38494951
Description
Flashcards by Lucy Clements, updated more than 1 year ago
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Created by Lucy Clements
almost 2 years ago
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| Question | Answer |
| Expression for value of sum of density parameters today | So universe very close to flat |
| Expression for sum of density parameters | |
| Proportionality of sum of density parameters to time if: - Radiation dom. - Matter dom. | |
| What is the flatness problem? | For the universe to be as close to flat as it is today, the initial density parameters must have been almost exactly equal to 1, due to how they evolve with time |
| What is the horizon problem? | CMB is isotropic but photons have free streamed since decoupling so must have initially been in thermal equilibrium (causal contact) BUT Regions of the Universe which are separated by more than ~2 degrees on the sky were not in thermal contact before the CMB photons were released at decoupling |
| What is the relic abundance problem? | Particle theory predicts massive particles, like monopoles, exist and would be produced in early Universe, would rapidly come to dominate Universe (since density decreases slower than radiation) and wreck successes of Big Bang (prevent nucleosynthesis etc.) |
| What is inflation? | Inflation is a period of accelerated expansion, ¨a > 0, which (potentially) occurred in the early Universe Requires negative pressure but not cosmological constant as that would dominate forever and inflation must end before big bang |
| What is the pressure of a substance causing inflation? | |
| Simplest scale factor evolution with time during inflation | |
| How does inflation solve the flatness problem? | If aH is growing with time, (aH)^-2 decreases, so density parameters would have been driven to sufficiently small value |
| How does inflation solve the horizon problem? | Since Universe expands exponentially during inflation, entire observable Universe can originate from within small patch initially in thermal equilibrium |
| How does inflation solve the relic abundance problem? What does this put a limit on? | Monopole density decreases proportional to a^-3. During inflation, a grows exponentially so monopole density tends to 0. Hence they are diluted away by expansion which is why they don't dominate the universe. Only works if monopoles aren't produced again: puts limit on temp after inflation called the reheat temperature |
| How is inflation quantified? How much is needed to solve flatness problem? | Number of e-foldings N=60 to solve flatness |
| What might drive inflation? | Scalar fields: have negative pressure Inflation occurs as field rolls down the potential (parabola). At end of inflation, field oscillates about the minimum, decays into radiation + particles during reheating then big bang starts |
| How could we detect scalar fields? | Scalar fields have quantum fluctuations --> density fluctuations --> temperature anisotropies in CMB So probe inflation models using CMB observations |
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