In this blog I return to my theory that Dark Energy is the gravitational pull of the cosmos.
In the last year, many papers have been published supporting the idea that the acceleration rate of the universe is increasing with time. Now it is accepted as a consensus but nobody can explain why.
Recently, even the assumption that the universe is isotropic has been questioned.
Cosmic gravity can help to explain Dark Energy, and much more.
The universe has always been much bigger that we thought.
Dark Energy
1998, unexpectedly the expansion of the universe is not slowing down but is accelerating. Schmidt and Reiss aware that there findings would turn the world of physics upside down had made plans for new careers if they were wrong. Reiss planned to use his skills in Wall St. Instead they won the Nobel Prize in 2011. Beware those who challenge the norm!
20 years later, another shock. Even this acceleration is not constant, but is increasing with time. 2020 another potential shock. The expansion, whatever it is, is not isotropic. It is stronger in the direction of the dipole in the CMB.
Prediction:- This one will also be fiercely contested. An isotropic universe is necessary for the standard model. Without it, the maths just becomes too difficult. Without maths you don’t have a theory. Spoiler alert, there’s no maths in this paper.
In my paper, “What Is Dark energy?” published in viXra 1901.0451 on 29th January 2019, I proposed that Dark Energy was the gravitational pull of the cosmos.
The assumption that our observable universe is not alone in the cosmos may be seen as the stuff of science fiction, but we should remember that history of science tells us that the universe has always been much bigger and older than we thought.
Changing the initial assumptions about the size and age of the cosmos may help to explain some of the biggest challenges facing cosmology and, without introducing new physics.
While this assumption can never be tested directly by observation it can be tested and/or falsified by measuring the gravitational effects on our observable universe.
Dark Energy is increasing with time
In “What is Dark Energy?” I quoted Risaliti and Luss, Nature Astronomy 3,272-277(2019) “Cosmological constraints from the Hubble diagram of quasars at high redshifts.”
“a deviation from the ΛCDM model emerges at higher redshift, with a statistical significance of ~4σ. If an evolution of the dark energy equation of state is allowed, the data suggest dark energy density increasing with time.”
Back then there were few papers supporting the idea that Dark Energy was increasing with time. It was this paper which encouraged me to write up an idea I had been working on ever since I saw that pie chart -
“ Cosmologists only understand 5% of the universe”.
Since then many more papers have been published on the tension in Ho and concluding that Dark Energy is increasing with time. The KITP Conference in July 2019: “Tension between the Early and Late Universe” in Santa Barbara has been well reported, mainly along the lines of “Tension or Crisis in Cosmology” Most commentators now conclude that the Hubble discrepancy is a real problem, we are missing some important physics somewhere.
Now I do not want to spoil a good argument, but if our universe is under the gravitational pull of the cosmos then both the Planck value and Reiss’s result could be correct.
More recently, September 2019, another paper from Chen et al. Using adaptive optics technology on the W.M. Keck telescopes in Hawaii, they arrived at an Ho of 76.8. Speaking to Science Daily - "More and more scientists believe there's a real tension here," Chen said. "If we try to come up with a theory, it has to explain everything at once."
I think it is now fair to say that there is a consensus that the rate of expansion of the universe is increasing with time. Dark Energy is increasing with time.
But why?
As Barnes and Lewis say in their great little book, “The Cosmic Revolutionary’s Handbook”, you have to explain all the data. LCDM cannot explain why Dark Energy is increasing with time. In truth the standard model can’t explain what Dark Energy is at all.
We have no idea what Dark Energy is. Vacuum energy, always a vacuous explanation, cannot explain an increasing rate of expansion. If Dark Energy is a constant then the rate of expansion should be slowing down.
Avi Loeb and Lisa Randall have both come up with alternative theories. Both admit that they are not satisfied with the results.
Loeb is not happy with his Late Universe Decaying Dark Matter, “you add two free parameters in order to resolve one discrepancy — and I’m uneasy about that”.
Quanta magazine April 27, 2020.
Randall devised a “rock ’n’ roll” solution to the Hubble tension. The density of dark energy oscillates, or rocks, while in others it rolls down from a high value to zero. But in all cases, the early dark energy must disappear after a few hundred thousand years. “The tricky part is that [early dark energy] can’t really stick around; it has to go away quickly,” she says. Quanta magazine April 27, 2020.
Although not included in the list of possible explanations in Quanta magazine, cosmic gravity does at least explain why the rate of expansion is increasing in time.
I have assumed that this is obvious. For those demanding mathematical proof I refer you to - Newton Philosophiæ Naturalis Principia Mathematica, first published on 5 July 1687. On this scale a good approximation to Einstein, General Relativity.
No need for new particles or creative mathematics; no new physics. It’s just gravity.
However with all this new data coming in to suggest that expansion is increasing in time, it’s time to take cosmic gravity seriously.
But there is more -
Not only is the observed acceleration increasing in time it appears that it is not equal in all directions. The cherished assumption of all astronomical mathematicians, the isotropic universe is under attack
Is the Universe really Isotropic?
A prediction of cosmic gravity is that the expansion of our universe will not be equal. There will be a dipole aligned towards the most significant mass of the cosmos.
Our galaxy is subject to the gravitational forces of our local universe producing so-called ‘peculiar’ velocities within our local cluster. Similarly, our universe will be subject to the gravitational pull of the local cosmos. This will result in expansion rates differing in different directions.
This is a significant challenge to the standard model - the expansion of the universe is equal in all directions. I have often asked the question - is the assumption that the universe is homogeneous and isotropic based on 5 sigma data or is it just to keep the maths simple?
Now the new data on an anisotropic universe is far from substantial. There is certainly no consensus on a real dipole in the expansion of the universe. But do remember, it is only a couple of years ago that Dark Energy was definitely constant. Within days of writing this blog another paper has been published adding to the growing evidence of directionality to the universe. Webb et al, see later.
Professor Subir Sarkar of Oxford University has written much on the subject of the measurements of Dark Energy. Here I refer to an interview given with Dr Sabine Hossenfelder published on YouTube on 2nd March 2020.
His team finds no evidence for acceleration, but a cosmic flow of spacetime in the same direction as the CMB dipole. Our galaxy is moving in the same direction as the dipole but 4x faster. (He gives credit to Singer who found this prior but was discounted). Bottom line he says “Evidence for isotropic acceleration is non-existent, and it is this that has had a major impact not just on cosmology but also fundamental physics.”
Quotes from interview
“ The universe is accelerating in one direction and decelerating in the opposite direction. This direction is pretty close to the CMB dipole, it’s within 23 degrees.”
“ The evidence for an isometric acceleration is non existent.”
“Interpreting this as due to vacuum energy is not what is written in the sky.”
“We found that the velocity was in the same direction as the CMB dipole but it was 4 times larger.”
Prof Sargar is of course careful to say;
“I want to emphasise that this does not mean that the universe has an axis. It means that the sample of supernovae that have been so far observed show this dipole. What one makes of this is another matter. I’m not commenting here. It’s hard to imagine how the universe could have an axis and how one could have a directionality in the metric.”
But there’s more.
In January 2019 the Risaliti and Luss paper came out in Nature Astronomy which supported the theory of cosmic gravity. Now in April 2020 a paper by Kostas Migkas et al has been published which is consistent with Prof Sargar’s conclusions. It has raised quite a storm.
“Probing cosmic isotropy with a new X-ray galaxy cluster sample through the Lx−T scaling relation.”
K Migkas et al arXiv:2004.03305
Galaxy cluster data
Astronomers have assumed for decades that the Universe is expanding at the same rate in all directions. A new study based on data from ESA's XMM-Newton, NASA's Chandra and the German-led ROSAT X-ray observatories suggests this key premise of cosmology might be wrong. I quote extensively from the blog of Kostas Migkas, a doctoral researcher in the Argelander Institute of Astronomy of the University of Bonn, Germany.
“The assumption of isotropy comes as a repercussion of the equations that describe the evolution of the cosmos, which are based on the theory of General Relativity. The main observational evidence for this is the CMB, which is the "picture" of the infant Universe when it had only 0.003% of its current age. The CMB seems to be isotropic, and cosmologists extrapolate this property of the very early Universe to our current epoch, nearly 14 billion years later. However, in about the last 4 billion years the so-called dark energy became the dominant element that drives the evolution of the Universe, constituting 70% of the latter's total content. Its baffling nature has not yet allowed astrophysicists to understand it properly. Therefore, assuming it to be isotropic is almost a leap of faith for now. This highlights the urgent need to investigate if today's Universe is isotropic or not.
In our first study in 2018, we came upon some intriguing results! That's why we decided to look into this more carefully and with more data. To do so, we analyzed 313 galaxy clusters using the Chandra and XMM-Newton telescopes and we combined them with 529 available clusters from previous studies. What we found was even more impressive than our 2018 results. We managed to pinpoint a region that seems to expand slower than the rest of the Universe, and one that seems to expand faster! Interestingly, our results agree with several previous studies that used other methods, with the difference that we identified this "anisotropy" in the sky with a much higher confidence and using objects covering the whole sky more uniformly.
So did we tear down one of the most crucial pillars of cosmology? Not so fast, it is not that simple. At least two scenarios may have led us to wrong conclusions.
Firstly, cosmic material might interfere with the light that travels from the clusters to the Earth. For example, previously unknown gas and dust clouds beyond the Milky Way could obscure a fraction of photons emitted from the clusters. Since we ignore the possible existence of such clouds, we do not account for their interference, and hence we would falsely underestimate the true luminosity of the clusters. Eventually, we could mistake this for a cosmological effect. We performed several tests that led us to believe that this scenario seems unlikely, but not impossible. However, considering that the direction of the anisotropy we find agrees with other studies that used observations in light at different wavelengths, where such obscuring effects are not expected, one could argue against the possibility of such biases in our analysis.
The second case is what we call "bulk flows". In a nutshell, some "superclusters" (groups of galaxy clusters!) exist that attract other clusters towards them through gravity. This can generate a coherent motion of some clusters (lying in the same sky region) towards a supercluster. But why is this important? Well, in our default analysis we assume that these “local” speeds of clusters, on top of the Universe’s expansion speeds, are small and random and that they do not matter in general. If this condition is not met, then our assumption does not hold. This might result in wrong distance (hence luminosity) estimations, producing "fake" cosmological anomalies. This scenario is not far-fetched and more tests are required to deliver a definite conclusion, although such large correlated speeds are not easily expected.
If none of the above is true, then the hypothesis of an isotropic Universe may be under question and a cosmological paradigm shift is possibly required. Of course for such a big change to occur, the astronomical community must perform other scrutinized tests obtaining consistent results every time.
The take-home message is this: the implications of this study could be profound either if a non-isotropic expansion of the Universe exists or if dominant bulk flow motion affects astronomers' measurements. Many studies in cosmology, including X-ray studies of galaxy clusters, assume that the Universe is isotropic and that correlated motions are not significant enough to consider them. Even if the mysterious gas and dust clouds are the origin of our results, the X-ray community might need to revisit their results, if their data were coming from that mysterious sky region."
Fine Structure Constant
Yet another paper out suggesting a directionality in the universe. Professor John Webb of New South Wales university spoke on Spacetime with Stuart Gary, series 23, episode 47 about his new paper.
"Four direct measurements of the fine-structure constant 13 billion years ago."
Michael R. Wilczynska and John K. Webb et al
Science Advances 24 Apr 2020:
From the Spacetime interview:-
"These new measurements (of the Fine Structure Constant, FSC) do not conflict with a directionality to the universe. In fact, a directionality is preferred over a non directionality when you take the data set as a whole.
What's new is that we have measurements which go back earlier, closer to the Big Bang time. They support the idea that there could be a directionality in the laws of physics."
"There is a bunch of other data which is entirely independent of my work on FSC which also suggests a directionality. Perhaps each is not especially compelling but they all seem to line up in the sky within the errors."
"We are above 3 sigma with our measurements alone. Whether we are up to 5 sigma with this collection, I don't know. I haven't looked into that."
" Several papers out there suggest directionality in the supernovae data and this lines up with the directionality in our FSC data."
Ethan Seigel offers words of caution (Forbes, 10th April 2020)
“But there are many different, independent ways to test the idea that the Universe is the same in all directions: what astrophysicists call "isotropy." In a new study in the April 2020 issue of Astronomy & Astrophysics, a new technique, analysis, and data set are all applied to this puzzle, and the authors claim that the Universe's expansion rate is different depending on which direction we look. It's an interesting result if true, but there are lots of reasons to be skeptical.
The Universe's expansion may not be the same in all directions, but it's going to take a lot more than this one study to prove it.
One of the biggest criticisms of the cosmic gravity idea is that the universe is observed to be isotropic. If our universe exists in a cosmos which is much bigger and older than we thought, then we should see anisotropies reflecting the gravitational pull of the masses out there in our ‘local cosmos’.
These studies suggest that the Big Universe theory could be correct, but as Ethan says, “it's going to take a lot more than this one study to prove it.”
Conclusion
Cosmic gravity is falsifiable on its two predictions.
There is now a consensus that the rate of expansion of the universe is increasing with time.
As required by cosmic gravity.
Cosmic gravity also predicts a dipole in the universe. More and more data is coming in to support this unwelcome idea. An isotropic universe is a rock on which LCDM is based. It is going to take a lot to get a consensus on anisotropy. It takes confidence to work on something which could turn the world of physics upside down. Ask Adam Riess.
Cosmology:
“the scientific study of the origin, evolution, and eventual fate of the universe” Wikipedia.
Lambda Cold Dark Matter (LCDM) explains a great deal about the structure of the universe. But how much does it tell us about the big questions of cosmology?
1. Origin - It tells us nothing about where all the stuff of the universe came from.
2. Evolution - It leaves 95% of our universe unexplained.
3. Fate - It tells us little about how the universe will end.
One change to the initial assumptions about our universe may explain Dark Energy, one of the biggest problems in cosmology.
Not only Dark Energy, but if the cosmos is bigger and older then the questions about how the universe started and how it will finish may also become much simpler.
The universe has always been much bigger and older than we thought.
References
Risaliti and Luss, Nature Astronomy 3,272-277(2019)
Chen et al, Monthly Notices of the Royal Astronomical Society, Volume 490, Issue 2, December 2019, Pages 1743–1773
Loeb, Late Universe Decaying Dark Matter can relieve the Ho Tension, arXiv:1903.06220
Randall, Rock ‘n’ Roll solutions to the Hubble Tension, arXiv:1904.01016
https://www.youtube.com/watch?v=B1mwYxkhMe8 Hossenfelder and Sarkar
arXiv:1808.04597 Evidence for anisotropy of cosmic acceleration
K Migkas et al arXiv:2004.03305
Seigel, Forbes 10th April 2020
Webb et al. Science Advances 24 Apr 2020:
Vol. 6, no. 17, eaay9672
DOI: 10.1126/sciadv.aay9672