Complete each of the following sentences about the early universe. Drag words from the left to complete the sentences on the right.
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-Most of the helium in the universe formed during the ERA OF NUCLEOSYNTHESIS.
-The GUT ERA refers to a time period in which the strong, weak, and electromagnetic forces were all unified.
-The PLANCK ERA refers to a time period in which all four forces are thought to have been unified.
-The COSMIC MICROWAVE BACKGROUND is our name for the photons we see that were first released when the universe was about 380,000 years old.
-The BIG BANG is the name we give to the moment when the expansion of the universe began.
-A very short period of extremely rapid expansion, called INFLATION, is thought to have occurred when the universe was about 10^-38 second old.
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Which of the following represent observations or measurements that have confirmed key predictions of the Big Bang model? Select all that apply.
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-Characteristics of the cosmic microwave background.
-The abundance of helium in the universe.
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Which of the following offers at least some evidence that inflation really occurred in the early universe?
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Measurements of brightness variations in the cosmic microwave background.
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Shown following are several times in the history of the universe. Rank these times from left to right based on the average temperature of the universe at each time, from coolest to hottest.
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Coolest -> Hottest
-Today
-1.5 billion years after the Big Bang
-100 million years after the Big Bang
-1 million years after the Big Bang
-500,000 years after the Big Bang
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Shown following are several times in the history of the universe. Rank these times from left to right based on the peak wavelength in the spectrum of the cosmic microwave background, from shortest to longest.
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Shortest -> Longest
-500,000 years after the Big Bang
-1 million years after the Big Bang
-100 million years after the Big Bang
-1.5 billion years after the Big Bang
-Today
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Shown following are several times in the history of the universe. Imagine that you were able to watch a single photon that has been part of the cosmic microwave background since it first became present in the universe. Rank these times from left to right based on the wavelength this photon would have at each time, from shortest to longest.
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Shortest -> Longest
-500,000 years after the Big Bang
-1 million years after the Big Bang
-100 million years after the Big Bang
-1.5 billion years after the Big Bang
-Today
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During the history of the universe, what important event occurred about 0.001 seconds after the Big Bang?
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Most matter was annihilated by antimatter.
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Which of the following important events occurred earliest in the history of the universe?
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Space-time rapidly expanded during a brief period of inflation.
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During the history of the universe, what important event occurred about 380,000 years after the Big Bang?
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Light began to travel freely through the universe.
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Essentially all the hydrogen nuclei that will ever exist in our universe were created ___________.
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by the time the universe was about 3 minutes old
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Compared to when the cosmic microwave background was first released, the radiation of the cosmic microwave background today is ____________.
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fainter and has most of its photons at longer wavelengths
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Although we can divide the history of the universe into many distinct "eras", sometimes it's useful just to have a broad perspective on what events occurred in the very early universe and what events occurred later. Listed following are events that occurred either before or after the first five minutes in the history of the universe. Match these events to the appropriate time period.
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Before the First 5 Minutes:
-Inflation occurred
-Strong force and electroweak force first became distinct
-Antielectrons (positrons) as common as electrons
-Temperature fell to 10^15 K
After the First 5 Minutes:
-Stars formed
-Galaxies formed
-Photons of cosmic microwave background released
-Carbon nuclei formed by fusion
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Shown following are the names of several eras that are used to describe the history of the universe. Rank the eras from left to right in the order in which they occurred, from first to last.
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First -> Last
-Planck Era
-GUT Era
-Electroweak Era
-Particle Era
-Era of Nucleosynthesis
-Era of Nuclei
-Era of Atoms
-Era of Galaxies
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Shown following are the same eras shown in Part A. Rank the eras from left to right based on the temperature of the universe during each one, from coolest to hottest.
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Coolest -> Hottest
-Era of Galaxies
-Era of Atoms
-Era of Nuclei
-Era of Nucleosynthesis
-Particle Era
-Electroweak Era
-GUT Era
-Planck Era
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Shown following are the same eras shown in Part A and B. Rank the eras from left to right based on the size of the observable universe during each one, from smallest to largest.
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Smallest -> Largest
-Planck Era
-GUT Era
-Electroweak Era
-Particle Era
-Era of Nucleosynthesis
-Era of Nuclei
-Era of Atoms
-Era of Galaxies
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Classify each statement below as an observation or as an inference based on the current Big Bang model. (Note that the helium abundance is defined as the mass of helium relative to the mass of hydrogen.)
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Observations:
-Large-scale structure looks about the same in all directions.
-The helium abundance is at least 25% in every galaxy studied so far.
-The temperature of the cosmic microwave background varies slightly with direction.
-The cosmic microwave background temperature is 2.73 K.
Inferences:
-The cosmic microwave background is radiation left over from the Big Bang.
- Large-scale structure grew around density variations present in the early universe.
-Fusion during the universe's first five minutes produced 75% hydrogen and 25% helium (by mass).
-Photons of the cosmic microwave background have traveled through space for almost 14 billion years.
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Consider this statement from Part A: "Photons of the cosmic microwave background have traveled through space for almost 14 billion years." This statement follows from our model of the Big Bang, because the Big Bang model is based on the idea that ____________.
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the universe began very hot and dense and has been cooling as it expands
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One of the inferred statements from Part A is that "Large-scale structure grew around density variations present in the early universe." Observational evidence that such density variations really existed comes from the fact the cosmic microwave background exhibits ___________.
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tiny temperature variations in different directions
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The Big Bang theory is closely linked to Hubble's discovery that the universe is expanding, which seems to imply that there was a time in the past when the expansion first began. Nevertheless, the Big Bang theory did not gain widespread acceptance among scientists until the 1960s. Why wasn't expansion alone enough to convince scientists that the Big Bang really happened?
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Although expansion seems to imply a Big Bang, no other specific predictions of the Big Bang theory were tested and confirmed until the 1960s.
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Today, most scientists accept the Big Bang theory because its predictions agree so well with observations. But a scientific theory can always be revised or discarded if future observations do not agree with its predictions. Consider the following hypothetical future observations. Which one(s) would be inconsistent with the Big Bang theory? Check all that apply.
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-Astronomers discover distant protogalactic clouds with a helium abundance below 20%.
-Careful studies of quasar spectra show that, 12 billion years ago, the temperature of the cosmic microwave background is actually 2.71 K rather than 2.73 K.
-Over the next 10 years, the temperature of the cosmic microwave background falls to 1 K.
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The horizontal axis of the graph measures the time since the Big Bang in seconds. The extreme left of the horizontal axis, where it meets the vertical axis, is labeled 10^-45 seconds (that is a decimal point followed by 44 zeroes and then a one). If we move along two tick marks to the right on the horizontal axis, it is labeled 10^-35 seconds. By what factor does the time increase from one tick mark on the horizontal axis to the next tick mark toward the right?
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1 x 10^5
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The vertical axis of the graph measures the temperature of the universe in kelvin. If we move up one tick mark to the next, by what factor does the temperature increase?
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100
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In basic terms, what does the graph show?
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The universe is getting cooler with time.
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To get your bearings on the horizontal time axis of this plot, it is useful to calculate the age of the universe in seconds today. If you multiply the age of the universe in years by the number of seconds in a year, approximately what is the current age of the universe in seconds?
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4 x 10^17 s
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Suppose you want to know what the temperature of the universe was 1 billion years ago. Where along the horizontal axis should you look?
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Almost all the way to the far right
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What was the approximate temperature of the universe when the universe was just 1 second old?
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10^10 K
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From Part C, you know that in basic terms, the graph shows that the temperature of the universe decreases with time. In more specific terms, this graph shows that the temperature of the universe ____________.
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fell very rapidly when the universe was young, but is changing very gradually today.
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What kind of particle does the Large Hadron Collider accelerate?
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Protons
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The Large Hardon Collider set a new world record in December, 2009. What was the record for?
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The highest ever kinetic energy of a proton colliding in a human-made particle accelerator.
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What famous (or infamous) United States collider, set to be built in Texas, was cancelled in 1993?
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Superconducting Super Collider
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Which of the following accelerators held the record for the highest energy collisions before the Large Hardon Collider broke it?
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The Tevatron at Fermilab
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The Large Hardon Collider is designed to reach high energies. The results of this experiment are relevant to which of the following astrophysical situations?
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The universe in its first trillionth of a second after the Big Bang.
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According to the article, the scientific impact of the Large Hadron Collider can be summarized by which of the following statements?
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Unknown. It will not explore truly new territory until it has been verified at lower energies for the first few years of use.
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What was the approximate temperature of the universe at an age of 10^15 s?
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About 100 K
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What was the approximate temperature of the universe at an age of 5 minutes?
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About 10^9 K
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How much cooler is the universe now (at an age of 4 x10^17s) than it was at an age of 1 second?
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Its current temperature is one ten-billionth (10^-10) the temperature at an age of 1 second.
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The charge of an antiproton is
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negative
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When a proton and an antiproton collide, they
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convert into two photons.
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The current temperature of the universe as a whole is
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A few K
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When the universe was 380,000 years old, its thermal radiation spectrum consisted mostly of
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Visible and infrared photons
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Which of the following does not provide strong evidence for the Big Bang theory?
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Observations of the amount of hydrogen in the universe
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Which of the following does inflation help to explain?
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The uniformity of the cosmic microwave background
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Which of the following does inflation help to explain?
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The origin of galaxies
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Which of these pieces of evidence supports the idea that inflation really happened?
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Observations of the cosmic microwave background that indicate a flat geometry for the universe.
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What is the earliest time in the universe that we can directly observe?
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A few hundred thousand years after the Big Bang.
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Which of the following best explains why the night sky is dark?
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The observable universe is not infinite.
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What will the temperature of the cosmic microwave background be when the average distances between galaxies are twice as large as they are today? (Hint: The peak wavelength of photons in the background will then also be twice as large as it is today.)
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1.4 K
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Using the inverse square law for light, determine the apparent brightness of the Sun in our sky. Express your answer using two significant figures.
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1350 W/m^2
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Using the inverse square law for light, determine the apparent brightness our Sun would have if it were at a distance of 15 billion light-years. Express your answer using two significant figures.
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1.5 x 10^-27
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From your answers to parts A and B, estimate how many stars like the Sun would need to exist at a distance of 15 billion light years for their total apparent brightness to equal that of our Sun. Express your answer using two significant figures.
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9.0 x 10^29
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Compare your answer to part C with the estimate of the total number of stars in our observable universe. Use your answer to explain why the night sky is much darker than the daytime sky. How much larger would the total number of stars need to be for "night" to be as bright as day?
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We estimated the number of stars in the observable universe to be around 10^(22), so we would need many times more stars than we have in the observable universe to make the night sky as bright as day. This explains why the night sky is dark and why even a finite number of stars would make the sky as bright as the Sun (and life as we know it impossible).
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