Imagine the weekend paper opening and looking through the puzzle pages for the Sudoku. You spend your morning working through this logical puzzle, just to discover with the last few squares that there is no consistent way to finish it.
“I must have made a mistake,” you think. So try again, this time starting from the corner you could not finish and work back the other way. But the same thing happens again. You are down to the last few squares and find that there is no consistent solution.
Working out the basic nature of reality according to quantum mechanics is a bit like Sudoku impossible. Wherever we start with quantum theory, we always end at a puzzle that forces us to rethink how the world basically works. (This is what makes so much fun for oceanic mechanics.)
I will take you on a short journey, through the eyes of a philosopher, of the world according to quantum mechanics.
1. Spout-at-a-distance action
As far as we know, the speed of light (about 300 million meters per second) is the limit of the ultimate speed of the universe. Albert Einstein was famous for expecting that physical systems would collide faster than a light sign could travel between them.
Back in the 1940s, Einstein called it a “spout-at-a-distance action”. When quantum mechanics earlier seemed to predict such sputum events, he said the theory doesn’t have to be finished yet, and some better theory would tell the real story.
We know today that there is very likely to be a better theory like that. And if we believe that the world is made up of clearly independent pieces of “material”, our world must be one where sputtering action at a distance between these pieces of material is allowed.
2. Opening our grasp of truth
“What if the world isn’t made up of well-defined independent pieces of ‘material’?” I hear you say. “Then can we avoid this act of bragging?”
Yes, we can. And many in the quantum physics community think this way too. But this would not be a comfort to Einstein.
Einstein had a long discussion with his friend Niels Bohr, a Danish physicist, about this very question. Bohr argued that we should indeed give in to the idea that the material of the world would be well-defined, so that we can avoid spout-at-a-distance action. In Bohr’s view, the world has no definite characteristics if we do not look at it. When we are not looking, Bohr thought, the world as we know it does not really exist.
But Einstein insisted that the world had to be done something whether we look at it or not, otherwise we could not talk to each other about the world, and science as well. But Einstein could not have both a fully-fledged independent world and no sputum action at speed… or could he?
3. Back in the future
The Bohr-Einstein debate is well known for fare in the history of quantum mechanics. So unfamiliar is the smoky corner of this quantum logical puzzle where we can save both an independent world with good definition and no sputum action. But we have to be weird in other ways.
If a test to measure a quantum system in the laboratory could affect what the system looked like before the measurement, Einstein could eat and eat his cake as well. This idea is called “retrocausality”, because the effect of this test would have to travel “back in time”.
If you think this is weird, you are not alone. This is not a very common view in the quantum physics community, but it has supporters. If you are opposed to taking sputum action at a distance, or have no knowledge of the world when we are not watching, revocation does not seem to be a strange choice after all.
4. No view from Olympus
Imagine Zeus standing at the top of Mount Olympus, exploring the world. Imagine being able to see everything that happened and will happen, everywhere and all the time. Say this is the “vision of the eye of God” of the world. It is natural to think that there must be some way to the world, even though only an all-knowing God can know it.
A recent study in quantum mechanics reveals that God ‘s view of the world is impossible, even in principle. In some strange quantum situations, different scientists can look carefully at the systems in their laboratories and make detailed recordings of what they see – but they will not agree about what happened when they come to compare notes. And there may not be a complete truth about who is right – not even Zeus would know!
So the next time you encounter an impossible Sudoku, be sure to be in good company. The whole quantum physics community, and maybe even Zeus himself, knows just how you feel.
Peter Evans is an ARC Early Career Research Fellow at the University of Queensland.
This article originally appeared on An Còmhradh.