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COSMOLOGY HOW IT BEGAN. Chris Impey University of Arizona. Norton, 2010. Space. Science is Seeing. A Scale Model. Set the Earth to the size of a walnut, or a 1:500,000,000 scale model. =. The Moon is a pea at arm ’ s length The Sun is a 3 m ball 300 m away

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Cosmology how it began



Chris Impey

University of Arizona

Cosmology how it began


Science is Seeing

Cosmology how it began

A Scale Model

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


  • 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

Cosmology how it began

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

  • 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

Cosmology how it began

Reduce the scale by a factor of 10,000,000 speed. There

  • 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

Cosmology how it began

Now reduce by another factor of 10,000,000 speed. There

  • 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

Cosmology how it began

The Contents speed. There

Cosmology how it began

Galaxies speed. There

Scattered in a universe 46 billion light years across

100 billion


Cosmology how it began

Stars speed. There

The Milky Way is typical with 400 billion stars

100,000 billion

billion stars

Cosmology how it began

Atoms speed. There

Almost all the simple elements hydrogen and helium



Cosmology how it began

Photons speed. There

A billion photons for every particle


Cosmology how it began

Mediocrity speed. There

  • We therefore live on an:

  • Average planet around

  • An average star in an

  • Average galaxy in a

  • Very large universe


Composition of the universe

Universal Pie speed. There

Composition of the Universe

Dark matter: 22%

Dark energy: 73%

Cosmology how it began

Cosmology speed. There

Cosmology how it began

Cosmology speed. There


Cosmology how it began

Lookback Time speed. There

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.

Distant Light = Old Light

Cosmology what we know

3C 273 speed. There

Cosmology: What We Know

  • Redshift – it’s a universal

    expansion of space-time,

    not a Doppler shift.

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

Cosmology how it began

Hubble Ultra Deep FieldHST•ACS

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

Cosmology how it began

Big Bang in the past

Evidence in the past

  • 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

Cosmic microwave background
Cosmic Microwave Background in the past

  • 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

Cosmology how it began

The CMB has highest in the pastredshift of anything we can see (z = 1000).

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

Cosmology how it began

Origin interactions with the big bang

Science is Seeing

Cosmology how it began

The big bang was extraordinary interactions with the big bang― 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.

Cosmology how it began

Cosmic Inflation interactions with the big bang

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.

Cosmology how it began

Status of Inflation interactions with the big bang

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.

Cosmology how it began

Beyond the Horizon interactions with the big bang

The 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 much

larger 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.

Cosmology how it began

THE UNIVERSE AND US interactions with the big bang



Solar System

Milky Way



Cosmology how it began

Multiverse interactions with the big bang

Cosmology how it began

Beyond the Horizon interactions with the big bang

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

Cosmology how it began

Quantum fluctuations are a mechanism for multiple realizations of the universe

…leading to the concept of the “multiverse”

Cosmology how it began

String Theory Landscape realizations of the universe


Perhaps 10 different vacua

de Sitter expansion in these vacua create quantum fluctuations and provide the

initial conditions for inflation. String theory provides context for the “multiverse”

Cosmology how it began

The realizations of the universe“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.

Eternal universe
Eternal Universe realizations of the universe

Cosmology how it began

Nature of the Expansion driving the cosmic acceleration.

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.