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The Question

(Submitted September 8, 2008)

In simple-minded 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 non-zero. 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

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