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2021年1月26日发(作者：儿童权益)
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No Ether !

In 1905, Albert Einstein published a paper that explained his
special theory of relativity. It solved a problem about how people
understood light.
At the time, scientists believed that light waves worked like waves
in the ocean. Ocean waves travel through the water. They thought
light waves had to travel through something, too. They called this
substance ether. There was one problem. Two scientists did an
experiment to measure the ether. They couldn’t find any.

Einstein’s paper started
with the work of other scientists. He used
their math to explain that light did not need to travel through
anything. Light was different from ocean waves. Light always
travels at the same speed. That speed is a very big number.
Instead of always writing the number, Einstein just wrote c.
Space-time

Einstein wasn’t done yet: Light was very different from ocean
waves!

Imagine you are on a sailing ship, traveling alongside the waves.
From your perspective on deck, the waves might appear to stop
moving. You could even travel faster than the waves; then, the
waves would appear to go backward!

Light works differently. Light always travels at c. Imagine you have
a fast bicycle and your friend has a flashlight. Your friend shines the
flashlight, and you pedal in the same direction. No matter how fast
you go, the light will always shine ahead as if you were standing
still.

Einstein said that the faster you go, the slower time goes and the
shorter everything gets. The front of your bike will shrink back
toward the end of your bike. The more you try to catch the light, the
slower time goes and the shorter you get. We don’t notice this in
everyday life; it only happens close to the speed of light.

Einstein demonstrated that the old definitions of space and time
needed to be changed. Because they are connected, Einstein
suggested calling them space-time.