Chapter 18: Chapter 18: Cosmology

WHAT DO YOU THINK?

What does the Universe include?Did the Universe have a beginning? Is the Universe expanding, fixed in size,

or contracting?Will the Universe last forever?

You will discover…You will discover…

Cosmology, which seeks to explain how the Universe began, how it evolves, and its fate.

The best theory we have for the evolution of the Universe – the Big Bang.

How astronomers explain the overall structure of the Universe.

Our understanding of the fate of the Universe.

In the Beginning – the Big BangIn the Beginning – the Big Bang

The Universe began 13.7 billion years ago with The Universe began 13.7 billion years ago with an event called the “Big Bang.”an event called the “Big Bang.”

All of space-time, matter, and energy were All of space-time, matter, and energy were created at the Big Bang.created at the Big Bang.

The left-over energy from the Big Bang can be The left-over energy from the Big Bang can be detected today as the Cosmic Microwave detected today as the Cosmic Microwave Background Radiation.Background Radiation.

The temperature of this radiation is only a few The temperature of this radiation is only a few degrees above absolute zero.degrees above absolute zero.

The Beginning – The Big BangThe Beginning – The Big Bang

In Search of The Earliest PhotonsIn Search of The Earliest Photons

Wilkinson Microwave Anisotropy Probe (WMAP) satellite, launched in 2001

WMAP’s Baby Picture of the Universe –WMAP’s Baby Picture of the Universe –Cosmic Microwave Background RadiationCosmic Microwave Background Radiation

The Universe is ExpandingThe Universe is Expanding

The Redshift of Superclusters shows us The Redshift of Superclusters shows us that the Universe is expanding. This that the Universe is expanding. This Redshift is called the “Redshift is called the “Cosmological Cosmological RedshiftRedshift,” because it is ,” because it is caused by the caused by the expansion of spaceexpansion of space..

The The farther awayfarther away a galaxy is from us, the a galaxy is from us, the faster it movesfaster it moves away from us. away from us.

The Expansion of the Universe –The Expansion of the Universe –Cosmological RedshiftCosmological Redshift

Space itself is expanding.

Expanding Cake AnalogyExpanding Cake Analogy

Just as all the chocolate chips move apart as the cake rises, all the superclusters of galaxies move away from each other as the space of the Universe expands.

The Observable UniverseThe Observable Universe

The cosmic light horizon today is about 13.7 billion light-years away in all directions.

HST – Galaxies >13 Billion LY AwayHST – Galaxies >13 Billion LY Away

This HST Ultra Deep Field Telescope image shows some of the most distant galaxies we have seen.

Early Universe Temperature VariationsEarly Universe Temperature Variations

Tiny temperature fluctuations in the Cosmic Microwave Background Radiation are related to the large-scale structure of the Universe today, indicating where Superclusters and voids grew.

The First Stars – much larger than the Sun – The First Stars – much larger than the Sun – with much shorter liveswith much shorter lives

The burst of star formation that occurred within a few hundred million years after the Big Bang.

Proto-Galaxy FormationProto-Galaxy Formation

Hubble and Keck telescope images of two groups of stars that are believed to be proto-galaxies, from which bigger galaxies grew

Creation of Spiral and Elliptical GalaxiesCreation of Spiral and Elliptical Galaxies

A galaxy begins as a huge cloud of primordial gas that collapses gravitationally.

If the rate of star formation was low, then a spiral galaxy formed.

If the rate of star formation was high, then an elliptical galaxy formed.

The Fate of the UniverseThe Fate of the UniverseThe fate of the Universe depends on the The fate of the Universe depends on the

shape of space-time.shape of space-time.The shape of space-time is determined by The shape of space-time is determined by

how much total matter and energy there is how much total matter and energy there is in the Universe.in the Universe.

Space-time could have one of three Space-time could have one of three shapes:shapes: Sphere = positive curvature = closed.Sphere = positive curvature = closed. Our floor = no curvature = flat.Our floor = no curvature = flat. Saddle = negative curvature = open.Saddle = negative curvature = open.

Possible Shapes of Space-time,Possible Shapes of Space-time,and the Fate of the Universeand the Fate of the Universe

• Closed – Closed – Universe Universe would would collapse.collapse.

• Flat – Flat – Universe Universe could slowly could slowly expand expand forever.forever.

• Open – Open – Universe Universe would would expand expand forever.forever.

Cosmic Microwave Background indicates that Space-Cosmic Microwave Background indicates that Space-time is Flat – Universe could slowly expand forevertime is Flat – Universe could slowly expand forever

BUT – dimmer distant Supernovae mean theBUT – dimmer distant Supernovae mean theexpansion of the Universe is speeding up.expansion of the Universe is speeding up.

100 billion years from now the Universe will

appear frozen in time as we look out into space. Only the light from the Local Group of

galaxies will remain visible, if anyone is still around to see

it.

Expansion of the Universe is speeding upExpansion of the Universe is speeding up

Very distant Type 1a Supernovae are not as Very distant Type 1a Supernovae are not as bright as they should be.bright as they should be.

This means the expansion of the Universe is This means the expansion of the Universe is speeding up instead of slowing down or staying speeding up instead of slowing down or staying the same.the same.

There is something really weird called Dark There is something really weird called Dark Energy (not the same as Dark Matter) that is Energy (not the same as Dark Matter) that is causing this acceleration.causing this acceleration.

Dark Energy acts like anti-gravity, pushing the Dark Energy acts like anti-gravity, pushing the Universe apart.Universe apart.

We do not know what this Dark Energy is, but it We do not know what this Dark Energy is, but it makes up 73% of the total energy/matter of the makes up 73% of the total energy/matter of the Universe.Universe.

Composition of the UniverseComposition of the Universe

Suppose all the matter and energy in the Universe is Suppose all the matter and energy in the Universe is $100 in your wallet or purse.$100 in your wallet or purse.

$73 would be $73 would be Dark EnergyDark Energy – the mysterious energy – the mysterious energy that’s pushing the Universe apart faster and faster.that’s pushing the Universe apart faster and faster.

$23 would be $23 would be Dark MatterDark Matter – matter that doesn’t give off – matter that doesn’t give off any kind of radiation, so we can’t see it – but it does any kind of radiation, so we can’t see it – but it does have gravity.have gravity.

So out of your Universe of $100, $96 represents Dark So out of your Universe of $100, $96 represents Dark Energy and Dark Matter that have yet to be identified.Energy and Dark Matter that have yet to be identified.

Only $4 would be Only $4 would be visible mattervisible matter – the regular stuff we – the regular stuff we can see, like stars, gas clouds, and dust – the same stuff can see, like stars, gas clouds, and dust – the same stuff we’re made of.we’re made of.

Of the visible matter ($4), only one-tenth of it shines as Of the visible matter ($4), only one-tenth of it shines as stars. That’s 40 cents out of your total $100. The rest of stars. That’s 40 cents out of your total $100. The rest of the visible matter is gas clouds and dust.the visible matter is gas clouds and dust.

Composition of the UniverseComposition of the Universe

Dark Energy (73%)

Dark Matter (23%)

Visible Matter exceptStars (3.6%)

Stars (0.4%)

WHAT DID YOU THINK? What does the Universe include? It is all the matter, energy, and space-time that

will ever be detectable from the Earth or that will ever affect us.

Did the Universe have a beginning? Yes, it occurred about 13.7 billion years ago in

an event called the Big Bang. Is the Universe expanding, fixed in size, or

contracting? The Universe is expanding, faster and faster. Will the Universe last forever? Current observations support the belief that it will

last (expand) forever.