Frontiers in Cosmology Eiichiro Komatsu (Max-Planck-Institut für Astrophysik) OIST Seminar, Okinawa Institute for Science and Technology June 13, 2013
What is Cosmology ? • 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? 3
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) 4
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) 6
Composition of our Universe 73% of our Universe 27% is not even matter 73% Matter Dark Energy 7
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” 8
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” 9
Imagine throwing up an apple 10
Dark Energy Exists • Dark energy makes the expansion faster • It was discovered through measurements of the expansion speed 13
つか Standard Candle Method • You use an object with the known intrinsic luminosity 14
Standard Candle Method Greater Distance • This method can be used to infer how fast the distance between galaxies is growing 15
Supernovae are too dim Acceleration Constant-velocity Dimmer Deceleration Brighter • Dim = Far = Bigger Universe = Faster Expansion = Acceleration 3000 30000 300000 16 Expansion Velocity (km/s)
Huge Discovery in 1998 • Supernovae were dimmer than expected • Universe’s expansion was faster than expected (assuming only matter) • Acceleration! 17
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 18
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) 19
Big Rip 20
(A Possible) Catastrophic Ending Scenario for Our Universe 21
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!) 22
Incredible Observational Fact(?) • Our Universe was accelerating even before the Big Bang? • On-going and ever-improving measurements of the cosmic microwave background (1992–) 24
Night Sky in Visible Light （ ~500nm ） 25
Sky in microwaves （ ~1mm ） 26
Sky in microwaves （ ~1mm ） Cosmic Microwave Background “Fossil Light of the Big Bang” T = 2.725 K 27
Fireball Universe Time “Big Bang” 28
Fireball Universe Time “Big Bang” Hot Expansion 29
Fireball Universe Time “Big Bang” Colder Hot Expansion 30
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 31
For example, 1% of noise in TV is from the Big Bang 32
4K Blackbody 2.725K Blackbody 2K Blackbody Rocket (COBRA) Satellite (COBE/FIRAS) Rotational transition of CN Ground-based Balloon-borne Satellite (COBE/DMR) Sky Brightness Spectrum of Microwave Background 3m 30cm 3mm 0.3mm 33 Wavelength
Early Universe = Hot Soup • Light (lines) is scattered by electrons (blue) • Universe was “foggy” proton photon helium electron 34
Universe became transparent • Electrons are captured 1500K by protons when the temperature dropped to 3000 Kelvin 3000K Time • Neutral hydrogen atoms do not scatter light as much: photons 6000K now travel freely proton electron helium photon 35
COBE/DMR, 1992 Fluctuations discovered 30 micro Kelvin on top of 2.7 Kelvin. One part in 100,000! 37
COBE to WMAP COBE COBE 1989 Compared to COBE: • 35 times better angular resolution WMAP • 10 times better sensitivity WMAP 2001 38
WMAP Science Team • WMAP: Launched in June 2001 • Mission completely ended just now. (Final set of papers have been accepted for publication) 39
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 40
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 41 determined ( remember [distance] = [speed] times [time]? )
Composition of Our Universe “Cosmic Pie Chart” 4% • Confession: • After all these years, we have 23% finally come to admit that we do not understand 95% of our Universe 73% Hydrogen and Helium Dark Matter Dark Energy 42
Fourier Analysis of Microwave Maps θ • C( θ )=(1/4 π ) ∑ (2l+1) C l P l (cos θ ) • “Power Spectrum” C l – l ~ 180 degrees / θ 43
Power Spectrum from COBE/DMR Data Angle ~ 180 degrees / l ~9 degrees ~90 degrees (Quadrupole) 44 Multipole Moment, l
Power Spectrum from WMAP Small Angular Scale Large Angular Scale Power Spectrum ~ １ degree COBE 45
Sound Wave Propagating in the Universe! “Photon-baryon* Fluid” Velocity 2 / [3(1+R)]; R=3 ρ b /(4 ρ γ ) Sound Velocity 2 = Light 46 *Hydrogen and Helium
Waveform to Parameters Large Scale Small Scale Hydrogen and Helium Power Spectrum 10% 5% 1% 47
Toward Even Earlier Epoch • Who dropped stones? • What created initial fluctuations? • What is the origin of structures in the universe (including ourselves)? 48
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 -15 m) was stretched to the size of Solar System (1AU~10 11 m) 49
Toward Understanding the Origin • 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? 50
Inflation = Primordial Dark Energy 51
According to Inflation: • “Micro became Macro” • Even the universe had to obey quantum mechanics! • Origin of structures in our Universe was quantum 52
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. 53
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. 54
Quantum Fluctuations (Energy You Borrow From Vacuum) = h / (Time For Which You Borrow Energy) • 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! 55
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