> I'm a biologist, and I don't agree.

I picked a bad example. Well, no, actually, a good one, but an example that does not lend well to online debate. And then I failed to make myself clear.

I already know about all of the corner cases, such as ring species, the fuzziness you get during speciation, sub-species, the constant reclassification of taxa, etc..

What I was trying to get at is that "species", like "photon" is a human word. A label for an abstraction that's useful.

No working biologist (sans a few creationist crazies) would disagree about that vast, vast majority of what makes a species a species. The chromosomes, the interbreeding capability, the genetics, DNA, etc... Where they disagree is on the finer points of classifications, such as whether two very similar specimens are a species, sub-species, or just a "trait" within a species. Those are just human labels, like the dewy decimal code. They're not the thing. They don't disagree that the specimens exist, that their DNA is different, etc...

Quantum theorists disagree with each other on things comparable to the existence of species. As in, some will say that there is such a thing as wave function collapse, others will say that this is nonsense and there's no such thing. They're not disagreeing on exactly when wave function occurs in some obscure corner case. No, they disagree on the existence of the concept itself.

This is a crucial distinction.

No two chemists will ever disagree that H2O is water or not. Ever. There's just no such argument, and hasn't been for well over a century.

In theoretical physics, specifically quantum mechanics and its cousins, there still is debate at this level, and shows no signs of resolution.

> But those particles exist to us only as the results of measurements...<snip>... you can only speak in terms of measurement outcomes.

That is a complex debate that's been had in the past: is it meaningful to speak of something existing if it cannot be measured, even in principle?

The issue with that is that sometimes people just state that certain categories of experiments are impossible, and then it turns out that oops.. no, it was possible, just really hard to do. This is my favourite example: https://tf.boulder.nist.gov/general/pdf/2723.pdf

Note the quote at the end: "Some observations can be made on the existence of ‘blinders,’both in theory and in experiment. Some theorists were accustomed to seeing problems in terms of the tools which had previously proven useful for describing experiments with large numbers of atoms, such as the optical Bloch equations. Their intuition seemed to fail for the case of single atoms, and they were unprepared to accept the phenomenon of macroscopic quantum jumps."

This is particularly common in the QM field, especially in relation to single particles or atoms. The tools are optimised for ensembles, so... people seem to forget that single particles exist. The experiments involving single interactions are crazy difficult, so some people will simply state that they're impossible, and it's difficult to argue with that when there are so few experimental results available to counter that.

Note that GR had some similarly "hard" experiments, such as the detection of gravitational waves. That doesn't mean that people seriously said that talking about gravitational waves was meaningless.

> Of course. That's why continuous spectra are a thing.

Okay, so you're on the photons-are-not-always-quantised side. I agree with you, but other people don't.

This is a fundamental disagreement much like Hinduism and Islam, to pick two random religions. Sure, there are silly people saying things like "all religions are equally valid", but.. no, no they are not. Some of them are just local church traditions, some are full on sects, and others aren't even vaguely compatible.