Chap 29 and 30 Flashcards
What are the basic observations about the universe that any theory of cosmology must explain?
The expansion of the universe, the universe is homogenous and isotropic, helium abundance, and CMB (cosmic microwave background).
Describe some possible futures for the universe that scientists have come up with.
What property of the universe determines which of these possibilities is the correct one?
density symbol: rho (ρ)
Closed universe
𝜌>𝜌crit , so gravity overcomes expansion, and the universe collapses on itself (the “Big Crunch”).
Open Universe: 𝜌=𝜌crit, so the universe expands forever, but at a rate that gradually approaches zero (steady expansion).
Empty Universe: 𝜌<𝜌crit, the universe expands forever at a constant rate (given Hubble constant stays constant).
Accelerating Universe: The universe’s expansion accelerates due to dark energy, regardless of 𝜌=𝜌crit
Property: critical density
Describe at least two characteristics of the universe that are explained by the standard Big Bang model.
Cosmic microwave background and hydrogen and helium abundance from fusion
Describe two properties of the universe that are not explained by the standard Big Bang model (without inflation).
How does inflation explain these two properties?
Does not explain the homogeneity/ isotropic elements of the universe and why the mass-energy density of the universe would be equal to the critical density
During the inflationary period, the universe expanded exponentially from a tiny, causally connected region. This rapid, early expansion stage also stretched the density to match the critical density and created the uniformation.
Why do astronomers believe there must be dark matter that is not in the form of atoms with protons and neutrons?
Because of the rotation rates of spiral galaxy, x-ray emissions from gas moving rapidly, and dark matter keeps galaxies materials intact and does not let it escape. Leading scientists to believe there must be some other form of material there with gravity.
What is dark energy and what evidence do astronomers have that it is an important component of the universe?
Dark energy accelerates the expansion of the universe, the type 1a supernova showed discrepancy in expansion rate.
Thinking about the ideas of space and time in Einstein’s general theory of relativity, how do we explain the fact that all galaxies outside our Local Group show a redshift?
Space is expanding so everything looks likes it’s moving away.
Astronomers have found that there is more helium in the universe than stars could have made in the 13.8 billion years that the universe has been in existence. How does the Big Bang scenario solve this problem?
In the brief moment of big bang, the temperature was high enough to have fusion with elements
Would acceleration of the universe occur if it were composed entirely of matter (that is, if there were no dark energy)?
The gravity and matter deaccelerate the expansion and there would be no acceleration
Assume that the average galaxy contains 10^11 MSun and that the average distance between galaxies is 10 million light-years. Calculate the average density of matter (mass per unit volume) in galaxies. What fraction is this of the critical density we calculated in the chapter?
Assume that the average galaxy contains 1011 MSun and that the average distance between galaxies is 10 million light-years. Calculate the average density of matter (mass per unit volume) in galaxies. What fraction is this of the critical density we calculated in the chapter?
What is the Copernican principle? Make a list of scientific discoveries that confirm it.
Our solar system and planets/stars are not unique, everything orbits each other
1. Earth orbits the Sun and is not the center of our solar system
2. Our Sun is one among billions of other stars in the Milky Way Galaxy and is not in any central position within the Galaxy
3. Our Galaxy is one among billions of other galaxies in the universe,
4. Planets are commonly found orbiting other stars.
Where in the solar system (and beyond) have scientists found evidence of organic molecules?
Molecular clouds, asteroids/meteors/commits, and from some of Saturn’s moons
What is a biomarker?
Give some possible examples of biomarkers we might look for beyond the solar system.
Something that indicates life
Oxygen and narrow radio signals
Why is traveling between the stars (by creatures like us) difficult?
They are many light years apart, which would require lots of energy to get there and many years
What kind of evidence do you think would convince astronomers that an extraterrestrial spacecraft has landed on Earth?
Physically seeing something not from Earth
