The Big Bang

A Timeline

What do you think you know about the Big Bang?

• Take a couple of minutes to write down what you know, or think you know about the big bang.

The Universe and Time

• The Big Bang is a theory that tells a story: the story of our universe.– That story begins with the “beginning of time.”– The Big Bang is not a theory that tries to explain

everything - it does not try to explain what happened “before time.”

– The Big Bang theory is derived from taking what we know about the universe and “running the clock backward.”

Setting Up the Big Bang

• Einstein’s Field Equations– All solutions to Einstein’s equations in which the

universe has the amount of matter we observe, all have one thing in common.• At one point, about 13.7 billion years ago, the distance

between neighboring galaxies (neighboring anything) was zero. • The entire universe was squashed into a single point.

Einstein’s Field Equations• The density of the universe and the curvature of space-

time would have been infinite. • Typically, physicists think of space-time as smooth and

nearly flat. Because the space-time curvature is infinite, according to physicists like Stephen Hawking, all our theories break down at the big bang.• Therefore, it appears we cannot use current equations

(like Einstein’s or Bohr’s – quantum theory) to predict or describe what happened before the big bang. • E=MC2 doesn’t apply here!

At the very beginning . . . Singularity

• Singularity – a point in space-time at which the space-time curvature becomes infinite. – At the very least, for a fraction of a second before

the big bang, there was a singularity.– Besides infinite space-time curvature and density,

the temperature would have been infinitely hot.

In the first fractions of a second

• The big bang was not an explosion (at least not as we think of explosions).– The big bang was the “appearance of space

everywhere in the universe.” • A universe that was growing exponentially.

• At 1/100th of a second – the universe’s temperature was 180 billion degrees F. – It consists of an undifferentiated soup of matter

and radiation (energy) dominates.

In the first fractions of a second

• At 1/10th of a second – the temperature has dropped to about 50 billion degrees (a temperature 1,000 times hotter than the center of our sun) and density is 10 million times that of water. – At this point, the universe would have consisted of

photons, electrons, neutrinos, neutrons, protons and their antiparticles.

– Example of antiparticles – the antiparticle of an electron is a positron.• If an electron and a positron meet, they annihilate each other

(works the same for all other antiparticles).

Hydrogen atom and antihydrogen

The meeting of anything made of particles and antiparticles ends in annihilation of both entities.

“If you ever meet your antiself, don’t shake hands.”

Inflation

• As the universe is being formed, inflation is occurring and the universe is growing at an exponential rate – doubling in size at least 90 times. – During inflation, the universe continued to cool. – The universe continued to grow after inflation but

at a lesser rate.

In the first seconds and minutes

• At 1 second the temperature had fallen to 18 billion degrees F and density had fallen to 400,000 times water.

• At 3 minutes and 45 seconds, the temperature has fallen to 1.8 billion degrees – cool enough that the nuclei of light chemical elements (H, He, Li) are created.

In the first seconds and minutes

• At 35 minutes, the temperature has dropped to 540 million degrees F but the universe is enveloped in a haze due to atoms crashing into one another – breaking apart.– This would continue for 380,000 years before the

temperature dropped enough that atoms would become stable and the haze would disappear.

Let there be light . . .

• At 380,000 years, the haze cleared, matter cooled enough to stabilize atoms, the universe became transparent and “light was unleashed.” – The light that was unleashed at this time is

detectable today in the form of radiation from the cosmic microwave background.

– There was no longer enough high energy radiation to break the atoms apart.

First Stars and Galaxies

• Roughly 400 million years after the Big Bang, clumps of gas collapsed enough to form the very first stars and galaxies. – The first high energy stars cooked up the heavy

elements that the universe needed to form planets and eventually you and me.

• Our Milky Way was born some 8.3 billion years ago.

Our Milky Way was born some 8.3 billion years ago.