Potential Wells and Hills
Key Concepts:
-
Quantum fluctuations from
the early universe generates both density
enhancements and deficits
-
Potential hills
appear in regions of deficit;
wells
in regions of enhancement.
-
Compression in the wells
corresponds to rarefaction in
the hills
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.
