Cosmology: Universe Origins, Composition, and Expansion Observations

What is the definition of Cosmology?

The study of the beginning and the end of the universe.

What are the five fundamental observations of the universe?

1. It gets dark at night. 2. The universe is expanding. 3. Universe expansion is accelerating. 4. Cosmological redshift is an expansion of spacetime, not direct movement of galaxies. 5. Cosmic microwave background radiation exists.

What is Cosmic Microwave Background Radiation?

Leftover radiation from the Big Bang theory.

What is Olbers's Paradox?

A question proposed in 1826: If the universe is infinite in size, infinite in age, and static, why does it get dark at night?

How is Olbers's Paradox resolved?

The assumptions that the universe is infinite in age and static are untrue. Some stars are too far away for their light to have reached us yet, and the universe had a beginning (the Big Bang).

Define Isotropy in a cosmological context.

The universe looks about the same in every direction on a large scale.

Define Homogeneity in a cosmological context.

Matter is uniformly spread throughout space on a large scale.

What is the Cosmological Principle?

The idea that any observer in any galaxy sees the same general properties for the universe.

What is the difference between the 'Universe' and the 'Observable Universe' regarding size?

The universe is infinite (no edge, no center), but the observable universe is finite.

Define Universality.

The physical laws we know on Earth apply everywhere in the universe.

What is Normal Matter and what percentage of the universe does it comprise?

Matter made of baryons (protons and neutrons); it makes up approximately 5% of the known universe.

What is Dark Matter and its estimated abundance?

Matter that emits no light, making up about 27% of the universe.

Define MACHOs and WIMPs.

MACHOs: MAssive Compact Halo Objects (e.g., black holes, neutron stars); at most 20% of dark matter. WIMPs: Weakly Interacting Massive Particles; non-baryonic, theoretical matter (e.g., neutrinos).

What is Dark Energy and its estimated abundance?

The energy that drives the observed acceleration of the universe's expansion; it makes up about 68% of the universe.