By Jonny Lupsha, Wondrium Staff Writer
A thought experiment about elevators helped inspire Albert Einstein. The sensation of gravity changing as an elevator ascends or descends caused him to realize the relationship between acceleration and gravity. On this week’s Wondrium Short, elevate your gravitational awareness.
In the early 1900s, Einstein realized that a person falling from a high place doesn’t feel their own weight—an occurrence that he would later call “the happiest thought” of his life. Years later, he traced the origin of his theory of general relativity to this same thought, which also brought a thought experiment to life: Why does it feel like gravity is changing when we’re in an elevator that suddenly begins to travel up or down?
Everyday technology owes much to Einstein’s work in physics, as well as, the work of those who followed in his footsteps. In his Wondrium video series Einstein’s Legacy: Modern Physics All around You, Dr. Chad Orzel, Associate Professor of Physics and Astronomy at Union College in Schenectady, New York, discusses the elevator experiment and its importance to general relativity.
Lovin’ an Elevator
“A milder form of this phenomenon of falling from a high place can be experienced by riding in an elevator,” Dr. Orzel said. “When you enter an elevator on a high floor and start down, for a brief moment as the elevator starts, you feel lighter; as you slow to a stop at your floor, for a moment, you feel heavier. The same thing happens in reverse when you start at ground level: As the elevator starts, you feel heavier, and as it stops, you feel light.”
Dr. Orzel said this happens because the sensation we experience which we often think of as “weight” in our daily lives isn’t gravity pulling us down—it’s the ground pushing up. We take it for granted and only notice it when it changes, such as in an elevator. So when an elevator descends, for example, it’s very close to the idea of someone pulling the floor out from under us.
“During moments when the elevator is accelerating—speeding up or slowing down—it’s as if the force of gravity changes.”
Einstein worked in a patent office for years and regularly found inspiration when left to his thoughts. It was such an occasion that led to his theory of general relativity.
“Einstein’s great insight, when he was daydreaming in the patent office, was that this is not an illusion of changing gravity—it’s indistinguishable from changing gravity,” Dr. Orzel said. “This set him on a path to extend his 1905 theory of special relativity—called that because it only applies to the special case of motion at constant speed—to a more general theory that could handle accelerating motion and, in the process, explain gravity.”
According to Dr. Orzel, general relativity comes from elevating—no pun intended—the connection between acceleration and gravity to “the status of a fundamental principle of physics.” In general relativity, it’s known as the Einstein equivalence principle, which declares that the effects of gravity and of the effects of acceleration are indistinguishable.
“For practical discussions of the equivalence principle, it’s useful to split it into two parallel statements,” Dr. Orzel said.
The first statement is, “Physics, according to an observer who is freely falling under the influence of gravity, is indistinguishable from physics according to an observer who is at rest in a world without gravity.” The second statement is, “Physics, according to an observer who is at rest in a gravitational field, is indistinguishable from physics according to an observer who is accelerating in a world without gravity.”
Experimenting on these ideas must be done in local measurements, in a metaphorical closed box. Luckily, elevators provide a perfect environment for both.
Einstein’s Legacy: Modern Physics All around You is now available to stream on Wondrium.