Frontiers in Cosmology Eiichiro Komatsu (Max-Planck-Institut fr - - PowerPoint PPT Presentation

Frontiers in Cosmology

Eiichiro Komatsu (Max-Planck-Institut für Astrophysik) OIST Seminar, Okinawa Institute for Science and Technology June 13, 2013

• Origin

–How was our universe born? –What was the physical state of our universe at its birth?

• History

–How old is our universe? –How did it evolve over time?

• Composition

–What is our universe made of? –Where do matter and energy come from?

What is Cosmology?

Observational Facts

• Our Universe is expanding!
• Edwin Hubble (1929)
• Our Universe was hot in the past! (Big Bang)
• Arno Penzias and Robert Wilson (1965)
• Cosmic Background Explore (COBE) team (1990)
• Fluctuations in the early universe!
• COBE team (1992)

From “Cosmic Voyage”

Incredible Observational Fact

• The present-day expansion of our universe is

accelerating!

• Supernova Cosmology Project team (1998)
• High-z Supernova Search team (1998)
• Wilkinson Microwave Anisotropy Probe (WMAP) team (2003)

Composition of

• ur Universe

27%

73%

Matter Dark Energy

73% of our Universe is not even matter

Matter and Expansion

• How would an empty universe expand?

–Answer： Constant-velocity expansion (no acceleration or deceleration)

• How would a universe with matter expand?

–Answer：Gravity from matter slows down the expansion (deceleration)

• A universe with too much matter will collapse again

–Going back to a fireball universe! Hot Universe Hot Universe “Big Bang” “Big Crunch”

Accelerating Universe

• How would a universe with matter expand?

–Answer：Gravity from matter slows down the expansion (deceleration)

• This contradicts with observations!

–Matter cannot do it –Some kind of invisible non-material energy:

• Dark Energy

Hot Universe “Big Bang”

Imagine throwing up an apple

Dark Energy Exists

• Dark energy makes the expansion faster
• It was discovered through measurements of

the expansion speed

Standard Candle Method

• You use an object with the known intrinsic luminosity

つか

Standard Candle Method

• This method can be used to infer how fast the

distance between galaxies is growing

Greater Distance

Supernovae are too dim

• Dim = Far = Bigger Universe =

Faster Expansion = Acceleration

Dimmer Brighter Expansion Velocity (km/s)

3000 30000 300000

Acceleration Constant-velocity Deceleration

Huge Discovery in 1998

• Supernovae were dimmer than expected
• Universe’s expansion was faster than

expected (assuming only matter)

• Acceleration!

Huge Problem

• No one knows what caused the expansion to

accelerate

• The only known: matter cannot do it
• Acceleration of the universe is considered as the

biggest issue in astronomy and physics

Working Definition of Dark Energy

• Difference between dark energy and matter lies in the pressure
• Acceleration is possible if pressure of the dominant energy component in

the universe is comparable to its energy density, with a negative sign

• Negative Pressure! How negative?
• W＝[Pressure] / [Energy Density] with W nearly equal to –1
• Current measurement: W = –1.04 ± 0.07 (68% confidence level)

Big Rip

(A Possible) Catastrophic Ending Scenario for Our Universe

Big Rip

• W determines the fate of our universe
• W=–1: Dark energy per unit volume is constant over

time

• W<–1: Dark energy per unit volume increases over
• time. Eventually, dark energy dominates everywhere

(including Okinawa!)

Incredible Observational Fact(?)

• Our Universe was accelerating even before

the Big Bang?

• On-going and ever-improving measurements of the cosmic

microwave background (1992–)

Night Sky in Visible Light（~500nm）

Sky in microwaves（~1mm）

Sky in microwaves（~1mm）

Cosmic Microwave Background “Fossil Light of the Big Bang” T = 2.725 K

Fireball Universe

“Big Bang”

Time

Fireball Universe

Hot

Expansion

Time

“Big Bang”

Fireball Universe

Hot Colder

Expansion

Time

“Big Bang”

Incredible Fact

• Photons from the Big Bang did not go anywhere.

They are still with us!

• 410 photons per cubic centimeter!
• By far the most numerous particles in our

universe

For example, 1% of noise in TV is from the Big Bang

Spectrum of Microwave Background

4K Blackbody 2.725K Blackbody 2K Blackbody Rocket (COBRA) Satellite (COBE/FIRAS) Rotational transition of CN Ground-based Balloon-borne Satellite (COBE/DMR)

Wavelength

3mm 0.3mm 30cm 3m

Sky Brightness

Early Universe = Hot Soup

• Light (lines) is scattered

by electrons (blue)

• Universe was “foggy”

proton helium electron photon

Universe became transparent

• Electrons are captured

by protons when the temperature dropped to 3000 Kelvin

• Neutral hydrogen

atoms do not scatter light as much: photons now travel freely Time 1500K 6000K

3000K

proton helium electron photon

COBE/DMR, 1992

Fluctuations discovered 30 micro Kelvin on top of 2.7 Kelvin. One part in 100,000!

COBE to WMAP

COBE 1989 WMAP 2001

Compared to COBE:

• 35 times better

angular resolution

• 10 times better

sensitivity

WMAP Science Team

• WMAP: Launched in June 2001
• Mission completely ended just now. (Final set of papers have been

accepted for publication)

Some representative scientific results from WMAP

• Age of our Universe is 13.7 billion years
• Composition of our Universe determined:

–Ordinary matter (hydrogen and helium): 4% –Extraordinary matter (dark matter): 23% –The rest (dark energy): 73%

• Peering into the epoch before the Big Bang

–New insights into inflationary universe

Microwave Background: Farthest and Oldest Light We Can Ever See

• These photons were emitted when the universe was 380,000 years old
• WMAP determined the distance to that epoch, from which the age is

determined (remember [distance] = [speed] times [time]?)

“Cosmic Pie Chart”

• Confession:
• After all these years, we have

finally come to admit that we do not understand 95% of our Universe

4%

23%

73%

Composition of Our Universe Hydrogen and Helium Dark Matter Dark Energy

Fourier Analysis of Microwave Maps

• C(θ)=(1/4π)∑(2l+1)ClPl(cosθ)
• “Power Spectrum” Cl

– l ~ 180 degrees / θ

θ

Power Spectrum from COBE/DMR Data Angle ~ 180 degrees / l

Multipole Moment, l

~9 degrees ~90 degrees (Quadrupole)

Power Spectrum from WMAP

Power Spectrum Large Angular Scale Small Angular Scale ~１degree COBE

Sound Wave Propagating in the Universe!

“Photon-baryon* Fluid” Sound Velocity2 = Light Velocity2 / [3(1+R)]; R=3ρb/(4ργ)

*Hydrogen and Helium

Waveform to Parameters

Power Spectrum

Large Scale Small Scale

Hydrogen and Helium 5% 10% 1%

Toward Even Earlier Epoch

• Who dropped stones?
• What created initial fluctuations?
• What is the origin of structures in the

universe (including ourselves)?

Primordial Universe

• Most promising idea: Inflationary Universe
• A. Starobinsky (1980); K. Sato (1981); A. Guth (1981)
• According to this idea:
• Our Universe began to expand exponentially as soon as

it was born: incredibly rapid accelerated expansion

• Inflation of space
• In 10-34 seconds, the atomic size (~10-15m) was stretched

to the size of Solar System (1AU~1011m)

• Leading Idea

–Our Universe was cold before the Big Bang –Because rapid expansion implies rapid cooling

• Inflationary (dark) energy was somehow converted to

heat at the end of inflation –This is the beginning of the Big Bang

• Big Bang is NOT the beginning of our Universe.
• How can we test this idea experimentally?

Toward Understanding the Origin

Inflation = Primordial Dark Energy

According to Inflation:

• “Micro became Macro”
• Even the universe had to obey quantum mechanics!
• Origin of structures in our Universe was

quantum

Quantum Fluctuations?

• You may borrow a lot of money if you promise to

return it immediately.

• The amount of money you can borrow is inversely

proportional to the time for which you borrow the money.

Quantum Fluctuations

• You may borrow a lot of energy from vacuum if you

promise to return it to the vacuum immediately.

• The amount of energy you can borrow is inversely

proportional to the time for which you borrow the energy from the vacuum.

• This is Heisenberg’s Uncertainty Principle, which is the

foundation of Quantum Mechanics.

Quantum Fluctuations

• Why is this relevant?
• The cosmic inflation (probably) happened when the

Universe was a tiny fraction of second old.

• Something like 10-36 second old (don’t faint just yet!)
• Time is short, so you can borrow a lot of energy:
• Quantum fluctuations were important during inflation!

(Energy You Borrow From Vacuum) = h / (Time For Which You Borrow Energy)

Are we stardust?

• Actually, we are more than stardust:
• We are children of Quantum Fluctuations.
• When the Universe was born and underwent

inflation, quantum fluctuations were generated.

• These quantum fluctuations were the seeds for ripples

in matter and radiation.

• We were born in the places where there was more

matter.

• And, we can (almost) directly observe the pattern of

the quantum fluctuations using microwave background!

Inflation also generates

• Primordial

Gravitational Waves

Primordial Gravitational Waves

• Quantum fluctuations create ripples in space =

Gravitational waves

• The Universe is extremely transparent to gravitational

waves

• We can use gravitational waves to directly

see the epoch of inflation (Amplitude of GW) = h x (Expansion Rate during Inflation) / (Planck Energy)

Gravitational Waves are coming toward you!

• Gravitational waves stretch

space, causing particles to move

Two Independent Modes

• How are these motions imprinted in

microwave background?

“+” Mode “X” Mode

Gravitational Waves to Temperature Fluctuations

Electrons

Redshift Redshift Blueshift Blueshift R e d s h i f t R e d s h i f t B l u e s h i f t B l u e s h i f t

Gravitational Waves to Temperature Fluctuations

And to Polarization

• What Cosmic Microwave Background

Has Done

• Proof of the fireball universe (Big Bang) [Penzias&Wilson

(1965)]

• Discovery of temperature fluctuations [COBE (1992)]
• Determination of the composition of our universe

[WMAP (2003+)]

• Precision measurements of initial fluctuations [WMAP

(2003+)]

• What we are doing now
• Toward the primordial universe: gravitational waves!

LiteBIRD

• Next-generation polarization-sensitive microwave

experiment

• Led by Prof. Masashi Hazumi (KEK); a collaboration of ~60

scientists in Japan, USA, Canada, and Germany

• We aim at detecting signatures of gravitational waves in the

cosmic microwave background

Frontiers in Cosmology

• Big Questions remain:
• What is Dark Matter?
• What is Dark Energy?
• Has Inflation Happened?

Frontiers in Cosmology

• Big Questions remain:
• What is Dark Matter?
• What is Dark Energy?
• Has Inflation Happened?
• A question for you:
• Would OIST join this endeavor?