Is Space Really Empty

On 2/11/2013 8:43 PM, Greg (Strider) Moore wrote:
"Brian Gaff" wrote in message ...

Well part of the problems (as I see them, someone correct me if I'm
wrong)

ok :-)

is that the larger a black hole is, the longer it takes to
evaporate, to the point that the largest would take longer than the
expected life of the universe. That said, I suppose if they still
exist, so would the universe, so not really sure how works. :-)


I have the same dilemma. In either case; that of a closed cyclical
universe or that of one that ends at zero energy with a local
super-cluster black hole there really isn't anything left surrounding
the event horizon we'd recognize as a Universe....

But I could see it evaporating so slowly that the particles would spread
out "infinitely" and by the time it does fully evaporate, there
basically would be such a low density that basically the definition of
the word universe ceases to have any meaning.


Well here's where I have to correct you a bit. Black holes do not
'evaporate' uniformly. The process is non-linear and actually speeds up
as the hole looses mass. Current theory claims that once the mass of
hole shrinks to Planck mass the dissolution would complete nearly
instantly in a violent burst of Gamma. But there are still missing
theoretical pieces to that model, I'll admit. But the current thinking
is that it does not end quietly.

http://en.wikipedia.org/wiki/Hawking_radiation

See bullet items and end of para. on Black Hole Evaporation.

Also, if particles are far enough that they never interact, what happens
to "time". Can time even exist if nothing is happening. (i.e. if there
is no way to measure the movement between particles (since they're too
far away to interact) there can be no concept of a clock and according
to some theories time simply ceases to exist.


My personal opinion (again FWIW, $0.02) is that time behaves just like
everything else is a near zero energy universe. It becomes quantized and
virtual. It winks in and out of existence along with all other virtual
'particles'. I've always considered time to be a scalar unit, without
individual form. It's a vector under differentiation but is itself
without reality. It can only be a measure or characteristic of a 'real'
phenom, the most fundamental probably being the photon.

Much of the thinking about end-state universe is unfortunately still
dominated (even in the early 21st century) by classical Newtonian
concepts of space and time.

We have to stop thinking about the vacuum of space as being empty. To
directly address the original topic of this post, under current quantum
theory the answer is no. Space is never really empty. Recently there has
been a better experiment than the one performed by Casimir et al back in
the late 40's, that seems to more directly address the issue known as
the 'Dynamic Casimir' effect. (As terrible nomenclature, since the
Casimir Effect is often stated as proof of the existence of vacuum
energy when it really isn't, but use of the concept (vacuum energy)
provided a calculation 'convenience' for explaining the phenomena at the
time.)

I refer to the work done by Wilson et al. at Chalmers University of
Technology in Goteborg Sweden and reported in Nature on 17 November
2011. A summary of this work can be found he

http://www.sciencedaily.com/releases...1118133050.htm

and if you want the details and are willing to spend USD $32 a on
reprint, he

http://www.nature.com/nature/journal...ml#/affil-auth

Dave

I've always considered time to be a scalar unit, without individual
form. It's a vector under differentiation but is itself without
reality. It can only be a measure or characteristic of a 'real'
phenom, the most fundamental probably being the photon.

Sorry, this is a confused (stupid) statement. What I meant to say was
that time, although scalar, has a preferred direction. Let's leave
differentiation out of it....

My apologies to mathematicians everywhere...

Dave

David Spain wrote:
and if you want the details and are willing to spend USD $32 a on reprint, he

http://www.nature.com/nature/journal...ml#/affil-auth

Or save yourself the USD $32 thanks to link provided by an MIT
Technology Review article to arXiv:

http://www.technologyreview.com/view...asimir-effect/

http://arxiv.org/abs/1105.4714

Dave

On 2/11/2013 8:42 PM, David Spain wrote:
On 2/11/2013 1:17 PM, Peter Fairbrother wrote:
On 11/02/13 13:00, David Spain wrote:

OTOH if an experimentalist can prove non-zero ground-state vacuum
energy, there would no doubt be a Nobel Prize in Physics lurking there
for such a clever scientist.... Need a goal?

Hasn't that been done? Casimir effect? It is standard model.


-- Peter Fairbrother


I don't think they are the same. One interpretation of the Casimir effect is that it measures "resonances" or fluctuations in the
vacuum energy between closely spaced parallel plates and can actually measure an attractive or repulsive force between them. But
there are other interpretations that don't invoke ZPE to explain the effect. Therefore it does not establish a definitive existence
of vacuum energy, nor does it establish a value for the ground state vacuum energy.


That's as applied to the original experiment by Casimir. But hey, theoretical physics is not my day job. Further research shows that
there were plenty of other experiments performed from 1958 on that actually DO demonstrate the "Static Casimir" effect and don't
bring up all the Van Der Waals and fine structure issues of Casimir's experiment.

A good summary of these I have subsequently discovered can be found he

http://iris.lib.neu.edu/cgi/viewcont...t=physics_diss

You learn something new every day....

However I'm still waiting to learn if ground state vacuum energy has been proven to be zero or non-zero....

Dave

In article ,
David Spain writes:
Black holes do not 'evaporate' uniformly. The process is non-linear
and actually speeds up as the hole looses mass.

Yes. There's a formula in the Wikipedia article you cite:
http://en.wikipedia.org/wiki/Hawking_radiation

Current theory claims that once the mass of hole shrinks to Planck
mass...

Current theory is known to be inadequate in this regime; there is no
theory of quantum gravity. However, a black hole of 1 kg mass
evaporates in about 8E-17 s. For other sizes, the time goes as M^3,
but this is an entirely classical (i.e., general relativity but no
quantum mechanics) calculation, so it won't be valid at very small
masses. (It should be fine at 1 kg and indeed several orders of
magnitude smaller.)

--
Help keep our newsgroup healthy; please don't feed the trolls.
Steve Willner Phone 617-495-7123
Cambridge, MA 02138 USA

On 02/15/2013 4:31 PM, Steve Willner wrote:
In article ,
David Spain writes:
Black holes do not 'evaporate' uniformly. The process is non-linear
and actually speeds up as the hole looses mass.

Yes. There's a formula in the Wikipedia article you cite:
http://en.wikipedia.org/wiki/Hawking_radiation

Current theory claims that once the mass of hole shrinks to Planck
mass...

Current theory is known to be inadequate in this regime; there is no
theory of quantum gravity. However, a black hole of 1 kg mass
evaporates in about 8E-17 s. For other sizes, the time goes as M^3,
but this is an entirely classical (i.e., general relativity but no
quantum mechanics) calculation, so it won't be valid at very small
masses. (It should be fine at 1 kg and indeed several orders of
magnitude smaller.)



Could you elaborate a little, or give a pointer to where I could get
more details? I get that the Schwarzschild radius of a 1 kg black hole
is about 1.5x10^-27 meter. I don't know how one can say that quantum
effects should be small for anything of that size?

I'm not saying that your claim that classical model should be fine
for several orders of magnitude smaller than 1 kg is false. I am
saying that I am ignorant of physics in that domain and I would like to
learn some.


Alain Fournier

In article ,
Alain Fournier writes:
Could you elaborate a little, or give a pointer to where I could get
more details?

I should have put in a disclaimer that I am no expert in this area.
I've heard experts speak but may have misunderstood or mis-remembered
what they said.

I get that the Schwarzschild radius of a 1 kg black hole
is about 1.5x10^-27 meter. I don't know how one can say that quantum
effects should be small for anything of that size?

Usually it's the mass, not the size, that matters for quantum
effects, but see above about "no expert." The point I was making was
that the decay time for such a small black hole is very short. If
there are quantum effects, they may lengthen or shorten the decay
time, but it would be surprising if quantum effects made such small
black holes last a macroscopic amount of time.

I didn't find any really good sources in a quick web search, but you
may have better luck. One note of interest is that people have been
looking for black hole decays at the LHC, so far without success.

--
Help keep our newsgroup healthy; please don't feed the trolls.
Steve Willner Phone 617-495-7123
Cambridge, MA 02138 USA

On 02/21/2013 7:26 AM, Steve Willner wrote:
In article ,
Alain Fournier writes:
Could you elaborate a little, or give a pointer to where I could get
more details?

I should have put in a disclaimer that I am no expert in this area.
I've heard experts speak but may have misunderstood or mis-remembered
what they said.

That disclaimer probably holds more for me than for you. I have never
attended any physics class at university level. Though I have read some
in my spare time (but I did like physics in high school, thanks Mrs
Kunderlik you were a great teacher).

I get that the Schwarzschild radius of a 1 kg black hole
is about 1.5x10^-27 meter. I don't know how one can say that quantum
effects should be small for anything of that size?

Usually it's the mass, not the size, that matters for quantum
effects, but see above about "no expert."

Isn't it a mix of both. It's all related to Heisenberg uncertainty
principle dx dp h/(2pi) [dx = uncertainty of position, dp =
uncertainty of momentum]. And since momentum depends on mass...

The point I was making was
that the decay time for such a small black hole is very short. If
there are quantum effects, they may lengthen or shorten the decay
time, but it would be surprising if quantum effects made such small
black holes last a macroscopic amount of time.

I was rather thinking the other way, that a 1 kg black hole would
evaporate in less than 8x10^-17 sec because of quantum effects. But I
don't know. My (naive) line of reasoning is the following:
Imagine that you want to add stuff into the black hole, so you hold the
black hole steady, let's say a speed of 0 plus or minus 1x10^-8 m/s.
Then by Heisenberg Uncertainty principle, you don't know the position
of the black hole within a few Schwarzschild radii, therefore you don't
know where to add the stuff. If you allow for more uncertainty to its
velocity (and therefore momentum) you can (theoretically) locate the
black hole to within its Schwarzschild radius. But with such
uncertainty in its velocity, it can move one Schwarzschild radius in
1.5x10^-27 m/(10^-8 m/s)= 1.5x10^-19 seconds. Therefore, you only have
that amount of time during which you know the position of the black hole
within one Schwarzschild radius and you need to add the mass you want
to add within that time or remeasure the position of the black hole. If
the uncertainty principle says that mass has to be added in a time
frame of 1.5x10^-19 seconds, or it probably won't be added at the right
spot, then I see no reason why mass that is already there will still be
in the right spot in 1.5x10^-19 seconds, and the black hole would
evaporate in that time. Note that this is not just a measurement
problem. It's not that we can't measure the position of the black hole.
It's truly that the position of the black hole probably isn't within
it's Schwarzschild for more than 1.5x10^-19 seconds, or at least that is
my understanding of this.


Alain Fournier

In article ,
Alain Fournier writes:
I was rather thinking the other way, that a 1 kg black hole would
evaporate in less than 8x10^-17 sec because of quantum effects.

My _guess_ is that no one can say, absent a proper theory of quantum
gravity. However, I repeat that I'm no expert. Existing knowledge
constrains some properties of quantum gravity, so maybe something
could be said about this question after all.

Given the difficulty of making a 1 kg black hole, I don't see much
practical need for an accurate answer. :-)

--
Help keep our newsgroup healthy; please don't feed the trolls.
Steve Willner Phone 617-495-7123
Cambridge, MA 02138 USA