A lady mentioned to me yesterday that during a conversation with others she heard one say that a black hole is a hologram. Can somebody explain how a black hole is a hologram?
She might have overheard(and misunderstood) just part of the conversation: There is a theory that the entire universe is a hologram, and that a black hole is a good example of this idea.
It’s the idea that all the information contained in a black hole is contained on its surface (i.e. horizon) as the entropy of the black hole is proportional to its surface area, rather than volume. In this way a black hole would be analogous to a hologram: apparently 3D, but essentially 2D (as it can be entirely described by a 2D surface).
It’s all esoteric stuff. A quick recap:
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The nature of the initial singularity that the Big Bang theory infers by means of the known laws of physics (which either do not apply to the initial singularity itself or apply to it in really mysterious ways) is deeply unknown;
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The enormous perceived universe represents a mere 5% of the real mass-energy content of all existence, 95% of which consists of dark energy and dark mass, things that no one really knows anything about;
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Based on the idea that the entropy of a black hole is not proportional to its three-dimensional volume (as it happens in the case of any other object) but to the two-dimensional surface area of the black hole, physicists speculate that the most profound description of our three-dimensional universe is embedded within a more fundamental two-dimensional surface whose three-dimensional projection makes the very cosmos we take for granted, but which turns out to be a mere hologram.
What is the nature of the two-dimensional surface that our holographic reality stems from and where is it situated? Nobody knows.
Knowledge is power.
This is the Holographic Principle. It’s not restricted to black holes or the universe as a whole – it says that any volume of space (and all the matter, energy and interactions that occur within it) can be understood as entities on the two-dimensional boundary of the region with different laws of physics. (Of course it can also be understood as the ordinary laws of physics in the three-dimensional volume; these are just two (remarkably different) ways of looking at the same thing.) This is a fairly speculative idea that originated from theoretical studies of black holes and string theory. Some people find it attractive because it does seem to provide a way to address the Black hole information paradox.
–Mark
A corollary of the Holographic Principle is that the maximum amount of information that can be packed into a region of space is determined by the surface area of that space and not its volume. This is quite non-intuitive. For example, suppose you have a 10’ x 10’ x 10’ room that you want to fill with as much information as possible. You could start filling it with disk drives, but of course current disk drives fall far below the theoretical maximum information density. But suppose that with highly advanced technology you can reach this limit, and you pack the room with these fantastic data storage devices. Now you find you need room for more information, so you open a wall to an identical adjoining room and pack this new 20’ x 10’ x 10’ space with the same type of disks. You might think you have doubled the amount of information you can store, but the surface area of the space has only increased from 600 square feet to 1000 square feet, so you’ve only increased your storage space by 66%, not 100%.
–Mark
Neither a black hole nor the universe is a hologram.
A hologram is “a method of producing a three-dimensional image of an object by recording on a photographic plate or film the pattern of interference formed by a split laser beam and then illuminating the pattern either with a laser or with ordinary light.”
There are physicists who draw an analogy between the process explained above and the possibility that our three-dimensional universe should stem on a more profound reality with fewer dimensions.
Despite its elegance, the holographic principle continues to be a mere speculation based on virtually no evidence.