Although the night sky is dark, it has been loved by many people for a long time. After all, in addition to the black background, there are bright stars and a bright moon all over the sky. It is quiet and beautiful, which makes people yearn for it.

All these seem to be very normal natural phenomena, but only a few people know that there is actually a desperate fact hidden in it. What is going on?

The Mystery of the Black Night Sky

Regarding the question of why the night sky is black, perhaps no one will delve into it except scientists. Human beings have adapted to this phenomenon for thousands of years, but for scientists, everything can be explained from a scientific point of view.

However, the achievement of this goal is not as easy as imagined. This seemingly common phenomenon has troubled the entire scientific community for many years.

In the early sixteenth century, Kepler questioned the blackness of the night sky for the first time, because according to scientific theory , there are countless stars distributed in the universe, some of which are brighter than the sun, but why are they still invisible? Can it illuminate the night, but only the sun of average brightness supports the day?

Restricted by the level of science and technology, this question was not answered at that time. Until the eighteenth century, a scientist named Olbers also had doubts about the dark night, and conducted research on it specifically, and wrote about the cosmic luminous celestial bodies . papers.

In this paper, he clearly pointed out that the light emitted by many luminous celestial bodies can travel a long distance, and no matter which area of ​​the earth is located, there is a chance to receive the light of these celestial bodies.

From this point of view, then there should be no night on the earth, but in fact it does not, so Olbers' view became a paradox in the scientific community, and it was not confirmed until the early twentieth century.

proven paradox

Olbers' paradox can be confirmed, mainly due to a special phenomenon that was accidentally discovered by scientists at that time -redshift . The so-called red shift means that when the electromagnetic radiation is abnormal, making the wavelength and frequency unstable, the spectral irradiation will change accordingly, not only the position will move, but the distance will also change accordingly.

After observing and studying various galaxies, astronomer Edwin Hubble found that redshifts can be found in the spectra of all galaxies . In fact , natural substances with wave properties may also undergo redshifts, such as sound waves.

The sound wave is a circular ripple that surrounds the sounding position and gradually spreads to the surroundings . However, if the sounding position changes, the sound wave will be difficult to maintain the original shape, but will become tighter or looser.

Generally, the higher the frequency of the sound wave, the higher the pitch. Just like a car driving on the road, when it is close to us, it will obviously feel a higher pitch, but after driving away, its pitch will be much lower.

But as we all know, the tone of the car itself does not change due to the distance, and human hearing does not change in this process. The reason for the different feelings is the red shift and blue shift of the sound wave.

As the sound waves get closer, the process of increasing frequency is called blue shift, and vice versa is called red shift, which is determined by the spectrum. So it is not difficult to understand why there is a night.

This is because the luminous celestial body is far away from the earth, so that the light waves that can be irradiated are getting smaller and smaller, and even become infrared rays, which cannot be seen by the naked eye, which also proves Olbers' paradox.

Although the universe is indeed filled with luminous celestial bodies, they gradually become invisible light under the influence of the redshift phenomenon, forming a dark night.

Why is the blackness of the night sky so desperate?

After discovering the redshift phenomenon, scientists have been observing cosmic rays non-stop through infrared detectors, and found that the universe is full of various rays of light , and these rays of light have appeared as early as the time of the big explosion of the universe, so scientists calculate the life of the universe About 13.9 billion years.

According to the general theory of relativity, the speed of light is the fastest speed, and any matter will not run faster than it, so even if the universe expands at the speed of light, the range of its matter is only about 12.9 billion light-years.

However, in fact, at this stage, the radius of the universe that can be measured is already 46.5 billion light-years, and there are obviously more celestial bodies distributed beyond this distance, so the scope of the universe should be more than 93 billion light-years.

So the expansion of the universe must be faster than the speed of light, but why do scientists despair about this? The reason is not difficult to understand.

Since the expansion of the universe is faster than the speed of light, it means that matter outside the radius of the universe will move away from the earth at a speed exceeding the speed of light , especially those celestial bodies that can emit light, and may never have a chance to touch them, even if they want to transmit information It's also difficult to implement, making it nearly impossible to pass information beyond that range.

More importantly, because the universe has been expanding at an accelerating rate, the matter outside the event horizon, even the matter within the event horizon, may also go far away at any time. In the end, there may be only one earth within the visible range of human beings.

However, this situation will not occur at this stage. The distance between the current cosmic matter is not too far, and human beings still have the opportunity to obtain more information and resources to conduct research.