Question

Describe the structure of the Universe, and how we know that it is expanding. Describe the Open and Closed Big Bang theories of the Universe, and the Inflationary model, and the differences between them. Discuss the current version of the Big Bang theory, and its implications for the future of the Universe. Discuss the theory of "dark" matter as it relates to the structure of the Universe.

Answer 1

The universe contains organized structures on all different scales, from small systems like the earth and our solar system, to galaxies that contain trillions of stars, and finally extremely large structures that contain billions of galaxies called clusters and superclusters.

By measuring the velocities of a large sample of galaxies it was found that a large number of galaxies recedes away from us only with a very few exceptions that advances towards us. And in fact, the farther away a galaxy is the faster it is moving away from us. The galaxies seem to be receding from us because the entire universe is getting larger. This indicates that the universe is expanding.

The open big bang theory states that the universe began in a big bang and will continue expanding forever.

The closed big bang theory states that the universe began in a big bang, but gravity will eventually overcome the inertia and contract, ending in a big crunch.

The Inflationary Model states that the universe expanded rapidly and exponentially shortly after the big bang and then slowed down.

The current version of Big Bang is known as the -CDM model. (Lambda) is a constant associated with dark energy and cold dark matter(CDM).

This model gives a good explanation of the following events:

• The existence and structure of the cosmic microwave background.
• Structure in the distribution of Galaxies( groups, cluster, supercluster)
• Abundance of hydrogen, helium and lithium in the universe.
• Accelerationg expansion of the universe.

This model accepts general theory of relativity as the correct theory of gravity on cosmological scales.

The letter represents the cosmological constant, which is currently associated with a vacuum energy or dark energy in empty space that is used to explain the accelerating expansion of the universe against the attractive effects of gravity.

The model includes a single originating event, the "Big Bang", which was not an explosion but the abrupt appearance of expanding space-time containing radiation at temperatures of around 10¹⁵ K. This was immediately followed by an exponential expansion of space by a scale multiplier of 10²⁷ or more, known as cosmic inflation. The early universe remained hot (above 10,000 K) for several hundred thousand years, a state that is detectable as a residual cosmic microwave background, a very low energy radiation emanating from all parts of the sky.

There are two theories of Dark matter: The cold dark matter and the hot dark matter.

According to the cold dark matter theory, structure grows hierarchically, with small objects collapsing under their self-gravity first and merging in a continuous hierarchy to form larger and more massive objects.

The hot dark matter theory is quite the opposite: in the beginning it forms the largest structure ( supercluster for instance) and gradually gets fragmented into smaller pieces( separate galaxies).