I’ve been reading about MOND, or Modified Newtonian Dynamics, as an alternate theory in the mystery of dark matter. The science community invented dark matter as a way to explain the motion of galaxies, which was inconsistent with classical Newtonian equations. That invention, that hypothesis, has led to a decades-long search for evidence of dark matter. With zero success.
I’ve always had some skepticism on the idea of dark matter, which according to the hypothesis makes up 80% of the universe. Really? 80% of reality is invisible and undetectable…that’s weird. The SF lover in me says well, maybe that’s evidence of the 15 or so dimensions that some folks think defines our reality (we only perceive four of those dimensions) – all that dark matter is simply rolled up in those extra dimensions. Maybe, but that’s hypothesis on top of hypothesis.
All MOND does is modify Newton’s gravitational law a tiny bit, basically saying that gravity isn’t a constant, isn’t linear, in all realms of space-time – rather, it’s a gradient that is defined by mass density in a region of space. Nothing else in General Relativity has to change – MOND only addresses gravity. That makes a whole lot of sense to me. With a simple edit of a long-cherished equation, the need for dark matter simply vanishes.
People a lot smarter than me are debating this fiercely, and that’s cool. My money, based more on logic and intuition than on deep understanding of the math, is on MOND. One last thought, the ever-entertaining and educational Sabine Hossenfelder has a unique take on the debate.