Astronomy: Chapter 11

Question 1

Describe the three main effects of traveling near the speed of light, according to Einstein’s Special Theory of Relativity.

Answer 1

• Time slows down when objects move quickly.
• —- time is relative, so it depends on where you are.
• —- the faster you move, the slower time moves.
• —- It is different to each observer.
• Mass Increases: It becomes harder and harder to accelerate past the speed of light.
• —- Length Contracts or Decreases: It will appear to shrink in its direction of motion becoming more and more distorted as it travels faster.
• Spaghettification: concept that the force of gravity is greater on an astronauts feet than on its head. the difference will lengthen him, eventually pulling him apart.

these events happen to every object, but they become more noticeable when they approach near the speed of light.

Question 2

Describe the effects of mass in space according to Einstein’s General Theory of Relativity.

Answer 2

• Gravitational Time Dilation: Explains how gravity affect the rate of time.
• —- A person on a high spot of a mountain will have a faster time on their clock than a person closer to the floor.
• —- Clocks run slower in regions of lower gravitational potential.
• Gravitational lensing: Describes how rays of light bend in a gravitational field.
• —- The presence of matter can curve Space-time and the path of the lights will be deflected as a result.
• Gravitational Redshift: Occurs when photons travel (away) through space-time.
• —- The universe expands quicker than the speed of light.
• mass warps space-time
• time slows down near mass

Question 3

Relate the story of the discovery of the microwave background radiation, including the roles of Gamow, Dicke, Penzias and Wilson.

Answer 3

• in the mid-1960s, two Bell laboratories physicists, Arno Penzias and Robert Wilson, were measuring the radio brightness of the sky when they discovered peculiar radio noise coming from all directions.
• In the 1940s, physicists George Gamow and Ralph Alpher had predicted that the big bang would have emitted blackbody radiation that should now be in the far-infrared and radio parts of the spectrum.
• In the early 1960s, physicists Robert Dicke and his team at Princeton began building a receiver to detect radiation.
• when Penzias and Wilson learned about the preceding work, they realized that the radio noise they had detected, now called the Cosmic Microwave Background (CMB), is actually radiation from the big bang. they received the 1978 Nobel Prize in physics for their discovery.

Question 4

What causes “gravitational lensing”? Describe some actual examples, as seen in Hubble photographs.

Answer 4

A gravitational lens is formed when the light from a very distant, bright source (such as a quasar) is “bent” around a massive object “such as a massive galaxy” between the source object and observer.

The most unique feature in a image taken with the NASA Hubble telescope is a group of five quasar images produced by a process called gravitational lending, in which the gravitational field of a massive object - in this case, a quasar - farther behind it.

Question 5

Discuss the possible different “shapes” of space-time and how they relate to the possible ways the universe could come to an end.

Answer 5

• Open Model: Space and time expand to infinity. There is a negative curvature and it is saddle shaped.
• Flat Model: expands forever to a limi and not to critical density. (Infinite) d=dc
• Closed Model: There is a collapse and a positive curvature is formed. collapse/contracts (finite) d>dc

In the near future, the universe can contract in what we call, a “ Big Crunch” only if the density is greater than the critical density.

Question 6

Briefly relate the early history of the universe, starting from 10^-40 second.

Answer 6

• 10^ -43 seconds: Big Bang happened. High temperature ad inflation state.
• 10^ -10 seconds: In a “blink of an eye”, particles were formed.
• 0.003 seconds: protons, neutrons, electrons were formed.
• 3 minutes: hydrogen and helium nuclei; proton- proton chain.
• 300,000 years: atoms and plasma were formed.
• 1 billion year: Stars and galaxies.
• Now: Humans observe the cosmos.

Question 7

Compare the Big Bang with the Steady State theory and discuss the observational evidence for the Big Bang.

Answer 7

•Steady State theory

   - New particles fill in space of the expanding galaxy. 
   - Universe looks the same. 
   - No beginning… no end…

• Big Bang theory
-Hubble discovered the redshift, or initial high density and high temperature state.
Redshift is proportional to its distance.
-Galaxies move or recede from each other since they have no center.
- the universe is constantly expanding, pushing galaxies further apart as it does.

Question 8

What is meant by “inflation”, and what problems does it solve in the Big Bang theory?

Answer 8

Inflation: an incredible burst of expansion

• The Flatness Problem:
  Imagine living on the surface of a soccer ball (a 2-dimensional world). It might be obvious to you that this surface was curved and that you were living in a closed universe. However, if that ball expanded to the size of the Earth, it would appear flat to you, even though it is still a sphere on larger scales. Now imagine increasing the size of that ball to astronomical scales. To you, it would appear to be flat as far as you could see, even though it might have been very curved to start with. Inflation stretches any initial curvature of the 3-dimensional universe to near flatness.
• The Horizon Problem:
  Since Inflation supposes a burst of exponential expansion in the early universe, it follows that distant regions were actually much closer together prior to Inflation than they would have been with only standard Big Bang expansion. Thus, such regions could have been in causal contact prior to Inflation and could have attained a uniform temperature.
• The Monopole Problem:
  Inflation allows for magnetic monopoles to exist as long as they were produced prior to the period of inflation. During inflation, the density of monopoles drops exponentially, so their abundance drops to undetectable levels.

Question 9

What did the COBE satellite discover and what do the WMAP measurements of the cosmic microwave background (CMB) radiation tell us?

Answer 9

COBE: a satellite that could measure the temperature of the background radiation to the 10,000th degree.

 - they found out its not that smooth as we believed. 
 - does explain the universe as we see it today. 

WMAP’s accuracy and precision determined that dark energy makes up 72.8% of the universe (to within 1.6%), causing the expansion rate of the universe to speed up. - “Lingering doubts about the existence of dark energy and the composition of the universe dissolved when the WMAP satellite took the most detailed picture ever of the cosmic microwave background (CMB).”

Question 10

How was it discovered that the expansion of the universe is accelerating, and what are the latest findings in this area?

Answer 10

Observations of type IA supernovae reveals that the explosion of the universe is speeding up. This is thought to be due to dark energy.

scientist were able to figure this out by looking into the past. The farther you look out, the farther back in time you are looking. they found white dwarf supernovaes, they measured their redshift and compared it to its brightness to see how fast the universe is slowing down. what they discovered is that the universe is actually speeding up.

Question 11

What is the evidence for the existence of “dark energy”, and what are the possible explanations for it?

Answer 11

Dark Energy: the energy believed to fill empty spaces and drive the acceleration of the expanding universe. does not contribute to starlight of the CMB.