The Early Universe as seen by the Cosmic Microwave Background Eiichiro Komatsu University of Texas at Austin TAMEST Meeting, January 4, 2007

Our Universe Is Old The latest determination of the age of our Universe is: 13.730.16 billion years How was it determined? In essence, (time) = (distance)/c was used. “Distance” to what?? It must be a distance to the farthest place we could reach. The Rule: “Farthest Place” = “Earliest Epoch” For the errorbar to make sense, obviously it must be earlier than 160 million years after the Big Bang. So, what is the earliest epoch that we can see directly?

The Most Distant Galaxy?

Going Farther…

How far have we reached? Our Universe is 13 billion 730 million years old. The most distant galaxy currently known is seen at 800 million years after the Big Bang. 1/17 of the age of the Universe today

How far can we reach? Galaxies cannot be used to determine the age of the Universe accurately. Distant galaxies are very faint and difficult to find. Fundamental “flaw” in this method: galaxies cannot be as old as the Universe itself --- after all, it takes some time (~hundreds of millions of years) to form galaxies. So, is 800 million years after the Big Bang the farthest place we can ever reach? NO!

Night Sky in Optical (~0.5nm)

Night Sky in Microwave (~1mm)

Penzias & Wilson, 1965 Full Sky Microwave Map Uniform, “Fossil” Light from the Big Bang Isotropic (2.7 K everywhere) Unpolarized Galactic Anti-center Galactic Center

A. Penzias & R. Wilson, 1965

Helium Superfluidity T = 2.17 K CMB T = 2.73 K

COBE/DMR, 1992 Isotropic? CMB is anisotropic! (at the 1/100,000 level)

COBE to WMAP COBE 1989 COBE Press Release from the Nobel Foundation [COBE’s] measurements also marked the inception of cosmology as a precise science. It was not long before it was followed up, for instance by the WMAP satellite, which yielded even clearer images of the background radiation. WMAP WMAP 2001

CMB: The Most Distant Light CMB was emitted when the Universe was only 380,000 years old. WMAP has measured the distance to this epoch. From (time)=(distance)/c we obtained 13.73  0.16 billion years.

Use Ripples in CMB to Measure Composition of the Universe The Basic Idea: Hit it and listen to the sound. Analogy: Brass and iron can be discriminated by hitting them and listening to the sound created by them. We can use sound waves to determine composition When CMB was emitted the Universe was a dense and hot soup of photons, electrons, protons, Helium nuclei, and dark matter particles. Ripples in CMB propagate in the cosmic soup: the pattern of the ripples, the cosmic sound wave, can be used to determine composition of the Universe!

Composition of Our Universe Determined by WMAP Mysterious “Dark Energy” occupies 75.93.4% of the total energy of the Universe. 76% 4% 20%

A Big, Big Challenge Let’s face it: “WMAP has done a great job in determining composition of our Universe very accurately, but…” We don’t really understand the nature of dark energy or dark matter. They occupy 96% of the total energy in our Universe! Even the most optimistic cosmologists would not dare to say, “we understand our Universe”. Definitely not. The next frontier: What is the nature of dark energy and dark matter? K. Gebhardt’s presentation

A Holy Grail: Go Even Farther Back… We cannot use CMB to probe the epoch earlier than 380,000 years after the Big Bang directly. Photons were scattered by electrons so frequently that the Universe was literally “foggy” to photons. We would need to stop relying on photons (EM waves). What else? Neutrinos can probe the epoch as early as a second after the Big Bang. Gravity Waves: the ultimate probe of the earliest moment of the Universe.

Go Farther! CMB Neutrino Gravity Wave (M.C.Diaz’s presentation)

Summary & Conclusions CMB offers the earliest and most precise picture of the Universe that we have today. A wealth of cosmological information, e.g. The age of the Universe = 13.73 billion years Composition: DE (76%), DM (20%), Ordinary Mat. (4%) CMB has limitations. It does not tell us much about the nature of the most dominant energy components in the Universe: Dark Energy (DE) and Dark Matter (DM) Expect some news on DM from the Large Hadron Collider (LHC) next year. DE is harder to do. (So we need to fund HETDEX.) Go beyond CMB. Neutrinos! (Very low energy: 1.94K -> hard to detect) Gravity waves! The ultimate cosmological probe.