EXPANSION OF UNIVERSE

• The universe is constantly expanding, a concept that has baffled astronomers and scientists for decades.
• Recently, researchers discovered that the universe is expanding at a rate of 68.5 (±0.6) km/second/megaparsec.
• Scientists have created the largest 3D cosmic map ever.
• DESI (Dark Energy Spectroscopic Instrument), located in the USA, helps measure the effect of dark energy on the expansion of the universe.

Major theories related to the expansion of the universe

Big Bang Theory

• Scientists believe that the universe originated from an extremely hot and dense singularity 13.8 billion years ago.
• The universe has been continuously expanding since the Big Bang.
• This theory has been proved by the cosmic microwave background (CMB) radiation.
• CMB: This is the oldest light in the universe, which tells us that the universe was once very hot and dense.

Lambda CDM Model (ΛCDM Model)

• This model states that matter and dark energy in the universe together control its expansion.
• Dark matter and normal matter slow down the expansion of the universe.
• Dark energy accelerates the expansion of the universe.

What are dark matter and dark energy?

• Dark matter: It is a mysterious substance that holds galaxies together with the effect of gravity.
• Dark energy: It is a mysterious force that speeds up the expansion of the universe.

Hubble's constant and cosmic expansion

What is the Hubble constant?

• In 1929, Edwin Hubble discovered that the universe is constantly expanding.
• He discovered a relationship between the speed and distance of galaxies, now called Hubble’s Law:

• v = the speed of the galaxy moving away
• H₀ = the Hubble constant
• d = the distance of the galaxy

How is the Hubble constant calculated?

• Scientists use two main methods to calculate the Hubble constant:

Studying the Cosmic Microwave Background (CMB):

• The expansion rate is measured by analyzing the initial radiation produced in the early period of the universe.

Using the Cosmic Distance Ladder:

• The Hubble constant is calculated by measuring the distance and redshift of nearby and distant galaxies.

Redshift and Blueshift:

• When a galaxy is moving away from us, its light is stretched into the redshift.
• When a galaxy is coming towards us, its light shifts to blueshift.

What is Hubble Tension?

• Two different ways of measuring the rate of expansion of the universe are giving different results.
• This difference is called Hubble tension, which remains a mystery for scientists even today.
• The CMB data shows a rate of 67 km/sec/megaparsec, while the Cosmic Distance Ladder shows a rate of 73 km/sec/megaparsec.

Composition of the Universe

• Dark Energy – 68%
  • It makes up 68% of the universe.
  • It accelerates the expansion of the universe by acting opposite to gravity.
• Dark Matter – 27%
  • It is a mysterious form of matter that cannot be seen directly.
  • It holds galaxies together due to gravitational effect.
• Visible Matter – 5%
  • It is only 5% of the universe.
  • It includes stars, planets, galaxies and ourselves.

Future of the Universe

• Scientists believe in three possible scenarios:

Big Crunch:

• If dark energy weakens, the expansion of the universe may slow down and start shrinking again.
• Finally, it may return to its initial state.

Big Rip:

• If dark energy becomes too powerful, it can rip apart all galaxies, stars, and even atoms.

Big Freeze:

• If the expansion continues indefinitely, the energy level in the universe will drop so low that no new stars or galaxies will form and the universe will slowly become cold and dark.