Simple Nature - Light and Matter

This was the state of things until 1999, when evidence began toturn up that the universe’s expansion has been speeding up ratherthan slowing down! The first evidence came from using a telescopeas a sort of time machine: light from a distant galaxy may havetaken billions of years to reach us, so we are seeing it as it was farin the past. Looking back in time, astronomers saw the universeexpanding at speeds that were lower, rather than higher. At firstthey were mortified, since this was exactly the opposite of whathad been expected. The statistical quality of the data was also notgood enough to constitute ironclad proof, and there were worriesabout systematic errors. The case for an accelerating expansion hashowever been supported by high-precision mapping of the dim, skywideafterglow of the Big Bang, known as the cosmic microwavebackground.So now Einstein’s “greatest blunder” has been resurrected. Sincewe don’t actually know whether or not this self-repulsion of spacehas a constant strength, the term “cosmological constant” has lostcurrency. Nowadays physicists usually refer to the phenomenon as“dark energy.” Picking an impressive-sounding name for it shouldnot obscure the fact that we know absolutely nothing about thenature of the effect or why it exists.2.4 Atomic PhenomenaVariety is the spice of life, not of science. So far this chapter hasfocused on heat energy, kinetic energy, and gravitational energy,but it might seem that in addition to these there is a bewilderingarray of other forms of energy. Gasoline, chocolate bars, batteries,melting water — in each case there seems to be a whole new typeof energy. The physicist’s psyche rebels against the prospect of along laundry list of types of energy, each of which would requireits own equations, concepts, notation, and terminology. The pointat which we’ve arrived in the study of energy is analogous to theperiod in the 1960’s when a half a dozen new subatomic particleswere being discovered every year in particle accelerators. It was anembarrassment. Physicists began to speak of the “particle zoo,”and it seemed that the subatomic world was distressingly complex.The particle zoo was simplified by the realization that most of thenew particles being whipped up were simply clusters of a previouslyunsuspected set of fundamental particles (which were whimsicallydubbed quarks, a made-up word from a line of poetry by JamesJoyce, “Three quarks for Master Mark.”) The energy zoo can alsobe simplified, and it’s the purpose of this section to demonstrate thehidden similarities between forms of energy as seemingly differentas heat and motion.Section 2.4 Atomic Phenomena 109