Accelerated expansion of universe and evolving ideas about gravity
Accelerated Expansion of the Universe,
Changing Ideas about GRAVITY itself!
Is the discovery of dark energy a turning point in Physics?
Grade 11 Physics
By Michael Marty
•appreciate the controversy surrounding the accelerating
universe and dark energy (The Lambda-CDM Model)
An artists interpretation of the Cold Dark Matter Model of big bang cosmology model
(Lambda-CDM,) attempts to illustrate the accelerated expansion.
What is Gravity and how does it Work?
•Sir Isaac Newton in 1665
revolutionized our model of
how the Universe works!
•Newton’s Law of Universal
Gravitation unified the rules
that govern the Heavens
and The Earth.
•Objects (including Apples)
fall to Earth and the Moon
moves around the Earth
because of the same force
that he called Gravity.
Newton’s equation of Gravity ( ) defines
the strength of gravity but not why gravity works!
"Revolution in Science – New Theory of the
Universe – Newtonian Ideas Overthrown“
Reference: The Times of London: headline, 7 November 1919
Einstein’s Theory of
explains how gravity
works: curving of the
fabric of space-time
causes gravity. General
developed into an
essential tool in
General Relativity indicates that gravity
can bend the space-time of the Universe
Introduction of the Cosmological Constant
needed for a Static Universe
•Albert Einstein believed the Universe had a
constant size and was therefore static. But
something was needed to "hold back gravity“!
•He introduced the Cosmological Constant
(denoted as the Greek capital letter lambda ’Λ’),
which gives the vacuum of empty space an
energy density value.
•Lambda Λ was necessary for the theory of
General Relativity to achieved a
Edwin Hubble Proved the Universe is
not Static: The Universe is Expanding!
• Red shifts from all
galaxies prove that there is
an increasing recessional
velocity as the distance
from Earth increases.
• Hubble’s Law is another
turning point in Physics
• Einstein abandoned the
idea of a static universe,
calling it his "greatest
The Big Bang
Expansion/Contraction of the Universe
• The Big Bang provides the
energy for the expansion.
• Gravity and matter
counteract the energy of the
• If the density of the universe
is sufficient, expansion
should turn into a
• The cosmological constant
must have a value of zero.
• The Big Bang is the model
from 1929 to 1998.
Type 1a Supernovae as Standard Candles
• All Type 1a Supernovae originate
from a neutron star, binary system,
that explodes after growing to the
same critical mass and same
thermo-nuclear fusion reaction.
• All reach the same peak value of
absolute brightness with absolute
• Can be uses as standard candles
because they all emit the same
Power = σAT4 ,where A = 4πR2
• Can be used to calculate distance
by comparing Absolute Magnitude
to Apparent Magnitude received at
Measurements in 1990’s extended
Hubble’s data and found something new!
Red Shift of Type 1a Supernovae
• Far distant supernovae
had a smaller red shift
than would be expected.
• These galaxies had been
moving slower in the past.
• Hubble Space telescope
was looking back in time
• These measurements
show the Universe has an
• Something (dark energy)
had to provide the vacuum
energy needed for this
The 2011 Nobel Prize in Physics
• Two Scientific teams (UC Berkeley and MIT) find
the same astonishing results.
• The Expansion of the Universe is Accelerating!
• Saul Perlmutter, Brian Schmidt and Adam Riess
What is causing the Accelerated Expansion?
• Because there is a force
overpowering gravity, then
constant” may be correct!
• The cosmological constant
idea is one possible way to
explain the acceleration.
• A name is needed for
scientists to talk about what
might be causing this cosmic
• Dark Energy is an other
means of explaining the
A new model of the Universe proposed in 1998
to explain the cause of this expansion
• Mass-energy of universe
must include 68% more
energy, the so called Dark
Energy as well as 27% more
mass called Dark Matter!
• The current standard model
of cosmology known as the
• Cold Dark Matter keeps the
galaxies together and is
balanced by the Dark Energy
required to accelerate the
Calculations need both
Dark Energy and Dark Matter
• If the Big Bang made
everything in the universe,
there needs to be
something more than just
protons, neutrons, or
• Gravitational attraction of
matter can only partially
balance the vacuum energy
of Dark Energy.
• There needs to be CDM
to keep galaxies together.
• We call this unseen
material Cold Dark Matter!
What do we know about Cold Dark Matter?
• CDM can not absorb or emit
light like ordinary matter.
• CDM is has to exist because
of its effect on gravity. (If
there was no dark matter the
galaxies would fly apart)
• CDM could be sub atomic
particles discovered through
• These are called WIMPS
(Weakly Interacting Massive
Particles) Cold Dark Matter Simulation. Image by: Gregory Bryan and Michael
Norman/National Center for Supercomputing Applications
What is the source of the energy for
the accelerating universe?
• Students should know that dark energy is a
hypothetical form of energy causing the
acceleration of the expansion of the universe.
• Dark energy amounts to about 70% of the total
mass-energy of the universe.
• What are the consequences if they can find
proof of the existence of dark energy?
• Is there a new way to incorporate ideas of
quantum mechanics into the theory of gravity?
Will theories of Dark Energy change our ideas?
•Is there really a Quantum Vacuum Energy or a maybe
some “particle” that could constantly come in and out
of existence to generate energy density needed?
•Can measurements of this energy resolve questions in
both quantum mechanics and the accelerated expansion
of the universe is in terms of general relativity?
•Can the new model called Lambda-CDM bridge the two
great pillars of modern physics:
Quantum Mechanics and General Relativity?
Three possible explanations of Dark Energy
1. “Empty space” has its own energy. As the universe
expands, more space comes into existence, and more of
this energy-of-space would appear. The Cosmological
Constant is reborn!
2. “Empty space" is actually full of temporary, "virtual
particles” that continually form and then disappear.
3. “Empty space" has a new kind of dynamical field or
energy fluid. The effect this “field” has on the expansion
of the Universe is opposite to the effect of matter and
normal energy. This idea is called "quintessence" .
Or maybe Einstein’s Theory of General
Relative needs to be adjusted with
new ideas of Gravity?
References from Course Plan:
• article on expanding universe
• long video of Adam Riess’s lecture at MIT on dark energy and the
• Dark Energy, Accelerated Expansion, and Energy Conservation: Does it all
• The Concept of Dark Energy; Dark energy, dark matter, and the cosmological
References for this PPt:
• DARK ENERGY, DARK MATTER FROM NASA ASTROPHYSICS:
• Dark Matter, Dark Energy, and the Expansion of the Universe By Michael Howard
• Expanding Universe
• General relativity & Gravity
• Gravitation and the General Theory of Relativity:
• The Hubble Deep Field
• Multiverse Controversy Heats Up over Gravitational Waves