It has been long theorized, but never proven

Jul 31, 2009 12:23 GMT  ·  By

Planck's law is one of the most basic in physics, and is widely used to explain what governs the heat transfer between two bodies. The fact that the law breaks down when the objects are very close to each other has been theorized for many years, but no one has been able to demonstrate scientifically that this is possible until now. In a groundbreaking investigation, scientists at the Massachusetts Institute of Technology (MIT) have managed to prove just that, and have learned that the heat transfer can be 1,000 times greater than the law predicts.

“Planck was very careful, saying his theory was only valid for large systems. So he kind of anticipated this [breakdown], but most people don't know this,” the MIT Carl Richard Soderberg professor of power engineering Gang Chen says. The expert is also the director of the Pappalardo Micro and Nano Engineering Laboratories. The find could have significant applications in the field of electronics, and especially in hard-drive designs, where the recording heads could be made a lot more effective.

Additionally, new methods of harnessing energy from sources that are otherwise lost could also be devised, significantly boosting the planet's overall energy-production abilities. Thus far, building such systems has relied heavily on Planck's law. Devised in 1900 by German researcher Max Planck, the law explains how radiations dissipate at various wavelengths from an ideal, non-reflective, black object, called a blackbody.

In a study to be published in the August issue of the journal Nano Letters, but that is now available online, the experts describe the two methods they used to analyze heat radiating from two bodies. In the past, the difficulty was to keep two bodies very close to each other for a time long enough to allow for measurement. But, at this level of closeness, it's very difficult to not actually touch the bodies to each other. In one method, they used a flat surface and a small, round, glass bead, while in the second they employed the technology of the bi-metallic cantilever from an atomic-force microscope, so as to measure the temperature changes with great precision.

“If we use two parallel surfaces, it is very hard to push to nanometer scale without some parts touching each other. We tried for many years doing it with parallel plates,” Chen adds. “Experimental confirmation has proved elusive because of the extreme difficulty in measuring temperature differences over very small distances. Gang Chen's experiments provide a beautiful solution to this difficulty and confirm the dominant contribution of near field effects to heat transfer,” Imperial College London professor Sir John Pendry, who has extensive training in this field of research, concludes.