In physics, are there such things that aren't one or many? For example quantum mechanics, etc. and so on?
The word "many" usually describes a countable quantity. If a type of object is countable, then it can be described, at least in principle as one or many. If we are talking about something that is not countable, then "neither one nor many" may apply. If the elements of some set can be put in correspondence with the real numbers, they would not be countable. However it's still possible to talk about one or many real numbers. "Many" unspecified real numbers always corresponds to a type of infinity. In terms of physical concepts, if "space" is not quantized, it might satisfy the concept of neither one nor many if we are not talking about particular spaces.
Thanks for the response. Other than "space", what are other things that can be described as "not one or many/one and many"? Perhaps there such things in quantum physics, etc. and so on? One more question, are "time" really limited and finite?
You can simply think of concepts that don't admit countability. Is time countable? We can invent units of time. We have units of volume, even for empty space. But any unique continuum can be considered non-countable. That's what a continuum is. If we don't admit multiple instances of some type of continuum (like space or time), this would seem to answer your question. That's about the best I can do. EDIT: For your second question, I have no idea in general, but I know mine is.
In my opinion, I think atoms, subatomic particles and the like is/are not one and many. Space and time, we can say can't be described as one and many. Or even universe itself is/are not one or even many, perhaps. But some people said "uncountable" are equal to "One", "absolute oneness/singularity" and "utterly unique" and so on. Do you think it is appropriate? What's your opinion?
I disagree with you about atoms and at least the stable "elementary" particles. The periodic table is based on the number of electrons/protons in an atom and atoms are countable. Isotope numbers are based on neutron counts. To say uncountable is equal to one is somewhat meaningless IMO. There is only one (continuous) electromagnetic spectrum. Therefore it makes no sense to distinguish one from many when speaking of unique continua. This argument could only make sense if we considered multiple universes with different physics. Since we can't discuss something hypothetical, it makes no sense to consider it in the context of your question.