What do we know about dark matter?

Dark matter certainly exists, and it is very strange and different from what we are familiar with. As for dark matter, we know that it has mass. It is not visible. It likes to stay with galaxies. Ordinary matter cannot touch it.

As for dark matter, we also know that it is not hiding in the distance. Dark matter tends to gather together to form a large mass mass and float in space with galaxies. This means that you are likely to be in dark matter right now. While you are reading, dark matter is probably passing through the book and you. However, if it is around us, why is it still a mystery? Why can’t we see and touch dark matter? One thing is clearly there, but we can’t see it.

It is very difficult to study dark matter because we have little interaction with it. We cannot see it ( so it is ” dark” ), but we know it has mass ( so it is ” matter” ). To explain all this, let’s first review how ordinary substances interact.

There are four main ways in which matter interacts:

( Universal ) Gravity: If two things have mass, then they will have this attraction to each other.

Electromagnetic force: if two particles are charged, electromagnetic force will be generated between the two particles. This force can make them attract each other or repel each other, depending on the electrical properties of the two charges.

In fact, you feel this force in your life every day. If you hold the book with your hand, the book will not be crushed and your hand will not pass through the paper, because the molecules of the book are tightly bound together by electromagnetic force and will repel your hand at the same time.

Weak nuclear force: This force is similar to electromagnetic force in many aspects, but it is much weaker. For example, neutrinos interact ( weakly ) with other particles through this force. When the energy is very high, this very weak force will become as strong as electromagnetic force. In fact, it has been proved that this weak action constitutes electromagnetic action.

Strong Nuclear Force: This is the force that binds protons and neutrons together in the nucleus. Without it, positively charged protons in the nucleus would repel each other and eventually disperse.

How does dark matter interact?

One important point to note is that we are describing these forces. To some extent, physics is similar to botany. We do not yet know why these forces exist. So far, we have been able to explain every experiment in particle physics with these four forces.

So, why is dark matter so dark? Well, dark matter has mass, so it has gravity. But this is the only information we can confirm about its function. At present, we think that it does not participate in electromagnetic action and will not reflect or emit light, so it is difficult for us to see it directly. Dark matter also seems to have no weak nuclear force or strong nuclear force.

Except for some new function that we haven’t found yet, no mechanism can make dark matter contact with telescopes, detectors and our bodies. This makes it very difficult to study.

Of the four basic forces known to interact with objects, the only one we have determined to be related to dark matter is gravity. This is the source of the word ” matter” in dark matter. Dark matter is matter, it has mass, so it has gravity.

What might dark energy be?

What is dark energy? We don’t know yet. We know that it is a force that is currently expanding the universe and pushing out all the important things in the universe. At this moment, it pushes me, pushes you, pushes everything we know away from each other. However, we still don’t know what it is.

The current popular view is that dark energy comes from the energy of empty space – yes, empty space. When we say something is empty, we mean there is no ” thing” in it. To be more professional, we think that things are the opposite of emptiness. Some spaces between galaxies have no matter particles or even dark matter. Now, please consider this situation: if this empty, immaterial space has energy ( such as a ray of red light or a buzz – like sound wave ), if this is the truth, this energy can provide a gravitational effect, pushing the universe outward.

This sounds absurd, but it has surprising rationality. In fact, in quantum mechanics, the existence of vacuum energy is very natural. According to quantum mechanics, the world operation rules of small objects ( such as particles ) and large objects ( such as people and pickled vegetables ) are very different. Particles can do things pickles can’t do, such as having uncertain positions, such as crossing insurmountable obstacles, such as showing different appearances when observed and when not observed. Also, according to quantum physics, particles can suddenly emerge from energy in an otherwise empty space and then return.

Quantum mechanics has given us a different world. Relativity has made us abandon the idea of absolute space and time. In this case, why can’t we accept that the seemingly empty space is actually filled with vacuum energy that can push the universe away?

There are other explanations for dark energy, such as new forces penetrating into space or special fields ( i.e. fields like electromagnetic fields ). Some of these fields change conceptually with time to explain why the accelerated expansion of the universe began 5 billion years ago. There are many different versions of such theories, and their common point is that it is difficult to verify them. After all, some of these fields do not interact with our particles, and it is difficult for us to detect them. Some action fields may have new characteristic particles ( just as the Higgs field has Higgs particles ), but the mass of those particles is very, very large, far beyond the range we can measure at present. How big is it? They are heavier than the particles we have seen before, but not as heavy as your cat.

These theories are all in the early stages of development. They are only the earliest prototype theories, guiding scientists to find better explanations until we finally understand most of the energy in the universe. By comparison, dark energy makes dark matter look simple and easy to understand – at least we know it is matter. It is no exaggeration to say that dark energy can be anything. If scientists 500 years later look back at us today, our current discussion on dark energy may make them feel funny, just as we now look at primitive people explaining stars and the sun. We will also find it strange to hear the ancients say that the weather is related to the robes worn by God. We know that there are powerful forces that are beyond our ability to understand. There are still many things waiting for us to learn about the universe.

Where is the space for more dimensions?

You may ask: If there is really a fourth dimension ( except time ), then why has no one ever seen it?

We cannot control or perceive our own movement in higher dimensions, because this part of ability is irrelevant and not conducive to our survival. Even so, if it is linear like the three ordinary dimensions, we should have noticed it. Even if we can only perceive things in three-dimensional space, if something moves in other dimensions, we will also see it repeatedly appear and disappear in three-dimensional space, which is easy to attract our attention.

Therefore, we can say with considerable certainty that there is no fourth dimension similar to the other three spatial dimensions. Even if other dimensions exist, they exist in some hidden and elusive way. There is a possibility that all forces and matter particles we know cannot enter these dimensions. In other words, there will be no object sliding in the fourth dimension, and no energy ( medium particles such as photons through force ) will diffuse into these dimensions. Is it possible for such puzzling dimensions to exist? It is possible, but if any known particles are difficult to enter these dimensions, our chances of finding and studying them are slim.

Another possibility is that only certain particles can enter higher dimensions. These particles are rarer, harder to study and harder to find than other particles. Most importantly, higher dimensions may not be easily discovered due to their own characteristics. What kind of characteristics would that be? For example, these dimensions may be curved and may form small circles or rings. This means that movement in this dimension will not allow you to go far. In fact, if you move along a circular dimension, you will eventually return to the starting point.

If you think the idea that dimensions can bend into loops is too strange, then you are not the only one who thinks so. Even the smartest people find this difficult to understand. In fact, perhaps all spatial dimensions are circular. In terms of the three spatial dimensions we are familiar with, this ring should be very, very large – larger than the observable universe.

If these dimensions are very small and circular, and only a few specific particles can enter, then it makes sense. In our view in three-dimensional space, the movement of objects in these small circular dimensions does not cause much change. However, there are ways to find these dimensions.

Do these higher dimensions exist? Do we live in a universe with more than three spatial dimensions? We don’t know. However, in terms of physics, there may be high dimensional space in the universe. What is more exciting is that we may find them. It will also understand the ways we may solve this mystery and make the four-dimensional physicists who feel good about themselves look at us with special respect.