######Is the universe a reincarnation? Astronomer: in billions of years, the universe may have another big bang

With the current knowledge of human beings, we can easily explain how human beings were born and where the elements in our bodies came from.For example, the most important elements in human body are carbon, oxygen and hydrogen, which originate from the remnants of star explosions in the universe. They combine with different substances to form a variety of organisms, and one of them eventually evolved into human beings.But where does the material that makes up stars come from?According to the law of conservation of mass, if the universe is isolated, its total mass remains the same no matter what happens to the matter in it, whether it becomes a dusty star or a black hole.That is to say, galaxies and stars in the universe existed in another material form before they formed. What were they then?After 13.8 billion years, will the universe continue to expand endlessly?Since ancient times, people have made countless conjectures about the origin of the universe, from the explosion theory to the particle theory, and even to the myth theory. Through observation and calculation, the most widely accepted theory by mainstream scientists is the theory of the origin of the big bang.According to this theory, the universe was originally a singularity. It suddenly exploded 13.8 billion years ago, and after a long evolution, it became the galaxy and space-time we see now.This singular point does not apply to all the laws of physics known to mankind at present, because there is no time and space here. It has only mass but almost no volume, so its density is infinite and the curvature of space-time is infinite.The instant of the explosion generated time and space. In the unimaginable energy, the mass was converted into basic particles such as electrons, photons and neutrinos. In the negative 33th power of 10 seconds, the speed of universe expansion experienced 100 times of doubling, and the space size was 10 to 30 times of the previous.About 300000 years laterThe universe gradually cooled to 3000 degrees Celsius. Under the action of chemical bonding, some neutral atoms began to form. The familiar celestial bodies began to conceive at this time. The first hydrogen atom was born. The hydrogen atom has only one nucleus and one electron. The combination of the two hydrogen atoms forms the slightly heavier element helium.Subsequently, helium atoms can be combined with hydrogen atoms or another helium atom. Under the action of its own gravity, these atoms will condense into gas clouds with higher density, which will collapse and explode after accumulating more and more, forming primary stars and star systems.It can be said that the formation of hydrogen atoms has created the colorful universe. Is our solar system also composed of hydrogen atoms?Hydrogen atoms are not only the most abundant element in the universe, but also the main constituent material of stars. However, the hydrogen atoms in the solar system are not the ones in the big bang, because the solar system is still a little young.According to observations, the hydrogen atoms in the sun are likely to be the remnants of the big bang after the death of the first generation of star systems. That is to say, the sun is actually the second generation of stars, and all the materials that make up human beings have existed in the universe for billions of years.So what is the final outcome of the sun?All the stars we can see in the sky are stars, and ordinary stars do not emit light. This is because nuclear fusion is taking place in the stars, and so is our sun. Therefore, from the earth's perspective, the sun is always so bright.Nuclear fusion is constantly consuming the hydrogen atoms in the sun. It will always be exhausted one day. After the hydrogen atoms are exhausted, the sun will not die immediately. Instead, it will continue to use helium as nuclear fusion fuel, leaving the main sequence star and entering the red giant stage. However, the reaction of helium is very unstable. The outer layer of the sun will expand rapidly and devour the surrounding planets, including the earth.At the same time, the core of the sun is shrinking constantly, balancing with the expanding force on the outside. However, this balance will not last long, and it will explode due to instability in about ten to several hundred million years.This explosion will throw all the materials outside the core away from the star body, leaving only a pale and dense white dwarf. The thrown materials undergo fission under huge energy, and return to the original state of matter: hydrogen atoms.They are loosely distributed and become nebulae composed of hydrogen atoms. Careful readers will find that this is not the place where the solar system was born?Yes, after the death of stars, they become nebulae. Nebulae breed new stars again, and the universe is evolving in this way.Since stars are like this, will the universe be like this?Since the universe can expand, can it collapse?Research shows that this is indeed possible, because the universe can expand because of the energy generated by the big bang. One day, the energy expanding outward will be exhausted, and the gravity of the universe itself will make the universe begin to shrink inward.In the process of contraction, huge celestial bodies are crushed into fragments, which will synthesize into larger celestial bodies. The larger gravitational center of these larger celestial bodies will accelerate the contraction speed and slowly exceed the speed of light. Finally, when all matter becomes a point again, time and space disappear here, and the universe returns to its original state: singularity.Then the singularity will explode again, forming the universe, and finally returning to the singularity?We have no way to know this. Maybe the universe repeats countless times in a continuous cycle, or maybe the universe will only go to heat death in the end