COSMOLOGYHOW IT BEGAN

Chris ImpeyUniversity of Arizona

Norton, 2010

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Science is Seeing

Space

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A Scale Model

Set the Earth to the size of a walnut, or a 1:500,000,000 scale model

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• The Moon is a pea at arm’s length• The Sun is a 3 m ball 300 m away• Neptune is a softball 9 km away• Nearest star is 80,000 km away

• The Moon is a seconds walk away• The Sun is 8 minutes walk away• 10 hours to walk the Solar System• 4 years to walk to the nearest star

And at this scale, light is reduced to very slow walking speed. There’s no way information in the universe can travel any faster

Reduce the scale by a factor of 10,000,000

• The Solar System is a grain of sand• The distance between stars is 20 m• The Milky Way is the size of the U.S.• The MW has 400,000,000,000 stars

Now reduce by another factor of 10,000,000

• The Milky Way is like a small plate• The nearest galaxy is 5 m away• The universe is the size a large city• Billions of galaxies within this space

The Contents

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Scattered in a universe 46 billion light years across

Galaxies

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The Milky Way is typical with 400 billion stars

Stars

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Almost all the simple elements hydrogen and helium

Atoms

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A billion photons for every particle

Photons

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Mediocrity

We therefore live on an:

• Average planet around• An average star in an• Average galaxy in a• Very large universe

Copernicus

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Composition of the Universe

Dark matter: 22%Dark energy: 73%

Universal Pie

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Cosmology

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Cosmology

Slipher

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Lookback Time

If the speed of light were infinite, light from everywhere in the universe would reach us at exactly the same time and we would see the entire universe as it is now.

But it is not, so we see distant regions as they were in the past.

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Cosmology: What We Know

1. Redshift – it’s a universal expansion of space-time, not a Doppler shift.

2. The microwave background radiation (CMB), a signal that is close to perfectly thermal, at temp of 2.726K.

3C 273

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3. Deuterium and Helium synthesized (much higher temperatures in the past).

Hubble Ultra Deep FieldHST•ACS

4. Galaxies in past look younger (smaller and more irregular). 19

Big Bang

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• A good scientific model should always make predictions which can be verified.

• The big bang model makes two predictions which have been verified since the 1960s:• the existence and characteristics of the cosmic

microwave background (CMB)• the expected Helium abundance in the Universe

• The model predictions agree with all current observations. There is much indirect evidence the universe was smaller and hotter in the past

Evidence

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Cosmic Microwave Background

• The universe is immersed in a sea of radiation.• 380,000 years after the big bang, the universe had

cooled enough for free electrons to become bound into atoms of Hydrogen and Helium

• Without electrons to scatter them, photons were able to travel unhindered throughout the universe

• The universe became transparent • The temperature of the universe was 3,000 K at this

time, similar to a stellar photosphere• It has expanded by a factor of 1000 since then,

reducing the temperature to 3000/1000 = 3 Kelvin

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When we look at the CMB, we look at the surface of the glowing “fog” that filled the entire early universe!

The CMB has highest redshift of anythinganything we can see (z = 1000).

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1% of the specks on any TV tuned between stations are interactions with the big bang

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Science is Seeing

Origin

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The big bang was extraordinary― the instantaneous creation of all of space and time, containing energy to drive the expansion and enough matter for 100 billion galaxies.

The initial state was so compact that it can only be described by a theory that unites gravity and the quantum world. We do not have such a theory at present.

The big bang can be thought of as a quantum event, originating from very chaotic space-time in which the other quantum fluctuations might have led to other parallel universes. 27

Cosmic Inflation

The standard big bang has trouble explaining why the universe is as smooth and flat as it is, leading to the idea of an epoch of extremely rapid inflation, just 10-35 sec after the big bang. The mechanism is unclear but probably associated with the Grand Unified theories that seek to unite all the forces except gravity. 28

Status of Inflation

Inflation makes the universe flat and smooth (by design!), and it implies vast region of space that are beyond view. It has tentative support from CMB satellite data.

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Beyond the HorizonThe universe is bounded in time and not space. General relativity sets no speed limit to the expansion. As time goes by, ever more distant regions come into view.

At z = 1.3, an object was moving away from us at c at the time the light was emitted.

At z = 1000, two distant points were moving apart at ~60c at the time the radiation was emitted.

Consequence of standard big bang: The physical universe is muchlarger than the observable universe, we are subject to a horizon.

Consequence of the inflationary big bang: A microscopic region of space-time became our universe; the universe is a quantum entity. 30

Us

Milky Way

Earth

THE UNIVERSE AND US

Solar System

Universe Multiverse?

Multiverse

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Science is Seeing

Life occurs in a range of scales that extends from

galaxies to the atomic nucleus, as symbolized by the ancient symbol of the ouroboros, the snake that eats its

own tail

Beyond the Horizon

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Quantum fluctuations are a mechanism for multiple realizations of the universe…leading to the concept of the “multiverse”

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String Theory Landscape

Perhaps 10 different vacua

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de Sitter expansion in these vacua create quantum fluctuations and provide the initial conditions for inflation. String theory provides context for the “multiverse”

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The “ekpyrotic” universe has a big bang, but it is not ever at an infinite temperature and density, and it is not the origin of all space-time… So our universe emerged from a collision of two 4D branes that are embedded in 5D space-time. The collision is the engine for expansion and matter creation. 36

Eternal Universe

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Dark matter binds galaxies and dark energy is currently driving the cosmic acceleration.

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Nature of the Expansion

The early expansion was rapid, driven by intense radiation. It slowed down as the dark matter began to dominate, and more recently has begun to accelerate due to the relative growth of dark energy.

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Within the expanding and cooling universe gravity formed stars, galaxies, and people. 40