This will be the philosophy post about the nature of existence–or metaphysics–with respect to anti-realism and realism.
Realism is essentially the idea that there is a world “out there,” independent of those who observe it. There is some sort of “objective reality.” Einstein once said it this way (paraphrasing): “That which is real is that which doesn’t go away when you close your eyes.”
Anti-Realism, on the other hand, can refer to the idea that there is no objective reality or the idea that there is no fact of the matter as to the truth value of provably unknowable statements.
The only realist perspective on Quantum Mechanics I’ve heard is a multiverse interpretation in which every possible state of a particle is realized in some universe. The anti-realist perspective is the state of particles has to do with their observability. Any attempt to observe the state of a particle collapses the superposition of states down to one. In this way, there is no objective reality of the particle that is independent of observers. I like to think, from a realist perspective, that there is a physical reality of particles, and those particles are sensitive in nature. This sensitivity is what accounts for the supposed dependence on observers. I know friends who define reality in terms of interactions. That’s another interesting idea that I won’t get into.
The following is a message to a friend about my stance on realism vs antirealism:
I am also mostly in the realist camp, save for some startling facts in mathematics. Gödel proved that in any sufficiently robust system of logic, there are statements which can’t be known to be true. Physicists call it the “provably unknowable.” even more troubling for me are the natures of logic and mathematics themselves. It seems to me that all of the conditional statements I’ve proven were true regardless of the fact that I proved them. They were true regardless of the fact that so-and-so proved them first. They are true, indeed, regardless of the fact that I live in a universe with matter and time. This is very troubling to my realist views, since it suggests that logic itself “exists” in some way independently from the universe. That is to say, logical truths don’t “exist out there” in the same way that the charge of an electron exists out there. So far, my solution has been to accept two special categories of existence: conditional truths / formal logic, and the “physical” universe in which I live (which may include any higher dimensions or multiple universes we may discover or which we may not discover but might actually exist). This is horribly unsatisfying for me. What do you think?