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Another question on this site deals with the question of interstellar trade without faster than light travel. I'd like inspiration for a related but more generic question. Why would people choose to take an expensive and years long interstellar journey in a world allowing ubiquitous fast, but sub-luminal travel?

Some useful scene setting information:

  • Fancy soft science fiction engines allow small (<100 person) space ships to travel at 0.99c in intergalactic space.
  • This travel can either be conscious, costing about 5 years salary per light year for an average worker, or in a sleeper state in which metabolic processes are slowed for two years salary per light year.
  • Larger cheap/government sponsored generational & sleeper ships have existed for a couple of centuries and have been used to terraform and colonise a region of space near the home world.
  • No alien species are known to exist.
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  • $\begingroup$ To be clear, do you mean intergalactic or interstellar? To travel to the Andromeda galaxy (a "close" galaxy) would take 2.5 million years at subluminal speeds $\endgroup$
    – Kys
    Mar 4, 2016 at 18:01
  • $\begingroup$ Ooops. Lets fix that. $\endgroup$
    – origimbo
    Mar 4, 2016 at 18:02
  • $\begingroup$ "Why would people choose to take an expensive and years long interstellar journey in a world allowing ubiquitous fast, but sub-luminal travel?" I'm not sure I understand. Are you saying the world has FTL or not? Because even at 0.99c that "ubiquitous fast, but sub-luminal travel" will still take years (in Earth's reference frame) to reach the nearest star. Is the choice between FTL and 0.99c? Or between 0.99c and something even slower? $\endgroup$
    – Schwern
    Mar 4, 2016 at 18:32
  • $\begingroup$ No FTL, just tricks with acceleration. The fundamental question is "is there a justifiable reason for normal(ish) people to take the time out of their lives to make such trips. $\endgroup$
    – origimbo
    Mar 4, 2016 at 18:36
  • $\begingroup$ Do note that if it's perfectly okay if no normal member of public wouldn't choose so - if only one-in-a-ten-thousand weirdos are eager to do it, it's completely enough for most intents and purposes. $\endgroup$
    – Peteris
    Mar 4, 2016 at 21:42

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I think this question really boils down to 'why would someone pay money to go somewhere?' And the answer to this question, in almost any case, is twofold:

1) - Get away from bad things where you are. Maybe you've made a lot of money by swindling a lot of important people, or perhaps you've profited from a war that now threatens to destroy the planet you live on. Either way, if it'll cost more to you to stay than it would to leave, then you're going to choose to leave. Since the cost of travel is so high and you probably won't be coming back, I'd say for most people, the cost of staying would have to be their life, or the lives of people they care about. Essentially, refugees.

2) - Go to good things where you aren't. Sometimes, the planet you're living on just isn't all that great. Maybe you're a painter, and the best painting teachers in the galaxy all live on the planet next to yours, or you're an entrepreneur on a planet with no resources. Or maybe you're the most brilliant scientist in your field, and someone wants to pay for your trip to their lab. In these and similar cases, your life probably won't be in danger, but there's got to be some pretty tantalizing rewards at the end of the road to leave everything behind and put down so much money.

There's also a third option:

3) - You're a decadent rich person looking to show off. How do you convince people to eat fish eggs and wear shiny rocks? You charge them a lot of money for it. In high-society parties, the rich people who can show off their rich-ness the best win. Even today, people love to tell everyone about the beautiful corners of the world they've traveled to; now imagine these corners are on different planets, and a vastly smaller percentage of people will have been able to visit them.

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One might choose to travel at .99c to take advantage of the significant degree of relativistic time dilation associated with that speed. If nothing else, it's an effective version of one-way time travel. It might be tempting to some to see what things are like a thousand years in the future.

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  • $\begingroup$ Also remember that the time dilation means the person travelling experiences much less time passing. That means that even though the people back home think it takes say 4 years for the ship to reach Alpha Centauri, to the person travelling it could be only a few weeks. Depending on acceleration, of course. See the Physics site for relevant math. $\endgroup$
    – jamesqf
    Mar 4, 2016 at 18:24
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    $\begingroup$ The relativistic time dilation makes a 1 year journey about 7 years "real" time. Not necessarily as much as you would expect. $\endgroup$
    – Lacklub
    Mar 4, 2016 at 18:34
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    $\begingroup$ This is a plot element of The Forever War where they use it as a human time capsule. And Wolfram Alpha will do the time dilation math for you. $\endgroup$
    – Schwern
    Mar 4, 2016 at 18:35
  • $\begingroup$ The time dilation would become more significant if they got even closer to c. For every 2 9's added to c, the time dialation grows by 10. So while .99c may not be that much, .999999c is a big leap forward. So it could be reasonable if OP's world isn't tied to just 2 9's. $\endgroup$
    – Lawtonfogle
    Mar 4, 2016 at 21:26
  • $\begingroup$ @Lacklub: Well, that's relative, isn't it? (Pun intended, of course :-)) For the traveller, the time s/he experiences is what's "real". $\endgroup$
    – jamesqf
    Mar 5, 2016 at 4:59
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This travel can either be conscious, costing about 5 years salary per light year for an average worker, or in a sleeper state in which metabolic processes are slowed for two years salary per light year.

This is the kicker right here, price. Getting to the closest star, at 4.3 ly, would take 21.5 years salary awake, or 8.6 years asleep. For the US the average wage is about $45,000 so a trip to the next star over is equivalent to buying a nice house! In cash!

If the economy is anything like it is now, the overwhelming majority of people could not amass the money to afford the trip. Average wage is deceptive, the majority of people make far, far less. The median (the point where half the people make more, half make less) US per-capita income is $15,500. To afford a trip, most people would have to go heavily into debt. Perhaps indentured servitude would return.

The price might be comparable to a 19th century person selling all their possessions and traveling to America from Europe, or to the American West, for a new life.

BTW, clever to do the pricing in light years traveled. If it were by time alone there could be a relativistic pricing problem.

Why would people choose to take an expensive and years long interstellar journey in a world allowing ubiquitous fast, but sub-luminal travel?

Even at 0.99c it takes years (in the frame of the place you departed from) to reach even the next star. For Earth, Alpha Centauri is the next star over at 4.3 light years. From Earth's perspective the ship will take 4.3 years (discounting time to accelerate), while from the traveler's perspective it will take 0.6 years (7x time dilation at 0.99c).

That is the problem with this question. It appears to want to compare "an expensive and years long interstellar journey" to "ubiquitous fast, but sub-luminal travel". But as shown above, the 0.99c journey is both expensive and years long.

So what is the alternative means of travel?

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At those prices they are unlikely to, only the rich can afford it and the rich are unlikely to want to take the risk.

Initially it would done just by explorers and adventurers.

If some tempting places to settle were found though then for some people the chance of a fresh start is going to seem appealing. Just think of how many months or even years of travel people used to put in to get from Europe to parts of the USA or even Australia.

The problem is that people willing to do that normally are not the super wealthy, and you've priced it to the point that only the super wealthy can afford it. You really need to drop the price if you want it to become more regular.

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Given the high cost of travel, I suspect that "indentured servitude" is the real answer. Since the average person cannot realistically come up with the money to travel to another star system, and since the price is per LY travelled, going beyond Alpha Centauri becomes very expensive indeed; Barnard's star is 6LY, 40 Eridani A is 16LY away and Vega is 25LY away. These are the nearest stars, globular clusters are tens of thousands of LY away at the far end.

However, given there is interstellar travel and presumably interstellar colonies, then sharp operators in the colonies will recognize the need for skills, labour and to broaden and deepen the local gene pool. You might be enticed to sign up for a trip to some distant star, but the promotor who is paying for this is going to:

a. Stick you in the freezer, and,

b. Have you on a long term contract where most of your wages pay for the ticket price plus interest.

This could be a win win for all concerned. You can remove yourself from a bad situation on the home planet, the new planet gets your skills and genes, and after a suitable period of time, you will be able to finish your contract and start afresh in the New World.

This is how many poor people came over to the 13 colonies of the Americas during the 1700's, and a lot of people considered it a good deal to take seven years indenture for the chance to live in the New World and have the ability to purchase land of your own after your indenture was done. While your starlight is quite costly, with the proper incentives in place, there will be a segment of the population which will still look at this as a good deal for them, and sign on the dotted line.

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