Nov 22, 2023 07:16 PM
https://iai.tv/articles/the-challenge-to..._auid=2020
INTRO: Dark matter is a central but contentious part of the dominant model of cosmology. It has never been observed directly and is seen as an arbitrary add-on to Einstein's theory of gravity, just to make the data fit. MOND has for a long time been considered the most credible alternative theory of gravity, doing away with the need to postulate dark matter. But a recent study lead by Indranil Banik, a past supporter of MOND, demonstrates that the theory is in fact wrong. The search for a more credible alternative continues.
EXCERPT (Indranil Banik): . . . The difficulties encountered by MOND on scales smaller and larger than the galaxy scales for which it was designed imply that MOND is not a fundamental theory. However, the standard cosmological model, known as ΛCDM – which predicts the existence of dark matter – faces its own challenges. I have come to the conclusion that Einstein’s theory of gravity (General Relativity) – which we know reduces to Newtonian gravity in galaxies and wide binaries – does not require substantial modifications on scales of up to several million light years.
But deviations are likely on much larger scales. This would help to explain why we appear to be in a huge void which is about 20% less dense than the average for the Universe as a whole out to a distance of a billion light years. Such a void can help to solve the Hubble and bulk flow tensions for ΛCDM. While these are all very serious tensions, the Hubble tension in particular has garnered a lot of attention because it relates to the present expansion rate of the Universe or the Hubble constant, one of the most basic cosmological parameters. Local measurements indicate that this is 10% higher than predicted based on observations of the early Universe if we use the ΛCDM framework.
Since observations also indicate that we are in a large and deep void, it would be natural if the Hubble tension is caused by matter flowing out of the void due to the gravitational pull from the higher density of matter outside the void. This would inflate the locally measured Hubble constant. It would also naturally account for the average velocity of galaxies out to a billion light years, an observation known as the bulk flow – which is about twice as fast as expected in ΛCDM.
Therefore, it is still quite likely that there are modifications to be made Einstein’s General Relativity theory. However, this would be on scales of tens to hundreds of millions of light years, not on the scales of individual galaxies or galaxy clusters. Such a modification may possibly have enhanced the formation of the most massive galaxy clusters. But it would leave unanswered the issue of why galaxies follow MOND so closely. This is not easily understood in the ΛCDM paradigm... (MORE - missing details)
INTRO: Dark matter is a central but contentious part of the dominant model of cosmology. It has never been observed directly and is seen as an arbitrary add-on to Einstein's theory of gravity, just to make the data fit. MOND has for a long time been considered the most credible alternative theory of gravity, doing away with the need to postulate dark matter. But a recent study lead by Indranil Banik, a past supporter of MOND, demonstrates that the theory is in fact wrong. The search for a more credible alternative continues.
EXCERPT (Indranil Banik): . . . The difficulties encountered by MOND on scales smaller and larger than the galaxy scales for which it was designed imply that MOND is not a fundamental theory. However, the standard cosmological model, known as ΛCDM – which predicts the existence of dark matter – faces its own challenges. I have come to the conclusion that Einstein’s theory of gravity (General Relativity) – which we know reduces to Newtonian gravity in galaxies and wide binaries – does not require substantial modifications on scales of up to several million light years.
But deviations are likely on much larger scales. This would help to explain why we appear to be in a huge void which is about 20% less dense than the average for the Universe as a whole out to a distance of a billion light years. Such a void can help to solve the Hubble and bulk flow tensions for ΛCDM. While these are all very serious tensions, the Hubble tension in particular has garnered a lot of attention because it relates to the present expansion rate of the Universe or the Hubble constant, one of the most basic cosmological parameters. Local measurements indicate that this is 10% higher than predicted based on observations of the early Universe if we use the ΛCDM framework.
Since observations also indicate that we are in a large and deep void, it would be natural if the Hubble tension is caused by matter flowing out of the void due to the gravitational pull from the higher density of matter outside the void. This would inflate the locally measured Hubble constant. It would also naturally account for the average velocity of galaxies out to a billion light years, an observation known as the bulk flow – which is about twice as fast as expected in ΛCDM.
Therefore, it is still quite likely that there are modifications to be made Einstein’s General Relativity theory. However, this would be on scales of tens to hundreds of millions of light years, not on the scales of individual galaxies or galaxy clusters. Such a modification may possibly have enhanced the formation of the most massive galaxy clusters. But it would leave unanswered the issue of why galaxies follow MOND so closely. This is not easily understood in the ΛCDM paradigm... (MORE - missing details)