The Big Bang

Question 1

Big Bang

Answer 1

Leading theory/explanation for how the universe began; the universe began as a single tiny, unimaginably high temperature and dense singularity that began expanding.

(Initiated the expansion and cooling of space)

Question 2

What does the Big Bang predict?

Answer 2

1. If there was a beginning, we should be able to see galaxies form and evolve.
2. Explain why hydrogen comprises most of the Universe.
3. Evidence of an initial hot state.

Question 3

How can we observe the early universe?

Answer 3

By looking at celestial objects that are far away; redshift indicates how far we’re looking in the past ! (Hubble’s Law)

Greater Distance in Light Years = Greater Redshift = Greater Lookback Time

Question 4

Evolution of Galaxies

Answer 4

The first galaxy was formed 400 million years ago.
Galaxies from the early universe were clumpy as opposed to disk shaped or elliptical.

Question 5

How were the early universe galaxies observed?

Answer 5

Cosmological Redshift (wavelengths of early universe light traveled through space and was stretched by expansion of universe)

Question 6

Nucleosynthesis

Answer 6

Occurred within the first few minutes of the Big Bang; As Universe expanded (and cooled), particles fused to form the first atomic nuclei.

Protons and neutrons fuse —> atomic nuclei of deuterium (hydrogen isotope) —> detrium nuclei fuse —> helium —> lithium —> beryllium

Formed LIGHT ELEMENTS: Hydrogen (73% mass), Helium (25% mass), Deutrium (0.01%) Lithium (<0.01%), Berylium nuclei

Question 7

Recombination

Answer 7

The first time Universe was cool enough for electrons to bind to the nuclei to make atoms.

Question 8

When did Recombination happen?

Answer 8

380,000 years after the Big Bang

Question 9

What was the Universe like before Recombination?

Answer 9

Very hot and opaque

Question 10

Why was Recombination important?

Answer 10

Created the Cosmic Microwave Background !

Recombination occurred —> Thermal radiation from matter —> light travels after Recombination —> Photons remain (very redshifted)

Question 11

Cosmic Microwave Background

Answer 11

Thermal radiation from all over sky and redshifted to the microwave.

Question 12

Who discovered the Cosmic Microwave Background and why is it so important?

Answer 12

In 1964, Penzias and Wilson discovered it !

The Cosmic Microwave Background is like the afterglow of the Big Bang. It proved that the Universe started out very hot.

Question 13

Ω

Answer 13

The ratio of the density of the Universe to the critical density.

Critical Density - the average density of matter required for the Universe to halt its expansion after an infinite time.

Question 14

What does future of Universe depend on?

Answer 14

Mass ! (& Ω)

Question 15

How does Ω relate to geometry of Universe?

Answer 15

1. If Universe has too much mass (Ω > 1) Expansion stops and reverses, curving back on itself and creating a sphere shape.
2. If Universe has too little mass, (Ω < 1), Expansion quickly makes cold, desolate universe, warps (hyperbolic curvature)
3. If the mass is “just right” (Ω = 1), expansion asymptotically slows to zero, flat geometry.

Question 16

What geometry is the Universe currently?

Answer 16

Leading towards flat; however, the current Ω matter of universe is less than one.

Luminous matter: Ω = 0.02
Dark Matter: Ω = 0.5

Question 17

How does Hubble relate to “flat” geometry of present Universe?

Answer 17

Expansion rate should change due to gravity. Comparing past and present Hubble Constant.

Question 18

Importance of White Dwarf Supernovae

Answer 18

Adds more distance to Hubble Plot as a Standard Candle; Brightest explosion in the Universe.

Question 19

What is happening to the Hubble Constant overtime? What does this mean?

Answer 19

It is increasing . . . Universe is expanding faster. This means that Dark Energy exists.

On the Hubble Plot, the graph should bend down since a larger distance means being more in the past.