On Saturday, August 24, 2019 at 11:24:20 AM UTC-5, Alan Grayson wrote: > > > > On Friday, August 23, 2019 at 7:48:19 PM UTC-6, Lawrence Crowell wrote: >> >> On Friday, August 23, 2019 at 5:48:13 PM UTC-5, Alan Grayson wrote: >>> >>> >>> >>> On Friday, August 23, 2019 at 3:31:36 PM UTC-6, Lawrence Crowell wrote: >>>> >>>> On Thursday, August 22, 2019 at 12:37:40 AM UTC-5, Alan Grayson wrote: >>>>> >>>>> >>>>> >>>>> On Wednesday, August 21, 2019 at 7:12:14 PM UTC-6, Alan Grayson wrote: >>>>>> >>>>>> >>>>>> >>>>>> On Wednesday, August 21, 2019 at 3:13:11 PM UTC-6, Lawrence Crowell >>>>>> wrote: >>>>>>> >>>>>>> On Tuesday, August 20, 2019 at 4:56:23 PM UTC-5, Alan Grayson wrote: >>>>>>>> >>>>>>>> https://en.wikipedia.org/wiki/Conformal_cyclic_cosmology >>>>>>>> >>>>>>>> Is this a viable theory for avoiding a BB interpreted as a >>>>>>>> singularity? AG >>>>>>>> >>>>>>> >>>>>>> Penrose proposed a conformal identification of spatial infinity in >>>>>>> the past and future i^±∞ of FLRW spacetimes. A cosmology expands and in >>>>>>> the >>>>>>> limit time → ∞ it transitions into a new cosmology. The de Sitter >>>>>>> vacuum is >>>>>>> not eternally stable, so the idea may have some germ of relevancy. I am >>>>>>> not >>>>>>> sure about how this would work with vacuum to vacuum transitions. The >>>>>>> exponential expansion of the universe is a sort of time dependent >>>>>>> conformal >>>>>>> transformation with a small vacuum expectation for the scale field. To >>>>>>> transition to a new cosmology, say with inflationary expansion, this >>>>>>> means >>>>>>> the vacuum expectation is increased. >>>>>>> >>>>>>> The overall physics community response to this has been tepid at >>>>>>> best. There are some possible conflicts with observed data. >>>>>>> >>>>>>> LC >>>>>>> >>>>>> >>>>>> FWIW, ISTM that what GR might be indicating about the BB, is that, >>>>>> insofar as it's a singularity, it couldn't have occurred, and didn't >>>>>> occur. This is to say the universe didn't become infinitely small in >>>>>> spatial extent, like a mathematical point, but rather that there was a >>>>>> maximal finite value of its energy density, hugely high but not >>>>>> infinite. >>>>>> For this reason I find the cyclic models promising, although, as you >>>>>> rightly indicate, they're far from complete or bug-free. AG >>>>>> >>>>> >>>>> Which brings up a possibly relevant question: If the total energy of >>>>> the universe occupied zero spatial volume (the presumed condition of the >>>>> universe at t=o according to the BB theory), wouldn't that contradict the >>>>> Uncertainty Principle? AG >>>>> >>>> >>>> The total mass-energy content of the universe is zero. >>>> >>>> LC >>>> >>> >>> Is that a provable fact, or something that can be measured? TIA, AG >>> >> >> It is provable, because in general spacetimes there does not exist a >> Gaussian surface to define mass. This sets the energy to zero. Think of it >> as meaning gravitational potential energy as negative is equal in magnitude >> to positive mass-energy. >> >> LC >> > > You claim it's a provable fact. Are you sure? I see many discussions on > the Internet which assert it's a conjecture. AG >
It is a canonical result that the Hamiltonian for general spacetimes is zero, or NH = 0 for N a lapse function. LC -- 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/70efcdc4-fcff-4928-b6fc-bb5d2222c325%40googlegroups.com.
