Science Friday - SciFri Extra: A Relatively Important Eclipse

Episode Date: May 28, 2019

This week marks the 100th anniversary of an eclipse that forever changed physics and our understanding of the universe. In May 1919, scientists set out for Sobral, Brazil, and Príncipe, an island off the west coast of Africa, to photograph the momentarily starry sky during a total eclipse. Their scientific aim was to test whether the sun’s gravity would indeed bend light rays from faraway stars, as predicted by Einstein’s theory of general relativity. After analyzing the data from the brief minutes of darkness, they declared Einstein correct. Carlo Rovelli, physicist and author, tells Ira the story. Subscribe to this podcast. Plus, to stay updated on all things science, sign up for Science Friday's newsletters.

This is Science Friday. I'm Irafledo. A hundred years ago this month, astronomers look to the skies, both to watch the majesty of a total solar eclipse, and to gather data, data that would test and support, the ideas of a certain German scientist named Albert Einstein. So we're opening up the sci-fri vault

to let physicist Carlo Rovelli explain what an eclipse has to do with relativity. Albert Einstein, of course, is a household name, today. But he wasn't always way back 100 years ago. He was in his mid-30s. He created his general theory of relativity, but that theory

needed to be tested before anyone would really take it seriously. So in 1919, soon after the dust settled from the First World War, two scientific teams sent out to take advantage of a unique astronomical phenomenon, a total

solar eclipse, to put Einstein's theory to the test. Let's take that trip back to yesterday year to 1919 to that most epic of eclipse experiments. And our guide is Carlo Revelli. He's the author of Reality is Not What It Seems and Seven Brief Lessons on Physics. He's a theoretical physicist at Ex-Marcée University in France. He joins us from Skype. Welcome back, Carlo.

Hi. Thank you very much. You're always welcome to join us. Please set the scene for us in terms of what Einstein was thinking about at that time back then? You used the word epic. I think it's very appropriate here. It's one of the great stories of science, I think, this eclipsis and the proof that Einstein was right in this prediction. Eisen has, was coming out from 10 years of major struggle, intellectual struggle, in which he was working mostly alone to build what we call today the theory of general relativity.

it, basically our current understanding of space and time. And it was an immense struggle for him. Ten years earlier, he realized that some major step ahead was needed. And he and a few friends worked very hard with very little ground. So it was mostly a purely intellectual adventure. He came out in 1915 with his beautiful theory. But of course, this is science. You don't believe a theory, even if it is a theory.

even if it is incredible beautiful, unless you can prove it right. And the eclipses of 1990 was a moment in which, I would say, spectacularly, beautifully, it was proven right. He actually proposed this experiment to look at the position of the stars during an eclipse and see if they had a different position during the night. I mean, the stars came out during the day, and he predicted that their path would be bent, the light from them, and they would appear in a different place in the sky, right? Right. He had this idea pretty early when he was beginning to work on his theory.

Already in 1911, so at sort of 10 years earlier, almost, at the beginning of his work on gravity, he had the idea that somehow light could be bent. Instead of moving straight, light could be attracted because that was his thinking. Space gets curved by a star, and time is slowing down near the star. So there are two phenomena that make the light bend.

And at the very beginning, he had only one of the two in mind. There's a slowing of time. So because of the slowing time, he was thinking that light slows near the star, and because of that, it bends. A little bit like when we put a stick into the water, we see bent, because light goes at different speed in the water and in air. So there was this bending, he completed this bending. Fortunately, nobody tested his first prediction because it was wrong.

So the 1911 prediction by Einstein was wrong. And later he developed the theory. The theory came in its full glory in 1915. This is during the war, during the big war in. Europe. And he realized that there are these two phenomena. So because of that, the effect is actually double than what he computed first. And in 1915 he came out with his definite prediction is that if my theory is right, you look at the stars when the sun is nearby. And of course eclipses is only needed for taking away the glow of the sun. When the sun is up, we don't see

the stars. But during an eclipse, we do see the stars. So in the moment in which, you know, there is an eclipses we see the star. We can look at the stars near, just very, very near to the sun. And that was a prediction. We should find them not the right position, moved a little bit away from the sun. It was quite spectacular,

the prediction, because this is something that was never observed before, and it was coming out from a very long series of deductions on the nature of space, on the nature of time, sort of a 10-year struggle by this solitary. I mean, if there's a moment which we can use the word genius, is this one. And there were various expeditions when Einstein made that prediction back in 1911. There was an expedition that went out in 1914, got caught just as the war was World War I was breaking out.

The expedition was arrested. Exactly. Right. And as you say, it's lucky that they didn't. They were not successful because he had a mistake in his theory. And by 1919, he had corrected that mistake. And then another expedition went out, right? Right.

So it was lucky that the first one did not get to the end. In a sense, I mean, he didn't have the theory complete. It was just trying to guess what the theory would give, still having a preliminary version of it. and of course if the measurement would have been different he would have thought well there's something wrong

it would have been less convincing even if we never even if we later had corrected it this way somehow chance was on his side because he could get to the end do the full calculation come out with a very precise number

1.75 seconds of arc so it's a very precise angle under which the star would would move and it worked. He's also fortunate that in that famous 1919 expedition, he had probably what, the best astronomer in the world

working from Sir Arthur Eddington, who went out to do the experiment. Arthur Eddington was a British astronomer, certainly a spectacularly good experimentalist, but also a very good theoreticians, and very rapidly he understood general relativity, very well. It's not an easy theory. It took some time to many great minds to digest it.

He understood it. He appreciated it. He got convinced that the theory could be right. It's a beautiful story because we should remember that was just at the end of the big first European war, which was a massacre, was a tragedy, was an immense killing in Europe. But that was a moment in which there was the hope that the world is over. and its peace and we live together. And this is an accomplishment of a German theoreticians and a British experimenter of the opposite side of the big war,

after years in which there was hate and violence and fury and despising one another. And now these two men on both sides collaborating intellectually and understanding one another could together accomplish this major step ahead in science. It's a beautiful story. The two men were both, and I don't think this is irrelevant in all this story, were both opposite to the war. Artur Edenton in England was a consciousness objector. He did not want to join the army, and this created problems for him. And in Germany, in Berlin, Eisen had fined a manifest against the war, again, creating not small problems for him. But I think that's the way it works. Great minds stay away from this human folly of the war and were thinking higher.

And they could understand one another. And from a distance, because they didn't meet before, they could collaborate. And the world was shocked by the result. It was an immense success. Very rapidly, the scientific community realized that there was a very strong element in favor of the theory. So Einstein became celebrated as a scientific hero. And it was a moment in which I think Europe, America, where thinking maybe we'll think about science and knowledge

and beautiful things now and not about wars. It didn't last long. It made Einstein an overnight. He made like a rock star of his time. It was all over the world. The news of it was splashed in newspapers. All over the world. There are famous clips from the New York Times, from the London Time.

I also looked at the Italian newspapers at the time in 1990, and it was immediately presented as an immense result. People were shocked because there are this title. Stars are not at their place. Space and time are not what we thought they were. The message that science is making a big revolution was out there and was well received by everybody in 1990. One thing a lot of the articles of the day seemed to mention

was that this experiment also proved that space could have limits that if it's bending around itself, then maybe it could bend all the way around. Yes, that's something that came out more or less at the same time because Einstein was immediately trying to use his own theory to understand what could be the shape of the universe as a whole and had this fantastic idea precisely in that moment that there's a possibility that the universe is not infinite,

because it bends on itself. So if we could travel in a direction forever, we would come back here, having made the tool of the universe. It's an extremely beautiful idea that somehow closes infinity. we still don't know that one if it is right or wrong. I personally think it's right, but I don't know. This is my guess. It's one of the open questions.

You know, science is not about closing questions. It's about opening questions and opening possibilities. And the possibility of a finite universe, it's very interesting, I think. It's very intriguing. Let's go to the phone. Let's go to Savannah, Georgia, one of my favorite cities. Omar, hi, welcome to Science Friday. Thank you for taking my call.

I hope I'm posing this question correctly, but are the observations as they pertain to general relativity the same and the experience, so to speak, the same around a large gravity well versus a smaller gravity well, like the sun versus the moon, something like that. I hope I posed that correctly. Yeah, I think you got it. Let's get, Carlos, thank you.

Yes, gravity is gravity of the effect. can be smaller or stronger or weaker depending on the mass, but it's exactly the same phenomenon. When they got very strong, we go to the black holes. And let me put in this way, 19 eclipses and edited an observation was the first spectacular confirmation of Einstein theory. Since then, we have had a series of them. the expanding universe, the existence of black holes.

And a couple of years ago, the gravitational waves produced by black holes, is the same phenomenon, the same gravity described by the same equations, but it's a variety of different consequences, all predicted by the theory, and in this century, one after the other one all verified. At the beginning, they all seemed crazy, and they turned out to be correct.

One last question for you, if this was such a dynamic and life-changing scientific event and the whole theory, both theories of relativity, why is it that that Einstein never won the Nobel Prize for these? He won it for something he did earlier. How did this escape? Well, he won the Nobel Prize for the photoelectric effect, which has nothing to do with all that. There's something else. seen from the eyes of today, Arisand could have deserved maybe four or five different Nobel Prizes, certainly the one for the electric effect he got,

but also for special activity and also for general activity. These theories were very complex, and in spite of spectacular prediction of 1919, the theory is a large, complicated theory. It took a long time before the... entire community actually took it for established physics. Now it is so. And the Nobel Committee, I would say correctly so, it's very cautious.

In a sense, it's not sufficient to explain something and to get one prediction right. It wants to see if the full theory works. So it waited. I think Nobel crisis cannot be done to somebody after the person is dead. I think now there will be no doubt I said it would deserve several other prizes. Well, Carlo, you deserve a prize for your books. They're so great to read. Carlo Ravelli, author of Reality is not what it seems,

and seven brief lessons in physics. Dr. Rivelli is a theoretical physicist at the Ex-Marcée University in France. That was Carlo Rivelli, recorded on Science Friday in the summer of 2017. Thanks for listening. Catch you on Friday. I'm Ira Flato in New York. Thank you.