In this series on the four fundamental forces of nature that shape our universe, we now come to the force that most expressively impacts our lives. We’ve seen how gravity shapes the large-scale structures of our universe, pulling matter together to form stars and planets. The strong nuclear force does its part to combine nucleons into elements essential for life, releasing its prodigious energies that cause stars to shine. With the electromagnetic force, we discover the essence of not only atomic structure, but of the form and visible beauty of everything that materially exists.
Atomic structure is determined by the electromagnetic force since this force alone holds the electrons in orbit around the nucleus. Gravity and the strong nuclear force play no role in the chemical properties and interactions of atoms. Gravity is far outmatched in strength by the electric force between electrons and protons (by a whopping factor of 1036), and the nuclear force doesn’t even act upon electrons.
The Finer Features of Atoms
Quantum mechanics governs the details of atomic structure due to the atomic size scale being so small that the wave properties of the electrons cannot be ignored. Therefore, Newtonian mechanics, which treats particles as localized solid bits of matter, fails to capture most of the finer features of atoms. Nonetheless, even in the equations of quantum mechanics (principally the Schrödinger equation), the strength of the electric force provides the specific outcomes of the nature of atoms.
Governed by the electromagnetic force, atoms interact with one another to form the substance of everything we see and are. The “wetness” of water, the smooth coldness of steel, the hardness of stone, the saltiness of salt, and every other property of matter owes its existence to manifestations of the electromagnetic force between the charged particles of which matter is composed.
Living Fields of Green Grass
Not only does the texture of material objects depend upon the electromagnetic force, but also their interactions with light, giving us their apparent color in the wavelengths of light the objects reflect rather than absorb. Why are living fields of grass green (and leaves and tree needles)? We might know that the molecule chlorophyll plays a role in producing this pleasant color, but at root lies the nature and strength of the electromagnetic force, tuned to allow vegetation to absorb red and blue light and to reflect green light from the rainbow spectrum of our sun. Adding significant benefit, chlorophyll’s interaction with light powers photosynthesis, by which plants extract energy and produce oxygen as a byproduct:
It would be impossible to overestimate the importance of photosynthesis in the maintenance of life on Earth….If photosynthesis ceased, there would soon be little food or other organic matter on Earth.
The electromagnetic force factors in through the strength of the attraction between the positive and negative particles (protons and electrons, respectively) that make up physical matter. In absorbing light, a harmonized match, or resonance, must exist between the energy of a particular wavelength or color of light and the available energy levels of the electron states of the substance. This match depends on the strength of our featured force.
A Simple Device from Middle School
In physics, the electric and magnetic forces are lumped together into the category of a single force. We see some hints of this unity in a simple device we might have made in middle school science class — an electromagnet. Wrap some wire around an iron nail, connect the ends to a flashlight battery, and you’ve got a magnet able to pick up small things like paper clips. Or scale this up and you can make an electromagnet strong enough to pick up old cars in a junkyard. In either case, moving electric charges (electricity flowing through the wire) create a magnetic field.
In the 1800s, Michael Faraday discovered that a moving (or changing) magnetic field can create electricity. The symmetry goes even further and can be stated this way: a changing electric field creates a changing magnetic field, and a changing magnetic field creates a changing electric field. Lest you think I’ve just gone too deep in the weeds of physics, what I’ve just described is radio waves, or any form of electromagnetic radiation, including light.
A Deeply Designed Nature
In the various materials that make up our physical world, the precise strength of the electric force on the outermost (valence) electrons determines whether that material acts as an insulator, conductor, or semiconductor. Our success in developing electrical technology and complex electronics depends upon the availability of all three varieties of materials; lacking just one of the three would render electrical technology impossible or severely limited.
The electromagnetic force is responsible for the properties of light, and it also determines how light interacts with atoms and molecules, providing foundational sustenance for life. The pervasively essential properties of the electromagnetic force undergird every chemical interaction, allowing the precise and complex biochemistry within our cells to properly function and keep us alive. As a physicist and someone with a vested interest in being alive, I stand positively in awe of the deeply designed nature of the electromagnetic force.