You can't capture all the energy. Basic thermodynamics. You have to black-body radiate away the heat of the star driving the system, or the only alternative is that it is all collecting within the system, cooking everybody within in a fairly short period of time.
I argue on the basis of real science that we know, not because we know it all but because we can't argue on the basis of science we don't know about. Given that, we damn well can make some guesses about what a space ship will look like, which inevitably includes some form of propulsion involving either the expulsion of very, very hot matter (to get optimum mass efficiency, propellant will be at a premium and no point dumping it out the back cold) or light directly (unlikely but at least plausible) in a directional manner.
The topic came up a few months ago during the discussions on whether it is rational for an alien civilization to summarily execute any other civilizations it discovers with relativistic planet-killers, but unfortunately trying to Google up a specific discussion about spaceships and relativistic projectiles is an exercise in futility. Still, work the math on what it takes to get a decent payload (at least several thousand tons would be nice) up to ~.1c, and then recognize that thanks to Newton's laws, the resulting mass-energy number you find must actually be coming out the back of your spacecraft in as close to a single direction as possible. Possibly literally as a laser, though as I said I'm pretty skeptical about the utility of a pure light-drive. It's pretty damned bright.
Look, I hate to be offensive, but if you don't fail basic thermodynamics and you actually take seriously the real science we already know, we don't have to retreat into romantic cliches about how we can't possibly understand advanced cultures. We can in fact put bounds on things if our understandings are basically correct, and if our understandings are basically incorrect then frankly we have bigger problems than the question of alien life.
The upshot of this, going back to your first post, is that if either of us is retreating into "religious dogma", romantic conceptions of reality held onto despite rational examinations of the evidence and science, taking shelter in the possibility of who-knows-what magic science may produce in the future and refusing to use what we already know, it's you, not me.
Look, it's not offensive but I do think what you're saying is naive.
Lets take a step back into the 1500s and talk about what an advanced culture able to move thousands of tons of goods from one side of the country to the otherside in a matter of days would look like. or what being able to search all of the worlds knowledge instantly would look like, etc etc. Any of their guesses are necessarily limited to their 'limited' perspectives.
We have had numerous paradigm shifts since then, each giving fundamentally new ways to conceive of problems, and I think it's incredibly likely that we will undergo another paradigm shift with regard to physics/space travel before our society is leaving the solar system, let alone the galaxy. If that's the case it's not an unnecessary romantic conception, it's a necessary repercussion of a historically verifiable phenomenon, paradigms change, and so do ways of thinking about problems.
Besides, I still don't understand how we are seeing a several-ton payload going .1c in a galaxy we just discovered.
I guess I just don't see a compelling argument that we would, from our vantage point and with our tools be able to make any type of reasonable observation against a hypothesis about other intelligent life.
I argue on the basis of real science that we know, not because we know it all but because we can't argue on the basis of science we don't know about. Given that, we damn well can make some guesses about what a space ship will look like, which inevitably includes some form of propulsion involving either the expulsion of very, very hot matter (to get optimum mass efficiency, propellant will be at a premium and no point dumping it out the back cold) or light directly (unlikely but at least plausible) in a directional manner.
The topic came up a few months ago during the discussions on whether it is rational for an alien civilization to summarily execute any other civilizations it discovers with relativistic planet-killers, but unfortunately trying to Google up a specific discussion about spaceships and relativistic projectiles is an exercise in futility. Still, work the math on what it takes to get a decent payload (at least several thousand tons would be nice) up to ~.1c, and then recognize that thanks to Newton's laws, the resulting mass-energy number you find must actually be coming out the back of your spacecraft in as close to a single direction as possible. Possibly literally as a laser, though as I said I'm pretty skeptical about the utility of a pure light-drive. It's pretty damned bright.
Look, I hate to be offensive, but if you don't fail basic thermodynamics and you actually take seriously the real science we already know, we don't have to retreat into romantic cliches about how we can't possibly understand advanced cultures. We can in fact put bounds on things if our understandings are basically correct, and if our understandings are basically incorrect then frankly we have bigger problems than the question of alien life.
The upshot of this, going back to your first post, is that if either of us is retreating into "religious dogma", romantic conceptions of reality held onto despite rational examinations of the evidence and science, taking shelter in the possibility of who-knows-what magic science may produce in the future and refusing to use what we already know, it's you, not me.