[samcottle (OP)]

Hi there, I recently drafted this article/paper on some recent work in cosmology on dark energy. I was wondering if anyone here would be good enough to provide some feedback. Best wishes, Sam Cottle.

‘Dark’ Energy is Probably Radiation Pressure, But That's Not The Whole Story.
                                                            Samuel P. Cottle,
                                                                Unaffiliated.


Abstract.

Experiments in the trapping and cooling of atoms using laser light, as well as observed phenomena due to radiation pressure, give a high likelihood for explaining the effects of so-called dark energy. Visible light, as well as photons from every other part of the electromagnetic spectrum would have been building up between galaxy clusters since their formation. The intervening 13.5 billion years or so would have seen vast numbers of photons amassed in the recesses of intergalactic space unable to escape to more distant reaches of the universe due to the reflective capacity of the intervening material. In this paper, I draw the conclusion that, while this is sufficient to explain the expansion of the universe, a deeper understanding of the Hawking radiation emitted from galaxy clusters (and its attendant contribution to the cosmological constant) is needed to fully elucidate the mode by which that expansion accelerates.


Atom trapping and manipulation at cosmic scales.

Given our knowledge [1] of how atoms may be trapped and manipulated using lasers in an experimental setting, and given that we are, of course, aware that galaxy clusters are formed of atoms, we may infer that radiation pressure makes a significant contribution to dark energy. Zhang and Wang (2021) [2] draw a similar conclusion, as did an independent researcher by the name of Wangchung Hu (2009) on the ‘Naked Scientists’ online forum [3]. The discrepancy in the results derived by Zhang, Wang and Hu with observation consists in the fact that we’re aware that the universe’s rate of expansion is not constant but accelerating [4]. If all the radiation pressure caused by this buildup of photons between galaxy clusters since the beginning of the universe were the only cause of expansion, we could anticipate that the rate of expansion would be roughly constant.

As it is, we’re aware of acceleration in the expansion of the universe. We must, therefore, add in additional variables to account for this acceleration; this would provide us with an accurate means of modelling the universe’s continued expansion. Hawking [5] famously noted that black holes emit radiation and, ultimately, evaporate. The conjecture I would add into this debate is that this effect is not limited to black holes. I would propose that all matter gives off Hawking radiation (in the form of photons) and would (in theory) eventually evaporate; evidence for this might be provided from observations of the Casimir effect [6], particularly any experiments aimed at gauging variations in the Casimir effect due to the presence of smaller or larger masses. And, if we thereby find that certain masses give off greater levels of Hawking radiation (in addition to whatever light they naturally reflect and/or emit) we may have isolated one of the additional parameters necessary in accounting for this acceleration.

Additionally, this notion of radiation pressure giving rise to cosmic expansion follows somewhat naturally from an idea I put forward (in rougher forms, online) back in 2016. Working on quantum gravity, I’d proposed that gravitational fields are formed of electron densities. Given the fact that electrons reflect photons [7], we’re thereby put in a position wherein we can reasonably assert that galaxy clusters must be reflecting large quantities of radiation. Following from this, we can infer that the recesses between these clusters, whose expansion we observe accelerating, therefore represent buildups of trapped radiation. The cosmological constant of galaxy clusters; if we’re invoking notions of regional variation in the value of the cosmological constant (if it were, so to speak, a cosmological variable); may be attributable to the electrons forming the gravitational field(s) of said clusters transporting photons to the recesses outside those clusters at varying rates due to differences in the varying, relative density of background electrons at different regions of space.

Likewise, the Hawking radiation of black holes (and any other massive object composed of atomic, or hadronic material) would be explained as a consequence of these gravitational electrons tunnelling to regions within the event horizon of a black hole, absorbing a photon there, then tunnelling outside the event horizon to deposit the photon in space. A partial consequence for this model of accelerating expansion is that it would need to incorporate considerations given to the reuptake of photons by these background (‘gravitational’) electrons. How this would vary in different regions of space, and the impact of these variations on the universe’s likelihood to expand in different regions, are further considerations within the proposed model. Hence, a consequence of this might be that, since the reuptake of a photon is less likely in a region with fewer background electrons, the fact of the universe’s expansion in and of itself is liable to cause its expansion to accelerate. This is because, if there are fewer electrons in a given region; such as between galaxy clusters; there is a lower probability that another background electron will absorb the emitted photon; or, it will take longer for a given photon to be absorbed once more by the background due to the larger spaces between background electrons.


Conclusion.

I broadly agree with the conclusions of Wang, Zhang and Hu insofar as radiation pressure is very likely a significant component of what we refer to as dark energy. Finessing this idea a little further, I’d have said that a degree of Hawking radiation (and/or Casimir force) generated by the background is necessary, in addition to considerations given to the background's liability for photon reuptake, in accounting for the universe’s accelerating expansion. The implications of this notion for our study of cosmological evolution would be profound if taken seriously in the community of cosmologists since, if the universe were to, at some point, lack a significant source of radiation to contribute to these buildups, we might anticipate its collapse at some future point due to gravity.


References.

[1] Phillips, W.D. (1998), Laser Cooling and Trapping of Neutral Atoms, Reviews of Modern Physics, Vol. 70, №3,

[2] G Zhang and X Wang (2021) J. Phys.: Conf. Ser. 2014 012010

[3] Wangchung Hu (2009), Is radiation pressure a significant factor in dark energy? https://www.thenakedscientists.com/forum/index.php?topic=22658.0#:~:text=Radiation%20pressure%20P%20is%20in,can%20perfectly%20fulfill%20our%20observation., Accessed: 16/06/2022,

[4] Rubin, D. and Hayden, B. (2016) Is the universe’s expansion accelerating? All signs point to yes, https://arxiv.org/abs/1610.08972, Accessed: 16/06/2022,

[5] Page, D.N. (2004), Hawking radiation and black hole thermodynamics, https://arxiv.org/pdf/hep-th/0409024.pdf, Accessed: 16/06/2022,

[6] Nguyen, T.T., (2003), Casimir Effect and vacuum fluctuations, http://www.hep.caltech.edu/~phys199/lectures/lect5_6_cas.pdf , Accessed: 16/06/2022,

[7] Bartell, L.S., (1967), Reflection of electrons by standing light waves, https://aip.scitation.org/doi/10.1063/1.1709723, Accessed: 16/06/2022,

[evan_au]

Hawking radiation emitted from galaxy clusters

Galaxies emit all the normal forms of radiation: light, radio waves, UV, X-Rays, cosmic rays, gravitational waves, neutrinos, etc.
- What is unique about (hypothetical) Hawking radiation is that it is emitted by black holes, which emit none of the above forms of radiation
- It is true that a galaxy also contains some black holes, but I guess that a single red dwarf star would emit more radiation than Hawking radiation from all the black holes in a galaxy (without doing the calculation!).

photons amassed in the recesses of intergalactic space ... due to the reflective capacity of the intervening material

We do see some galaxies at very high red shift, and the James Webb Space Telescope should reveal many more.
- Photons from these galaxies did reach us, without being reflected away by the intergalactic medium, which is extremely tenuous.
- If the intergalactic medium were reflective, we would see a reflection of our own galaxy, much brighter than we see these distant galaxies.

radiation pressure caused by this buildup of photons between galaxy clusters

Radiation pressure is a real thing - there have even been some experiments using radiation pressure to change the orbit of a satellite in Earth orbit.

But radiation pressure occurs when photons are reflected from a mirror surface, or absorbed by a non-mirror surface (the latter provides only half of the momentum).

However, if these photons are still in intergalactic space, they have not struck anything in our galaxy, and have imparted any momentum to our galaxy.

At this point, I gave up and moved this topic to "New Theories".

[samcottle (OP)]

If Hawking radiation were to be anything, it would almost certainly be gamma-ray photons. In spite of any new physics in this proposition, the gravitational effects near black hole event horizons would shift photons to such an extreme on the blue end of the EM spectrum that they would be among the highest energy realm of gamma rays. When there is less gravitational influence on photons, they become red-shifted and lose energy rather than gaining it.

I fail to see why there should be something special about black holes, or why a black hole would emit a special form of radiation that wouldn't also be emitted by a pulsar, neutron star, red dwarf, or, for that matter, any other celestial body. If physics remains consistent between these more familiar bodies (which, to a reasonable extent, it does) why would we need to invoke any special weirdness so far as black holes are concerned? I am (admittedly) less concerned with what we characterise in an acute sense as 'Haking radiation' (i.e. supposed special radiation from black holes) and with the broader implications of Hawking's thesis on this matter. Given a background of photon-emitting particles, i.e. probably electrons (which, for various reasons, I suspect is highly probable), then we have an explanation of the Casimir force and the so-called 'vacuum energy' of the universe. Gravitational fields construed as electron densities also neatly provide a reflective capacity for galaxy clusters which can then be used to explain 'dark' energy through invoking a notion of radiation pressure. Sure, a fair bit of distant light would be getting through to us; the fact that all the light from distant galaxies clearly isn't reaching us is a smoking gun for the idea of some absorbent medium lying in the intervening reaches of space. I also don't think we'd see a reflection of our galaxy. By the time the light emitted from our galaxy has reflected off the medium, we'd have moved to a different point in our orbit around the centre of the Local Group. If we were in Andromeda, we would be seeing the Milky Way at some point in the past; undoubtedly this must, in its turn be reflected, or transported, via some medium; 'spacetime', or otherwise (otherwise it'd reach us instantaneously).

It would, of course, not be a 'mirror surface' reflecting these photons, however, as you rightly point out, a 'non-mirror' surface would impart 'half the momentum'. My suggestion is that this trapped radiation between galaxies (or galaxy clusters) is being reflected by the tunneling electrons forming their gravitational fields; if there were no such clouds of electrons then the photons would be reflected by electrons regardless since the light bouncing off any object is reflected by the electrons in the atoms comprising that object. It seems likely to me, given the fact that space seems to emit photons of its own accord, that electrons (very occasionally) tunnel to great distances from their host atoms, and that, given how often they'd be tunneling in general, these incredibly rare occurrences actually become somewhat routine. In any case, if these photons are in intergalactic space, the clear implication is that they have 'struck something' in our galaxy/cluster.

[Bored chemist]

If Hawking radiation were to be anything, it would almost certainly be gamma-ray photons.

Nope.
Go and look it up.

[samcottle (OP)]

Ok, what would it be other than gamma-ray photons then? I'll grant you neutrinos and some more massive particles may escape organically via quantum tunneling though, in the case of quarks and hadrons, I suspect they wouldn't make it very far away from the event horizon before being drawn back in due to the black hole's overwhelming gravity. Neutrinos might get further; then again, what I suspect about background electrons and the neutral currents leading to neutrino oscillations might impede a neutrino's progress beyond the event horizon; then again, it might not. In any case, any and all photonic radiation (either incoming or outgoing) near an event horizon will be de facto gamma radiation due to the blueshifting near the horizon. See these two papers on the gamma-ray signals from primordial black holes:

https://arxiv.org/pdf/2110.05637.pdf
https://academic.oup.com/mnras/article/283/2/626/988213

[Bored chemist]

Ok, what would it be other than gamma-ray photons then?

Black body radiation, so photons.
The spectrum depends on the temperature, and thus the size of the BH. For all but the smallest holes, the temperature is below that of the cosmic background. So the emissions are in the microwave and redo frequency spectrum

But, if you don't know these basic things about the subject, why are you posting tosh, rather than learning facts?

[samcottle (OP)]

"Black body radiation, so photons." and what wavelength would these photons be given the gravitational potential energy they're subject to near a black hole event horizon? We know that photons lose energy and are shifted into the red end of the EM spectrum as objects move away from us. This corresponds to a weakening of the gravitational influence over these photons due to the recession in space of the bodies from which they're emitted. The exact opposite happens in very strong gravitational fields. Photons furthermore fall into superposition with other (already very high-energy) photons creating superposed 'particles' or perhaps even 'photon fluids' or 'photon-plasmas' very close to black hole event horizons whose energies are (as I've alluded to) already very high. Granted, as photons escape the pull of a black hole, they may lose energy via redshift. However, at the point of being emitted, they are gamma rays. They might remain gamma rays for some time, but, depending on where in space they're emitted (i.e. depending on the gravitational potential of their background) they might be subject to greater or lesser degrees of redshift. But thank you for your condescending (and self-contradicting) comment. Perhaps you ought to stick to chemistry. https://astronomy.swin.edu.au/cosmos/g/Gravitational+Redshift

[samcottle (OP)]

Also, take some more unsolicited advice. Next time you make an assertion to me, try and back it up with some sources.

[Bored chemist]

We are talking about Hawking radiation.
From the point of view of Prof Hawking (a long way from any black holes) the radiation is in the form of a black body spectrum; it's not gamma rays.

Since you insist on a reference.
"Hawking radiation is thermal radiation that is theorized to be released outside a black hole's event horizon because of relativistic quantum effects."
https://en.wikipedia.org/wiki/Hawking_radiation

[samcottle (OP)]

You are choosing the wrong hill to die on.
https://energyeducation.ca/encyclopedia/Radiant_heat#:~:text=Radiant%20heat%2C%20also%20known%20as,(unlike%20convection%20and%20conduction).

[Kryptid]

and what wavelength would these photons be given the gravitational potential energy they're subject to near a black hole event horizon?

That depends upon the mass of the black hole. The more massive the hole, the longer the wavelength of the photons. This calculator can be used to determine the wavelength of the peak photons emitted as Hawking radiation: https://www.vttoth.com/CMS/physics-notes/311-hawking-radiation-calculator

For a black hole of 3 solar masses (and radius of about 8.86 kilometers) , the peak photon wavelength is about 178.5 kilometers. That's well into radio wave territory. If you want to get a black hole with gamma rays as the peak wavelength (about a picometer or less), then the black hole would need to have a mass on the order of 3.34 x 10¹⁰ metric tons and have a radius of about 49.66 femtometers. So stellar mass black holes and above are primarily radio emitters, not gamma emitters. Primordial black holes, should they exist, could be much smaller and thus plausible gamma emitters.

In any case, any and all photonic radiation (either incoming or outgoing) near an event horizon will be de facto gamma radiation due to the blueshifting near the horizon.

That's not true. Photons are blueshifted when moving towards a source of gravity and redshifted when moving away. Your link about gravitational redshift even confirms this:

Einstein’s theory of general relativity predicts that the wavelength of electromagnetic radiation will lengthen as it climbs out of a gravitational well. Photons must expend energy to escape, but at the same time must always travel at the speed of light, so this energy must be lost through a change of frequency rather than a change in speed. If the energy of the photon decreases, the frequency also decreases. This corresponds to an increase in the wavelength of the photon, or a shift to the red end of the electromagnetic spectrum – hence the name: gravitational redshift. This effect was confirmed in laboratory experiments conducted in the 1960s.

The exact opposite happens in very strong gravitational fields.

Please provide a source for this, as it contradicts what your link says. According to your link, gravitational redshift should become stronger with increasing mass because a photon would have to expend more energy to climb up against a stronger gravitational field.

[Bored chemist]

You are choosing the wrong hill to die on.
https://energyeducation.ca/encyclopedia/Radiant_heat#:~:text=Radiant%20heat%2C%20also%20known%20as,(unlike%20convection%20and%20conduction).

What point were you trying to make?
I'm guessing that only one of us is actually a spectroscopist.

[samcottle (OP)]

That you seem ignorant of the fact that gamma rays can impart heat to an object.

[Bored chemist]

I had a look at one of the references.(labeled as [2] in the OP.)
"There can be no dark energy or space expansion because radiation pressure forces can cause the universe to expand
G Zhang1 and X Wang2"
There's a copy here
https://iopscience.iop.org/article/10.1088/1742-6596/2014/1/012010

And the essential claim is
"calculations show that the sun's total gravitational forces towards the entire universe, excluding nearby galaxies, is 1.645×10^19N, while the sun's average total radiation pressure force is 1.33×10^21N. So, the sun's radiation pressure force is much (80 times) larger than its gravitational force. "

Well that's interesting.

Imagine I consider the Earth.
Near the Earth, the Sun's radiation pressure is about 4.5 µ Pa
So the total force on the Earth is about 500,000,000 Newtons
And the gravitational attraction between them is 3.67 x 10^22 newtons

So, for the Earth, we know that the gravity beats the solar pressure. (Just as well really, or we wouldn't be here.)
The ratio is about 14 orders of magnitude.
Interestingly, both effects scale as 1/R^2 so the ratio would  stay the same even if we considered a hypothetical Earth at a different distance from the Sun.

Imagine we consider a smaller planet - 1/10 the size of the Earth, but otherwise similar (i.e the same density).
It would have a hundredth of the area so the solar force would be 1/100 as big.
But the mass would be 1/1000 of that of Earth.

So the ratio of radiation pressure force to gravitational force would be 10 times smaller.

And in general, for an object X times smaller than Earth, the ratio would be X times smaller than 10^14
So, for an object 10^14 times smaller than the Earth, the solar radiation pressure would exceed the gravitational effect (assuming it was made of the same stuff that the Earth is.)
So for a particle with a radius less than about 64 nm the net effect is repulsive.

So it looks kind of plausible.
But consider some grain of sand in outer space; the Sun attracts it (overall) as long as it's bigger than something like 100nM across.
The Sun also attracts everything in the shadow of that particle
But the Sun does not shine on anything in the shade. So those things in shade only experience an attractive force.
Moreover, the sand grain attracts stuff towards it.
In the same way that the Earth can hold an atmosphere (made of particles far smaller than 100 nm) the dust grain acts as a "relay" for the Sun's attraction.

So, overall, I'm far form convinced that the overall effect of the Sun is repulsive.
It isn't for anything that's bigger than 100 nm or so. (I'm not worried about the  odd order of magnitude)
And it isn't for small particles near big things (like the atmosphere).
And I think that covers quite a lot of the universe- everything in the milky way is "near" the SMBH in the middle of it. (Though the density is smaller, someone else can do that arithmetic for me, if they can be bothered).

But Black holes still won't emit gamma rays as Hawking radiation .

[Bored chemist]

That you seem ignorant of the fact that gamma rays can impart heat to an object.

How did you come to that absurd conclusion?
Where did I say anything that looked like I said anything about the effects of gamma rays?

[samcottle (OP)]

The radiation pressure force is acting between galaxy clusters, so the sun's gravity is somewhat irrelevant in this context. You need to consider the fact that the sun is very far away from the recesses of space between galaxy clusters where this radiation will have been building up for billions of years. Also, the research I linked to clearly states that primordial black holes have been observed to evaporate in a burst of gamma radiation. That *is* Hawking radiation. Also, because you said this (to respond to your second (somewhat chippy) response). Black body radiation, so photons.
"The spectrum depends on the temperature, and thus the size of the BH. For all but the smallest holes, the temperature is below that of the cosmic background. So the emissions are in the microwave and redo frequency spectrum"

[samcottle (OP)]

In any case, any and all photonic radiation (either incoming or outgoing) near an event horizon will be de facto gamma radiation due to the blueshifting near the horizon.

That's not true. Photons are blueshifted when moving towards a source of gravity and redshifted when moving away. Your link about gravitational redshift even confirms this:

You're just reiterating what I said. In the presence of a very strong gravitational field (i.e. near an event horizon), any photons in the vicinity, whatever their wavelength, and whether or not they're incoming or outgoing photons, will be BLUESHIFTED due to the gravity. I grant you, if a photon somehow manages to move sufficiently far out of a gravitational field (as I believe I've already mentioned) then it may well become redshifted and you'd have your microwave or radio wave radiation. The overwhelming majority of Hawking radiation photons will be emitted somewhat close to the black hole's horizon, their likelihood of further escape from the black hole's gravity is actually somewhat negligible; granted, also, any photons we OBSERVE coming from a black hole are also; granted, more than likely; going to have been REDSHIFTED at some point.

[samcottle (OP)]

Also, granted, Toth's calculator seems reasonable. Smaller black holes evaporate very quickly and, hence, we'd observe gamma rays coming from them. For larger black holes their radiation, at the point of emission, would be in the gamma spectrum and almost all of it would fall back into the BH due to its overwhelming gravity. Perhaps no one here is wrong, per se, and we're talking somewhat at cross purposes, but the truth stands; HR is always gamma rays initially unless said radiation gets far enough away from the black hole to allow it to become redshifted.

[Kryptid]

No, merely being near a strong source of gravity does not blue shift anything. Moving further into the gravity well will blue shift the light, whereas light moving up and out of the gravity well will be redshifted.

No, Hawking radiation is not always gamma rays. Go look at that calculator I linked. Photons with a wavelength in the range of kilometers absolutely are not gamma rays.

[samcottle (OP)]

Being near a strong gravity source would blueshift the light. That's sort of one of the basic underlying truths of general relativity. If gravity in an area is getting stronger; if, for instance, one galaxy is moving towards another; more gravity is acting on the light and hence its wavelength shrinks, and its frequency increases. The reverse is true in redshift. You admit as much yourself, and you sort of undermine your own point in doing so. As a galaxy recedes from other galaxies, creating space in between them, the light entering that space is experiencing progressively less gravity and is therefore redshifted. I also acknowledged the validity of Toth's calculator and explained why it gives the results that it does. I can't understand why we're arguing about this.