A Physicist Who Denies That Dark Matter Exists

Particle physics has a long history of noticing gaps in the experimental data that don’t match up with current theories and positing that maybe a new particle would solve the problem. This goes right back to things like the neutrino (which was posited to preserve momentum in certain particle interactions IIRC) and even the neutron.

Sometimes the suggestion pans out, sometimes it doesn’t. You can see this kind of thing in action - when there was that anomaly in the CERN data a year or two ago there were a flurry of papers suggesting possible particles, none of which panned out because the anomaly turned out to be statistical noise. The various particulate explanations for the observed discrepancy between the spiral galaxy rotation curves and the observed distribution of matter are very similar: Take a gap in the data & speculate about what kind of particle would fill the hole.

When you combine the fact that, historically, speculating about whether new particles could explain anomalies in the observed data has been very productive for C20th physics with the reality that physicists are also loath to toss aside general relativity (which has been spectacularly successful) just because of one observed anomaly that has yet to be explained, it’s entirely unsurprising that physicists are keen on new particles as explanations for the galactic rotation curves.

At the same time, every physicist will happily admit that there’s a great big hole in the standard model - i.e. that it doesn’t include gravity at all - and that any unifying theory might also explain away the galaxy rotation curves in a way that doesn’t require new particles. Indeed, if a unifying theory could pull off that trick it would be evidence that the theory has a good chance of being true. Sadly, to date, no one has managed to come up with such a unification, and we have no real idea what such a theory would look like beyond the obvious: that it should explain the observed facts & match QFT & GR in the regimes where those theories are accurate.

That's a nice example of a prediction being wrong, inventing an as-yet-unobserved chunk of matter to fix it, and that invention then being correct.

Of course, there's a counter-example in the inner solar system in the form of Vulcan. It was invented to explain Mercury's orbit, but the solution ended up being Relativity. So it's not always the right answer.

If you want examples involving entirely new classes of matter, I believe neutrons and neutrinos would fit the bill. Both were invented to explain discrepancies in theories well before they were directly observed.

Remember that coming up with a new type of matter is a form of fixing the model. The model is, essentially, "what does the universe actually look like?" If adding a new type of matter gets you closer, then that's fine. If changing the equations works better, then that's fine too.

Remember that dark matter isn't just some arbitrary fudge factor that gets inserted into the observations to make the numbers come out right. It is a comprehensive theory that allows for observations and predictions. No, nobody knows just what it actually is, but there's a great deal of evidence that there is a lot of "stuff" in the universe which interacts gravitationally but not in other ways.

I see this sentiment a lot, and I'm not sure that dark matter skeptics understand just how much supporting evidence there is for dark matter, or just how difficult it is to "fix Newton." People have been trying real hard for a long time, and nobody has been able to come up with anything like a coherent modification of gravitation that explains the observations.

Correct me if I'm wrong, which is quite likely, but isn't it one of the qualities ascribed to dark matter that it doesn't interact with 'ordinary' matter or photons in any way other than gravity, and therefore can't be directly observed?

Or to turn the question around, is the dark matter hypothesis actually falsifiable?

This is a great line! But, it's not fair.

The inventing of invisible stuff is an attempt to fix the model. The current model is known to be wrong, because the experimental data isn't matching the model. We have evidence of motion we can't explain... ok, something must be causing it. Right?

Black holes and gravity are invisible things predicted by physics.

They include some non-luminous matter, but only require 1/5th to 1/10th as much as would be required by Dark Matter theories. So I think saying they require 'Dark Matter' is confusing. They don't really require a new class of matter and could easily be explained by the presence of some amount of non-luminous baryonic matter in some cases which hardly seems outrageous.