Transcript How big is the Universe? - Contemporary Science Issues

Contemporary science issues
Lesson 16: Has the universe always been there?
© 2006 Gatsby Technical Education Projects
Has The Universe Always Been
Here?
The Evolution of the Universe.
Think!
How big is the Universe?
• Sort out the following in order of their size (smallest to largest):
The Milky Way
The Moon
The Solar System
The Earth
The Universe
Think!
How big is the Universe?
• Sort out the following in order of their size (smallest to largest):
The Moon
~ 3500 km
The Earth
~ 12500 km
The Solar System
~ 12 Billion km
The Milky Way
~ 100 000 Light Years
The Universe
~ 50 Billion Light Years
What is a Light Year?
• A “light year” is the distance travelled by a ray of light in one year.
• If light travels 300 000 km every second, how far would it travel in one
year?
– Number of seconds in one year =
60 x 60 x 24 x 365.25 = 31 557 600
– Distance light travels in one year =
31 557 600 x 300 000 ~ 9 500 000 000 000 km
• A car that travels at 100 km/h (about 60 mph) would take nearly 11
million years to travel that distance.
How big is the Universe?
• The visible universe is huge!
• The question that has been puzzling people for thousands of years is:
– Where does the universe come from?
• How and why do we “make a theory” and what do we need to support
our theory?
Where did the Universe come from?
• Many different theories have been put forward to describe how the
universe began or to explain why it is here. The earliest accepted
theory was proposed by the Greeks.
A Timeline of Theories
When were the theories
first suggested?
(~2500 years ago)
Static Universe:
The Universe does
not change with
time. It appears the
same every time it is
observed.
What do you notice about
the amount of time
between the theories?
(~80 years ago)
The Big Crunch:
The Universe expands
to a certain size before
gravity causes it to
collapse in on itself.
(~50 years ago)
The Big Bang:
The Universe began
with all matter
concentrated in a
small volume that
suddenly expanded.
Number
of years
ago
2500
2000
(~2500 years ago)
Infinite Universe:
The Universe has no
edge.
It carries on forever in
all directions.
150
(~80 years ago)
Slowing
Expansion:
The Universe
expands forever but
the expansion
becomes slower.
100
50
(~80 years ago)
Accelerating
Expansion:
The Universe
expands forever but
the acceleration
becomes faster.
0
(~50 years ago)
Steady State
Universe:
The Universe has no
beginning but it does
expand. The gaps
that form are filled in
with new matter.
Things to do ...
Task 1
Look at the cards that describe the theories of the evolution of the
universe.
–
Divide the theories into two groups
(e.g. Those with a with a beginning and those without)
–
How else could you group the theories?
erase
What do we think now?
• Even today scientists are not agreed on what will happen to the
universe, though they do have some idea.
• Scientists have made observations that they use to develop and support
their theories.
• We are now going to look at these observations.
The Unchanging Universe
• When you look into the sky at night the stars are in the same
positions as they were the night before.
• In fact their positions have changed very little since the time of the
Ancient Greeks.
• So, why do you think the Ancient Greeks thought the universe was
unchanging?
• How long would you need to observe the stars to see changes happen?
The Gravity Riddle
• The Greeks and religions thought the universe was static, its size
was constant.
• Is this possible?
• Gravity would cause the universe to collapse in on itself!
• Do we see this happening?
• The only solution to this was
for the galaxies to be moving
away from each other. The
universe was expanding!
• But where is it expanding
from?
Red Shift
– In 1929 Hubble showed that the wavelength of light from stars had
been “stretched” or red-shifted.
– This was evidence that the stars and galaxies in the universe were
moving away from each other.
– The universe was expanding.
Hubble also discovered that the
further away from us a galaxy
was the faster they were
moving!
What does this mean?
Cosmic Microwave Background
– If the universe began with a “Big Bang” scientists expected there to
be a small amount of heat energy left over.
– This left over energy has been detected and is called the Cosmic
Microwave Background.
– The Cosmic Microwave Background means that space has a
temperature 3 °C above absolute zero.
Things to do ...
Task 2
• Using the cards, match the evidence to the theories they support.
(Some cards might go to more than one theory)
• Why do you think the Ancient Greeks thought the Universe was
“Static” or unchanging?
• Which theory do you think is most likely?
• Which of Friedmann’s Universes do you think is right? Why?
erase
Think!
• Why did people living in Ancient times draw the conclusions they did?
• What is the need for scientists to observe the universe over longer
period of time?
• What is the need for evidence?
Think!
Extension
• Why is the sky dark at night? The answer to this question might seem
obvious;
– That the night side of the Earth is facing away from the Sun.
• In fact the answer is not so straightforward.
Olber’s Paradox
• Our Sun is one of a seemingly
infinite number of stars in our
infinitely large Universe, each
one emitting light.
• If the number of stars is
infinite then each patch of the
sky would be covered by a
star. Every line of sight would
end on the surface of a star
(see picture).
• No matter how far away these
stars are from Earth some of
their light would reach us.
• Therefore light would be
coming from all parts of the
sky. Even at night!
• This means that the night sky
should be at least as bright as
the sky in the day!
• From everyday experiences we
know this is not the case.
(look at the sky at night!)
The Answer?
• If an infinite universe would be very hot and bright why is our universe
cold and dark?
– Perhaps its not infinite!!
– This means that the universe could have a beginning!