
The Question
(Submitted September 8, 2008)
In simpleminded engineering terms, the Cosmological Constant term
is a 'fudge factor' used to make theory match observations. Einstein
put it in to make General Relativity match the static universe model
then in vogue. When Hubble's results came in, Einstein disavowed it.
Now some Cosmologists are saying that the Cosmological Constant is
in fact nonzero. If their observations prove true, that would
suggest that GR is missing something now being approximated by the
CC term. Has this been noted by anyone in the astrophysics field?
The Answer
Yes, you're right, this is a huge deal for physicists precisely because
they want to go beyond the mere description (using the cosmological
constant) to a deeper understanding of what it is.
The Cosmological Constant (CC) has long been debated, even since the
time Einstein added it. He, indeed, added it to keep the Universe
static  without the CC, General Relativity (GR) required that the
Universe either be contracting or expanding. When Hubble's results
came in, the CC dropped out of GR. However, even after that, the CC
remained in people's minds  I remember during my undergraduate days,
there was still debate about whether the CC was really equal to zero
or not.
In even more recent history, it has been discovered that there is
another component to the Universe that had not been observed until
1997  this is dark energy, which you may have heard of. We can only
observe the effects of dark energy on the largest scales, which is one
reason it took so long to discover. The remarkable thing about dark
energy is that it has the property of negative pressure (think of
blowing into a balloon and having it deflate with each breath), which
is causing the rate of expansion of the Universe to increase.
One proposed way to account for this dark energy in cosmology is the
cosmological constant. You can read more about that here:
http://map.gsfc.nasa.gov/universe/uni_accel.html
We hope this helps!
Barbara & Koji
For the Ask an Astrophysicist team
