Hello everyone, I am Fuyao, and welcome to explore the unsolved mysteries with me. Today we will discuss “the secret behind the dark space.”
I believe everyone once looked up at the starry sky and the sky full of stars at night. The ancient Chinese also developed astrology to judge the good or bad of the world by observing the sky at night. Many people also take it for granted that if people come to space without the obstruction of the atmosphere, the starry sky should be even brighter. However, this is not the case.
After the American Apollo spacecraft landed on the moon, people were stunned when they saw the photos sent back by the astronauts. Um? Why is the background of the universe so dark? Where are the stars? For this reason, some people once questioned whether the Apollo ever landed on the moon. However, as more and more countries went on space trips, after taking pictures of outer space, people discovered that the “Apollo” was really wronged. The outer space was really dark.
Peculiar atmosphere
Why can we see countless stars on the earth instead? Because the earth has an atmosphere. The atmosphere is a layer of mixed gas surrounding the earth. With different heights, the atmosphere contains different elements and exhibits different characteristics. It is currently believed that the atmosphere can be roughly divided into troposphere and stratosphere. The plane we take is flying in the stratosphere, because the atmosphere flows more smoothly in this layer. And humans also use the temperature-increasing layer to achieve short-wave radio communication, so that people who are far apart can communicate with each other. Outside of the dissipative layer, although there are still rare gas and elementary particles, it is generally counted as outer space.
The atmosphere is the protective umbrella of human beings. It helps humans resist harmful cosmic rays and prevent the earth from turning into a desolate world like Mars. This atmosphere is like a huge lens, or a huge remote field of view, capable of reflecting the light emitted by distant stars. Speaking of this, some thinking viewers are about to ask, the Hubble telescope floating in space and the astronauts on the International Space Station can also take star pictures full of stars?
That’s because they haven’t really left the earth’s atmosphere yet. The Hubble Astronomical Telescope is 559 kilometers from the ground, and the International Space Station is mostly about 400 kilometers from the ground, and none of them exceeds the dissipative layer. It’s really beyond the dissipation layer, except for the stars of the solar system, no other stars can be photographed. Scientists say that the original photos sent back from outer space by the spacecraft will look completely dark if they are not post-processed. I believe everyone will have a big question mark in their minds at this time-why is this? Where are the stars? Before answering this question, let us first talk about the “Albers Paradox.”
Albers Paradox
The “Albers Paradox” was proposed by the German astronomer Heinrich Wilhelm Matthäus Olbers in 1823. The question he was thinking about was, why is the night sky not bright? At that time, it was generally believed that the universe that we could observe and perceive was static and infinite, and time was also infinite. Based on this, Olbers deduced that the sky should be bright, because it can be proved mathematically that there will be countless stars covering every point in the sky, and one should be seen no matter where you look in the sky. For a star, there should be no dark place between the stars, and the whole sky will be bright in the dark.
However, the facts tell us that outer space is not bright, but pitch black. How can this be explained? Albers himself put forward a hypothesis. That is to say, the universe is not transparent. There are dark stars in it, such as non-luminous planets, cosmic dust, and cosmic gas. Due to their obstruction, light from extremely far away can only travel a limited distance and cannot reach it. Earth. Human eyes can see things because they perceive visible light. If the light does not reach the earth, of course they cannot see it. It is black.
This theory sounds reasonable, but physicists came out to protest. They said that according to the first law of thermodynamics-the law of conservation of energy, these so-called barriers, namely planets, dust and other substances, will eventually be heated, and then they will also become luminous bodies. This brings us back to the conclusion of the paradox: the sky should be bright.
In the more than one hundred years since the “Albers Paradox” was put forward, people have been suffering from it, trying to find a reasonable explanation, but they are always hitting a wall. It was not until an American astronomer observed a very special cosmic phenomenon that this paradox found an explanation that at least made sense. This astronomer is the famous Edwin Powell Hubble (Edwin Powell Hubble), the Hubble Astronomical Telescope is named after him in honor of him.
Hubble Law
One of Hubble’s greatest achievements is the discovery of “Hubble’s Law.” He discovered by observing galaxies that the speed of stars moving away from the earth is proportional to the distance between them and the earth. In short, the farther a star is from the earth, the faster it moves away from the earth.
So how did Hubble discover it? Here we have to mention another concept “Doppler effect.” Doppler is a mathematician and physicist in Austria. Once, when he was passing by a railway crossing, a train was passing by him. He found that the whistle sound became louder when the train was near and far, but the pitch became slender, while the whistle sound became smaller when the train was near and far. But the tone became more vigorous. He was very interested in this physical phenomenon and conducted research, and finally found that when the sound source is away from the observer, the wavelength of the sound wave increases and the frequency becomes lower, and when the sound source approaches the observer, the wavelength of the sound wave decreases. , The frequency becomes higher.
Not only sound, the “Doppler effect” can also be applied to the movement of light. This picture is a spectrum, from top to bottom, the wavelength increases from small to large. The small section of color in the picture is visible light, and light with a wavelength in this range can be seen by humans. I have to sigh here. Compared to the entire spectrum, the range of visible light is really too small, and what the human eye can see is too limited. There are far more things in this universe that are invisible to human eyes but actually exist than what people can see.
Let’s continue to talk about the “Doppler effect” of light. When a star moves away from the earth quickly, the wavelength of the light waves it emits will increase, and the spectrum will move to the red side, which is called redshift in astronomy. The opposite is blue shift. You can find galaxy maps taken by astronomical telescopes and processed on the Internet, and you will find that the farther away the galaxy is from the earth, the more reddish it looks. To make another analogy, when we look at the sun now, we see that the light it emits is yellow and white, but if the sun keeps away from us, we will find that its light becomes orange-red, and farther away, it becomes red and deep red. , Dark red…until you can’t see it.
By observing the speed and direction of the stars, Hubble found that the stars are all moving away from us. He judged that the universe is not stationary, but constantly expanding.
Reasons for the dark space
Hubble’s observations on the “expansion of the universe” have allowed scientists to find an answer to the “Albers Paradox.” According to the current scientific community, the universe was formed in the 13.82 billion-year-old Big Bang, and then it continues to expand and expand. If at the moment of the Big Bang, the universe was bright, as bright as the surface of a star. As the universe continues to expand, the distance between the stars increases. Studies now show that the universe is expanding at a speed faster than the speed of light, so the light from many ancient and distant galaxies has no chance to reach the earth at all. There are also many galaxies, and the expansion of the universe causes the starlight from them to accelerate redshift and redshift. Beyond a certain distance, the light will be transferred outside the visible spectrum of the human eye, making these stars invisible.
Of course, these are all reasoning and explanations based on the “Big Bang Theory”. There are actually many interesting theories and speculations about the birth of the universe, which I will share with you in the future.
How big is the universe
Now that scientists have generally recognized that the universe is finite, how big is this universe? Let’s watch a video.
This is the diameter of the moon, 3,500 kilometers. This is our lovely earth, 13,000 kilometers in diameter. The largest planet in the solar system, Jupiter, has a diameter of 150,000 kilometers. Compared with the sun, it is still so inconspicuous.
When you think the sun is already big, please continue to look at it. Compared with some other stars in the universe, the sun can only be regarded as a younger brother.
UY Scutum is a red supergiant star with a radius 755 times that of the sun. At this point, we already need to change the unit of measurement, and adopt the unit of light day, which is the distance traveled by the speed of light in a day.
The unit of measurement became light years. The speed of light runs a year’s distance. It is about 9,460 billion kilometers in a light year. The closest star to the sun is also 4.2 light-years away. It keeps increasing in light years, and countless galaxies are contained in it.
The Milky Way, where our solar system is located, is between 100,000 light-years and 180,000 light-years in diameter, with an estimated 100 to 400 billion stars. However, the Milky Way is only a drop in the universe.
This is reminiscent of the fact that more than 2,500 years ago, Shakyamuni said: There are three thousand worlds in a grain of sand. If a solar system is counted as a world, these bright spots that look the size of gravel, each contains countless worlds. How did Shakyamuni know this at the time? Did he already see the truth of the universe?
Cosmic web is densely packed. And this is the distance of 5.6 billion light-years. Scientists call the “visible universe” the farthest range that can be observed in all directions with the earth as the center. This range is a sphere. The diameter of this sphere is currently believed to be 92 billion light years.
However, this does not represent the final size of the universe. Marcus Chown, a former radio astronomer at the California Institute of Technology, said that the edge of the visible universe should be a concept of a “cosmic horizon,” like a sea horizon. When people look at the sea, they know that farther than the sea horizon, there is also the ocean-beyond the “cosmic horizon”, there should be more, even endless galaxies.
Such a shocking picture is awe-inspiring and humble. People can’t help but think of Newton’s famous saying, known as the “father of modern science,” and an interesting story about him.
Newton was a great scientist, but also a pious and faithful man. When he published his scientific masterpiece “Mathematical Principles of Natural Philosophy,” he wrote a paragraph to the effect that the entire universe is so perfect and perfect, it must be the masterpiece of the great creator.
However, Newton’s friend Halley, who was the one who discovered Halley’s comet, dismissed it, thinking there was no god. One day, he visited Newton’s house and saw that Newton’s house had a model of the solar system with a gold-plated sun in the center. The surrounding planets were arranged in an orderly manner. When the handle was pulled, the planets immediately moved in their own orbits. Orderly.
After Halley saw it, he was full of praise, and while playing around, he asked casually, who made this? Newton replied that no one made it. It was made up of various parts accidentally. Halley thought Newton was joking with him and insisted on asking who did it. He also said that he must be a genius to make such an ingenious model.
Newton patted him on the shoulder and said, “Although this model is very delicate, it is really insignificant compared to the real solar system. You can believe that a small model must be made by someone. In contrast, this model is more delicate and billions of times larger. Isn’t the galaxy a masterpiece of the creator?”
With Newton’s words, Halley suddenly realized…
Okay, I will share it with you today. Unsolved mystery, I am Fuyao, we will see you next time.
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