Three decades ago, the theoretical physicists presented the “holographic principle,” an incredible theory asserting that our 3D Universe is a hologram.
Recently, physicists decided to apply such a principle to black holes. Here is what you need to know.
Black Holes vs. Holograms
Black holes, as defined by general relativity, are only simple objects. All we need to describe them mathematically is their spin, mass, and electric charge. So, there would be no visible difference if we threw something into a black hole – nothing that would hint to what that object might have been. That data is lost forever. But problems occur when quantum gravity kicks in because the rules of quantum mechanics say that data can never be lost.
In quantum mechanics, black holes are extremely complex objects, and they should comprise a lot of information. Jacob Bekenstein, for instance, discovered in 1974 that black holes have a temperature. Then, Stephen Hawking tried to prove that wrong but ended proving it right instead. He said that the black holes develop some thermal radiation.
So, black holes must also possess entropy – a means of figuring out how many different ways we can reset the atoms of an object and still have it look the same. Hawking was the first to evaluate that entropy, introducing the notion of “Hawking radiation.”
The notion states that the black hole can emit a bit of energy, lowering its mass by a similar amount, evaporating over time. The smaller the black hole, the quicker it disappears. But what happens to the information it comprised? Is it lost, thereby breaking quantum mechanics, or is it preserved in the Hawking radiation?
The holographic principle is based on the string theory as a meant solution to that information paradox in the 1990s. It states that the data about a black hole’s core could be encoded on its 2D surface area rather than within its 3D volume.
Recently, Gerard ‘t Hooft and Leonard Susskind extended that notion to the whole Universe, comparing it to a hologram: our 3D Universe arises from a 2D source code. Then, another discovery brought incredible results. Juan Maldacena found an essential duality (AdS/CFT correspondence). Such a thing sums to a mathematical reference that lets physicists go back and forth between the two worlds.
“The holographic principle allows us to describe gravity using a language that does not contain gravity, thus avoiding friction with quantum mechanics,” explained researcher Paolo Milan. In the future, maybe we can find more answers. Until then, the scientists still have to figure a multitude of things.