In the very small measured units of space and time in the Universe, not much happens. In a new search for quantum fluctuations in space-time on the Planck scales, physicists have discovered that everything is smooth.
This means that, at least now, we still cannot find a way to solve general relativity with quantum mechanics.
It is one of the most annoying problems in our understanding of the Universe.
General relativity is the theory of gravitation that describes gravitational interactions in the large-scale physical universe. It can be used to make predictions about the Universe; general relativity predicted gravitational waves, for example, and some black hole behaviors.
Space-time under relativity follows what we call the principle of locality, that is, objects are only directly influenced by their immediate environment in space and time.
In the quantum realm – atomic and subatomic scales – general relativity breaks down and quantum mechanics takes over. Nothing in the quantum realm happens at a particular place or time until it is measured, and parts of a quantum system separated by space or time can still interact with each other, a phenomenon known as non-locality.
Somehow, despite their differences, general relativity and quantum mechanics exist and interact. But so far resolving the differences between the two has proved extremely difficult.
This is where the Fermilab Holometer comes into play, a project led by astronomer and physicist Craig Hogan of the University of Chicago. It is an instrument designed to detect quantum fluctuations in space-time in the smallest possible units: a Planck length, 10-33 centimeters and Planck time, how long it takes for light to travel a Planck length.
It consists of two identical 40-meter (131-foot) interferometers that intersect in a beam splitter. A laser is fired against the splitter and two arms are sent to two mirrors to reflect it back to the beam splitter to recombine it. Any fluctuation in Planck scale would mean that the returning beam is different from the emitted beam.
A few years ago, the Holometer made zero detection of quantum agitation back and forth in space-time. This suggested that space-time itself, as we can measure it today, is not quantified; that is, they could be broken down into discrete or indivisible units or quanta.
Because the arms of the interferometer were straight, it could not detect other types of fluctuating motion, as if the fluctuations were rotating. And that could matter a lot.
“In general relativity, rotating matter drags space-time along with it. In the presence of a rotating mass, the local non-rotating frame, measured by a gyroscope, rotates relative to the distant universe, measured by distant stars, “Hogan wrote on the Fermilab website.
“It could be that quantum space-time had a Planck-scale uncertainty of the local frame, which would lead to random rotational fluctuations or turns that we would not have detected in our first experiment, and too small to detect them in any normality. gyroscopes “.
Therefore, the team redesigned the instrument. They added additional mirrors so they could detect any quantum rotational motion. The result was an incredibly sensitive gyroscope that can detect Planck-scale rotational rotations that change direction a million times per second.
In five observation tests between April 2017 and August 2019, the team collected 1,098 hours of double interferometer time series data. In all this time, there was not a single shock. As far as we know, space-time is still a continuum.
But this does not mean that the Holometer, as some scientists have suggested, is a waste of time. There is no other similar instrument in the world. Returning results (null or not) will shape future efforts to probe the intersection of relativity and quantum mechanics on Planck scales.
“We may never understand how quantum space-time works without a measure to guide the theory,” Hogan said. “The Holometer program is exploratory. Our experiment began with only approximate theories to guide its design, and we still do not have a single way to interpret our null results, as there is no rigorous theory of what we are looking for.
“Are the annoyances a little smaller than we thought they might be, or do they have a symmetry that creates a pattern in space that we haven’t measured? The new technology will allow for better future experiments than ours and possibly give us some clues.” on how space and time emerge from a deeper quantum system “.
The research has been published in arXiv.