Transcript expanding universe

Unit 2
Section A
Einstein’s Repulsive Idea
Albert Einstein (1879---1955)
Do you have any idea about the formation of our
universe before reading this article?
A human being is part of the whole called by us universe,
a part limited in time and space. We experience ourselves, our
thoughts and feelings as something separate from the rest. A
kind of optical delusion of consciousness. This delusion is a
kind of prison for us, restricting us to our personal desires and
to affection for a few persons nearest to us. Our task must be
to free ourselves from the prison by widening our circle of
compassion to embrace all living creatures and the whole of
nature in its beauty. The true value of a human being is
determined by the measure and the sense in which they have
obtained liberation from the self. We shall require a
substantially new manner of thinking if humanity is to survive.
---Albert Einstein, 1954
An Overview of Cosmology
Objectives
• Develop perspective on the history of human
knowledge of the universe
• Understand the process of scientific
exploration of the universe
• Contemplate the current state of astronomy
and think about future missions
What is Cosmology?
For thousands of years, astronomers wrestled with basic questions about the
size and age of the universe. Does the universe go on forever, or does it have an
edge somewhere? Has it always existed, or did it come to being some time in the
past?
Our View of the Cosmos - the story of scientific models
Three scientific revolutions in cosmology
2nd Century: Claudius Ptolemy (Physics of Aristotle)
Model: Earth-centered Cosmology
16th Century: Nicolaus Copernicus (Physics of Newton)
Model: Sun-centered Cosmology
20th Century: Edwin Hubble (Physics of Einstein)
Model: Big Bang Cosmology
Earth-centered Cosmology: Claudius Ptolemy, 100-170 AD
Big idea: Earth was viewed as a stationary center of the universe, with sun,
moon, and stars revolving about it in circular orbits and at a uniform rate.
Sun-centered Cosmology: Nicholas Copernicus 1473-1543
Big idea: Copernican system placed the sun motionless at the center
of the solar system with all the planets, including the earth, revolving
around it.
Big Bang Cosmology: Edwin Hubble and Albert Einstein
Big idea: The universe had exploded and expanded from a
small, hot, dense state into what we see today.
Big Bang Theory
the theory of the cosmic explosion that marked the origin of the universe.
According to the big-bang theory, at the beginning of time, all of the matter
and energy in the universe was concentrated in a very dense state, from
which it exploded, with the resulting expansion continuing until the present.
This big bang is dated between 10 and 20 billion years ago. In this initial
state, the universe was very hot and contained a thermal soup of quarks,
electrons, photons, and other elementary particles. After many millions of
years the expanding universe, at first a very hot gas, thinned and cooled
enough to condense into individual galaxies and then stars.
Einstein’s Repulsive Idea
History of expansion: A rough picture of how the universe's expansion
decelerated, then began to accelerate. Fate is not known.
Einstein’s Repulsive Idea
This diagram reveals changes in the rate of expansion since the universe's
birth 15 billion years ago. The more shallow the curve, the faster the rate of
expansion.
Some theorists think the Universe is filled with a mysterious dark energy, a
sort of negative gravity.
The Hubble Space Telescope recently captured light from a supernova
located farther from Earth than any previously seen.
The finding has bolstered cosmological models for the universe's expansion
and a mysterious “dark energy” pervading it. The supernova, or exploding star,
is located 10 billion light-years from Earth.
“Normal Matter”
4%
Dark Energy
73%
Dark Matter
23%
Conclusions
• Big Bang model describes our current understanding
of the universe.
• New discoveries, such as dark matter and accelerating
expansion (Dark Energy), lead us to refine our model.
• Science is an ongoing process - forcing us to test
our model through prediction and observation. The
more tests it passes, the greater is our confidence in it.
New technology has made cosmology
one of the most exciting sciences today,
but not all the answers have been found.
Watch the video segment the Gravity and
the Expanding Universe and answer the
following two questions.
1. What does it mean to say that the universe is accelerating?
2. What are the difficulties in studying and understanding the
universe?
Einstein’s Repulsive Idea
The scientific style is dictated by the purpose of the
type of writing. The scientist or engineer will generally
write to describe a phenomenon, an experiment or a
process, or to explain a theory. Hence they belong to the
category called exposition. In this text, the author explains
Einstein’s repulsive idea and its relationship to the latest
research of expanding universe.
Key words in the text
cosmological term
general relativity
gravity and antigravity
supernova
Hubble Space Telescope
Relativity
After all, his special and general
relativity theories made the
astonishing assertion that time,
space and matter could be squeezed
and stretched like so much India
rubber. (Para.1)
Special Relativity
---We cannot catch up with light.
---Mass is a form of energy.
E = m c2
General Relativity
GR encompasses gravity and
describes the expanding universe
and black holes.
Einstein in 1905, at the age of 26
Einstein’s Repulsive Idea
The trouble was that some sort of
antigravity force——Einstein called it the
“cosmological term”—— was required to
make the predictions of general relativity
match what astronomers believed the
actual universe looked like. (Para. 1)
Question: Why did Einstein hypothesize the cosmological constant? Why did he
later discard it?
Einstein’s Repulsive Idea
The great physicist was hugely relieved when the discovery of
the expanding universe in the 1920s let him cross out what he
declared was “my greatest blunder.” (Para. 1)
Question:
1. Why did Einstein call his
cosmological constant his
“greatest blunder”?
2. What is the assumption taken
from Hubble’s discovery
and recent astronomical
data?
Using the Hubble Space Telescope to find and study a
distant supernova, astronomers from two rival research teams
have jointly gathered the strongest evidence yet that the
expansion of the universe is actually speeding up. (Para. 2)
Hubble Space Telescope (HST): the first
general-purpose orbiting observatory,
Named after American astronomer Edwin
P. Hubble. The Hubble Space Telescope
was launched on April 24, 1990.
The first hint came a couple of years ago, when two
independent teams of astronomers tried to calibrate the cosmic
expansion using Type Ia supernovas, a kind of exploding star
whose intrinsic brightness is highly consistent. (Para. 4)
Supernova: a stellar explosion that
produces an extremely bright object made
of plasma that declines to invisibility over
weeks or months.