The standard interpretation of quantum mechanics places a lot of emphasis on the act of measuring. Before scaling, quantum systems exist in many states simultaneously. After a measurement, the system “collapses” to a set value, so it’s only natural to ask what’s really going on when measurements aren’t made. There is no clear answer, and the different ideas can go in some really wild directions.

One of the first lessons physicists learned when they began examining subatomic systems in the early 20th century was that we do not live in a deterministic universe. In other words, we cannot accurately predict the outcome of each trial.

For example, if you fire a beam of electrons through a magnetic field Half of the electrons will be bent in one direction while the other half will be bent in the opposite direction. While we can construct mathematical descriptions of where the electrons are headed as a group, we cannot say which direction each electron will take until we have actually run the experiment.

in a Quantum mechanics This is known as an overlay. For any experiment that can yield many random results, before a measurement is made the system is said to be in a superposition of all possible states simultaneously. When we make a measurement, the system “collapses” into a single state that we observe.

Quantum mechanics tools exist to make sense of this mess. Instead of giving accurate predictions about how a system will evolve, quantum mechanics tells us how a superposition (which represents all the different outcomes) will evolve. When we make a measurement, quantum mechanics tells us the probabilities of one outcome over another.

And that’s it. Standard quantum mechanics is silent as to how this superposition actually works and how measuring the task of superposition collapse leads to a single result.

Schrödinger’s cat
If we take this line of reasoning to its logical conclusion, analogy is the most important action in the universe. It turns arcane possibilities into tangible results and transforms an exotic quantum system into verifiable results that we can interpret with our senses.

But what does that mean for quantum systems when we don’t measure them? What does the universe really look like? Is everything there but we are simply unaware of it, or does it have no definite state until a measurement is made?

Ironically, Erwin Schrödinger, one of the founders of quantum theory (it’s his equation that tells us how superposition will evolve over time), criticized this line of thinking. He developed his famous cat-in-a-box thought experiment, now known as Schrödinger’s cat To show how silly quantum mechanics is.

This is a very simplified version. Put a (live) cat in a box. Also put in the box some kind of radioactive element associated with the release of poisonous gas. It doesn’t matter how you do it; The point is to introduce some component of quantum uncertainty into the situation. If you wait a while, you won’t know for sure if the item has worn off, so you won’t know if the poison was released and therefore whether the cat is alive or dead.

In an accurate reading of quantum mechanics, the cat is neither alive nor dead at this point; It exists in a quantum superposition of both the living and the dead. Only when we open the box will we know for sure, and it is also the act of opening the box that allows this superposition to collapse and the cat’s existence (suddenly) in one state or another.

Schrödinger used this argument to express his surprise that this could be a coherent theory of the universe. Do we really think that until we open the box, the cat isn’t really “there” – at least in the normal sense that things are always definitely dead or alive, not both at the same time? For Schrödinger, this was too far, and he stopped working on quantum mechanics shortly thereafter.

decoherence
One response to this strange condition is to point out that the macroscopic world does not obey quantum mechanics. After all, quantum theory was developed to explain the subatomic world. Before we had experiments revealed how atoms It worked, there was no need for superposition, probabilities, scaling, or anything else quantum related. We had normal physics.

So it makes no sense to apply quantitative rules where they don’t belong. Niels Bohr, another founder of quantum mechanics, proposed the idea of ”decoherence” to explain why subatomic systems comply with quantum mechanics while macroscopic systems do not.

From this point of view, what we understand as quantum mechanics is true and complete for subatomic systems. In other words, things like superposition do happen to small particles. But something like a cat in a box is certainly not a subatomic system; A cat is made up of trillions of individual particles, all constantly vibrating, colliding, and scrambling.

Every time two of these particles collide with each other and interact, we can use quantum mechanics to understand what is going on. But once a thousand, a billion, trillions or trillions of particles enter the mix, quantum mechanics loses its meaning – or “decoheres” – and is replaced by ordinary microscopic physics.

From this point of view, one electron – not a cat – can exist in a box in a strange superposition.

However, this story has limits. Importantly, we have no known mechanism for translating quantum mechanics into macroscopic physics, nor can we point to a specific scale or situation at which the switching occurs. So, while it looks good on paper, this decoherence model doesn’t have a lot of solid support.

So does reality exist when we don’t search? The final answer is that it seems to be a matter of interpretation.