Hi,
I was fascinated by the idea that Newton's law of gravity may need to be modified in small weak fields. However, it is really a disappointment that the theory is not getting too much of impulse mostly dues to its inability to explain gravitational lensing.
I want to gauge your opinions in this matter, do you still consider MOND or some modified version of it?
Said Laaroua,
You ask an excellent question. When I first encountered MOND, I laughed. Now, I consider the work spearheaded by Mordehai MIlgrom to be most extraordinary. As you are likely aware, the flatness of the rotation curves in spiral galaxies does not fit with GR. MOND empirically fits them with considerable accuracy over a super wide range of spiral galaxy sizes and central masses. Those who work with GR had a problem. In order to fit spiral galaxy rotation curves to GR they added Dark Matter.
Apparently, the proponents of Dark Matter are shifting away from it. This is partly due to the need for dynamic Dark Matter. MOND is empirical. In order to get a theoretical basis for modified gravity, I think one needs to consider time dilation in a way that runs completely counter to GR. For my part, I think time in the universe continually slows. This likely sounds completely ridiculous. Wouldn't we already have discovered if time slowed? I don't think so. My personal belief is that time slows everywhere in the universe at the same rate. This, combined with the very small rate of slowing makes it difficult to detect. I consider MOND gravity to be the detection of this slowing.
I think physics is at a crossroads with no clear direction in this question. If we treat time dynamically, all physics becomes challenging. This is especially true for GR. Time no longer becomes a valid dimension at cosmological distances. Thank you for asking the question.
Rich
Thank you for your responses J.A Souza and Richard Marker.
I find your idea of slowing time to be compelling, after all if we assume the universe is isotropic and homogenous why then claim space is the only entity that expands, why wont time expand as well.
I completely agree that the solution to all the chaos that we see going on (the hubble tension, the very recent star age problem ,dark matter...) , the solution would be something in the basics, the fundamental physics. I definitely can think of reasons that make time slow: maybe the universe self gravity? or maybe our universe orbiting other universes ?... Richard Marker
Said Laaroua,
To me the slowing of time seems evident. If one considers gravitational time dilation as causing gravity rather than vice-a-versa. If matter causes time to slow locally and propagate outwards, then what speeds time back up to maintain a constancy? I think nothing does that. This leads to time slowing universally. Such a concept is difficult to grasp because we are accustomed to thinking of time as a background process that just keeps going at a constant rate.
From a modified gravity concept, gravity from a distant source is stronger because it was generated when time was faster. It is also weaker from dissipation into the 'flywheels' of space during it journey to the distant matter. This is difficult for me to model because time does not take on its usual role.
I hope this makes some sense to you.
Rich
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