. I believe every fruit farmer understands the principle that apples are mature and landed better than Newton. However, it is Newton who discovered that gravity is the one who is Newton.
What we are going to discuss today is also a common phenomenon of life: Why is the sky dark at night?
Some friends may say, the sun is setting, but it will get dark?
Have you ever thought about it? The vast universe is full of all kinds of shining stars. If the universe is infinitely large and still and stable, no matter which direction we look, we should be able to see countless stars. No matter how far away the stars are from us and how weak the light emitted by the stars is, can't the light emitted by so many stars in still illuminate our night sky?
Astronomers' debates continue to
This seemingly naive but actually profound question has attracted the attention of astronomers a long time ago. It was first in 1610 that the famous German astronomer Kepler had already noticed something was wrong.
However, in his era, astronomy and astrology were not completely separated, let alone large-scale observations and research. So although Kepler made outstanding contributions to astronomy and pioneered astrophysics, it is difficult for him to explain the question of "why the sky is dark at night".
Until more than 200 years later, the German astronomer Obers first proposed the Obers paradox in 1826. He believed that: If the universe is really stable, infinite, and straight in time and space, the same luminous body should be evenly distributed on it.
Since the illuminance of the luminous body is inversely proportional to the square of the distance, and the number of luminous bodies in the sphere shell on a certain distance is proportional to the square of the distance, even if these luminous bodies are far and near to the earth, the total light should be able to shine the night sky infinitely bright.
After the Obers paradox was proposed, it immediately attracted widespread attention from the astronomy community. At first, many astronomers explained: That's because there are a lot of gas and dust in the universe. The light from distant stars is absorbed by them before they reach the earth, so our night is dark.
However, this statement is difficult to convince, because if the total light of the stars in the universe is infinite, even if interstellar matter absorbs the light of the stars, it will become hot and luminous because of the energy brought by these lights, rather than completely swallowing the light. Therefore, it will still come to the conclusion that the night should be bright, and is completely inconsistent with the facts.
That's it, astronomers have argued for a century but have no conclusion. It was not until Einstein's general theory of relativity published in 1915 that people saw a glimmer of light on solving problems.
General Relativity theory mentions: matter is distorted because of its own mass, and the distorted space-time will affect the distribution of matter and energy to some extent.
And just this year, American astronomer Sriver discovered that most of the spectral lines of galaxies outside the Milky Way deviate from their normal positions and are shifting towards the red end. What does this mean?
We all have this experience in life. When the high-speed rail train comes towards us, we will find that the sirens of the train become sharper and sharper. On the contrary, when the train is far away from us, the whistle will become low. This is the Doppler effect discovered by Austrian physicist Doppler.
Doppler effect is also applicable to light waves. When the light source is far away from the observer, the frequency of the light wave becomes lower and the wavelength becomes longer, which creates a redshift phenomenon on the spectral line. This discovery just shows that extra-river galaxies are moving away from us.
The universe is expanding, and the light cannot keep up with the speed of the universe's expansion?
In 1922, Russian physicist Friedman boldly speculated based on Srivers' discovery that if calculated based on general relativity and combined with redshift phenomenon, the size of the universe is not static, but rather the expansion and contraction of . The universe is in a period of continuous expansion.
However, his theory was immediately criticized by astronomers at that time, because at that time, including Einstein himself, everyone believed that the universe was still. In order to keep the universe in his equation still, Einstein even introduced a cosmic constant. Isn’t it against mainstream science that the universe will expand and contract?
However, in 1929, American astronomer Hubble told people through practical observations that even Einstein would make mistakes, and Friedman's speculation was completely correct!
Hubble not only observed that galaxies in all directions were far away from us, but also calculated that the distance of the galaxies was proportional to the size of the redshift. That is to say, the farther galaxies are from us, the faster they are away from us, and the universe is expanding in all directions !
This is the famous Hubble's Law. This discovery can be said to have slapped Einstein in the face, but Einstein was very pleased and immediately admitted that introducing cosmic constants was an extremely stupid mistake. After all, bowing to the truth is a happy thing, and from then on, the dynamic view of the universe has begun to be accepted by people.
Since the universe is constantly expanding, the farther away from us, the greater the redshift, the weaker the light emitted, so the energy emitted by distant galaxies is likely to be zero before the light reaches the earth, so our night sky will appear black as a whole.
But do you think the problem was solved perfectly like this? Well, since astronomers say that the universe is expanding, a series of new questions arise: When did the universe begin to expand? What is the reason for swelling in
? Is it possible for
to shrink?
…
This series of questions can be said to be the question of the astronomers speechless.
In order to avoid these problems, American astronomers have proposed a new hypothesis, saying that the reason why our night sky is dark is because we see the state before the birth of the universe.
Think about it, no matter how fast the light propagates, it is limited, 300,000 kilometers per second, and the universe is so big, it takes a certain amount of time from birth to transmission. The stars and universe we see now are actually not their current state.
Even if the sun is closest to us, what we see is just what it looked like 8 minutes ago. Not to mention the stars farther away from us. So the night sky we see now is the state of the birth of stars and the universe. Their light has not reached the earth yet, so the night is pitch black.
However, this statement also has great loopholes, because no one can tell how the universe was formed and how it evolved into what it is today.
Of course, there are imperfections behind the proposal of any hypothesis, which require further observation, research, and evidence collection. And I believe scientists will continue to study the issue of night sky.
In this process, you will inevitably encounter challenges from authority, and there will inevitably be many discoveries and theories that subvert our traditional cognition. Scientists should all have the spirit of Friedman and Hubble, and dare to use facts to subvert traditions and express their doubts and introductions. After all, authority and tradition may not be the truth. Only by constantly asking questions, exploring, and observing and researching can we find the answer to the final solution to the problem.
