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posted by martyb on Friday December 04 2015, @03:27AM   Printer-friendly
from the arrow-of-time-goes-only-one-way? dept.

Researchers at the Federal University of ABC, in Brazil, have made a major breakthrough: they've confirmed that thermodynamic processes cannot be reversed, even in a quantum system. This revelation not only explains a fundamental aspect of our universe but could also influence how quantum computing systems are designed.

[...] The microscopic and macroscopic worlds currently operate using two different standards -- general relativity governs the macroscopic world while quantum physics rules the microscopic. In our macro world view, thermodynamic (entropic) processes only move in one direction. That is, using an egg analogy, you can't uncook an egg much less get it to hop back into its shell and seal the crack. But in the subatomic world, many of these processes are "time-symmetric" -- essentially, they're reversible.

However, what Tiago Batalhão and his team at the UFABC discovered actually runs counter to our expectations. Their experiment sought to measure the entropy change within a closed system of carbon-13 atoms submerged in liquid chloroform while they're subjected to an oscillating magnetic field. The idea is that polarizing the field should cause the atoms' nuclear spins to all rotate one direction, while reversing the field's polarity would make their spins flip and rotate the opposite direction.

Now, if this process were time-symmetric as our current understanding of physics dictates, the atoms' spins should flip back and forth without issue and return to their initial states once the magnet was turned off. But the UFABC team found that the atoms' spins couldn't keep up with the magnet's oscillation rate and some would eventually fall out of sync with their neighbors. This means that entropy within the closed system was actually increasing -- precisely the opposite effect from what should be happening. It effectively proves that thermodynamic processes are not reversible at the quantum level. What's more, it reveals a disconnect between the current laws of physics and what we're actually observing.

Yet, earlier this year scientists did figure out how to unboil eggs...


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  • (Score: 2, Insightful) by Anonymous Coward on Friday December 04 2015, @08:13AM

    by Anonymous Coward on Friday December 04 2015, @08:13AM (#271719)

    What's more, it reveals a disconnect between the current laws of physics and what we're actually observing.

    No, it doesn't.

    To quote from the actual scientific article: [aps.org]

    Let us discuss the physical origin of such time asymmetry in a closed quantum system. Using an argument put forward by Loschmidt in the classical context, its time evolution should in principle be fully reversible [1]. How then can a unitary equation, like the Schrödinger equation, lead to Eq. (1) that contains a strictly non-negative relative entropy? The answer to this puzzling question lies in the observation that the description of physical processes requires both equations of motion and initial conditions [1,13]. The choice of an initial thermal equilibrium state singles out a particular value of the entropy, breaks time-reversal invariance, and thus leads to the arrow of time. The dynamics can only be fully reversible for a genuine equilibrium process for which the entropy production vanishes at all times. Moreover, issues linked to the “complexity” of the preparation of the initial state to be used in the forward dynamics (or the corresponding one associated with the time-reversed evolution) have to be considered [33].

    So there's nothing missing in our laws of physics, they can explain the observed behaviour quite fine.

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