Ch 27 Homework

Match the words in the left-hand column to the appropriate blank in the sentences in the right-hand column. Use each word only once. 1. A __________ predicts that the strong, weak, and electromagnetic forces should become indistinguishable at high temperatures 2. The _______________ is a single force that unifies the electromagnetic and weak forces. 3. _________________ was a dramatic expansion of the universe thought to have occurred when the universe was only a tiny fraction of a second old. 4. __________________ forces us to think about why the sky is dark at night. 5. Observations of the ___________ provide a way to test our theory of the Big Bang. 6. When a particle of ordinary matter meets its precise opposite particle of antimatter, the result is _____________ with complete conversion of mass into energy.

1. grand unified theory 2. electroweak force 3. inflation 4. olbers' paradox 5. cosmic microwave background 6. annihilation

Classify the given types of matter as either baryonic (meaning ordinary matter that contains protons and neutrons) or as nonbaryonic (meaning "extraordinary" matter that consists of more exotic subatomic particles). Drag the appropriate items to their respective bins.

Baryonic matter (contains protons and neutrons) - matter in our bodies - matter in stars - matter in brown dwarfs - dark matter consisting of Jupiter-size objects in galactic halos Nonbaryonic matter - dark matter consisting of weakly interacting subatomic particles - matter that probably makes up the majority of dark matter Feedback: Correct The two main candidates for making up the majority of dark matter are WIMPs (weakly interacting massive particles) and MACHOs (massive compact halo objects). WIMPs are subatomic particles that are not baryons, and hence they are a type of nonbaryonic matter. MACHOs are made of ordinary (baryonic) matter and may include objects including planet-size bodies, brown dwarfs, and small dim stars; they are dark matter only because they are so far away that we cannot detect them. Evidence suggests that while some dark matter is present in MACHOs, the majority of dark matter must be nonbaryonic, which is why most astronomers suspect that most dark matter consists of WIMPs.

Cosmic Evolution Part A The history of the universe can be divided into seven major phases. Taken together, these phases make up the cosmic evolutionary scheme—the continuous transformation of matter and energy that has led to the appearance of life and civilization on Earth. Rank the phases in the history of cosmic evolution from earliest to most recent.

Earliest - particulate - galactic - stellar - planetary - chemical - biological - cultural Most Recent Feedback: Correct Taken together, these phases make up the cosmic evolutionary scheme. Starting with the initial matter and energy, the universe progresses through stages of particulate, galactic, stellar, planetary, chemical, biological, and cultural evolution.

During the history of the universe, what important event occurred about 380,000 years after the Big Bang?

Light began to travel freely through the universe. Feedback: Correct This time when light could first travel freely marks the release of the cosmic microwave background, which we can still observe today.

During the history of the universe, what important event occurred about 0.001 seconds after the Big Bang?

Most matter was annihilated by antimatter. Feedback: Correct Although most matter was annihilated, virtually all antimatter suffered this fate. That is why antimatter has been very rare in the universe ever since that time, which marked the end of what is known as the "particle era."

Which of the following important events occurred earliest in the history of the universe?

Space-time rapidly expanded during a brief period of inflation. Feedback: Correct As you can see in the video, inflation is thought to have occurred when the universe was only a tiny fraction of a second old.

Suppose that, rather than starting with an electron and a positron, the event shown in Figure a started with two electrons. What would happen?

The two electrons would: move away from each other without meeting. Feedback: Correct Particles with the same electrical charge repel each other.

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.

Within the first five minutes - antielectrons (positrons) as common as electrons - inflation occurred - strong force and electroweak force first became distinct - temperature fell to 10^15 K Sometime after the first five minutes - galaxies formed - photons of cosmic microwave background released - stars formed - carbon nuclei formed by fusion

According to our best estimates, the line that best describes the universe in Figure 27.10 in the textbook ("Flatness Problem") is

accelerating.

Which part of the figure shows an example of energy conservation?

both Figures a and b Feedback: Correct The law of conservation of energy tells us that energy must always be conserved, so it is conserved in both annihilation and pair-production events.

Essentially all the hydrogen nuclei that will ever exist in our universe were created __________.

by the time the universe was about 3 minutes old Feedback: Correct Hydrogen nuclei are protons, and protons were formed during the particle era. During the next three minutes, many of these protons fused and then broke back apart, but by the end of that period these reactions stopped. Essentially all the hydrogen that will ever exist was therefore present in the universe when the universe was just 3 minutes old. Subsequent fusion in stars has consumed some of this hydrogen, but it has not made any more.

It is likely that the density of the universe is made up mostly of

dark energy.

The structure we observe in the universe is the result of

dark matter clumping long ago.

Part B Somewhat surprisingly, there is not a single generally accepted definition of life. Depending on the set of criteria used to define life, some generally accepted non-living things might fulfill all of the criteria and be categorized as living. Likewise, some generally accepted living things might fail to meet all of the criteria and be classified as non-living. For example, one working definition of life requires that living things exhibit the following four characteristics. This working definition fits the easy cases of things that are obviously alive, but does not always hold up in all cases. Use these four characteristics as a working definition of life to see which generally accepted living and non-living things from the table would be considered alive based on these characteristics. They can react to their environment and can often heal themselves when damaged. They can grow by taking in nourishment from their surroundings and processing it into energy. They can reproduce, passing along some of their own characteristics to their offspring. They have the capacity for genetic change and can therefore evolve from generation to generation and adapt to a changing environment. From the descriptions and the working definition of life, determine which things do and do not exhibit these characteristics

exhibits the four characteristics - dogs - trees does not exhibit the four characteristics - rocks - stars - viruses Feedback: Correct Somewhat surprisingly, it is very difficult to completely define what it means to be alive. For example, viruses isolated from living organisms are absolutely lifeless, but when placed inside a cell the virus takes on all the properties of life. This difficulty may someday challenge us as we search for life on other planets. Because we only know of life on Earth, our perspective is based on these observations. Thus, if a form of life on another planet did not closely resemble life on Earth, it may be difficult to recognize it as life.

Compared to when the cosmic microwave background was first released, the radiation of the cosmic microwave background today is __________.

fainter and has most of its photons at longer wavelengths Feedback: Correct The universe is expanding and cooling with time, causing the cosmic microwave photons to stretch to longer wavelengths.

In what part of the electromagnetic spectrum does this wavelength lie?

gamma rays or hard X-rays

Of the normal elements around us, the Big Bang produced:

hydrogen and helium.

The horizon problem in the standard Big Bang model is solved by having the universe

inflate rapidly early in its existence.

Concerning dark energy, we do know:

its density remains constant over time, so it is not important in the early Universe.

Which part of the figure shows an example of matter/antimatter annihilation?

only Figure a Feedback: Correct Figure (a) shows a positron and an electron annihilating each other, so that their combined mass is converted into energy in the form of two photons.

About half a million years after the Big Bang, the universe had cooled to the point that

protons and electrons could combine to form atoms.

Matter and energy clumping in the early universe result in

small but observable red shifts.

Present-day Grand Unified Theories unite all of the fundamental forces except

the gravitational force.

The best answer to both the flatness and horizon problems is:

the inflationary epoch.

One of the problems with the standard Big Bang model is that

the temperature is almost exactly the same everywhere.

Elements more massive than lithium were not formed in the early universe because the temperature was

too low.

Immediately after its birth, the universe

was dominated by photons.

At what wavelength did the background radiation peak at the start of the epoch of nucleosynthesis? Express your answer using one significant figure.

λ = 3×10^−9 mm