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In the smallest measured units of space and time in the Universe, not much is happening. In a new search for quantum fluctuations in space-time at the Planck scale, physicists have found that everything is smooth.
This means that – for now at least – we still can’t find a way to solve general relativity with quantum mechanics.
This is one of the thorniest issues in our understanding of the Universe.
General relativity is the theory of gravity that describes gravitational interactions in the physical universe on a large scale. It can be used to make predictions about the Universe; general relativity has predicted gravitational waves, for example, and certain behaviors of black holes.
Space-time under relativity follows what we call the principle of locality – that is, objects are directly influenced only by their immediate environment in space and time.
In the quantum realm – atomic and subatomic scales – general relativity collapses and quantum mechanics takes over. Nothing in the quantum domain happens at a specific 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.
One way or another, despite their differences, general relativity and quantum mechanics exist and interact. But so far, resolving the differences between the two has proven extremely difficult.
That’s where the Fermilab Holometer comes in – a project led by astronomer and physicist Craig Hogan of the University of Chicago. It is an instrument designed to detect quantum fluctuations of 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 at a beam splitter. A laser is fired at the splitter and sent two arms to two mirrors, to be reflected back to the beam splitter to recombine. Any fluctuation on the Planck scale will mean that the returning beam is different from the beam that was emitted.
A few years ago, the Holometer performed zero detection of quantum jitter in space-time back-and-forth. This suggests that spacetime itself as we can currently measure it is not quantified; in other words, could be decomposed into discrete and indivisible units or quanta.
Because the interferometer’s arms were straight, it could not detect other types of fluctuating movements, as if the fluctuations were rotational. And that could mean a lot.
“In general relativity, rotating matter drives space-time with it. In the presence of a rotating mass, the local non-rotating frame, as measured by a gyroscope, rotates relative to the distant Universe, such as than measured by distant stars, ”Hogan wrote on the Fermilab website.
“It may well be that quantum spacetime has a Planck scale uncertainty of the local frame, which would lead to random rotational fluctuations or twists that we would not have detected in our first experiment,” and far too small to be detected in a normal gyroscope. “
Thus, the team redesigned the instrument. They added additional mirrors so that they could detect any rotational quantum motion. The result was an incredibly sensitive gyroscope capable of detecting Planck-scale rotational twists that change direction a million times per second.
In five observation cycles between April 2017 and August 2019, the team collected 1,098 hours of dual interferometer time series data. During all this time, there has not been a single shake. To our knowledge, space-time is still a continuum.
But that doesn’t mean the Holometer, as some scientists have suggested, is a waste of time. There is no other such instrument in the world. The results it returns – zero or not – will shape future efforts to probe the intersection of relativity and quantum mechanics at the Planck scale.
“We may never understand how quantum space-time works without some 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 unique way of interpreting our null results, as there is no rigorous theory of this. that we are looking for.
“Are the hassles just a little smaller than what we thought they might be, or do they have a symmetry that creates a pattern in space that we haven’t measured? New technology will allow experiments future better than ours and perhaps give us clues as to how space and time emerge from a deeper quantum system. “
The research was published on arXiv.
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