PHY 201 : Ch. 18
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What is cosmology?
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The study of the structure and evolution of the Universe as a whole.
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Is the universe expanding or shrinking?
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Expanding.
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What is the universe filled with?
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Low-energy background radiation.
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How long ago did the universe begin?
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13.7 billion years ago.
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What did the Universe begin as?
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A hot, dense, violent burst of matter and energy.
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What is the hot, dense, violent burst of matter and energy known as?
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the Big Bang.
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What is the "smooth clumping"?
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It implies a similar distributions for the whole Universe.
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What is the motion away of galaxies due to?
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Expansion of space itself.
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What is a good example of the galaxies moving away due to expansion is..?
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Buttons attached to an expanding balloon.
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What happens to the wavelengths as the Universe expands?
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The wavelengths increase.
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Is there a center to the Universe's expansion?
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No.
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What is "Primeval Atom"?
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All mass confined into a very small volume at this earlier stage of Universe.
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What leads to the misconception that the Milky Way is the Universe's center?
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The recession of distant galaxies. (their motion away).
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What is the cosmological principle?
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The lack of a preferred center of expansion.
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How does the universe expand?
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Uniformly.
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What is Olber's Paradox?
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If the Universe extends forever and has existed forever, the night sky should be bright - but of course it isn't.
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What is an example of the Olber's Paradox?
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Standing in the center of a forest that extends forever. You would see trees in every direction.
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What is the resolution to Olber's Paradox?
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A finite speed and age of light means only a finite volume of starlight is available.
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What limits the distance we can see?
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The age of the Universe because the speed of light is finite.
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What is the distance determined from?
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the Universe's age and the speed of light.
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What is the maximum distance one can see?
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Cosmic horizon.
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What is the space within the cosmic horizon called?
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The visible (or observable) Universe.
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How do we find the radius of the (visible) Universe?
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The distance to the cosmic horizon gives a rough measure.
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What is the radius of the (visible) Universe?
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14 billion light-years.
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How hot was the early Universe?
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10 trillion K
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Who discovered cosmic microwave background (CMB)?
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Arno Penzias and Robert Wilson
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What is the recombination era?
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The cooling and expansion of the Universe to make it become transparent.
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When did the Universe become transparent?
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When the temperature dropped to about 3000 K.
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Does the Cosmic microwave background have a perfect blackbody spectrum?
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Yes.
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What is the temperature of CMB?
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2.725 or 3 K, a bit above absolute zero.
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What does the early Universe consist of?
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Protons, neutrons, and electrons.
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What did the initial hot and dense state allow?
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Nuclear reactions to create helium.
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What is an open universe?
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Expanding forever meaning that as all the stars consume their hydrogen, the Universe will become black and empty.
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What is a closed universe?
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A Universe that collapses as a "Big Crunch" might lead to another "Primeval Atom", leading perhaps to the birth of another universe.
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What is a flat universe?
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The expansion speed of the Universe becomes zero when the Universe has reached infinite size.
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What type of energy content does an open universe have?
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Positive total energy.
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What type of energy content does a flat universe have?
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Zero total energy.
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What type of energy content does a closed universe have?
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Negative total energy.
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What is the energy content of the Universe the sum of?
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Its positive kinetic energy of expansion and its negative energy of gravitational binding.
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What is the critical density?
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The theoretically calculated density.
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What will make the Universe recollapse?
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If the observed density is greater than the critical density.
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What is the actual density of matter?
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Approximately one-third of the critical density.
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What accounts for other 2/3 of the critical density?
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Dark energy.
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What is the Universe based on the amount of observed mass?
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It looks to be open.
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Is the universe expansion speeding up or slowing down?
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Speeding up!
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What type of star blast can find both the distances and redshifts of these systems?
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Type Ia supernova blasts.
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What is the type Ia supernova blast?
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An excellent "standard candle".
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What is the cosmological constant?
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A cosmic repulsive force to offset gravity's attraction.
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What is the additional expansion energy called?
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Dark energy.
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What does the dark energy contribute to?
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The total mass of the Universe. Bringing its density up to the critical density.
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What is the positive curvature?
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Resembles the surface of a sphere. Parallel lines meet and triangles have interior angles with a sum greater than 180 degrees.
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What is the negative curvature?
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Resembles the surface of a saddle. Parallel lines never meet. Triangles have interior angles with a sum less than 180 degrees.
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What is the flat curvature?
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Parallel lines do not meet. Triangles have interior angles with a sum equal to 180 degrees.
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How do we find the estimation of the mass content of the universe?
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Based on observations of temperature fluctuations in the Cosmic Microwave Background.
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How did mass and radiation interact during the early Universe?
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They mingled in a manner unlike their sharp distinction today. The radiation was so energetic that it easily transforms to mass. They behaved as a single entity.
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What caused radiation to so easily transform into mass?
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It was very energetic.
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What is the name of the pair to ordinary matter?
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Antimatter.
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What is the antiparticle of the electron?
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Positron.
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What is the antiparticle of the proton?
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Antiproton.
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What happened one microsecond after the Big Bang?
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The temperature was hot enough for photons to create quarks and antiquarks. Then the Universe expands at near speed of light and cools. Then the lower temperature no longer produces quarks/antiquarks. Quarks/antiquarks annihilate asymmetrically leaving an excess of quarks.
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What do surviving quarks become?
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Protons, & nuetrons.
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What is the diameter of the Universe one microsecond after the Big Bang?
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Smaller than the Earth's orbit.
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What happens 5 seconds after the Big Bang?
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The Universe cools enough for the creation of matter to cease.
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What happens 3 minutes after the Big Bang?
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Temperature is a few hundred million degrees. 1/4 of protons fuse into helium.
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What happens in the next half million years after the big bang?
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Further expansion and cooling. Electrons begin to bind to protons to make hydrogen molecules.
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What formed protogalaxies?
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Gravitational collapse of clouds.
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When did galaxy formation start?
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Soon after recombination era.
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What is used to create galaxies in time scales needed?
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Dark matter is used to speed things up because gravity is too feeble.
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What do areas rich in dark matter form?
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Large scale galaxy chains and sheets.
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What do areas depleted in dark matter form?
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Voids.
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What was the state of the Universe before one microsecond?
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Universe was even hotter and denser. It was smaller than the size of a proton. Gravity was not a force of attraction, but one of repulsion.
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What is inflation?
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The violent explosion created by the repulsive force of gravity.
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When does the inflation period end?
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Where the previous Big Bang ideas begin.
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What gives information of the curvature of the Universe?
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The size of small temperature fluctiations
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What else does the size of small temperature fluctuations give information about?
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The Universe's age and the amount of ordinary and dark matter.
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What causes space to be "curved"
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All of the mass and energy contained in the Universe.
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What would happen without the imbalance in the annihilation of quarks?
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our Universe would have been essentially empty.
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1. The light travel time distance to the cosmic horizon is about ____.
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14 x 10^9 light years.
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2. If the universe had _____, that would resolve Olber's paradox.
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Either A or B or both. (A finite age & An edge in space)
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3. The curvature of space can be measured by
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Studying the fluctuations in the cosmic microwave background radiation.
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4. The discovery that the universe is expanding faster today than in the past was possible because of observations of
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Type Ia (white-dwarf) supernovae.
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5. The observational evidence in favor of the existence of dark energy involves using ___ to calculate ____.
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The method of standard candles; the distance to distant galaxies.
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6. The Big Bang refers to
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The origin of the Universe.
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7. The cosmic microwave background (CMB) radiation is
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Radiation from the birth of the Universe.
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8. If the density of the universe is less than the critical density, then
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The universe will expand forever.
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9. When the Universe was young, it was
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Both B & C (Smaller and hotter & Denser)
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10. The cosmic background radiation has a low temperature today because
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The Universe has expanded and expansion causes cooling.
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11. The age of the Universe can be deduced from
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Hubble's law.
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12. The study of the structure and evolution of the Universe is called
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Cosmology.
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13. Dark energy appears to make up approximately __ of the Universe.
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70%
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14. The Cosmological Principle states that
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There is not a preferred location in the Universe.
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15. If the density of the Universe is ___ than the critical density, then the Universe will __.
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Larger, eventually collapse in a "Big Crunch"
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16. Recent measurements of the variations of the cosmic background radiation suggest that the curvature of the Universe is ___.
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Flat (i.e., no curvature)
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17. According to the Big Bang model, most of the __ in the Universe were formed ___.
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Hydrogen and helium; during first 3 minutes.
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18. Why does the observation that all distant galaxies are moving away from the Earth not violate the Cosmological Principle?
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Any other galaxy in the Universe will also see Universe expanding in the same way.
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19. As space expands, everything in it is also getting bigger.
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False
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20. Dark energy is speeding up the expansion of the Universe.
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True
