Assuming you're a hyper-evolved super-intelligent post-singularity being, I predict that nothing is going to make you feel better about your surprisingly boring extra-dimensional existence than watching the pathetic little meat sacks on unevolved worlds continually missing opportunities for advancements and obsessively focusing on irrelevant trivia (why it's just like the good old days!). Just insert the galactic laughtrack signal and hilarity ensues, reality television on a galactic scale.
In fact, for all we know, we're already the galaxy's equivalent of Sea Monkeys (http://en.wikipedia.org/wiki/Sea-Monkeys) whilst assuming we were closer to the Sand Kings.
Or as Edmund Kean said on his death bed: "Dying is easy, it's comedy that's hard."
Probably information -- art, music, culture, scientific discoveries, technological blueprints (that could be "printed" anywhere), software, genetic material, anything informational.
Information has the benefit of weighing nothing and being easily transmissible at the speed of light.
This is also probably true for interplanetary trade, such as with a Mars colony... though return of very precious materials via something inexpensive like gun launch can't be totally ruled out.
Going full sci-fi mode: if something like consciousness uploading were possible, it would also be possible for people to travel interplanetary and interstellar distances at the speed of light as information as long as something at the other end existed to reconstitute them. So one mechanism of interstellar colonization would be to send unmanned drone ships first, then encode ourselves and go.
Information has the benefit of weighing nothing and being easily transmissible at the speed of light
There is the interesting twist that if you could position some sort of device on an interstellar information trade route, you could harvest both sides trades "for free".
So one mechanism of interstellar colonization would be to send unmanned drone ships first, then encode ourselves and go.
Richard Morgan has a bunch of books about something like this, his hero Takeshi Kovakz travels digitally from planet to planet, sometimes waking up in a cheap or worn out body and having to upgrade later. In this case the bodies are "dumb" and need a mind loaded into them. I can't remember if its one of his books where there is a colony ship that grows children from babies, educating and socializing them with robots, which goes horrifically wrong.
Yes, long-term everything could be printed via nano-robots. Even if not directly but as a sequence of building different plants. So something like a seed nano-robot colony + manufacturing blue-prints.
Interstellar migration could be not unlike booting an embedded device via a slow serial link. First send the slow robotic "boot loader," then use it to download the colonists to the new star system and boot up a civilization.
Matter is everywhere. Information is what it's all about, and information travels at 'c'.
Well remember physics constrains everything, so it's interesting to look at that too. The reason we'll look into expanding in the first place is because of energy/material constraints in our own system. Some systems will require large "seeds" to boot up depending on how advanced we are at a particular point and how long can we wait for booting. Then as soon as it boots it will start receiving updates on how to improve itself, otherwise it would be terribly outdated by the time it starts exporting computing. What we choose to colonize will probably depend on the specifics of the system, like solar power output, material availability at planets, etc. There's a question on what kind of information the seeds will produce too: improving themselves should be largely redundant with the improvements made by the colonizers, which would be streamed to the new planets. So they'll be some very long term tasks so it can be efficiently divided across the decade-or-more latency separated systems.
I need to write a book about this some day. It's just so fun to imagine :)
It might not be practical to send information as light. You'd need a powerful transmitter so your signal can be detected among the noise from stars. It might turn out that sending a spaceship is actually cheaper and just about as fast. The spaceship can steer itself and doesn't spread out the further it goes.
I think galactic civilization will either solve noise problem or install enough repeaters if that's cheaper. Repeater network will have enormous fixed cost, but I don't think its variable cost will be higher than spaceships.
Shlepping atoms around between stars is probably way more expensive than it's worth, unless the destination star's orbiting bodies have a debilitating paucity of those particular kinds of atoms.
But, really, why would we consider colonizing somewhere so iron-deficient, for example, that we need to tow space rocks of the stuff in?
