There is day and night on earth, but is there day and night in the universe? Is it also alternate black and white?

There is day and night on Earth, and the night is dark without the sun. So where did all this darkness come from? Is it the universe? In the photos of humans landing on the moon, we can see that the universe in the background is also dark, but there are 200 billion stars in the Milky Way, and there are 100 billion galaxies in the universe, so many stars are constantly illuminating the universe, why? Is the universe still dark?

lunar surface

As early as 1833, German astronomer Heinrich Oberth proposed the theory that space is dark. Augustus pointed out that if our universe is static, uniform, infinite, and uniformly distributed with a large number of stars, then we look at the universe from anywhere on the earth, and the light of these stars will hit the earth to be seen by us , which means that the entire universe should be bright, without any darkness, and there should be no night on the earth. The night is as bright as the day, but the night sky is actually black. Olbers explained that there is gas and dust in the universe that blocks the light from distant stars, and that distant light values ​​can travel a finite distance. and cannot reach Earth. However, this explanation is not convincing, because according to the first law of thermodynamics, energy must be conserved, so the barrier in the middle will be electrically heated and start to emit radiation. As a result, the universe has uniform radiation, and the temperature should be equal to the surface temperature of the luminous body, so the universe It should still be bright. In fact, however, this phenomenon was not observed. This discrepancy between theory and observation is known as Olbers' paradox.

Heinrich Oberth (1758-1840)

The astronomical community generally believes that our universe is static. Even Einstein established a static universe model when he was studying the theory of relativity. This static universe model considers our universe. Our universe is a boundless and boundless static curved closed body.

static universe

Until 1929, through a large number of astronomical observations, astronomers found that distant galaxies existed, and there was a redshift phenomenon. Redshift refers to the reduction of the frequency of the electromagnetic radiation of an object for some reason. In the visible light band, it is manifested as a distance where the spectral line moves toward the red end and the wavelength becomes longer and the frequency decreases. All galaxies are constantly moving away from us, and the farther away a galaxy is, the faster it is moving away from us. According to this phenomenon, Hubble summed up Hubble's law.

red shift phenomenon

Hubble's law tells us that our universe is not static, it is a dynamic universe that is constantly expanding, which is also an important basis for supporting the Big Bang theory. Due to the expansion of the universe, stars are constantly moving away from us, and the expansion speed of the universe is three times the speed of light, which means that in the scope of the observable universe, the light emitted by unexpected stars will never reach the earth. Within the scope of the observable universe, although light can reach the earth. But it is no longer visible light. The expansion of the universe elongates the wavelength of visible light and reduces the frequency accordingly. This is why the universe appears dark.

speed of light imagined

In fact, there is another kind of light in the universe, which is the light radiated from the Big Bang. After 13.8 billion years of cosmic expansion, these lights have long been transformed into microwaves that cannot be observed by human eyes. If you use a microwave telescope to observe the night sky, you will find that the night sky is actually bright, but we cannot see it with our naked eyes. The earth is very small in front of the universe.