sample questions to be asked on the largest scales
Sample questions will be asked on the intermediate scale.
Sample questions can be asked on the smallest scales.
They are exciting.
There is a lot of mystery, adventure, and discovery.
The fact that the answer always leads to a new question makes the satisfaction of finding the answer greater.
The picture of nature becomes more complete, yet it still retains its mystery and awe.
There is a beautiful view of physics.
Nature seems to be clever in its rules.
We are looking at the basic structure of matter, energy, space, and time and wondering about the scope of the universe, its beginnings and future.
You are in a great position to explore the forefronts of physics, both the new discoveries and the unanswered questions.
With the concepts, qualitative and quantitative, the problem-solving skills, the feeling for connections among topics, and all the rest you have mastered, you can more deeply appreciate and enjoy the brief treatments that follow.
You will enjoy the quest for a long time to come.
When you are away from city lights, look at the sky.
There is a faint glowing background of millions of stars.
The word "galaxias" means "Milky Way" in Greek and has been used since ancient times to refer to the arm of our galaxy of stars.
We know a lot about the billions of other galaxies beyond our own.
There are many unanswered questions.
The explanation of the universe's character and evolution are tied to the very small scale when viewed on a large scale.
The answers to questions about the very small scales may also be found in the answers to questions about the very large scales.
The Hubble Space Telescope photographed these clusters of galaxies.
There are trillions of stars linked by gravity, glowing with light and showing evidence of undiscovered matter.
The motion of the moon and planets can be explained by the nature of gravity on Earth.
The chemistry of substances is explained by minute atoms and molecule.
The hot interior of the Earth is explained by the decays of tiny nuclei.
The energy of stars is explained by the fusion of nuclei.
The evolution and character of the universe seem to be explained by the patterns in particle physics.
The nature of the universe has implications for unexplored regions of particle physics.
The observable part of the universe has about a dozen or so galaxies.
Our galaxy is larger than average, both in its number of stars and its dimensions.
Ours has a diameter of 100,000 light years and a thickness of 2000 light years in the arms with a bulge of 10,000 light years across.
The center of the sun is near the galactic plane.
There are clouds of gas and a halo of stars around the main body.
There is strong evidence that there is a large amount of additional matter in the universe that does not produce light.
The size, shape, and presence of gas and dust are typical of large spiral galaxies.
We are fortunate to be in a place where we can see out of the stars and see the larger universe around us.
Light years measure the distance traveled by light in one year.
The Magellanic Clouds are close to our own, some 160,000 light years away.
Ours is 2 million light years away from the Andromeda galaxy.
It is visible to the naked eye because of the extended glow in the Andromeda constellation.
We can see individual stars with our larger telescopes in the close proximity of the largest galaxy in our local group.
It is 14 billion light years away from Earth.
Young and emerging stars can be seen in the blue regions, while dark streaks of gas and dust can be seen in the dark regions.
A small satellite galaxy is visible.
It is in an older part of the universe.
The light we receive from these vast distances has been on its way to us for a long time.
The time in years is the same as the distance in light years.
The light that is reaching us left the Andromeda galaxy 2 million years ago.
Andromeda would be different if we could be there now.
14 billion years ago, light from the most distant galaxy left it.
We have a great view of the past.
We can try to see if the universe was different if there was an evolution in time.
Our data has great uncertainties.
We must be especially cautious in drawing conclusions because of the large uncertainties in astronomy.
There are many competing theories because there are more questions than answers.
Any hard data can produce a big result.
The hallmark of a field in its golden age is the discovery of some importance on a regular basis.
All of the universe seems to be moving away from us at the same rate as we are.
The conclusion is based on the work of Hubble.
In the 1920s, Hubble showed that other galaxies were outside of our own.
The wavelength is stretched from the source to the observer.
The red shift is doubled if the distance is doubled.
The red shift is not a Doppler shift because space is expanding.
There isn't a center of expansion in the universe.
The other objects in space seem to be moving away from the stationary observers.
Hubble was responsible for discovering that the universe was much larger than previously thought, and that it had a characteristic of rapid expansion.
Universal expansion on the scale of galactic clusters is an important part of modern cosmology.
The expansion is uniform for galaxies farther away than 50 Mly.
The Hubble constant is a central concept.
All but the closest galaxies have an average behavior.
There can be variations in this speed due to local motions.
The last calculation assumes the expansion rate was the same 5 billion years ago.
The Hubble measurement changed the idea that the universe is unchanging.
There is a linear relationship between the red shift and distance for the galaxies, with larger red shifts at greater distances implying an expanding universe.
The value of the expansion rate is given by the slope.
The discovery that the expansion of the universe may be faster than in the past is one of the most intriguing developments.
Various groups have been looking at supernovas in moderately distant galaxies to get better distance measurement.
The observed red shifts suggest that the expansion was slower than expected.
The consequences of this are discussed in Dark Matter and Closure.
The first results were published in 1999 and are the beginning of emerging data.
The recession of the universe looks like the remnants of a big explosion.
All matter would have been at a point between 13 and 15 billion years ago.
Immediately, questions arise.
Galaxies are flying apart from one another, with the more distant moving faster as if a primordial explosion ejected the matter from which they formed.
The speed of light relative to us is what the most distant galaxies move at.
The remnants of the primordial fireball should be visible and blackbody radiation should be present if there was a Big bang.
The radiation from this fireball has traveled to us since the Big bang.
It will look like the fireball has cooled over time.
Blackbody radiation from the explosion should have a temperature of about 7 K and a peak intensity in the microwave part of the spectrum.
The radiation was detected by Arno Penzias and Robert Wilson, two American scientists working with Bell Telephone Laboratories on a low-noise radio antenna.
The spectrum of this microwave radiation is shown in Figure 34.7(b).
The temperature of the fireball remnant is determined from the blackbody spectrum.
Wilson and Penzias won a prize for their discovery.
10 to 20 billion years ago, there was an explosion.
The remnants of the primordial fireball form galaxies after expanding and cooling.
It is a temperature of 2.725 K, which is the expansion-cooled temperature of the Big Bang's remnant.
The radiation can be measured from any direction in space.
It is compelling evidence that the universe was created in a huge explosion.
There are many connections between physics on the largest scale and particle physics on the smallest scale.
The dominance of matter over antimatter, the perfect homogeneity of the microwave background, and the existence of galaxies are among these.
We know that antimatter is rare.
The Earth and the solar system are not made of any other substance.
The landing of the Viking probes on Mars would have been spectacular if Mars were antimatter.
Most of the universe is dominated by matter.
The relative absence of 0.511-MeV rays created by the mutual annihilation of electrons and positrons is proof of this.
It was possible that there could be entire solar systems made of antimatter in perfect symmetry with our systems.
Matter and antimatter can be brought together in large amounts.
In nature, antimatter is created in particle collisions and in decays, but only in small amounts that quickly destroy.
Particle physics is related to matter and antimatter.
The answer is that particle physics is not perfect.
The decay of one of the neutral -mesons creates more matter than antimatter.
There is a small asymmetry in the basic forces.
The early universe produced slightly more matter than antimatter.
The stars and galaxies we see today are formed by nearly pure matter if there was only one part in more matter.
The vast number of stars we see may be a small remnant of the original matter.
There is a real and important asymmetry in nature.
Most physicists are impressed by how small it is.
The mutual annihilation would be more complete if the universe were completely symmetric.
There is a troubling aspect of microwave background radiation.
The Big bang was verified, the temperature was correct, and the blackbody spectrum was expected.
The CMBR looked the same in every direction.
The existence of fluctuations in the primordial stages of the universe means there should be hot and cool spots in the CMBR, which correspond to dense and sparse regions of gas caused by turbulence or early fluctuations.
The galaxies formed a long time ago because they were observed very far from us.
The problem was to explain how the universe formed so quickly if the remnant fingerprints were smooth.
The answer is that if you look closely, the CMBR is very smooth.
A satellite called the Cosmic Background Explorer carried an instrument that made very sensitive and accurate measurements.
In April of 1992, there was a lot of publicity about COBE's first results.
NASA's WMAP was launched in 2001 and was used to carry out further measurements.
WMAP provided a more detailed picture of the fluctuations.
The temperature fluctuations are better than one part in 1000.
The WMAP experiment will be followed up by the European Space Agency.
The map of the sky uses color to show fluctuations in the microwave background.
For clarity, the Milky Way has been removed.
Blue is lower in temperature and density than red.
The fluctuations are small, less than one part in 1000, but they are still thought to be the cause of the formation of galaxies.
There are many orders of magnitude in time, energy, temperature, and size of the universe.
The two lines approach but do not cross.
They stay indefinitely in ever-smaller time intervals.
Particle physics at the earliest stages of the universe's evolution are tied to the laws of physics.
The universe is not static.
The unification of forces at high energies may be verified by their shaping of the universe and its evolution.
If expansion stopped and gravity pulled the galaxies together, all matter would be compressed and heated.
The density and temperature were too high for stars.
There was a time when the temperature was too hot for atoms.
There was a time when the temperature and density were so high that no nuclei could exist.
The temperature was so high that it was possible to create short-lived particles, and the density was high enough to make this possible.
This is a time after the big bang.
It is not close to the instant of creation.
The unification of forces is tied to important stages before this time.
The average particle separations were smaller than we could achieve with accelerators at those stages.
What happened in the early stages is crucial to all later stages and may be seen by observing current conditions in the universe.
The smoothness of the CMBR is one of these.
Key conditions are represented by the names given to early stages.
The strong force is expected to be the same as the electroweak force at energies of about.
If there are no surprises in the unknown physics at energies above 1 TeV, the average particle energy would be great.
Imagine starting at TOE and moving forward in time to see what type of universe is created from various events along the way.
The universe reaches the stage where average particle separations are large enough to see differences between strong and weak forces when temperatures and average energies decrease.
The forces are no longer unified or symmetric after this time.