Why did the universe begin with the big bang and how did scientists come to this conclusion? Now let’s take a look.
Before we can explain this problem, we should start with the “orbs paradox”. Obers is an astronomer. He came up with a conclusion which is completely opposite to the feeling in real life, also called paradox. He said that if our conventional universe is stable, that is, from a macro point of view, the universe is static, uniform, and infinite, then when you look up at the sky at night, the sky should be bright, not just a few stars.
Why is that? There is no sun at night. Why is it bright? Because the universe is uniform and infinite, so the luminous stars in the universe diffuse in the universe. The diffuse result is that you can see a star anywhere on the earth, and the sky is lit by the brightness of these stars. But is this the case?
Obviously, we look up at only a few scattered stars in the night sky, while other places are dark. In fact, we can use the mathematical formula to calculate.
If there is a planet, it will shine, and the earth is near the planet. In this way, when the planet is shining, only part of its light can reach the earth. Suppose that the luminous power of the planet is p, and the distance between the earth and the planet is r, then the planet will send its power to the whole sphere, so the power received by the earth is called P, which should be proportional to P / (4 π R ^ 2) divided by the surface area.
Because the power P is distributed on the whole sphere, the power that can be received is proportional to 1 / (4 π R ^ 2), that is to say, the farther the distance is, the less the power is received.
But the problem is that when the earth is collecting the light from the planet in one direction, there is a surface in front of the earth, and the light from each point on this surface may reach the earth, and the area s of this surface is proportional to the distance R ^ 2. Because there is an assumption that the planet is uniform, that is to say, the density of the stars in each place is the same, so the planet is at this angle The number of elements in is proportional to the area s.
According to the similarity, we know that the area s is proportional to R ^ 2. Then you will find that the light emitted by each planet is proportional to 1 / R ^ 2 when it reaches the earth, and the number of planets you have at this angle is proportional to R ^ 2, so the light emitted by them at a certain angle has nothing to do with the distance to the earth. Whether it is far or near, it should look the same bright So the whole sky should be bright all the time.
But the sky you are looking at is not like this. Why?
At first, people thought that the universe was really static. Orbs and other scientists made four hypotheses about it
1、 The luminous stars are blocked by a blackbody, but we have already thought that the universe is infinite, infinite time and infinite space, so any blackbody will glow as long as it is illuminated by the star, so the sky is still bright, and this assumption is not tenable.
2、 Suppose that all the stars are in a straight line in a certain direction, but the universe is uniform, resulting in contradictions, so it is not true.
3、 If the universe is not static, but expanding, then the planet will move outward and red shift will occur. After moving away, the energy that the planet brings to the earth will become smaller, which will not meet the above two formulas. Therefore, as long as the planets are far enough away from us, they will all look black.
4、 The universe is limited, the universe is limited space, so there is nothing outside the universe, there is no star in a certain direction. The universe is limited in time, so the light from a certain planet can’t be seen before it reaches the earth.
Now, we may be right about the latter two. So who first proposed the big bang? This is still derived from general relativity. Einstein put forward general relativity. From the beginning, general relativity was put forward to explain the universe. Unfortunately, when Einstein put forward general relativity, he thought that the universe was still static. So he introduced something called cosmological constant to correct this model. He still used the static model to deal with it.
Later, Alexander Friedman, a Russian scientist, solved Einstein’s equation and found that if the universe was not static but expanding, then the cosmological constant would not be needed.
Einstein also admitted that he was wrong, also known as the biggest mistake in his life.
Later, the scientist Hubble came to a conclusion by observing the redshift phenomenon: the distant stars are indeed leaving us, and the farther away they are, the faster they run. This is called Hubble’s law.
Well, through Hubble’s law, we can understand that the universe is expanding. If the universe is expanding, it must be limited, because the universe is expanding circle by circle. Before the expansion, we push back, the result of the universe must be smaller and smaller, and it will eventually concentrate on a point, and the density of this point is infinite, which is called the super dense state, All the laws of physics do not hold at this point, so we can only call it the “Big Bang”.
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