Question 1

What is the central idea in relativity concerning the speed of light? Describe at least two unusual consequences of this idea.

Accepted Answer

The central idea is that the speed of light in a vacuum will be the same for all observers,regardless of their relative motion with respect to one another.Some consequences are that moving clocks will run slower,that moving masses will be larger,and that distances will be shorter in the moving frame.

Question 2

According to Einstein's relativity,which two quantities are different manifestations of the same thing?

Accepted Answer

A) mass and gravity 
B) light and energy 
C) energy and mass 
D) temperature and energy 
E) distance and time 
A) mass and gravity 
B) light and energy 
C) energy and mass 
D) temperature and energy 
E) distance and time C

Question 3

What are gravitational waves? Have they been detected?

Accepted Answer

Gravitational waves are ripples in spacetime that occur when a massive object undergoes acceleration.They have not yet been detected,but there are ongoing experiments such as the Laser Interferometer Gravitational-Wave Observatory (LIGO)that are attempting to find them.

Question 4

In the rubber-sheet analogy for spacetime,what would you expect for objects (such as golf balls)rolling around in the presence of a massive object that is stretching the rubber sheet?

Accepted Answer

A) Their paths would be straight if they were moving slowly enough. 
B) Their paths would curve more the closer they come to the massive object. 
C) Their paths would curve by the same amount no matter how close they come to the mass. 
D) Their paths would curve towards the mass if they passed close,but bend away from the mass if they passed far from the mass. 
E) Their paths would curve less the closer they come to the massive object. 
A) Their paths would be straight if they were moving slowly enough. 
B) Their paths would curve more the closer they come to the massive object. 
C) Their paths would curve by the same amount no matter how close they come to the mass. 
D) Their paths would curve towards the mass if they passed close,but bend away from the mass if they passed far from the mass. 
E) Their paths would curve less the closer they come to the massive object.

Question 5

Explain why Einstein's theory of general relativity predicts the existence of gravitational lensing.

Accepted Answer

Einstein's theory of general relativity

Question 6

A geodesic is the name for:

Accepted Answer

A) the aberration of starlight 
B) the gravitational field of the Earth 
C) the solid crust of a terrestrial planet 
D) the path followed by a freely-falling object in spacetime 
E) the shape of a body that has mass 
A) the aberration of starlight 
B) the gravitational field of the Earth 
C) the solid crust of a terrestrial planet 
D) the path followed by a freely-falling object in spacetime 
E) the shape of a body that has mass

Question 7

If the Sun were to be instantly replaced by a 1M⨀ black hole,the gravitational pull of the black hole on Earth would be:

Accepted Answer

A) much greater than it is now 
B) the same as it is now 
C) much smaller than it is now 
D) larger or smaller,depending on the location of the Moon 
E) irrelevant because Earth would be quickly fall into the Sun and be destroyed 
A) much greater than it is now 
B) the same as it is now 
C) much smaller than it is now 
D) larger or smaller,depending on the location of the Moon 
E) irrelevant because Earth would be quickly fall into the Sun and be destroyed

Question 8

Hawking radiation is emitted by a black hole when:

Accepted Answer

A) the black hole rotates quickly 
B) the black hole accretes material 
C) a supernova explodes and forms a black hole out of its core 
D) synchrotron radiation is emitted by infalling charged particles 
E) a virtual pair of particles is created from the vacuum of space 
A) the black hole rotates quickly 
B) the black hole accretes material 
C) a supernova explodes and forms a black hole out of its core 
D) synchrotron radiation is emitted by infalling charged particles 
E) a virtual pair of particles is created from the vacuum of space

Question 9

How might we be able to detect events like colliding neutron stars even if we don't detect any light from them?

Accepted Answer

One way to detect such an event would be

Question 10

The principle of equivalence states that the gravitational mass is equal to:

Accepted Answer

A) the mass when moving nearly the speed of light 
B) the resistance to acceleration 
C) the mass when near a black hole 
D) the object's weight 
E) the density divided by the volume 
A) the mass when moving nearly the speed of light 
B) the resistance to acceleration 
C) the mass when near a black hole 
D) the object's weight 
E) the density divided by the volume

Question 11

The gravitational redshift of light should be smallest for light emitted from the surface of:

Accepted Answer

A) a black hole 
B) the Sun 
C) a white dwarf 
D) a planet like the Earth 
E) a neutron star 
A) a black hole 
B) the Sun 
C) a white dwarf 
D) a planet like the Earth 
E) a neutron star

Question 12

You have a 1 kg mass at rest sitting on a lab bench in front of you.You see somebody fly by in a spaceship traveling at 0.2c.That astronaut flying by also has a 1 kg mass sitting on a bench in front of her.She would measure that mass to be 1kg.

Accepted Answer

A) True 
 B)False

Question 13

How fast must a muon be moving if it looks to an observer at rest that it lived for 2 × 10−4 seconds before it decayed when,in fact,it lived for only 2 × 10−6 seconds in its moving reference frame?

Accepted Answer

A) 0.05c 
B) 0.50c 
C) 0.95c 
D) 0.995c 
E) 0.99995c 
A) 0.05c 
B) 0.50c 
C) 0.95c 
D) 0.995c 
E) 0.99995c

Question 14

General relativity predicts that pairs of objects with nonzero masses undergoing accelerations can produce:

Accepted Answer

A) pulses of electromagnetic radiation 
B) gravitational waves 
C) high-energy particles 
D) a slowing of clocks here on the Earth 
E) redshifted light from the surface of the object 
A) pulses of electromagnetic radiation 
B) gravitational waves 
C) high-energy particles 
D) a slowing of clocks here on the Earth 
E) redshifted light from the surface of the object

Question 15

The singularity of a black hole has an infinitely small radius,but its event horizon is finite.

Accepted Answer

A) True 
 B)False

Question 16

Suppose you detect a pulsar that gives us 1,000 radio pulses per second,but the pulsar is in a distant galaxy that is apparently moving away from us at 50 percent of the speed of light.An observer at rest with respect to the pulsar in that faraway galaxy would measure a pulse rate of:

Accepted Answer

A) 870 per second 
B) 1,150 per second 
C) 1,250 per second 
D) 1,366 per second 
E) 1,450 per second 
A) 870 per second 
B) 1,150 per second 
C) 1,250 per second 
D) 1,366 per second 
E) 1,450 per second

Question 17

What is the "rubber sheet" analogy for spacetime,and why is it useful for explaining gravity and gravitational waves?

Accepted Answer

Spacetime can be thought of conceptually

Question 18

Has relatively ever been tested?

Accepted Answer

A) No,because it would require us to set up physics experiments in faraway galaxies. 
B) Yes,because even ordinary motion in automobiles and airplanes produces easily noticeable effects predicted by relativity. 
C) No,because no one has been able to think of experiments that are able to measure the small differences between the predictions of Newtonian physics and relativity. 
D) Yes,because (for example)subatomic particles can be accelerated to speeds approaching that of light. 
E) No,because the theory of relativity contains paradoxes and contradictions,like the twin paradox. 
A) No,because it would require us to set up physics experiments in faraway galaxies. 
B) Yes,because even ordinary motion in automobiles and airplanes produces easily noticeable effects predicted by relativity. 
C) No,because no one has been able to think of experiments that are able to measure the small differences between the predictions of Newtonian physics and relativity. 
D) Yes,because (for example)subatomic particles can be accelerated to speeds approaching that of light. 
E) No,because the theory of relativity contains paradoxes and contradictions,like the twin paradox.

Question 19

Galileo supposedly experimented with gravity by dropping two objects of different masses from the leaning tower of Pisa at the same instant and observing that they hit the ground at the same time.If Albert Einstein had done the experiment,how would his conclusion have differed from Galileo's?

Accepted Answer

Galileo would say that the acceleration

Question 20

While traveling the galaxy in a spacecraft,you and a colleague set out to investigate a 10M⨀ black hole.Your colleague hops aboard an escape pod and drops into a circular orbit around the black hole maintaining a distance of 50 km from it,while you remain much farther away inside the spacecraft.After doing some experiments to measure the strength of gravity,your colleague signals the results back to you using a green laser.What would you see,and why?

Accepted Answer

What you see depends on where your colle

Exam 18: Relativity and Black Holes

What is the central idea in relativity concerning the speed of light? Describe at least two unusual consequences of this idea.

According to Einstein's relativity,which two quantities are different manifestations of the same thing?

What are gravitational waves? Have they been detected?

In the rubber-sheet analogy for spacetime,what would you expect for objects (such as golf balls)rolling around in the presence of a massive object that is stretching the rubber sheet?

Explain why Einstein's theory of general relativity predicts the existence of gravitational lensing.

A geodesic is the name for:

If the Sun were to be instantly replaced by a 1M⨀ black hole,the gravitational pull of the black hole on Earth would be:

Hawking radiation is emitted by a black hole when:

How might we be able to detect events like colliding neutron stars even if we don't detect any light from them?

The principle of equivalence states that the gravitational mass is equal to:

The gravitational redshift of light should be smallest for light emitted from the surface of:

You have a 1 kg mass at rest sitting on a lab bench in front of you.You see somebody fly by in a spaceship traveling at 0.2c.That astronaut flying by also has a 1 kg mass sitting on a bench in front of her.She would measure that mass to be 1kg.

How fast must a muon be moving if it looks to an observer at rest that it lived for 2 × 10−4 seconds before it decayed when,in fact,it lived for only 2 × 10−6 seconds in its moving reference frame?

General relativity predicts that pairs of objects with nonzero masses undergoing accelerations can produce:

The singularity of a black hole has an infinitely small radius,but its event horizon is finite.

Suppose you detect a pulsar that gives us 1,000 radio pulses per second,but the pulsar is in a distant galaxy that is apparently moving away from us at 50 percent of the speed of light.An observer at rest with respect to the pulsar in that faraway galaxy would measure a pulse rate of:

What is the "rubber sheet" analogy for spacetime,and why is it useful for explaining gravity and gravitational waves?

Has relatively ever been tested?

Galileo supposedly experimented with gravity by dropping two objects of different masses from the leaning tower of Pisa at the same instant and observing that they hit the ground at the same time.If Albert Einstein had done the experiment,how would his conclusion have differed from Galileo's?

Why Learn Astronomy

Patterns in the Skymotions of Earth

Motion of Astronomical Bodies

Gravity and Orbits

Light

The Tools of the Astronomer

The Birth and Evolution of Planetary Systems

The Terrestrial Planets and Earths Moon

Atmospheres of the Terrestrial Planets

Worlds of Gas and Liquid the Giant Planets

Planetary Adornments Moons and Rings

Dwarf Planets and Small Solar System Bodies

Taking the Measure of Stars

Our Starthe Sun

Star Formation and the Interstellar Medium

Evolution of Low-Mass Stars

Evolution of High-Mass Stars

The Expanding Universe

Galaxies

The Milky Waya Normal Spiral Galaxy

Modern Cosmology

Large-Scale Structure in the Universe

Life

Filters

If the Sun were to be instantly replaced by a 1M_⨀ black hole,the gravitational pull of the black hole on Earth would be:

How fast must a muon be moving if it looks to an observer at rest that it lived for 2 × 10⁻⁴ seconds before it decayed when,in fact,it lived for only 2 × 10⁻⁶ seconds in its moving reference frame?