Is space-time smooth or foamy “particle soup”?

Beijing time on May 2, according tomedia reports, the nature of reality is what? Is space-time, the four-dimensional structure of the universe, smooth on the tiniest scale, or does it exist in other forms? These questions touch the heart of the most basic theory of physics, and a new study tries to find the answer behind the question.

It may not seem possible to measure the nature of space-time, but with advanced telescopes, researchers have been able to peer into the depths of the universe by billions of light-years away, perhaps leading to a new understanding of space-time.

Ultimate Net

Einstein’s general theory of relativity is the only way we can understand gravity, and through tedious mathematics, we have some understanding of so-called “space-time”. This is a unified structure of four-dimensional structures (three-dimensional space and one-dimensional time). In the language of relativity, matter and energy bend and distort the fabric-like space-time structure, and in response, the bending and distortion of space-time determines how matter and energy move, which is the “gravity” we experience together.

In order for the mathematical principles of general relativity to work, this space-time structure must be absolutely smooth at the smallest scale. No matter how far you pull the camera, time and space will be as wrinkle-free as a newly ironed shirt. Time and space have no holes, no cracks, no tangles, everything is so pure, clean and smooth. Without this smoothness, the mathematical calculations of gravity would immediately collapse.

However, general relativity is not the only theory that describes space-time, and we also have quantum mechanics (and its successor, quantum field theory). In the quantum world, all microscopic things are determined by random probabilities or probabilities. Particles can appear and disappear in a flash (usually much shorter than you think of”);

Various theories predict that if space-time is indeed blocky, the speed of light may not be completely constant, but may change slightly depending on the energy of light. High-energy light has a shorter wavelength, and when the wavelength becomes short enough, it can “see” blocky space-time. Imagine walking on the sidewalk: if your feet are large, you won’t notice any tiny cracks or bumps, but if your feet are small, you’ll be tripped and slowdowned by every uneven spot on the road. But the change is very small; if space-time is discrete, it is likely to be a billion times smaller than the one we have detected in the most powerful experiments we have detected so far.

So, as physicist John Wheeler pointed out in 1960, space-time should not look smooth if we had narrowed it down to the smallest possible scale (the so-called Planck length, 1.616252 x 10 s. 35 meters). Instead, space-time should be a tumble, boiling thing that can be thought of as a frothy “particle soup” that constantly rips holes in the air and then mends them up before anyone in the macro world notices them.

Rough roads

The problem is that these two views of time and space cannot be true at the same time. Either general relativity is correct, space-time is smooth, or quantum mechanics is right, space-time is blocky. Physicists believe the final answer may lie in a combination of the two ideas, known as quantum gravity. Of course, we don’t yet know what the final answer is. If we could turn on space-time and look at the tiniest scales, we might get some clues.

If space-time is really full of foam and constantly rolling, then any object passing through space-time should be affected. For example, a beam of light will encounter various microscopic bumps in the path. On the Planck scale, the path of the beam is more like a gravel road than a flat highway. Sometimes these tiny collisions push light with a thrust, pushing up its energy levels; The end result is that as the beam travels in the air of a foam-filled time, it spreads slowly in the form of energy.

The effect is so small that it’s incredible, and we can’t measure it in the lab. Fortunately, however, nature can provide us with a laboratory. If we can find a good continuous beam of light in space (in other words, a natural space laser), which has been captured by telescopes on Earth over billions of years, we can measure the energy it carries and measure the “bubble” of space-time.

The foam of “espresso”

That’s what a team of astronomers did, and they contributed to the results of the study in the Monthly Notices of the Royal Astronomical Society, which was also published on the preprinted website arXiv. Coincidentally, the tool they used to search space-time is “ESPRESSO” (the same name as espresso), known as the “Ladder Spectroscometer for Exoplanets and Stable Spectroscosphere” (EchelletroGraph for Rocky Planet and Geosphere Spectroscopics). The instrument is installed on the Very Large Telescope (VLT) of the European Southern Observatory.

As the name “ESPRESSO” suggests, although the instrument was not designed to look for “space-time bubbles”, it was ultimately the best tool for the job. Astronomers point it to a perfect source: a cloud of gas 18 billion light-years away. It may seem trivial, but this cloud of gas can play an important role. This is because: first, there is a bright light source behind it that illuminates it, and second, there are iron atoms in the gas cloud that absorb background light at a specific wavelength.

So, from our point of view on Earth, if space-time is completely smooth, then the background light gap caused by a gas cloud should be as narrow as when the gas cloud is right next to us. But if space-time is foamy, the light that travels over billions of light-years will spread, changing the width of the gap.

Astronomers have found no evidence of “bubbles” in space-time, but this does not mean that the “foaming” of space-time does not exist. This just means that if there is a “bubble” in space-time, we need more than 18 billion light-years to observe it using current technology. However, these findings are enough to rule out some quantum gravity models and throw them into the well-known dustbin in the history of physics.

What if future experiments do find evidence of a space-time “bubble”? There is no doubt that this will be our first window into the quantum gravitational world, something physicists have been looking for since the 1950s. (Any day)