THE MATRIMONIAL MOMENTUM AND THE EVOLUTION OF PARTICLES

In “The Matrimonial Momentum,” Season 9, Episode 1, Leonard’s wedding vows invoke the evolution of particles.

[Democritus says:] “By convention sweet is sweet, by convention bitter is bitter, by convention hot is hot, by convention cold is cold, by convention color is color. But in reality, there are atoms and the void. That is, the objects of sense are supposed to be real and it is customary to regard them as such, but in truth they are not. Only the atoms and the void are real.”

—Democritus (460–370 BC), as described by Diogenes Laërtius (third century AD)

It All Started with the Big Bang!

As the Barenaked Ladies song goes, “Our whole universe was in a hot, dense state/Then nearly fourteen billion years ago expansion started . . . a fraction of a second and the elements were made . . . it all started with the big bang!” And, as Sheldon and Leonard are physicists who study matter in motion, all potential roads of inquiry lead back to the big bang. That’s where it all began, at least according to a consensus of physicists today. Every scrap of physical matter and energy bears witness to this history, which is why scholars spend so much time learning how to read its evidential traces. Astrophysicists scour the earth for evidence of things that happened long ago, but not necessarily far away.

First up: matter is made of atoms. As has been pointed out elsewhere in this book, this idea was established long ago. Ingenious ancient Greeks, such as Democritus and Epicurus, were the first Atomists. And yet the idea that the mass of each atom is centered at its nucleus came much later. In the early twentieth century, Ernest Rutherford, the son of Scottish immigrant farmers born at the edge of empire in 1871, became the father of nuclear science, a great charismatic figure who mapped the landscape of the subatomic world. He charted the atom’s constituent parts, discovered that elemental decay was the cause of radiation, and became the first true alchemist in the history of science when he forced platinum to change into gold.

The physicists soon found that the mass of an atom consists mostly of the protons and neutrons in its nucleus. The exception to this is simple hydrogen, whose nucleus is a sole proton. The total number of neutrons and protons in an atom’s nucleus gives its atomic weight. And from this nano-scale architecture (for instance, a helium atom has the size of 0.1 nanometers or 10^–10 meters) derives much of the structure of our macro-world.

Second, matter is also frozen energy. This fact is packed into Albert Einstein’s most famous equation of e = mc². In plain English, energy is equal to mass, multiplied by the speed of light squared. As the speed of light is a rather large number (186,000 miles or 300,000 kilometers a second), Einstein’s innocuous-looking formula packs a lot of punch. It predicts that small amounts of mass harbor huge amounts of energy. And it accounts for cosmic events, such as the stars that burn for billions of years and more down-to-earth but dramatic incidents, such as why a small nuclear bomb the size of a satsuma can lay waste to Nagasaki.

The Elements Were Made

Physicists such as Sheldon and Leonard claim that these two ideas—that matter is made of atoms and is also a form of frozen energy—only make sense in the light of big bang theory. All matter is a product of universal history, and physicists account for the way things are because they were as they were at the very beginning. In other words, matter can be analyzed for data about the way in which the cosmos evolved.

Take the question of matter as frozen energy, for example. It is so because the cosmos began in a state of high energy, but cooled down and solidified into cold matter. Why did the cosmos cool? Because the expansion of the universe, mentioned in the Barenaked Ladies song, means that the same amount of energy in a larger and increasing volume of space results in a lower universal level of energy. In short, energy froze out into matter.

As to the question of why matter is actually made of atoms, the answer also lies in the big bang. The light and simple elements of hydrogen, helium, and lithium were first fused in the early minutes of the cosmic expansion, as the universal energy cooled and neutrons and protons were able to get together to form the nuclei of atoms. But here’s where the Barenaked Ladies song got it wrong. It’s not the case that “a fraction of a second and the elements were made.” The rest of the chemical elements, those heavier than hydrogen, helium, and lithium, were forged later, in the cores of stars.

One of the first physicists to realize that the big bang could not have made any elements heavier than lithium was Italian Nobel Prize-winning scientist Enrico Fermi. Fermi had a dark sense of humor. It was he who jokingly took bets on whether the Earth’s atmosphere would be set on fire at the first detonation of a nuclear device, the Trinity test, on July 16, 1945. Fermi was mocking concerns that the fission explosion of the bomb might trigger runaway fusion of the nitrogen that makes up over 70 percent of the air that surrounds the entire planet!

It’s the same kind of fusion that happens in the very cores of stars. Stars like our sun burn differently from how things on earth do. Here on Earth, when something burns, such as wood, a chemical reaction with oxygen occurs. But stars are made mostly of hydrogen gas, and hydrogen is what usually burns at the star’s core. That’s due to a star’s size, and the fact it’s so packed with particles that the temperature at its center is around 16 million degrees centigrade. That’s hot enough to burn the hydrogen into helium gas. In the case of the sun, this burn is at the rate of about 4 million tons of gas every second, which is the same energy as seven trillion nuclear explosions, every second. A star is essentially a bomb that goes off slowly.

Stars like the sun never really die. They simply spend their lives changing the fuel for their fires. They may spend most of their lives burning hydrogen into helium, but in time they can burn carbon, oxygen, and silicon, too. Indeed, there are different life journeys a star can take. And each journey depends on the strength of the star’s fire. But whichever way they go, stars recycle their viscera out into space, ejecta richly made of the chemicals created inside the stars. And that star stuff is a future part of the interstellar mixture, an ingredient of the cosmic recipe for a new generation of stars to be made out of the old.

Rewriting the Wedding Vow

Back in the 1940s and 1950s, physicists made the same mistake as the Barenaked Ladies and tried to explain the cosmic presence of all the chemical elements from the big bang theory alone. Until, that is, along came British physicist Fred Hoyle. A talented popularizer of science who made regular appearances on TV and radio and also wrote sci-fi, Fred had a good grasp of math and theoretical physics but also possessed a penchant for unpopular concepts.

Indeed, Fred is even credited with coining the term “big bang.” During a 1949 BBC radio broadcast, he said: “These theories were based on the hypothesis that all the matter in the universe was created in one big bang at a particular time in the remote past.” It is often thought that Fred, who favored the alternate “steady state” cosmological model, intended this as an insult. But he later denied it, saying it was merely a striking way to contrast the two models.

In the late 1950s, Fred led a group of anti-big bang physicists who finally showed how the heavier elements originate in stars. The stellar fusion reactions were the engine of elements heavier than carbon. Along with Caltech scholar William Fowler, and husband and wife astronomers Geoffrey and Margaret Burbidge, Fred set out the details of eight fusion reactions that turned light elements into heavy ones. Once made, these elements are recycled into space through stellar winds, red giants, and supernovae.

And so perhaps a more accurate wedding ceremony vow from Leonard would have been “Penny, we are made of particles that have existed since the beginning of cosmic time. Those atoms went on a journey of over 14 billion years, brewed up by stars and supernovae, and sailing through space on stellar winds to create us, so that we could be together and make each other whole.”