Origins of the Universe

What we know

• We know that stars are not fixed in place in the universe– they are moving rapidly apart

• This means the universe is expanding• If something is expanding, it must

have come from somewhere• That “somewhere” is where the Big

Bang took place

How can we tell how fast stars move?

• When something moves that emits waves, the waves in front of the object are compressed and the waves behind become spread out

• You notice this when a police car, ambulance, or train passes you. The sound has a higher pitch as it gets closer to you and lower after it passes

– lower pitch = longer sound waves, lower frequency

– higher pitch = shorter sound waves, higher frequency (pitch)

• This change in wavelength & frequency (of sound waves in this example) is called the Doppler effect

Ok, but we’re talking stars, not cars…

• For visible light, the colour of light that we see depends on the length of the waves

• Red light has a long wavelength (low frequency)• Blue light has a short wavelength (high frequency)

and ...• If a star is moving away

from us, its waves are stretched (longer)– its spectral lines appear at

the RED end of the spectrum

• called RED SHIFTED

• If a star is moving towards us, its waves are squished (shorter)– its spectral lines appear at

the BLUE end of the spectrum

• called BLUE SHIFTED Spectral lines of this galaxy cluster are shifted to the red end of the spectrum compared to our Sun

p. 369

and finally …

• When we look into the sky all the stars we can see are red shifted

• The farther a star is from us, the more red shifted it is

• Scientist Edwin Hubble observed that galaxies moving 2x as fast are 2x as far away from Earth (the Hubble Law)

• The only explanation for this is that everything is moving away from us

• This means the universe is expanding

But where did the universe come from then?

• Since the universe seems to be expanding outwards, it is logical to assume that it started at a point

• This is the basis of the Big Bang theory

An artist’s depiction of space after the

Big Bang

The Big Bang Theory

• A theory for the formation of the universe • Scientists believe about 14 billion years ago, the

universe was unimaginably compact, small, and dense• Universe began its expansion after a giant explosion,

coined the Big Bang• It began expanding with unimaginable force from a

hot, dense state to its present state over a loooong time (~ 13 750 000 000 years or 14 billion if rounded up)

But the galaxies didn’t just pop out of the explosion, right?

• There were steps after the Big Bang

• First, energy cooled to form matter, then the first stars formed

• Eventually galaxies formed • We are a second or third

generation star

Timeline on p. 375

Proof of the Big Bang theory

1. Expansion– we know from red shift the universe is expanding

2. Leftover heat – called cosmic microwave background (CMB) radiation

– basically stretched out energy waves (gamma rays that are now microwaves)

– scientists believe this heat is left over from the giant explosion that set the formation of the universe in motion (the Big Bang)

Evidence to support CMB radiation

• 2 satellites captured false-colour images from 7 years of travel in the universe – show types of radiation that we

can’t see (like microwaves)• Images gathered by these

satellites support the concept of CMB radiation– 1st = COBE, launched in ’89– 2nd = WMAP, launched in ’01

How did the Solar System form?• Started as a nebula• Gravity set the gas & dust particles into motion around the

core of the young star– called a protostar (a hot & condensed object)

• Particles began to gather in the centre of the spinning cloud (analogy: stirring a glass of water with salt or sand in it)

• Spinning nebula began to contract and tiny grains started to collect

• Grains built up into bigger, rocky lumps– called planetesimals

• The planetesimals that survived all the collisions with other objects built up and eventually developed into planets

p. 334

Continued…

• Planets are mostly round due to the effects of gravity

• Over time, as the nebula spins, it flattens into a disk-like shape

• Planets and other objects (e.g., asteroids) form in the flat plane of the disk– hence why the orbits of planets in our solar system are

largely in the same plane– all revolve around the Sun in the same direction

• counter-clockwise if looking from above or eastward– most rotate in the same direction too (eastward)

What about Earth?

• The planet itself formed about 4.6 billion years ago– bombardment by planetesimals stopped ~ 4 billion years ago

• The first signs of life began forming ~ 3.5 billion years ago– when oxygen became rich in the atmosphere

• Single-celled bacteria ~ 3 billion years ago• Multi-celled organisms ~ 1.5 billion years ago• First land animals were millipedes ~ 420 million years ago• Pangaea happened ~ 200 million years ago• Humans appeared on Earth ~ 1 to 4 million years ago

(more recognizable state 250 000 years ago, homo erectus) – their ancestors were on Earth much earlier

To Recap…

• The Doppler Effect– A change in wavelength & frequency of energy that bounces off an object,

which tells scientists which way the object is moving (toward or away)– Easily observed when an emergency vehicle passes by (sound waves)

• When an object is considered redshifted, it is moving away– Galaxies are redshifted, which demonstrate they’re expanding

• When an object is considered blueshifted, it is moving closer• The Big Bang Theory

– A theory for the creation of the universe– How cosmologists believe it formed --- by a big explosion that sent

particles flying outwards– Expansion and CMB radiation support this theory

• The Big Bang– Term used to describe the explosion that started the formation of the

universe– Happened about 14 billion years ago

• “Looking back” in time– it takes more than 8 minutes for light to travel from the Sun to Earth– so when we look at the Sun, we’re seeing it as it was 8 minutes ago– looking at galaxies that are 10-billion light years away gives us an idea of

that part of the universe as it was 10 billion years ago

• International science organizations, like CERN (Conseil Européen pour la Recherche Nucléaire), located in Switzerland– created a particle accelerator called the Large Hadron Collider (LHC)

• built underground between the French & Swiss border

– this massive machine is used to conduct experiments at energies that approach those found 10-12 s after the Big Bang

• Studying cosmology can lead to the creation of technologies that the public can use, like the World Wide Web– originally created by a scientist at CERN so he could share information

with other scientists around the world

Other little diddies…

Some Food for Thought…

• Extrasolar planets– Many believe planets are by-products of star formation

• Astronomers have discovered over 1200 planets orbiting stars other than the Sun– when the planet comes between the observer on Earth

and the star, the amount of light coming from the star decreases

– planet impedes or sort of eclipses the star– see p. 335 for a cool image of planets revolving around

the star HR 8799

Where next?

• Who knows?!

• We could stop expanding and collapse back (aka the big crunch)

• We could keep expanding till everything is so far away that there is no heat left (aka the big chill)

• We could collide with another galaxy (Andromeda??)

• Don’t worry…