Because there is a paradox here, if the smallest substance that constitutes our world is three-dimensional, then it must have length, width and height, because only with length, width and height can it be a three-dimensional object.
With length, width and height, this object has a surface and an interior, and it must have an internal structure. The interior contains substances, as long as it contains substances, it can be subdivided.
Theoretically, three-dimensional objects that cannot be subdivided do not exist.
If matter has the smallest three-dimensional structure, then the density is limited, and the density of the smallest three-dimensional structure object is the limit of the density of our universe.
At present, the densest object is called a black hole. Planets are also made up of atoms. When the mass of the planet is large enough, the internal gravity will be great. When gravity is enough to press electrons outside the atoms on the planet into the nucleus, the planet will become a neutron star. The density of neutron stars varies from 8 14 to 8 15 grams per cubic centimeter.
When the mass of neutron stars increases, they will collapse into quarks, and the density of quarks is dozens of times larger than that of neutron stars.
Further on, it will become a black hole. No theory can determine the density of a black hole, but it is many times larger than that of a quark.
At present, the object with the highest density is known as BIGBANG singularity, which is infinitely small in volume and infinite in mass, so the density is infinite.
Current theories cannot explain the existence of singularities, but some theories show that the minimum composition dimension of matter is 0. Without length, width and height, an infinite number of substances can be compressed together.
The elementary particles in the universe are all produced by the smallest structural interaction in 0-dimension.
So there is no limit to density, and it can be infinite.
In physics, density refers to the mass of matter per unit volume. For example, the density of water is per cubic centimeter 1 g, and the density of gold is per cubic centimeter 19.26 g. The densest substance on earth is osmium. The density reached 22.59 grams per cubic centimeter.
Figure: osmium
Observing atoms in the microscopic world, we will find that the nucleus only occupies a small part of the space, and the main mass is concentrated on the nucleus. So there is still room for further improvement in density.
Figure: Solar energy structure
In the solar system, the highest density of matter is the core of the sun. Due to the huge mass of the sun, the pressure at its core reaches 330 billion atmospheres, making the density here reach 0/50g per cubic centimeter150g, which is 0/50 times that of water and 6.64 times that of osmium.
Photo: White Dwarf
When the fuel in the sun's core is exhausted, there will be no radiation pressure to resist the compression of gravity. At this time, gravitational collapse will occur until the outer electrons are compressed to the lowest energy orbit, and then degenerate matter of electrons is formed. Electronic degeneracy pressure can resist the pressure of 1.44 times the mass of the sun. At this time, the sun became a white dwarf. The material density of white dwarfs reaches per cubic centimeter 1 ton.
Photo: neutron star
If the mass exceeds 1.44 solar masses, the electron degeneracy pressure cannot resist gravitational compression. Electrons will be compressed into the nucleus to form neutron degenerate matter. This is a neutron star. The density of neutron stars has reached 80 million tons and 2 billion tons per cubic centimeter.
Figure: Double black holes merge
When the mass exceeds 3.2 times that of the sun, nothing can resist gravitational collapse. It will collapse into a singularity. The density of singularities is considered infinite. But in fact, there will be no infinity.
"Everything specific is limited; Only abstraction is infinite. " This is a basic principle of our human understanding, and it is also a standard for us to judge whether our understanding is correct or not. Because zero or infinite things are unimaginable in the real world.
For example, if the universe is expanding, then the volume of the universe must be limited. Expansion with zero or infinite volume has no physical meaning.
In fact, zero or infinity is just an abstract concept in mathematics. In the real world, there is no zero or infinity.
So is the specific physical concept of density. There is no object with zero or infinite density.
It is easy to understand that there is no object with zero density, that is, there is no absolute vacuum. Otherwise, it is nothing and has no physical meaning.
For human beings, nothingness is only a temporary lack of understanding and induction of the physical meaning of existence, rather than the real existence of nothingness space.
For example, the atomism in ancient Greece believed that atoms were the smallest entities, and the gaps between atoms were nothingness. However, with the progress of human understanding, air and space are gradually discovered. The former is composed of discrete gas molecules, and the latter is composed of discrete and inseparable smallest particles-quantum.
As for the density of objects, it is increasing with the discovery that particles are getting smaller and more basic.
For example, when the atomic level is recognized, the celestial body discovered is the sun, and its density is roughly equivalent to the density of matter on the earth;
Later, I learned that there are white dwarfs formed by electron degeneracy pressure, which are many times denser. It is said that a white dwarf the size of a matchbox weighs several tons.
Later, I learned that there were neutron stars, that is, electrons and protons were squeezed into neutrons. Therefore, the density of neutron stars is many times larger, which is equivalent to the density of elementary particles.
Finally, according to the formula of universal gravitation, when the distance is zero, the gravity is infinite, and the singularity of infinite density is deduced. For a specific celestial body, a black hole is formed from which even light cannot escape; For our universe, the singularity is reversed, forming a huge explosion that exceeds the speed of light.
The last point is questionable, because the singularity with infinite density loses its specific physical meaning. The problem lies in the infinity of the formula of universal gravitation when the action distance is zero.
In the real world, there is no such thing as zero distance. And when the distance is zero, there is no spatial effect, so the gravity of the distance disappears.
In fact, every celestial body with increased density is composed of more elementary particles, and the upper limit of its density is the density of the particles themselves. The radius of particles limits the further increase of density.
For our universe, the limit of its density is the smallest particle that cannot be subdivided-the distance between quanta is equal to zero.
Due to the existence of Planck constant H, its physical dimension is the angular momentum of particles, which is the intrinsic parameter of quantum, indicating that the mass and radius of quantum are greater than zero. According to calculation, the radius of quantum is equal to 3.58x 10-2 1 cm.
Therefore, as a relatively independent closed system, our universe is composed of discrete quanta, and the number of quanta contained in the universe is constant. Just because of the expansion of the universe, the distance between quanta is getting bigger and bigger, filling the whole universe.
When the universe contracts, the distance between quanta will decrease. The limit of cosmic contraction is that the quantum spacing is equal to zero. As a result, the universe began to reverse and formed the Big Bang. So there is no singularity in the universe, and the upper limit of the density of the universe is the density of the quantum itself.
In a word, the concrete and finite universe is composed of the smallest indivisible particle-quantum. The lower limit of the density of the universe is the infinity of quantum spacing, when the universe dies; The upper limit of the density of the universe is that the distance between quanta is zero, that is, the universe begins to reverse, leading to violent expansion.