Quote of the Day

The principle that heat spontaneously flows from higher temperatures to lower temperatures is a cornerstone of classical thermodynamics. While this principle holds true for macroscopic systems at equilibrium, here we show that, when a quantum system undergoes two thermalization processes in an indefinite causal order, it can absorb heat even if its initial temperature was higher than the temperature of the reservoirs involved in the two thermalizations. Exploiting this anomalous heat flow, we design a quantum Otto cycle with indefinite causal order, which generates work and simultaneously achieves refrigeration.

Qing-Feng Xue, et. al.
July 15, 2026
Anomalous Heat Flows and Quantum Otto Engine with (In)definite Causal Order

See also Scientists reversed a law of physics by scrambling cause and effect.

Fascinating stuff, but it is not a blueprint for a perpetual motion machine. As explained by Grok:

Bottom line

• First law: energy is conserved once you count the control, the measurement apparatus, and the reset.
• Second law: the unconditional process does not decrease entropy; the conditional process is paid for by Landauer erasure and by the free energy you invested in the control.
• No closed cycle produces net work from a single heat bath, and no heat is pumped from cold to hot without a work (or coherence) input when every degree of freedom is included.

The result is interesting as a demonstration that coherent control and post-selection can rearrange which branch of a process looks hot or cold. It is not a loophole in thermodynamics.