Because, as far as we can tell, everything that is part of our universe is governed by physics.

Our brains are part of this universe, and conciousness is dependent on our brains.

> Because, as far as we can tell [...] conciousness is dependent on our brains.

This is neither a logical/mathematical proof, nor an empirically established fact. So how do you know? Why are you making statements of faith in what seems to be the scientific worldview, when the actual scientific worldview is that we should never make statements of faith?

It's as established empirically as we can observe. Shut off oxygen to your brain for ten minutes or put a bullet through it and determine its responsiveness thereafter.

>everything that is part of our universe is governed by physics.

Roughly 68% of the observable universe cannot be explained by physics ("dark matter").

What's the alternative?

Lets assume there is some sort of physical process involved that we don't understand or even know about (unlikely), it would still be part of the physics that govern our universe.

The alternative, according to the scientific method is: "We don't know"

> Lets assume there is some sort of physical process involved

You're begging the question. Why is "some sort of physical process" the only hypothesis space you're considering?

Whatever it is, it follows a deterministic ruleset, else there be madness. If it follows a deterministic ruleset, and we can observe it directly or indirectly, and write those rules down- theorize about those rules - we can allmost call it physics.

If the feeling of beeing a clock, winds up a spring in the clock that works a mechanism that feels like fear on beeing predictable (aka exploitable) - that does not make the clock less observable.

At the very bottom of physics, if we ever reach it with our observations and theories, there will be something that simply is, and is not explained by the interactions of some sub-system. The foundational elements of physics are probably non-conscious (assuming the currently known particles and fields are indeed non-conscious).

What grounds do we have for asserting as certain that consciousness is not a foundational thing-that-simply-is, but must definitely be composed from sub-systems that are themselves non-conscious?

Quantum physics has thrown a wrench into the 17th century Newtonian theory of the universe being totally mechanical, like a game of billiards.