Re: Question on dark matter?
- From: "N:dlzc D:aol T:com \(dlzc\)" <dlzc1@xxxxxxx>
- Date: Wed, 2 Apr 2008 17:38:38 -0700
Dear Juan R. González-Álvarez:
"Juan R. González-Álvarez" <juanREM@xxxxxxxxxxxxxxxxxxxxxx> wrote
in message news:pan.2008.04.02.10.08.27@xxxxxxxxxxxxxxxxxxxxxxxxx
dlzc wrote on Tue, 01 Apr 2008 12:12:34 -0700:
Take next example (due to Hawking i believe).
Vertical line is event horizon and nothing can
cross (inside-outside) it according to GR.
Which is a classical, not a quantum, theory.
This trivial comment is asking for another:
It is not trivial, it is fundamental. GR does not have black
holes evaporating, quantum mechanics does.
Nobody said here that GR is a quantum theory.
You invoked Hawking, which reference is a quantum mechanical
reference.
According to QFT pairs (x y) are
spontaneously generated
Not in GR. Argument fails.
That you can split physics into different
disciplines and study them often in isolated
way does not mean that Universe works
that way.
It does mean that *our models* are patchwork quilts, when they
must be applied to Nature. You point at a QM arguement, and say
how funny GR looks from here. Not surprising, the two theories
are mutually exclusive.
As remarked above. I believe i read the virtual
pair model from own Hawking. I have not the
book at hand now to check that, but i can provide
you two online references on Hawking radiation.
The first from "ask to an astrophysicist":
http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/011125b.html
{BLOCKQUOTE
You are correct that there are multiple ways to
visualize the generation of Hawking radiation.
The first is indeed the separation of virtual
matter / antimatter pairs by the intense
gravitational force exerted by the black hole and
the other is the quantum tunneling of a particle,
such as a photon out of the black hole event
horizon.
}
And? All the "second option" does is ignore the antiparticle to
the one that survives, since it reenters the BH.
Another is from Carlip website:
http://www.physics.ucdavis.edu/Text/Carlip.html#Hawkrad
{BLOCKQUOTE
There are a number of ways of describing the
mechanism responsible for Hawking radiation.
Here's one:
The vacuum in quantum field theory is not really
empty; it's filled with "virtual pairs" of particles
and antiparticles that pop in and out of
existence, with lifetimes determined by the
Heisenberg uncertainty principle. When such
pairs forms near the event horizon of a black
hole, though, they are pulled apart by the tidal
forces of gravity. Sometimes one member of a
pair crosses the horizon, and can no longer
recombine with its partner. The partner can
then escape to infinity, and since it carries off
positive energy, the energy (and thus the mass)
of the black hole must decrease.
}
The argument fails, since the "energy carried off" did not come
from the BH, but from the pair. This Hawking radiation model
does not evaporate the hole, but actually grows it.
from fluctuations and next anihilated. If a pair is
generated on the event [#] horizon
|
x | y
\ | /
\ | /
\ | /
\|/
|
|
the particle x inside the horizon is trapped
whereas the particle y outside is not. Now
the particle x cannot cross the horizon
(nothing can) and cannot anihilate y.
The external particle y survives and it is
said that Black hole has emited radiation.
*And* the BHs net mass is decreased
thereby. Hence "evaporation". Interior
annihilation, still keeps the net energy /
mass internal.
Thus radiation (bunch of ys) has not
escaped from inside the event horizon,
which was my point.
Both descriptions (NASA and Carlip
websites) very much agree with i offered in
previous message, and in both cases i
remark again no radiation crossed the
horizon from inside the Black hole.
NASA's does not support you, and the Carlip citation describes
what may occur, but does not evaporate the BH... which is what
Hawking radiation is about.
Another posibility is you say of
quantum tunneling of a photon y
|
|
.... ? .... y
|
|
Where i have symbolized the crossing with
a "?". I have done this because quantum
tuneling does *not* involves crossing of any
class.
Actually it does. At the event horizon, escape
velociity is c. So any photons on the "inside"
have a net velocity towards the inside,
regardless of orientation. Your imagination fails.
As remarked in a previous message quantum
tuneling does not involve crossing of any class.
Wrong, and wrong.
You are repeating a common misconception
about quantum tuneling.
Sorry, no.
That is addressed in both the online blog
article and also in the American Journal of
Physics article cited.
Only in your narrow, flawed intepretation.
David A. Smith
.
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