Older science fiction had two basic forms of FTL travel: “hyperspace” meant that you left our universe for somewhere else and reentered our universe elsewhere. If the trip was instantaneous, it was like the jump drives on the new Battlestar Galactica. If it took a finite amount of time, the ship traveled through the “space” of some other dimension, sort of like what was depicted on Babylon Five. The “warp drive” meant that although you were traveling faster than light, you maintained a one-to-one correspondence between your path and a path through normal space. Actually not unlike Star Trek.
I’m not sure why you are arguing with me. I pointed out that the issue is not the fuel needed to travel long distances, it is the fuel need to decellerate to earth’s velocity. I agree that there is no need to carry along the mass of the initial booster. Someone smarter than me can calculate the mass of the fuel needed to slow down a vehicle from .9 C (including the mass of fuel needed to slow down the mass of fuel needed to slow down the mass of fuel…).
That would be the beauty of a solar sail for interstellar travel. You don’t need to carry any fuel at all. You get your departure boost from the Sun, and your arrival brake from the destination star. As I recall, you could get up a pretty fair speed, too. (I read about it in Science News sometime in the '80s, I think.)
A solar sail is not an easy ship to build, and not fast enough to go ten light years in a mere lifetime, I suppose, but just because we’re impatient creatures doesn’t mean alien life forms must also be impatient.
I adhere to the notion that life must exist beyond our solar system. To think otherwise seems, well, immodest to me. And I agree with whoever it was who said our odds of meeting an extrasolar culture depend largely on how long, on average, an intelligent species can survive in our galaxy, and whether we’re above or below average.
I’d be really surprised if we happened to meet up with aliens at this early date in our existence. If we can hang in there for just a few more millennia, then I think the odds will start looking a lot better.
As I pointed out in my first post there seem to be two different paradigms which both use the word “aliens”, which IMHO are completely unrelated, yet keep getting conflated. One is the debate over the possible existence of intelligent life elsewhere in our galaxy, and the feasibility of interstellar travel. The other is the assertion that “Grays” are routinely visiting the Earth and performing biological experimentation on humans, while the Umbra-level secret “Men in Black” keep the whole thing classified. If the latter could be true, it would make arguments based on the former irrelevent.
It’s like claiming that someone has secretly invented antigravity, and then debating whether it could be true by discussing the practicality of using superconductors to build magnetically levitated trains. The conventional paradigm is only relevent to the extent that the briefest of discussions suffices to show that the unconventional paradigm is hopelessly incompatable with it.
Sorry, I was just following the thread with my conventional comments. As regards the unconventional, if you postulate an alien intelligence at all, you’ve let in the gamut. There’s no telling what “they” might want to do, or what they could or could not do if they wanted to.
One idea that I discard entirely is that humans could know, and keep it secret. You know all those government scams and conspiracies and whatnot that we hear about all the time? Sooner or later, we always hear about them. I don’t excuse the conspirators or diminish the importance of whatever harm they do. I’m just echoing Poor Richard, “Three may keep a secret if two of them are dead.”
Sorry I never replied, but in case you are still interested, I wasn’t referring to the aliens specifically. I claimed I know a secret can be kept until the truth is lost; how could I know the truth if the secret had been kept? A DNA test with surprising results. I was just answering a question before it was asked.
Carry on.
And you can your departure boost from more conventional means also, and use the sail to decelerate. It would be a lot faster.
Another possibility for acceleration, probably better for probes than people, is a mass driver - a la Moon is a Harsh Mistress. You can set the stages for this thing up in space, and make it as long as you want.
I also agree that there is no reason to require .9 c. Any civilization advanced enough to think about sending out interstellar probes would have developed technology to get around their planetary system in reasonable time. That would be the starting point, not our pitiful chemical rockets.
So tonight my girlfriend is watching X-Files on DVD and the episode is “War of the Coprophrages” and they had a quote in there that was very fitting for my earlier post, in that the X-Files quote helps illustrate my point.
Who says The Grays are not robots?
Just because they appear fleshy, doesn’t prove that they’re of biological origin. Perhaps it’s an advanced material that is far more resilient than it appears.
After all; it is rather strange that the aliens would wander about another world naked (I suppose they could be trying to make it clear they’re looking for some anal probing action 
).
Yes, I know I’m responding to a fictional character, but his opinion is a popularly held one.
Oh, and just in case I’m implying otherwise: I don’t believe we’ve been visited by aliens.
You’re so right: a secret can be kept right up until the truth gets out. Thanks for that insight.
I see you all liked this subject
But I’m too lazy to read through all 40 comments now o.o
omg, we read through them all in order to be able to make those comments, in response to your post! The least you could do is read 'em!
At least read mine!
gasp :o
Now I feel guilty to respond on a 50-comment long thread in English… lol.
What have I done!? 
But honestly, I have readed through the post fast, and it looks like you mostly fuss with eachother^^
But I will have a closer look tomorrow.