Scientists from the Vienna Technological University (Tu Wyen) have challenged the notion that quantum physics contradicts the second law of thermodynamics. According to a new study, the entropy of closed quantum systems also increases over time until it reaches its maximum value.
Previously, it was believed that knowing the quantum state of a system would keep its entropy unchanged. This idea was based on the works of mathematician John von Neumann 90 years ago. However, the crucial point is that it is fundamentally impossible to have complete information about a quantum system as measurements are always associated with uncertainty.
The researchers have put forward a new approach suggesting the use of Shannon’s entropy instead of the traditional von Neumann entropy. Claude Shannon, a mathematician, proposed this concept in 1948 to measure the level of uncertainty resulting from a specific measurement. The entropy increases with higher uncertainty.
Initially, when a quantum system begins to evolve, its entropy is low due to the ease of predicting measurement results. However, over time, the entropy increases until it reaches its maximum level, mirroring classical thermodynamics where system entropy rises until equilibrium is reached.
“By redefining the concept of entropy correctly, there is no longer a contradiction between quantum physics and thermodynamics,” said the authors of the study. The research, published in PRX Quantum, confirms that the second law of thermodynamics is applicable even to fully isolated quantum systems.