From the perspective of quantum physics, the universe may be fundamentally agnostic in some respects.

In quantum physics, every object, such as an electron, corresponds to a mathematical entity known as a wave function. This wave function encodes all details regarding an object’s quantum state. By combining the wave function with other equations, physicists can effectively predict the behavior of objects in experiments.

If we accept that the entire universe operates on quantum principles, then even larger entities, including the cosmos itself, must possess a wave function. This perspective has been supported by iconic physicists like Stephen Hawking.

However, researchers like Eddie Kemin Chen from the University of California, San Diego and Roderich Tumulka from the University of Tübingen in Germany, have demonstrated that complete knowledge of the universal wave function may be fundamentally unattainable.

“The cosmic wave function is like a cosmic secret that physics itself conspires to protect. We can predict a lot about how the universe behaves, yet we remain fundamentally unsure of its precise quantum state,” states Chen.

Previous studies assumed specific forms for the universal wave function based on theoretical models of the universe, overlooking the implications of experimental observations. Chen and Tumulka began with a more practical inquiry: Can observations help in identifying the correct wave function among those that reasonably describe our universe?

The researchers utilized mathematical outcomes from quantum statistical mechanics, which examines the properties of collections of quantum states. A significant factor in their calculations was the realization that the universal wave function depends on numerous parameters and exists in a high-dimensional abstract state.

Remarkably, upon completing their calculations, they found that universal quantum states are essentially agnostic.

“The measurements permissible by the rules of quantum mechanics provide very limited insight into the universe’s wave function. Determining the wave function of the universe with significant precision is impossible,” explains Tumulka.

Professor JB Manchak from the University of California, Irvine states that this research enhances our understanding of the limits of our best empirical methods, noting that we essentially have an equivalent to general relativity within the framework of quantum physics. He adds that this should not come as a surprise since quantum theory was not originally designed as a comprehensive theory of the universe.

“The wave function of a small system or the entire universe is a highly theoretical construct. Wave functions are meaningful not because they are observable, but because we employ them,” remarks Sheldon Goldstein from Rutgers University. He further explains that the inability to pinpoint a unique, accurate universal wave function from a limited range of candidates may not be problematic, as any of these functions could yield similar effects in future calculations.

Chen expresses hope to connect his and Tumulka’s research with the exploration of large-scale systems smaller than the universe itself, especially through techniques like shadow tomography, which aim to determine the quantum state of such systems. However, the philosophical consequences of their work are equally crucial. Tumulka emphasizes the need for caution against over-relying on positivist views that deem non-experimental statements as meaningless or unscientific. “Some truths are real, but cannot be measured,” he asserts.

This rationale might influence ongoing debates regarding the interpretation of quantum mechanics. According to Emily Adlam from Chapman University in California, the new findings advocate for incorporating more components into the interpretation of quantum equations, such as wave functions, emphasizing the relationship between quantum objects and individual observer perspectives, moving away from the assumption of a singular objective reality dictated by a single mathematical construct.