states that as one approaches the speed of light, time slows down. This has been proven in several ways, but the simple way of explaining it will follow in this example.

Let's say that John was catapulted to the other side of our galaxy (not the far side of the universe, as he claims, but just The Milky Way.), a mere 100,000 light years away. (This isn't far by cosmic terms.) To the non mathematically oriented, that's 586,569,600,000,000,000 miles, or the equivalent of about 24 billion trips around the equator of the earth. We're all on the same page now, yes? Good.

Now, since the speed of light is a constant, we have the distance traveled, and we can figure he spent about 5 minutes in the wormhole, we have a nice little equation.

D=C*T where D is distance, C is the speed of light (186,000 miles/second), and T is time (or, in this case, 300 seconds.) Uh, oh.

186,000 * 300 is nowhere near 586 quadrillion.

The speed of light cannot be exceeded.

The far side of the galaxy didn't get any closer.

That only leaves one variable. Yeppers, time.

Yes, kiddies. If the wormhole accelerated JC right up to the speed of light, he's been gone 100,000 years.

Now, because the theory of relativity states that time will, in essence, stop at the speed of light, and five minutes did elapse to him, we know that he was going less than the speed of light, which means that even more time must have elapsed on earth. Not much. We're talking a matter of days, here, and over 100,000 years, that doesn't count for squat.

Because time elapsed in a foward direction as far as Crichton knew, he didn't cross the speed of light. Good for him.

Now, let's say that when Moya starbursts, she can actually exceed the speed of light. Time would, in essence, begin to run backwards on her ship, but be made up upon deceleration. (Due to the excessive brevity of the starburst.) However, although aboard the ship, it would appear that no time elapsed, it's more than likely that more than a few years passed on stationary (relatively) objects, like planets.

ERGO : If John wanted to go back to earth, he'd find an earth 200,000 years older than he left it. (100,000 years each way.)

FURTHER : If they ever go back to a planet they've visited before, the populace would have aged a considerable number of years, with the exception of those who have starbursted just as far.

FURTHER STILL : Those who have been imprisoned on the ship for prolonged periods of time through many starbursts are CONSIDERABLY older than they claim, unless they automatically adjust age upward after each starburst. For example, it's quite possible that Zhaan has only lived through 40 years, but is in a year 812 years past her birth because of the distance she has traveled.

Just something to think about.