Origins of the universe

1. The ‘Big Bang’ theory

• According to this theory our universe began 13.7 billion years ago as a singularity. Prior to this there was nothing.

• At this time the universe had almost infinite density and temperature.

• At a moment, it became unstable and began to expand rapidly. As it expanded, it cooled and continues to expand and cool today.

Singularity

• Inflation occurs. This is an expansion of space, filled with energy. The universe suddenly becomes 100 000 000 000 000 times bigger.

• The inflation stops when this energy is transformed into matter and energy as we know it.

One millionth of a second after the big bang:

• Expansion slows down

• The universe becomes less dense and cools

• Matter and antimatter form, apparently in uneven amounts.

• Matter and antimatter annihilate each other in a burst of light energy as they collide. There is a residue of matter which forms the universe as we know it.

100 seconds

• Temp has cooled to 109 K.

• Quarks combine in threes to form protons and neutrons.

• Protons and neutrons combine into nuclei.

• 75% hydrogen & 25% helium.

• The universe is foggy and opaque.

380 000 years

• Protons and electrons combine to form neutral hydrogen

• Universe becomes transparent as matter draws together into swirling clouds of plasma.

• Temp = 3000 K

100 – 200 million years

• First stars and galaxies form• Heavier elements, carbon, nitrogen, etc

from in the large stars• Stars explode in supernova forming

heavier elements, iron and the heavier metals

• Iron is the most common metal in the universe because of its very stable nucleus

4.6 billion years ago

• The sun forms within a cloud of gas in a spiral arm of the Milky Way Galaxy.

• A vast disc of gas and debris that swirls around this new star gives rise to planets, moons and asteroids.

• Earth is the third planet out

3.8 million years ago

• The earth has cooled and an atmosphere develops.

• Primitive microscopic organisms begin to flourish in the Earth’s many volcanic environments

Now

• Average temp of the universe: 2.725 K

Misconceptions about BBT• It is about the origin of the universe.

BUT: It is not as much about the origin of the universe as it is about the development of the universe over time.

• The “bang” exploded matter into space:

BUT: The origin of the universe was not an explosion of matter into already existing space. Before the Big Bang, there was nothing.

And, in fact:• The Big Bang was not an explosion at

all.

• It is the expansion, or stretching of space from a tiny size to a vast size, so that all things are moving away from each other.

• It is like having an infinite rubber sheet with people sitting on it. Stretch the rubber sheet, and all the people move away from one another. Each thinks they are at the center of an explosion. It is an optical illusion - everybody moves away from everybody else and

there is no center.

• Run the story going back in time, and the sheet was more and more un-stretched and the people were closer together. When everybody is so close they are on top of one another, that is is the beginning of the big bang picture - the cosmic singularity. At that time, the universe has nearly infinite density and temperature.

• The famous cosmologist P. J. E. Peebles stated this succinctly in the January 2001 edition of Scientific American (the whole issue was about cosmology and is worth reading!): "That the universe is expanding and cooling is the essence of the big bang theory. You will notice I have said nothing about an 'explosion' - the big bang theory describes how our universe is evolving, not how it began." (p. 44).

What we know, and the Evidence for this:

• The universe is expanding, at an increasing rate

– Red shift.• We would expect to find remnants of

the radiation emitted during the initial inflation

– Cosmic microwave background radiation.

What we know, and the Evidence for this:

• We would expect to find the lighter elements in higher abundance as a result of the processes of synthesis of atomic nuclei during the Big Bang (nucleosynthesis)

– Hydrogen ± 75% and Helium ± 25%• The evolution and distribution of galaxies

– Detailed observations of the size, shape and distribution of galaxies and quasars is in agreement with

the current state of the BBT

Red shiftHubble’s Law

• Hubble’s law states that; the further away a galaxy is the faster it is moving away from us.

• This is supported by the greater red shift exhibited by the light from these distant galaxies.

• By tracking backwards, we can see that objects in the universe were once much closer together. This leads us to the conclusion that the universe was once so close together that it coincided at a point.

Red shift – Atomic spectra from light emitted by stars show a shift towards the

red end of the spectrum

Normal

Spectrum

Red shift

moving away

Violet shift

Moving towards

Cosmic Background Radiation

1965 two researchers Arno Penzias and Robert Wilson, verified the existence of Cosmic microwave background radiation. These are the ‘stretched out’ electromagnetic waves that were left over from the inflation period right at the beginning, when matter and anti-matter were annihilating each other in bursts of light.

The electromagnetic spectrum

Abundance of primordial lighter elements

• Using the Big Bang model, it is possible to predict, mathematically, the ratios of Helium-4, Helium-3, Deuterium and Lithium-7, in the universe to Hydrogen.

• These ratios are confirmed by measured observations of primordial gas clouds that haven’t yet condensed into stars and therefore formed heavier elements.

The evolution and distribution of galaxies

• The observations of newly formed galaxies, when compared with older galaxies, show that they are markedly different from each other and suggest that they follow a lifecycle.

• These are strong arguments against a steady state model of the universe.

Theories about the future of the universe (see text p.75)

1. Open universe

2. Closed universe

3. Flat universe

4. Accelerating universe

Open Universe

• The universe will continue to expand at a decreasing rate, gradually becoming colder and darker until it ‘runs down’.

The Closed universe theory• A popular theory at one time was the

oscillating universe theory, (oscillating means to move back and forth).

• This theory of birth, death, rebirth, states that the universe would expand to a point then collapse on itself (due to gravity) creating a ‘BIG CRUNCH’ and then explode again in a new big bang event.

• The discovery of background radiation by Penzias and Wilson turned opinion away from this model to the expanding universe model.

Flat universe theory

• This theory proposes that the universe will eventually stop expanding but will not contract in on itself (no big crunch)

• Again, this universe will eventually run down and grow cold and dark

Accelerating universe

• Current evidence supports this theory.

• The red shift observed in light coming from stars (Doppler effect) indicates the universe is expanding at an increasing rate.

• The presence of Dark Energy has been proposed which is driving the accelerated expansion of the universe. Very little is understood about dark energy.

Difficulties in obtaining information about the universe [5.9.1c]

• Huge distances to overcome• Age of universe (estimated at approx13.7

billion years)• Limitations of current technology limit

amount and type of data we can collect• Interference to telescopes from atmospheric

gases and pollutants that distort and refract incoming light from stars.