On 7/14/2020 12:22 PM, Alan Grayson wrote:
On Tuesday, July 14, 2020 at 11:31:42 AM UTC-6, Brent wrote: On 7/14/2020 3:34 AM, Lawrence Crowell wrote:On Monday, July 13, 2020 at 6:30:46 PM UTC-5, Alan Grayson wrote: On Monday, July 13, 2020 at 5:19:30 PM UTC-6, Lawrence Crowell wrote: On Monday, July 13, 2020 at 4:42:24 PM UTC-5, 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. AGBut 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 It is unfortunately apparent that you are pretty highly confused by some of this. You need to sit down and read a comprehensive book or text on GR and related subjects. It is not going to be possible to clear this up with dozens of email posts. LC About the EP; I merely stated that it demonstrates that acceleration is locally indistinguishable from gravity, and then I stated what "locally" means. This is what Wiki and other sources say. Yet you say I am confused. How so? About masses of BH's, I watch documentaries which feature astrophysicists offering their opinions, and they *uniformly* claim that BH's have mass. How could it be otherwise if they're remnants of massive collapsed stars? Not one makes Brent's claim, that they're just geometric manifestations. AGI didn't say they lacked mass. I said they lacked matter. Thus countering your assumption that gravity requires matter. BrentI could have said that gravity requires mass/energy. What's the distinction between matter and mass? TIA, AG
Some things, e.g. black holes, have mass without matter (at least as far as GR goes).
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