Recent content by fhenryco

Something that may be went unnoticed in this discussion is that in the cited theoretical paper by Crocker &all even though the action is that of GR, the way the field equations are derived is not the usual way: for instance to get the new Friedmann like equations they are not extremizing the...

I avoided the blabla about killing vectors as did Weinberg. I notice that Weinberg again was not quite correct...you should apply for the Nobel prize !

it's what i said because it was hard to believe that given the context someone would "understand" it literally

but curiously it's the time coordinate Weinberg uses to estimate at which time the external observer will receive the signal so he is apparantly assuming that this is also the time of distant observer clocks...

A region of spacetime that cannot send light signals outside itself (outside the horizon) is of course what i meant from the begining !

To summarize: In weinberg chapter 9 entitled gravitationnal collapse and badly reproduced in jbrigs444 post, he makes the simplifying assumption of negligible pressure to study the spherical collapse of dust thus acted on by purely gravitational force so that it falls freely and can be...

What i'm trying to understand is the difference between my sentence "such region (BH) would take an infinite time to form from the point of view of an external observer" and Weinberg sentence p347 in Gravitation and cosmology: "The collapse to the Schwarzschild radius therefore appears to the...

Right but people need to have an idea of a volume being cut out from the rest of the universe by the presence of the BH so extrapolating the euclidean notions that we have far enough from the BH to the BH itself is may be not so useless...may be all the more since there is negligible curvature...

If you really mean that light can escape the horizon then almost all i read almost everywhere about the BH is wrong... probably because people want to present it in a pedagogical way and neglect rigor... can you recommand one of these threads ? if a black hole has a mass M and a Volume...

The first time i hear about your definition: a black hole is most often merely described as a region of spacetime that cannot send light signals at all...But such region would take an infinite time to form from the point of view of an external observer, and your definition seems to take this...

your answer looks a bit like a more rigorous formulation of what i was trying to say... but i'm not sure

I found related questions being debated on the web so i'm not sure wether the question is closed. The following simple reasoning seems to imply that indeed the contracting universe is able to destroy its blackholes but what's wrong with it ?: The black hole solution is usually computed outside...

Another possibility i was thinking about is that they treat it like a classical field because of it's extremely low mass (extremely large wavelength) ... this is what they do for fuzzy dark matter ... but i found nowhere the same argument for inflation fields

It's also what i suspected but i wanted confirmation because i did not realize before that the scalar fields used for instance in inflation are understood as pure classical fields: i believed that in modern physics everything was always quantum and that nobody would accept a field which is not a...

Why the equation of state parameter w for a quintessence field with potential m²Phi² is not in between 0 and 1/3 depending on the energy of its particles relative to the mass of the field instead of the w resulting from formula 9 of https://arxiv.org/pdf/1504.04037.pdf which seems to be...