Imagine pouring a cup of hot coffee into a mug. You would think that the heat conducted into the cup would eventually be transferred to your hands as well. Such a common daily experience dates back 200 years to Fourier’s Law of Heat Conduction. What if this centuries-old rule doesn’t always apply? New findings from the University of Massachusetts Amherst suggest exactly that, and it might just significantly alter what we had thought about how heat moved.
Basically, the Fourier’s Law states that heat flowing across a solid will be proportional to the temperature gradient and to the area over which the heat flows. The law has been very basic in understanding such heat diffusion within materials. It generally explains why your mug has heated up when filled with hot coffee, why insulation materials are able to keep your house warm during the winter seasons, or generally why systems tend toward equilibria. However, researchers at UMass Amherst scoped some scenarios led by Steve Granick wherein this rule fails.
The researchers made this discovery while working on a type of translucent polymer and inorganic glass. Such classes of transparent materials could mean that energy will diffuse through them in strange ways. Granick explains, “It’s not that Fourier’s Law is wrong, just that it doesn’t explain everything we see when it comes to heat transmission. Fundamental research like ours gives us an expanded understanding of how heat works, which will offer engineers new strategies for designing heat circuits.”
Part of what drove the research was curiosity. Granick and his colleagues did what any of us might: they asked a really simple, profound question—what if heat could be conducted by some other pathway not traditionally assumed? They took samples of translucent materials and isolated them in a vacuum to eliminate interference from air. Then they heated small areas of those samples with a laser and observed with an infrared camera what happened. The discovery was a real surprise.
“No one’s done this before,” says Kaikai Zheng of UMass Amherst, a senior research fellow. It turns out that energy inside the material could radiate outward from within and then be .scatter off structural imperfections at the atomic scale. Those scattering events produced secondary sources of heat that kept radiating heat an anomaly not described by Fourier’s Law.
It was something they did over and over and over again, and the result defied explanation. Its consistency finally forced them to consider revisiting classical notions of heat conduction. Sometimes, Granick notes, “creativity requires that you put the textbook aside for a moment.”
Huge implications. The discovery opened new viewpoints that engineers and scientists might consider while designing materials and systems to get a better handle on heat. This could transform everything from the efficiency of electronics to building materials that permit more efficient ways of controlling heat flow.
Next time that steaming cup of joe comes into your hands, consider the kind of sort-of-complex journey heat takes through your mug. We now know, from these researchers, much more to it than meets the ordinary eye. Who would think that such a simple question could lead to a discovery that challenges a 200-year-old scientific law? It’s an ode to the never-ending possibilities of scientific inquiry and a reminder to never stop asking, “What if?”
