Although they didn't like their current state very much, Hua Feng and Yun Meng had to admit that taking classes and cultivating in the past few months had become the main theme of their daily life, although they were confused about what the road ahead was, they both believed that everything they were doing now was right, and for them, it was enough.

Dark energy accounts for 74% of all matter in the universe, and it is the driving force behind the accelerated expansion of the universe. The expansion process of the universe is in the balance of two opposing forces, just like yin and yang. One of these forces is gravity, which slows down the expansion, and another powerful counterforce is dark energy, which accelerates the expansion of the universe. And now, it seems, dark energy wins.

The visible matter in the universe is far from enough to unite the universe, and if it were not for the existence of a mysterious and invisible matter, galaxies would have fallen apart long ago. Scientists call this unseen, mysterious substance "dark matter." Dark matter is the primary type of matter that causes the universe to expand and form a specific structure under its own gravity.

Astronomical observations indicate that our universe is doing an accelerated expansion motion.

Theoretically, there is some kind of critical density. If the average density is less than the critical density, the universe will continue to expand, which is called the "open universe", and if the average density is greater than the critical density, the expansion process will sooner or later stop and contract, which is called the "closed universe".

At present, it is more likely to open the universe.

Accelerated Expansion:

Nobel laureate Brian Schmidt noted: "The space between matter and matter is increasing. “

In 2011, Brian Schmidt and his colleagues won the Nobel Prize in Physics that year for using "supernovae" as "space probes" to discover the accelerated expansion of the universe.

"We look at the speed of an object moving away from us, just as Doppler radar uses Doppler shifts to locate and measure," he explains. We measure the distance, and the distance divided by these actions, to calculate the expansion rate of the universe.

Our method of measurement is to look at distant objects, make the same measurements at different times, and draw conclusions by comparison. From this point of view, it is a very simple experiment. By comparing the different distances measured in the past and now, we know that the universe is now expanding much faster than before.

The researchers calculated that the current rate of expansion of the universe, known as the Hubble constant, is about 73.2 km/s (seconds·million parsecs). Each million parsecs is equivalent to 3.26 million light-years, so for every million parsecs a galaxy is farther away from Earth, its speed away from Earth increases by 73.2 kilometers per second. This means that in 9.8 billion years, the distance between cosmic objects will double.

Speculation on the end of the universe:

The laws of thermodynamics do not allow the universe to gain eternal life, and when new stars cannot continue to form, the universe reaches the equilibrium point of heat death, and the state of the universe is like the bowl of soup at the beginning of its birth. Heat death is the thermodynamic end, and the temperature in any part of the universe is just above absolute zero, meaning that nothing will survive.

A small number of scientists believe that if the universe ends up in a big collapse, all matter will eventually become atomic, and then after an accidental quantum fluctuation, a new round of Big Bang will be formed, and the next universe will be born.

Cosmologists believe that if the energy density of the universe is equal to or less than the critical density, the expansion will gradually slow down, but it will never stop. Star formation eventually stops as interstellar gas is gradually depleted in each galaxy, and stellar evolution eventually leaves only white dwarfs, neutron stars, and black holes.

Quite slowly, the collision of these compact stars with each other causes masses to accumulate and create larger black holes one after another. The average temperature of the universe will asymptically approach absolute zero, leading to the so-called Great Freeze. In addition, if protons were to be as unstable as the Standard Model predicted, the baryonic matter would eventually disappear entirely, leaving only radiation and black holes in the universe, and eventually all black holes would evaporate due to Hawking radiation.

The entropy of the universe will increase to such an extreme point that there will no longer be a form of self-organizing energy, and eventually the universe will reach a state of heat death. In the λcdm model, dark energy exists in the form of cosmological constants, a theory that only matter from gravitationally bound systems such as galaxies gathers and that as the universe expands and cools, it also reaches heat death.

Other explanations of dark energy, such as the phantom energy theory, hold that eventually groups of galaxies, stars, planets, atoms, nuclei, and all matter will be torn apart in a continuous expansion, known as the Great Tear.

Big Bang Theory: The framework of the Big Bang model is based on Einstein's general theory of relativity, and some simplifications have been made in solving the field equations. In 1932, Lemaité first proposed the modern Big Bang theory, and in 1946, the American physicist Gamow officially proposed the Big Bang theory.

The Big Bang universe model suggests that the universe originated from a primordial fireball more than 10 billion years ago. The inflation model solves three major problems in cosmology: the horizon problem, the flatness problem, and the magnetic monopole problem.

The Big Bang is based on the cosmological principle that a singularity explodes in all space.

The earliest and most direct observational evidence of the Big Bang theory includes the Hubble expansion observed from the redshift of galaxies, the fine measurement of cosmic microwave background radiation, and the abundance of light elements in the universe, and now large-scale structure and galaxy evolution have become new supporting evidence. These four types of observational evidence are sometimes referred to as the "four pillars of the Big Bang theory."

The Big Bang model consistently illustrates the following observational facts:

(a) The theory asserts that all stars are created after a drop in temperature, and therefore the age of any celestial body should be shorter than the period from the temperature drop to today, i.e., less than 20 billion years. This is evidenced by the measurements of the ages of various celestial bodies.

(b) Systematic spectral redshifts have been observed in extragalactic objects that are roughly proportional to distance. If we use the Doppler effect to explain it, then the redshift is a reflection of the expansion of the universe. But in 2012, it was suggested that this was a cosmological redshift, not a Doppler redshift. In cosmological redshift, the wavelength of a light wave changes with the expansion of space during propagation. The redshift of the spectral lines is a reflection of the expansion of the universe.

(c) The helium abundance is quite large in a variety of celestial bodies, and most of them are 30%. Using the stellar nuclear reaction mechanism is not enough to explain why there is so much helium. And according to the Big Bang theory, the early temperatures were high and the efficiency of helium production was also high, which explains this fact.

(d) The temperature of each period of the universe can be calculated in detail according to the rate of expansion of the universe and the abundance of helium.

According to the Big Bang theory, the universe had no beginning. It is just a cyclical process, the process of the creation and destruction of the universe and its re-creation.

Theory:

The evidence for the Big Bang theory is as follows:

(a) Red displacement

Distant galaxies are leaving us from any direction of the Earth, so we can push out the universe expanding, and the farther away from us, the faster we move away.

(b) Hubble's Law

Hubble's Law is a definite relation to the speed and distance of galaxies from each other. Still illustrates the movement and expansion of the universe.

V=H×D

where V(Km/sec) is the distance velocity, H(Km/sec/Mpc) is the Hubble constant of 50, and D(Mpc) is the galactic distance. 1Mpc = 3.26 million light years.

(c) Abundance of hydrogen and helium

The model predicts that hydrogen is 25% and helium is 75%, which has been confirmed by experiments.

(d) Abundance of trace elements

For these trace elements, the abundance of these trace elements is estimated in the model to be the same as that measured.

(e) Cosmic background radiation of 3K

According to the Big Bang theory, the universe was cooled by expansion, and there should still be radiation embers in the universe today, and in 1965, 3K background radiation was measured.

(f) Trace inhomogeneity of background radiation

It proves that the original state of the universe was not uniform.

(g) New evidence for the Big Bang theory

In the December 2000 issue of the British journal Nature, scientists said they had found new evidence that could be used to confirm the Big Bang theory.

Theory of Quadratic Expansion

Some scientists at the U.S. Department of Energy's Brookhaven National Laboratory and other institutions believe that there may have been a relatively brief period of secondary expansion in the early universe, a hypothesis that may explain the excessive amount of dark matter in the universe.

Homan Dewoodiaso, head of the laboratory's High Energy Theory Group, said there may be another expansion between these important events, which is not as violent as the first explosion but can "dilute" dark matter, making the density of dark matter in the universe what it is today.

Physical equality

The Big Bang theory was founded on two basic assumptions: the universality of the laws of physics and the cosmological principle. The cosmological principle states that the universe is homogeneous and isotropic on a large scale.

All parts of the universe (homogeneity) and all directions (isotropy) appear to be the same, which is an important basis for the Big Bang theory. The theory holds that the entire universe, everything we see, originates in a fiery, dense, and unified state, where the laws and initial conditions are the same everywhere.

The most basic principle of cosmology is the principle of megranality. It argues that all the laws of the earth apply everywhere else.

Multiverse Guess:

The multiverse is a theoretically infinite or finite collection of possible universes. The various universes contained in the multiverse are known as parallel universes. Very few theoretical physicists believe that there is a multiverse in different states.

According to inflation theory, the Big Bang, as it is commonly called, may not be the beginning of time and space, but the beginning of our observable universe. Before this was the inflationary period of the universe. It was an exponentially expanding universe, filled with the energy inherent in the fabric of space-time. The inflation of the universe is also a theory that has been inherited and developed.