Even Physicists Don’t Understand Quantum Mechanics

Quantum mechanics, assembled gradually by a group of brilliant minds over the first decades of the 20th century, is an incredibly successful theory. We need it to account for how atoms decay, why stars shine, how transistors and lasers work and, for that matter, why tables and chairs are solid rather than immediately collapsing onto the floor. Scientists can use quantum mechanics with perfect confidence.

But it’s a black box. We can set up a physical situation, and make predictions about what will happen next that are verified to spectacular accuracy. What we don’t do is claim to understand quantum mechanics.

Physicists don’t understand their own theory any better than a typical smartphone user understands what’s going on inside the device. There are two problems. One is that quantum mechanics, as it is enshrined in textbooks, seems to require separate rules for how quantum objects behave when we’re not looking at them, and how they behave when they are being observed.

When we’re not looking, they exist in “superpositions” of different possibilities, such as being at any one of various locations in space. But when we look, they suddenly snap into just a single location, and that’s where we see them. We can’t predict exactly what that location will be; the best we can do is calculate the probability of different outcomes.

The whole thing is preposterous. Why are observations special? What counts as an “observation,” anyway?

When exactly does it happen? Does it need to be performed by a person? Is consciousness somehow involved in the basic rules of reality?

Together these questions are known as the “measurement problem” of quantum theory.

Source: nytimes.com