11 Cosmology

Cosmology

2015 / Gerco Onderwater

Pleiades

Carl Sagan

Cosmology

Particle physics : understand nature at the smallest scale– needs special relativity and quantum mechanics

Cosmology : understand nature at the largest scale (universe)– needs general relativity

Both have a very successful “Standard Model”

In recent years, more and more links

Beginning of time

Merger of - special relativity : c = 3·108 m/s- quantum mechanics : ħ = 1·10-34 m2·kg/s- general relativity : G = 7·10-11 m3/kg/s2

Dimensional Analysis

Can we form a time from c, ħ and G?And a length, mass and temperature?

t=C⋅ℏα⋅cβ⋅Gγ

t p=(ℏGc5

)1 /2

=5⋅10−44 s l p=c t p=(ℏGc3

)1/2

=1.6⋅10−35 m

M p=(ℏ cG

)1 /2

=2⋅10−8 kgT p=(ℏ c5

GkB2 )

1/2

=1.4⋅1032 K

CERN’s “outreach” posters

Standard Model of Cosmology

At the instant of the Big Bang, all the matter in the Universe was condensed into a single point*. Other than that, we know nothing about what went on in the first instants of the Universe's existence. But by looking far out into today's Universe and peering deeply into the world of fundamental particles, scientists have managed to piece together the evolution of the universe from the inconceivably short time of just 10-43 seconds after the Big Bang.

The “father” of the Big Bang was the Belgian Jesuit priest Lemaître, who found in 1927 a solution in which the Universe starts out with a “Big Bang”, as it was later called

*The Big Bang theory is a cosmological model, developed in the 20th century, based on the 1916 theory of General Relativity applied to the Universe, and motivated by the observation of the expansion of the Universe by Hubble

The very beginning ...

The spectral lines of a moving star or galaxy are Doppler-shifted by Δλ=λobs–λlab

Redshift is z=Δλ/λlab and thus the velocity is v=cz

Hubble used the new Mt. Wilson telescope to observe variable stars in the nearby “nebula” Andromeda. He realized that the fuzzy patches called nebulae were actually distant galaxies, outside of our own Milky Way.

This implies a uniform and homogeneous expansion of the Universe with time!

Discovery of the expanding universe

From his data, Hubble deduced the relation:v = H0d = cz

– v = velocity from spectral line measurement– d = distance to object– H0 = Hubble constant in km s-1 Mpc-1

– z = the redshift

Andromeda nebula

At that point in time, things were happening very fast. When the Universe was 10-43 seconds old Nature's forces were indistinguishable*. Particles of matter and antimatter (the white circles in the picture) existed in equal portions. They were constantly annihilating to produce radiation, represented by red spirals, and being recreated from that radiation. Matter was compressed so densely that even light could not travel far and the Universe was opaque. Just before this time physicists think that Universe expanded at a dizzying rate. This period of so-called Cosmic Inflation** is necessary in the Big Bang theory to explain the large scale uniformity of the Universe today.

*This is the (unproven) hypothesis of the existence of a Grand Unified Theory of particle physics.

** This (unproven) theory of inflationis due to Alan Guth (1981).

Inflation

During the next phase of the Universe's existence, up to around 10 -34 seconds after the Big Bang, the strong force that binds particles called quarks together into protons and neutrons became distinct from the electromagnetic and weak forces which remained indistinguishable. Protons and neutrons did not start to form, however, because any groupings of quarks were rapidly broken up by the high-energy radiation that still pervaded the Universe. Matter was a sort of high-density cosmic soup * called the quark-gluon plasma . The carriers of the weak force, W and Z particles, were as abundant as photons and they behaved in the same way.To understand fully this phase of the Universe's existence, physicists try to recreate the quark-gluon plasma in the laboratory, for instance at Brookhaven's Relativistic Heavy Ion Collider (RHIC)

* The strong interaction between quarks & gluons has some very curious properties:

- at short distances quarks & gluons do not interact; this is the famous “asymptotic freedom”- quarks and gluons are confined (locked up) in protons, neutrons and other nuclear particles

Quark-gluon plasma

Collision @ RHIC

Also around this time a tiny excess of matter over antimatter , just one matter particle surviving for every thousand million particles to annihilate with antimatter, began to develop. It is these survivors that make up our Universe today*. The precise mechanism that has allowed some matter to survive is poorly measured up to now, but it is another phenomenon that will be studied in depth at the LHC and elsewhere.

* This profound idea of baryogenesis is due to Andrej Sakharov

Baryogenesis

Between 10 -34 seconds to 10 -10 seconds the electromagnetic and weak forces separated*. There was no longer enough energy to produce W and Z particles and those that had already been made decayed away. The energy of the radiation had also fallen sufficiently to allow protons (red) and neutrons (green) to form ** as well as short-lived particles, called mesons, made of a quark and an antiquark (blue).Antimatter started to disappear because when quarks annihilated with antiquarks there was no longer enough energy in the radiation to recreate them.Particle physics experiments have begun to probe back in time as far as this by crashing particles together with enough energy to recreate the conditions of the early Universe at laboratories like CERN.

*According to the unified electroweak theory, formulated by Glashow, Weinberg & Salam, and proven consistent by ‘t Hooft & Veltman.

**The proof of this quark confinement in QCD is still lacking (prize: M€ 1,-)

Forces separate

Up to about 10 -5 seconds proton and neutron building continued. The remaining antimatter, in the form of positrons, disappeared as the radiation energy density dropped below that necessary to create electron-positron pairs. With no antimatter left in the Universe other than a few particles locked up inside mesons, all that is left is the one-in-a-thousand-million matter particles* resulting from Nature's apparent preference for matter.

*The Standard Model of particle physics fails to explain this: it does not have enough breaking of a mirror symmetry called “CP-invariance”.

Antimatter disappears

After that, things really started to slow down. Up to around three minutes * protons and neutrons started to combine to produce light atomic nuclei . Only deuterium (heavy hydrogen), helium and a tiny amount of lithium were made. The Universe was like a giant thermonuclear reactor until, at around three minutes, the reactions stopped leaving a Universe composed of hydrogen, deuterium, helium, and a little lithium**. Even today, the Universe is made up of about 75% hydrogen and 25% helium, with just traces of heavier elements cooked up in stars to make everything else that we consider to be "ordinary" matter.

*cf. S. Weinberg: “The First 3 Minutes.”

**This primordial or Big Bang Nucleosynthesis provides very strong support for the Big Bang model.

Nucleosynthesis

Agreement of abundancesover 10 orders of magnitude

⇓Major success of Big Bang

Observational concordance

η = nB/ng = (4±1)x10-10

CMB: ng = 411 cm-3

Conclusion of BBN: - most matter is not nucleons

Abundances of the light elements

After about 5 minutes, the elemental composition of the Universe remains unchanged until the first stars form several billion years later…

Time evolution of BBN

Most protons remain free

Most neutrons in 4He nuclei

Rest of neutrons decay away

During the next 380,000 years the Universe became transparent as photons no longer interacted * as soon as they were made. Electrons became captured by the hydrogen, deuterium, helium and lithium nuclei to form the first atoms.

The CMB anisotropies contain important information about cosmological parameters and will be measured with even higher precision by Planck, launched in 2009.

*These photons cooled as the Universe expanded, resulting in today’s Cosmic Microwave Background of 2.7 Kelvin, a nearly-perfect black-body spectrum. The CMB was discovered by accident in 1965 by Penzias & Wilson. Fluctuations in the CMB were detected by the COBE satellite and studied in detail by the WMAP & Planck satellite missions.

Atom formation

Bell Labs

COBE1992

Wilson Penzias

(+Robert Dicke)

Discovered in 1965 as “excess noise” (Noble Prize in 1978)

George Gamow (1904-1968)

Gamow (1946), Alpher & Herman (1949) predict 5 K relic radiation from Big Bang

Cosmic Microwave Background

First observation of the CMB

“The microwave light captured in this picture is from 379.000 years after the Big Bang, over 13 billion years ago: the equivalent of taking a picture of an 80-year-old person on the day of their birth.”

Isotropy of the universe

Planck results

*Then, the dark ages start, which only end when clustering of matter leads to the re-ionization period and the first generation of stars and, later, galaxies. This period will be studied in depth by LOFAR, a digital radio telescope, under construction in Drenthe, designed to detect the 21 cm line of hydrogen red-shifted to radio frequencies.

Cosmological dark ages

LOFAR

Galaxy formation took 1000 million years as matter began to clump together in a way that is still not clearly understood. Gravity pulled the light elements together to form stars which ignited, cooking up elements as heavy as iron. Some stars, at the end of their lives, exploded in spectacular supernovae, rapidly generating even heavier elements like gold and scattering them around the Universe *. Slowly, these elements began to clump together into planets. Molecules formed and chemical processes began.

*Supernovae are also one of the (more conservative) hypotheses for the origin of ultrahigh-energy cosmic rays (Baade & Zwicky).

Crab supernova remnantSN 1987A

Fritz Zwicky

Galaxy formation

Molecules in space

Sagittarius B : billion billion billion liters of alcohol

Ultra-high energy cosmic rays

The origin of ultra-high energy cosmic rays is presently a mystery. The Pierre Auger Observatory in Argentina will, hopefully, shed light on this.

Pierre Auger observatory

The Fly’s Eye : A cosmic-ray detector of the University of Utah, near Salt Lake City.

On the night of October 15, 1991: the Fly’s Eye detected a proton with an energy of (3.2±0.9)x1020 eV, i.e. 320 EeV.

This energy, 50 Joule, is enough to light a 40 Watt light bulb for more than a second, equivalent to “a brick falling on your toe,” or a decent baseball pitch.

Its speed is (1 ‒ 5·10-24)c ; it would lag only 4 nm behind a photon after 1 light year.

Oh-My-God particle

Finally, after 15.000 million * years, people emerged on one of those planets and began to contemplate the Universe around them, trying to piece together the story which led to us being here.

*Actually, after 13.7 billion years…

Self-reflections

Blabla… Big BangNucleosynthesis… bla…

Blabla… Cosmic Micro-wave Background… bla…

This Standard Model of Cosmology (the “hot Big Bang model”), based on the Standard Model of particle physics and the theory of General Relativity is now in trouble, as evidence for something far more bizarre keeps growing…

Physics is done?

The energy budget of the Universe

The Standard Model of the 80s is dead!

ROSAT (Röntgen Satellite, 1990-1999): in (fake) purple one sees hot gas that is

being confined by the gravitational force of invisible, dark matter.

Hubble space telescope (1990-…):Velocity measurements at large scales point to the existence of much more mass (gravity) than can be explained from the luminous matter present.

The existence of dark matter was discovered by Zwicky in 1933

Loose ends ...

Loose ends ...

“Bullet cluster”:Red: luminous matter (Chandra X-ray Observatory)Blue: dark matter (gravitational lensing)Orange and white: galaxies (Magellan, Hubble)

Direct proof of dark matter

Observations of the luminosity of very far-away supernovae suggest that the expansion of the Universe is accelerating…

Since recently, it appears that an invisible vacuum energy in the Universe is building up a negative pressure. The nature of this dark energy, however, is a complete mystery…

Dark energy

The future of the Universe

Future ...