Transcript Big Bang theory with thanks to St Andrews Academy

Key Areas covered
• The temperature of stellar objects is
related to the distribution of emitted
radiation over a wide range of wavelengths.
• The wavelength of this distribution is
shorter for hotter objects than cooler
objects.
• Qualitative relationship between radiation
per unit surface area and temperature of a
star.
• Cosmic microwave background radiation as
evidence for the big bang and subsequent
expansion of the universe.
What we will do today
• State how temperature of stellar objects is
related to the wavelengths of the radiation
they emit
• Describe how their wavelengths vary for hot
and cold objects
• State the relationship between radiation per
unit surface area and temperature of a star
• Describe the Big Bang Theory
• Give evidence to support the Big Bang Theory
Big Bang Theory
What happens to the colour of
objects as they are heated?
• When an object is heated it does not initially
glow, but radiates large amounts of energy as
infrared radiation. We can feel this if we
place our hand near, but not touching, a hot
object.
• As an object becomes hotter it starts to glow
a dull red, followed by bright red, then
orange, yellow and finally white (white hot).
At extremely high temperatures it becomes a
bright blue-white colour.
Practical application - Pottery
• Early potters used the
fact that materials glow
different colours at
different temperatures
to
determine
the
temperature
inside
their kilns.
• In 1792 the famous
porcelain maker Josiah
Wedgewood noted that
all bodies become red at
the same temperature.
Colour
Temp
(oC)
550
Dark
red
Cherry 750
red
Orange 900
Temp
(K)
823
1023
1173
Yellow
1000
1273
White
1200
1373
Light and temperature
• We can see that the temperature of an
object affects the light it gives off.
• This means that the temperature of an
object is linked to both the frequency
and wavelength of the light it emits.
• A graph of intensity versus wavelength
has a characteristic shape and can be
shown in a “Planck distribution.”
Planck distribution
•
Is also known as a black-body
spectrum and has three main
features:
1.
The basic shape is more or
less the same
As the temperature of the
object increases, the peak
intensity wavelength
decreases (so frequency
increases)
As the temperature of the
object increases, the intensity
and energy increases
2.
3.
•
•
Summarised as follows:
T ↑ λ ↓ therefore f ↑ intensity
↑ energy ↑
2014 Revised Higher
B
Lesson starter – Olber’s paradox
• If the night sky is full of stars why is it
dark?
• Why is the sky dark at night? [VIDEO]
Thinker - what have we learned so far?
•
•
•
•
Redshift – when objects move away from us
their wavelength is increased, we now know that
galaxies are moving away from us
Hubble’s law – can help us work out the speed
and distance of stellar objects, we now know
galaxies that are further away from us are
speeding up
Expanding universe – scientific evidence shows
us that the universe is expanding and this
expansion is accelerating
QUESTION: What does all the evidence
above tell us about the beginning of the
universe?
How did the universe begin?
•
There was a sudden appearance of energy
which consequently became matter and is
now everything around us.
• There were two theories regarding its
beginning:
1. The Steady State Universe – where the
universe had always been and would always
continue to be in existence.
2. The Created Universe – where at some time
in the past the universe was created
What is the Big Bang
Theory?
The Big Bang
What is the Big Bang Theory?
•
•
•
•
•
•
The Big Bang Theory took place around 13.8 billion
years ago.
The universe was originally very hot and very dense
concentrated in a tiny point known as a singularity
(smaller than an atom).
It caused our universe to expand suddenly from the
singularity bringing time and space into existence.
Following the Big Bang, temperatures rapidly cooled
and tiny particles of matter began to form.
The first atoms to form were hydrogen and helium.
This matter created stars, galaxies and planets.
What evidence is there for
the Big Bang Theory?
Big bang video clips on Twig
What evidence is there for the
Big Bang?
•
There are a number of factors that
provide evidence for the Big Bang:
1. The expanding universe
•
•
•
Light from the stars in the galaxy is
enough to light our sky at night.
The only explanation that it is not is
that the stars are moving away from
us.
An expanding universe must have
started out infinitely small and agrees
with the Big Bang Theory
2. Cosmic Microwave Background
Radiation
•
•
•
•
This radiation can be detected on Earth
coming from all directions in space.
This radiation is constant throughout the
universe.
As the universe expands the wavelength of
the radiation emitted increases (less
frequency) down to the microwave region.
This
radiation
provides
a
constant
temperature throughout the universe
(approximately 3K).
3. Abundance of light elements
•
•
The universe has an abundance of light
elements such as Hydrogen and
Helium.
As the universe grew these elements
fused together to create the other
known elements.
2014 Revised Higher
D
2012 Revised Higher – Qu: 22 (1/2)
2012 Revised Higher – Qu: 22 (2/2)
Solution
Solution
2013 Revised Higher – Qu: 25
Solution (a)
Possible solution (b)
• Light travels at approximately 3 x 108 ms-1
• One light year is the distance travelled by light in one
year – 3 x 108 x 365 days x 24 hours x 60 mins x 60
seconds = 9.46 x 1015 m.
• As stars in our galaxy can be well over hundreds and
thousands of light years away the time it takes their
light to reach us is massive.
• For example our nearest star (apart from the Sun) is
over 4 light years away, this means that the light we
see from this star was sent over 4 years ago.
• Effectively, we are looking back in time.
Open-ended question
2014 Revised Higher
Possible answer
• Yes the Universe is expanding. We know this because of:
1. Stars / galaxies are moving away from us;
2. Cosmic microwave background radiation; and
3. The abundance of light elements
• It is expanding in all directions with the space between each
galaxy increasing as they move away from each other
• “as fast as it can go, at the speed of light” – this lyric is wrong
as it suggests a constant speed however the expansion is
actually accelerating.
• “12 million miles a minute” - using 1610 metres per mile this
converts to 1.932 x 1010 metres a minute which is 3.22 x 108 m/s
and this is slightly more than the accepted value for the speed
of light.
• “the fastest speed there is” – this is true as nothing can travel
faster than the speed of the light
Questions
• You can now answer the questions on
The Big Bang Theory in your class jotter