Who can explain to me in layman's terms what the "cosmological constant" is?

Buck540

If the cosomological constant (denoted by the Greek letter lambda) equals zero, the future of the universe depends solely on the density of matter. This is because in the absence of a cosmological constant, gravity is the only force affecting the expansion rate of the universe. Gravity causes the expansion to decelerate. However, if the cosmological constant is nonzero, this means there is "dark energy" in the universe that opposes the force of gravity. As the universe expands, the amount of empty space increases, which means the density of matter decreases and the amount of dark energy increases. The dark energy overtakes the force of gravity and causes the universe's expansion to accelerate. Dec 21 04, 2:27 PM

peasypod

Just to expand on what Buck has said... It's a force of repulsion (a kind of antigravity) that arises naturally in some theories of the very early Universe involving the break-up of a primordial superforce into the four forces of nature known today. The effect of this cosmological constant is to cause an extremely rapid (exponential) expansion of the Universe (known as inflation) in the first split second of its existance, before the constant fades away to zero, leaving the more sedate expansion that we see today. Dec 21 04, 6:45 PM