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Curated by RSF Research Staff

The arrow of time is not so absolute, new experiment shows

Time is such a basic property of our physical universe that it seems it would be easily and clearly defined scientifically in any physics model. Yet, on closer examination, time is a tricky property to pin down and delineate---and our “common sense” conceptions of time may not be as reliable as we would presume. Accordingly, a very big and outstanding question in science is: what is time?

Quantum mechanics and general relativity, the two predominant theories of modern physics, both agree that fundamentally there is no preferred direction of time---in quantum mechanics particle transformations and interactions look the same whether occurring “forwards” or “backwards” in time, a property known as time-reversal symmetry of microscopic laws of motion (part of CPT symmetry); and general relativity famously melds “past”, “present”, and “future” into one continuous spacetime manifold (the spacetime continuum).

With such ambiguity regarding the nature of time coming from our two pillars of modern physics theory, where then do we find a physical correlate for the preferred directionality of time that seems to be very much an observable and important way the universe works, at least within the macroscopic domain. The physics that describes the preferred directionality of time comes from the laws of thermodynamics, where the law of entropy (the description of the microscopic order of a system) produces the so-called thermodynamic arrow of time.

This notion is simple to understand: things go from being hot to being cold because heat flows to systems with lower temperature until equilibrium is achieved, and the same is true for pressure, particle concentrations, etc. Thus, it is observed that systems generally go towards equilibrium, what is often the lowest energy state and what often appears as the most disordered---hence the inevitable increase in entropy produces a definite directionality of time.

How then is this observable phenomenology of the law of thermodynamics reconciled with the microscopic time-reversal symmetry, or invariance under time reversal, of quantum mechanics? Boltzmann, originator of the epitomal Boltzmann’s constant, offered a solution to the apparent paradox by noting that initial conditions break the time-reversal symmetry of otherwise reversible dynamics---a postulate that was recently confirmed quantitatively in experimentation with an electrical RC circuit.

Schematic of Experiment

Schematic of the experimental setup pictured above. (A) Heat flows from the hot to the cold spin (at thermal contact) when both are initially uncorrelated. This corresponds to the standard thermodynamic arrow of time. For initially quantum correlated spins, heat is spontaneously transferred from the cold to the hot spin. The arrow of time is here reversed. (B) View of the magnetometer used in our NMR experiment. A superconducting magnet, producing a high intensity magnetic field (B0) in the longitudinal direction, is immersed in a thermally shielded vessel in liquid He, surrounded by liquid N in another vacuum separated chamber. The sample is placed at the center of the magnet within the radio frequency coil of the probe head inside a 5mm glass tube. (C) Experimental pulse sequence for the partial thermalization process. The blue (red) circle represents x (y) rotations by the indicated angle. The orange connections represents a free evolution under the scalar coupling, HJHC = (πh/2)JσzHσzC , between the 1H and 13C nuclear spins during the time indicated above the symbol. We have performed 22 samplings of the interaction time τ in the interval 0 to 2.32 ms. Credit: arXiv:1711.03323 [quant-ph]

 

A new experiment has now shown that the initial conditions not only break the time reversal symmetry, they also determine the direction of the arrow of time. As experimenters have recently discovered, the laws of thermodynamics always predicted one direction for the arrow of time because it was always assumed that in the initial starting condition there was no correlation among the components of a system. What the latest experiment has shown for the first time is that when there is correlation in interacting systems at the initial conditions the arrow of time can appear to go the opposite direction, or “backwards” in time. Thermodynamically, this equates to heat flowing from a cold system to a hot one, so that initially correlated systems a hot particle will get hotter.

The researchers explain that this does not violate the laws of thermodynamics because those laws do not address the role of correlation, and in fact assume that there is no correlation in the system. In addition to the assumption that the system is isolated, the “normal” increase of entropy of thermodynamic flow only holds true when there is no initial correlation of interacting systems.A new experiment has now shown that the initial conditions not only break the time reversal symmetry, they also determine the direction of the arrow of time. As experimenters have recently discovered, the laws of thermodynamics always predicted one direction for the arrow of time because it was always assumed that in the initial starting condition there was no correlation among the components of a system. What the latest experiment has shown for the first time is that when there is correlation in interacting systems at the initial conditions the arrow of time can appear to go the opposite direction, or “backwards” in time. Thermodynamically, this equates to heat flowing from a cold system to a hot one, so that initially correlated systems a hot particle will get hotter.

Such results are highly confirmatory and supportive of the main theory put forward in the study by Haramein et al. in the Unified Spacememory Network publication, in which Haramein, Brown, and Dr. Val Baker explain that strong correlation, or entanglement, is an integral mechanism underlying the observed increase of order of the universe and its subsystems over time, particularly those ordering dynamics that lead to life and sentience. The very name, unified spacememory network, alludes to the fact that it is a description of the connectivity circuits of entangled or correlated systems that lead to time-symmetric interaction and a kind of communicative network and memory property of the quantum structure of spacetime.

The recent experiment represents a discovery of a veritable new phenomenon in science and should hold important implications for theories, such as the USN postulate of Haramein et al., and potential technological applications.

Article: Experiment shows that arrow of time is a relative concept, not an absolute one

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