The

Fermilab Fermi National Accelerator Laboratory (Fermilab), located in Batavia, Illinois, near Chicago, is a United States Department of Energy United States Department of Energy National Labs, national laboratory specializing in high-energy particle phys ...

Holometer in

Illinois Illinois ( ) is a U.S. state, state in the Midwestern United States, Midwestern United States. It borders on Lake Michigan to its northeast, the Mississippi River to its west, and the Wabash River, Wabash and Ohio River, Ohio rivers to its ...

is intended to be the world's most sensitive laser

interferometer Interferometry is a technique which uses the '' interference'' of superimposed waves to extract information. Interferometry typically uses electromagnetic waves and is an important investigative technique in the fields of astronomy, fiber opt ...

, surpassing the sensitivity of the

GEO600 GEO600 is a gravitational wave detector located near Sarstedt, a town to the south of Hanover, Germany. It is designed and operated by scientists from the Max Planck Institute for Gravitational Physics, Max Planck Institute of Quantum Optics a ...

and

LIGO The Laser Interferometer Gravitational-Wave Observatory (LIGO) is a large-scale physics experiment and observatory designed to detect cosmic gravitational waves and to develop gravitational-wave observations as an astronomical tool. Prior to LIG ...

systems, and theoretically able to detect

holographic Holography is a technique that allows a wavefront to be recorded and later reconstructed. It is best known as a method of generating three-dimensional images, and has a wide range of other uses, including data storage, microscopy, and interfe ...

fluctuations in

spacetime In physics, spacetime, also called the space-time continuum, is a mathematical model that fuses the three dimensions of space and the one dimension of time into a single four-dimensional continuum. Spacetime diagrams are useful in visualiz ...

. According to the director of the project, the Holometer should be capable of detecting fluctuations in the light of a single attometer, meeting or exceeding the sensitivity required to detect the smallest units in the

universe The universe is all of space and time and their contents. It comprises all of existence, any fundamental interaction, physical process and physical constant, and therefore all forms of matter and energy, and the structures they form, from s ...

called

Planck units In particle physics and physical cosmology, Planck units are a system of units of measurement defined exclusively in terms of four universal physical constants: ''Speed of light, c'', ''Gravitational constant, G'', ''Reduced Planck constant, ħ ...

. Fermilab states: "Everyone is familiar these days with the blurry and

pixelated Pixelization (in British English pixelisation) or mosaic processing is any technique used in editing images or video, whereby an image is blurred by displaying part or all of it at a markedly lower resolution. It is primarily used for censorshi ...

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 Frequency is the number of occurrences of a repeating event per unit of time. Frequency is an important parameter used in science and engineering to specify the rate of oscillatory and vibratory phenomena, such as mechanical vibrations, audio ...

limit imposed by nature."

Craig Hogan Craig Hogan is an American professor of astronomy and physics at the University of Chicago and director of the Fermilab Center for Particle Astrophysics. He is known for his theory of " holographic noise", which holds that the holographic pri ...

, a

particle In the physical sciences, a particle (or corpuscle in older texts) is a small localized object which can be described by several physical or chemical properties, such as volume, density, or mass. They vary greatly in size or quantity, from s ...

astrophysicist at Fermilab, states about the experiment, "What we’re looking for is when the lasers lose step with each other. We’re trying to detect the smallest unit in the universe. This is really great fun, a sort of old-fashioned

physics Physics is the scientific study of matter, its Elementary particle, fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. "Physical science is that department of knowledge whi ...

experiment where you don’t know what the result will be." Experimental physicist Hartmut Grote of the

Max Planck Institute The Max Planck Society for the Advancement of Science (; abbreviated MPG) is a formally independent non-governmental and non-profit association of German research institutes. Founded in 1911 as the Kaiser Wilhelm Society, it was renamed to the M ...

in Germany states that although he is skeptical that the apparatus will successfully detect the holographic fluctuations, if the experiment is successful "it would be a very strong impact to one of the most open questions in fundamental physics. It would be the first proof that space-time, the fabric of the universe, is quantized." Holometer has started, in 2014, collecting data that will help determine whether the universe fits the

holographic principle The holographic principle is a property of string theories and a supposed property of quantum gravity that states that the description of a volume of space can be thought of as encoded on a lower-dimensional boundary to the region – such as a ...

. The hypothesis that holographic noise may be observed in this manner has been criticized on the grounds that the theoretical framework used to derive the noise violates Lorentz-invariance. Lorentz-invariance violation is however very strongly constrained already, an issue that has been very unsatisfactorily addressed in the mathematical treatment.Backreaction, Holographic Noise
/ref> The Fermilab holometer has found also other uses than studying the holographic fluctuations of spacetime. It has shown constraints on the existence of high-frequency

gravitational waves Gravitational waves are oscillations of the gravitational field that travel through space at the speed of light; they are generated by the relative motion of gravitating masses. They were proposed by Oliver Heaviside in 1893 and then later by H ...

and primordial black holes.

Experimental description

The Holometer will consist of two 39 m arm-length power-recycled

Michelson interferometer The Michelson interferometer is a common configuration for optical interferometry and was invented by the American physicist Albert Abraham Michelson in 1887. Using a beam splitter, a light source is split into two arms. Each of those light be ...

s, similar to the

instruments. The interferometers will be able to be operated in two spatial configurations, termed "nested" and "back-to-back". According to Hogan's hypothesis, in the nested configuration the interferometers' beamsplitters should appear to wander in step with each other (that is, the wandering should be ''correlated''); conversely, in the back-to-back configuration any wandering of the beamsplitters should be uncorrelated. The presence or absence of the correlated wandering effect in each configuration can be determined by cross-correlating the interferometers' outputs. The experiment started one year of data collection in August 2014. A paper about the project titled ''Now Broadcasting in Planck Definition'' by Craig Hogan ends with the statement "We don't know what we will find." A new result of the experiment released on December 3, 2015, after a year of data collection, has ruled out Hogan's theory of a pixelated universe to a high degree of statistical significance (4.6 sigma). The study found that

space-time In physics, spacetime, also called the space-time continuum, is a mathematical model that fuses the three-dimensional space, three dimensions of space and the one dimension of time into a single four-dimensional continuum (measurement), continu ...

is not quantized at the scale being measured. Based on what the authors call the ″''final measurements and analysis ..from the first-generation Holometer''" it was reported in 2017 that it "''has tested and conclusively excluded a general class of models of quantum geometrical shear noise correlations''". An upgraded version of the holometer was used in 2020 to probe models in which the correlations are seen in rotational degrees of freedom. The results were consistent with a classical spacetime, constraining the tested models.

References

External links

Fermilab Holometer
{{Gravitational wave observatories Science and technology in the United States Experimental physics Experimental particle physics Fermilab 2014 inventions Fermilab experiments