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A New Measurement of Quantum Space-Time Has Found Nothing Going on

There is hardly much happening in the Universe's tiniest measurable units of space and time. It has been discovered by scientists conducting a fresh search for quantum fluctuations of space-time on Planck scales that nothing is irregular.

This indicates that, at least for the time being, quantum mechanics cannot be used to address the general relativity problem.


It's one of the most challenging issues we have with how the universe works.

The gravitational interaction theory that represents gravitational interactions in the large-scale physical Universe is called general relativity. It may be used to make predictions about the cosmos; general relativity, for example, predicted gravitational waves and some black hole behaviors.


The concept of locality, which states that things only directly affect their immediate surroundings in space and time, governs space-time under relativity.


General relativity fails at the atomic and subatomic sizes, where quantum mechanics takes control. Parts of a quantum system that are separated by space or time can nonetheless interact with one another, a phenomenon is known as nonlocality. In the quantum world, nothing happens at a specific location or time until it is measured.

General relativity and quantum physics coexist and interact despite their differences. But reconciling the gaps between the two has proven to be rather challenging thus far.


This is where the Holometer at Fermilab, a project led by University of Chicago astronomer and physicist Craig Hogan, comes into play. A Planck length, or 10-33 centimetres, and a Planck time, or how long it takes for light to travel a Planck length, are the smallest units that may be detected by this device.

It is made up of two identical interferometers that are 40 meters (131 feet) long and meet at a beam splitter. In order to recombine, a laser is shot at the beam splitter and delivered down two arms to two mirrors. The beam that returns will differ from the beam that was emitted if there are any Planck-scale variations.

The Holometer produced a null detection of space-time quantum disturbances a few years ago. According to this, space-time itself, as we now understand it, is not quantized, i.e., it cannot be divided into discrete, indivisible units, or quanta.

The interferometer could not detect other types of fluctuating motion, such as if the fluctuations were rotating, because the arms of the interferometer were straight. And that can be quite important.

"According to general relativity, space-time is pulled along by rotating matter. In the presence of a spinning mass, the local nonrotating frame rotates in relation to the distant Universe, as measured by far-off stars, as measured by a gyroscope, "On the Fermilab website, Hogan posted.

It's possible that there is Planck-scale uncertainty in the local frame in quantum space-time, which would cause random rotational fluctuations or twists that we would not have seen in our initial experiment and that is far too minute to be seen by a standard gyroscope.


The team decided to rework the instrument. They increased the number of mirrors so they could pick up any rotating quantum motion. The outcome was a very sensitive gyroscope that can recognize rotational twists on the Planck scale that reverse direction a million times each second.

Between April 2017 and August 2019, the team conducted five observing runs and gathered 1,098 hours of dual interferometer time series data. There was not a single jiggle at the time. Space-time is still a continuum as far as we know.


However, contrary to what some experts have said, the Holometer is not a waste of time. It is unlike any other instrument in existence. The outcomes—whether they are null or not—will influence future investigations into the nexus between relativity and quantum physics at Planck scales.

Without any measurement to inform theory, Hogan warned that we would never fully comprehend how quantum space-time functions. "The Holometer program is a research project. Since there is no definite theory of what we are searching for, our experiment was designed using only a few broad theories as a guide. As a result, we still do not have a special way to interpret our null data.

Do the jitters have asymmetry that produces a pattern in space that we haven't measured or are they somewhat smaller than we initially believed they may be? Future tests will be more successful than ours thanks to new technology, which may also provide some hints about how space and time arise from a deeper quantum system.

The study has been made public on arXiv.

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