Transcript dark matter. - Gordon State College

Conceptual
Physical
Science
5th Edition
Chapter 28:
THE STRUCTURE OF
SPACE AND TIME
© 2012 Pearson Education, Inc.
© 2012 Pearson Education, Inc.
This lecture will help you
understand:
•
•
•
•
•
•
•
Hubble’s Law
The Big Bang
Cosmic Inflation
General Relativity
Dark Matter
Dark Energy
The Fate of the Universe
© 2012 Pearson Education, Inc.
Hubble’s Law
• The Beginning of our
Modern View
– Until the 1920’s, many
people believed that the
Milky Way Galaxy made up
the entire universe.
– In the early 1920’s, Edwin
Hubble disproved this
belief by discovering that
the Andromeda “nebula”
was in fact a distant galaxy,
separate from our own.
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Hubble’s Law
• Hubble’s Measure of
Distance
– Hubble could deduce the
distance of a star from the
Earth by comparing its
luminosity (energy) and
brightness.
– The brightness of light
obeys an inverse square
law. (An object twice as far
away will appear one
quarter as bright)
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Hubble’s Law
CHECK YOUR NEIGHBOR
If the distance between your eye and a lamp is halved,
A.
B.
C.
D.
The light will appear to be two times brighter.
The light will appear to be two times dimmer.
The light will appear to be four times brighter.
The light will appear to be eight times dimmer.
© 2012 Pearson Education, Inc.
Hubble’s Law
CHECK YOUR ANSWER
If the distance between your eye and a lamp is halved,
A.
B.
C.
D.
The light will appear to be two times brighter.
The light will appear to be two times dimmer.
The light will appear to be four times brighter.
The light will appear to be eight times dimmer.
Explanation:
The apparent brightness of light is subject to an inverse-square
law. Near objects appear brighter than distant objects.
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Hubble’s Law
• Hubble’s Measure of Redshift
- Light emitted from a source
moving toward us will be shifted to
the blue (high frequency), while
light emitted from a source moving
away from us will be shifted to the
red (low frequency).
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- The faster an object moves
toward us or away from
us, the greater its emitted
light will be shifted.
Hubble’s Law
CHECK YOUR NEIGHBOR
How will the spectrum of a star moving toward us change?
A.
B.
The wavelength of the light will be stretched, making it redshifted.
The wavelength of the light will be compressed, making it
blueshifted.
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Hubble’s Law
CHECK YOUR ANSWER
How will the spectrum of a star moving toward us change?
A.
B.
The wavelength of the light will be stretched, making it redshifted
The wavelength of the light will be compressed, making it
blueshifted.
Explanation:
Remember that light emitted from objects moving away from us
will have the wavelength stretched, while light from objects
moving toward us will have its wavelength compressed. A
redshift indicates that the wavelength has been stretched, while a
blueshift indicates that the wavelength has been compressed.
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Hubble’s Law
• Hubble found that most every object that he
could see was moving away from every
other object.
• The farther away an object, the faster it
was moving away (the greater the redshift).
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Hubble’s Law
• From the graph, Hubble wrote down his
famous equation:
v= H0 x d
This equation shows that the velocity that of an object is
proportional its distance.
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Hubble’s Law
• Hubble’s law implies that the universe is
expanding.
– The expansion of the universe is like an ant on
a balloon that is being blown up. The ant sees
every point on the balloon moving away from it.
– Hubble’s law also provides extremely strong evidence
for the Big Bang.
© 2012 Pearson Education, Inc.
Hubble’s Law
CHECK YOUR NEIGHBOR
Hubble’s law has to do with the
A.
B.
C.
D.
expansion of the universe.
steady state of the universe.
contraction of the universe.
cosmic background radiation.
© 2012 Pearson Education, Inc.
Hubble’s Law
CHECK YOUR ANSWER
Hubble’s law has to do with the
A.
B.
C.
D.
expansion of the universe.
steady state of the universe.
contraction of the universe.
cosmic background radiation.
© 2012 Pearson Education, Inc.
The Big Bang
The Big Bang:
• Theory—our universe began with a primordial
explosion some 13.7 billion years ago
• Marks the beginning of space and time
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The Big Bang
Evidence for the Big Bang:
• Continuing expansion of the universe
• Measured cosmic background radiation,
predicted before it was discovered and
measured
• Measurements of element abundances,
predicted before measured
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The Big Bang
CHECK YOUR NEIGHBOR
Scientific evidence supports the date of the Big Bang
event at
A.
B.
C.
D.
7000 years ago.
100,000 years ago.
5 billion years ago.
13.7 billion years ago.
© 2012 Pearson Education, Inc.
The Big Bang
CHECK YOUR NEIGHBOR
Scientific evidence supports the date of the Big Bang
event at
A.
B.
C.
D.
7000 years ago.
100,000 years ago.
5 billion years ago.
13.7 billion years ago.
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The Big Bang
Cosmic Microwave Background (CMB):
• If the Big Bang did occur and the
universe is expanding, the light
emitted at the instant of the Big
Bang would have been redshifted so much that it would
appear as microwave signals if
we received them today.
• Arno Penzias and Robert Wilson
observed these signals in 1964,
which became known as the
Cosmic Microwave Background.
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The Big Bang
Cosmic Microwave Background (CMB):
• The figure below shows the temperature of the CMB at
every point in space. The uniformity of the CMB means
that at some point in time all the matter in the universe
was very close together.
• The discovery of the Cosmic Microwave Background
provides some of the best evidence that the Big Bang
did occur.
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The Big Bang
Relative Abundance of Light Elements
• In order for elements to form, fusion of lighter elements
must occur. Fusion only occurs when matter is very hot
and very dense.
© 2012 Pearson Education, Inc.
The Big Bang
Relative Abundance of Light Elements
• In order for elements to form, fusion of lighter elements
must occur. Fusion only occurs when matter is very hot
and very dense.
• Scientists predict that if the Big Bang occurred, there
would not have been enough time to form any heavy
elements due to the rapidly expanding universe; only
hydrogen and helium could have been formed.
© 2012 Pearson Education, Inc.
The Big Bang
Relative Abundance of Light Elements
• In order for elements to form, fusion of lighter elements
must occur. Fusion only occurs when matter is very hot
and very dense.
• Scientists predict that if the Big Bang occurred, there
would not have been enough time to form any heavy
elements due to the rapidly expanding universe; only
hydrogen and helium could have been formed.
• Strong evidence for the Big Bang came when scientists
measured that about 75% of all the matter in the
universe is hydrogen and about 25% is helium. (Heavy
elements make up less than 1%)
© 2012 Pearson Education, Inc.
The Big Bang
The evidence from
• Hubble’s discovery of the expansion of the universe
• The Cosmic Microwave Background
• The relative abundance of light elements
has made the Big Bang Theory widely accepted in
the scientific community.
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General Relativity
This theory, published by Einstein in 1915,
states that gravity is the consequence of
mass distorting the fabric of spacetime.
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General Relativity
• Furthermore, the
effects of gravity
cannot be
distinguished from the
effects due to
accelerated motion.
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General Relativity
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General Relativity
The Principle of Equivalence
Local observations made in an
accelerated frame of reference cannot
be distinguished from observations
made in a gravitational field.
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General Relativity
The Principle of Equivalence
Two points of view of the same event.
© 2012 Pearson Education, Inc.
General Relativity
The Principle of Equivalence
Two points of view of the same event.
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General Relativity
General relativity tells us why starlight
bends as it passes by a large mass.
Light is affected by gravity!
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General Relativity
General relativity also tells us that time
runs slower within a gravitational field.
Time is affected by gravity!
© 2012 Pearson Education, Inc.
Dark Matter
• What is ordinary matter?
– What we think of as ordinary matter is made
of protons, neutrons, and electrons that form
atoms which combine to make people,
planets, stars, and suns.
– Ordinary matter is composed of the elements
listed in the periodic table.
© 2012 Pearson Education, Inc.
Dark Matter
• What makes matter “dark”?
– We cannot walk through a wall because it is
made of atoms that we can interact with
through the electromagnetic force.
– If matter does not exert the electromagnetic
force, then normal matter cannot interact with
it.
– This “invisible” form of matter that we cannot
see or interact with is known as dark matter.
© 2012 Pearson Education, Inc.
Dark Matter
• If we can’t see it or interact with it, how do we
know that it exists?
– Remember how gravity effects the motion of planets
orbiting the Sun: the closer the planet is to the Sun,
the more gravitational force it experiences.
– The greater the force on a planet, the faster that
planet orbits the Sun.
– Planets closer to the Sun orbit faster than planets
farther away.
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Dark Matter
• Apply the same principle to galaxies
– We should expect that objects closer to the center of
a galaxy (which contains most of the ordinary matter)
should orbit around the center faster than objects
farther from the center.
– This is not the case!
– Objects in galaxies orbit at about the same speed no
matter what their distance from the center of the
galaxy.
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Dark Matter
• What does this imply?
– If all objects in a galaxy have about the same orbital velocity,
most of galactic mass must be outside of the galaxy in an
“invisible halo” much bigger than the galaxy itself.
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Dark Matter
• But what is it really?
– There have been no direct measurements of dark matter
interactions.
– Until we can directly observe it, we can only make hypotheses
that explain the fundamental nature of dark matter.
© 2012 Pearson Education, Inc.
Dark Matter: Galaxy Formation
• After the Big Bang, ordinary
matter, as well as dark matter
began to clump together due to
gravity.
• When ordinary matter interacts
with itself, energy is lost as
heat.
• As ordinary matter loses
energy, it clumps together
further and becomes
concentrated at the center.
© 2012 Pearson Education, Inc.
Dark Matter: Galaxy Formation
• The concentrated clump of
ordinary matter in the center
allows for the formation of stars.
• The group of stars that forms in
the center of the clump becomes
a galaxy.
• As the matter becomes more
concentrated, the matter begins
to spin very quickly because it
must conserve angular.
© 2012 Pearson Education, Inc.
Dark Energy
Careful measurements of distant galaxies
tells us that the universe is expanding at
faster and faster rates. In other words, the
universe is accelerating outwards.
© 2012 Pearson Education, Inc.
Dark Energy
Careful measurements of distant galaxies
tells us that the universe is expanding at
faster and faster rates. In other words, the
universe is accelerating outwards.
As described in Chapter 1, however,
acceleration requires the application of some
force. What might be the nature of the force
causing the universal acceleration?
© 2012 Pearson Education, Inc.
Dark Energy
Scientists don’t know the answer to that
question, but they have given it a name,
which is
© 2012 Pearson Education, Inc.
Dark Energy
Scientists don’t know the answer to that
question, but they have given it a name,
which is
DARK ENERGY
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Dark Energy
The accelerated expansion began
about 7.5 billion years ago.
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The Fate of the Universe
The composition of the universe
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The Fate of the Universe
Two possible scenarios include
• Heat Death
• The Big Rip
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The Fate of the Universe
Two possible scenarios
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The Fate of the Universe
CHECK YOUR NEIGHBOR
Which scenario do you think is more likely?
A.
B.
C.
D.
Heat Death.
The Big Rip.
Other.
We really don’t know.
© 2012 Pearson Education, Inc.
The Fate of the Universe
CHECK YOUR ANSWER
Which scenario do you think is more likely?
A.
B.
C.
D.
Heat Death.
The Big Rip.
Other.
We really don’t know.
Explanation:
The more we learn through science the more questions that arise!
Remember, science far more than a set of facts and figures. It is a
systematic method by which we can learn more about our
universe and our place in it. There is so much we don’t know, but
we know more today than we have ever known in our past.
© 2012 Pearson Education, Inc.