Physics: Cosmology

Question 1

Georges Lemaître

Answer 1

20th century Belgian cosmologist who formulated the modern big-bang theory, which holds that the universe began in a cataclysmic explosion of a small, primeval “super-atom.”

Question 2

Fred Hoyle

Answer 2

20th century English astronomer who rejected the Big Bang theory, championing the Steady-State theory instead.

Question 3

Steady-State Theory

Answer 3

The theory that the universe doesn’t have a single starting point but that new matter is continuously created to maintain a constant density as the universe expands.

Question 4

Doppler Effect

Answer 4

The Doppler effect refers to the change in frequency or wavelength of a wave in relation to an observer who is moving relative to the source of the wave. Was theorized in 1842 by the Austrian physicist Christian Doppler.

Question 5

Red shift

Answer 5

The Doppler effect for light; objects moving further have larger wavelengths and appear redder whereas objects moving closer have shorter wavelengths and appear bluer.

Question 6

What are the key pieces of evidence that the universe is expanding?

Answer 6

• Redshift of galaxies
• Cosmic Microwave Background Radiation

Question 7

Hubble’s Law

Answer 7

The redshift of distant galaxies is proportional to their distance from us; v=H0*d

Question 8

Radial Velocity

Answer 8

The component of an object’s velocity that is directed along the line of sight of the observer.

Question 9

Recession Velocity

Answer 9

The apparent velocity at which a distant object (such as a galaxy) is moving away from an observer due to the expansion of the universe.

Question 10

Cosmic Microwave Background Radiation

Answer 10

Radiation in the form of low-energy photons, which transitioned from high-energy photons when the universe began to expand and cool; consists of the uniform glow across the entire universe.

Question 11

Planck Epoch

Answer 11

Period within the first 10^(-43) seconds after the big bang in which the effects of quantum mechanics and gravity were comparable.

Question 12

Inflation

Answer 12

Period immediately after the big bang in which the fabric of space grew exponentially, thus allowing the matter contained within the singularity to expand; had the effect of making the distribution of matter and energy more uniform on large scales; occurred within 10^(-36) to 10^(-32) seconds.

Question 13

Reheating

Answer 13

Period immediately after inflation, where the energy stored in the inflation period was converted into various particles (quarks, electrons, etc.), thus reheating the relatively cold and dilute inflation-universe.

Question 14

Recombination

Answer 14

The period 370,000 years after the big bang, where the universe had expanded and cooled enough for protons and electrons to combine and form neutral hydrogen atoms. This transition made the universe transparent to radiation as photons could now travel freely through space.

Question 15

Sagittarius A*

Answer 15

Black hole at the center of the Milky Way

Question 16

The Local Group

Answer 16

Galaxy group which includes the Andromeda (largest), Milk Way (2nd largest), and 52 other galaxies.

Question 17

Big Bounce Theory

Answer 17

The theory that the universe undergoes a repeating cycle of Big Bangs followed by contractions, resulting in a series of cosmic cycles.

Question 18

Big Bang Theory

Answer 18

Theory that the universe began as an extremely hot and dense state approximately 13.8 billion years ago and has been expanding ever since.

Question 19

The Planck Scale

Answer 19

The energy and length scales at which our current understanding of physics breaks down and quantum mechanics and gravity become comparable.

Question 20

Accretion Disk

Answer 20

A swirling disk of gas and matter caused by gravitational attraction; rotational velocity of objects moving towards center increases as distance between them decreases (to preserve angular momentum), which has a tangential component, ultimately leading to the spiral.

Question 21

Horizon Problem

Answer 21

Fact that temperature is constant around the universe, which can’t be explained without the cosmic inflation

Question 22

Flatness Problem

Answer 22

Fact that the universe is relatively flat, which can’t be explained without the cosmic inflation.

Question 23

Evidence of Black Holes

Answer 23

• High-velocity gas clouds (Accretion disks)
• High amounts of radiation (The high gravitational forces near the black hole cause the surrounding material to heat up (as gravitational potential energy is converted to kinetic energy) and emit radiation as it spirals inward; Detectable by using telescopes which are sensitive to X-rays since X-rays are high radiation)

Question 24

Singularity

Answer 24

Point which is so dense that as you get closer to it, its gravitational pull becomes infinitely strong

Question 25

Quasars

Answer 25

Extremely bright and energetic core of a distant galaxy, typically powered by a supermassive black hole. Caused by emittance of light/radiation of objects spiraling into black holes.

Question 26

Cosmology

Answer 26

The science of the origin and development of the universe.

Question 27

Active Galactic Nucleus (AGN)

Answer 27

An AGN refers to the central region of a galaxy where a supermassive black hole is actively accreting matter. Quasars are a type of AGN.