Question: Suppose there is a physical theory that predicts that the observable physical laws differ when applied to the observer himself rather than to the other people, for any given observer. 

Would existence of such theory invalidate the applicability of scientific method?

I am referring to [a paper by Thomas Breuer](https://homepages.fhv.at/tb/cms/?download=tbDISS.pdf) where he has proven that an observer in quantum mechanics cannot measure certain parameters about himself or a system that includes himself, even if he can measure similar parameters of other people. This means his own wavefunction appears differently to him, a phenomenon which Breuer called "subjective decoherence".

So my question is whether this result disproves usefulness, credibility or validity of scientific method?

Answer: 
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> So my question is whether this result disproves usefulness, credibility or validity of scientific method?
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It would problematize the scientific method **only for those cases where results are not repeatable through controlled observation**.

Most (if not all) mysterious quantum effects disappear at the level of everyday objects, so the odds of these kinds of things actually causing a practical problem for science as it is routinely practiced are vanishingly small.
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> So my question is whether this result disproves usefulness, credibility or validity of scientific method?
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At the worst, it only means that the scientific method is in some need of revision.

Understand that what we call the scientific method is, even at the present, in no way the provably-best method that we can use. Like eating, breathing, not tormenting prides of hungry lions, and logical argumentation, it is just one of an increasingly elaborate suite of "best practices" that we have settled upon for achieving certain objectives; in this case, being able to reliably predict or even control certain pieces of the universe about us.

If you want to be skeptical of the "validity" of the scientific method, you don't have to wait for an exotic experiment to come about to vindicate your doubts. But at the same time, the existence of an exotic experiment doesn't invalidate all of the past successes of the scientific process. What it would indicate — as with all scientific revolutions — is that *reality is more subtle than we previously thought*, and that our methodology is in some need of revision. It's not clear in advance what this revision would look like, but whatever the new methods are, there should **also** be a good explanation in retrospect — as was true with, for instance, Newtonian mechanics — why it worked so well for so long, if it was wrong. And we can expect that the answer will be that it *wasn't very wrong*, just *somewhat wrong*, and that the degree of wrongness only became apparent in newly discovered and somewhat exotic circumstances.

Science as it is practiced now may not be science as it is practiced a thousand years in the future: but we may regard it as being part of the same continuous tradition if it remains concerned with *somehow* going *very carefully and precisely about* finding out how the world works. It might be running up a blind alley a thousand years hence, or we might currently be doing so now; but science is not about being *right* (which we cannot verify), but by doing our methodical best to be *the least wrong that we can manage*.