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. 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
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. AG
I didn't say they lacked mass. I said they lacked matter. Thus
countering your assumption that gravity requires matter.
Brent
Black hole mass is a pure spacetime physics. There is no material
stuff anyone can get their hands on. With the tortoise coordinate the
distant observer might say the matter-fields that made of a black hole
exist, but if one tried to reach them they always recede away. Black
holes do not have mass in a standard sense, though they have an ADM
mass defined by the curvature of spacetime.
LC
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