"The real amount of information out there is no more than the amount in our head." If it is only "out" there, then it is not "in" our head. Where did your "information about physics" come from, if it was not in papers, books and the minds of your professors, before it got copied into your head, and probably had to overwrite older information stored there, in order to make room for it?
"Our brains can only hold a hundred terabytes of information which is tiny compared to what is required to determine the physical position of all the particles around us" - Or in us. The information content of either a computer or a brain, is not just that stored in its "memory". It requires much more information, to specify how to construct the computer, or brain, in the first place.
"This computer is not a real thing." That is your illusion. The universe merely "computes" itself, by simply being itself, just like every other computer, brain or being; things can only be whatever they are, and can only do whatever it is that they do. Humans do not have enough information storage capacity, to ever store all the information contained within all these other beings. That is no cause to believe that such other things, do not exist.
Information has nothing to do with consciousness, thought or life. As Shannon stated on the first page of his A Mathematical Theory of Communication: "semantic aspects of communication are irrelevant to the engineering problem." In other words, his conception of "information" has nothing to do with "meaning", it is simply a "quantifiable", observable pattern, encoded into an observable, physical "substance", waiting to be correctly recognized, by some other entity in the future. The fact that such an entity may not have appeared yet, and correctly copied and "decoded" that information into its circuitry, or brain, has no bearing on the existence of the information "out there"; if I write a note on a piece of paper, and cast it into the wind, the fact that some other being does not yet know that it exists, much less know what I wrote on it, is irrelevant to the fact that the paper, with its writing, does exist, and may be eventually discovered and "correctly decoded", by something.
You seem to be totally ignoring the fact that the key word in the title of Shannon's paper, is the word communication - thus, Shannon's "information" is entirely concerned with a possibility, the potential, to transfer (AKA communicate) "information", from one inanimate entity to another, without any "thought" or "meaning" entering into the process - such as the process embodied in an inanimate radio receiver. Some other entity, like a human being, may subsequently come along and attempt to attach some "meaning" onto this acquired "information", but as Shannon stated, that is "irrelevant to the engineering problem", involving the "information transmission" itself.
Rob McEachern