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May 1, 2020 08:00 am

Is Space-Time Quantized Or Analog?

"What are the implications if 'space-time' (as conceived of in the Einstein Theory of General Relativity) is quantized like all other aspects of matter and energy?" asks Slashdot reader sixoh1. Space.com reports of a new study that tried to find out: In order for the math of general relativity to work, this fabric of space-time has to be absolutely smooth at the tiniest of scales. No matter how far you zoom in, space-time will always be as wrinkle-free as a recently ironed shirt. No holes, no tears, no tangles. Just pure, clean smoothness. Without this smoothness, the mathematics of gravity simply break down. But general relativity isn't the only thing telling us about space-time. We also have quantum mechanics (and its successor, quantum field theory). In the quantum world, everything microscopic is ruled by random chance and probabilities. Particles can appear and disappear at a moment's notice (and usually even less time than that). Fields can wiggle and vibrate with a will all their own. And nothing can ever be known for certain. [...] That's exactly what a team of astronomers did, submitting their results for publication in the Monthly Notices of the Royal Astronomical Society, and also posting their work to the online preprint site arXiv. And in a perfect coincidence, they searched for the frothiness of space-time using ... espresso. No, not the drink. ESPRESSO, the Echelle Spectrograph for Rocky Exoplanet and Stable Spectroscopic Observations, an instrument based at the European Southern Observatory's Very Large Telescope. As its name suggests, ESPRESSO was not designed to search for space-time frothiness, but it turned out to be the best tool for the job. And the astronomers pointed it at a perfect source: a run-of-the-mill gas cloud sitting over 18 billion light-years away. What makes this particular gas cloud especially useful is two facts. One, there is a bright source sitting just behind it, illuminating it. And two, there's iron in the cloud, which absorbs the background light at a very specific wavelength. So from our vantage point on Earth, if space-time is perfectly smooth, that gap in the background light caused by the gas cloud should be just as narrow as if the cloud was sitting right next to us. But if space-time is frothy, then the light traveling over the billions of light-years will spread out, changing the width of the gap. The astronomers didn't find any hint of frothiness, which doesn't mean that it doesn't exist -- it just means that if space-time is frothy, we need more than 18 billion light-years to see it with our current technology. But the results were able to rule out some models of quantum gravity, sending them into the proverbial dustbin of physics history.

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