Size of a quantum computer to effectively calculate macroscopic reality from quantum mechanics Assuming the correctness of QM: Would the size of such a computer be smaller than the observable universe? If it were to represent all available information in the universe it seems that it's minimal necessary size would relate to a black hole of a certain mass. Would this lead us to believe this theoretical quantum computer (assuming it didn't represent itself) could be constructed smaller than the universe? Or if the information content of an object is truly expressed in relation to a surface area is the universe the object with the minimal surface required to represent the totality of it's information? 
 A: If you are looking for the exact simulation of the whole universe, the answer is definitely no!
Because of this technical issue, that the computer itself is unfortunately a part of this universe, therefor it has to simulate itself as well alongside the rest of the universe! This means that the computer should produce results of its own calculations in the future (as well as the rest of the universe), which itself contains the whole simulation of the universe and the state of the computer, and again in the state of the computer the same thing is embedded again and again.
The other issue of a computer simulating itself is that it should produce its own results before they are even produced :)
In-fact larger grained simulations are possible(although not 100% accurate) and doable(even nowadays). Or if our universe had some fractal structure, then some smaller parts of it(like our computer) could represent its whole; which is unfortunately not the case.
A: Assuming the correctness of QM, you can encode $2^{n}$ complex amplitudes with the computational basis of n entangled qubits. This suggests that the answer to the question is yes, much smaller than the universe in fact.
Unfortunately quantum computing technology isn't there yet to maintain useful amount of entangled qubits, or getting that much information out of the qubit system for that matter.
This is one of those questions that makes studying quantum computation very interesting.
