Researchers from the University of Surrey have unveiled a study, published in Scientific Reports, suggesting time might not be a one-way street. Their findings indicate that at the quantum level, time could theoretically flow both forwards and backwards, challenging our fundamental understanding.

Schematic showing the concept behind the time-reversal transformation.

(Guff et al., 2025)

For centuries, the “arrow of time”—our consistent experience of it moving only from past to future—has puzzled scientists. While everyday events like spilled milk clearly demonstrate this forward progression, the underlying laws of physics don’t inherently favor this direction.

The research team focused on “open quantum systems,” investigating how tiny, sub-atomic particles interact with their environment. Their aim was to understand why our macroscopic world perceives time so differently from the possibilities at the quantum scale.

Schematic showing the concept behind the time-reversal transformation.

“Quantum Gravity Photon Race” by NASA Goddard Photo and Video is licensed under CC BY 2.0.

To model these quantum interactions, the scientists made two critical assumptions. First, they computationally isolated the quantum system from its larger environment. Second, they assumed that any energy and information dissipating from the system into its surroundings would do so irreversibly.

The mathematical models based on these assumptions yielded a surprising result: in specific quantum systems, time could theoretically move both forwards and backwards. This directly challenges the traditional, intuitive view of time’s unidirectional flow.

This groundbreaking discovery could have profound implications for various fields of physics, including quantum mechanics, cosmology, and thermodynamics. It opens new avenues for exploring one of the universe’s deepest mysteries and may reshape our understanding of reality itself.