On Wed, Jan 15, 2020 at 6:54 PM Alan Grayson <[email protected]> wrote:
>> Already about 74% of the matter/energy in our universe is in the form of >> Dark Energy, and as time progresses that percentage can only increase and >> we'll get closer and closer to a pure de Sitter universe. That's because >> the Cosmological Constant is a property of empty space, so as the >> accelerating universe creates more space it also creates more Dark Energy, >> however the total amount of matter (both regular and dark) remains fixed. >> > > *> Why does the total amount of matter, both regular and dark, remain > fixed as the universe expands? AG* The simple answer is in General Relativity there is a mechanism for creating new space but not for creating new matter. The Cosmological Constant is the energy that is always inherent in space even when it has no matter in it. General Relativity says that this vacuum energy will cause space to accelerate, that is to say more space will be created, so unlike the matter in it vacuum energy will not become diluted as the universe expands but will remain constant in both space and time. According to General Relativity the curvature of Spacetime (NOT the curvature of space) is determined by the energy and momentum in it, and as Sean Carroll says "*the manifestation of spacetime curvature is simply the fact that space is expanding*". And if vacuum energy is constant then the spacetime curvature (NOT spatial curvature) of the universe is constant so the universe is accelerating at a fixed rate, that is to say it always takes a fixed amount of time to double in size. General Relativity allows for the existence of vacuum energy but does not insist on it, Einstein's theory has no way to calculate it's value, it could be anything even zero and can only be determined by observation. For many years astronomers thought the value was indeed zero and so they could forget about it, but then in the late 1990's they found that the universe was accelerating and the vacuum energy density consistent with this was 6*10^-10 joules per cubic meter. Curiously unlike General Relativity with Quantum Mechanics you CAN calculate the value of vacuum energy, however when you do so you find it is in error by a factor of 10^120; it's been called the worst discrepancy between theory and observation in the entire history of science. So if the goal is to find a Theory Of Everything maybe people should leave General Relativity alone and monkey around with Quantum Mechanics rather than the reverse, it might be worth a try. By the way, we don't know for sure that vacuum energy is the cause of Dark Energy but it seems like the best guess at the moment. 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 view this discussion on the web visit https://groups.google.com/d/msgid/everything-list/CAJPayv2PkN68tnQkSOsHn3BJt32nXaBZx8JGRhOU9Neb9jLFbA%40mail.gmail.com.
