Soundings: What makes life possible makes it risky |

Soundings: What makes life possible makes it risky

Things fall apart … so easily that one might wonder why anything holds together.

Earth orbits the sun at roughly 65,000 miles an hour. Why don’t we fly off into space? What holds the solar system together?

In the 1600s, legend has it, Isaac Newton sat beneath an apple tree when an apple fell to the ground, triggering his realization that gravity – the force that pulls apples downward – also binds the moon to the Earth, Earth to the sun.

Our bodies feel gravity. Why doesn’t it pull our heads off our necks and down to the ground?

Our bodies are held together by a force that’s even stronger than gravity.

The smallest magnet can lift a pin from the floor, overwhelming the gravitational pull of the entire Earth. The electromagnetic force, which links atoms into molecules, tissues, organs and us, is much stronger than gravity.

An atom consists of a nucleus, surrounded by a cloud of electrons. The nucleus is filled with protons. All protons carry a positive charge; the electromagnetic force causes them to repel one another.

What keeps all those mutually repellent protons within the nucleus?

The nucleus also contains neutrons, neutral particles that sandwich themselves between the protons. By preventing the protons from getting too close to each other, neutrons mellow their mutual repulsion. But not enough to keep them from blowing the nucleus to bits.

Protons (and neutrons) are bonded together within the nucleus by a force even stronger than electromagnetism: the strong nuclear force, or, more simply, the “strong force.”

The strong force is stronger than the electromagnetic force; the electromagnetic force is stronger than gravity. Suppose we could shift the balance, and make electromagnetism a bit stronger. Atomic nuclei would fall apart – and we would not be here.

Working backward from what we see today, we conclude that the universe began, some billions of years ago, in a gigantic explosion. Suppose gravity were a bit stronger than it is. A fraction of a second after the Big Bang, the universe would have ended in a Big Crunch, a gigantic collapse in which it would collapse in on itself – and we would not be here.

That the forces that bind our universe are neither too strong nor too weak, but are “just right” for us to exist is one of many deep mysteries of the universe. Perhaps other universes exist, universes in which the forces have different strengths – universes in which life is impossible.

That the various forces have just the strengths they have not only make life possible – they make it risky.

In the heaviest nuclei – uranium, for instance – the balance between strong nuclear attraction and electromagnetic repulsion is so delicate that the nuclei are unstable. From time to time, a particle escapes, propelled out of the nucleus at nearly the speed of light: Uranium is radioactive.

As the world raced toward war in the late 1930s, scientists discovered a uranium nucleus could be tweaked into a state so unstable it would break in two: nuclear fission.

When, in a chemical reaction, atoms re-arrange themselves in response to the electromagnetic force, they typically release a certain amount of energy.

When, in a fission reaction, protons and neutrons re-arrange themselves in response to both electromagnetism and the strong force, they typically release 200 million times as much energy.

The forces that make life possible have also given us extraordinary power. As Einstein put it, the release of nuclear energy has changed everything – but our mode of thinking.


Alan Stahler trained as a biologist and is an amateur astronomer. He teaches private enrichment classes for students of all ages. His science programs can be heard at noon on alternate Tuesday on KVMR-FM (89.5).

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