Of all the irresistible forces in the universe, progress may be the toughest to slow down. And the progress of progress itself? Forget about it! The characters in The Light Years, the new play by The Debate Society that just opened at Playwrights Horizons, learn this lesson the hard way as progress swallows them all up - and washes the meal down with what's left of an economically ravaged America. No amount of human suffering, leavened or not by good intentions, can stop innovation. And the real lesson at work here - in more ways than one - is that that's sometimes a good thing, casualties be damned. . . .