In the silent night, whenever we look up at the sky, all we can see is pitch black. So why is the night sky black? This seemingly simple problem has plagued humanity for 200 years.
It all starts with how we see objects. After the light enters our eyes, it is refracted through the lens and imaged on the retina, and the optic nerve that connects the retina reports these signals to the brain, and we see this complex world. Whether it is a mobile phone screen that can emit light, street lamps, etc., or books, tables, chairs, trees, etc. that can reflect light, when their light reaches our eyes, they will present corresponding images in our minds.
The night sky is dark except for thousands of shining stars
In the vast universe, we can see the Big Dipper, the moon and other celestial bodies, which is also based on the same reason. However, because they have a certain distance from the Earth, it takes a certain amount of time for light to travel from its transmission to our eyes.
In the case of the Sun, it takes about 8.3 minutes for sunlight to reach Earth after it shoots out of the Sun's surface. If a star is too far away from us and the speed of light is limited, the light it emits will not have enough time to reach our eyes, and we will not be able to see it. The universe was born in the Big Bang about 13.8 billion years ago, and in a limited time, the light of a large number of distant stars has not yet reached The Earth, that is, the light has not filled the entire cosmic space, so the night sky looks black.
The light emitted by many stars in the delta galaxy has reached Earth
The mystery of the dark night sky is often referred to as the "Obers paradox", a concept spread and popularized by the German astronomer Heinrich Obers. Scholars such as Obers argue that our inability to see stars in every corner of the night sky proves that the universe cannot be infinite and eternal: if the universe were infinite, the sky would be filled with stars, and the infinite time would be enough for the stars' dazzling light to reach Earth, and the night would be as bright as day.
Seemingly ordinary phenomena actually contain cosmic mysteries, and today we especially recommend this book, The Nature of the BBC Universe: Why the Night Sky Is Dark.
One
Focus on cutting-edge research and interpret the essence of the universe!
People's confusion about the universe is far more than the darkness of the night sky. Will the universe expand forever, or will it collapse into a single point? Is time flowing from the past to the future? Are there other universes besides ours? Are there other intelligent beings in the universe? The answers to these popular questions can be found in The Nature of the BBC Universe: Why the Night Sky Is Black.
From the fate cycle of stars to the ultimate fate of the universe, and then from the search for extraterrestrial life to the exploration of another universe, this book contains many cutting-edge theories, such as relativity, multiverse, inflation theory, quantum mechanics, etc. The author elaborates these obscure abstract theories with vivid language and schematic diagrams from a professional perspective, solving many cosmic problems for us.
A schematic of a singularity in space-time. It can describe both a collapsing black hole and an expanding universe
When the mass possessed by a universe produces enough gravity to counter its expansion, we call it a closed universe. Conversely, if a universe is not massive, gravity is not enough to reduce its rate of expansion, and we call this universe an open universe. In addition to this, there is a special case -
(also known as the flat universe). Each of the three corresponds to the last 3 possible endings of the universe: collapse, eternal expansion, and equilibrium.
Stephen hawking
Based on these three models of the universe, the scientific community has a variety of opinions about the fate of the universe, and the most concerned of these views is Hawking's cosmic hypothesis. In the early 1980s, British physicist Stephen Hawking proposed a hypothesis that the universe was closed. He hypothesized that the universe must have no boundaries (neither in time nor in space" any "edge"). This is actually not difficult to understand, assuming that we can stand at the moment of the big bang, it is equivalent to standing on the north pole of the earth, at this time, all directions are south, and there is no edge in space.
In the same way, every direction of time is headed for the future. Hawking believes that the gravitational pull of this universe is large enough that the expansion will tend to stop, and space will inevitably collapse in the direction of the big squeeze after reaching the maximum. After the universe enters the halfway point of collapse, time may turn back.
In a collapsing universe, time flows backwards, so water droplets will "fly upwards" from the ripples in the pond.
Hawking's theory is based on the concept of multiple worlds. The word "multi-world" can't help but remind us of many film and television works, which introduce the concept of parallel worlds, such as the American science fiction movie "The Night the Comet Came", the Netflix brain-burning German drama "Darkness", and various cross-over dramas, etc., all of which are based on the background of staggered parallel worlds and tell us about the adventures of the protagonist. Have you ever imagined that one day you would be walking on the road and another of your own would come up to you?
Thought experiment "Schrödinger's Cat" designed by Erwin Schrödinger
Do parallel worlds really exist? This involves knowledge of the quantum multiverse. We've all heard of the "Schrödinger's Cat" experiment. This experiment is a thought experiment, let's imagine putting a cat in a closed box full of poisonous gas, the probability of the cat surviving and dying is 50% each. We don't live to know whether to be dead or alive until we open the box. The standard interpretation of quantum mechanics holds that the cat in the box belongs to a superposition of both dead and alive, shrinking into one of the eigenstates of "living" and "dead" when the box is opened. The multi-world interpretation of quantum mechanics holds that there are two worlds, and the living cat and the dead cat exist in two parallel worlds when the box is opened. According to this theory, you are reading this article on your phone in this world, and you may have placed an order for this book in another world.
Two
Combining theory and practice, scientifically sort out the process of human exploration
Today's cutting-edge cosmic research results have undergone a difficult and long process of exploration. Take, for example, the method of measuring the distance of celestial bodies: Initially, triangulation was used for celestial ranging, but this mapping method could only measure objects closer to Earth, such as the Moon and Mars. After the launch of space probes such as the ElBagu satellite, humans began to measure the distance between many stars and the Earth with high accuracy. With the help of measurement techniques such as spectral analysis, the size, distance, and even its composition, speed and mass of stars are gradually clarified.
Radio astronomical observatories such as the Very Large Array (VLA) connect multiple radio telescopes to achieve the resolution of larger-sized devices
With the continuous breakthrough of space exploration technology, astronomical data is becoming more and more perfect, and the theory of the universe is constantly changing. The competition between the steady-state model and the Big Bang model was once fierce, and their supporters engaged in a fierce debate about how matter in the universe was created. Eventually, astronomers explored space using radio telescopes and optical telescopes to confirm the idea that the universe changes over time. Steady state eventually became a "model", and the Big Bang became a proven "theory".
The early universe was extremely hot and expanded around the singularity. As the expansion progresses, the universe gradually cools, producing particles such as protons and neutrons, which in turn form nuclei such as deuterium and helium
At present, the universe understood by human beings is only a drop in the ocean, and with the deepening of research, the theory of the universe also needs to be constantly revised. When building a model of the universe, even the "strongest brain" Einstein inevitably made mistakes. After Einstein proposed general relativity, in order to ensure that this model of the universe is static, the concept of "cosmological constant" was artificially created and the equation of general relativity was introduced. However , this view was later shown to be wrong , precisely because the introduction of the cosmological constant almost ruined the equations of general relativity. Einstein said it was the biggest mistake of his life.
Einstein's general theory of relativity laid the foundation for human understanding of the universe
Three
More than 230 astronomical photos and schematic diagrams show the magnificent universe!
The book contains more than 230 exquisite pictures, using astronomical photos taken by authoritative institutions such as the Hubble Space Telescope, showing us a stunning and magnificent galaxy, and the book is also interspersed with computer simulations, astronomer photos and illustrative schematic diagrams, etc., aesthetics and interpretation coexist, bringing an excellent visual experience.
Pillar of Creation
Seamount II (the constellation η) is ejecting material outward
Simulation of the living environment of other intelligent life
The expanding shock wave from an exploding star (left) is squeezing a cloud of gas and dust, triggering the formation of a new star (right).
Different wavelengths of electromagnetic radiation can penetrate different depths of the Earth's atmosphere
Four
Dr. John Gribbing, Ph.D. of Cambridge University and author of douban high-scoring book "Esoteric Simplicity", reviewed by astronomy experts of the Chinese Academy of Sciences!
The author, John Gribbin, is a PhD in astrophysics from the University of Cambridge, with deep academic skills, proficient in cosmology, always paying attention to cutting-edge theoretical research, and is also the author of many best-selling books on astronomy, and has won the Lifetime Achievement Award of the British Association of Science Writers. His books have been well received at home and abroad, and the book "Esoteric Simplicity" has been highly recommended by Dr. Fan Deng, the founder of Fan Deng Reading.
In addition to having a professional author, the book was also reviewed by experts from the Purple Mountain Observatory of the Chinese Academy of Sciences, who verified the professional knowledge and proper nouns in the book in detail, updated the content according to the new progress of relevant research, and added some necessary notes for better understanding of readers.