If you think you understand quantum mechanics, go stand in the corner in a dunce’s hat

_{Graphic: MIT}

Can you get your head around quantum mechanics or does your brain go foggy? It’s a fascinating subject one turns to again and again trying for a glimmer of understanding. Simplistically, Einstein’s theory of general relativity attempts to describe the very large while quantum mechanics looks at the very small, subatomic and beyond. Weird things happen. A particle can be a wave and a particle at the same time. Observe a particle even at a considerable distance and it will move. Shift a particle here and another one in Australia or somewhere faraway like Mars, will move too. In the realm of quantum mechanics, you get into the daft world of string theory and time travel appears possible.

The experts are as mystified by quantum mechanics as the rest of us:

NIELS BOHR: If quantum mechanics hasn’t profoundly shocked you, you haven’t understood it.

ALBERT EINSTEIN: As far as the laws of mathematics refer to reality, they are not certain, and as far as they are certain, they do not refer to reality.

RICHARD FEYNMAN: Science is imagination in a straitjacket. It is ironic that in the case of quantum mechanics the people without the straitjackets are generally nuts.

YUVAL NOAH HARARI: The theory of relativity and quantum mechanics argue that you can twist time and space, that something can appear out of nothing and that a cat can be both alive and dead at the same time. This makes a mockery of our common sense.

STEPHEN HAWKING: Quantum physics tells us that no matter how thorough our observation of the present, the (unobserved) past, like the future is indefinite and exists only as a spectrum of possibilities.

CARL SAGAN: There is an idea — strange, haunting, evocative — one of the most exquisite conjectures in science or religion . . . An infinite hierarchy of universes, such as an electron, would if penetrated, reveal itself to be an entire enclosed universe. Within it, organised into the local equivalent of galaxies and similar structures, are an immense number of other, much tinier particles, which are themselves universes at the next level, and so on forever — an infinite downward regression, universes within universes endlessly. And upward as well. Our familiar universe of galaxies and stars would be a single elementary particle in the next universe up, the first step of another infinite regress.

(We looked at trying to give you an account of what the local universities are up to in the weird field of quantum mechanics, but started to get a headache . . . )

Then there’s the story of Professor Schrodinger’s cat: Mr S took his pet to the vet. The doctor examined it and said, “Mr Schrodinger, about your cat, I have good news and bad news.”

The immortal Terry Pratchett: “What’re quantum mechanics? I don’t know. People who repair quantums, I suppose.”

We close with a favourite story about professors: On the ocean floor there is a certain kind of sea urchin, who gets around at first with a brain. When he finds the perfect place to roost for the rest of his life, he eats his own brain. Just like a tenured professor.