Among Albert Einstein’s most compelling theories is the idea of “spukhafte Fernwirkung,” also known as spooky action at a distance. In this video, science writer George Musser gives a crash course in Einstein’s fascinating model, which seeks to explain how objects separated by great distance can still seem to be in sync.

Musser is the author of Spooky Action at a Distance: The Phenomenon That Reimagines Space and Time–and What It Means for Black Holes, the Big Bang, and Theories of Everything.

George Musser: So spooky action at a distance was [Albert] Einstein’s kind of appellation for the idea of nonlocality. Non-locality is the technical term for it. And what it means is that there’s a connection between different objects or places in the universe. There’s some kind of link or bond between particles or places or just objects in general that can be quite far apart from one another. In principle, they can be on the other side of the universe even. And the natural world is filled with connections of different sorts. That’s really what science is all about — making sense of those connections. But what’s unusual about these connections is there doesn’t seem to be a connector. There’s no mechanism that actually relates the object in one place to the object in the other. And yet those objects still act in unison. They’re able to coordinate what they do. So that’s kind of the mystery of this whole subject why Einstein thought it was spooky that there was this connection and yet no seeming mechanism to explain it.

This phenomenon of nonlocality that worried Einstein actually comes out in many different ways. So the original way that Einstein was worried about concerned subatomic particles. So electrons, photons, neutrons, ions, you know, small things because they’re just easy to manipulate. And what you would do is you would create them together or you might bring them together and it has some kind of interaction and you develop a connection between them. They develop some kind of bond. And then they separate and in the original experiments they would go to the other side of the laboratory or the laboratory bench. And then they got more sophisticated and went to the other side of the city or the island chain. And in principle, you could take it, as I've said, to the other side of the known universe or even the unknown universe. And then once they have it in those — the two particles, in this case, in those remote locations they manipulate them. They perform some kind of action on them. They might measure them just to see what their properties are. And they can do that in several different ways. And what turns out to happen is that the particles are able to coordinate. They come up with the same measurement values.

So the example I often give is two coins. So you can treat some of these particles as having two possible outcomes of a measurement. And you can think about it as heads or tails of a coin. So you create two of them. You give one to your friend. Your friend goes off somewhere and you keep the other. And you both flip the coin and you come up with heads, they come up with heads. You come up with tails, they come up with tails. Heads, tails. It just goes back and forth. And yet they’re the same answer on both sides. And again there’s no mechanism. There’s no reason they would be. The scientists have gone through the different possible tricks like, for instance, are they double-sided coins? Are they trick coins? And they’ve kind of done experiments to rule that out. Is there some kind of surreptitious radio signal passing between them? They’ve ruled that out. Is there some kind of predetermination? I mean they would have gone through all the options and yet they can’t explain why these coins land on the same side. But now I think the progress of science and understanding the nature of space and time have taken us to a possible explanation.

So if you think of those two coins — they’re on opposite sides of the universe or the continent or wherever they may be. But they act as though they’re right next to one another. They act as though they’re kind of nuzzled up together. So they don’t seem to have any distance between them. They’re acting as though there’s no distance between them although if you go and measure the distance, it’s enormous. So the proposition is that the distance between them is somehow an illusion; it’s somehow kind of a mirage. Or maybe a better way of putting it, it’s a construction that those particles or those coins, the metaphor, are rooted in a layer of reality where the distance doesn’t seem to exist. They’re juxtaposed even though they look like they’re far apart. And the distance is real to us. So it’s real at our level of reality, but it’s not real to the particles. So the idea is that the concept of space, of distance, all the spatial concepts we deal with in science are emerging from that deeper level. They’re not fundamental in the world. They’re derivative.