VIEWS: 12 PAGES: 68 POSTED ON: 2/17/2012
The Universe Origins and Change “If we do discover a unified theory of the universe, it should in time be understandable in broad principle to everyone, not just a few scientists. Then we shall all, philosophers, scientists, and just ordinary people, be able to take part in the discussion of the question of why it is that we and the universe exist. If we find the answer to that, it would be the ultimate triumph of human reason- for then we should know the mind of God”. Stephen Hawking “There is a theory which states that if ever anyone discovers exactly what the Universe is for and why it is here, it will instantly disappear and be replaced by something even more bizarre and inexplicable. There is another theory which states that this has already happened.” - The Hitchhiker's Guide to the Galaxy by Douglas Adams The Big Bang • Current theory of how universe was formed • All matter concentrated in a single point called a singularity • Matter exploded outward • Universe has continued to expand ever since Monsignor Georges Henri Lemaître (July 17, 1894 – June 20, 1966) a Belgian Roman Catholic priest, proposed what became known as the Big Bang theory of the origin of the Universe, which he called his 'hypothesis of the primeval atom‘ in 1927 Big Bang Model Universe expanded from an extremely dense and hot state and continues to expand today Like raisins in a rising loaf of bread The graphic scheme above is an artist's concept illustrating the expansion of a portion of a flat Universe • Expanded from a hot and dense initial condition called the singularity • Approximately 13.7 billion years ago and continues to expand to this day Misconception Revealed • The Big Bang theory cannot and does not provide any explanation for such an initial condition; rather, it describes and explains the general evolution of the Universe since that instant Physical Cosmology PART 1 History •In 1912 Vesto Slipher •measured the first Doppler shift of a spiral galaxy •discovered that almost all such galaxies were receding from Earth. In 1924, Edwin Hubble developed a series of distance indicators, using the 100-inch Hooker telescope at Mount Wilson Observatory. This allowed him to estimate distances to galaxies whose redshifts had already been measured, mostly by Slipher. In 1929, Hubble discovered a correlation between distance and recession velocity—now known as Hubble‘s Law validating Lemaître Big Bang Theory Underlying assumptions • The Big Bang theory depends on two major assumptions: the universality of physical laws, and the Cosmological Principle. The Cosmological Principle states that on large scales the Universe is homogeneous and isotropic. (uniform is all directions) FLRW metric Friedmann–Lemaître–Robertson–Walker • General relativity describes space-time by a metric, measuring distances that separate nearby points (galaxies, stars, or other objects) • A coordinate chart or "grid" is laid down over all space-time Horizons and Big Bang Space-Time An important feature of the Big Bang space-time is the presence of horizons The Universe has a finite age and light travels at a finite speed there may be events in the past whose light has not had time to reach us This places a limit or a past horizon on the most distant objects that can be observed Horizons and Big Bang Space-Time • Conversely, space is expanding and more distant objects are receding more quickly. – light emitted by us today may never "catch up" to very distant objects. – This defines a, future horizon. (limiting the events in the future that we will be able to influence). In general relativity, an event horizon is a boundary in space- time, most often an area surrounding a black hole Doppler Effect • Doppler effect changes the pitch of a sound coming from something moving toward you, or away from you (police siren, an ice cream truck's music, a mosquito buzzing) • Sounds moving toward you are a higher pitch because the sound waves are compressed together, shortening the wavelength • Sounds moving away from you are a lower pitch because the sound waves are stretched apart, lengthening the wavelength • Light behaves in the same way Continuous Spectrum • A rainbow is an example of a continuous spectrum • Most continuous spectra are from hot, dense objects like stars, planets, or moons • The continuous spectrum is also called a thermal spectrum, because hot, dense objects will emit electromagnetic radiation at all wavelengths or colors • Any solid, liquid, and dense (thick) gas at a temperature above absolute zero will produce a thermal spectrum Light Which way the spectral lines are shifted tells you if the object is moving toward or away from you. Blueshift - toward you the waves are compressed, so their wavelength is shorter. Redshift - away from you the waves are stretched out, so their wavelength is longer. • This explanation also works if you are moving and the object is stationary or if both you and the object are moving. The doppler effect will tell you about the relative motion of the object with respect to you. The spectral lines of nearly all of the galaxies in the universe are shifted to the red end of the spectrum. This means that the galaxies are moving away from the Milky Way galaxy and is evidence for the expansion of the universe. • You can also see this effect with the light bulb wired to a dimmer switch. • Dim bulb will have an orange color and as you make it brighter, the bulb will turn yellow and even white. Absorption and Emission http://www.learner.org/teacherslab/science/light/color/spectra/index.html All matter is concentrated in a single space called a singularity. It Proto- explodes galaxies violently outward. As the universe Singularity expands the Explosively gas cools into a expanding cloud. cloud of Sections of the gas cloud collect under the force of gravity and form proto- galaxies. Gases in the proto-galaxies continue to cool and collect as nebula. Inside the nebula stars are born Nebula Proto-star Solar System Galaxy Can You Imagine? • All the material of the universe exploding outward • As it spreads and cools large clouds of gas and dust called nebulae begin to coalesce and cool –We’re talking millions of light years large • As portions of the nebulae came together under the force of gravity, stars were born – Nebular Theory There are billions of galaxies in the universe Galaxies are collections of billions of stars Stars are spinning clouds of gases that radiate electromagnetic energy through a fusion reactions, changing hydrogen into helium Lifecycle of a Star • Stars are born, live and die • How a star dies is determined by its mass – Massive stars (7-10X the mass of our sun) turn into supernova, neutron stars or black holes – Smaller stars cool to become white or brown dwarfs A Star is Born • Nebula - huge clouds of dust and gas in galaxies • Dust and gas collects under the force of gravity • If a critical mass is reached – A fusion reaction occurs – Star is born Background Information • Stars’ sizes from .08 to 120 times the mass of our sun (one solar mass) • For a star to be born the internal temperature must reach about 10 million degrees Kelvin (about 18 million degrees Fahrenheit) • At these temperatures atomic nuclei can be fused - a fusion reaction The Bigger They Are… • The more massive the star the faster the fusion reaction and the more energy emitted • Our sun will take about 10 billion years to fuse its hydrogen to helium • A star three times as massive as our sun can do the same thing in 500 million years because of the higher rate of fusion A Star’s Life • Produce energy through fusion reactions fusing hydrogen to helium • Force of fusion reaction pushes out against the pull of gravity • The balance between these forces determines the size of the star • As the star fuses all its hydrogen the push of the fusion reaction decreases and the pull of gravity takes over Gravity Fusion Gravity Solar Collapse • The star lacking the push of the fusion reaction collapses in on itself • As the core collapses it generates intense pressure and heat, the outer gases expand and the star becomes a red giant • All stars are born as proto-stars, fuse hydrogen to helium until the hydrogen runs out, suffer core collapse and become red giants • At this point what happens depends on the mass of the star Stars Like Our Sun • Fuse hydrogen to helium • When the majority of hydrogen is used up the core begins to collapse • There is not enough mass for the core to reach the 100 million degrees K needed to start fusing helium to carbon • There is enough pressure to cause the remaining hydrogen in the outer shell to start a fusion reaction Stars Like Our Sun • The outer shell expands to become a red giant • When that hydrogen is fused, the star fizzles out and becomes a white dwarf Massive Stars • If it is massive enough, it will build up enough pressure and temperature during the collapse to start a fusion reaction turning helium into carbon in the core • In the outer shell the remaining hydrogen will fuse to helium • Very massive stars can have fusion occurring in several shells Massive Stars • For stars of less than 8 solar masses this is the end. They can not generate the heat and pressure required to fuse carbon • Fusion stops and they fizzle into white dwarfs Shell Fusion • Stars larger than 8 solar masses are big enough to fuse carbon to oxygen in the core • While that is happening the temperatures outside the core are hot enough to fuse helium to carbon • In the next layer up hydrogen is being fused to helium The process continues • With each successive conversion the core collapses further into itself and becomes hotter eventually reaching 3 trillion degrees K when the core fuses from silicon to iron • At each stage new shells form and convert the lighter elements • Hydrogen fused to helium becomes helium fused to carbon, to oxygen, to silicon ….. Supernova • The giant star now resembles an onion with a core at 3 trillion degrees K and multiple fusing shells • The iron core absorbs energy as other elements fuse to it instead of emitting it • The iron core collapses and becomes so dense protons and electrons fuse to become neutrons Supernova • The by-product of this process are neutrinos • The core continues to collapse until the neutrons become so dense they begin to repel each other • The core rebounds violently outward • The rebound of the core and the neutrinos push the outer shells out explosively Supernova • The explosive force of the supernova last only seconds • The added energy of the neutrinos causes fusion of heavier elements in the ejected shells • The core collapses again to become a neutron star • The shell, a nebula to start the process again A neutron star's magnetic fields radiate as rings of energy, and accelerated beams of gamma rays stream out from the star's pole. Supernova • The explosive force of a supernova is equal to 10 trillion, trillion atomic bombs • That’s 10,000,000,000,000,000,000,000,000 Neutron Stars Returning to the neutron core left over from our supernova Ifit is less than 3 solar masses the force inward of gravity and the force outward of the neutrons balance each other It becomes a stable neutron star Black Holes Ifthe mass of the neutron star is greater than 3 solar masses the force of the neutron repulsion cannot overcome the force of gravity and the core continues to collapse The core becomes denser and smaller until it creates a black hole Newton vs. Einstein Newton believed gravity was caused by the attraction of all objects to each other It’s a great theory and it works well on earth, but unfortunately it runs into some problems in space If gravity only attract object to each other why hasn’t the moon crashed into the Earth or the Earth into the Sun? Einstein Einstein solved that one by saying that space and time are like a fabric Massive objects warp the fabric Smaller objects travel in straight lines around that warp Think of a large rubber sheet. Now put a bowling ball on it. It creates a warp in the sheet. Absent of friction you could roll a marble in a straight line and it would orbit around the bowling ball Back to Black Holes If you put a shot put on the sheet instead of the bowling ball the warp would be sharper and deeper In theory neutron stars do the same thing to the fabric of space-time They are so small and so dense that a teaspoon would weigh as much as 3000 aircraft carriers or 290 million tons Black Holes Because they are super dense neutron stars, they exert enormous gravitational force The force is so strong it pulls other matter and objects into itself getting more dense and of greater mass all the time It continues to sink deeper into the fabric of space and time Black Holes At some point it becomes so massive that not even light can escape its gravitational attraction With no emissions escaping there is nothing for us to detect, hence a black hole We believe we can detect black holes by their event horizon as matter accelerates towards the hole Planets Remnants of supernovae are rich in heavier elements necessary to life Matter drifts free of a core and eventually begin to cool and collect Eventually they clump together and begin to collapse again forming new stars and planets Planets are nebular material not massive enough to start a fusion reaction Organization of the Universe Think concentric circles Satellites orbit around planets Planets orbit around stars Stars orbit around the center of a galaxy Galaxies are zooming through space in an expanding universe Satellites Satellites are natural or man made objects that orbit around planets Our moon is a natural satellite There are thousands of man made satellites orbiting the earth transmitting radio waves for cell phones, pagers, televisions etc. The space shuttle and space station are satellites Solar Systems As satellites orbit around planets; planets, asteroids and comets orbit around stars The collection of objects that orbit around a star is called a solar system Galaxies Galaxies are collections of billions of stars which orbit around the center of the galaxy Galaxies are huge Our galaxy The Milky Way is 120,000 Light Years across There are billions of galaxies in the Universe The Universe EVOLUTION OF A THEORY Geocentric Universe Since the time humans walked the earth and became aware they observed a constant pattern of the sun, moon and stars rising in the eastern sky and setting in the west. Since they had no perception of moving it was only reasonable to believe all these objects revolved around the earth Ptolemy Greek astronomer Ptolemy developed a model for a geocentric universe in about 140 AD That model was the standard until the 1600s Heliocentric Universe Ptolemy’s model had only one problem To make the model work the planets had to occasionally make small backward circles to adjust their orbit These are know as retrograde motion Polish astronomer Copernicus proposed a heliocentric model in the 1600s This model worked without the retrograde Kepler The heliocentric model still possessed some irregularities, it didn’t work mathematically Kepler inherited 20 years of very accurate observations made by Tycho Brahe, a Danish noble Kepler studied planetary movement mathematically Kepler’s Laws Kepler found that the planets traveled in elliptical not circular orbits (1st) Each planet covered and equal area in equal time, i.e. did not travel at the same speed (2nd) The period squared of the planet is equal to the cube of its distance from the sun (3rd) Galileo and Newton Galileo used the telescope he invented to observe the planets. His observations confirmed the heliocentric model Newton provided the why with his Laws of Gravitation And so the universe stood until the 1900s The Speed of Light Einstein calculated the speed of light at 186,000 miles per second (300,000kmps) His theories state that nothing can travel faster than the speed of light Distances in space are so vast they are measured by the distance light will travel in a year or a light year Aliens Let us suppose there is other intelligent life in our galaxy. The Milky Way is 120,000 light years across The next closest star (potential solar system) is 4.5 light years away. If we send out a radio signal how long will it take to reach the closest star and a response to get back? To the other side of the galaxy?
Pages to are hidden for
"The Universe The"Please download to view full document