FORMATION OF THE UNIVERSE

THE BIG BANG THEORY To understand how the universe was formed, scientists study the movement of the galaxies. Careful measurements have shown that most galaxies are moving away from each other.

Having discovered that the universe is expanding, scientists have worked backward to see how it was formed. This research showed that all matter was squeezed into a small space.

The BIG BANG Theory This theory says that the universe began about 13.6 billion years ago from an infinitely dense, single point all matter and energy in the universe was compressed in this point!

A Tremendous Explosion Then the universe rapidly expanded and cooled.

Expansion of Spacetime

Within the first 3 minutes of this ”big bang,” the initial elements, forces of nature, like gravity, and seeds of galaxy formation were determined.

Primary Evidence for BB We have detected the leftover radiation from the Big Bang. The Big Bang theory correctly predicts the abundance of helium and other light elements. The night sky is dark.

Evidence: Cosmic Background Radiation The energy from the original explosion, called the cosmic background radiation was distributed in every direction as the universe expanded.

Evidence: Abundance of Hydrogen and Helium Big Bang theory prediction: 75% H, 25% He (by mass) observations of nearly primordial gases matches it.

Evidence: Dark Nights Olbers’ Paradox If universe were 1) infinite 2) unchanging 3) everywhere the same Then, stars would cover the night sky and the night would be like the day! Evidence: Dark Nights

Night sky is dark because the universe changes with time As we look out in space, we can look back to a time when there were no stars

Evidence for Big Bang

Will the universe expand forever? Will the universe end? Are there other universes?

Possibilities for the Future of the Universe Flat: The expansion of the universe will slow down and stop Closed: The universe will begin to contract Open: The universe will continue to expand forever Possible future depends on dark matter & dark energy

Dark matter and dark energy Dark Matter: An undetected form of mass that emits little or no light but we can see its gravitational influence on objects Dark Energy: An unknown form of energy that seems to be the source of a repulsive force causing the expansion of the universe to accelerate

Dark Energy/Dark Matter Dark matter accounts for a large proportion of the mass of the universe Astronomers estimate the amount of dark energy based on rate of expansion

What is dark matter?

Dark Matter Fred Zwicky – 1930’s, studied galaxy clusters Obtained spectra and found they were spinning too fast Vera Rubin – 1960’s, studied spiral galaxies and got the same results

Evidence for dark matter Spiral galaxies tend to have flat rotation curves; indicates large amounts of dark matter

Evidence for dark matter Gravitational Microlensing Distribution of x-ray emitting clouds in galaxy clusters Galaxy clusters, the largest objects in the Universe, held together by their own gravity, are made up of three main components: stars, clouds of hot gas, and dark matter. When galaxy clusters collide, the clouds of gas enveloping the galaxies crash into each other and slow down or stop. The stars are much less affected by the drag from the gas and, because they occupy much less space, they glide past each other like ships passing in the night. Because the clouds of gas are very hot - millions of degrees - they glow brightly in X-ray light (pink). When combined with visible-light images from Hubble, the team was able to map the post-collision distribution of stars and also of the dark matter (blue). Astronomers can map the distribution of dark matter by analyzing how the light from distant sources beyond the cluster is magnified and distorted by gravitational effects (known as "gravitational lensing.") Map of dark matter (light blue), digitally superposed on a photograph made by HST, shows that a giant ring of invisible mass surrounds the dense core of a giant cluster of galaxies called ZwC10024+1652

What could dark matter be made of? Ordinary Dark Matter (MACHOS) Massive Compact Halo Objects: dead or failed stars in halos of galaxies Extraordinary Dark Matter (WIMPS) Weakly Interacting Massive Particles: mysterious neutrino-like particles

What do we know about dark energy? Estimated amount based on HST images of distant supernovae Universal expansion speed has changed It may be a property of space It may be a new kind of energy Maybe Einstein’s theory of gravity is wrong One explanation is dark energy is a property of space. Einstein was first person to realize that empty space is not nothing, it’s possible for more space to come into existence. Also, "empty space" can possess its own energy. Because this energy is a property of space itself, it would not be diluted as space expands Another explanation comes from the quantum theory of matter. In this theory, "empty space" is actually full of temporary ("virtual") particles that continually form and then disappear. But when physicists tried to calculate how much energy this would give empty space, the answer came out wrong - wrong by a lot. The number came out 10120 times too big. Another explanation is that it’s a new kind of dynamical energy fluid or field, something that fills all of space but something whose effect on the expansion of the Universe is the opposite of that of matter and normal energy. A last possibility is that Einstein's theory of gravity is not correct

Brightness of distant white-dwarf supernovae tells us how much the universe has expanded since they exploded

Accelerating universe is best fit to supernova data The most distant supernovae appear to be fainter, and hence further away than expected. This suggests a speeding up of the expansion rate. The only way cosmologists can get General Relativity to have an increasing expansion rate is to introduce the cosmological constant back into the formulation. What this actually means is unclear--there is something called "vacuum energy" which appears to push space apart. In fact, since energy and mass are equivalent to the same thing (E = mc2), in the "flatness = 1.0" formulation, this vacuum energy must account for >70% of EVERYTHING! Accelerating universe is best fit to supernova data

What are the largest structures in the universe? Maps of galaxy positions reveal extremely large structures: superclusters and voids

Structures in galaxy maps look very similar to the ones found in models in which dark matter is WIMPs