[QUOTE=Don’t fight the hypothetical]
My main question, though, was could we with current technology build one of these ships.
[/QUOTE]
No. With existing technology–and we’re talking Sixties-era tech here–we could build an Orion-type vessel that could concievably attain a large fraction of of a percent of c. At .01c dialation effects work out to about 1 part in 20000, or a .005% decrease in experienced time (by someone aboard the vessel); this is measureable–about half an hour difference over the span of a year–but not significant. Faster velocities–those necessary for interstellar travel within a reasonable timeframe–will require higher impulse than an Orion-type vessel can provide; a Daedelus-type fusion proplusion system could probably achieve a few percent of c, but there are two limiting factors to any type of conventional propulsion system; the maximum impulse it can achieve (i.e. the momentum flux of the propellant) and the compound effect of needed reaction mass (i.e. the faster you want to go the more mass you have to carry, which forces you to carry yet more mass to propel the extra mass, which forces you to carry more mass, ad infinium.)
A system in which you do not have to carry fuel, re: a Bussard ramjet, would merely limit you to your maximum impulse (i.e. when the velocity of the exiting reaction mass equals the velocity of the vessel you can’t get any more thrust out of it); however, there are also some practical limitations; specifically, the ability of your vessel to survive ablation from inertial matter (dust, gas) in the interstellar medium, and the ability of your habitat to insulate the occupants from lethal radiation and (in the case of a Bussard or magnetic containment fusion) strong magnetic fields. It’s not just a matter of getting up to speed, but also not coming apart like a cheap gold watch or reducing your passengers to microwave dinners.
As for traveling to the future, although many people have made farcical (and oft-amusing) asides, the essential point is true; we’re all moving through the future, and in a sense, we’re doing so at velocity c; travelling in an accelerated inertial frame like a fast-moving spaceship doesn’t fundamentally change that; what it does is, in a sense, shift our velocity from the time axis to a time-like path along a spacial path; hence, the spaceman racks up fewer minutes in exchange for more miles.
The one thing about time that you seemingly cannot do, however, is go backwards (or directly “sideways”). You are constrained in the areas of space-time in which you can possibly occupy or even observe, the so-called “light cone” of your future. Why? Uhnuno, but it would make life seriously complex. I mean, if you thought Momento was confusing, just try to figure out the plot of a movie in which the characters go back and change the plot in mid-film.
With regard to downloading consciousness, pleased be advised that this is highly speculative technology. We still struggle with trying to define the essential characteristics of consciousness, and it’s not clear that you can isolate the patterns that comprise consciousness from the physical matrix in which they reside. Memories, concepts, and active neuropsychological activity seem to be controlled by the connections within the network of neurons rather than being stored as static data and instruction codes as per a microprocessor. Desipte with Kurzweil says, I wouldn’t go taking out a second morgage and investing in the IPO of a mind transference startup any time soon.
Stranger
