the big bang theory: origin & evolution of the universe

The Big Bang Theory:

Origin & Evolution of the Universe

Newton’s Static Universe

• Universe is static and composed of an infinite number of stars that are scattered randomly throughout an infinite space.

• Universe is infinitely old and will exist forever without any major changes.

• Time and Space are steady and independent of one another and any objects in existence within them.

Newton’s Error

If universe is as how Newton describes, then why is the sky dark at night?

Olber’s Paradox

• If space goes on forever with stars scattered randomly throughout, then in any line of sight in any direction will eventually run into a star.

• Using this logic, the sky should be the average brightness of all of these stars.

But isn’t the sky dark at night…?

Yes, of course - that is what we observe now and have always observed.

Something is wrong with Newton’s idea of a static, infinite universe.

Einstein’s Relativity

• Einstein overturned part of Newton’s theory with his theories of special and general relativity - time and space were indeed related, as were the objects existing within them.

Special Relativity

Time and Space and their rates are intertwined and depend on the motion of the observer (1905).

General Relativity

Gravity bends the fabric of space time - the matter that occupies the universe influences the overall shape of space and the rate of time (1916).

Implications of Einstein’s Ideas

• Based on the general relativity equations, the structure of universe is either always expanding, always contracting, or always static.

• Einstein theorized that the universe’s expansion is directly balancing gravitational collapse due to the objects existing within the universe, thus yielding a static universe.

• Without this idea of a “cosmological constant”, Einstein could’ve been the first to predict that the universe is not static.

Hubble’s Discovery• The wavelengths of the light

emitted by distant objects is elongated as it travels to earth (doppler effect).

• Hubble noticed that the further away the galaxy, the greater the redshift of its spectral lines.

• Longer the light travels, the more it gets redshifted.

Hubble’s Lawv = H0d

v = recessional velocity of the galaxy

H0 = Hubble constant

D = distance of galaxy to earth

• Galaxies are getting farther apart as time progresses, therefore the universe is expanding.– Not only is it expanding… it’s accelerating!

• The age of the universe can be derived from Hubble’s constant:For example, if H0 = 73 km/s*Mpc, then

T0 ~ 13.7 ± 0.2 byo

Origin of the Universe• The universe began about 13.77 billion years ago.

• The Big Bang Theory states that, in the beginning, the universe was all in one place.

• All of its matter and energy were squished into an infinitely small point, a singularity.

• Then…. it exploded.

Cosmic Background Radiation

• Leftover thermal radiation from the Big Bang.

• Uniform; from all directions.• Weak microwaves that are

very close in energy to predictions made by the Big Bang Theory.

Origin of our Solar System

The tremendous amount of material blown out by the explosion eventually formed the stars and galaxies

After about 10 billion years, our solar system began to form

We have now discovered many planets orbiting other stars

The processes that created our solar system have also created an uncountable number of other solar systems

Other Solar Systems

In cosmogony, the Nebular Hypothesis is the currently accepted argument about how a Solar System can form

The Nebular Hypothesis

A large gas cloud (nebula) begins to condense

Most of the mass is in the center

The Nebular Hypothesis

Small chunks grow and collide, eventually becoming large aggregates of gas and solid chunks

The Nebular Hypothesis

Gravitational attraction causes the mass of gas and dust to slowly contract and it begins to rotate

The dust and matter slowly falls towards the center

The Nebular Hypothesis

Pictures from the Hubble Space Telescope show newborn stars emerging from dense, compact pockets of interstellar gas called evaporating gaseous globules

The Nebular Hypothesis

Protostar

After sufficient mass and density was achieved in the Sun, the temperature rose to one million °C, resulting in thermonuclear fusion.

H atom + H atom = He atom + energy

The Sun

Birth of the Solar System

Gravitational forces allow the inner planets to accrue and compact solid matter (including light and heavy atoms)

Solar radiation blew gases (primarily hydrogen, helium) away from inner planets

These gases were collected and condensed into the gas giants (Jupiter, Saturn, Uranus, Neptune)

Beyond Neptune, ice and frozen gases form Pluto, Sedna and the Kuiper Belt Objects

Left-over debris form comets and asteroids

Protoplanets

Earth is ~ 4,570,000,000 years old

The Age of the Earth

Meteorites give us access to debris left over from the formation of the solar systemWe can date meteorites using radioactive isotopes and their decay products

Finally Resulting In….

Possible Fates of the Universe

Open Universe: It Expands Forever

• The universe will continue to expand. All stars will die as the last of their energy is released. Eventually, all matter will be reduced to single atoms moving away from each other. There will be nothing left.

Closed Universe: Collapse

• Gravitational attraction between objects will cause the expansion of the universe to slow and, eventually, come to a halt. Gravity will then begin to pull everything back to the center of the universe.

Closed Universe: Déjà vu

• Eventually, all matter and energy will again condense into a single point, possibly no larger than a dime. Another Big Bang will occur and the formation of the universe will begin all over again.

In any case . . .• Whatever happens to the

universe, we are pretty lucky here on earth.

• We have the two main requirements for life:– Liquid water– Protection from UV radiation

• Perhaps elsewhere in the universe, other planets or moons do, too

Research Today• Today, particle accelerators such as the

Large Hadron Collider are trying to replicate conditions just after the Big Bang so that we understand how the universe formed.

• Currently, all cosmic evolution after inflationary epoch can be modeled and described pretty accurately, but the time before this (10-15 sec) is basically unknown; understanding this time remains one of the greatest mysteries in physics.

Remaining Questions• What is dark matter?• What is dark energy?• Can dark energy and matter be detected and

studied in labs?• What happened from the birth of the

universe, at the instance of the Big Bang, until the end of the inflationary epoch?

• What is the ultimate fate of the universe?• What caused the Big Bang?