The Equation

The Equation

Thursday, June 21, 2012

Behind the "Most Astounding Fact"

In March of 2012, a video about science went viral: Neil DeGrasse Tyson (obviously) shares the "Most Astounding Fact" - that all the atoms in our bodies are made in the end stages of stars - accompanied by a stirring soundtrack and a montage of images showing humans and the heavens. Though it may not have been the first scientifically themed viral video, it took me by surprise. Considering the interview was several years old, were the music and pictures what NDT needed to be a YouTube sensation? Maybe, but the end result is no less moving. If you haven't seen it yet, watch it here before continuing:

Never mind that a least a few atoms of carbon from the carbon dioxide of Hitler's last breath are also in each of us, the sentiment that "we are all stardust" resonates with people. As Tyson says, it helps us - tiny humans on a pale blue dot - place ourselves in the universe. The idea is relatively well-known; even Moby incorporated it  in his song "We Are All Made of Stars". But where did this idea come from ? (Hint: it's not the Bible)

The "most astounding fact" is just the face of unsung science that Tyson has spent effort to inform the public about. Elsewhere, Tyson has suggested that everyone should know the names Margaret Burbidge, Geoffrey Burbidge, Willie Fowler, and Fred Hoyle, the authors of the paper that showed how all the elements needed to make us are themselves made in stellar cores, a paper so famous, it simply is known by the names of it's authors: B2FH. Sadly, most people do not know these names. Part of it is general ignorance of science and scientists, part of it because of Fred Hoyle, last on the paper alphabetically, though first in importance to 20th Century astrophysics. This post is meant to help those whose curiosity was piqued by the video get a deeper understanding of the science and scientists that helped us come to the understanding we have about the origins of the elements that make us. We will get to Hoyle later, first we get to ask, "what is nucleosynthesis?"


Being about 70% water, humans are comprised mostly of hydrogen atoms. But we obviously have many other, heavier, elements in us: calcium, potassium, zinc, iron. In a universe where the vast majority of the atoms are hydrogen or helium, the lightest of elements, we have to ask where the heavier ones came from. Big Bang cosmology allows for the creation of Hydrogen and some Helium, but the Universe would have cooled too quickly to allow the formation of anything heavier. So, where did they come from? Stars have always been the prime candidate in the Big Bang paradigm to produce the rest of the periodic table, since we've known for years that they 1) are hot enough to provide the energies necessary for the fusion of elements and 2) their spectra show that their chemical compositions include trace amounts of metals.

Though fusion reactions are not quite as simple as adding atomic numbers to get new elements, where A+B=C or even A+A=B, it will suffice to say that elements are formed in collisions, where some atoms must combine with either other atoms or fundamental particles to form a new element. Elements, then, are formed in stages, where some cannot be made until others have already been created. Even the most primary stellar fusion reaction, the transformation of hydrogen into helium, must go through the complex proton-proton chain.

But in the 1950's, scientists were puzzled; they couldn't come up with the right equations that led to the formation of key elements, particularly carbon, that would match the frequency with which we find them in the universe.

Why you haven't heard of Fred Hoyle

Fred Hoyle, a British astrophysicist at Cambridge, finally found the missing piece: a new "resonance", or state, for carbon that would allow it to be made in stars in sufficient quantities to explain the abundance of carbon found on Earth. Actually, he predicted it - by reasoning that humans are made from carbon, so there must be a way to create it  - and other scientists found it, exactly as Hoyle had described. This new form of carbon was created by having three alpha-particles combine, rather than, say, two lithium atoms or an alpha particle and a beryllium atom.

With the formation of carbon now explained, Hoyle and his colleagues went on to write the B2FH paper, the keystone of the field of Nucleosynthesis. Their paper was able to account for the creation of all the elements necessary to sustain life on earth, from carbon on up. It was truly a monumental achievement. As Simon Mitton writes in Fred Hoyle: A Life in Science:
The four decided to publish their work as a single encyclopaedic paper, 108 pages in extent [...] They could have produced a series of shorter papers instead [...] had they done so, their work would have lost much of its magisterial quality and would have had less impact. B2FH remains a key paper. It defined the landscape for nuclear astrophysics, establishing a grammar and a lexicon, and providing (sic) an arithmetic and an algebra. (218)

But it was only Fowler who received the 1983 Nobel Prize in Physics for "his theoretical and experimental studies of the nuclear reactions of importance in the formation of the chemical elements in the universe." So why wasn't Hoyle, the godfather of stellar nucleosynthesis, included in the award? Nobel prizes can be shared by at most three people, but the 1983 prize was only given to two - Fowler and Subrahmanyan Chandrasekhar - so that wasn't the reason. Though nobody knows for sure, it probably had to do with the fact that in addition to being a brilliant scientist, Hoyle was also an obdurate, iconoclastic, stubborn man, whose disagreements with others became legendary both for their intensity and their duration. 

In 1974, Hoyle criticized the decision to award the Nobel to Anthony Hewish for discovering pulsars, when it was his student, Jocelyn Bell, who first noticed them. The 1974 prize was also split between Hewish and British radioastronomer Martin Ryle - chief among Hoyle's rivals. Beyond the 1974 Nobel dispute, which was a public embarrassment for him, Hoyle often clung to ideas long after the consensus had abandoned it, often in the face of overwhelming evidence. He never, even until his death, completely accepted the big bang cosmology, favoring instead a "steady-state" universe, though ironically it was Hoyle who derisively coined the term "big bang". Hoyle also published works alleging that the fossil archaeopteryx was a hoax. Scientists, alas, are no less immune to politics and favor than the rest of us. 

What it all means

We live in an complex and evolving universe. Nucleosynthesis is just a link in the chain of ideas that we can draw from ourselves to the fundamental constants of physics. From those constants comes the ability for nuclei and atoms to form; for disparate atoms to condense into stars under the force of gravity; for elements to be forged in the centers of stars; for those elements to be redistributed into the interstellar medium; and for new stars and planets to coalesce from that medium, rich with the elements necessary to sustain life.

Because I cannot say it better than Neil DeGrasse Tyson, I'll paraphrase him: we are part of the universe and the universe is a part of us.

Enjoy yourself some Moby!

No comments:

Post a Comment