blackboard

waynehu

Professor, Department of Astronomy and Astrophysics
University of Chicago

Group Contact CV SnapShots
CMB Introduction '96   Intermediate '01   Polarization Intro '01   Cosmic Symphony '04   Polarization Primer '97   Review '02   Power Animations   Lensing   Power Prehistory   Legacy Material '96   PhD Thesis '95 Baryon Acoustic Oscillations Cosmic Shear Clusters
Transfer Function WMAP Likelihood Reionization PPF for CAMB Halo Mass Conversion Cluster Abundance
Intro to Cosmology [243] Cosmology I [legacy 321] Cosmology II [321] Current Topics [282] Galaxies and Universe [242] Radiative Processes [305] Research Preparation [307] GR Perturbation Theory [408] CMB [448] Cosmic Acceleration [449]

Potential Wells and Hills

Key Concepts

Actually, we don't really believe that there were isolated potential wells in the early universe.  We believe that structure in the universe  is seeded by random quantum fluctuations.  In the very early universe, we think a period of rapid expansion, called inflation , caused these quantum fluctuations to be stretched into cosmic scales.

These fluctuations in the energy density imply fluctuations in the local gravitational potential.  Regions of high density generate potential wells .  Regions of low density generate potential hills .  This modifies the picture of acoustic oscillations to:


The analogue of compression in potential wells is rarefaction in potential hills .  In the latter, gravity tries to make the fluid fall off the hill and therefore the fluid there is in an expansion phase.   When we speak of compression in potential wells, you should also bear in mind that there is a correponding potential hill where the opposite is going on.