Do you ever get those days when you question reality? One scientist has gone a step further; he is currently building an experiment that will hopefully answer whether or not we all exist as a result of a universal hologram.
Confused? You're not alone. The holographic universe hypothesis is steeped in complex mathematics and descriptions that belong in hard science fiction novels.
As discussed by my Discovery News colleague Jennifer Ouellette in March, Fermilab particle physicist Craig Hogan renewed interest in the holographic universe concept after investigating the noise measured by a gravitational wave detector called GEO600 in Germany.
Before we can understand what this “noise" is (let alone why the Universe could be a hologram), we need to understand how gravitational wave detectors work.
Where are the Space-Time Ripples?
Gravitational waves are a consequence of Einstein's general relativity equations. Einstein's famous realization that space-time warps around massive objects (such as planets and stars) led to the prediction that any massive object moving through space should generate waves in space-time, carrying energy away from the object — analogous to a boat generating waves in its wake as it cruises along a river.
As these waves are very difficult to detect, only the most massive objects undergoing violent events would generate gravitational waves we can “feel" on Earth. To “feel" these waves, gravitational wave detectors have been built, hoping to detect the waves generated by black hole collisions or supernovae.
To do this, gravitational wave detectors use a sophisticated arrangement of lasers and interferometers. Firing a laser beam down a 600 meter “tube," GEO600 scientists split the beam and send it in different directions. The two components of the split beam are then recombined in a very sensitive interferometer. Should one of those beams have shifted phase — due to the passage of a gravitational wave through the volume of space we live in — the interferometer will detect it and flag a gravitational wave signal.
But how can a gravitational wave change the phase of a laser beam? It is theorized that as a ripple through space-time propagates, it can slightly change the distance between two points in space. Due to the very precise nature of the GEO600 experiment, it can detect a fluctuation of an atomic radius over a distance from the Earth to the sun. So, if a gravitational wave should pass through local space, the distance that the laser has to travel is ever-so-slightly changed (as one of the beams will have to travel a little further than the other), thus shifting the laser's phase.
Although the hunt has been intense, little evidence for these elusive waves has presented itself, even though GEO600 can detect such a tiny shift in space-time distances.
But, for the German gravitational wave detector, it did find something odd in its results. No gravitational wave signals, just static.
Calling on the help of Hogan, the GEO600 experiment found a possible answer to this inexplicable noise. Could one of the most sensitive gravitational wave detectors in the world — designed to measure very big “ripples" in space-time (pictured right) — have accidentally probed the smallest scales possible? This noise, Hogan reckons, is the “fuzziness" of the fabric of space-time itself.
In Einstein's view of space-time, it is smooth and continuous. However, it is generally thought that even space-time is built from tiny pixels measuring the smallest possible scale allowed by physics: 10-35 meters, known as the Planck Length. That's one ten-trillionth of a trillionth the diameter of a hydrogen atom.
But GEO600 — or any other experiment for that matter — cannot hope to probe to scales this small. This is where things get weird.
The GEO600 experiment can probe down to scales of around 10-16 meters, but if the noise it is detecting is due to the pixelated nature of space-time, what's going on? GEO600 is probing scales 10,000,000,000,000,000,000 times larger than the Planck Length, so the quantum “fuzziness" is operating at scales much larger than one would have thought (if space-time has quanta, quantum fluctuations should occur more toward Planck scales).
Now we enter the realm of bizarre physics, where our view of the Universe could change forever.
In the early 1990′s, University of Florida physicist Charles Thorn conceived the holographic universe hypothesis. In Thorn's view of the Universe, the 3-dimensional world we know and love is actually a hologram projected from the furthest-most reaches of the cosmos. The easiest way to imagine it is that we are contained within the Universe's event horizon and any 3D object we conceive (as 3D objects ourselves) are projected from the event horizon's 2-dimensional “shell." We are basically a projection.
The idea that information is encoded in an event horizon comes from the “black hole paradox," a fascinating debate between heavyweight physicists Kip Thorne, Stephen Hawking and John Preskill:
Information encoded in an event horizon “is born from other well known interpretations of the cosmos, in particularly the black hole paradox. As something falls into a black hole, passing the event horizon, the quantum information held in the event horizon can be encoded to reveal information about the interior. Therefore, the information inside the black hole's event horizon is not destroyed (for details on this, see
It is worth pointing out that there is no physical evidence to suggest this is correct — and it's a view that has proven to be rather controversial — it is purely a hypothesis that has bubbled up from complex mathematics handed down from black hole theory.
However, motivated by the odd noise being generated by GEO600 and Thorn's holographic universe idea, Craig Hogan is currently building a souped-up gravitational wave detector with a difference: it's not looking for gravitational waves.
If the Universe is a holographic projection from the universal event horizon, it is predicted that the projection will be fuzzy. Although all the information to create the Universe is “encoded" in Planck-scale “bits" in the universal event horizon, by the time it's projected over billions of light years to our location, these “bits" will have become enlarged — like the light being emitted from a projector onto a wall.
The smaller scales you probe, the more fuzzy the projection becomes. It's a bit like zooming in on a photograph or magazine text; it becomes less defined and more pixelated the closer you zoom in.
It is this fuzziness that Hogan believes GEO600 is currently seeing as noise, possibly giving Thorn's hypothesis from the early 90′s some of its first observational evidence.
So, at Fermilab, Hogan's team has devised a holographic interferometer (or “Holometer," pictured above) that is currently being built to probe even smaller scales than GEO600:
“The holometer attempts a direct experimental test of one form of [the holographic universe] hypothesis. In a Michelson interferometer, a light beam is split into two parts that travel in different directions, then are brought back together. The vibrations of light in the two directions tend to drift apart by about Planck length per Planck time when they are traveling in different directions. When they are recombined, the difference in light phase can be measured. In the holometer, signals from two different interferometers — that is, two completely separate systems, each with its own pair of beam arms — are compared. If they are close enough to probe the same volume of spacetime — that is, if light in both systems is traveling in about the same direction, at about the same time — their signals should display the same, correlated jitter, sometimes called 'holographic noise.'" —
What will the Holometer find? Hogan is hoping to see more static, or “jitter."
But what does this mean?
It is doubtful that the human brain could ever fully imagine how a universe is actually a 3-dimensional representation of a 2-dimensional universal event horizon, and it doesn't physically change how we experience our world. Even if this space-time noise is found to persist at smaller and smaller scales, it's not necessarily evidence that the holographic concept is real. Perhaps it's a phenomenon that mathematics or the most advanced physics theory cannot explain (yet).
But it's one hell of a mind-bending idea that will no doubt boost our understanding about how our Universe works on the tiniest of scales.
Image: Hubble Deep Field (NASA/HST). Edit by Ian O'Neill/Discovery News.