In a major scientific breakthrough, researchers at the University of Cambridge have discovered a way to track the "secret movements" of quantum particles when they are not being observed – a concept which was previously thought to be impossible.

One of the primary principles of quantum theory is that quantum objects can either exist as particles or waves but that they do not exist as either until they are measured. This theory is the basis of Erwin Schrödinger's now infamous "Schrödinger's cat" theory – the thought experiment that involved the dead-or-maybe-not-dead cat in a box (yes, it's the same one Sheldon Cooper so often brought up in the immensely popular The Big Bang Theory show).

The theory is also the reason why physicists thought it was impossible to track unobserved quantum particles. However, in a new study, Cambridge University researchers suggest that quantum particles can be tracked by studying the way particles interact with their environment – by exploring a physics premise called the "wave function".

"This premise, commonly referred to as the wave function, has been used more as a mathematical tool than a representation of actual quantum particles," David Arvidsson-Shukur, a Ph.D. student at Cambridge's Cavendish Laboratory and the study's first author, said in a statement. "That's why we took on the challenge of creating a way to track the secret movements of quantum particles."

As part of the new research, physicists suggested that instead of measuring quantum objects, researchers could track unobserved particles by studying the way a quantum object interacts with its environment. The scientists found that quantum particles "tag" their environment as they move, which can be tracked without the particles being observed directly.

According to Arvidsson-Shukur, the tagging method can also help "verify old predictions of quantum mechanics, for example, that particles can exist in different locations at the same time".

The new research not just refutes what was once thought to be an impossibility but can also help scientists test other older quantum mechanics predictions. Researchers could further explore concepts such as whether a particle can exist in two places at once or even explore the potential reality of telepathy, which involves the transmission of information between two people, without any particles travelling between them.

"Our result suggests that the wave function is closely related to the actual state of particles," said Arvidsson-Shukur. "So, we have been able to explore the 'forbidden domain' of quantum mechanics: pinning down the path of quantum particles when no one is observing them."

The new research has been published in the journal Physical Review A.