One of the facets of science, or good science at least, is the lack of dogma. Most statements are of the form, “To the best of our knowledge … “ They are theories. Then there are scientific principles that are more secure, called laws. So there is a theory of evolution and there is a law of gravity, for instance. But even then, the scientific process never ends. Laws are always open to scrutiny, no matter how axiomatic they may be.
Gravity is a force that acts on matter. If there was no matter, it would be difficult to detect it. Through that interaction, the nature and size of the force can be calculated. It seems to be a constant. The force of gravity is the same everywhere in the universe. The reverse is also possible. From knowing about gravity, it is possible to determine or predict the movement of matter under its influence.
There are four known forces and gravity is the weakest. Forces are believed to be effected through the action of subatomic particles, like photons that constitute electromagnetism, another one of the forces. Because a force is ultimately composed of units or quanta, it is all part of the quantum theory. Gravity is predicted to be the effect of gravitons, which have not been detected so far, so weak is the force and therefore the effort needed to detect their quanta. Gravity has other peculiarities. Since it acts over vast distances, gravitons, if they exist, are thought to be massless, meaning it could actually be impossible to detect them. The effect of gravity is felt here on earth from all the matter in the universe.
The interesting thing is that the vast expanses of matter, galaxies and gas clouds and such, in the distant universe, seems to move greater than it should through gravity. That is a problem for the theories and the laws, but not a problem for physicists and cosmologists. It is an exciting challenge to do more science. Maybe the law of gravity is flawed or has exceptions, or maybe there is something about matter we do not understand. Or maybe there is something else not known about.
A long time ago Einstein, one of the great theoretical physicists, could not match an equation to the observed results, so he patched it up with a “place holder” until more was known. Well scientists have put in a place holder that seems to cater to the discrepancy between gravity and how the matter in the universe is moving – expanding. Blackjay founder John calls it a “fudge factor” in his post “The Failure of Galactic Dynamics” at https://blackjay.net.au/the-failure-of-galactic-dynamics/
They call it dark matter, and dark energy. Remember matter and energy are the same thing really, interchangeable. No explanation of this dark stuff has been offered and nothing of the sort has been detected. Importantly, not everyone agrees with the concept because with it, it may be necessary to modify the law of gravity. That would mean it is not a fixed and immutable law after all. And that would be messy for Einstein, or at least for his theory.
Scientists released papers on 19 November 2024 on arXiv discussing the 4th year interim results of a 5-year research project to analyse the largest map so far of the cosmos, 6 million galaxies over an 11 billion year timeframe. Their findings support Einstein’s theory of general relativity and its description of gravity. In other words gravity is gravity is gravity, sol!
“General relativity has been very well tested at the scale of solar systems, but we also needed to test that our assumption works at much larger scales,“ says Pauline Zarrouk, a cosmologist at the French National Centre for Scientific Research (CNRS) who co-led the analysis. They analysed data from DESI, the Dark Energy Spectroscopic Instrument in Arizona.
Another group of astronomers led by McGaugh in a paper published 12 November 2024 in the Astrophysics Journal analyzing data from (JWST), the James Webb Space Telescope, say some of the oldest galaxies in our universe appear much larger and brighter than expected, suggesting they formed early and grew rapidly — potentially without the influence of dark matter. So if not, what? One alternative to the existence of dark matter and dark energy is the so called Modified Newtonian Dynamics or MOND, which is supported by these JWST findings.
John believes, “Cosmologists have lost the plot but maybe some new unifying theory will pop up although I doubt it. I reckon General Relativity is holding everything back. GR hasn’t come up with anything relevant since the 1920s.“
It is all up for grabs and a great time to be a cosmologist.