Can it be falsified as an hypothesis?
Neither theories nor hypotheses in the sciences can, generally speaking, be falsified. The term is typically misused to mean something like "evidence can be presented that demonstrates the hypotheses/theory to be false." However, there is a very good reason why Popper and followers used words like falsifiability and falsification rather than "testable" or "confirmation" or similar terms that mean any scientific hypothesis or theory must be such that empirical (and in some cases theoretical) tests may show it to be wrong, incorrect, false, etc.
Falsification is supposed to solve to problems: Hume's problem of induction and the demarcation problem. It solves the latter simply by asserting falsifiability to demarcate scientific hypotheses/theories from non-scientific/pseudoscientific ones. It is partially in this sense that the term is too often thrown about today. But the bigger problem falsification/falsifiability was supposed to solve is the former: that of Hume's problem of induction.
Popper granted that Hume's argument was sound, and that there is no way to confirm the truth of some hypothesis or more generally any proposition through induction (and by extension through any sort of empirical methods). However, he believed that scientific practice, knowledge, and progress must rest on something solid. Hence falsifiability.
An example:
Suppose one believes that all swans are white. One tries to support this empirically by observing thousands of swans. But, as with the problem of the sun rising tomorrow, no amount of this kind of inductive evidence suggests that all swans are indeed white. There is no logical validity to any sort of argument that says "because the sun has risen in the past, and always has, it will tomorrow" or "because all previously observed swans have been white, all swans are white". Indeed, Hume and Popper and others argued that such experiences/observations couldn't even count as evidence, let alone confirmation. It is simply (they argue) invalid inference and therefore fundamentally unsound.
However, Popper's falsification method proposed an alternative. We may never be able to confirm that all swans are white, but a single observation of a black swan proves this hypothesis false.
Hence falsification: there can never by any evidence that confirms or supports any scientific hypothesis/theory, only evidence that falsifies it.
This part is hard to swallow, and is therefore usually ignored in textbooks, popular science, science education, and (I'm ashamed to say) all to often by practicing scientists in scientific literature.
After all, the implication is that a theory of e.g., gravity I come up with today is as good a theory as is general relativity, because it has not yet been falsified.
It also doesn't work. In practice, scientific theories are not like the "theories" one finds in the philosophy of science literature of Popper's time, which are usually represented using symbolic logic and make no contact with scientific practice. Most scientific theories cannot be states in simple terms like this. And even those that can be written down in mathematical form cannot be falsified in the manner Popper suggested.
What is the scientific evidence for it?
Presupposition, usually. At least in part. Actually, there is a sense in which practice in certain sciences cannot so easily rest on physicalist grounds:
"The alleged closure (also referred to as completeness) of physics implies that anything that has a physical effect must itself be physical. This is one of the reasons why many philosophers of science have taken
physicalism for granted. Physicalism started as an ontological doctrine of the
Vienna Circle of logical positivists and says (roughly) that ultimately everything is explainable by physics...To define physicalism as the doctrine that all facts, including intention and meaning, are reducible to physical facts, or as the claim that every physically acceptable effect has a physically acceptable cause, is not as clear as it seems...
The claim that physics is closed and the idea of physicalism indicate a fundamental misunderstanding of physics. There are a number of non-trivial presuppositions of the natural sciences, such as the necessity to distinguish between the observer and the observed. Physics is based on experiments and fundamental theories. In order to test, or support, a hypothesized cause-effect relationship experimentally, it is indispensable that the experimenter has
the freedom to deliberately choose (within well-understood limits) a stimulus and then to record the response. Clearly we cannot make measurements on a closed system on which outside influences are disregarded by definition. Yet, there are no known first principles for open systems: the first principles of physics refer to strictly closed and isolated systems where no distinction between cause and effect is possible.
Since all first principles of physics are
invariant under time translation and time reversal, concepts such as “past”, “present”, or “future” have no place in fundamental physics. Accordingly there are no physical laws which cover memory and intentions. Memory of past episodes is a necessary precondition of personal identity—in the sense that a person at one time and a person at another time can be said to be the same person.
We conclude that the space-like time of physics does not take into account all aspects of time. In particular, the “arrow of becoming” cannot be consistently integrated into a universally valid picture of physics. Since physics systematically leaves out human intentions, the first principles of physics are not even enough to describe physical experiments or engineering physics exhaustively." (pp. 158-159)
Primas, H. (2017).
Knowledge and Time. Springer.
Similarly:
"The assertion that “modern science is premised on the assumption that the material world is a causally closed system” (Heil, 1998, p. 23) is in striking contradiction to experimental science. Every experiment requires an irreversible dynamics. No experiment refers to a closed physical system. In a strictly deterministic world it would neither be possible to perform meaningful experiments nor to verify the partially causal behavior of a physical system.
We conclude that science neither assumes that the material world is a causally closed system, nor that physical laws imply the causal closure of physics"
Primas, H. (2009). Complementarity of Mind and Matter. In H. Atmanspracher & H. Primas (Eds.)
Recasting Reality: Wolfgang Pauli's Philosophical Ideas and Contemporary Science (p. 171). Springer.