Astronomy Chapter 27

Which of the following statements about quantum tunneling is not true?

Although it has been observed to occur, it violates all other known laws of nature and explaining it therefore represents a major challenge to physicists.

What else always happens when an electron is produced from energy in a particle accelerator?

An antielectron (positron) is also produced.

Which statement about antimatter is not true?

Antimatter has been hypothesized to exist but has never actually been detected.

Why is there a limit to how much compression can be counterbalances b electron degeneracy pressure?

At extreme compression, the electron speeds approach the speed of light and therefore cannot increase further.

How does degeneracy pressure differ from thermal pressure?

Degeneracy pressure continues to be felt even if an object becomes very cold, but thermal pressure is drastically reduced as an object gets cold.

Affects only electrically charged particles

Electromagnetism

Transmitted by photons

Electromagnetism

Uh oh, the malicious eight-dimensional beings are back. This time, imagine that they suddenly changed nature so neither the uncertainty principle nor the exclusion principle applied to electrons. What would happen almost immediately to atoms?

Electrons would fall into the nuclei of atoms.

Governs large-scale structure of the universe

Gravity

Weakest force (across short distances)

Gravity

Following are the four fundamental forces. Rank these forces from left to right based on their relative strengths between two protons located within the nucleus of an atom, from weakest to strongest.

Gravity; weak; electromagnetism; strong

According to the uncertainty principle, which of the following statements are true?

It is impossible to measure both the position and the momentum of a particle at the same time.

What do we mean by the spin of a subatomic particle?

It is one of the basic properties of any particle, and is a measure of the particle's angular momentum.

How is quantum tunneling important to our existence here on Earth?

It plays a crucial role in nuclear fusion in the Sun, so that our Sun would not shine brightly without it.

Does the uncertainty principle affect our ability to follow the path of a baseball? Why or why not?

No, because the uncertainties in the position and momentum of the baseball are so small in comparison to its size and total momentum that they are unnoticeable.

Which of the following best explains the hypothesized phenomenon of black hole evaporation?

Particles (or anti-particles) are created by a quantum mechanical effect near, but outside, the event horizon of a black hole. The law of conservation of energy maintains that the black hole must lose energy to "pay" for the creation of this mass.

Given that many of the ideas of quantum mechanics seem so strange to our intuition, why do scientists think these ideas are correct?

Quantum ideas can be used to make precise predictions that have been tested and confirmed through observations and experiments.

Holds nuclei together

Strong force

Transmitted by gluons

Strong force

Suppose that, through the malicious act of an eight-dimensional alien being, the strong force was suddenly turned off throughout the universe. What would happen almost immediately to atoms?

The nuclei of atoms would fall apart.

The force of gravity is only one of the four forces felt on very large size scales. Which of the following best explains why the other forces don't play a major role on large scales?

The strong and weak forces act only on very small scales, and large objects tend to be electrically neutral and therefore don't feel and electromagnetic force.

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.

Which of the following statements about electrons is not true?

They are composed of quarks.

All the following statements are true. Which one can be attributed to the exclusion principle?

Two electrons within the same spin cannot occupy the same energy level in an atom.

What does the exclusion principle say?

Two fermions cannot occupy the same quantum state at the same time.

Following are the four fundamental forces. Rank these forces from left to right based on their relative strengths between two protons separated by a few centimeters, from weakest to strongest. If you think two (or more) forces have equal strength (or essentially zero strength) in this case, show the equality by dragging one on top of the other(s).

Weak and Strong (on top of each other) are weakest, then Gravity, then Electromagnetism (strongest)

Following are the four fundamental forces. Rank these forces from left to right based on their relative strengths acting between Earth and the Sun, from weakest to strongest. If you think two (or more) forces have equal strength (or essentially zero strength) in this case, show the equality by dragging one on top of the other(s).

Weak and Strong (on top of each other) are weakest; then Electromagnetism, then Gravity (strongest)

Governs nuclear fission and radioactive decay

Weak force

What is Hawking radiation?

a hypothesized way for black holes to gradually shrink in mass.

An alternative statement of the uncertainty principle tells us that we cannot know precisely both____

a particle's energy and the time during which it has this energy

Which of the following is not considered a fundamental particle?

a proton

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

both figures A and B

Degeneracy pressure occurs as a result of a combination of the uncertainty principle and the exclusion principle. This pressure play an important role in the astronomical objects known as __________.

brown dwarfs, white dwarfs, and neutron stars

The idea that space can contain virtual particles has been verified in laboratory experiments. In astronomy, this idea is used to predict that black holes __________ .

can "evaporate" over time, even though nothing escapes from inside a black hole's event horizon

The primary scientific purpose of a particle accelerator is to

create particles and study their behavior

Brown dwarfs do not collapse due to ____

electron degeneracy pressure

The ___ is consistent with the notion that two electrons cannot exist in the same place at the same time.

exclusion principle

Based on their spin, all particles fall into one of the following categories.

fermions and bosons

Neutron stars do not collapse into black hole because they are supported against the crush of gravity by _____

neutron degeneracy pressure

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

only figure A

The location, momentum, and spin of a proton are part of what we call the proton's ____

quantum state

Hydrogen nuclei in the core of the Sun do not seem to be moving fast enough to overcome the electromagnetic force of repulsion, but they nevertheless can fuse together thanks to the process we call ____

quantum tunneling

The four fundamental forces are:

strong force, weak force, electromagnetism, gravity

What is the primary topic of study in quantum mechanics?

subatomic particles and the forces with which they interact

Which of the following is not one of the basic properties by which we classify a subatomic particle?

temperature

Quantum tunneling (such as an electron being able to "tunnel" from one place to another without crossing the space in between) sounds almost too strange to be true, but in fact it is a well-tested process that turns out to be important both in our everyday lives and in astronomy. For example, quantum tunneling is important in our everyday lives in __________, and it is important in astronomy in explaining __________.

the operation of electronic devices such as computers / nuclear fusion in the Sun

What are the two fundamental laws that lie at the heart of quantum mechanics?

the uncertainty principle and the exclusion principle

A balloon filled with air does not collapse due to ____

thermal pressure

According to modern understanding, protons and neutrons are each composed of

three quarks

Knowing both the exact position and velocity of an electron simultaneously is a violation of the ____

uncertainty principle

Recall that an up quark (u) has a charge of +2/3 and a down quark (d) has a charge of -1/3. Which of the following quark compositions describes a proton?

uud