# Are we in a black hole?

by ubavontuba
Tags: black, hole
 Sci Advisor PF Gold P: 3,274 Astrophysics is the science of understanding 'what goes on up there' (astro-) by understanding 'what goes on down here' (-physics) - in the laboratory. Rather than beginning to understand the Unruh effect of the expansion of the universe start with the laboratory. The Unruh effect is observed for non-inertial observers, we are non-inertial observers. This effect predicts that empty vacuum in a suported laboratory should have a non-negative density in that frame of reference. I make this Unruh vacuum density to be ~ 10-113 gms/cc, as a point of interest SSC predicts a vacuum density near the Earth of ~ 10-9 gms/cc, caused by reconciling the divergence of its two field equation solutions for a gravitational field. Garth
P: 1,047
Thank you George. I was thinking about my question you tried to answer and I am not sure to understand this:
 Quote by George Jones "The explanation comes from a consideration of the agency that brings about the acceleration of the detector in the first place. As the detector accelerates, its coupling to the field causes the emission of quanta, which produces a resistance against the accelerating force. The work done by the external force to overcome this resistance supplies the missing energy that feeds into the field via the quanta emitted from the detector, and also into the detector which simulaneously makes upward transitions. But as far as the detector is concerned, the net affect is the absorption of thermally distributed quanta."
However, I came to another conclusion: The question is not correctly formulated, because it is unclear that spacetime with a scalar field in it should be flat at all. I mean, the usual treatment of Unruh radiation starts with a scalar field in flat spacetime. Radiation in the accelerated frame should induce a back-reaction. However, even in the inertial frame we do not know how to compute the quantum corrections to the flat geometry. Nevertheless spacetime is assumed to be flat (as usual in QFT) per definition. Same should then apply for the accelerated frame. Does this "answer" make sense?
Mentor
P: 6,248
 Quote by hellfire Radiation in the accelerated frame should induce a back-reaction. However, even in the inertial frame we do not know how to compute the quantum corrections to the flat geometry. Nevertheless spacetime is assumed to be flat (as usual in QFT) per definition.
Sometimes, for simplicity, back-reaction is negelcted, but in the example I gave, there is no back-reaction caused by quantum field because the renormalized stress energy tensor of the field is zero in all frames.

Other examples could start with an excited field for the inertial observer, and then there would be back-reaction.

Regards,
George
P: 167
Forum,

As I have had a recent post in this thread removed for being too speculative, I wish to resubmit the ideas presented in the removed post as questions. I will include a couple of citations in reference to these questions that I hope will allow it to get by the censors as being in the ballpark of opinions that are "currently held by the scientific community." Here goes:

 The aim of all this activity is, of course, to answer the question, what is the dark energy? If w is about -1, then a cosmological constant might be the solution. If w is more than -1, the right answer might be quintessence. And we cannot rule out a new twist to gravity that even Einstein did not foresee: while most theories that link gravitational and quantum physics predict novel behaviour on microscopic length scales or at very early times in the universe, few, if any, anticipate new effects on the largest length scales in the present day. And what if w is less than -1? Whatever the answer, something mysterious is at work in the cosmos.
Please note particularly where it states: "And we cannot rule out a new twist to gravity that even Einstein did not foresee:"

And in this citation:
 Other ideas Some theorists think that dark energy and cosmic acceleration are a failure of general relativity on very large scales, larger than superclusters. It is a tremendous extrapolation to think that our law of gravity, which works so well in the solar system, should work without correction on the scale of the universe. However, most attempts at modifying general relativity have turned out either to be equivalent to theories of quintessence, or are inconsistent with observations. Other ideas for dark energy have come from string theory, brane cosmology and the holographic principle, but have not yet proved as compelling as quintessence and the cosmological constant.
Note particularly where it states: "Some theorists think that dark energy and cosmic acceleration are a failure of general relativity on very large scales, larger than superclusters. It is a tremendous extrapolation to think that our law of gravity, which works so well in the solar system, should work without correction on the scale of the universe."

So, with these references in mind, I will reitterate the main concepts in my deleted post:

It seems to me that the current thinking in dark energy is to look for an energy density between the galaxies to explain it. My questions are:

What if the energy density between galaxies is irrelevent? What if the galaxies are apparently simply falling outward toward the CEH, rather than being forced outward from an internal pressure?

What if due to a quirk of relativity, the universe appears to be accelerating from all reference frames, but may or may not actually be accelerating? What if the apparent expansion acceleration is simply caused by relativistic effects of very distant mass in motion?

Could these proposed relativistic effects cause an apparent infinite density to the CEH that essentially causes it to behave much like a black hole event horizon in that it emits Unruh and other radiation (that we perceive as the CMBR) and gravity/acceleration (that we perceive as the effects of dark energy)?

That is, (in deference to my citations) could gravity itself be a relativistic effect in the extrenum of the cosmological event horizon?

Note: This post has been edited by ubavontuba
 Sci Advisor PF Gold P: 3,274 From my calculations above is it not clear that any Unruh coming from the CEH is many orders of magnitude smaller than that required for the CMB? Garth
P: 167
 Quote by Garth From my calculations above is it not clear that any Unruh coming from the CEH is many orders of magnitude smaller than that required for the CMB? Garth
No, but I've always had trouble paying attention in math.

Anyway, let's think about what's happening at the CEH. Isn't mass heading (falling?) into it?

Now let's think about the CEH like how we might think about black holes. In this case, let's think about black holes with halos of matter around and falling into them. They emit a lot more energy in IR than simply the Unruh and Hawking radiation, don't they?

P.S. It looks to me like the expansion model must still hold, but the universe needn't be quite as young or old as we might measure. Also, it isn't the concept of expansion that is in question, but rather the acceleration effect known as dark energy. In other words, is it possible that even a linear expansion might be perceived as an acceleration in the extrenum of relativity and the CEH?
P: 1,308
 Quote by George Jones ... "The explanation comes from a consideration of the agency that brings about the acceleration of the detector in the first place. As the detector accelerates, its coupling to the field causes the emission of quanta, which produces a resistance against the accelerating force. The work done by the external force to overcome this resistance supplies the missing energy that feeds into the field via the quanta emitted from the detector, and also into the detector which simulaneously makes upward transitions. But as far as the detector is concerned, the net affect is the absorption of thermally distributed quanta."
Is the cosmological constant or dark energy considered to be the due to the acceleration of spacetime? Or is it the other way around? Is the cosmological constant considered to be due to the acceleration of the expansion rate or the acceleration of a constant expansion rate as more distant objects recede more quickly as they recede?

I wonder if acceleration radiation is the same as vacuum energy of the cosmological constant? If so, then it would seem that since zero acceleration gives zero energy density, then inertial frames traveling arbitrarily close to any point in space (even with zero velocity) would feel no temperature and would prove that there is no zero point energy/vacuum energy/cosmological constant. I could use some clarification on this. Thank you.
PF Gold
P: 3,274
 Quote by Mike2 Is the cosmological constant or dark energy considered to be the due to the acceleration of spacetime? Or is it the other way around?
The latter
 Is the cosmological constant considered to be due to the acceleration of the expansion rate or the acceleration of a constant expansion rate as more distant objects recede more quickly as they recede?
The cosmological constant is one possible cause of cosmic acceleration.
 I wonder if acceleration radiation is the same as vacuum energy of the cosmological constant?
As in a previous post above any acceleration radiation (if it exists in the first place) is many many orders of magnitude smaller than the CMB or the cosmological constant energy density
 If so, then it would seem that since zero acceleration gives zero energy density, then inertial frames traveling arbitrarily close to any point in space (even with zero velocity) would feel no temperature and would prove that there is no zero point energy/vacuum energy/cosmological constant. I could use some clarification on this. Thank you.
The temperature we "feel" is that of the CMB radiation, 2.70K, a real temperature of radiation emitted by real hot gas (at z >1000). It might indeed be the case that there is no cosmological constant but that possibility would not be proven by the non-observance of cosmological Unruh radiation.

Garth
P: 1,308
 Quote by Garth As in a previous post above any acceleration radiation (if it exists in the first place) is many many orders of magnitude smaller than the CMB or the cosmological constant energy
I wonder if particle creation (virtual or real) might be types of acceleration radiation - even the zero point energy or the cosmological constant. What I mean is this: force itself is described in terms of mass(energy) and the acceleration. Even with virtual particles, they are produced in pairs (and only pairs?) that move away from each other and then come back together. So even there they are accelerating with respect to each other. So there seems to be some sort of accelerating reference frames even at the local scale that produces particles (or is at least associated with particle production). Any thoughts on this? Thanks.
PF Gold
P: 3,274
 Quote by Mike2 I wonder if particle creation (virtual or real) might be types of acceleration radiation - even the zero point energy or the cosmological constant. What I mean is this: force itself is described in terms of mass(energy) and the acceleration. Even with virtual particles, they are produced in pairs (and only pairs?) that move away from each other and then come back together. So even there they are accelerating with respect to each other. So there seems to be some sort of accelerating reference frames even at the local scale that produces particles (or is at least associated with particle production). Any thoughts on this? Thanks.
You are mixing up Quantum effects and GR gravitational effects. As we do not yet have a quantum gravity theory your speculation cannot be assessed. In virtual particle pair production there is no sum total change of momentum and no overall acceleration so there is no Unruh radiation, or are you claiming to have detected it?

Garth
P: 1,308
 Quote by Garth You are mixing up Quantum effects and GR gravitational effects. As we do not yet have a quantum gravity theory your speculation cannot be assessed. In virtual particle pair production there is no sum total change of momentum and no overall acceleration so there is no Unruh radiation, or are you claiming to have detected it? Garth
I'm just marvelling at the fact that acceleration produces radiation, thus particles. OK.... how many ways are there to produce "particles". It would seem to me that there would have to be only one way of producing particles. Some fundamental transformation is involved. If it is acceleration in one instance, could it be acceleration in all instances? So I remembered that virtual particles do appear in pairs, they first separate, and then come back together in a brief enough time so as to not violate the uncertainty principle. Separating and coming back together involves a change in velocity, thus it involves acceleration as well. The only alternative is to suppose particles can be produced in many different inequivalent ways, when they all end up having the same properties.

This would give us a connection between the properties of spacetime and the properties of matter, so that QFT might lead to QG.
 P: 167 Forum, Hey, take a look at this article in the current issue of NewScientist! Apparently life inside a black hole, isn't quite such an absurd notion afterall.

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