In fact, more than one research group found that the expansion of the universe is accelerating, because in the late 1980s and early 1990s, the "Supernova Cosmology Project" led by Perlmutter was launched in 1989. The "high redshift supernova detection group" led by Schmidt, Rees and Filipenco also started in the following 1994, aiming at the standard candlelight type Ia supernova in the universe, but this is very difficult, because there are fewer type Ia supernovae and it is required to be as far as possible (the expansion and redshift of the universe will be more obvious on a large scale).
Many things happen and both teams have found enough target celestial bodies. Through statistics and research, they respectively came to the conclusion that the luminosity of type Ia supernovae as standard candlelight looks darker (redshift is more serious) than the expansion at the "standard speed" of the universe, and if calculated by distance, it is about 10%- 15%.
According to this research, the two teams shared the 20 1 1 year Nobel Prize in Physics.
What is redshift?
Here is a brief introduction to some cosmological terms, which are different from the familiar horn approaching and leaving in daily life. When the light source approaches and leaves, it will have a similar effect, which is called Doppler frequency shift!
When the light source approaches, the frequency is compressed, and the light you see will move in the blue-purple direction, which is called blue shift. If the light source is far away, the frequency of light will be compressed, and the seen light will move in the direction of red light, which is called red shift. The speed of a distant celestial body will vary according to the distance, so the redshift value of a celestial body will indicate how far it is from the earth.
What star is Type Ia supernova?
This supernova is a kind of supernova formed under special conditions. Generally, one of the two stars first evolved into a carbon-oxygen white dwarf. Due to the lack of temperature, the inner core of a star collapses into a carbon-oxygen white dwarf without hot pressing, and when the other of the two stars evolves into a red giant, its inflated gas shell will fall into the Roche leaf of the white dwarf and be swallowed up. With the increase of phagocytic substances, the pressure in the core increases, and the increase of temperature will trigger carbon fusion. Unlike the self-regulating hot pressing of the star core, this degenerate matter fusion is not controlled by the mass of white dwarfs. In the end, this uncontrolled nuclear fusion reaction will completely blow up the whole white dwarf without leaving any celestial bodies in the center.
The mass of type Ia supernova explosion is relatively stable, and the core is out of control when it collapses beyond Chandraseka limit. The luminosity of this supernova explosion is very stable, so astronomers often use it as a "standard candlelight" reference to measure the distance between galaxies.
Another type Ia supernova is the merger of two white dwarfs (there is also a special type IaX, which interested friends can search for).
The relationship between cosmic expansion and type Ia supernovae
Above we explained the reason of redshift, the universe is expanding. According to the latest measurement, the Hubble constant is 67.15km/s/million parsec. According to this result, the scale of galaxy redshift has a range. The research of the above two teams shows that the universe is expanding at a speed beyond our estimation, which is the reason for the accelerated expansion of the universe.
1, the critical density of the universe
Since the BIGBANG model was gradually accepted, the determination of the expansion speed of the universe and the future outcome of the universe have been very interesting topics. The expanding universe has a major constraint, because the space-time with curved mass will eventually bring together the celestial bodies in the whole universe, but there is a metric, which is based on Friedman-Lemaistre-Robertson-Volcker metric and general relativity.
The Friedman-Lemaistre-Robertson-Walker metric is based on the principle of cosmology. There are only three shapes of the universe that meet the requirements of uniformity and isotropy, but the name is too long to pronounce, and it is generally called Robertson-Walker metric.
Of course, there is also a premise, that is, the value of K. The Planck satellite launched in 2009, through the comprehensive observation of cosmic microwave background radiation, gravitational lens and baryon acoustic oscillation, found that the flatness of the universe is 0.00 1.006, that is, the universe is still flat with an accuracy of 6‰. Then based on this standard, the formula for calculating the critical density of the universe is derived:
When H = 70km/s/ million parsec, the critical density of the universe is 3.6× 10-30g/cm 3, and the current expansion rate of the universe is 67. 15km/s, which are very close.
2. Dark energy
It seems that our universe is going to maintain such a critical state, but the expansion of the universe observed from the type Ia supernova explosion in 1998 seems to be exceeding the expansion speed of the universe we observed before, and it is higher than 10- 15%. According to the observed type Ia supernova, the expansion of the universe began to accelerate in 9.8 billion years, and this expansion began to accelerate about 4 billion years ago.
Astronomers are masters of larceny. They immediately revised the model of the expansion of the universe and introduced the concept of dark energy to explain why the expansion of the universe will accelerate. WMAP and subsequent Planck satellites calculated the most accurate proportion of matter in the universe through observation, which is the second surprising data. In the universe, there are only 4.9% matter, 26.8% dark matter and 68.3% dark energy. According to this ratio, the future expansion model will end in the infinite expansion of the universe.
Dark energy: This is a concept put forward by American theoretical cosmologist michael turner in 1998 due to the accelerated expansion of the universe. Astronomers believe that dark energy is some kind of energy that directly acts on the space-time structure, which, contrary to gravity, causes the space-time structure to expand. Please note that dark energy is still only a calculated value.
Under the guidance of dark energy, the future of the universe is a predictable result, infinitely expanding until it is in a state of thermal silence, although cosmological models put forward several endings of the future of the universe.
However, from the observation of modern astronomy, all the evidence points to the infinite expansion of the universe, and we can easily understand what this thermal silence means. Due to the infinite expansion of space, the density of the future universe will reach below the critical density, and the gravity of matter will no longer make the universe stable or collapse again, and eventually the nebula will dissipate. After the red dwarf goes out, no new stars will be born, and the universe will fall into darkness, but this is only the beginning of thermal silence.
A voice of doubt
From June, 2065438 to June, 2005, three experts in related fields published an article in Science Report, and analyzed 740 samples of type Ia supernovae provided by JLA (several times higher than those used by two earlier groups). They believe that the certainty of the accelerated expansion of the universe is less than 3σ (σ is lowercase, which is used to represent the statistical standard deviation), while the commonly used standard in particle physics is 5σ.
As a bystander, are you relieved? But please don't be happy too early, because the good play of instant reversal is yet to come!
Instantaneous inversion: supporting sound
The voices of the three skeptics are still in our ears. In the same year 10, Hayden of Lawrence Berkeley National Laboratory and Rubin of Florida State University and Lawrence Berkeley National Laboratory published a paper on arxiv, expressing their support for the research work of two groups from 65438 to 0998. They also made a rigorous analysis of the Ia supernova samples provided by JLA, and were convinced that the universe did show signs of accelerating expansion at this scale.
The final conclusion of the Nobel Prize
20 1 1, leading two groups of leaders who reached their own conclusions to win the 20 1 1 Nobel Prize in physics, and sharing the prize according to their respective contributions to the team.
Perhaps everyone knows that Einstein never won the Nobel Prize in physics for his theory of relativity. It's not just that the selection committee can't understand his theory like those antiques, but it's difficult to verify his theory. The Nobel Prize is particularly cautious in this respect. This time, two groups won the prize, basically because the scientific community supported the idea of accelerated expansion in the theory of cosmic expansion.
The goal of accelerating the expansion of the universe is directed at the thermal silence, also known as the big tear, but you don't have to worry too much, because this distance is still early, and the expansion of the universe is not obvious on the scale of local galaxy groups. In this range, gravity dominates, because dark energy needs to take over the rod dominated by gravity on a large scale.