QotD: The dark science of dark matter

Roughly a decade ago, it was discovered the expansion of the universe is accelerating, not decreasing as expected. This led to the assumption there must be "dark energy" as well as the conjectured "dark matter," because some force must be providing the impetus of the cosmic acceleration. Dark matter, if it exists, is substance in some guise other than stars, planets, nebulae and black holes, and would explain why celestial objects move as if the galaxies contain substantially more mass than can be detected. Dark energy, if it exists, would be roughly the opposite of gravity. Gravity attracts, its effect declining with distance. The conjectured dark energy repels, and increases with distance — the farther the galaxies move apart as the cosmos expands, the more punch dark energy packs, steadily increasing cosmic acceleration. It's just that, um, er, science has only vague indications of what dark matter is and not the slightest clue what dark energy might be. Physics and astronomy departments at leading universities rather cavalierly have embraced an assumption that as much as 96 percent of all mass and energy in existence is dark matter and dark energy, neither of which can be located or explained. We can't locate 96 percent of the universe — but trust us, we're experts!

Gregg Easterbrook, "TMQ: Ministers of defense", ESPN Page Two, 2009-01-06