Name: アインシュタインの革命科学のクラッシュコースの歴史#32 (Einstein's Revolution: Crash Course History of Science #32)
Uploaded: 2021-01-14T10:27:57.000Z
Duration: 12 min 7 s
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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.

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

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

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

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

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アインシュタインの革命科学のクラッシュコースの歴史#32 (Einstein's Revolution: Crash Course History of Science #32)

constant

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