The sun’s natural gravitational lensing is more powerful than you thought

Let’s turn the sun into a telescope. In fact, we don’t have to do any work—we just have to be in the right spot.

But how can the sun be a telescope? The sun is not a mirror, but it is a lens. And we understand it’s a lens through the magic of gravity.

When Einstein developed general relativity, he realized that gravity can strongly bend the path of light—far more than previous calculations using only Newtonian gravity predicted. In fact, one of the first tests of Einstein’s theory of relativity was the Eddington expedition to look at the deflection of starlight near the surface of the sun during a total solar eclipse.

Massive objects bend the path of light. Lenses, like pieces of curved glass, bend the path of light.

Coincidence? Yes.

It’s a total coincidence, but it does mean that everything we know about optics, about grinding lenses, about bending light, about focusing light from a distant object onto a focal point to magnify it and increase the resolution, all that, we can take all that language, all that mathematics, and transport it over into gravity.

We can create gravitational lenses where the gravity of a massive object can bend all the light that comes near it and send it to a focal point where you can just sit and enjoy the magnified image exactly as if there was a giant piece of curved glass right there.

This technique already works. We already use gravitational lenses in the universe to leapfrog vast distances and see into the early universe where some of the first galaxies to appear in the universe are simply too far away, too small, and too dim for us to see.

But when they happen to coincidentally just randomly sit behind a giant massive cluster of galaxies, the gravity of that cluster of galaxies will bend that light, focus that light, amplify that light, and increase the resolution. And we can use an entire cluster of galaxies as a giant lens to magnify what’s behind it and allow us to see some of the most distant galaxies in the universe.

In the solar system, the most massive object by far is the sun. We know that the gravity of the sun bends the path of light around it as if it were a giant lens.

It’s like we have a giant telescope just sitting there in the center of the solar system, and it is by far the most powerful telescope we can conceive of with reasonable extensions of our current technological limits.

The sun as a gravitational lens is the most powerful accessible telescope in history.

We use Einstein’s relativity to calculate what the magnifying power of the solar gravitational lens could be. Its angular resolution goes all the way down to 10 to the minus 10 arcseconds. That is 1 million times better than the Event Horizon Telescope.

And because of the effects of gravitational lensing, you don’t just get higher resolution. You also get amplification of brightness because it combines a bunch of light rays and focuses them. You get brightness amplification up to a factor of 100 billion.

To say this is better than any known telescope is an understatement. This is better than any possible telescope that we could possibly build in any possible future for the next few hundred years, and it’s just sitting there.

What do you get with that kind of resolution? Let me give you an example. We know there is a planet orbiting our nearest neighbor star, Proxima Centauri. We call the planet Proxima b.

We know this planet. We know it’s rocky. We know it’s Earth-like. We know it’s sitting in the habitable zone of Proxima Centauri. A telescope constructed from the solar gravitational lens would be able to map the surface of Proxima b to a resolution of less than 1 kilometer.

That’s not 1 pixel containing the entire planet. That’s creating a detailed map of the surface down to 1 kilometer.

Take a look at an image of Earth with a resolution of around a kilometer. It looks like… Earth. You can see coastlines. You can see hurricanes. You can see jungles. You can trace out rivers.

The solar gravitational lens could build a decent map of any exoplanet sitting within roughly 100 light years of us. Compare that to any telescope past and future, and there’s simply no competition.