Re: Question about Gravitation of Vacuum Self-Energy
From: vernonner3voltazim (vnemitz_at_pinn.net)
Date: 08/04/04
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Date: Wed, 4 Aug 2004 06:23:15 +0000 (UTC)
Thanks for the replies, folks!
Sorry about my delay in responding; for a few days after I
posted my query, I never saw that it passed the moderator,
so gave up looking. Today I found it by accident.
> chronon (stephen@chronon.org) wrote:
> You ask why vacuum self-energy gives a repuslion rather
> than a gravitational attraction. My understanding of
> this is as follows: If the vacuum has energy then you
> need supply that energy to create more vacuum. Think
> of a piston in a sealed container – you have to do work
> to pull it out. In that case it's the external air
> pressure pushing, but you should imagine a case where
> the work has to be done simply to create more vacuum.
> This means that there is effectively a negative
> pressure in a vacuum with self-energy.
I do understand this, but it still does not make sense
in the context of the Universe. The expanding Universe
is creating more vacuum, right? The energy to do that
should be coming FROM that expansion. Next, if that
new vacuum is now a source of repulsion in the Universe,
causing acceleration and the creation of even more
vacuum, then what happened to Energy Conservation?
Finally, it is not clear that this "negative pressure
property of the vacuum" is something that must be
explained in terms of virtual particles popping into
the vacuum. Maybe the vacuum itself ("fabric of
space/time") is the culprit, and the virtual
particles are just doing their own thing,
independently and blamelessly.
On the other hand, if QM and GR are ever to be
merged, "blameless" may not be allowed.
rgregoryclark@yahoo.com (Robert Clark) wrote:
>
> I have a related question that I posed once to
> sci.physics:
> =======================================================
> Date: 1997/10/02
>
> I had some questions on the same theme. In regards
> to the quantum vacuum, aka zero-point energy, is this
> regarded as being negative energy simply because the
> classical vacuum itself is considered to have zero
> energy so anything "below" that must have negative
> energy?
It was my understanding that the zero-point energy was
positive and not negative! GR may want it to be
negative per preceding text above by chronon, but
QM never said that, so far as I know. And, in fact
my own Question is, IF QM SAYS THAT, THEN HOW????
> The 'virtual' particles of vacuum fluctuations are
> regarded to exist only for extremely short times.
> Is this the only physical difference between them and
> 'actual' particles?
To the best of my knowlegdge, that is the case. Virtual
particles exist on borrowed energy, but while they
exist, they are mostly normal. One exception (not to
exclude others) is the photon. An ordinary real photon
always has the same amount of energy. A virtual photon
does not need to vanish when its energy drops below a
certain point (as would, for example, a virtual W boson)
so its energy can be described as "decaying smoothly
with time" -- and the shape of this curve is identical
to that of the simple function 1/X. This of course is
why the virtual photons associated the EM Force can
go out to infinite range, while the Weak Force is
extremely range-limited.
> If it is, then wouldn't this depend on the frame of
> reference? In a strong grav. field, time will appear
> to run slow compared to our (approximate) inertial
> frame. So particles that were virtual in the strong
> grav. field would appear to us to be real particles
> and we could observe them.
Sorry, but the rate of our perception/measurment-ability
is identically slowed, in that grav field. So the
virtual particles will still remain unseen.
> This seems to be implied by both the phenomena of
> Hawking radiation and the Unruh effect. In Hawking
> radiation, a black hole will appear to radiate because
> virtual particles close to the event horizon can
> escape out of the vicinity of the black hole.
The hole loses mass/energy in that process, so every
escaping virtual particle is no longer virtual.
> In the Unruh effect an accelerated mirror will
> appear to radiate due to the virtual particles it
> encounters, and time for an accelerated frame is
> also regarded as slowed compared to ours. However,
> this implies that whether or not you regard particles
> as real or virtual depends on your frame.
In this case any virtual particles that become real
to an accelerating observer, will do so at the expense
of the observer's energy of motion.
> This creates problems for general relativity,
> because to compute the gravitational field within
> a region we need to include all the mass-energy in
> the region.
I'm pretty sure that when done, this leads to the
historic discrepancy ("worst embarassment in Physics")
between QM and GR. 50+ orders of magnitude!
> So for us, we would include these 'virtual'
> particles because to us they are actual. But in
> the strong grav. field the particles are virtual
> and are not observed; so the calculation of the
> grav. field for the region would be less.
It is the AVERAGE of their >0 temporary existence
that leads to the discrepancy. I think.
> This assumes that the only difference in 'virtual'
> particles is their extremely short time frames.
> So are there other physical differences? One
> possibility is the fact that they are assumed to
> be created in only particle-antiparticle pairs.
> Then a way out of the problem with GR would be if
> the particle created positive gravity and the
> antiparticle created negative gravity. So in
> both frames the result would be no net
> contribution. Of course, the idea that
> antimatter creates negative gravity is not the
> standard view. However, the gravitational
> effects of antimatter have not been precisely
> measured so this question is still open. There
> are experiments in the works to test this using
> antihydrogen so this should be resolved in the
> next few years. See the Physics FAQ, "Does
> Antimatter Fall Up or Down,"
> http://wwwhpcc.astro.washington.edu/mirrors/physicsfaq/grav_antimatter.html.
Antimatter will fall DOWN, and the logic is:
Remember that a gamma ray can be converted
into a particle/antiparticle pair. The gamma
ray consists of ordinary energy that ATTRACTS
gravitationally. Half that gamma's energy
becomes the ordinary particle, which also
ATTRACTS gravitationally. The other half of
the gamma becomes the antiparticle, and the
gravitational essence of that energy
has no reason to change. Electric charge
(and some oddball aspect of the Weak Force)
is the only difference between matter and
antimatter particles.
> Another possible resolution would be that
> we should always include the virtual energy
> in a region to compute its gravitational
> field. This would result in a marked
> increase for the calculated grav. field so
> I don't know if this is a workable solution.
No, by 50+ orders of magnitude :)
> Bob Clark
>
> Note: I checked the Physics FAQ article,
> "Below Absolute Zero - What Does Negative
> Temperature Mean?", and found that the
> question of negative temperature is a
> separate one from that of negative energy.
> So I changed the subject line of the post.
Yeah, ordinary negative temperatures are merely
values relative to some arbitrarily-specified
zero value.
> Psychogamer64 <psychogamer@juno.com> wrote:
> > I have found a reason why negative energy wouldn't
> > exist, or how you can drop temperatures below 0K.
> > I have studied physics books. Heat IS energy.
> > The more energy something has, the more heat it
> > usually has. Only at 0K in which anything is
> > totally devoid of energy. To have negative energy,
> > one has to cool something below absolute zero.
> > This is a physics impossibility (even though in
> > the future, someone could succeed at this) as we
> > all know it. Finding negative energy or below 0K
> > temperatures will pave the way for whole new physics.
> > Psychogamer64
> =====================================================================
Right, on an ABSOLUTE temperature scale, one cannot
cool ordinary matter below 0 Kelvin.
> This also has relevance to the question of the
> possibility of worm-holes or warp-fields. Producing
> these has been called impractical because of the
> large amount of negative energy required. But if the
> interpretation of what is "negative energy" is frame
> dependent, how can it be said that large amounts can
> not be produced?
Good question, and the perfect opportunity to speculate
wildly. Remember those virtually fluctuating energies
in the vacuum? WHY is it that the Uncertainty Principle
is only invoked to talk about fluctuations ABOVE the
zero-level? It seems to me that fluctuations BELOW
zero should be just as possible. All that is needed is
a tiny modification to the standard (Energy * Time) form
of the Uncertainty equation, such that Planck's Constant
is allowed to be a negative value. This is no worse an
assumption than saying, "Special Relativity does not
forbid tachyons from existing, if we can accept the
notion of imaginary mass." (Actually, negative mass
should be easier to accept than imaginary mass!)
Virtual particles that pop into being whenever
Uncertainty goes negative will possess negative
mass/energy, of course. One might EXPECT equal
quantities of ordinary and negative virtual
particles in the vacuum. Their total AVERAGE
energy goes back down to Zero, so their total
gravitational effect also goes to Zero, nicely
wiping out Physics' most embarrassing discrepancy.
There are other Good Things that come from accepting
the idea of negative mass/energy, and allowing the
consequences of such existence to permeate Physics.
Some of those consequences can be found here:
http://www.nemitz.net/vernon/BALANCD2.pdf
Finally, negative Temperature, on an Absolute
temperature scale, is nothing more than the
kinetic energy possessed by particles of
negative mass.
- Next message: Daniel: "Re: is frequency/wavelength of a photon quantized?"
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