[boris]

"I dunno, can you see Cherenkov radiation, or any other traces of the use of undiscovered (by us) means of propulsion, with your eyeballs? Seems to me that I was taught there are some pretty narrow limits to human vision in biology."

Swimming pool reactors glow visibly blue by Cherenkov radiation.

And if any of these schemes were feasible, they would (he repeated) have been perfected by intelligent ETs thousands or millions of years ago. At 5% of light speed, there has been ample time to visit every single star in the galaxy, using self-replicating 'von Neumann' robot probes. If intelligent species are common (and we are the latest on the block as Carl Sagan pointed out) there should be a traffic jam of probes all over the galaxy. In particular we should have been visited multiple times and there is no reason such visits should not be continuing. Yet we see no evidence (such as aliens landing on the White House lawn) of such visits.

Hence, he repeated, either we are alone or none of these schemes is feasible.

--Boris

[William Terrell]

What percentage of, say, physics do you figure we know of all there is to know about physics?

[RadioAstronomer]

Swimming pool reactors glow visibly blue by Cherenkov radiation.

I have seen this with my own eyes. On top of a Triga-A bathtub reactor at the Uinversity Of Ill.