THE CAT IS IN QUESTION; THE SCHRODINGER IS NOT:

So, what is going on here? How can a particle be in two places at the same time? This is also akin to asking whether particles have properties in and of themselves. Why should making a measurement change anything? And what exactly is a measurement? Do you need a person to make a measurement, or can you say that any interaction at all with the rest of the world is a measurement?

These kinds of questions have spawned a library's worth of so-called quantum interpretations. Some of them try to preserve the classical worldview by finding some way to minimize the role of measurement and preserve the reality of the quantum state. Here, "reality" means that the state describes the world by itself, without any reference to us. At the extreme end of these is the "Many Worlds Interpretation," which makes each possibility in the quantum state a parallel Universe that will be realized when a quantum event -- a measurement -- happens.

This kind of interpretation is, to me, a mistake. My reasons for saying this are simple.

When the inventors of quantum mechanics broke with classical physics in the first few decades of the 1900s, they were doing what creative physicists do best. They were finding new ways to predict the results of experiments by creatively building off the old physics while extending it in ways that embraced new behaviors seen in the laboratory. That took them in a direction where measurement began to play a central role in the description of physics as a whole. Again and again, quantum mechanics has shown that at the heart of its many weirdnesses is the role played by someone acting on the world to gain information. That to me is the central lesson quantum mechanics has been trying to teach us: That we are involved, in some way, in the description of the science we do.

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