This past week saw the start of an experiment to test the holographic principle, which has lead to several request for a simple explanation of what the holographic principle is. Although it is not my specialty, I will try to provide a basic overview.

This idea starts with work in the 1970s on black holes. A black hole is an object in space that is so dense, not even light can escape from it. Nothing can ever escape from it (except possibly for thermal energy through Hawking radiation). Which led Bekenstein to question what happens to the information that falls into a black hole. For technical reasons it cannot be destroyed, and because Hawking proved that black holes eventually evaporate and disappear there is a paradox in modern physics. Either the black hole leaves a remnant full of information, or information is destroyed in spite of the laws of physics. But that is a subject for another day.

The work of Bekenstein, Hawking, and many others since have proven that the amount of information that a black hole can contain is proportional to its surface area. Consider a stack of books - if you want to double the amount of information in that stack then you must double the number of books and therefore double its volume. But if you want to double the amount of information contained in a black hole, you are only doubling its surface area. If you were to compress the original stacks of books into a black hole, you would find that they did not contain as much information as we thought.

However any system could in theory be compressed into a black hole. That means that no system - not the earth, not the galaxy, and not even the entire visible Universe - contains as much information as we normally assume. In fact the information contained in the entire Universe must be less than the information that could be contained in a two-dimensional shell that surrounds the Universe.

This is the crux of the holographic principle. That everything we can see or measure, or interact with, is consistent with a two-dimensional Universe that gives the illusion of being three dimensional. If this is true, then we are nothing more than a complicated hologram. It is an interesting thought.

The experiment that was started this week is going to try to test this theory. It is too complicated to give in detail here, but the basic principle is that the experimenters will use high-frequency lasers to compress as much information as they can into a small region of space in the lab. An interferometer will then be used to determine if the tiny region of space contains enough information in the form of photons to fill its volume, or a shell surrounding it. 

So perhaps in the near future, we as a society will need to rethink our very existence!