April 14, 2026 -- Imagine you’re baking a cake. You carefully follow the recipe, measuring ingredients and mixing them precisely. In the end, you have a delicious dessert.

A well-written cake recipe should produce a perfect cake every time because it tells you what to do. But it doesn’t explain why it works. It doesn’t tell you that sugar must be mixed with butter to create tiny air pockets that expand while baking, for example.

We can make a similar observation about the science of quantum mechanics. While quantum mechanics’ predictive abilities – the recipe of quantum, if you will - repeatedly produce accurate results, the interpretation of why it works hasn’t been settled. And without that interpretation, quantum mechanics can often seem contradictory to the physics of everyday life. In fact, quantum can come across as downright weird. Look no further than Heisenberg’s uncertainty principle, which states that it’s impossible to simultaneously know a particle’s exact position and momentum.

“If a particle has a definite position, does that mean it has no momentum? Or just that you can’t know the momentum?” asks David Schmid, PSI Fellow at Perimeter. “There’s no accepted consensus to these kinds of questions.”

“If we had a proper theory – which some people call interpretation – it would answer those questions. There would be no debate or confusion about it,” explains Schmid.

At Perimeter Institute, researchers in quantum foundations are rejecting the idea that they must simply accept that quantum mechanics is weird. Using rigorous, systematic approaches, researchers aim to strengthen quantum theory by taking the recipe of quantum mechanics and finding the why underneath it all.

Different quantum views

The physics that shape our universe can be divided into two types: classical and quantum. Classical physics covers the forces the govern our everyday lives – Newtonian forces, thermodynamics, and so on. The story of an apple falling out of a tree and striking Newton on the head is an illustration of classical physics at work.

Quantum physics takes over at the smallest scales of matter and energy: the realm of fundamental particles like electrons and photons. At the quantum level, mathematics and experimentation have revealed a seemingly alien world.

Perhaps most famously, a particle’s quantum state – the mathematical information that describes the particle’s characteristics like energy, location, and spin – is described with something called a wave function.

“Even if you know the quantum state, the outcomes of measurement are probabilistic,” explains Marina Maciel Ansanelli, resident PhD student at Perimeter. Imagine measuring a quantum system to determine spin, which can be measured as ‘spin up’ or ‘spin down’. “The wave function can tell me that when I measure the spin of a particle, there will be a 60 percent chance of seeing spin up and a 40 percent chance of seeing spin down. But it does not tell me for sure what spin orientation I am going to see.”

But what does that actually mean for reality outside of a mathematical equation?

A survey published last year by Nature dug into physicists’ views on quantum mechanics. With more than 1,100 respondents, the survey found that there is no consensus on what quantum tells us about the reality of the universe. When polled about the wave function, only 36% of respondents agreed that a wave function represents reality.

The leading theory of wave functions, the Copenhagen interpretation, suggests that a wave function represents future possibilities that ‘collapse’ into a single reality when measured. Another interpretation is called ‘Many-Worlds,’ which posits that all the possible outcomes of a quantum measurement are real, but they occur simultaneously in parallel universes. A third is pilot wave theory, in which waves and particles are separate objects, with a wave guiding a particle’s path. None of these theories, nor any others, have majority support among physicists.

What is the goal of the theory of quantum mechanics?

Understanding why researchers have such diverse viewpoints on quantum mechanics requires an understanding of the different scientific philosophies guiding researchers. Many set aside interpretation and simply work with the results.

“Most people treat quantum theory as a recipe to obtain predictions,” explains Maciel Ansanelli, resident PhD student at Perimeter. “And if you believe that is the sole goal of a scientific theory, obtaining predictions, then you are an operationalist or empiricist.”

Even within quantum foundations there are people in both camps. Not all researchers in quantum foundation are scientific realists, and many operationalists are working to better understand quantum theory.

For Maciel Ansanelli herself, the goal of science is not just to predict things, but to actually understand why things are the way they are. “I think understanding the correct underlying reality might guide us to the next theories, to really understand topics like quantum gravity, for example.

“I don’t like to say quantum is weird,” she says. “I want to understand it.”

Separating the quantum world from the classical

One promising avenue forward for those looking for a clearer interpretation of quantum theory is to narrow down the exact places where quantum differs from the classical world.

“There are two angles we take: we rule out certain phenomena as being weird by constructing explicit classical models for them, while on the flip side, we prove that remaining quantum phenomena are rigorously non-classical according to some well-motivated definition,” says Schmid. “There are a lot of phenomena that we don’t know yet which camp they’re in.”

One way that researchers interrogate a phenomenon is a tool called a toy model. A toy model can be used to construct a universe with no quantum mechanics, instead using only classical principles to define its world. Researchers then try to recreate a quantum phenomenon in their toy theory using only classical rules.

Toy theories can push researchers to consider alternatives to quantum explanations for ‘weird’ phenomena. But toy theories are just a tool for probing quantum mechanics. They’re not meant to represent reality. “The model can’t be extended to reproduce all possible phenomena,” says Schmid. “It just reproduces the specific phenomena that people have claimed are sufficient to include all this weirdness – and we’re saying, no, these phenomena are perfectly understandable in isolation. But once you start looking at everything together, you can’t reproduce all of it.”

That leads to the next part of Schmid’s research: trying to pick out the phenomena that can’t be explained classically. “There are certain quantum phenomena that do resist classical explanation,” he says. “Not just because we don’t see how to do it, but because we’ve proven theorems that show that, given our assumptions, these particular phenomena will never have classical explanations. It’s impossible.”

For example, one phenomena that’s stood up to interrogation is Bell nonlocality, where the outcomes of measurements on two entangled particles far away from one another show a quantitative signature of non-classicality.

“We’re trying to build rigorous theorems to pick out the specific phenomena that are actually weird.”

Why researchers need to look beyond the quantum recipe

“When quantum theory came about, it contained a lot of abstract mathematical symbols that are sufficient to let you make predictions. But nowhere is there a clear specification of the things that exist and the properties they have,” explains Schmid. “When you frame it that way, you realize how much work we have left to do.”

A proper quantum theory would eliminate debate and confusion, explains Schmid. To achieve this, quantum theory must include a clear specification of what’s called the ontology and then the dynamics.

“The ontology means a specification of exactly what exists,” says Schmid. “Are they particles? Are they waves? Or are they something else? What properties do they have?” And the dynamics, he explains, would explain how quantum systems and their properties would evolve over time.

It’s important to interpret quantum theory not only to solidify our understanding of the quantum world, but to explore applications to other fields. “We don’t yet know how to apply quantum theory in gravity or causal inference or machine learning,” says Schmid. “What are the consequences of quantum theory for all these other fields of science? That’s still very much an open question.”

The search to fill in the physics beneath the quantum recipe card continues. “There’s no reason we can’t eventually construct a better theory that is compelling,” says Schmid. “That’s what we’re trying to do.”