A whole new view of the Universe became accessible to humanity when classical rules that governed electricity, magnetism and light didn’t necessarily apply to the smallest, subatomic scales.
There are 10 essentials of quantum mechanics that will give us pause on how we “picture” the Universe.
- Everything is quantum. Everything obeys the same laws of quantum mechanics — it’s just that quantum effects of large objects are very hard to notice.
- Quantization doesn’t necessarily imply discreteness. “Quanta” are discrete chunks, by definition, but not everything becomes chunky or indivisible on short scales.
- Entanglement not the same as superposition. A quantum superposition is the ability of a system to be in two different states at the same time, and yet, when measured, one always finds a particular state, never a superposition. Entanglement on the other hand is a correlation between two or more parts of a system — something entirely different.
- There is no spooky action at a distance. Nowhere in quantum mechanics is information ever transmitted non-locally, so that it jumps over a stretch of space without having to go through all places in between. Entanglement is itself non-local, but it doesn’t do any action — it is a correlation that is not connected to non-local transfer of information or any other observable. When you see a study where two entangled photons are separated by a great distance and then the spin of each one is measured, there is no information being transferred faster than the speed of light. In fact, if you attempt to bring the results of two observations together (which is information transmission), that information can only travel at the speed of light, no faster!
- Quantum physics an active research area. Quantum optics, quantum information, quantum computing, quantum cryptography, quantum thermodynamics, and quantum metrology are all recently formed and presently very active research areas.
- Einstein didn’t deny it. He said something else is out there but he didn’t research it because he was older and knew he’d have to rededicate his life to it. He left that to other scientists. Einstein instead argued that the quantum theory was incomplete, and believed the inherent randomness of quantum processes must have a deeper explanation.
- It’s all about uncertainty. The central postulate of quantum mechanics is that there are pairs of observables that cannot simultaneously be measured, like for example the position and momentum of a particle. In quantum mechanics, this uncertainty is fundamental, not due to experimental shortcomings.
- Quantum effects are not necessarily small… We do not normally observe quantum effects on long distances because the necessary correlations are very fragile. Treat them carefully enough, however, and quantum effects can persist over long distances.
- …but they dominate the small scales. In quantum mechanics, every particle is also a wave and every wave is also a particle. The effects of quantum mechanics become very pronounced once one observes a particle on distances that are comparable to the associated wavelength. This is why atomic and subatomic physics cannot be understood without quantum mechanics, whereas planetary orbits are effectively unchanged by quantum behavior.
- Schrödinger’s cat is dead. Or alive. But not both. It was not well-understood in the early days of quantum mechanics, but the quantum behavior of macroscopic objects decays very rapidly. This “decoherence” is due to constant interactions with the environment which are, in relatively warm and dense places like those necessary for life, impossible to avoid. We now understand that while small things like atoms can exist in superpositions for extended amounts of time, a large object would settle extremely rapidly in one particular state. That’s why we never see cats that are both dead and alive.
This post was contributed to Starts With A Bang by Sabine Hossenfelder. Sabine is a theoretical physicist specialized in quantum gravity and high energy physics. She also freelance writes about science.
“In fact, the mere act of opening the box will determine the state of the cat, although in this case there were three determinate states the cat could be in: these being Alive, Dead, and Bloody Furious.” –Terry Pratchett
10 Quantum Truths About Our Universe was the source for this post.