A Stunning Experiment Reveals That Time Might Actually Be Reversible—in Glass
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From our point of view, time is always flowing forward. But in the molecular properties of non-crystalline materials such as glass, things aren’t quite so uniformly directional.
Scientists from the Technical University of Darmstadt in Germany and Roskilde University in Denmark used dynamic light scattering and tracked fluctuations in the “physical aging” process of glass that were “stationary and reversible.”
This doesn’t mean that scientists can miraculous turn back the clock on these experimental objects, but it does suggest that time isn’t as... straight forward... as we assume.
In 1973, American folk singer Jim Croce first crooned his famous lyric: “If I could save time in a bottle...” If that bottle was made of glass, he might’ve actually been on to something. Thanks to a research team from the Technical University of Darmstadt in Germany and Roskilde University in Denmark studying the age of glass, we now have the first physical evidence of a material-based time reversal.
Ok, let’s back things up a bit.
From our limited human perspective, time marches inexorably forward as the universe experiences Isaac Newton’s Second Law of Thermodynamics and entropy increases with time. This is a concept known as “time’s arrow,” and it describes the fact that things can move forward, but not backward. A sandwich molds, a car rusts, living things die.
However, that’s not always the case. In the case of mathematics, for example, one can simply flip an equation and work backward. And as this new study in Nature Physics states, novel traits found within glass also exhibit properties of time reversal.
“Few persons would claim that time can be reversed—all living creatures age and eventually die, a dropped glass breaks while the reverse never happens, mixing cold and warm water leads irreversibly to an intermediate temperature and so on,” the paper reads. “On the other hand, the fundamental equation-of-motion laws of nature are all time reversible: for example, Newton’s laws of classical mechanics, the Schrödinger equation of quantum mechanics, Maxwell’s equations for electromagnetism, and the Einstein equation of gravity and spacetime.”
The process known as “physical aging” refers to the changes in molecular structure as a material gets older. Non-crystalline materials, such as glass, experience this process as their “glassy state” slowly relaxes toward a stable equilibrium. However, this takes a long time—much too long for scientists to have any hope of keeping their sanity while endlessly watching molecular glass. Instead, according to ScienceAlert, scientists used scattered laser light (aka dynamic light scattering, or DLS) to create fluctuations in the form of “interference patterns” to track material time—the time it takes for molecules to thermodynamically move through... well... time.
“We determined the material time for an aging sample of the glass-former 1-phenyl-1-propanol after temperature jumps close to the glass transition from the time-autocorrelation function of the intensity fluctuations probed by multispeckle dynamic light scattering,” the paper reads. “These fluctuations are shown to be stationary and reversible when regarded as a function of the material time.”
While this proves the existence of reversible time, that doesn’t mean this paper describes a physical process of rearranging molecules and turning back the clock on a glass’s age.
“It was a huge experimental challenge,” condensed matter physicist from the Technica University of Darmstadt and lead author Till Böhmer said to ScienceAlert about his team’s research. “However, this does not mean that the aging of materials can be reversed.”
As with most breakthroughs, finally finding physical evidence of time-reversibility only brings up more questions—chief among them being how universal this characteristic is to aging in general. To use a particularly poignant turn of phrase, only time will tell.
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