CH18 Cosmology
Slighter shorter wavelengths mean it is going to be
slightly warmer.
What is Olber's paradox?
the argument that the darkness of the night sky conflicts with the assumption of an infinite and eternal static universe
Because the early photons are redshifted,
the energy they have is decreasing. So the universe is cooling as it expands
The universe has now been compressed into a single point of infinite density, the
the primordial singularity.
It is fascinating to ponder the fact that because light travels at a finite speed, we see distant stars, not as they are now, but the way they were when their light first started on its journey to Earth.
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The detection of the cosmic microwave background is the principal reason why the Big Bang is accepted by astronomers as the correct cosmological theory.
---- Today the presence of this universal background of microwave radiation convinces most scientists that the universe not only had a beginning but also that it began in the gigantic explosion that we call the "Big Bang."
Astronomers calculate that the entire milky way is moving relative to the cosmos at a rate of what?
600km/s - some 1.3 million mi/h
What was the universe like according to Aristotle?
the universe that is infinite in extent. The universe is eternal. It has always been there. Without beginning and end.
The issue as that the original Big Bang Theory did not what?
did not require space to be isotropic - aftere accounting for Earth's motion through the cosmos, the temp. in one direction could have been many degreees, different in temp. than any other direction but it is not.
Rather than expanding into preexisting spacetime, the Big Bang explosion created spacetime, and that spacetime
has expanded ever since. In this sense, the Big Bang led to the formation of all spacetime, matter, and energy.
Early universe was filled with what?
high-energy electromagnetic radiation.
In 1948, Gamow and his colleagues Ralph Alpher and Robert Herman argued that if indeed the Big Bang hypothesis is correct, then in order to produce a universe of the phenomenal mass and energy that we see today,
it must have started in a state of incredibly high density and temperature!
What is the oscillating universe idea?
What makes it attractive, in the view of some, is that requires NO BEGINNING. Perhaps we are not surprised to learn that science popularizer Carl Sagan was among those in favor of this hypothesis. -- Recently, however, it has been demonstrated that even if the universe contains enough mass so that its gravity eventually halts the present expansion and forces a collapse, the collapse will not produce a bounce. (It really does not look right now as if there is enough mass). Because of the huge entropy generated by the universe, any ultimate collapse would be more like a "Big Crunch" than a "Big Bounce." The universe, it seems, either will go through only one cycle of expansion and contraction, or, it will expand forever.
number of galaxies remain constant with respect to
With respect to both distance and direction.
18-4 Remnants of the Big Bang have been detected.
[In 1927, the Belgian astrophysicist and Catholic priest Georges Lemaitre proposed that, as a consequence of the equations of Einstein's theory of general relativity, the universe is expanding.]
Hubble discovered what kind of relationship between the distaances to galaxies in other superclusters and the redshift of those galaxies' spectral lines
a LINEAR relation between the distaances to galaxies in other superclusters and the redshift of those galaxies' spectral lines
As we move towards Leo, our motion through the cosmic microwave background radiation creates what?
a normal Doppler shift that causes photons from that direction to appear to have shorter wavelegnths - radiaiton from the direction of Leo is blue shifted, wheereas radition from from the opposite direction Aquarius is redshifted, because we are moving away from that spot.
Ancient radiation has the spectrum of a blackbody with a temperature of 2.73
--- This is known as 3 degree background radiation. 2006 noble peace prize for John C mather and George F Foot.
18-2 The expansion of the universe creates a dopplerlike redshift
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Hubble's work proved conclusively that many of the objects referred to earlier as nebulae in fact represent instead "island universes" - new galaxies within the universe.
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Based on the Hubble Law, we can calculate the recessional velocities for galaxies anywhere in the universe. Let's say that we have discovered a heretofore unknown galaxy at a distance of 500 Mpc. The graph predicts that its velocity must be around 30,000 - 35,000 km/sec (roughly 80,000,000 miles/hour, an enormous speed compared to the Earth's relatively "leisurely" 67,000 mph in its orbit around the Sun, or the Sun's speed of 515,000 mph with which it revolves around the center of the Milky Way).
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18-1 General Relativity predicts an expanding [or contracting] universe
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18-3 The Hubble constant is related to the age of the universe
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This means that the galaxies probably moved at GREATER speeds in the PAST than our estimate above allows for. This implies in turn that the universe must be YOUNGER than it would seem to be according to our "back-of-the-envelope" analysis. On the other hand, many astronomers argue - based on their methods for the measurement of galactic distances - that the value of the Hubble constant is considerably smaller than the 65 km/s/Mpc (which we assumed in our calculation). And, more recently, there's even talk about evidence for a cosmic repulsion that would accelerate (rather than slow down) the motion of galaxies. Clearly, the final chapter on this issue is yet to be written, but, perhaps our estimate is close to the middle of the range of ages of the universe.
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Einstein's theory of special relativity forever shattered this old belief in the absolute nature of space and time.
According to Einstein, the distances between objects and the lengths of bodies will have different values for different observers (observers that are moving with respect to each other). ---------------------------- Similarly, the rate at which time elapses and the duration of processes depends on the RELATIVE motion of the observer. Also, two physical events that appear to happen simultaneously according to one observer, may happen at different times for another observer. Finally, energy and mass are equivalent, and their relationship is mathematically expressed by the celebrated formula E = mc2.
The universe consists of what?
All matter, energy, and spacetime that we can ever detect or that we will ever be able to affect us.
Ralph Apher and George Gamow proposed that a fraction of a second after the Big Bang, the universe was what?
An incredibly hot blackbody.
When Einstein attempted to apply this complicated equation to a simple model of the universe, a model that was meant to describe the cosmos as a whole, he realized - to his dismay - that it lead to a solution that appeared to be unstable! --> It appeared to produce a universe that either had to contract or expand. Now Einstein was really worried! General relativity theory, in his opinion, appeared to fail since it would not produce a static and eternally unchanging universe (which was, of course, the prevailing prejudice of all astronomers at that time). This situation proved immensely disturbing to Einstein who firmly believed in traditional cosmology.
Consequently, in order to force his theory to produce the desired static universe, he introduced the now famous "cosmological CONSTANT" into his equations. The effect of this artificial "fudge factor" was to produce a certain cosmic pressure which COUNTERACTED the attractive gravitational force among stars and galaxies, thereby creating a static universe.
What is the proper name for the redshift that Edwin Hubble observed?
Cosmological Redshift In other words, the photons that we observe from galaxies in other super clusters are all redshifted because space is expanding. - The resulting expansion, stretches the photon's waves. - The longer the photon's journey, the more its wavelength is stretched by the expansion of the universe.
Arno Penzias and Robert Wilson were known for what?
Discoverers of the Cosmic Microwave Background
Who is credited with discovering that we live in an expanding universe?
Edwin Hubble
What is the cosmological constant?
Einstein adjusted his equation to a static cosmos, he did this by adding a repulsive, outward pushing term, called the cosmological constant. Einstein later said that this was the biggest blunder of his career. Concept itself may be correct.
The radiation generated from the remnants of energy from the Big Bang create what
It creates radiation. This radiation is called the Cosmic Microwave Background because the peak of its blackbody spectrum should lie in the microwave part of the radio spectrum.
What is cosmology?
It is the study of the large-scale structure and evolution of the universe.
The raison bread model suggests what about the expansion of the universe?
It slowly enlarges in size. Distances between raisons become greater. The yeast in the dough begins to work the bread loaf expands. At the same time, the raisins within the dough get carried along. When viewed from the position of any one of the raisins, all of the other raisins appear to be moving away from it. The reason for this is NOT a movement of the raisins through the dough, but rather their being carried along by the expanding bread.
Newton's Universe:
Newton argued that the fixed stars in the heavens are evidence for an unchanging and unending universe. Since only in the case of a uniform and infinite cosmos the gravitational pull exerted on the stars is equal in all directions, allowing the observed overall distribution and static order of the cosmos to be maintained. Newton believed that our universe is infinitely old and that it would continue to exist without any significant large-scale changes in its structure - in its present physical state - forever.
Isotropy is not limited to what?
Not limited to the blackbody radiation observed throughout the universe.
18-5 The universe has two symmetries-isotropy and homogeneity.
Observations reveal the cosmic microwave background is almost perfectly isotropic: Its intensity is nearly the same in every direction in thee sky.
One of the reasons for the differences of temperature is caused by what?
One difference is caused by our motion through the cosmic microwave background.
Life and Death of Stars
Other evidence of a beginning comes from the chemical composition of stars. By studying the spectral composition of light emitted by stars, astronomers have learned that stars consist mainly of hydrogen, the lightest of all elements. We now know, furthermore, that hydrogen is used up in fusion processes during a star's "life-time." Within the nuclear furnace at the center of the star, hydrogen is continuously converted into helium and other heavier elements. Just as a campfire converts wood to ash and then dies out when the wood has been consumed, so stars move toward extinction as they use up their hydrogen fuel. The largest stars end that process in a catastrophic explosion called a supernova, which scatters into space the heavier elements produced inside the star. Evidently, the planets of our solar system were formed from such debris, which is why astronomers have spoken of the Earth as made of the ashes of stars. (You and I are made of stardust!) Because the change from hydrogen to heavier elements is irreversible, the amount of hydrogen in the universe is constantly decreasing. The universe thus resembles a clock that is running down. The universe must have started some finite time ago. If the universe was indeed infinitely old, there would be no twinkling stars around at this time!
Modern Science says that
Our universe cannot be eternal; it must have had a beginning! Modern astronomy indeed confirms that the universe is not infinitely old.
What else was discovered as a result of the Big Bang Theory?
Photons and neutrinos. Several million neutrinos pass through our body each day.
What was Allan Sandage's contributions?
Precision measurements of distances in the universe, ,and the determination of the Hubble constant. Discovery of the optical counterparts of quasars.
How can we determine the age of the universe?
Since Hubble's Law states that each galaxy's speed is proportional to its distance from us, it follows that the age of our universe is given by the INVERSE of the Hubble constant. Assuming a reasonable average value of Hubble's constant of around 65 km/s/Mpc we obtain an estimate of the universe's age of around 15 billion years!
The large redshifts of the spiral nebulae - that is, the large shifts of certain spectral components toward the red or long wavelength end of the visible spectrum - indicated to Slipher that they must be moving away from us at enormous speeds.
So the redshift of the galaxies could be interpreted as caused by the MOTION of galaxies through space, or in terms of the STRETCHING of photons in an expanding universe. The latter option is the one we choose since it is consistent with our overarching theoretical understanding of the nature of our cosmos.
Because of uniformity with distance, we can say what?
That the universe is homogenous.
A redshift of clusters and superclusters mean what?
That they appear to be shifting away from us.
A photon's wavelegnth determines its what?
The amount of energy is directly proportional to the photon's electromagnetic frequency and thus, equivalently, is inversely proportional to the wavelength. The higher the photon's frequency, the higher its energy. Equivalently, the longer the photon's wavelength, the lower its energy.
Photographs of five elliptical elliptical galaxies all taken at the same magnification. The spectrum of each galaxy is the hazy band between the comparison spectra at top & bottom of each plate. The recessional recessional velocity, calculated from the Doppler Doppler shifted shifted H and K lines, appears below each spectrum.
The fainter & more distant the galaxy, the greater its redshift! galaxy, the greater its redshift!
What is the steady state theory? [Fred Hoyle, the British mathematician, physicist, and astronomer, was the first to use the now familiar expression "Big Bang." Hoyle meant it as a derogatory term since, in his opinion, the notion of an actual cosmic beginning is completely unsatisfactory.]
The steady-state theory is a view that the universe is ALWAYS expanding but maintaining a CONSTANT AVERAGE density, matter being continuously created to form new stars and galaxies at the same rate that old ones become unobservable as a consequence of their increasing distance and velocity of recession. ----- As the galaxies are moving apart, new matter in the form of hydrogen atoms and neutrons was conjectured to come into existence out of a mysterious c-field (c for creation).
Our universe is not just expanding, it is accelerating outward. What are the implications of this?
There must be an outward pressure that more than counter acts the effect of normal gravitation.
Hubble's law gives us a way to estimate the age of the universe.
Time since the Big Bang = Separation distance / recessional velocity ------ Recall that Hubble found the relationship Recessional velocity = Ho * separation distance which we can rewrite as Ho = recessional velocity / separation distance. Hubble's constant is the reciprocal of the time since the universe began. Using a hubble constant of 71.1 km/s/Mpc = 13.77 billion years. [SEE TEXtbook for more information]
How did he propose the universe began?
Universe began as an extremely hot and dense primordial atom of energy. [The primordial energy created at the beginning of time caused the universe to expand]. This is called the Big Bang.
