The Island of Knowledge by Marcelo Gleiser

Author:Marcelo Gleiser [Gleiser, Marcelo]
Language: eng
Format: epub
ISBN: 9780465080731
Publisher: Basic Books

CHAPTER 21

LEARNING TO LET GO

(Wherein we begin our exploration of quantum physics and how it imposes limits on what we can know of the world)

Within a decade, Einstein’s theories of special relativity and of light quanta had turned physics upside down. From a placid wave traveling in the luminiferous aether, light had become profoundly mysterious: not just the fastest of all phenomena but with a speed that, unlike anything else, was independent of the motion of its source; a wave that, unlike any other wave, could travel in nothingness; an entity that was both particle and wave, thus defying commonsense intuition that things could only be one or the other. Light’s speed wasn’t only the fastest known; it was also the limiting speed, the maximum allowed in Nature. No signal could travel faster than light; no information could arrive before light did. Looking out to the near and far corners of the Universe, physicists and astronomers learned that light was information, as they carefully collected the many kinds of electromagnetic radiation that distant objects emit to build a picture of the world. And in this book we have explored how this limiting speed leads to the existence of a cosmic horizon beyond which we cannot receive any information.

More mysteriously, light can only travel at its speed because it has no mass. Those little grains of light, that later were called photons, are massless bundles of pure energy. Physics was thus proposing that something could exist without mass, that things could exist without being material. Since what exists defines physical reality, the new physics suggested that reality could be immaterial. Energy is more fundamental than mass, more essential. A deeper understanding of Nature demanded a new worldview. Physicists had to let go of the old ways.

In his fourth paper of 1905, only a few pages long, Einstein derived the famous E = mc 2 formula. He wrote: “If a body gives off the energy L in the form of radiation, its mass diminishes by L/c 2.”1 Einstein went on to conclude that “the mass of a body is a measure of its energy-content.” We could thus refer solely to the energy of things, in things. Energy unifies mass and radiation, making one potentially become the other. At the end of his paper Einstein speculated: “It is not impossible that with bodies where the energy-content varies to a high degree (e.g. with radium salts) the theory may be put successfully to the test.”2 How right he was! Indeed, the radium salts Einstein referred to are radioactive nuclei that emit either small particles or pure radiation as they decay. The radiation kind of decay, comprised of gamma-ray photons, has energy corresponding precisely to the mass loss of the nucleus (times the square of the speed of light), just as Einstein had predicted.

The next twenty-five years were nothing short of explosive. The quantum revolution was indeed a revolution, not only in the way we see the world but in the way we live in the world.

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