© 2012 Pearson Education, Inc. Conceptual Physical Science 5 th Edition Chapter 28: THE STRUCTURE OF SPACE AND TIME © 2012 Pearson Education, Inc

© 2012 Pearson Education, Inc.

Conceptual PhysicalScience5th Edition

Chapter 28:

THE STRUCTURE OF SPACE AND TIME



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


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.


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)


If the distance between your eye and a lamp is halved,

A. The light will appear to be two times brighter.

B. The light will appear to be two times dimmer.

C. The light will appear to be four times brighter.

D. The light will appear to be eight times dimmer.

Hubble’s LawCHECK YOUR NEIGHBOR


A. The light will appear to be two times brighter.

B. The light will appear to be two times dimmer.

C. The light will appear to be four times brighter.

D. 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.

If the distance between your eye and a lamp is halved,

Hubble’s LawCHECK YOUR ANSWER


Hubble’s Law• Hubble’s Measure of Redshift

- The faster an object moves toward us or away from us, the greater its emitted light will be shifted.

- 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).


How will the spectrum of a star moving toward us change?

A. The wavelength of the light will be stretched, making it redshifted.

B. The wavelength of the light will be compressed, making it blueshifted.



How will the spectrum of a star moving toward us change?

A. The wavelength of the light will be stretched, making it redshifted

B. 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.



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).


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.


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.


Hubble’s law has to do with the

A. expansion of the universe.

B. steady state of the universe.

C. contraction of the universe.

D. cosmic background radiation.



Hubble’s law has to do with the

A. expansion of the universe.

B. steady state of the universe.

C. contraction of the universe.

D. cosmic background radiation.



The Big BangThe Big Bang:• Theory—our universe began with a primordial

explosion some 13.7 billion years ago• Marks the beginning of space and time


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


Scientific evidence supports the date of the Big Bang event at

A. 7000 years ago.

B. 100,000 years ago.

C. 5 billion years ago.

D. 13.7 billion years ago.

The Big BangCHECK YOUR NEIGHBOR


A. 7000 years ago.

B. 100,000 years ago.

C. 5 billion years ago.

D. 13.7 billion years ago.

The Big BangCHECK YOUR NEIGHBOR

Scientific evidence supports the date of the Big Bang event at


The Big Bang

• If the Big Bang did occur and the universe is expanding, the light emitted at the instant of the Big Bang would have been red-shifted 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.

Cosmic Microwave Background (CMB):


The Big BangCosmic 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.


The Big BangRelative 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.




• 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%)


The Big BangThe 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.


General Relativity

This theory, published by Einstein in 1915, states that gravity is the consequence of mass distorting the fabric of spacetime.


General Relativity

• Furthermore, the effects of gravity cannot be distinguished from the effects due to accelerated motion.


General Relativity


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.


General Relativity


Two points of view of the same event.


General Relativity


Two points of view of the same event.


General Relativity

General relativity tells us why starlight bends as it passes by a large mass.

Light is affected by gravity!


General Relativity

General relativity also tells us that time runs slower within a gravitational field.

Time is affected by gravity!


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.


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.


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.


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.


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.


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.


• 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.

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.

Dark Matter: Galaxy Formation


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.

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.

Dark Energy

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?


Scientists don’t know the answer to that question, but they have given it a name,

which is

Dark Energy


Scientists don’t know the answer to that question, but they have given it a name,

which is

Dark Energy

DARK ENERGY


The accelerated expansion began about 7.5 billion years ago.

Dark Energy


The composition of the universe

The Fate of the Universe


Two possible scenarios include

• Heat Death

• The Big Rip



Two possible scenarios



Which scenario do you think is more likely?

A. Heat Death.

B. The Big Rip.

C. Other.

D. We really don’t know.

The Fate of the UniverseCHECK YOUR NEIGHBOR


Which scenario do you think is more likely?

A. Heat Death.

B. The Big Rip.

C. Other.

D. 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.

The Fate of the UniverseCHECK YOUR ANSWER

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© 2012 Pearson Education, Inc. Conceptual Physical Science 5 th Edition Chapter 28: THE STRUCTURE OF SPACE AND TIME © 2012 Pearson Education, Inc