Transcript Expanding Universe

Expanding Universe
Doppler effect Einstein’s Equation (
Hubble’s law Models of the Universe
Doppler Effect –
ReD ShIfTs
• Doppler effect is the result of sound increasing or decreasing in
pitch as an object moves towards or away form you. (APPLIES
TO ANY WAVES)
• If a light-emitting object is moving away from a person,
each wave of light leaves the object from a point slightly
farther away from the person than the previous wave did.
Therefore, the distance between waves, or wavelength,
that the person sees is longer than it would be if the
object were motionless.
• In visible light, the longest wavelength belongs to red
light, and shortest to the violet light
• most often used by astronomers to measure the velocity
of galaxies.
Vesto Slipher
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First to encounter redshifting galaxies
• Discovered a new cosmic
riddle for astronomers of his
time.
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In 1916, he observed about fifty nearby
galaxies in Lowell Observatory in
Arizona, spreading his light out using
a prism, and recorded the results onto
film
• Almost every object he observed had its
light stretched to redder colors,
indicating essentially everything in the
universe was moving away from earth.
Hi, I’m Vesto
Edwin Hubble
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discovered the existent of other
distant galaxies
In 1929, while working at the Carnegie
Observatories in Pasadena, California, he
measured the red shifts of a number of distant
galaxies and their relative distances
When he plotted the numbers, he discovered,
that the red shift of distant galaxies increased
as a linear function of their distance =
universe expands
Also discovered that the galaxies were
receding from us at a velocity proportional to
their distance.
The more distant the galaxy, the greater its red
shift, and therefore the higher the velocity; this
relationship was known as Hubble’s law.
Hubble’s Law
• is a statement of a direct link between the
distance to a galaxy and its recessional
velocity as determined by the red shift. It
states that the velocity (v) of a galaxy
moving away from Earth is proportional
to the galaxy's distance (d) from Earth.
As distance increases, velocity also
increases. The constant value that
relates velocity and distance is called
Hubble's constant and is usually written
as H0.
Or mathematically like this:
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H0 is the proportionality between recession velocity and distance of a
galaxy = the universes’ rate of expansion
• H0 identified in 1929, but its numeric value is still uncertain.
• Astronomers know that it falls between 50 and 80
kilometers per second-megaparsec. A megaparsec
is a unit of length equal to 1 million parsecs. A
parsec is 30.86 trillion km (19.18 trillion mi).
• These units are used to make redshift calculations
easier.
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Could be represented as 1.5 × 10-15 to 3.1 × 10-15 1/s or
• How do you find the the velocity of moving
galaxies?
Astronomers know the speed of which the
galaxies are moving by their color. As I stated
when something moves toward you very, very
fast, it looks a little bit bluer, and when it
moves away it looks redder. So astronomers
can measure speeds by how red a galaxy
looks.
• How do you find the distance of the moving
galaxy?
You tell me because I already told you the answer.
So what’s my point…
• Hubble’s law could determine the age of our universe, about 12-15 billion
years old because Ho offers the needed information.
• When we know the definite value of the Hubble constant, the
future of the universe could be determined.
• Hubble’s law has an apparent linearity  our universe is
uniformly expanding  no matter which galaxy we are in,
all of the other galaxies are moving away from us  earth is
not the center of the universe and everything else is receding
from us.
• Suggests that the galaxies are not moving away through space, they
are moving away with space.
And again…….
Loser who said the Universe was finite
Heinrich
Olbers
• In the early 1800s, German
astronomer, argued that our
universe were finite.
• He said, “If the universe was finite and
contained starts throughout, then if
you looked in any particular direction,
you line of sight would eventually fall
on the surface of a star. Although the
apparent size of a star in the sky
becomes smaller as the distance to
the star increases, the brightness of
the smaller surface remains a
constant.”
• Therefore, if the universe was infinite, then
the whole surface of the night sky should
be as bright as a star. However, as we know,
the sky has dark areas, proving that it is
finite.
Confused with the IDEA?
Isaac
Newton
• discovery of the law of
gravity
• realized that gravity is
always attractive.
• Every object in the sky
attracts each other If the
universe were finite, the
attractive forces of all the
objects in the universe
should have caused the
entire universe to collapse
on itself.
Albert Einstein
• theory of gravity in the general
theory of relativity
• encountered same as Newton’s
problem
• His equations said the universe
was either expanding or
collapsing.  Created the
My name is Albert!
cosmological constant :
BAD!
• “the greatest blunder of my
life”
But why didn’t the universe collapse like Newton and
Einstein’s equation suggested ?
•Because the universe had
been expanding from the
moment of its creation
and it is in a constant
state of change.
Models of our universe
• Closed (left) – [high mass] a universe that would
eventually stop expanding and re-collapses on itself,
possibly leading to another big bang.
• Flat (center) – [critical mass] a universe which would also
expand forever, but the expansion rate would slow to close
zero after an infinite amount of time .
• Open (right) – [low mass] a universe that will continue
its expansion forever
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The fate of the universes