Although it’s utterly beyond our engineering prowess today, we know the physics required to travel anywhere in the universe in the blink of an eye…from the point of view of the traveler. And without any g-forces either. Enter Robert L. Forward’s “gravitational catapult”. We manipulate electromagnetic fields on an everyday basis by taking electromagnetic charges and moving them near the speed of light along a path; well, turns out we can manipulate gravitational fields the same way…only the powerful gravitational charges moved near the speed of light would be something like masses of neutronium or micro-black holes in a tube, which demands energies far beyond what we’re able to generate. Like, it takes us some effort to accelerate individual atoms, and this method would entail accelerating Mount-Everest-sized masses of material!
Nevertheless, what a technology that would be: the gravitational field so generated can be projected even to an area where there is no mass, and can be made either attractive or repulsive. Imagine a structure shaped like a circle, then maneuvering a starship inside it. You turn the gravitational catapult on, and a field is projected that catapults the ship out to the desired direction at a speed of, say, 99.999835% of light virtually instantaneously.
No g-force would be felt, since the entire ship and everything and everybody in it is subject to the exact same force at the exact same time; with a normal propulsion system it’s just the ship that’s accelerating and so your inertia causes your body to want to stay in the same place, hence the experience of being shoved back in your seat, but with this method every part of your body is being accelerated along with the ship, so not even a jolt would be felt!
Making a galactic Itinerary
Anyway, I use 99.999835% of light specifically because that’s about the velocity the cosmic background radiation is shifted into the visible spectrum, making for a nice glow; go all that much faster and it’s blueshifted even further into the gamma rays, which requires more protection (probably easily provided by a civilization that can do stuff like this, but whatever). The Lorentz factor for such a velocity is 550, which means for every second that passes on the ship 550 seconds, or 9 minutes 10 seconds, pass back home.
So if you wanted to go from here to Proxima Centauri (where another catapult would have to be waiting to decelerate you, by the way, if you ever wanted to come out of that relativistic time warp…) you would experience 2.8 days of travel time, while the solar systems around you have experienced 4.246 years of time.
A destination like the galactic center, 26,000 light-years away, would take 17 years ship time at this velocity, so you’d want to speed it up further beyond Lorentz factor 550. In any case 26,000 years will have elapsed back on Earth; if you came back it would be 52,000 years later on Earth, no matter how little time you experienced on your own trip.
We don’t need Faster-than-Light to have a bright Future!
Obviously it’s just not going to be feasible to run a galaxy-spanning civilization with such time lags. So let’s say more exotic techniques like wormholes don’t work out for whatever reason, and higher and higher levels of relativistic spaceflight are the best we’ve got, the technological basis for our interstellar expansion. What would such a civilization look like?
With the vast time differentials between ships and colonies it really wouldn’t even be a civilization, though a meaningful shared culture may well persist for a long time into the future. So let’s call it an interstellar culture rather than a civilization.
I would submit that the optimal path for our expansion in such a scenario would be something like the “worldship” concept: scale up your vessel to be as big as can be made so you can take as much of your civilizational base as possible with you. If you have the entire technological, industrial, etc. base of your civilization, enough to be a self-contained self-sufficient unit, right there with you being accelerated and decelerated, you don’t really need to concern yourself with whether the homeworld will still be there in thousands or millions of years after your voyage is completed.
Effectively, this would amount to a civilization splitting itself up into these starship units, much like a sessile dandelion splits into spores that are carried on the wind and can traverse enormous distances at high speed.
These vessels could in principle be very large; although they’d have much less mass they might easily be comparable in volume to a decent-sized planet such as our own. Imagine if that’s how we make first contact with aliens: a cosmic wilderness lulls us into thinking we’re alone, and then bam, a starship bigger than our whole planet pops out of nowhere.
If they’re planet-sized these civilization-ships may well develop their own ecologies and the like, whole lineages of the tree of life that are optimized to survive only on these ships under the patronage of the higher civilization, being none the wiser as to their true origin or the true nature of their little universe.
Which provokes a much wilder thought: what if we’re such an ecology? Sure, our universe obviously isn’t a starship like we’d think or it or build, but think a little deeper: might it be one on a higher-dimensional level? That is, the four dimensions we see are only one slice of a five- or even-higher-dimensional structure? Think of it like a two-dimensional creature crawling along a sheet of paper, which is attached to a ship that exists in three dimensions; the creature’s world would look like a flat expanse of paper, with no direct perception of the bigger picture. Sure, a ship the size of our whole universe, which is at least 94 billion light-years across and probably many orders of magnitude greater even than that figure, would be big, but hey, if you want to make a worldship you want it to be as big as possible, right? Maybe that’s the sort of scale that’s just natural to the beings of five or more dimensions who are using the same method to travel fast through their level of the multiverse. Hmm. Makes you think, doesn’t it?