Transcript Origins of the Universe

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)
• If a star is moving away
from us, its waves are
stretched (longer)
and ...
– 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
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 creation 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
p. 334
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
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
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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
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… 
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
Other little diddies…
• “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