Irreversibility is a longstanding puzzle in physics. While microscopic laws of motion are invariant under time reversal, all macroscopic phenomena have a preferred direction in time. Heat, for instance, spontaneously flows from hot to cold. Eddington has called this asymmetry the arrow of time. At the phenomenological level, the second law of thermodynamics allows one to predict which processes are possible in nature: only those with non-negative mean entropy production do occur. A microscopic resolution of the apparent paradox of irreversibility was put forward by Boltzmann, when he noted that initial conditions break the time-reversal symmetry of the otherwise reversible dynamics.
In addition to breaking time reversal, initial conditions also determine the arrow’s direction. The observation of the average positivity of the entropy production in nature is often explained by the low entropy value of the initial state. This opens the possibility to control or even reverse the arrow of time depending on the initial conditions.
In standard thermodynamics, systems are assumed to be uncorrelated before thermal contact. As a result, according to the second law heat will flow from the hot to the cold body. However, it has been theoretically suggested that for quantum correlated local thermal states, heat might flow from the cold to the hot system, thus effectively reversing the arrow’s direction.
We report the experimental demonstration of the reversal of heat flow for two initially quantum correlated qubits (two spin-1/2 systems) prepared in local thermal states at different effective temperatures employing Nuclear Magnetic Resonance (NMR) techniques.
Read more: Nature Communications 10, 2456 (2019) | pdf |
Quanta Magazine: Quantum Correlations Reverse Thermodynamic Arrow of Time.
The Times (of London): Time really can flow backwards . . . but don’t blink or you’ll miss it.
Science News: ‘Arrow of time’ reversed in quantum experiment. Science News
PhysOrg: Experiment shows that arrow of time is a relative concept, not an absolute one.
Newsweek (U.S. edition): Arrow of time reversed by physicists in quantum experiments. Newsweek (U.S. edition)
Big Think: Scientists reverse the arrow of time in quantum systems.
IFLScience: A quantum experiment just reversed the thermodynamic arrow of time.
MIT Technology Review: Physicists Demonstrate How to Reverse of the Arrow of Time.
Programa Pesquisa Brasil, Rádio USP: Termodinâmica invertida,
Revista Pesquisa (FAPESP): Experimento inverte a seta termodinâmica do tempo: O frio que aquece.
Folha de São Paulo: Brasileiros conseguem reverter a direção do tempo em experimento.
Rádio UFRGS: Termodinâmica quântica e a seta do tempo. Programa Fronteiras da Ciência,
PBS / WGBH: Scientists reverse arrow of time in quantum experiment.
Live Science: How to Temporarily Undo the Universe's Endless Chaos with Chloroform. Live Science
Revista Exame: Cientistas fazem o tempo correr ao contrário em laboratório.
Ifuun (Chinese science portal): 逆轉「時間之箭」的量子實驗.
SCIENCEmag cz (Czech science portal): Teplo proudí ze studeného objektu na horký.
Europa Press: El concepto de que el tiempo discurre en dirección única es relativo.
Inovação Tecnologica: Experimento faz tempo andar para trás.
The Daily Express: Scientists manage to ‘REVERSE the arrow of time’ in astonishing study.
The Inquisitr: Physicists demonstrate that time can actually travel in a reverse direction under the right conditions.
Science alert: Physicists Have Created a Set of Conditions in Which Time Seems to Run in Reverse.
Portal Terra: Experimento mostra que o tempo pode não "andar" somente para frente.
Futurism: Physicists have created a set of conditions in which time seems to run in reverse. Futurism
Diario ABC (Spanish newspaper): Logran, por primera vez, que el tiempo fluya hacia atrás.
Dialectica (Romanian news portal): Fizică: Un nou experiment inversează „săgeata timpului”.
UP'Magazine (French innovation news): Des scientifiques ont découvert que le temps pouvait s’écouler à l’envers.