On Fri, Feb 17, 2017 at 11:19 PM, Brent Meeker <[email protected]> wrote
> > > The cosmological constant appears as an integration constant in solutions > to Einstein's equations. > > Yes, so mathematically it could have any value including zero. > > > It would be good to know more about the CC, but we actually "know" more > about it than we do about dark matter. > The Cosmological Constant amount s to a repulsive effect that comes from space itself, and you can set that constant to anything and mathematically the field equations of General Relativity would still work just fine. Originally Einstein saw no physical reason for that additional complication so he set it to zero. But then he noticed that if it was zero the universe could not be stable, it must be expanding or contracting and at the time everybody including Einstein thought the universe was stable so he set it to a non zero value and the cosmological constant was born. However just a few years later Hubble found the universe was expanding, so Einstein thought the cosmological constant no longer had a purpose and said that changing it from zero was the greatest mistake of his life. Then people working with quantum mechanics found that empty space should indeed have a repulsive effect, but the numbers were huge, gigantic astronomical, so large that the universe would blow itself apart in much less than a billionth of a trillionth of a nanosecond. This was clearly a nonsensical result but most felt that once a quantum theory of gravity was discovered a way would be found to cancel this out and the true value of the cosmological constant would be zero. But then just a few years ago it was observed that the universe is not just expanding but accelerating, so now theoreticians must find a way to cancel out, not the entire cosmological constant, but the vastly more difficult task of canceling it all out *EXCEPT* for one part in 10^120. There are only about 10^90 atoms in the observable universe. Nobody has a clue how to do this. John K Clark -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at https://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/d/optout.
