On Monday, July 13, 2020 at 3:42:24 PM UTC-6, Alan Grayson wrote: > > > > On Monday, July 13, 2020 at 1:42:49 PM UTC-6, Alan Grayson wrote: >> >> >> >> On Monday, July 13, 2020 at 11:57:50 AM UTC-6, Brent wrote: >>> >>> >>> >>> On 7/12/2020 11:50 PM, Alan Grayson wrote: >>> >>> There can be because it's consistent with the equations. A black hole >>>> doesn't include any matter. General relativity is non-linear, that's why >>>> there can be non-flat cosmologies that contain no matter. Of course there >>>> may be some different, better theory in which spacetime can't be curved >>>> without matter...but it seems unlikely since we have good evidence that >>>> gravitational waves exist. >>>> >>>> Brent >>>> >>> >>> Yes, good evidence that gravitational waves exist, but as far I know >>> they're always associated with material interactions such as collisions of >>> black holes. In the case of EM waves, I'd be more receptive of your claim >>> that they can exist independent of charges and/or currents, but as far as I >>> know there's no evidence of that. AG >>> >>>> >>> But a collision of black holes does NOT involve matter. Black holes (as >>> far as the theory goes) are purely geometric things, i.e. made of empty >>> space. >>> >>> Brent >>> >> >> How then does the BH at the center of our galaxy weigh in at 4 million >> solar masses? AG >> > > It's measured by observing the rotation rates of stars near the galactic > core, and not so small by comparison with other BH's at the center of > galaxies, called Super Massive BH's. AG >
If you assume zero mass solutions in GR, or no charges or currents in EM, the solutions you get are expected; namely, that in regions of space or space-time which are vacuums, waves can propagate. AG -- 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/e48a3881-650d-48d0-9ada-7508f6b579b2o%40googlegroups.com.
