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The Question

(Submitted August 21, 1998)

I was listening to a few scientists talk on the radio about a force that is causing or assisting the expansion of the universe. I only had a brief moment to catch the radio show before having to go to work. They where saying that an anti gravity is causing the universe to expand. Is any one familiar with these ideas that may be able to point me in the right direction to get more information on this?

The Answer

You ask very good questions, that astronomers, physicists, and cosmologists are debating intently right now. A group of researchers recently published findings that the universe may be expanding faster now than in the distant past. This would imply a non-zero value for the 'Cosmological Constant' (CC).

Einstein's original cosmological model was a static, homogeneous model with spherical geometry. The gravitational effect of matter caused an acceleration in this model which Einstein did not want, since at the time the Universe was not known to be expanding. Thus Einstein introduced a cosmological constant into his equations for General Relativity. This term acts to counteract the gravitational pull of matter, and so it has been described as an anti-gravity effect. see: http://www.astro.ucla.edu/~wright/cosmo_constant.html for a good but technical description of the 'force'.

Until recently people just put a value of zero in for the (CC), now things may be different. We have yet to see what will hold up with newer instruments such as MAP. http://map.gsfc.nasa.gov/ coming online.

The March 1998 issue of Sky & Telescope magazine also has a report on this same item.

I hope this helps,
Mike Arida and Tim Kallman for the Ask an Astrophysicist Team

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