Download Dark Energy

What can electromagnetic waves tell us
about the movement of planets, stars,
and galaxies?
 What
happens when an object is emitting a
constant frequency sound wave as it moves
towards you?
 What
happens when an object is emitting a
constant frequency sound wave as it moves
away from you?
 What
was this called?
 The
Doppler effect effects electromagnetic
waves just like it effects sound waves.
 We
cannot hear electromagnetic waves, so
we detect the wavelength shift with our eyes
 Blueshift
– If an object is moving towards us,
its light is shifted to shorter wavelengths.
Shorter wavelengths of visible light are bluer.
 Redshift
– If an object is moving away from
us, its light is shifted to longer wavelengths.
Longer wavelengths of visible light are
redder.
 How
could redshift, blueshift effect
spectroscopy?
 What problems can this cause?
 If
we are constantly reflecting light, why
don’t we observe either a blueshift or a
redshift when we move?
 The
speed of light is so much faster than any
movement we make so the Doppler Effect is
negligible.
 What
kinds of shifts do we have for the rest
of the electromagnetic spectrum?
 To
keep everything simple we only use the
terms, “blueshift” and “redshift”.
 What
kind of shift would we observe from
Earth for each moving star?
 Is
it possible for a star or galaxy to have both
a blueshift and a redshift?
 Yes,
 We
if it is rotating!
can tell if a star or galaxy is rotating or
not by looking for a blueshift on one side and
then a redshift on the other.
 We can also calculate the rotation speed of
the object.
 Does
the speed of the electromagnetic wave
change during a Doppler shift? Why or why
not?
 Similar
to how sound waves cannot travel
faster than the speed of sound,
electromagnetic waves cannot travel faster
than the speed of light.
 If
a dust cloud is emitting infrared light as it
is traveling toward Earth is it plausible for us
to see it with our un-aided eye?
 Yes!
 If
a dust cloud is emitting ultraviolet light as
it is traveling toward Earth is it plausible for
us to see it with our un-aided eye?
 No!
 What

is the Big Bang Theory
Not the TV show
 After
the Big Bang the universe has nothing
left to keep making it expand right?
 So
eventually gravity will pull everything
back together and we will have another Big
Bang right?
 Edwin
Hubble was an American astronomer in
the 20th century who observed that distant
galaxies have redshifts.
 He
was able to show that the recessional
velocity of a galaxy increases with its
distance from Earth, implying the universe is
expanding.
 Hubble’s
Law
 So
it is still possible that the universe is
expanding at a decreasing rate so maybe one
day gravity will win and we will have a
second big bang right?
 Nope,
in 1998 observations were made that
suggested that the expansion of the universe
has been accelerating.
 Why?
 We
don’t know.
 Most believe it is because of Dark Energy!
 Dark
Energy: A hypothetical form of energy
that permeates all of space and tends to
accelerate the expansion of the universe.
 In
the current Standard Model of Cosmology
(which explains where everything ever came
from) the universe contains:
 26.8%
Dark Matter
 68.3% Dark Energy
 4.9% Ordinary Matter

We believe that dark energy is scattered evenly
throughout the whole entire universe, even on
Earth.

There is not enough dark energy or dark matter
on Earth for it to be noticed by us, or mess up
anything.

We’ve estimated that we would find just 6 tons
of dark energy within the radius of Pluto’s orbit.

However, it comes to dominate the mass-energy
of the universe because it is uniform across
space.
 Tomorrow
we will review
 What you need to know:








What is the electromagnetic spectrum?
Properties of light
Wave-Particle duality of light
Energy of light
Spectroscopy
Energy Levels and Energy Level Transitions
Find temperature of stars
Doppler Effect and the electromagnetic spectrum