Argument from simulation?

As far as I understand the situation, when it was found that simulations of galaxies operating on the force of gravity and mass alone did not output motions consistent with observations of actual galaxies, astrophysicists, rather than deciding that gravity and mass are not the only factors affecting galactic motion, decided to simply add a certain amount more unobserved mass. When they had added enough to get a galactic motion output from their simulation that matched observations in the real world they announced it as the discovery of dark matter, and the amount they needed to add became the accepted amount in existence.

This seems to me to be fallacious reasoning:


Simulation A does not output results consistent with observations.

Phenomena B, although unobserved, is added to Simulation A until output matches observations.

Unobserved Phenomena B therefore exists in the real world despite being undetectable by any known means.


Is this fallacious? Is it a known fallacy, and if so, what is it called?

Not sure about the simulation or the facts of the question itself, but yes, as you have described it, it does not follow that dark matter is the definitive answer to this problem. There could be any number of explanations for why the simulation did not work as intended initially, and to posit dark matter as the answer would obviously be jumping to a hasty conclusion. Presumably the creators of this simulation would recognise this, and note that dark matter is only one possible explanation, and all things considered it would be wayyy more likely to NOT be the correct explanation than otherwise. A physicist would need to dig deeper into the math to make predictions about how likely an explanation this would be.
I'm not so good with naming fallacies off the bat, so I will have to let someone else answer that I'm afraid!

This is a good example of a domain-specific argument that cannot be properly evaluated without subject matter expertise.

I can see how this sequence of syllogisms could lead to concern, if they were asserted to explain someone's conclusions. The fallacies might be either "ad ignoratiam" (what else could it be to account for the differences?) or an old favorite "non-sequitur".

The possibility is that Daniel is the one engaging a fallacy in the way the question is asked. Why? Because the physics of what's called the "standard model" has dozens of supporting examples that keep some other kind of answer from immediate proposal, and the proposition of dark matter is not a scientific conclusion, but a working hypothesis. To be sure, it does NOT settle the issue of universal attraction of gravity despite evident expansion of the universe, but is only presented by popular media as if it were because MSM makes a buck with oddity or sensationalism.

For myself, I read such information/stories the way I read science-fiction, giving the author the benefit of "suspension of disbelief".

It's not Daniel's job to come up with a better hypothesis, and the criticism may be valid, but not, imo, because it had a logical error. At the moment, the error if any is that it's ad hoc

Cosmology and astrophysics is much more dependent on observation and induction (<< on controlled experiments) than the more prosaic atmospheric warming of the globe's past century, but the popularization of answers (MSM) in both speaks more to the hope/anticipation (the demand for Answers !) than to the slogging work that will have been expended when the issue falls off the radar and stops being popular and a revenue source.

If that were indeed the reasoning, then that would be IMO, a simple non-sequitur, and it certainly is not particularly uncommon as a non-sequitur, both in science, the courtroom, and everyday "thinking" (you should excuse the expression).

However, commonly it is not the reasoning, or if it were, it would be blown out of the water by the first peer review if it got past the first supervisor. As someone else remarked, the proposed nature of the reason for the deviation of observation from prediction is a hypothesis. If the adjustment of the prediction of the model approaches the limits of measurement, then we could say it is a working hypothesis. In this example, we have the hypothesis of dark matter as assumed in the simulation, and the hypothesis is working.

Does that prove that there IS dark matter? Of course not. What id does show is that if our assumptions are correct, then we know something more about the existence of dark matter and its distribution, as a straightforward calculation. If someone else does a simulation showing how much different it would be if it were space expanding or fairies dancing on the camera, then they could compare their adjustments and decide or argue about which hypothesis were the stronger. Then they could get back to work comparing the rest of their assumptions in the light of their extant conclusions, after which they do new simulations, rationalisations, and measurements.

It is called science, in certain connections. And tremendously powerful at that.