I have a complaint about the claim "We see that [the wavefunctions of] chairs and tables are collapsed". It seems obvious that it's true, but think about what it would mean to be otherwise.
In quantum mechanics, the behavior of a superposition (or mixture--there is a technical difference which isn't important here) is completely determined by the behavior of the corresponding pure states. Suppose you set things up so that there is a consequence of being in one state or another:
- If the system is in state |A\rangle, then consequence C_A happens.
- If the system is in state |B\rangle, then consequence C_B happens.
Then if the consequence itself is governed by quantum-mechanical laws, then we conclude:
If the system is in a superposition/mixture of states |A\rangle and |B\rangle, then the consequence will be a superposition/mixture of C_A and C_B
So how does this apply to tables and chairs? Well, suppose you have a folding chair, and for simplicity, we consider two states, either "open" or "folded". So you take a notebook and walk into the room where the chair is, resolved to record what you see:
- If it is open, you write "open".
- If it is folded, you write "folded".
- If it is in a superposition or mixture of these two states, you write "both"
Well, according to QM if you yourself are governed by quantum mechanics, then you'll never write "both". Instead, what will happen is:
- If it is open, afterward the notebook will contain the word "open"
- If it is folded, afterward the notebook will contain the word "folded"
- If it is in a superposition or mixture, afterward the notebook will be in a superposition or mixture of having the word "open" and having the word "folded"
There is no possibility of your writing the word "both" in the notebook (at least not if we assume that you always write "open" if it's open, and "folded" if it's folded)
Another way to say it is that the three possible consequences: write "open", write "folded", write "both" are contradictory; if the first two happen, then the third will never happen.
Note: this is assuming that you yourself are governed by quantum mechanical laws. Some
interpretations of quantum mechanics treat observers as special cases. But in these interpretations, observing the chair causes its wavefunction to "collapse". So you wouldn't write "both" in that interpretation, either.