It’s research happening privately without publishing, usually going into products

Equivalent? In the analogy of the math or physics results it would be a mental model in someone's brain that you can't access or verify. You just hope it's true

Open source is much more than source available though. Its about licensing.

But that doesn't map to software at all right?

I think the idea does: the point is that closed-source software isn't useful for anyone else than the (copyright)owner. In scientific standards, that is. Similar to esoteric and cryptic theories that resist accessible explanations.

Like if CERN published the discovery of the Higgs boson with 99.9997% certainty, but refusing to tell you how they calculated that number, or what equipment they used and how they calibrated it, in order to prevent other labs from copying their methods.

Or like a machine learning lab claiming SOTA on a benchmark, beating a well-known method that they re-implemented, possibly with bugs, on their private dataset, for millions of compute. But you don't get the source to check, and they don't release any intermediate results or ablation experiments. Aka, from the outside you can't distinguish it from corporate marketing.