Accelerated Expansion of the Universe, Changing Ideas about GRAVITY itself!

Is the discovery of dark energy a turning point in Physics?

NIS, TaldykorganGrade 11 PhysicsBy Michael Marty

Objective:•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 General Relativity explains how gravity works: curving of the fabric of space-time causes gravity. General Relativity has developed into an essential tool in modern astrophysics.

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

Static Universe.

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 blunder“!

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 Big Bang.

•If the density of the universe is sufficient, expansion should turn into a contraction.

•The cosmological constant must have a value of zero.

•The Big Bang is the model from 1929 to 1998.

Critical Density and Size of Universe

Models for Contracting, Expanding or Accelerating?

Hubble Space Telescope and The Deep Field Project provide data from VERY far away galaxies!

Galaxies with Type 1a Supernovae

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 magnitude -19.3.•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 Earth.

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 accelerated expansion!

•Something (dark energy) had to provide the vacuum energy needed for this acceleration!

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 Einstein’s “cosmological 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 acceleration.•Dark Energy is an other means of explaining the observed acceleration.

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 Lambda-CDM model. •Cold Dark Matter keeps the galaxies together and is balanced by the Dark Energy required to accelerate the measured expansion.

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 electrons.

•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 Quantum Mechanics. •These are called WIMPS (Weakly Interacting Massive Particles)

Cold Dark Matter Simulation. Image by: Gregory Bryan and Michael Norman/National Center for Supercomputing Applications https://www.nsf.gov/about/history/nsf0050/astronomy/darkmatterpic.htm

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 Energy1.“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• www.bbc.co.uk/news/science-environment-15165371• http://www.nytimes.com/2011/10/07/opinion/the-universe-dark-energy-and-us.

html• long video of Adam Riess’s lecture at MIT on dark energy and the accelerating

universe• http://video.mit.edu/watch/a-brief-history-of-dark-energy-and-the-accelerating-

universe-8525/

• Dark Energy, Accelerated Expansion, and Energy Conservation: Does it all make sense?

• http://scienceblogs.com/startswithabang/2011/12/02/dark-energy-accelerated-expans/

• The Concept of Dark Energy; Dark energy, dark matter, and the cosmological constant

• http://www.learner.org/courses/physics/unit/text.html?unit=11&secNum=6

References for this PPt:

• DARK ENERGY, DARK MATTER FROM NASA ASTROPHYSICS:• http://science.nasa.gov/astrophysics/focus-areas/what-is-dark-energy/• Dark Matter, Dark Energy, and the Expansion of the Universe By Michael Howard• https://www.google.kz/search?q=Talk2DarkMatterEnergy&oq=Talk2DarkMatterEnergy&a

qs=chrome..69i57.1575j0j8&sourceid=chrome&es_sm=122&ie=UTF-8#

• Expanding Universe• http://hyperphysics.phy-astr.gsu.edu/hbase/astro/hubble.html• General relativity & Gravity• http://www.youtube.com/watch?v=0rocNtnD-yI • Gravitation and the General Theory of Relativity:• http://csep10.phys.utk.edu/astr162/lect/cosmology/gravity.html • The Hubble Deep Field• http://www.stsci.edu/ftp/science/hdf/hdf.html • Multiverse Controversy Heats Up over Gravitational Waves• http://www.scientificamerican.com/article/multiverse-controversy-inflation-gravitational-w

aves/