The importance of being constant: the fundamental things apply … as time goes by

An object's temperature directly measures the average energy of motion of its jiggling atoms or molecules. Of course, within this average some of the particles jiggle very fast, whereas others jiggle relatively slow. All this activity emits a sea of light, spread over a range of energies, just like the particles that emitted them. When the temperature gets high enough, the object begins to glow visibly. In Planck's day, one of the biggest challenges in physics was to explain the full spectrum of this light, particularly the bands with the highest energy

Planck's insight was that you could account for the full sweep of the emitted spectrum in one equation only if you assume that energy itself is quantized, or divided up into itty-bitty units that cannot further he subdivided: quanta.

Once Planck introduced h into his equation for all energy spectrum, his constant began to appear everywhere. One good place to find h is in the quantum description and understanding of light. The higher the frequency of light, the higher its energy: Gamma rays, the band with the highest frequencies, are maximally hostile to lift, Radio waves, the band with the lowest frequencies, pass through you every second of every day, no harm done. High-frequency radiation can harm you precisely because it carries more energy. How much more? In direct proportion to the frequency: What reveals the proportionality? Planck's constant, h. And if you think G is a minuscule constant of proportionality, take a look at the current best value for h (in kilogram-meters squared per second): 0.0000000000000000000000000000 000066260693.

One of the most provocative and wondrous ways h appears ill nature arises from the so-called uncertainty principle, first articulated in 1927 by the German physicist Werner Heisenberg. The uncertainty principle sets forth the terms of all inescapable cosmic trade-off: for various related pairs of fundamental, variable physical at tributes--location and speed, energy and time--it is impossible to measure both quantities exactly. In other words, if you reduce the indeterminacy for one member of the pair (location, for instance), you're going to have to settle for a looser approximation of its partner (speed). And it's h that sets the limit on the precision you Call attain. The trade-offs don't have much practical effect when you're measuring things in ordinary life. But when you get down to atomic dimensions, h rears its profound little head all around you.

It may sound more than a bit contradictory, or even per verse, but in recent decades a lot of physicists have been looking for evidence that constants don't hold for all eternity. In 1938 the English physicist Paul A.M. Dirac proposed that the value of no less a constant than Newton's G might decrease in proportion to the age of the universe. Today there's practically a cottage industry of physicists desperately seeking fickle constants. Some are looking for a change across time; others, for the effects of a change in location; still others are exploring how the equations operate in previously untested domains. Sooner or later, they're going to get some real results. So stay tuned: news of inconstancy may lie ahead.