Albert Einstein is justly famous for devising his theory of relativity, which revolutionised our understanding of space, time, gravity, and the universe. Relativity also showed us that matter and energy are just two different forms of the same thing—a fact that Einstein expressed as E=mc2, the most widely recognised equation in history.
But relativity is only one part of Einstein’s prodigious legacy. He was equally inventive when it came to the physics of atoms, molecules, and light. Today, we can see technological reminders of his genius almost everywhere we look.
Here are a few of the everyday products that showcase Einstein’s contributions to science beyond relativity.
Credit for inventing paper towels goes to the Scott Paper Company of Pennsylvania, which introduced the disposable product in 1907 as a more hygienic alternative to cloth towels. But in the very first physics article that Einstein ever published, he did analyse wicking: the phenomenon that allows paper towels to soak up liquids even when gravity wants to drag the fluid downward.
This process is what pulls hot wax into a candle wick (thus the nickname). More formally known as capillary action, it is also what helps sap rise in trees and keeps ink flowing into the nib of a fountain pen. Einstein’s paper, published in 1901, was an attempt to explain how this attraction worked. It wasn’t a very good attempt, as he himself later admitted. He argued at the time that water molecules were attracted to molecules in the walls of a tube via a force similar to gravity, which isn’t correct.
Nonetheless, that first paper did demonstrate that Einstein was already embracing the notion of atoms and molecules—something that was controversial at the time. Because these tiny, hypothetical lumps of matter were far too small to see or measure, a lot of senior physicists claimed that they could not be part of rigorous science.
Einstein was siding with younger, more radical physicists who believed that capillary action was just one of many phenomena that could be explained by the way atoms and molecules interact. In that sense, he was right, and so helped lay the scientific foundation for modern paper towels.
STOCK MARKET FORECASTS
Wall Street trading firms hire armies of mathematicians to analyse the daily ebb and flow of stock prices using the most sophisticated tools at their command. If these math wizzes can come up with even a slight hint about which way the prices will jump, their employers stand to make billions.
However, stock markets follow what mathematicians call a random walk: Unless some spectacular event occurs, the prices at the end of any given day are just as likely to have decreased as they are to have risen. If there are patterns that can be exploited, they must be extremely subtle and hard to find—which is why financial mathematicians are so highly paid.
And some of the math behind these delicate stock market analyses can be traced back to Einstein.
He was trying to explain an odd fact that was first noticed by English botanist Robert Brown in 1827. Brown looked through his microscope and saw that the dust grains in a droplet of water were jittering around aimlessly. This Brownian motion, as it was first dubbed, had nothing to do with the grains being alive, so what kept them moving?
A full explanation had to wait for Einstein’s paper on the subject in 1905. Still thinking about atoms and molecules, Einstein realised that the visible grains were actually getting jostled by invisible water molecules. On average, he reasoned, the impacts would come from every side equally. But at any given instant, more water molecules would be hitting one side of the grain than the other, giving it a quick kick in some random direction.
Einstein turned this insight into an equation that described the jittering mathematically. His Brownian motion paper is widely recognised as the first incontrovertible proof that atoms and molecules really exist—and it still serves as the basis for some stock market forecasts.
In March 1958, the U.S. Navy launched a grapefruit-size sphere dubbed Vanguard I into orbit around Earth. People paid attention, partly because it was the first to be powered by a futuristic technology known as solar cells—shiny slabs of semiconductor that turned sunlight into electricity.
Today, solar cells power almost all the hundreds of satellites orbiting Earth, along with many of the probes being sent to planets as distant as Jupiter. On the ground, solar cells are spreading across suburban rooftops, as rapidly falling prices bring them closer to being competitive with conventional electric power.
Again, Einstein didn’t invent solar cells; the first crude versions of them date back to 1839. But he did sketch out their basic principle of operation in 1905. His starting point was a simple analogy: If matter is lumpy—that is, if every substance in the universe consists of atoms and molecules—then surely light must be lumpy as well.
After all, Einstein argued, physicists had recently discovered that when a solid object absorbed or emitted light, it could do so only by taking a discrete step up or down in energy. And the easiest way to understand that weird fact, said Einstein, was to assume that light itself was just a swarm of discrete energy packets—particles of light that would later be named photons.
According to Einstein, the energy of each packet would be proportional to the light’s frequency, and that suggested an easy way to test the idea: Point a light beam at a metal surface. If the frequency was high enough, at least a few of its energy packets would have enough zing to knock electrons loose from the metal and send them flying out, so that experimenters could detect them. Solar cells work in essentially this way: Light streaming from the sun kicks electrons in the cell up to higher energy levels, producing a flow of electric current.
No one before Einstein had been able to fully explain this phenomenon. His achievement was considered so important that when Einstein finally won the Nobel prize in physics in 1921, it wasn’t for relativity but for explaining this co-called photoelectric effect.
If you’ve been to a conference or played with a cat, chances are you’ve seen a laser pointer in action. In the nearly six decades since physicists demonstrated the first laboratory prototype of a laser in 1960, the devices have come to occupy almost every niche imaginable, from barcode readers to systems for hair removal.
All of it grows out of an idea that Einstein had in 1917, as he was trying to understand more about how light interacted with matter.
He started by imagining a bunch of atoms that are bathed in light. As he knew from his previous work, atoms that are sitting in their lowest energy state can absorb photons and jump to a higher energy state. Likewise, the higher energy atoms can spontaneously emit photons and fall back to lower energies. When enough time has passed, everything settles into equilibrium.
That assumption gave Einstein an equation he could use to calculate what the radiation from such a system ought to look like. Unfortunately, his calculations didn’t match what physicists actually saw in the lab. Something was missing.
So Einstein made an inspired guess: Maybe photons like to march in step, so that the presence of a bunch of them going in the same direction will increase the probability of a high-energy atom emitting another photon in that direction. He called this process stimulated emission, and when he included it in his equations, his calculations fit the observations perfectly.
A laser is just a gadget for harnessing this phenomenon. It excites a bunch of atoms with light or electrical energy, then channels the photons they release into an army marching in perfect step in precisely one direction. The tribute to Einstein is right there in the word “laser,” which is an acronym for Light Amplification by Stimulated Emission of Radiation.
Header Image: Albert Einstein is seen during a visit to Washington, D.C., in the 1920s. PHOTOGRAPH BY HARRIS & EWING, LIBRARY OF CONGRESS