What is quantum mechanics? | New Scientist

Quantum mechanics is the best tool we have to understand how the universe works on its smallest scales. Everything we can see around us, from far-off galaxies to our own bodies, is made up of subatomic particles, unimaginably tiny entities whose interactions produce the macroscopic effects we experience day-to-day. While it’s tempting to imagine that these interactions obey the laws of physics that we’re familiar with in our everyday lives, they are actually much much stranger.

One of the first physicists to confront this strangeness head-on was Max Planck. In order to explain unusual observations produced when objects were heated to high temperatures, he made a radical assumption. Instead of energy being emitted in a continuous stream, he assumed that there must be some indivisible base unit of energy that could be split no further. In other words, energy could only be exchanged in finite chunks, which he called quanta.

While Planck only came up with this idea in order to simplify his calculations, other physicists rapidly leaped on the real-world implications. Over the coming decades, Albert Einstein, Niels Bohr, Werner Heisenberg, Erwin Schrödinger and others completely restructured the standard picture of reality.

Quantum superposition or quantum entanglement concept illustration. Superposition is the ability of a quantum system to be in multiple states at the same time until it is measured. Quantum entanglement is a physical phenomenon that occurs when pairs or groups of particles are generated or interact in ways such that the quantum state of each particle cannot be described independently.

Rethinking reality: Is the entire universe a single quantum object?

In the face of new evidence, physicists are starting to view the cosmos not as made up of disparate layers, but as a quantum whole linked by entanglement

The new picture that emerged showed a world totally unlike the one we knew. A world where objects could travel through walls, particles led parallel lives as waves, and information appeared to be transmitted faster than the speed of light. Many of these apparent paradoxes are so mind-bending as to have entered popular culture. Perhaps most famous is the case of Schrödinger’s cat, which imagines a cat trapped in a box that is both dead and alive until somebody bothers to look inside. Small wonder Nobel laureate Richard Feynman supposedly said: “If you think you understand quantum mechanics, you don’t understand quantum mechanics.”

Not that physicists have stopped trying. In their attempts to make sense of quantum weirdness, they have come up with a host of different interpretations of the mathematics at the theory’s heart. As of the time of writing, it remains anyone’s game.