Prof Jonathan Sievers (UKZN) NITheP Associate Workshop talk

Jonathan Sievers NITheP Sep. 19, 2014

High Resolution CMB

What Do We Want to Know?

• What is the universe made of (the answer may surprise you)?

• How much stuff is there in the universe, anyways?

• When was the Big Bang?

• How quickly is it expanding?

• What’s going to happen to it?

• Can we say anything about physics in the very, very, very young & hot universe? (when it was far hotter than anything we can make with particle accelerators today)

The Plot Heard Round the Universe• Edwin Hubble discovers in 1929 that

galaxies are moving away from us.

• Their speed is proportional to their distance.

• Modern cosmology began with this simple law.

Left: Edwin Hubble!Above: First measurement of distance-velocity relation.

Big Bang Prediction

• Big Bang would also have produced photons.

• Earlier in time, denser universe means hotter temperature.

• Alpher & Gamov looked at helium in universe, saw there was too much for stars to have made it all.

• Helium could have been made in Big Bang - if so, residual photons should mean ~5 Kelvin temperature wherever we look.

Discovery of the Cosmic Microwave Background

4.08 GHz (7.35 cm) ! “microwave”

Penzias & Wilson (Bell Labs) discovered excess radiation it while building & testing antennas. !First thought it might have been a “white dielectric substance.” Tried many things, but couldn’t get 3K to go away. Showed up everywhere they pointed in the sky. !Wandered up the road to Princeton to ask if anyone there had any ideas. Dicke: “Boys, we’ve been scooped.” Nobel prize in 1978

Frequency Spectrum of the Microwave Background

This plot has error bars!

COBE Satellite measured temperature of sky in lots of direction. Universe almost perfectly smooth. Biggest difference, at 0.1% caused by our motion through universe.

Nearly There…

• Basic picture of cosmology mostly in place. Not quite, though.

• Two classic problems in cosmology:

• Horizon - temp./density same in all directions (to 10 ppm). Light from my right edge hasn’t had time to get to my left edge. Why so similar?

• Flatness - universe very closely balanced between expansion/contraction. If I throw a ball up, either it comes back down, or leaves earth orbit. 13.8 billion years later, still to close to call?

Matter curves space, bending light rays. Critical expansion means light rays stay parallel.

Inflation

• Phase changes in early universe generically give rise to huge expansions.

• Expansion takes something the size of a proton to something the size of the solar system in ~10-27 seconds.

• Expansion drives metric to flat, like blowing up a balloon.

• Because universe was tiny before inflation, plenty of time to reach thermal equilibrium.

An ant on a balloon that inflates. Before, the balloon looks curved. Afterwards, it looks flat.

Inflation Predicts

• Heisenberg Uncertainty Principle: I can’t tell you where something is and how fast it is going simultaneously.

• Alternative: I can’t tell you how much energy something had and when it happened simultaneously.

• Energy equals mass (E=mc2), so energy uncertainty equals mass uncertainty.

• Inflation freezes in mass uncertainties. Makes predictions about what they should look like. In inflation, the largest things in the universe come from the Heisenberg Uncertainty Principle.

A Brief History of the Universe

The First 500,000 Years

• Inflation (or something similar) happens after big bang - sets initial conditions, predicts “almost” scale-invariant density spectrum.

• Universe expands, cools. ~25% of hydrogen burned to helium in first several minutes. (lithium made)

• Perturbations from Heisenberg Uncertainty Principle evolve under gravity/photon pressure.

• T~3000K (~400k years) electrons/protons combine to form hydrogen. Universe becomes transparent.

• These photons come (almost) straight towards us. T now 2.72548±0.00057. Observe with mm telescopes.

• Temperature, density uniform to ~10 PPM → linear physics (unlike stars, galaxies) Initial conditions+universe contents+physics=quantitative statistical prediction.

What do We Expect to See?

• Sound! Matter wants to collapse under gravity.

• Because universe is opaque, the matter drags photons with it. Photon pressure provides restoring force

• This leads to sound waves. All waves start as density perturbations at inflation, so are in phase. Long waves take longer to evolve than short waves.

• If we stop at any point in time, some waves will be at max amplitude, some at zero.

What do we Expect to See?Sound! Driven by gravity, photon

pressure. Normal modes sine waves, like piano strings. (If strings were longer than size of universe)

Sound speed=c/√3 Inflation: Everything starts at the same

time. Longer waves take longer to oscillate.

Because we see a surface, we see a snapshot in time.

WMAP and the CMB sky.

Wave Amplitudes vs. Wavelength (Power Spectrum)

Plot mean variance of waves vs. k to get power spectrum. Physics affects the “sound quality” of the universe. !Axes: Horizontal is l, full moon is l~400. Vertical noise in µK2. Typical signals are a few to a few dozen millionths of a degree. !This is space in which data and theory are compared.

larger smaller

“Cosmic Graphic Equalizer”

What This Looks Like: ns

!Inflation sets the initial amplitude of the fluctuations. Inflation predicts almost scale-invariant noise, but maybe with slightly more amplitude on larger scales. !We call this parameter ns - if we can measure it, we learn about inflation! !!!

ns=2

ns=1

ns=0

Initial Slope (ns) of Power Spectrum in PS

Change in power spectrum as initial slope changes. !

l200 600 1000 1400 1800

Some Parameters: Regular Matter DensityMatter wants to collapse. It drags light with it, but the light doesn’t want to be squeezed. The more matter there is, the more it can compress the photons. So, more baryons means brighter patches. !Photons also spread out (“Silk damping”). More electrons means less spreading, and so power on small scales falls off less quickly. !(spectrum also falls off since we’re really averaging over a finite-thickness shell)

Some Parameters: Dark Matter DensityDark matter doesn’t scatter light, so it falls right through the photons. So, no pressure means the dark matter just collapses. !Dark matter tries to pull baryons with it through gravity, so 1st, 3rd etc. peaks, DM works with baryons, 2nd, 4th etc. peaks, DM works against baryons. !Lots of DM + lots of baryons = big 1st, 3rd peak, smaller 2nd, 4th... Can basically read off baryon/DM ratio from relative even/odd peak heights.

So, How do we Measure This?

Pontificia Universidad Catόlica de Chile University of Oxford Stony Brook University West Chester University of Pennsylvania National Aeronautics and Space Administration Goddard Space Flight Center (NASA GSFC) University of British ColumbiaInstituto Nacional de Astrofisica, Óptica y Electrónica (INAOE) Carnegie Mellon University University of Pennsylvania Haverford College Institute for Advanced Study (IAS) National Institute of Standards and Technology

University of California, Berkeley Canadian Institute for Theoretical Astrophysics (CITA) Princeton University Cardiff University University of Michigan University of KwaZulu-Natal University of Miami University of Pittsburgh Academia Sinica Rutgers, The State University of New Jersey Cornell University The Johns Hopkins University

PhRvD 87, 3012 JCAP 10,60 JCAP 7,25 arXiv:1301.1037

The Atacama Cosmology Telescope

6m primary, 5200 meters in Chilean Atacama

THE TELESCOPE: DETECTORS +

OPTICS

32X32 array

32X32 array

32X32 array

Transition Edge Sensors Beams

1.4’

1.0’

0.9’

3000 detectors (c.f. 72 for Planck) @3 frequencies

ACT: Data Challenge

Requirements: Unbiased sky estimate (need ~1% signal accuracy). Optimal (data is precious). Ability to handle complex noise. Fast - ACT has a ton of data.

Go from to

(Linear) Least Squares

!

• Least squares has formed core of data analysis for >200 years, going back to Gauss.

• First use was to rediscover Ceres. Been in constant use ever since.

• ACT challenge:

• N is very complicated

• A is very complicated

• Have to invert huge matrices to solve for ~107-1010 parameters from 1012 data points.

�2 = (d� hdi)TN�1(d� hdi)

25

SciNet @UofT:

GPC: 3780 nehalem nodes=30240 cores 306 TFlops debut as #16 in

Top500

1 Rack: 692 cores, 7 TFlops, 1.3 TB RAM.

Mapping one ACT frequency from one season takes ~13 CPU-years.

We’ve used >25 million CPU- hours. Solve for 1010 params from >1012

data points.

radio galaxy

SZ cluster

ACT &PlanckDunner et al. 2012

Have to Clean up a Bit

Das et al. 2013

Marginalised CMB-only likelihood

Restricting the range l < 3500 where the Cls are Gaussian – marginalize over the secondary parameters!

Data from 4 totally independent experiments. There is a model curve under there - the data are so precise that you can’t see the curve!

Baryon Density

• Through the CMB, we measure the density of ordinary matter (baryons) to an accuracty of 1%. Ordinary matter makes up 4.82±0.06% of the universe.

Dark Matter

30

• Through the CMB, we measure the density of dark matter to 25.8±0.4% of the universe.

• What is the dark matter? No idea! Would really like to know…

• “But wait” I hear you say. “25.8 + 4.8 only adds up to 30%. What’s the rest?” Also a good question. Also would really like to know… (cosmological constant? Something that evolves?)

ns

31

• Combination of CMB data measure ns to be 0.9614±0.0063, 6σ away from 1.

• Remember - inflation predicts ns to be a little bit less than one. This is pretty strong evidence that inflation happened!

•

r<0.11

!Matter PS is a fundamental quantity. Observed CMB is matter PS + snapshot effects + baryon physics. Others also measure matter PS, nonlinear structures are biased tracers. !Perturbation stop growing when subhorizon during radiation-dominated era, kink gets frozen in at transition to matter dominated. Angular scale tells redshift of equality.

Matter Power Spectrum/Effective # Neutrinos Neff

Tegmark 03

l

Effective relativistic speciesAny extra light particles would leave a signature in the CMB. We detect the three neutrino species we expect, but don’t currently see anything else.

neff=3.30+0.54-0.51

NB: highL=ACT+SPT(K11)

Particle Equilibrium in Big Bang

• In early universe, particles in thermal equilibrium.

• nx ~nγ if kT>>mxc2.

• As T drops, particles decouple from photons. For stable particles, if Tdecouple >> mxc2, then final particle density set by temperature at Tdecouple.

• If Tdecouple <mxc2, density suppressed by exp(-mxc2/kT)

• Energy from these particles gets converted into photons.

• neutrinos decouple above mec2, so energy from e+e- goes into photons, not neutrinos.

• Means photons hotter than neutrinos, Tν~(4/11)1/3Tγ

• Temp. of any light stable particle suppressed vs. γ by # of species that annihilate after particle decoupling.

Jonathan Sievers, Columbia, March 7 2011

Gravitational lensing of the CMB

Intervening large-scale potentials deflect CMB photons and distort the CMB.

The RMS deflection is about 2.7 arcmins, but the deflections are coherent on degree scales. Lensing picks up intervening matter power spectrum.

Jonathan Sievers, Columbia, March 7 2011

� ⌧ �FS� � �FS

Graphics from Y. Wong

MASSIVE NEUTRINOS SUPPRESS STRUCTURE FORMATION ON SMALL SCALES

Effective relativistic speciesAny extra light particles would leave a signature in the CMB. We detect the three neutrino species we expect, but don’t currently see anything else.

neff=3.30+0.54-0.51

NB: highL=ACT+SPT(K11)

Claims of deviation from unity at low redshifts z~2 using quasar absorption spectra (Webb et al.) !!!!!α changes the physics of

recombination !WMAP7+ACT – consistent with no deviation at z~1100

Fine structure constant

Sievers, Hlozek et al. 2013+Planck+BAO=0.9989±0.0037

Upgraded ACT to be polarization sensitive !Regular science observations started a year ago. !

Polarization Results!

We put out first paper only 8 months after beginning science observations! Peaks in polarization spectrum are very clear.

Left: UKZN postdoc Simon Muya Kasanda and I measured phase of polarization peaks. They are indeed out of phase with the intensity peaks, to an accuracy of a few degrees.

ACTpol Summary

• Mapping speed ~16 times ACT. • Cover 4000 square degrees to 20 uK-arcmin, 150 to 5 uK-arcmin.

• Planck+ACTpol measures sum of neutrino masses to ~0.06 eV - detection expected.

• Planck+ACTpol measures # of relativistic species to 0.11

• Have first science data coming in now. With ~2 months of data, 1/3 final # of detectors, already close to ACT depth over large patches.

Parameter forecasts from Galli et al. Blue=Planck, Red=ACTpol, Green=CMBpol (far future, unfunded).

Summary• Leftover radiation from the Big Bang surrounds us, and at some frequencies is the brightest thing in the sky.

• The universe appears to have been created in an explosion just under 14 billion years ago we call the Big Bang. There are multiple independent lines of very strong evidence for this.

• Also strong evidence the universe underwent inflation. • Detailed measures of the CMB from when the universe was 400,000 years old gives us our best current handle on cosmology. We now routinely make percent-level accurate measurements of the basic parameters of the universe.

• Detailed measurements of the polarization of the CMB will open tell us even more about the universe, particularly about inflation (and particle physics).

• Advanced ACT (planned upgrade to ACTPol) got fully funded by NSF a few months ago! Even better neutrino mass, will also constrain formation of first generation of stars.