2.2.3 The Expanding Universe

• In Hubble's Law, the constant H_0 is known as Hubble's constant.
• What phenomenon occurs when the wavelength of light from a receding object appears to stretch?

  Redshift
• Cosmological redshift indicates that distant galaxies are moving towards us.

  False
• Hubble's Law provides evidence for the Big Bang theory.
• Match the type of shift with its characteristics:

  Redshift ↔️ Wavelength increases

  Blueshift ↔️ Wavelength decreases

  Cosmological redshift ↔️ Supports Big Bang theory
• What does the Big Bang theory propose about the universe's origin?

  Began from a singularity
• What is the name of the constant in Hubble's Law?

  Hubble's constant
• Blueshift occurs when the wavelength of light shifts towards the blue
• Arrange the following concepts in the order they relate to the Big Bang theory:

  1️⃣ Singularity

  2️⃣ Expansion

  3️⃣ Formation of galaxies
• The mathematical expression for redshift includes the observed wavelength, the emitted wavelength, and the parameter z
• What does the expanding universe refer to in cosmology?

  Increase in distance between galaxies
• What is the mathematical expression for redshift?

  $z =$$\frac{\lambda_{obs} - \lambda_{emit}}{\lambda_{emit}}$
• What is the prevailing cosmological model for the universe called?

  Big Bang theory
• The expansion of the universe is primarily evidenced by Hubble's Law
• In Hubble's Law, the symbol 'd' represents the distance of the galaxy
• What does the observation of cosmological redshift provide strong evidence for?

  Expanding universe
• Match the evidence with its significance for the Big Bang theory:

  Cosmic Microwave Background ↔️ Supports the hot early universe

  Redshifting of Galaxies ↔️ Evidence for the expansion of the universe
• Redshift occurs when the wavelength of light from a celestial object appears to be stretched
• The mathematical expression for redshift is $z$
• The wavelength of light increases in redshift
• What does Hubble's Law describe about galaxies?

  Recession velocity is proportional to distance
• Blueshift occurs when an object is moving towards the observer.
• The CMB has a uniform temperature of approximately $2.725 K$
• An open universe has a density less than the critical
• The Cosmic Microwave Background complements Hubble's Law by supporting the expansion of the universe.
• What is the density of an open universe compared to the critical density?

  Less than critical density
• What happens to a closed universe if its density is greater than the critical density?

  It collapses back
• A flat universe has no curvature of spacetime.
• What is the uniform temperature of the Cosmic Microwave Background (CMB)?

  2.725 K
• What does the symbol 'H_0' represent in Hubble's Law?

  Hubble's constant
• What is redshift and why does it occur?

  Stretching of light wavelength due to recession
• Redshift indicates that an object is moving away from the observer.
• Steps in the Big Bang theory

  1️⃣ Extremely hot and dense singularity

  2️⃣ Rapid expansion begins

  3️⃣ Cooling allows neutral atoms to form

  4️⃣ Galaxies and structures emerge
• What is the Cosmic Microwave Background (CMB)?

  Thermal radiation from early universe
• What are the three possible fates of the universe based on its density and curvature?

  Open, closed, or flat
• What does the Cosmic Microwave Background provide evidence for?

  The Big Bang theory
• The fate of the universe is determined by its overall density and curvature
• An open universe will expand forever because its density is less than the critical density
• Order the universe types based on their density relative to the critical density:

  1️⃣ Open (less than critical density)

  2️⃣ Flat (equals critical density)

  3️⃣ Closed (greater than critical density)
• Dark matter interacts with gravity but does not emit or absorb light