Baking a universe

Or, how we came looking like this out of the Big Bang

The Big Bang

How do we know the universe is expanding?

Looking at distant galaxies:• They are all moving away from us and form each other• Their speed is proportional to their distance

Precisely as if they were “carried away” by an expanding universe

We mix • Theory of relativity• Gravitation• Thermodynamics• Particle physics

We get a “story” …… and some of the scenes can be compared with data

As in the theory of evolution,The details of some periods are heatedly discussedBut the paradigm is not.

How do we use this to understand the present universe?

An atom primer

Atoms are made of a small nucleus of radius 10-15m

Surrounded by an electron cloud of darius 10-10 m

The nucleus is made of protons and neutrons

Protons and neutrons are made of quarks

To date no “parts” of quarks or electrons have been found

The earliest fossilsIn the earliest times the universe was very hotUp until 100 microseconds protons and neutrons could not form The universe was a soup of quarks, electrons and radiation

At 1s, and a temperature of 9 £ 109 oK: Protons and neutrons formed

At 200s, and a temperature of 8 £ 108 oK: Atomic nuclei formed

But not all nuclei were created!

For light nuclei…

Electric repulsion

High speed(large temp.)

Electric repulsion

High speed(large temp.)

For heavier nuclei…

Only• Deuterium• Helium• A bit of Lithiumwere “cooked” in the early universe

The amounts are also predicted.

CONFIRMED

The earliest light

At 1/3 million years, Atoms formed

Atoms are neutralThey interact little with lightFrom that time on the early-universe radiation has traveled (almost) unimpeded

As the universe expands the wavelength of the radiation also expands

The current universe is suffused by a uniform bath of microwaves

CONFIRMED

Inhomogeneities in the Early Universez

• Very faint (about 0.001%)• The seeds of clusters of galaxies• Each has expanded to a region 5£ 109 light years across

If we could see microwaves …

A mysterious matter

The fate of the universe depends on how much matter it contains:

• Too much: it will expand to a maximum size and then re-contract• Too little: it will expand forever

There is a critical value separating these two cases(about 1 mass of the Moon in every 30 cubic light years)

Luminous matter: about 4% of critical

• From counting galaxies and gas clouds• From the synthesis of D, He and Li in the early universe

Unless there are othrer contributions …

… the universe will expand forever

Another way of measuring matter

Looking at the Moon I can weight the Earth.

To go around the Earth takes meT = 27.3 days = 0.07479 years

R = 3.8 £ 105 km

So MEarth = 6 £ 1024 kg

For the planets I get:

And I can do the same for a galaxy:

Measure the speeds of stars orbiting it.Measure their distance to the center

) get the mass of the galaxy

Rotation curves for near-by galaxiesCan be explained if the force is / 1/r not / 1/r2.

Are Newton & Einstein wrong?

Are we missing matter?

Dark Matter

The hypothesis is that the universe has enough of a new kind of matter to explain the rotation curves of galaxies.

This new matter is called Dark Matter …… because it does not shine.

Then the density should be / 1/r2 and its temperature should be uniform

So galaxies would be surrounded by a dark matter haloStars orbiting the galaxy are plowing through a dark-matter mist

There is other evidence of Dark Matter:

If we observe distant galaxies and there is a lot of dark matter in between, we should see a characteristic distortion …

… and we do!

Images distorted … perhaps by a great deal of dark matter

And then there’s the “bullet” cluster:

Two galaxies with few stars and a lot of gas collidedMost of the matter is in the form of gas

The stars were almost unaffectedThe gas of each interacts a lot so it stayed in the middle

But the strongest gravitational effects are localized near the stars … not the gas!

Matches perfectly the Dark Matter hypothesisHard to explain with other hypotheses

Update on the cosmic census

Ordinary matter: 4% of criticalDark Matter: 23% of critical

If there is Dark Matter,

Can we detect it in some way?Is there only one kind?

Could it be that Dark Matter cosmologists are wondering what that annoying 4% is all about?

Could it be something else?

Another mystery

The rate of expansion is increasingThe universe is accelerating … why?

The best current hypothesis:

There is a new form of energy causing this … dark energy

If so then it gives about 73% of critical

The decade of cosmology

Over the next 10-15 years

The nature of Dark Matter will be understoodThe nature of Dark Energy will be understood

Or else

We’ll have to revise our understanding of space matter and gravitation