In the 1920s, when an astronomer from the United States was observing distant galaxies, he accidentally discovered a commonality, that is, all galaxies in the universe have redshift phenomena! The discoverer was Edwin Hubble
When it comes to redshift, many people may have some questions, what is redshift in the end, and why do galaxies have redshift phenomena?
In fact, the redshift phenomenon and the Doppler effect of sound are very similar, we know that during the propagation of sound, the mechanical waves emitted will change with the speed of the observer's movement.
That is, when the wave source is close to the observer, the frequency of the sound will become higher, and the frequency of the sound will become lower when it is far away from the observer, such as a train driving towards us, when it approaches the observer from far to near, we will hear the sound of the train at different frequencies, away from us is low, close to us to sharp, this is the Doppler effect of sound, in 1842 by an Austrian physicist named Doppler discovered.
In fact, the Doppler effect is not only reflected in the sound, but also in the electromagnetic wave will also appear, to know that light has wave-particle duality, there are two characteristics of wavelength and frequency, so he also has a Doppler effect, only the Doppler effect of light is shown through color
For example, when a celestial body is moving away from us, its wavelength increases, then the color will move to the red end, if it is close to us, the wavelength decreases, the color will move to the blue end, which is what we usually call red shift and blue shift!
At that time, the famous astronomer Edwin Hubble observed the galaxy, that is, he found that distant celestial bodies showed redshift phenomena, and through the amount of redshift, he also knew that the farther away the celestial bodies were from us, the faster they regressed!
So Hubble came to the conclusion that the reason why galaxies are far away from us is because the space in the universe is constantly expanding, which causes galaxies to separate from each other! Because there is no other reason than the expansion of the universe that perfectly explains why galaxies are far away from us!
So far, after the expansion of the universe has been confirmed, scientists have deduced backwards based on the distance of galaxies that our universe may have been born about 13.8 billion years ago, starting from a dense singularity of infinite heat, and then evolving into the universe today through continuous expansion. And also believe that since the universe was born from a singularity, shouldn't the universe also have an end day?
Indeed, the universe may also be coming to an end!
We know that nothing escapes the fate of entropy increase, because according to the law of entropy increase, in an isolated system, entropy increases over time, developing from order to disorder, and is irreversible. For example, if there is a complete cup, when you break it, it cannot spontaneously change into its original form, but only changes from an ordered state to disorder, so the entropy increase cannot be reversed
Rising into the large-scale structure of the universe means that the star will irreversibly exhaust all the energy in the universe for a long time, from the death of the first generation of stars to the birth of the second generation of stars, until the last star is completely extinguished, it will not be able to continue to form new stars, at this time the universe will be completely plunged into darkness, because no nebula material can collapse into stars.
All that's left are black holes and planets, but with the passage of time, black holes will disappear due to a little evaporation of Hawking radiation! Planets and other celestial materials will decay into leptons in billions of years!
At that time, the entropy value in the universe reaches the highest, in a state of thermal equilibrium, and finally the entire universe has no life, and only the dark space remains, which is the ultimate fate of the universe, and it is also the state of cosmic heat and death that scientists speculate according to the theory!
However, the demise of the universe is meaningless to human beings, because human life expectancy is only a hundred years, and it is not what we worry about at the scale of billions and billions of years.