What is gravity? Newton believed that it was an attraction between two mass objects, Einstein’s general theory of relativity believed that it was a kind of space-time bending, and quantum mechanics believed that it was a kind of particle called a graviton between different substances. Of exchange. General relativity is right, quantum mechanics is also right. The contradiction between the two sets of theories on the issue of gravity tells us that we have not really figured out what gravity is.
Perhaps gravity is not what we think it is. Some people think that gravity may be produced by a certain “string”, and some people think it is produced by a certain “field”. These two views come from superstring theory and loop quantum gravity theory respectively. What’s more interesting is that some people even think that gravity does not exist at all. It is not a force, but a phenomenon of entropy increase. What is going on?
Gravity is a vibration mode of superstrings?
An apple can be divided into two equal parts, two parts can be divided into four parts, and four parts can be divided into eight parts. It seems that it can be divided indefinitely until it can no longer be divided. So, what is the smallest unit of matter (the elementary particle)? In 1789, the French scientist Lavoisier defined the term atom and believed that the atom is the smallest unit in chemical change. After the early 19th century, humans discovered neutrons and protons smaller than atoms. In the 20th century, other hadrons smaller than protons and neutrons were discovered. In the middle of the 20th century, quarks, the constituent unit of hadrons, were discovered. Can quarks be divided?
No one can separate the quarks, but scientists soon proposed: Maybe, inside the elementary particles, there is something more subtle and unknown that determines the phenomena and laws of the world, this more subtle thing. Maybe it can solve the contradiction between general relativity and quantum mechanics. The superstring theory was put forward under this kind of thinking. The theory believes that the basic units of nature are not basic particles such as electrons, photons, neutrinos, and quarks. These things that look like particles are actually very Small “string”-inside each elementary particle, there is a thin line vibrating, just like the vibration of a violin string, so this thin line is vividly called ” string”.
Space is dependent on field lines
Pluck a string of the guitar and you will hear a note. Pluck another string, and you will hear a different tone, because different strings vibrate in different patterns. A musician can create countless beautiful music by vibrating these strings at different frequencies through a six-string ensemble of a guitar. Just like the different vibration modes of the strings play different tones, the strings inside the particles also have different vibration modes, but the vibration of this string does not produce music, but produces individual particles. The properties of different particles are determined by the different vibration modes of the string. Different particles are just different vibration modes of the string—electrons are strings that vibrate in a certain way, and up quarks vibrate in another way. String, and so on. The more violently the string vibrates, the greater the energy (mass) of the particles; the softer the vibration, the smaller the energy (mass) of the particles.
The string itself is very simple, just a tiny thread, the string can be closed into a loop (closed string) or opened, and it looks like a hair (open string). Strings can be broken down into smaller strings, or they can collide with other strings to form longer strings. For example, an open string can be split into two small open strings, or into an open string and a closed string; a closed string can be split into two small closed strings; the collision of two strings can produce two A new string. Therefore, all interactions that occur in nature can be explained by the split and combination of strings.
In quantum theory, every particle also has the characteristics of waves, which is the wave-particle duality. Now we can understand that the wave of particles is produced by the vibration of the string. Physicists also discovered that there is a direct connection between the vibration mode of the string and the four interaction forces between particles-the gravitation, electromagnetic force, weak force and strong force generated by a string are completely determined by its vibration mode.
The movement of the string is so complicated that the three-dimensional space can no longer accommodate its trajectory. There must be up to ten-dimensional space to satisfy its movement, which is determined by the nature of the string. Just as human movement cannot be done in a two-dimensional plane, it can only be done in a three-dimensional space. Therefore, the superstring theory believes that the space of this world actually has ten latitudes. In addition to the three-dimensional space we live in, there are seven spatial dimensions that we don’t know (the extra dimensions are called extra dimensions).
The appearance of objects in different dimensions
The universe begins at a point, which hides the ten-dimensional space secret at the moment the universe began. Later, this point exploded, which meant that the ten-dimensional space had broken. General relativity and quantum mechanics are only manifestations of physical laws at different latitudes. From this perspective, general relativity and quantum mechanics are not contradictory, and they are not completely compared on the same platform. When we look at them in the three-dimensional space of life, we are as incomprehensible as looking at a leopard in a tube, and we feel that their contradictions are understandable.
Loop quantum gravity theory
However, the extra dimension is difficult to be accepted. Perceptually, we live in a world of three-dimensional space that we are already familiar with. Rationally speaking, no other spatial dimension has been detected so far. It only exists in In theory. Compared with superstring theory, there is a theory called loop quantum gravity that seems more “real”. This theory is only based on the four-dimensional space-time (three-dimensional space, one-dimensional time) we live in and does not add any additional dimensions. Loop quantum theory still starts from the perspective of the quantization of gravitation that has plagued the world of physics today (in general relativity, gravitation is continuous, and quantization of gravitation is an attempt to describe gravity as gravitons) to achieve unification.