Verified Answer :

  • The universe consists of dark energy, dark matter, and baryonic (ordinary) matter.
  • According to the standard Lambda-CDM model, baryonic matter accounts for roughly \(5\%\) of the total mass-energy density.
  • Comparing this to the given options, \(5\%\) is the correct percentage.
  • The correct choice is \(\boxed{a}\).

Explanation

  1. Analyze the composition of the universe

The universe's composition is a central topic in modern cosmology. According to the standard Lambda-CDM (ΛCDM) model, which describes the evolution of the universe from the Big Bang to the present, the contents of the universe are classified into three primary categories: dark energy, dark matter, and baryonic (ordinary/observable) matter.

  • Dark Energy: This is a mysterious form of energy that permeates all of space and accelerates the expansion of the universe. It constitutes approximately 68-70% of the total energy density.
  • Dark Matter: This is a hypothetical form of matter that does not interact with electromagnetic radiation (light), but its presence is inferred from gravitational effects on visible matter. It makes up about 25-27% of the total energy density.
  • Baryonic Matter: This is the ordinary matter that makes up stars, planets, gas, and us. It comprises atoms and subatomic particles. Current cosmological observations indicate that this makes up only about 4-5% of the total energy density of the universe.
  1. Select the correct percentage from the options

Comparing the established cosmological estimate of baryonic matter (approximately 5%) with the provided options:

A5%
B10%
C50%
D95%

It is clear that 5% is the most accurate value based on scientific consensus. Options b, c, and d are far too high, as they would contradict our current understanding of dark matter and dark energy dominance in the universe. Therefore, the correct choice is (a).

Examples

In an astronomy class, students often discuss the "composition of the universe" to understand that the world we can see—stars, planets, and galaxies—is just a tiny fraction of what actually exists. By learning that baryonic matter is only \(\approx 5\%\), students gain a deeper appreciation for the role of invisible components like dark matter and dark energy in shaping our cosmic history. This understanding helps them analyze light curves and gravitational lensing data, as they must account for the overwhelming majority of non-visible mass.

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