Is space-time smooth or lumpy?

Beijing time on November 25news, our basic reality is continuous, or is it divided into countless small, discrete parts? In other words, is space-time smooth or lumpy? This question touches the core of the most basic theory of physics, linking space and time to our physical existence.

However, it is impossible to test the nature of space and time through experiments, as extreme energy is required to detect such a tiny scale in the universe. However, a team of astronomers has come up with an ambitious new plan to use a group of tiny spacecraft to detect subtle changes in the speed of light. In some of the most puzzling cosmic theories, changes in the speed of light are very important parameters. If this study proves that space and time are indeed broken down into small pieces, it may lead to a new understanding of reality.

Block vs Smooth

What is space and time? This problem dates back thousands of years, and our understanding of it today is based on two strange and incompatible pillars: quantum mechanics and Einstein’s general theory of relativity.

In general relativity, space and time are woven into a unified space-time structure, which is the four-dimensional stage that supports the universe in which we live. This space-time is continuous, meaning there is no space anywhere, everything is smooth. However, space-time is not only a “stage for us to perform”, it is also a player: the bending and deformation of space-time gives us the experience of gravity.

In another corner, quantum mechanics controls the interaction slots between the very small things in the universe. Quantum mechanics is based on the idea that most of our daily experiences are not smooth, continuous, but blocky. In other words, it’s quantum. The energy, momentum, spin, and many other properties of matter are divided into discrete pieces.

What’s more, quantum mechanics itself splits into two camps. On the one hand, the particles that make up our daily life familiar with things, such as electrons and protons, and their interactions cause many interesting phenomena. Obviously, these particles are divided into “blocks” because they are discrete “things”. On the other hand, we have a quantum field. In the subatomic world, each particle has its own field of time and air travel. When we mention particles, the first thing that comes to mind is the tiny vibrations in the field, which in turn interact with other particles and occur other interesting phenomena. As you can imagine, these fields are very flat.

Fragments of time and space

So part of our imagination of the universe is smooth, and the other part is blocky. When it comes to space-time itself, it is easy to extend the concept of quantum mechanics to its logical conclusions and to conclude that space and time are discrete: the structural division of reality is like pixels on a computer screen, and the smooth, continuous motion in our experience is actually just the smallest scale of the grid discrete pixels.

Physicists have come up with many theories that combine quantum mechanics with general relativity, such as string theory and the theory of quantum gravity in circles. These theories predict some form of discrete space-time (although little is known about the precise prediction, interpretation, and meaning of such block structures). If we can find evidence of discrete space-time, it will not only completely rewrite our understanding of reality, but will also start a revolution in physics.

This dispersion can only manifest itself in the most subtle way, otherwise we would have found out. 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.

Looking for the Holy Grail

Let’s take a look at GrailQuest, the “Gamma-ray Astronomy International Laboratory for Quantum Exploration in Space-Time Quantum Exploration” An abbreviation for Space-Time. A group of astronomers have presented their proposals for the task after the European Space Agency (ESA) called for new ideas to be explored in space-time. They only detailed the proposal in the arXiv database, so it has not been peer-reviewed by the industry.

Is space-time smooth or lumpy?

Simply put, in order to observe changes in the speed of light at different energies, we need to collect the most energetic light in the universe, which GrailQuest hopes to do.

GrailQuest consists of a small, simple set of detectors (the exact numbers vary, if the detectorises are larger, only a few dozen, and if the detector is smaller, it will require a few thousand), to continuously monitor gamma storms in the sky. Gamma-ray bursts are the most powerful bursts of energy in the universe, releasing large amounts of high-energy photons, also known as gamma rays. These gamma rays take billions of years before they reach the detector. The probe records the energy of gamma rays and the time difference that occurs when gamma rays explode on the spacecraft.

If accurate enough can be achieved, GrailQuest may be able to reveal whether space-time is discrete. At the very least, the idea is correct: the detection of the highest-energy light (which is most affected in the theory of predicting blocky time and space); gamma rays have spread billions of light-years (the effects of the changes will increase over time); and the use of simpler detectors, Mass production can be produced (the entire detector group can detect as many events as possible throughout the sky).

If GrailQuest could find evidence of space-time dispersion, how would our concept of reality change? This is unpredictable – our current theory is still in disarray when it comes to the meaning of space-time. In any case, we all have to wait. The European Space Agency’s proposal will be rolled out between 2035 and 2050. Until we get the exact results, we can only theoretically discuss whether space-time is smooth or lumpy. (Any day)

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