The Dark Side of the Universe

Scott WatsonDept. of Physics

Brown University

watson@het.brown.edu

http://www.het.brown.edu/people/watson/

Cosmic Conundrums

How will the Universe end?

How old is the Universe?

How did the Universe begin?

What is the Universe made of?

Are we smart enough to

answer these questions?

Cosmic Timeline

Observational CosmologyCosmic Background Radiation (CMB)

Large Scale Structure (LSS)

Supernovae Ia

The Earth is one of nine planets orbiting our Sun. Itis the third closest to the Sun, and so far it is the onlyplace in the universe where we know there is life.

Large Scale Structure

Analyzing large scale structure provides information about the physics of the early universe!

Large Scale Structure

Quantum fluctuations in the early universe result in the large scale structure we see today!

Cosmic Microwave BackgroundQuick Facts:

• Cosmic microwave background (CMB) primordial light. • 3 degrees above absolute zero (-270 degrees celcius) • mm-cm wavelength• 400 photons per cubic centimeter •10 trillion photons per second per squared centimeter • Few percent of TV "snow" • Temperature slightly different on different patches of the sky - 1 part in 100,000.

Cosmic Microwave BackgroundFluctuations in density give rise to cold and hot

spots in the photon fluid

Cosmic Microwave Background

Quantum fluctuations also lead to temperature fluctuations in the CMB

Not Just a Bunch of Pretty Pics

Power spectrum characterizes

and provides a testing of theoretical

models

Power spectrum measures the

strength of the fluctuations verses their

angular size of the sky

Type Ia Supernovae

Type Ia Supernovae are exploding stars

all of which behave in the

same way.

This allows us to deduce their

distance from us and how fast they are moving away

from us.

Type Ia Supernovae

•The Universe is Flat!

• The Universe will live forever!

• The Universe is made of 65% unknown energy!

This is the so-called,

DARK ENERGY!

• The Universe is approximately 15 Billion years old!

Putting it All Together

What is the Dark Energy?

Why has it taken over the expansion today?

More to come…

How are we going to figure this one out?

The Dark Energy must have the following properties,– Non-luminous (DARK)– Relativistic energy-like (ENERGY) due to

large negative pressure p<-1/3– Can only clump on scales beyond horizon– Couples to matter ONLY gravitation– Dominates only recently z ~ few (can not

interfere with LSS, BBN)

Detecting the Dark Energy is a SNAP!

SuperNova Acceleration Probe

SNAP will allow us to “weigh” the Dark Energy and deduce its properties

Keep an Eye on the Dark Energy!