'' I THINK I can safely say that nobody really understands quantum mechanics.'' observed the physicist and Nobel Laureate Richard Feynman.

That's not surprising, as far as it goes. Science makes progress by confronting our lack of understanding, and quantum mechanics has a reputation for being especially mysterious.

What's surprising is that physicists seem to be O.K. without understanding the most important theory they have.

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 to account it 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 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 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 ''super positions'' of different possibilities., such as being at any one of various locations in space. But when we look, they suddenly snap into just one 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 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.

The other problem is that we don't agree on what it is that quantum theory actually describes, even we're not performing measurements.

We describe a quantum object such as an electron in terms of a ''wave function,'' which collects the superposition of all the possible measurement outcomes into a single mathematical object.

When they're not being observed, wave functions evolve according to a famous equation written down by Erwin Schrodinger.

But what is the wave function? Is it a complete and comprehensive representation of the world? Or we do need additional physical quantities to fully capture reality as Albert Einstein and others suspected?

Or does the wave function have no direct connections with reality at all, merely characterizing our personal ignorance what we will eventually measure in our experiments?

Until physicists definitely answer these questions, they can't really be said to understand quantum mechanics - thus Feynman's lament.

The honor and serving of the latest operational research on Quantum Physics and Mechanics, continues. The World Students Society thanks author Sean Carroll.


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