One Thing Leads to Another

My dad is hugely interested in physics. (He keeps telling me that he used to be interested, but not anymore. But that’s another story…). Unlike Rutherford who called other fields “stamp collecting”, my dad doesn’t have contempt for other fields. But I wonder whether even with his non-Rutherfordian worldview, my dad knew how totally unrelated fields drove physics even in the last century.

Everyone can imagine how somewhat similar fields like chemistry could influence physics, but geology? Or paleontology (remember Ross from Friends? The field of fossils and dinosaurs)? How could they possibly have pushed the boundaries of physics?

But influence they did. It all started when people tried to compute the age of the earth a couple of centuries ago. As geologists started analyzing layers of rocks, they could not assign values to the ages of any of these layers since there was no known method to do so at that time. Then a renowned physicist got involved in the effort: Lord Kelvin. He came up with an upper limit on the age of the earth: 24 million years. Before you laugh, remember he was basing his upper limit using the physics of the day. There were two known facts he used in his calculations:

1)      The earth radiates heat: anyone who’s read or seen the inside of a coal mine knows that.

2)     The sun burns continuously and must be using up fuel.

Kelvin was seeing how long the known means of generating energy could last when factoring in facts #1 and #2, and that’s why he went so horribly wrong in his calculations.

Enter the fossil finders. As the fossils started piling up, it became obvious that the earth had to be much, much older than Kelvin's limit. It was beginning to look like the fossil records were contradicting the limit imposed by physics! Something had to give…

The fossils were right, the physics of the day had been missing a colossal source of energy. But this didn’t become clear until Henri Becquerel discovered phosphorescence. And with that, physicists had found that radioactive decay could serve as a new source of energy. This was both good and bad news: good because it allowed the upper limit on the age of the earth to be increased to match the fossil records; bad because a source that could provide energy without any apparent depletion violated physics!

Until, that is, Einstein came up with his famous equation,

E = mc²

and voila! All was right with the universe again. The equation helped explain how even an extremely tiny depletion in the source could generate a huge amount of energy. That meant the source of energy was indeed getting depleted after all, albeit very, very slowly.

Radioactive decay also provided a means to date items using the famous half-life of elements. When the technique was applied to finally find the age of the earth (4.5 billion years), it created a new problem for astronomers: the earth was now older than the accepted age of the universe! Which forced astronomers to revisit the topic. And ultimately to revise the age of the universe to be 14 billion years.

I found this whole story very interesting: the way we learn things when we are kids, each field is made to look isolated and proceed without influence from any other field. But that is clearly not at all how knowledge evolved.