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Definition of the universe

The universe is defined as everything that space contains, and it includes living organisms, the Earth, the moon, other planets, and their satellites, in addition to asteroids, comets, the sun, huge numbers of stars, estimated to number hundreds of billions, and galaxies.

The universe also includes all things that scientists have not been able to observe or access.

Definition of the universe


The emergence of the universe passed through many stages, and the following is a detail for each of them:

The first expansion of the universe and the movement of elementary particles

Almost all of the observable matter and energy about 15 billion years ago was concentrated together in a very small area, and then this matter and energy started expanding and expanding at a tremendous speed.

As the temperature of the universe cooled to 100 million times the sun's core, the forces of nature took on the properties they currently possess and the elementary particles (which make up matter known as quarks) began to roam freely in this void, and when the universe expanded 1,000 times, they formed part of the solar system.

Formation of atomic nuclei

The free quarks were only neutrons and protons, and after an additional 1,000 years of evolution of the universe, neutrons and protons came together to form atomic nuclei, including; Helium and deuterium are now known.

The emergence of neutral atoms and stars

The universe was still too hot for atomic nuclei to get electrons, and after 300,000 years of continuous expansion, the universe was still 1,000 times smaller than it is now.

Neutral atoms appeared, then fused together to form gas clouds, which later evolved into stars, and when the universe expanded to a fifth of what it is now, the stars became divided into groups known as small galaxies.

Formation of the solar system

When the universe expanded to become half its size now, the nuclear reactions taking place in stars resulted in most of the heavy elements that make up the planets, and when the size of the universe became two-thirds of its current size, approximately five billion years ago, the solar system and its components were formed.

Over time, star formation used up galaxies' supplies of gas; So their number is dwindling, which means that fifteen billion from now, stars will become relatively rare.

Age of the universe

According to studies, the age of the universe is about 13.8 billion years, and scientists were able to determine this after measuring the rate of expansion of the universe and the ages of the most ancient stars, and they measured the expansion by observing the Doppler effect (in English: Doppler Shift), which expresses the change of light emitted by galaxies with its movement.

The beginning of life in the universe

Here are some theories that explain how life began in the universe:

Primal soup theory

The primordial soup theory is the first theory adopted by scientists to explain the beginning of life in the universe, and it indicates that the Earth, while still young, had its oceans rich in simple chemicals necessary for life, which eventually gathered together to form living cells. simple.

This theory was proposed in the twenties of the last century by two researchers working separately from each other, namely: Alexander Oparin, a British geneticist in the Soviet Union, and was supported by the Miller-Urey experiment carried out by an American graduate student named Stanley Miller, under the supervision of Harold Urey Nobel Laureate.

That experiment was in 1953 AD, during which amino acids (the main component of proteins) were produced from chemicals. Miller put four simple chemicals in glass tubes, then heated them and subjected them to electric sparks simulating lightning, and this experiment resulted in a lot of amino acids, That experiment showed that chemicals can form naturally.

Protein hypothesis

The hypothesis of proteins, according to biochemist Sydney Fox, which spoke about after the aforementioned Miller-Urey experiment, refers to the assembly of amino acids into simple proteins, and these proteins found in modern living organisms perform a large number of functions, including working as enzymes to speed up reactions chemical; However, this hypothesis quickly dissipated.


The time of the origin of life in the universe is still a question for scientists; It is known for certain that the Earth was formed 4.5 billion years ago, and the oldest confirmed fossils were 3.4 billion years ago. A group of paleontologists tried to determine the oldest traces of life, but their results were different.

Theory RNA

One theory is that life in the universe began with the advent of RNA.

RNA can carry genes and copy itself just as DNA does, but it can also act as an enzyme like proteins do.

This theory suggests that the organisms that arose first were those that depended on RNA, and later evolved both DNA and protein, but later, too, scientists found that RNA could only really do its job when It binds to proteins, and for life to begin, both must be present.

Bubble theory

One theory states that the first organisms were simple bubbles, and their cells shared one basic characteristic with the cells of modern advanced organisms, which is that both worked to carry all the other components or elements of life to the organism.

Primary Metabolism Theory

Metabolism-first theory indicates that life was formed and started as a result of a set of chemical reactions, which in turn extracted energy from the environment, and then consumed this resulting energy to build the elements and components of life.

At the end of the eighties, the German chemist Günter Wächtershäuser supported this theory, but this idea has now been replaced, as a result of the proposal made by Michael Russell, according to which the first life was a result of currents of electrically charged protons present Inside holes in the sea floor.

Components of the universe

Scientists believe that the universe consists of three types of matter:

  • natural material

Natural matter consists of the atoms that make up the planets, stars, humans and all visible objects in the universe, and it is almost certain that natural matter makes up the smallest proportion of the universe, between 1% and 10%.

  • dark matter

In the form of the currently known universe, 70% of it is believed to be dark energy, 25% dark matter, and 5% natural matter.

  • dark energy

Astronomers believe that humanity lives in a low-density universe in which a mysterious substance (dark energy) represents 70% of its content and that it dominates everything.

Scientists now believe that the dark energy that dominates the universe as previously mentioned does not exist, according to new information provided by the X-ray Observatory of the European Space Agency (XMM-Newton), which found clear differences between the shapes and numbers of current galaxies and those in the universe seven years ago. Approximately thousands of million years ago, the presence of so much matter in the universe does not allow for the existence of dark energy.

The shape of the universe

According to the general theory of relativity; The universe must take the form of one of the following three shapes: closed like a ball, flat like a leaf, or open like a saddle, and the universe holds the flat shape (three-dimensional) if the density of the universe is very low, and at the same time if the universe is expanding in every direction without any curvature.

But if the density of the universe is large to the extent that its gravity overcomes the force of expansion, then the universe will have the shape of a ball, which is known as the closed model, but if its density is low and it is not able to stop the expansion, this means that the universe will wrap In the opposite direction, to give an open shape with some bend, resembling a saddle.

In light of this difference, it was agreed that the universe bears the shape of a sphere; This is according to the paper published by Alessandro Melchiorri at the end of 2019, which indicated that measurements of the cosmic microwave background (CMB), which is the radiation after the Big Bang, indicate a closed universe.

The size of the universe

Because of the ever-expanding space, scientists have found that the radius of the visible universe (the observable universe that we can see) is currently 46.5 billion light-years.

As for the invisible universe, scientists do not know anything about it, and its size is impossible to answer, according to astrophysicist Sarah Gallagher at Western University in Ontario, Canada. However, one study indicated the possibility that the actual universe is 250 times larger than 46.5 billion light-years at the time. the least.

The expansion of the universe

Using NASA's Hubble Space Telescope, astronomers have concluded that the universe is getting bigger every second and that the space between galaxies is expanding. Scientists calculate how fast the universe is expanding over time using a value called the Hubble constant. The current estimate for this constant is 74 km/s per megaparsec; The parsec is the unit of measurement of the distance between celestial bodies.


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