The Problem with Star Wars

[Michael]

This thread was originally posted on Aug, 8th 2008, 09:39 AM by Dominick

Many of us enjoy a good Science Fiction movie, from the popular Star Wars series to the original 1972 version of Solaris, while cult series such as Star Trek have a devoted, even fanatic fanbase. Some people even base their views on the future of mankind upon them. Visions of humans spreading across the interstellar space and colonizing planets here and there and forming a community that spans lightyears instead of miles.

Alas, it's not possible.

Einstein's relativity tells us that absolute space and absolute time do not exist. In other words, the concept of simultaneous events happening in different star systems which all these movies and series rely on, does not occur in nature. Space and time are intertwined. You can't move about in the universe without it affecting the time you, or any clock, register. And more importantly, that time is not the same for everybody.

Say you made a date with someone on a planet a lightyear away. You have a spaceship that travels at 90% of the lightspeed, so that you could get there in 1/(0.9) years, i.e. 13 months and 10 days approx. If you start on Jan, 1st 4000 you would set the date for Feb, 10th 4001. But there's a twist. If one applies the formulas of relativity to the person waiting over at the one lightyear distant planet, it results that that person has July, 18th 4002 on his or her calendar by the time you arrive there. So when it was Feb, 10th 4001 at your destination, you were nowhere in sight, and unless your date waited a year and some 5 months for your arrival, the two of you would never meet. Now imagine having to organize a space battle, let alone an Empire, in these conditions. You'd not only have to figure out where your opponent is, but also when he is. Larger distances and higher speeds only increase this time difference. If you were to rush off at 99% of the speed of light to a fight 100 lightyears away, you'd get there no less than 5,000 years after the fight broke out.

It's not a problem of technology. No matter which method of travel one uses, the time dilation would still be there. Faster than light travel may some day turn out to be possible, but that would only still increase the time difference. Wormholes, which IMO have an extremely low probability of ever being able to be made good use of, do not resolve the issue either. You're still trying to reach the same point in spacetime, and the faster you get there, the larger the time dilation, i.e. time difference is.

Neither is not a problem of the theory. Sure, the theory of relativity may and probably will be superseded by even more precise theory some day, but the fundamental fact of the non-existence of absolute time and space will still be a part of that new theory, whatever it is. Relativity is a fact of nature as much as gravity is.

In conclusion, for better or worse, a Galactic Empire will never exist.

[Michael]

A few replies to the original thread...

I could be mistaken, but are you sure you haven't gotten the time-dilation effect backwards in your example?
If you traveled to somewhere a light-year away at 90% C, then to the observers frame of reference you would arrive after approx. 13 months and 10 days. It would merely seem shorter to you, the one traveling at such high speed. After all, if we take the scenario to the extreme and say you actually traveled at C, then from the perspective of the observer it would take you precisely one year to travel one light year. From your perspective, you would arrive at your destination instantly, with no time passing at all.

And, let us not forget, in all those sci-fi universes they've generally managed to beat gravity with a handy machine, so why not relativity? :)

I could be mistaken, but are you sure you haven't gotten the time-dilation effect backwards in your example?
If you traveled to somewhere a light-year away at 90% C, then to the observers frame of reference you would arrive after approx. 13 months and 10 days. It would merely seem shorter to you, the one traveling at such high speed.
No, it's correct.
If you would apply it as you suggest, the traveller would bridge the distance of a lightyear in substantially less than a year (the 13 months and 10 days divided by the dilation factor) and that would imply faster-than-light speeds, which is impossible.

But it doesn't matter in this context really. The factor of the dilation remains the same, and thus also the discrepancy between the two parties, and thus also the logistic problems.

After all, if we take the scenario to the extreme and say you actually traveled at C, then from the perspective of the observer it would take you precisely one year to travel one light year. From your perspective, you would arrive at your destination instantly, with no time passing at all.
Actually, in this scenario, with v=c, relativity is undefined, because the equations give division by zero here. In one interpretation, this means that for the person waiting, you would never arrive. The saying "one can't travel at, or faster than the speed of light" is precisely substantiated by the result of the equations with these parameters.

The traveller on the other hand would still take a year to get there. A lightyear is the distance light travels at the speed of light in a year by definition after all. You'd have to travel infinitely faster than the speed of light to arrive instantly.

And, let us not forget, in all those sci-fi universes they've generally managed to beat gravity with a handy machine, so why not relativity? :)
Well, yes, they do, but how would you go about achieving that in reality, even in concept ? Gravity is one of the fundamental forces. It's not like people will ever be able to walk through walls, and that's a less fundamental force, i.e. chemical bonds. Maybe it would be possible at a quantum or even Plack scale, where pretty much anything is possible, but on a macroscopic scale, you'd need metaphysics rather than physics.

Not to harp on this, because I'm really not knowledgeable on the subject, but I still feel a little uncomfortable with this.

If, as you correctly noted, "A lightyear is the distance light travels at the speed of light in a year by definition..." then shouldn't we perceive that it takes something traveling at the speed of light exactly one year to travel one light year?

Or, from a more familiar view, the sun is approximately 8 light minutes away and thus it takes (from our frame-of-reference) approx. eight minutes for light to travel from the sun to us. If you were in a (very sturdy) spaceship on the surface of the sun and launched toward earth at (or right on the verge of) the speed of light, it would (from earth's frame-of-reference) take you approximately 8 minutes to arrive, just like the light.
Otherwise it would take something traveling at the speed of light more than a minute to travel a light-minute, and that can't be right.

Or, using the mathematical equations from you first post, you've set up a system in which the closer on gets to the speed of light (i.e. the faster one travels) the longer it takes them to arrive (from the perspective of a person at the destination). This is a result of your using the time-dilation effect to effectively lengthen the "wait-time" at the destination. Yet, I think we be quite certain, from common sense and experience, that the slower one travels the longer it takes one to arrive. So if I want to get to somewhere 1 light year away sooner (from the perspective of the person on the other end) should I travel at .9 c or .999999999c? Slower or faster?

Am I missing something here?

This seems to be a problem of logistics, as described. But, I'd imagine it no more difficult to calculate in "4000" than we struggle to take into account the geometry of the globe when flying around the world (head North/South to make the distance shorter). That concept would have created the sort of confusion 200 years ago, perhaps, that this one does now. But, if the technology were available to travel at speeds approaching light, I have to imagine that this would be accounted for in calculations/practicality.