Scientists find first observational evidence linking black holes to dark energy

On the other hand we do not have models of a galaxy evolution based on solving equations of General Relativity. Typically the assumption is that Newtonian gravity with minimal relativistic corrections should be enough. But there is no proof that it is so.

Moreover, there were relatively recent papers that showed that better accounting for General Relativity could be enough to explain rotational curves for Galaxies without any notion of Dark Matter and that the need for Dark Matter was simply ab artifact of the assumption that Newtonian gravity can be used at the galaxy scale.

Then there are speculations that electromagnetic forces do play role at the galaxy scale affecting the rate of evolution of galaxies.

So it can be that the observed discrepancy in the growth of Black Holes caused by holes in galaxy evolution models, not by the proposed new effect.

Today people think the universe is a kind of simulation because they’re so impressed with how algorithms tinged with randomness can tickle their human sensibilities and create illusions of meaning.

We can observe the laws of physics as it applies to the universe, but why they are there is far less clear, something we may never know.

He contacted her but she refused to collaborate on a common paper, calling him a plagiarist and a crank. She did the same to Tim Palmer (a Royal Society meteorologist) when he approached her with ideas on superdeterminism:

> But Tim Palmer turned out to not only be a climate physicist with an interest in the foundations of quantum mechanics, he also turned out to be remarkably persistent. He wasn’t remotely deterred by my evident lack of interest. Indeed, I later noticed he had sent me an email already two years earlier. Just that I dumped it unceremoniously in my crackpot folder.

http://backreaction.blogspot.com/2019/12/the-path-we-didnt-t...

Back to Petit and plagiarism: compare:

https://link.springer.com/article/10.1007/s10509-014-2106-5

https://januscosmologicalmodel.com/cptsymmetry

with Julian Barbour's Janus Point book blurb:

> In a universe filled by chaos and disorder, one physicist makes the radical argument that the growth of order drives the passage of time -- and shapes the destiny of the universe. Time is among the universe's greatest mysteries. Why, when most laws of physics allow for it to flow forward and backward, does it only go forward? Physicists have long appealed to the second law of thermodynamics, held to predict the increase of disorder in the universe, to explain this. In The Janus Point, physicist Julian Barbour argues that the second law has been misapplied and that the growth of order determines how we experience time. In his view, the big bang becomes the "Janus point," a moment of minimal order from which time could flow, and order increase, in two directions

Source: https://www.amazon.com/Janus-Point-New-Theory-Time/dp/046509...

There are more players in the field with very similar ideas (the refinement of twin universes as a two-sided universe), Petit contacted them all but was never given a reply:

- Neil Turok: https://physicsworld.com/a/our-universe-has-antimatter-partn...

- Our universe may have a twin that runs backward in time: https://www.livescience.com/mirror-universe-explains-dark-ma...

- Neil Turok again a few weeks ago: https://www.newscientist.com/article/mg25734230-100-neil-tur...

And now we have that paper that talks about black holes without a singularity and their coupling with the universe's expansion limited to a maximum k-factor of 3.

This sounds a lot like the conclusion from this paper by Petit:

> Supermassive objects, whose formation will be explained in a future article, are also subcritical objects, Plugstars. The theory gives all plugstars a gravitational redshift of 3. This is exactly what is shown by the measurements of the images of two hypermassive objects located at the center of the galaxies M87 and the Milky Way.

> We predict that this redshift of 3 will accompany future images of hypermassive objects that will appear in the future.

Source: https://hal.science/hal-03835483/document

Embedded in my comment was the thought that if the empirical evidence for this observation was overwhelming then this tight and specific coupling between QM and GR would be so embarrassing that mathematicians would have no option but to significantly up the ante (and also this new evidence may bring a fresh approach).

We've seen this leapfrogging between math and physics many times before, Newton/calculus, Hamilton/quaternions, Galois/group theory, etc.

Wishful thinking perhaps, but the standoff/gulf has to collapse eventually. It'd be nice if this observation was the impetus.

First, let's understand a bit about the cosmological frame: it lets us consider the universe as 3-dimension-of-space ordered by a "scale factor" dimension of time. The coordinates of each 3d space are Euclidean, but the coordinates don't line up exactly between different scale factors. Colloquially, the coordinates expand with the expansion of space, or equivalently the space between coordinates grows over time. You could think of it this way: if at some early point we label every point in space with an integer, in the future of that point we have to add new labels between the integers.

If we add in a pair low-mass freely-falling test matter at the time when everything is labelled with an integer, e.g. at point (1,1,1) and (2,1,1), then they stay at those coordinates even as more and more labelled (with non-integer) space appears between them.

To this we add a set of gasses, dusts, or fluids representing radiation, ordinary nonrelativistic matter, and maybe others (e.g. relativistic dark matter (e.g. neutrinos), non-relativistic dark matter ("cold dark matter"/"particle dark matter")). Again, any "mote" of the ordinary matter dust stays at the same coordinate forever. Rather than coping with the "motes" of radiation not staying put, we average every point in space and see there is some quantity of matter (a mote, or a fraction thereof), some quantity of radiation (a mote, or a fraction thereof), some quantity of dark matter, and so forth.

The dusts dilute away because more and more space appears between each original coordinate. In our averaging picture, we get a smaller and smaller fraction of a mote at eacn point on average as the universe expands.

This is the essence of the Friedmann-Lemaître-Robertson-Walker model that is the standard cosmology.

The view here is that of boring old observers freely floating in deep inter-galaxy-cluster space. That leads to (from that view point) concrete calculations of the various contributions to the averaged energy-density at each point in space at a particular scale factor ("at a given age of the universe"). In general, that figure is higher in the past and lower in the future, with different contributions to the total (average) energy density at a point dropping at different rates (this is the "equation of state" for each of radiation, baryons, neutrinos, dark matter, ...), but they all drop away towards nothing in the far future.

We can then think of where stress-energy goes at an average point. For freely falling baryons, almost nothing interferes with the whole of the stress-energy flowing from (microsecond-before,0,0,0) to (now,0,0,0) to (microsecond-after,0,0,0). There's some cosmic mircowaves and neutrinos that have a tiny ghost of a chance of transferring in some momentum via scattering at each point, but that falls away when we consider the average across each of these three 3d spaces.

Flipping things back around, while a "mote" of the baryon gas stays "at the integers" as we add more and more digits after the decimal point as space expands, each time we add digits we get more dark energy fluid "motes". If we change coordinates, the coordinate-distance between "motes" of the fluid grows with the expansion, e.g. as the distance between these proxies for galaxy clusters goes from 1 to 10 to 100 to ... the 9, 99, ... has "new" motes of dark energy.

Given this it is straightforward to treat some aspects of the expansion as another fluid with an energy density that is the same at every point in every space. It does not dilute away like the others. It imposes a tension ("negative pressure") on the other sources of energy-density.

If we think of a single point in one of these 3d spaces as being imprisoned within a tiny six-sided cubical cell, we can track the flow of momentum through each (pair of) face(s) of the cell. At very early times radiation flowing through the cell dominates. The inflow is tracked as the normal stress <https://external-content.duckduckgo.com/iu/?u=https%3A%2F%2F...> on each face. When the normal stress is identical on all six faces (or spherically symmetrical if we switch from a cube to a sphere), we call that pressure.

Negative pressure is just flipping the arrows around. We can call that "tension".

Colloquially we're interested in how much the pressure changes the energy level of the imprisoned matter. In general, large positive pressure leads to the imprisoned matter becoming more energetic. Large negative pressure would lead to the imprisoned matter becoming less energetic. "Large" here is relative to the energy-density within the cell, and varies by component ("equation of state" again).

In the comsological frame, freely-falling imprisoned matter (baryons, dark matter) in a cell at (t,1,1,1) will thus cool with the expansion across (t',1,1,1), (t'',1,1,1) and so forth, with the energy sucked out by the constant outward tension.

> 16 simultaneous partial differential equations

You can start with understanding the stress-energy tensor.

This is it laid out in a 4x4 matrix form <https://en.wikipedia.org/wiki/Stress%E2%80%93energy_tensor#/...>. The indices running 0,1,2,3 correspond to the timelike dimension and the three spacelike ones. Each element of the matrix has two indices i and j (e.g. for T^00 in the top left, we have i=0, j=0) indicating the "comesinfrom" and "goesoutto" directions.

Energy pouring in and staying in is the orange column. Energy already there and staying put is the top left.

Let's use spherical coordinates and call the 1 direction "in/out", i.e., described by the radial coordinate. We'll place our cell of interest microscopically displaced radially from the spherical coordinate origin.

If we were in a dense object like the core of a planet or star, T^11 would be dominated by the inwards flow of inwards-momentum and the reaction-pressure of outwards-momentum flowing outwards. In high-mass stars' cores, this number will dominate all the others in the stress-energy tensor. Also in general T^ij, i=j, i!=0 (the green bar) will not be completely identical.

However, if we're in a cosmological setting (deep inter-galaxy-cluster space), T^11 is [a] small, [b] it's the same as T^22 and T^33, and [c] they are interpretable as the flow of energy-momentum out of the cell. In the very very far future, T^00 drops to zero, and T^ii, i!=0 (despite being small) dominates.

Another difference here is that in the stellar core positive pressure case, T^11 is not a constant. However, if we got rid of all possible radiation pressure and the like, in the resulting cosmological vacuum T^11 would be a constant (and identical to T^22 and T^33).

This is an interpretation that depends on our choice of viewpoint (that of a freely floating low-mass observer who feels only the expansion and not attractive influences from dense matter, because all matter is completely evenly smeared out). The interpretation does not hold up well as we change our point of view (e.g. to a relativistic observer, to a different set of coordinates, to an observer who is close to or part of a self-gravitating mass overdensity).

Consequently it is probably better to start with the idea that dark energy is the Cosmological Constant (until this possibility is disproven, which has not happened yet). It is simply a constant of nature, like the speed of light or like the charge of an electron. Where does the constant come from? Who knows!

Sometimes it is convenient to think of this constant as if it were a substance with appropriate properties, or as if it were "the cost of empty space" (vacuum energy). However it's also possible to be misled by this. It's a scalar quantity, and it has an exact relationship to a tensor quantity (the metric). Scalars and tensors are generally covariant, so we can always make that pairing work for any possible observer, even e.g. an ultrarelativistic cosmic ray or a photon or a relativistic compact object like a black hole.

Finally, the reason for "sometimes" is: while the total tensor value of T is the same for everyone, the value of the individual components of the tensor depends on the frame of reference.

One of the sometimeses is the very early universe when radiation pressure is extremely important for smoothing out temperature and density differences; it is natural to want to do accounting of the expansion as an offset against that radiation pressure instead of the "truer picture" of the radiation pressure falling because the radiation is diluted and de-energized (redshifted) by the early expansion.