TAKE a look around you. The walls, the chair you're sitting in, your own body - they all seem real and solid. Yet there is a possibility that everything we see in the universe - including you and me - may be nothing more than a hologram.
It sounds preposterous, yet there is already some evidence that it may be true, and we could know for sure within a couple of years. If it does turn out to be the case, it would turn our common-sense conception of reality inside out.
The idea has a long history, stemming from an apparent paradox posed by Stephen Hawking's work in the 1970s. He discovered that black holes slowly radiate their mass away. This Hawking radiation appears to carry no information, however, raising the question of what happens to the information that described the original star once the black hole evaporates. It is a cornerstone of physics that information cannot be destroyed.
In 1972 Jacob Bekenstein at the Hebrew University of Jerusalem, Israel, showed that the information content of a black hole is proportional to the two-dimensional surface area of its event horizon - the point-of-no-return for in-falling light or matter. Later, string theorists managed to show how the original star's information could be encoded in tiny lumps and bumps on the event horizon, which would then imprint it on the Hawking radiation departing the black hole.
This solved the paradox, but theoretical physicists Leonard Susskind and Gerard 't Hooft decided to take the idea a step further: if a three-dimensional star could be encoded on a black hole's 2D event horizon, maybe the same could be true of the whole universe. The universe does, after all, have a horizon 42 billion light years away, beyond which point light would not have had time to reach us since the big bang. Susskind and 't Hooft suggested that this 2D "surface" may encode the entire 3D universe that we experience - much like the 3D hologram that is projected from your credit card.
It sounds crazy, but we have already seen a sign that it may be true. Theoretical physicists have long suspected that space-time is pixelated, or grainy. Since a 2D surface cannot store sufficient information to render a 3D object perfectly, these pixels would be bigger in a hologram. "Being in the [holographic] universe is like being in a 3D movie," says Craig Hogan of Fermilab in Batavia, Illinois. "On a large scale, it looks smooth and three-dimensional, but if you get close to the screen, you can tell that it is flat and pixelated."
Quantum fluctuation
Hogan recently looked at readings from an exquisitely sensitive motion-detector in Hanover, Germany, which was built to detect gravitational waves - ripples in the fabric of space-time. The GEO600 experiment has yet to find one, but in 2008 an unexpected jitter left the team scratching their heads, until Hogan suggested that it might arise from "quantum fluctuations" due to the graininess of space-time. By rights, these should be far too small to detect, so the fact that they are big enough to show up on GEO600's readings is tentative supporting evidence that the universe really is a hologram, he says.
Bekenstein is cautious: "The holographic idea is only a hypothesis, supported by some special cases." Better evidence may come from a dedicated instrument being built at Fermilab, which Hogan expects to be up and running within a couple of years.
A positive result would challenge every assumption we have about the world we live in. It would show that everything is a projection of something occurring on a flat surface billions of light years away from where we perceive ourselves to be. As yet we have no idea what that "something" might be, or how it could manifest itself as a world in which we can do the school run or catch a movie at the cinema. Maybe it would make no difference to the way we live our lives, but somehow I doubt it.
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