Name: Einstein's Eclipse Changed the Course of Physics Forever
Uploaded: 2020-03-25T02:57:20.000Z
Duration: 9 min 14 s
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Adverbs of manner

About every 18 months, the Moon passes directly between the Sun and the Earth for a total

This alignment casts a brief shadow on Earth that we can track … and its location changes

This year’s eclipse swept across South America, stretching over Chile and Argentina.

It was visible over the Atacama desert, hovering right above some of the world’s most famous

telescopes, and gave a spectacular 2 minute show.

Eclipses are grand celestial events, a chance to witness the mechanics of our solar system

But they also play an important role in the timeline of scientific discovery.

Over a hundred years ago, a relatively unknown German scientist introduced a new theory that

would completely shift our understanding of space, time, and motion.

And if you’re someone who doesn’t really understand this theory today, well, neither

It took two intrepid astronomers, and an ambition solar eclipse expedition in the midst of a

world war, to prove it and turn Einstein into a household name.

So it’s November 25, 1915, and Albert Einstein presents his famous field equations to the

He challenged the reigning genius, who saw space as flat and unchanging, and defined

gravity as a force that objects exert upon each other.

Now, space and time are a four dimensional thing called spacetime, and it can be warped

That warpage creates the effect of gravity.

This was just wild new territory for scientists.

If you try to do calculations in Newton's theory with the new rules of relativity, it

actually gets you a different answer depending on who's doing the measurement or the calculation.

Of course that's uncomfortable for a physicist, how do I know which answer is the right one?

Einstein himself was very conscious of the need to test the theory.

And so, Einstein quickly realized, "Well, what I propose is that astronomers could go

to an eclipse, take a photograph of the stars close to the sun...and compare that to a photograph

of the same stars at night when the sun isn't there.”

An eclipse gives scientists a unique opportunity to study light as it passes near the sun.

Einstein’s theory predicted that the sun’s gravitational field would bend the starlight’s

path, making the stars appear slightly out of place in a photo, by 1.75 arcseconds to

If Newton was correct, it’d only be by half as much.

He got a German Astronomer colleague called Erwin Freundlich to try to observe an eclipse

in Russia.Freundlich was German, so the Russians arrested him as an enemy alien.

We have this picture of Einstein furrowing a kind of a lonely path, trying to persuade

astronomers that this is something they should do and finding that it's difficult and not

And that’s partly because the backdrop on all of this is World War I.

You couldn't get German journals delivered to you in Britain during the war.

The telegraph cables, which would have been the internet of the day, were cut physically

so that you couldn't send a telegraph and the astronomers really depended on these telegraphs.

It really was a very clean break in scientific relations and furthermore, the nature of the

First World War soured relations between the scientists themselves.

But Einstein’s theory did grab the attention of a British astronomer.

The sheer intrinsic scientific excitement and potential of the theory were recognized

by important people like Astrophysicist Arthur Stanley Eddington.

And it's probable that he went to Dyson, who was a close friend of his.

Dyson said, "Well, you know, if you were going to test this theory, absolutely the best time

That eclipse will take place when the sun is in a special place in the sky, right in

That is the closest star cluster to the earth and therefore there will be an unusual number

So, that really lit a fire under them The eclipse prep started with maps.

They needed to track the path of totality and pinpoint the best location for the expedition.

A good part of the track was the Mid-Atlantic Ocean, that's not much good.

You can't do this experiment from a ship.

The rest of the track passed through the world’s two great jungle basins, the Amazon in South

America and the Congo in Africa.You need a railway or a port and the middle of the jungle

Sobral, a city in Northeastern Brazil, quickly emerged as the best contender.

And the Island of Principe off the coast of West Africa was one of the few places that

They decided that they should go to different locations because that would give them a better

chance of at least one of them avoiding bad weather and to some extent, the two expeditions

They needed telescopes to take images of the star field during the eclipse, but they weren't

in a position to take the complete telescope with them.

They took the lens the most important part of the telescope out of the telescope.

Then they brought with them what's called a coelostat mirror.

You set it up so that the mirror turns and cancels out the motion of the earth and the

lens and the telescope tube doesn't have to turn at all.

The plates obviously were critical to the whole enterprise because it was only by comparing

the positions of stars that you could actually make this tiny measurement.

Using photography to measure celestial objects was a pretty cutting edge technique at the

They had exactly the right expertise for this problem.

It was a very, very delicate measurement.

And as a matter of fact, we have a perfect example in the case of this eclipse.

After photos were taken and analysis completed, the teams had three sets of data in front

of them, with bad weather and other complications to consider.

One of the two instruments had a faulty mirror.

Now you have a real problem and it's the kind of problem that comes up all the time in science.

You have three instruments, which gives you three measurements.

Two of them agree with Einstein, one agrees with Newton.

They deliberated and ultimately determined, we don't trust this instrument.

Then that leaves us just two instruments agreeing with Einstein, so we think Einstein is right.