116 reputation
17
bio website dcgeorge.com
location Eureka, California
age 76
visits member for 2 years
seen 22 hours ago

I'm a theoretical physicist (old-amateur/hobbyist division).


Sep
7
comment Is it mathematically possible or topologically allowable for cutouts, or cavities, to exist in a 3-manifold?
@Jerry Schirmer. "I don't know of any dynamic process that would cause a gap to appear in a spacetime,..." How about simple cavitation? If the spacetime manifold is a fluid-like entity, couldn't the negative pressure from expansion of the universe pull it apart or boil it?
Aug
4
answered Why do we care about black hole interiors' physics?
Jul
25
comment Why do we care about black hole interiors' physics?
@Manishearth: "Spacetime doesn't really end at the horizon." Perhaps not but Polchinski and Bousso have both made comments to that effect; granted, they did add "somehow" into their comments. Whether it does or not is, IMHO, the most interesting question going these days.
Jul
25
comment Why do we care about black hole interiors' physics?
@Manishearth: "... modern physics is much less about predictions and much more about having a beautiful, mathematically rigorous model of the universe." Au contraire, science is all about prediction. If a model of reality doesn't allow for predictions, it's philosophy, not science.
Jul
25
comment Why do we care about black hole interiors' physics?
@Manishearth: "... because our final goal is a set of laws of physics that describes any part of the universe ...". If space and time end at the event horizon, the interior wouldn't actually be a part of our universe.
May
30
revised Does a black hole have an interior or does the spacetime manifold itself end at the event horizon?
I just ran across this fairly recent interview and its related article.
Apr
21
revised How does gravity escape a black hole?
Given all the interest in the question and considering there are no comments or votes on my answer, I thought it needed to be expanded and made more clear.
Nov
5
comment Does a black hole have an interior or does the spacetime manifold itself end at the event horizon?
Thanks Ben, I had that totally screwed up (we're dealing with a 75 year-old brain here). I edited it accordingly. This mass scaling issue is also mixed up somehow with entropy and surface area and Bousso's take on the holographic principle. I'm trying to sort it out.
Nov
5
revised Does a black hole have an interior or does the spacetime manifold itself end at the event horizon?
Correction needed as noted by Ben Crowell
Oct
27
revised Does a black hole have an interior or does the spacetime manifold itself end at the event horizon?
I wanted to re-word the title to make it more clear, as suggested.
Oct
24
comment Does a black hole have an interior or does the spacetime manifold itself end at the event horizon?
The equivalence principle doesn't allow anything special to happen at the event horizon. Only if you assume that the spacetime manifold is unbroken, that it continues past the event horizon. Which means you also have to ignore the whole issue of black hole firewalls and Bousso's idea that "space and time actually end there."
Oct
24
comment Does a black hole have an interior or does the spacetime manifold itself end at the event horizon?
The Schwarzschild solution has m∝r. It's proportional to neither its area not its volume. This is wrong, Ben. The Schwarzschild radius is proportional to the mass but the mass of the black hole itself is proportional to either the radius squared or cubed depending on who you ask. Ron Maimon says "... the scaling of the Schwarzschild radius is linear in mass, while the scaling of mass is cubic in the radius, ..." Raphael Bousso (re the holographic principle) says the black hole's mass is proportional to its radius squared, i.e. its surface area. This is the black hole scaling problem.
Oct
23
comment Does a black hole have an interior or does the spacetime manifold itself end at the event horizon?
We discussed this here. It's not wrong, just meaningless. With all due respect, Ben, in that discussion, you tried to disparage the paper by calling the MNRAS a crap journal (guilt by association, I guess). Now you're saying their conclusion isn't wrong, it's just meaningless. Frankly, I don't understand your conclusion that all the mass of a black hole being outside the event horizon is meaningless. The meaning is perfectly clear to me. Not only is it clear, since it is directly counter to the accepted view, if it's correct, it's astoundingly significant.
Oct
23
revised Does a black hole have an interior or does the spacetime manifold itself end at the event horizon?
added 764 characters in body
Oct
22
asked Does a black hole have an interior or does the spacetime manifold itself end at the event horizon?
Oct
7
comment About the Ether Theory acceptance
A great answer, Trevor. I find it fascinating that the Michelson-Morley experiment actually had two conclusions, the second of which is almost universally ignored. The alternate conclusion was that it is simply not possible to detect the ether drift because of Lorentz contraction effects.
Sep
20
comment Does the total mass of an isolated object include the mass stored in its gravitational field?
"... If their measure of energy density implies that all the energy of a black hole is outside the horizon, then that's in fact an argument against taking their result as having any deep significance." It does indeed imply that. But, if it disagrees with the general consensus and is correct, it's likely of great significance. Lynden-Bell and Katz are not exactly lightweights in the field.
Sep
20
comment Does the total mass of an isolated object include the mass stored in its gravitational field?
"... MNRAS is a crap journal that publishes lots of papers that are nonsense ..." That may be true but you might want to take a look at Lynden-Bell's Wikipedia page before you conclude the paper is nonsense. en.wikipedia.org/wiki/Donald_Lynden-Bell
Sep
20
comment Does spacetime in general relativity contain holes?
@Ben Crowell. Sorry Ben, my intention wasn't to reduce your answer to a sound bite. You give very interesting and informative answers. For instance: "The singularity is not considered part of the spacetime manifold, ..." That's fascinating. I assume the same could be said for a hole (a 3D singularity) in the manifold.
Sep
17
comment Does spacetime in general relativity contain holes?
@Ben Crowell. "There is no restriction on the size of the hole or its topological features such as whether it's knotted, etc. The only condition is that what's left over after cutting is still a manifold." So, am I understanding it correctly that, given the above conditions, you think holes or cutouts in the spacetime manifold are possible? Do I have that right?