# Is dark energy from cosmic Hawking radiation?

1. Apr 14, 2008

### jal

http://arxiv.org/abs/0803.1987
Is dark energy from cosmic Hawking radiation?
Authors: Jae-Weon Lee, Hyeong-Chan Kim, Jungjai Lee
(Submitted on 13 Mar 2008)
We suggest that dark energy is the Hawking radiation from a cosmic horizon. Despite of the extremely low Hawking temperature this dark energy could have the appropriate magnitude and the equation of state to explain the observed cosmological data, thank to its huge entropy proportional to the horizon area. If the horizon is an event horizon and the entropy of the radiation satisfies the holographic principle, then the radiation gives the holographic dark energy with the parameter $d\simeq 1$, as observed. Albeit simple, this model could explain many mysteries of dark energy in a consistent way.

2. Apr 14, 2008

### MeJennifer

Interesting thought.

3. Apr 14, 2008

### jnorman

IMO, hawking radiation is a myth, and dark matter is a myth. we need to re-examine GR.

4. Apr 14, 2008

### vincentm

That's nice and all but what do you base this argument on?

5. Apr 14, 2008

### jal

These guys are not only thinking outside the box (which they know as demonstrated by their citations) but doing work outside the box.

6. Apr 15, 2008

### jal

If anyone is interested in knowing more about "The Holographic dark energy", I have gathered a few papers, (to get you started), in my latest blog.
Jal

7. Apr 15, 2008

### jnorman

vincent - try this:
http://arxiv.org/PS_cache/hep-th/pdf/0409/0409024v3.pdf

and AFAIAC, dark matter and dark energy are futile attempts at trying to avoid the idea that perhaps we do not know everything there is to know yet about gravity. i put dark matter about on the same level as media headlines which claim that "SCIENTISTS STOP LIGHT!!!"

8. Apr 16, 2008

### Chronos

Dark matter and dark energy may be weak verbalizations, but, something that behaves in such fashion is observationally present in the universe.

9. Apr 16, 2008

### jal

I do not believe in “coincidence” at a cosmic scale. I was surprised to see that Holography dark energy could be applied by so many approaches. (LQC/LQG, Branes, Brans-Dicke Theory and I’m sure that there are more.)
This is revealing a unifying principle/mechanism underlying all of these approaches.

I gathered from Abraham Loeb paper that dark energy agglomeration was the catalyst for galaxy formation and that it was not the other way around. Dark energy was not attracted to matter but rather dark energy affected spacetime which affected the distribution of matter.
Perhaps, the Gurus and moderators of this forum will give us their insight and speculation on Holography dark energy.

Last edited: Apr 16, 2008
10. Apr 22, 2008

### scupydog

HEY i was thinking down those lines back in January, in the 'edge of space' thread.

Last edited: Apr 22, 2008
11. Apr 22, 2008

### shalayka

jal,

From what I understand, anisotropies in the cosmic expansion are indeed viewed to be the source of bodies of matter, in so much that if the expansion of space had been perfectly isotropic, solar systems, galaxies, etc, would not have formed. I think this is an old idea that goes all the way back to Lemaitre, although I'm not certain he also applied this idea to atoms/quarks as well (not that quarks had been discovered back then, but still...).

12. Apr 22, 2008

### jal

Thanks for the comment.
I hope that more comments will come from other experts who are not just looking under the street lamp.
jal

13. Apr 29, 2008

### foolosophy

Estimates of the proportion of dark energy in the Universe are in the general vicinity of 70%.

Baryonic matter makes up a mere 5% of the total universe.

My understanding of Hawking Radiation was that it is specifically related to the event horizons of black holes.

If the source of dark energy is the Hawking Radiation then the majority of the universe's stellar objecs must have been black holes. This is not supported by the WMAP data which showed great details of the anisotropic nature of the early universe. And great voids too!

So I suppose you would need to estimate the number of black holes in the present and in the past. From this number you can estimate the total cummulative amount of Hawking radiation released. I doubt if this amount would account for 70% of the universe's dark energy.

Did the researchers in the paper you quoted carry out such calcualtions to see if they matched the observational data?

Interesting though!

Last edited: Apr 29, 2008
14. Apr 29, 2008

### jal

foolosophy
The paper considered the universe within a cosmic horizon, not individual horizons from black holes.
Here is another paper along the same line of approach.

http://arxiv.org/abs/0804.4326
Thermodynamics of noncommutative de Sitter spacetime
Authors: B. Vakili, N. Khosravi, H. R. Sepangi
(Submitted on 28 Apr 2008)

15. Apr 29, 2008

### foolosophy

Last edited: Apr 29, 2008
16. Apr 30, 2008

### Bob3141592

I'm not at all sure about this, but I suspect he might mean you see the surface where the hawking radiation originates from the other direction. That is, from the inside.

I know you can't see outside a black hole's event horizon, but can't you see to that horizon? I've read that given a sufficiently large black hole, someone could fall through without even noticing it. Well, if all of a sudden I could no longer see half the universe behind me, I think I'd notice. Let's say I fall through the event horizon of a black hole and the tiniest instant later a particle pair is created and one of the pair escapes. That means the other one falls inwards and will catch up with me. The closer I get to the singularity, the longer it takes for anything else falling into the hole, even photons, to catch up with me, and the horizon will appear increasingly redshifted, but it will appear. Right?

Unfortunately, this notion uses terms like "tiniest instant" and "closer" and I've read that space-like and time-like dimensions sort of change roles, and I've no idea what that means. I don't know if you could detect that transformation if you were experiencing it as long as it's conformal.

Does that make sense?

17. May 1, 2008

### foolosophy

From what I gathered from the original post, the suggestion was made that dark energy is the result of Hawking radiation.

Hawking radiation is specifically created at the event horizon of singularities such as black holes. It would be a simple case of calculating the number and size of black holes in the universe that would be required to produce the amount of dark energy present in the universe today - ie about 70% of the universe is estimated to be composed of dark energy.

I would be very surprised if there are sufficient number of black holes in the universe to produce this relative amount of dark energy.

And also, How does one arrive at what DARK ENERGY is actually made of? What evidence and mechanism points to dark energy being made up of Hawking radiation.

18. May 20, 2008

### pixchips

Isn't Unruh radiation the radiation viewed by an object due to the event horizon created by the objects acceleration? Isn't that the same mechanism as Hawking radiation? If so, then radiation is present at event horizons. Characteristic of an event horizon is that things on either side can't interact anymore. Two virtual particles that separate right at a horizon become decoupled. For the universe, we are on inside of event horizon (if it has one) and the particle on the inside becomes real to us, which is opposite to black holes where one on the outside becomes real to us.

Further questions: if the universe has an event horizon, is it expanding at or near c? (seems like it must be) If so, how would this affect the radiation? Almost seems like it would be infinitely redshifted out of existence. Black Holes have stationary event horizons (except when they swallow planets and stars and stuff), seems like this would make a difference.

Black Hole reference for simple folks like me: http://en.wikipedia.org/wiki/Hawking_radiation

19. May 21, 2008

### PanTheory

jnorman, did you mean dark energy is a myth, in this I agree. Hawking radiation as a mathematical theory has a number of opponents. But as a concept or hypothesis there are a number of theorists that have supported the idea. The only way that I know that GR would imply dark energy would be through Einstein's originally notorious cosmological constant, which he said was his biggest theoretical mistake. Present mathematical theory concerning dark energy still uses GR but there have been numerous proposals and concepts like the above to explain dark energy. There still are a number respected opponents to this theory.

20. May 21, 2008

### PanTheory

I hate it when they use terminology you've never heard of and you can't find a definition on the net.

Your quote "I know you can't see outside a black hole's event horizon" this would be providing you were inside that event horizon. If you were inside the horizon, however according to theory, you would probably very soon be spaghetti-ized. If you're way outside the horizon you could see it as a glowing ring. It probably would be a lot easier to see face on than edge on. If there were a large vortex near the event horizon as in young galaxies you may not be able to see much red-shifting. But if matter were generally "spiraling in" rather than just orbiting its radiation would be spread out by this inward velocity and therefore moving away from the observer and red-shifted. If it would be moving very fast the light seemingly could be shifted into the infra-red spectrum where you would not be able to see it.