The already-baffling black holes offer another mindbender.
In Plato’s “Allegory of the Cave,” he imagines people chained in the darkness, forever in one position, unable to turn around or move their heads. A fire behind them, which they cannot see, casts flickering shadows on the wall before them; shadows of people walking by, animals, inanimate objects and of themselves. These two-dimensional, distorted illusions are all they know, and to them, this is reality. Some cosmologists think Plato’s cave might be more than just a metaphor, but in reverse. The three-dimensional world we see around us might be a holographic projection generated by two-dimensional information processes unfolding on a distant boundary surface surrounding the universe.
Physicists Stephen Hawking and Jacob Bekenstein showed that the information storage capacity of a black hole isn’t related to its volume, but rather to its surface, or the event horizon. As new matter and energy enter the black hole, the area of its surface increases in proportion to the amount of information it has absorbed. The unanswered question, which physicists have pursued for decades, is whether this is merely an effect or whether the information is actually stored on the black hole’s surface. The consensus is that, at least when viewed from the outside, the information is probably stored at the event horizon. However, when viewed from the inside, everything in the black hole would appear normal, except for the crushing effects of its high gravity.
If everything in the universe is a three-dimensional projection, then like any hologram or even photo film, there should be a kind of “graininess” when you look closely enough.
How does this relate to everything being a hologram? As physicist Brian Greene points out in his book “The Hidden Reality,” “This doesn’t merely highlight a peculiar feature of black holes. Black holes don’t just tell us about how black holes store information. Black holes inform us about information storage in any context.” The information required to describe the contents of any given region of space can be fully encoded on a surface surrounding that region. So perhaps that surface, such as the event horizon of a black hole — or the edge of the universe, is where all the real action is, and what’s seen from an inside observer point of view is a holographic projection of a two-dimensional process taking place on that distant surface. If it turns out to be true for a black hole, it might be true for the universe as well.
Attempts have been made to actually test this hypothesis, with mixed results. If everything in the universe is a three-dimensional projection, then like any hologram or even photo film, there should be a kind of “graininess” when you look closely enough. One experiment found this sort of pixilation at 10-16 meters, while another found no sign of grain all the way down to 10-48 meters, which is 10 trillion times smaller than the “plank length” — the smallest unit of length in quantum mechanics. Both these results can’t be right, so we just don’t know. Maybe the graininess is forever beyond our ability to detect, if it exists. Even if the holographic principle doesn’t apply to the universe, it’s still a fascinating topic and very useful in understanding quantum mechanics and the weird properties of black holes.