There was physics before Einstein… in the same way that there was biology before Darwin.
Einstein didn’t just add some new ideas to physics. And he didn’t just add a unifying
framework for doing physics, like Newton. Einstein took what people thought was physics,
turned it upside down, then turned it inside out.
In the same way Darwin’s work made people see life itself differently, Einstein’s
work made humanity reexamine time and space.
[Intro Music Plays]
The classical worldview—associated with names you know, like Euclid, Aristotle, and
Newton—held that the rules governing space and time were absolute. One meter was always
one meter long; one hour would always be one hour long…
Matter was made up of immutable and indivisible atoms.
And energy moved through a medium called ether—because everything had to move through something,
right? God wouldn’t just make, I dunno, a howling void?
And with new disciplines like thermodynamics and fun applications like steam power and
light bulbs, human understanding of the fundamental forces of nature seemed pretty solid.
To quote historian of science Milena Wazeck, by 1900, “physics
was perceived by many to be an almost completed discipline.”
But within this almost-completeness lurked many unanswered questions. One of the biggest
was the failure of the Michelson–Morley experiment in 1887. They’d attempted to
demonstrate that the speed of light changed just a little when measured from the earth,
which is always moving, relative to the ether, which never moves.
But despite meticulous efforts, they couldn’t find any slowing-down. Light moved at a constant
speed—almost as if there was no ether. Then there was the electron and radioactivity.
In 1897, English physicist J. J. Thomson showed that cathode rays were made up of discrete
particles, way smaller than whole atoms—electrons. And around the same time, Marie Curie proposed
the theory of radioactivity, which classical physics didn’t predict.
Then, in the early 1900s, Ernest Rutherford experimented on radioactive decay. He named
radioactive alpha, beta, and gamma particles, classifying them by their ability to penetrate
different kinds of matter. And Henri Becquerel measured
beta particles and realized they were actually electrons exiting the nuclei of atoms at high
speeds. So by the early 1900s, radioactive decay was
understood, and the crisis of the immutable atom was as deep as the crisis of the ether.
A bunch of folks were investigating Maxwell’s equations and looking at black-body radiation,
or the heat emitted by dark objects when they absorb light.
Then Heinrich Hertz, the original radio wave guy, discovered the photoelectric effect,
or the paradox that certain metals produce electrical currents when zapped with wavelengths
of light above a certain threshold. Things started to get messy. Energy was thought
to be a continuous wave. But according to wave-based theory, there might be infinite
energy radiated back by black bodies zapped with certain wavelengths. This seemingly violated
the newly established laws of thermodynamics. Like, infinite energy doesn't seem right. So, in trying to explain the weird results
about light and heat, German physicist Max Planck theorized that light
may not be a wave after all, but a series of particles or quantum units. All very non-“classical.”
Sorry, Aristotle! Check out Crash Course: Physics for more about
quantum weirdness! Enter Albert.
Einstein was born in 1879 and grew up in southern Germany, Italy, and Switzerland. He dropped
out of high school, then studied to teach physics and math and became a Swiss citizen.
But he couldn’t get a teaching job—because he was Jewish.
So in 1901 he took a job at the patent office and started a Ph.D. at the University of Zurich,
which he finished in 1905. You’re going to want to remember that year…. 1905.
Now, Al wasn’t an academic hotshot or self-funded amateur. He was a working-class nobody who
did physics on the side. But he was also a patent officer who spent his days pouring
over technical documents. He was an outsider obsessed with math because
math is beautiful, and yet he was a deeply practical person who believed that good math
and science could be communicated plainly. Plus, he was young and bold. And he had a
super smart and supportive first wife, Serbian mathematician Mileva Marić.
So, the year he finished his Ph.D., 1905,
Al published his dissertation and four papers that changed physics overnight. This was his
annus mirabilis or miracle year, like 1666 had been for Newton.
Help us out, ThoughtBubble. At age twenty six, Einstein published revolutionary
work on:
1. Brownian motion, or the random motion of particles in fluids;
2. the photoelectric effect, supporting the idea of energy as a series of particles, not a wave;
3. the equivalence of mass and energy; and
4.special relativity.
Special relativity, especially made Einstein a scientific rock star. He proved that nothing
can move faster than light. This explained why Michelson and Morley hadn’t observed
light slowing in ether. And a lot of other things. Einstein got rid of all reference frames for
space and time. There was no longer some universal space in which physics happened. All measurements
became relative to the position and speed of the observer.
Space and time became one mathematically continuous spacetime. So an event at one time for observer
A could take place at a completely different time for observer B.
And the only constant in the entire system became the speed of light—which classical
physics predicted could change! From special relativity followed the equivalence
of mass and energy proof. Which was also mind-blowing. It’s probably the most memorable physics
formula ever, since it’s printed on mugs and T-shirts the world over: E = mc2. Or,
energy equals mass times the speed of light, squared. Or, mass and energy can be converted
into each other! Or, as Einstein said: “…mass and energy
are both but different manifestations of the same thing—a somewhat unfamiliar conception
for the average mind.” Now, it’s important to note that Einstein’s
new system of physics is simply a different system than Netwon’s. “Mass” and “energy”
mean something different in the two systems—because, to put it bluntly, Newton’s system turns
out to be not so universal. It only seems to work on earth, because we aren’t particularly
massive or fast-moving, compared to stars.
Thanks Thought Bubble. We don’t have time to explain all of the cool science that Einstein
and his generation of physicists did around World War One, but two things stand out:
In 1915, Einstein published the theory of general relativity. Special relativity was
all about comparing physical effects from different observer positions in terms of velocity,
or speed in a particular direction. General relativity provided all of the complicated
math regarding relativity and acceleration, or speeding up or down.
General relativity explains the physics of all situations. Special relativity is one
specific case of general relativity. General relativity nailed the coffin shut
on the classical, Euclidean worldview: now gravity itself was shown not to be a force like light,
but an effect, a distortion in the shape of space due to mass…
So the planets didn’t follow certain paths because of the attraction of the sun’s gravity,
but because the space before them was curved by the sun’s mass.
Einstein’s universe wasn’t a series of perfect spheres in an ether, but a void whose
very dimensions—whose rules, basically, other than the speed of light—could change.
Many of his colleagues initially objected to this, but Einstein was confident—and
patient. Astronomers awaited a solar eclipse in 1919, that allowed them to experimentally
confirm Einstein’s theory.
The confirmation of gravitational lensing made Einstein a scientific hero and an icon of
pop culture. As The Times of London reported, “Newtonian Ideas Overthrown.”
The second major act of science Einstein did around World War One was contribute to the
birth of modern particle physics. This story is about, in part, Einstein getting it wrong.
In 1911, Ernest Rutherford and Danish physicist Niels Bohr [“NEELS BOAR”] theorized a
model of the atom with electrons zipping around a heavy nucleus. Scientists began to study
the physics of the very small, just as Einstein was working out the physics of the very large.
But over the 1920s, these particle physicists saw a lot of weird quantum or particle-like
effects. Basically, Bohr’s Copenhagen group showed
that very small particles tend to act like particles sometimes but like waves at other
times. Like waves, their behaviors have probabilities. But when measured, individual particles are,
well particles. They are or aren’t there. In 1926, two German physicists worked out
the math behind these quantum mechanics: Werner Heisenberg invented matrix mechanics, which
[large exhale] are complex and Erwin Schrödinger, wave mechanics. And lots of dead/not-dead
cat jokes. Because, in 1927, Heisenberg proposed his
uncertainty principle: any observer can detect the position or velocity of any quantum particle,
at any given time interval, but not both at the same time.
Einstein haaated this. He believed in a universe ordered by an ultimate rationality, and he
famously quipped, “God doesn’t play dice with the world.” But Al, who had contributed
in lots of ways to the emerging model of atoms and particles of energy, was wrong about uncertainty.
By the 1930s, Einstein was easily the most famous scientist since Darwin. There was just
one problem. He was still Jewish. And living in Germany.
So in 1933, Einstein renounced his German citizenship and took a professorship at Princeton.
As a celebrity genius with intimate knowledge of the cutting-edge of German science—and
perfect hair—Einstein had the ears of politicians anxiously planning for another great war in
Europe. And, after one of his physicist buddies demonstrated
that an atom could be straight-up, stone-cold split open, Einstein felt that he had a moral
obligation to explain to the American establishment just how powerful atomic energy could be…
We’ll pick up this thread next time. Suffice to say, World War Two eventually ended,
and a new Cold War started—with scientific discovery, especially in the physics that
Einstein had created, as the new measuring stick of imperial might.
Israel offered Einstein the presidency, which he turned down. He lived the rest of his life
in the home of technological innovation and “fat sandwiches”—New Jersey.
Einstein always regretted that his work was used for violent ends. In fact, he was generally
skeptical of modernity. Way back during World War One, he wrote: “Our entire much-praised
technological progress, and civilization generally, could be compared to an axe in the hand of
a pathological criminal.” And yet, in the end, even the horrors of two
world wars never shook his faith that there was great meaning in the universe—a code
to be deciphered by science. He died never quite accepting quantum randomness,
and believing that, one day, humans would crack the code.
Next time—the Americans use Einstein’s world-threatening Bomb, and warfare changes
forever. It’s the birth of nuclear physics, the end of World War Two, and the beginning
of the Cold War.
Crash Course History of Science is filmed in the Dr. Cheryl C. Kinney studio
in Missoula, MT and it's made possible with the help of all these nice people.
And our animation team is Thought Cafe.
Crash Course is a Complexly production. If you wanna keep imagining the world complexly with us,
you can check out some of our other channels like
Scishow, Eons, and Sexplanations.
And, if you'd like to keep Crash Course free for everyone forever, you can support the series at Patreon,
a crowd funding platform that allows you to support the content you love.
Thank you to all of our Patrons for making Crash Course possible with your continued support.