by Paul M. Sutter at Popular Mechanics: As theoretical physics delves deeper into the fundamental nature of reality, we’re left to grapple with the questions it leaves us. For example, some physicists claim that our universe is merely an illusion, a product of quantum machinations happening in a lower-dimensional setting—in other words, a hologram.
But do these latest theoretical insights offer revelations into reality, itself, or merely serve as mathematical tools to help us solve thorny problems? When it comes to the most cutting-edge physical theories, what is a product of our imaginations, and what is a product of the universe?
Black Holes May Be Evidence
The trouble began with those bothersome boogeymen of the cosmos, black holes. On the surface (and careful readers will be rewarded later with the realization that this is a pun), black holes are simple; stuff falls in and never gets out. All the information about that stuff gets locked away behind the event horizon, never to be seen again. But in the 1970s, famed astrophysicist Stephen Hawking realized that black holes aren’t entirely black. They’re a little gray and a little leaky, emitting a tiny amount of radiation, which causes black holes to evaporate slowly, but inevitably, from existence altogether.
However, that radiation carries no information with it, which brings up a nasty paradox: information goes in, but doesn’t come out, and then the black hole goes away. So what happened to all the information?
In this context, information is the list of all the properties of all the particles that fell into the black hole—in other words, everything you need to reconstruct the original objects that fell in. Instead, what comes out of a black hole, due to Hawking radiation, is just a bunch of random particles. You can’t tell what fell in based on the radiation coming out.
A major clue came in the decades that followed Hawking’s extraordinary discovery. One way to measure the amount of information is through entropy, a thermodynamic concept that is loosely related to the amount of disorder in a system. Black holes have a surprising property: their entropy is proportional to their surface area, not their volume. In other words, the amount of information in a black hole is related to its two-dimensional surface, not its three-dimensional volume
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