The room really expands continuously

How big are the meshes of the universe?

The "world formula" would be a quantum field theory of gravity. How can these quantum effects be demonstrated and at what order of magnitude do they start? New research on the quantization of spacetime

String theory, loop quantum gravity and direct further developments of the relativity theory agree on one point: At some level, space is no longer continuous, but discrete. Now, for the first time, researchers have succeeded in setting an upper limit for the maximum size of these quantum structures that is independent of the specific theory.

Both quantum theory and general relativity are among the best-reviewed theories in modern physics. And yet the scientists are fully aware that in certain extreme cases they will have to collapse. At very high energies, as they must have prevailed shortly after the Big Bang or should be found in a black hole, both approaches fail. The researchers unanimously see the solution to the quantization of space-time - only the approach is very different.

The universe is no longer gigantic, but the grain of sand under your shoe

The basis of loop quantum gravity, for example, is the vivid idea that the material that the universe is made of has a lot in common with the material that people dress in. It consists of fibers that twist around each other (loops) and form knots. The loops are tiny. One square centimeter of "universe material" consists of about 1066 such threads. The smallest physically meaningful volume is 10 in the loop space-99 Cubic centimeters. As a result, our idea of ​​"huge" should actually be reversed. Because the universe itself is "only" about 1085 Cubic centimeters in size. In theory, 10 cubic centimeters fit into one cubic centimeter99 Loops quanta.

This means that a perfect microscope that can look into the micro-world with any sharpness can register around 100 trillion more events than a perfect telescope that has the entire universe in view. The universe is no longer gigantic, but the grain of sand under your shoe. Or every grain of sand is a cosmos - while the universe is shrinking. In these scales, spacetime no longer feels continuous, but rather discreet - space can only grow by adding a knot or a loop, no less.

The string theory

String theory, on the other hand, imagines one-dimensional strings as the smallest basic building block that spans the multi-dimensional space. The fact that no one has ever seen a string (if the theory has anything to do with reality) is due to the tiny size of these objects. Their typical length is around 1.6 * 10 in the area of ​​the Planck length-35 Meters. No man-made instrument will ever be able to show objects of this size. But this is not a problem as long as the theory only perfectly predicts the observable reality.

However, a string alone is not enough for matter to arise - just as the mere existence of a guitar string is not enough to make music sound. The vibrations of the strings are decisive. Each of these tiny objects can vibrate in several different ways. The stronger the vibration, the more energy it contains - and the larger the particle it manifests itself.

The M-theory extends this notion to include branes. Branes therefore have the following properties:

  1. They have a certain space dimension, from 0 to 9. A bran of dimension 0 is called D0-bran, a three-dimensional bran is D3-bran.
  2. They can contain a charge.
  3. They also expand in the direction of time
  4. They have surface tension. The stronger the surface tension, the less the branes can be influenced by interactions.

If space is quantized, different light particles would have to take different paths

Before researchers can go ahead and prove any of these theories, they must first clarify the fundamentals. If the space is really quantized, this property would have to affect everything that crosses the space - including light, for example.

If space is quantized, different light particles would have to take different paths. These differ very little, but if the distance that a photon has to cover is just large enough, even the smallest deviations in the distance should have a measurable effect at some point.

In an article in Nature Physics, researchers have now analyzed data from the Fermi telescope that it had recorded from a gamma-ray burst. The idea behind it: If the space is actually quantized, the incoming photons would have to be subject to a Gaussian distribution depending on their energy. In fact, after carefully excluding all sources of error, the researchers were unable to find any relevant clues.

Taking into account the measurement accuracy, this results in a general upper limit for the quantum effects in the dimension of the Planck length (10-34 Meter) - completely independent of the respective theory. That does not rule out the common theories, but some of their special formulations, for which the upper limit must be far below. The researchers now hope that the upcoming Cherenkov Telescope Array, with its ten times greater sensitivity, will be able to provide further information.

The author's eBook "The Fascinating World of Relativity, Standard Model and String Theory" is available from Apple (iPad version with videos and photos) and from Amazon, among others.

(Matthias Matting)

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