Physicist Erwin Schrödinger summarized this theory in 1935 with his famous cat paradox – using the metaphor of a cat in a closed box that is both dead and alive until the box is opened, thus collapsing the cat's condition and revealing its fate.

However, applying these rules to real-world scenarios faces challenges, and this is where the real paradox emerges. While quantum laws apply to the world of elementary particles, larger objects behave according to classical physics as predicted by Einstein's theory. General theory of relativity , and are never observed in a superposition of states. Describing the entire universe using quantum principles poses even greater hurdles, as the universe appears to be quite classical and lacks any external observer to serve as a measuring device for its state.

“The question is, can the universe, which has no surrounding environment, exist in such a superposition?” Lead author Matteo Carliso The theoretical physicist at the University of Trieste in Italy told Live Science in an email. “The observations say no: everything goes according to the classical predictions of general relativity. So, what breaks such a superposition?”

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To address this question, Carleso and his colleagues proposed modifications to the Schrödinger equation, which governs how all states, including those in superposition, evolve over time.

“Specific modifications to the Schrödinger equation could solve the problem,” Carleso said. In particular, the team added terms to the equation that explain how the system interacts with itself, as well as adding some other specific terms. This in turn leads to the collapse of the superposition.

“Such effects are stronger the larger the system,” Carleso added.

Importantly, these modifications have little effect on microscopic quantum systems, such as atoms and molecules, but allow larger systems – such as the universe itself – to collapse at recurring intervals, giving them specific values that fit our observations of the universe. The team described the modified Schrödinger equation in February in the journal Journal of High Energy Physics .

Remove the cat from the disinfectant
Illustration of an atom (Image credit: Getty Images)
In their modified version of quantum physics, the researchers eliminated the distinction between measured objects and measuring devices. Instead, they proposed that the state of each system undergoes spontaneous collapse at regular intervals, causing it to acquire specific values for some of its attributes.

For large systems, spontaneous collapse occurs frequently, making them classic in appearance. Subatomic objects interacting with these systems become part of them, leading to the rapid collapse of their state and the acquisition of specific measurement-like coordinates.

“With no action on the part of external entities, any system automatically settles (or collapses) into a certain state,” Carleso said. “Instead of a cat being dead and alive, one finds it dead or alive.”

The new model may explain why we… Free time Geometry does not exist in a superposition of states and is governed by the classical equations of Einstein's theory of relativity.

“Our model describes a quantum universe that eventually collapsed and effectively became classical,” Carleso said. “We have shown that models of spontaneous collapse can explain the emergence of the classical universe from a quantum superposition of universes, where each of these universes has a different geometry of space-time.”

While this theory may explain why the universe appears to be governed by the laws of classical physics, it does not make new predictions about large-scale physical processes.

However, it makes predictions about how atoms and molecules will behave, albeit with minimal deviations from classical quantum mechanics.

As a result, testing the modified quantitative model will not be so simple. Future work will aim to develop such tests.

“Together with experimental collaborators, we are trying to test the effects of collapse modifications or derive limits on their parameters. This is exactly equivalent to testing the limits of quantum theory.”