There are more interesting and less implausible hypotheses out there than the "just so" dark matter one.
Yes, dark matter is the best way we currently have for fitting the data within most of our existing frameworks for understanding the universe. I really don't see the relation to epicycles.
There are people out there working very hard on modified gravity theories. I'm not aware of any that are able to explain the current data. If anything, trying to modify gravity to fit the dark matter data would be most similar to epicycles, it's devilishly difficult to come up with increasingly complex theories that fit more and more data that's coming in.
This is the key problem. Since there is no theory of what dark matter is made of or how it is created and destroyed, you can always have as much or as little of it as you need to fit the data.
As for gravity, we don't have anything close to a working theory of quantum gravity. We can't even measure the classical gravitational constant to more than about 4 digits. The reproducibility by different experiments has not demonstrably improved since the 1940's! Clearly there is a lot more we have to learn about gravity.
And yes, quantum gravity is also something we don't understand. But the domain where we are missing that understanding doesn't overlap with the dark matter "problem".
Falsifiability comes from having specific predictions, which means one theory that's an island, not a bunch of approximations.
It's not just a fudge factor, it's a fudge factor that behaves exactly like mass.
For dark matter, one of the problems is that any given instance is allowed to have whatever amount of dark matter gives the output we want. This makes the math work out great, but weakens its predictive power.
Dark matter and dark energy are the simplest (literally single parameter) fits to the cosmological data we see. Why we see data consistent with these parameters (e.g. what is the non-interacting massive particle) is up in the air, but adding multi-parameter new forces without more justification seems a little too interesting.
Eg, if we’re looking at pseudo-tangles in shadow projections, that would solve why QM looks statistical while relativity looks continuous.
But that would raise deep questions about “warp” in the macro and whether galactic scale tangles would generate additional binding energy — ie, dark matter. Large scale tangles hiding mass would explain why we can’t interact with it, for instance.
For instance, I've seen a convincing argument[1] that dark matter researchers consistently underestimate galactic inclination, which in turn results in poor fits between model and data, leading to the epicycle-like fudge inclusion of dark matter as "everywhere we would expect mass to be, given xyz".
[1] https://tritonstation.com/2022/01/10/the-curious-case-of-agc...
Einstein would be happy!
Why are "epicycles" embarrassing?
"Epicycles" worked fine for a very long time. They are predictive. And accurate! And can be translated to a physical compuation mechanism (see: Antikythera mechanism).
In addition, "epicycles" are a manifestation of Fourier decomposition, which is a perfectly fine mathematical tool. The errors are due to the fact that reality isn't purely mathematical.
"Epicycles" were quite fine until we got both 1) much better clocks and 2) much better astronomical observations.
People forget that physics was in pretty close to this same state about 150 years ago (roughly) right before quantum mechanics. Physics was pretty much buttoned down except for that really strange Black Body Radiation problem (Ultraviolet Catastrophe), but they'd have that sorted in a couple of years. Certainly no later than 1900--the end of the century. No big deal.
HAH! We know how that turned out.
One interesting approach I've heard of is abandoning reductionism and looking at how the macroscopic might actually determin the microscopic. We'll know how it pans out in half a century or so.
In the case of dark matter, we only observe their downstream effects but have no other direct evidence of its existence.
“The most successful technique with which to investigate [dark matter] has so far been the effect of gravitational lensing. The curvature of space-time near any gravitating mass (including dark matter) deflects passing rays of light - observably shifting, distorting and magnifying the images of background galaxies”.
“Dark matter appears not to interact via the electromagnetic force, and therefore neither emits nor reflects light.”
I am sure you know that, but perhaps not everyone does?
I must confess, when you said "pedantic", I expected something more annoying and less worthwhile. That's the best "pedantic" I've seen in quite a while.
I'd love to hear about all of the less implausible hypotheses you're referring to.
I bet one coffee that there is no dark matter in the form it's been looked for in the last decades. I bet two coffees that when somebody will discover the cause of the measured effects we'll be able to build some great new stuff, much like general relativity eventually gave us GPS and then navigation, etc.
Dark matter is a simple theory that explain a wide variety of unrelated observations.
In any case, until we actually are able to test that this is one "thing" rather than a bunch of things we still have no idea about, we should stop calling it "dark <foo>". Because I think that a lot of people are under the impression that there is some discrete substance out there causing this discrepancy, and there really is no reason to believe that's the case.
most people creative enough are driven to the arts, which in modern society are only good for entertainment.