As an expert in the field of astrophysics, I can tell you that the composition of the universe is a fascinating and complex topic. The universe is made up of various forms of matter and energy, and understanding what constitutes the majority of it is crucial to our understanding of cosmology and the evolution of the cosmos.

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The universe is an incredibly vast and complex system, and its composition has been a subject of intense study and debate among scientists for many years. While it was once thought that the universe was primarily composed of what astronomers refer to as "baryonic matter" - which includes all material made up of protons, neutrons, and electrons - it is now understood that this is only a small fraction of the universe's total mass-energy content.

The discovery that baryonic matter is not the dominant component of the universe came through a series of observations and measurements. One of the most significant was the realization that galaxies and galaxy clusters are held together by a much greater mass than can be accounted for by visible stars, planets, and other baryonic matter. This led to the concept of dark matter, a form of matter that does not interact with electromagnetic radiation and thus is not directly observable through telescopes. Dark matter is believed to make up approximately 85% of the matter in the universe.

In addition to dark matter, the universe also contains a significant amount of dark energy. Dark energy is a mysterious form of energy that is thought to be responsible for the accelerated expansion of the universe. It is estimated that dark energy constitutes about 68% of the total energy content of the universe.

Baryonic matter, which includes everything from stars and planets to gas and dust, makes up a much smaller portion of the universe, roughly 5%. This is the "ordinary" matter that we are familiar with and that makes up the visible components of the universe.

The remainder of the universe's composition is made up of radiation, which includes the cosmic microwave background (CMB) radiation left over from the Big Bang, as well as other forms of electromagnetic radiation.

Understanding the nature of dark matter and dark energy is one of the greatest challenges in modern physics. These components are crucial to explaining the large-scale structure of the universe and its evolution over time. While we have indirect evidence for their existence through their gravitational effects on visible matter and the expansion rate of the universe, their exact nature and properties remain a mystery.

Scientists continue to study the universe through various means, including ground-based and space-based telescopes, particle accelerators, and other experiments. The hope is that by gaining a deeper understanding of the universe's composition, we can unlock the secrets of its origins, its current state, and its ultimate fate.

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Astronomers like to call all material made up of protons, neutrons and electrons "baryonic matter". Until about thirty years ago, astronomers thought that the universe was composed almost entirely of this "baryonic matter", ordinary atoms.Jan 24, 2014read more >>