Projects: Holometer

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Fermilab holometer prototype cavity
Aaron Chou and Ray Tomlin use a small laser to align the first holometer prototype cavity in the MP8 tunnel
The Holographic Interferometer, or Holometer, is a machine designed to test a particular idea about how space, time, matter, and energy behave on the very smallest scales.

If there is a minimum interval of time, or a maximum frequency in nature, there is a corresponding limit on the fidelity of space and time. Everyone is familiar these days with the blurry and pixelated images, or noisy sound transmission, associated with poor internet bandwidth. The Holometer seeks to detect the equivalent blurriness or noise in reality itself, associated with the ultimate frequency limit imposed by nature.

About a hundred years ago, the German physicist Max Planck introduced the idea of a fundamental, natural length or time, derived from fundamental constants. We now call these the Planck length, lp = √hG/2π c3 = 1.6 × 10-35 meters. Light travels one Planck length in the Planck time, tp = √hG/2π c5 = 5.4 × 10-44 seconds. The physics of space and time is expected to change radically on such small scales. For example, a particle confined to a Planck volume automatically collapses to a black hole.

More recently, theoretical studies of black holes, and later in string theory and other forms of unification, have suggested that physics on the Planck scale is holographic. It is conjectured that space is two dimensional, and the third dimension is inextricably linked with time. If so, our three-dimensional world is a kind of approximate illusion that emerges only on scales much larger than the Planck length.

Fermilab holometer prototype vacuum mirror mount
Prototype vacuum mirror mount
for the Fermilab Holometer.

It could be that the illusion is imperfect and blurry. The maximum frequency may introduce a particular kind of noise or jitter into spacetime, as measured by the propagation of light in different directions.

The holometer attempts a direct experimental test of one form of this 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 travelling in about the same direction, at about the same time -- their signals should display the same, correlated jitter, sometimes called "holographic noise".

Measurement of holographic noise would be the first direct experimental access to the Planck scale, and provide fundamental insights into the fundamental nature of space and time. It would directly measure the Planck time, and the absolute natural bound on information transmission, about 10^43 bits per second.

The project is currently in the construction stage.


Project Members
Aaron Chou Henry Glass Gaston Gutierrez Craig Hogan
Jason Steffen Chris Stoughton Ray Tomlin Jim Volk
William Wester