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A Star-Crossed 'Scientific Fact': The Story Of Vulcan, Planet That Never Was

There's a common misconception that science is purely about cold, hard facts — concrete evidence, mathematical models and replicable experiments to explain the world around us.

It's easy to forget that there are people behind the data and equations. And when people are involved, there is always room for human error.

In The Hunt for Vulcan, author Thomas Levenson, a professor at the Massachusetts Institute of Technology, explores one glaring error that was taken as fact for more than 50 years: the belief that there was another planet in our solar system that we couldn't see behind the sun.

The mistake started with good science, Levenson says: the observation of something odd, and the development of a reasonable hypothesis to explain it.

"In the mid-19th century, an extremely talented astronomer — a really, really top-flight guy — was studying the orbit of the planet Mercury, and he found that there was a wobble in it. There was an unexplained extra residue of motion," Levenson tells NPR's Michel Martin.

And, Levenson says, according to the prevailing science of the time, there was a clear explanation for that: "another planet that we hadn't yet discovered, inside the orbit of Mercury, that could tug it just slightly off its expected course."

Professor Thomas Levenson, during the History Channel 2008 Summer Television Critics Association Press Tour.
Frederick M. Brown / Getty Images
Getty Images
Professor Thomas Levenson, during the History Channel 2008 Summer Television Critics Association Press Tour.

After the theory was announced, both amateur and professional astronomers reported that they'd actually spotted the planet. The planet was named Vulcan, and its orbit was calculated. It all appeared quite cut and dried.

Then Albert Einstein came along.

Interview Highlights

On Einstein's role in debunking Vulcan's existence

Albert Einstein had a problem in the first decade of the 20th century. In 1905, he invented the special theory of relativity, which explained motion in all kinds of circumstances but one — which was motion under the influence of gravity.

And so, from about 1907 on, he started trying to reconcile the fact that his special theory of relativity and Newton's laws of motion — Newton's ideas about gravitation — were incompatible, they clashed. He spent eight years on the problem, completed 100 years ago this month. He showed that it was the actual shape of space and time that produces this visible wobble in [Mercury's] orbit that requires no extra explanation for it. It's just that's the way the shape of space is where it happens to be.

On Einstein's reaction to this conclusion

He kind of lost his mind for a little bit. He did the calculation to see ... if his theory produced an account of Mercury that behaved as the real Mercury does. He was working through the calculation, and there are a bunch of steps, and he got to the end. And he got the number, and he looked at the number and he looked at the table of what astronomers had observed, and he saw that they matched. He said he had palpitations — I mean, his heart was literally shuddering in his chest. I just have this vision — it's completely made up — but I have this vision of Einstein, sockless, dancing at his desk when he got that number.

On why the story of Vulcan isn't better known

We don't teach the history of science by the things that people messed up on; we teach the history of science — we teach all of history — by the things that worked. You know, the transcontinental railroad goes through, and you drive the golden spike and there it is. You don't talk about all the railroad companies that went bankrupt somewhere in the Great Plains, right? And in science, you don't dwell on the blind alleys.

But the blind alleys are most of what science actually does. You have to go down the blind alley, you bang your head against that blank wall at the end of it, come back out again and try something else. And that's the real experience! And that's why Vulcan is so wonderful. It shows how you do that and ultimately how you get out of that.

The blind alleys are most of what science actually does.

On the ideas we believe today that may turn out to be ridiculous

I'd bet real money on this: that 100 years from now, somebody's going to look back on things we believe about who knows what, our current theories of the brain or consciousness, some of the deep ideas of the people working in physics, ways that social relations are presumed to work. You name it, there's something out there. We have an assumption, we have a mental model, we have a theory that just isn't right.

And 100 years from now somebody's going to look at them and say, "Wasn't that ridiculous? How could they get it so wrong? Isn't it obvious?"

I mean, yeah — human beings don't get things right all at once. It takes us a lot of time, we make a lot of mistakes, we have category mistakes. And it takes a great leap of the imagination to get from what you really know you know to the wacky thing that turns out to be more true than your remembered but erroneous past.

Copyright 2023 NPR. To see more, visit https://www.npr.org.

NPR Staff