... possible1.1
For homogeneous and isotropic slices, that is. 
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
... laboratory.1.2
We don't need to go into space to find WIMPs. Earth is just as good as any other random point in the Galaxy to look for them! 
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
... scooped.'2.1
This account is almost verbatim from Partridge (1995), who had it from Dave Wilkinson who was present at the meeting. 
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
... Physics.2.2
Actually they won a half share in the prize; the other half went to Pyotr Kaptiza for his work in low temperature physics. 
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
... equilibrium2.3
Another proviso is that the co-moving number of particles does not change: for an exception to this see the discussion of the factor g(T) in Section 2.3.2. 
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
... electron2.4
Photons also collide with protons, but the much higher mass of protons makes their interaction radius much smaller, so these collisions are much rarer. 
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
... scattering.2.5
If you are curious, Compton scattering is where high-energy photons transfer energy to electrons. This was historically an important proof of the reality of photons. 
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
....2.6
In fact an accurate measurement at 11 GHz show a much smaller deviation, so I am bending over backwards to allow a little transparency to the CMB! 
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
... Century.2.7
There is a remarkable passage by Pascal in his Pensées (written 1656-58) in which the concept of a heirarchical universe is used to attack the entire project of science, but especially cosmology. See Pensée 72 in this online version. 
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
... place!2.8
Because the labelling of events with space and time coordinates is to some extent arbitrary (c.f. Section 1.2.6), this rather paradoxical way of stating the problem only applies for a particular choice of coordinates. 
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
... amplitude.2.9
Don't confuse the changing amplitude (peak-to-trough height) of the ripple with its changing wavelength $ \lambda$, which, as always, increases proportional to R. 
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
... baseline2.10
Actually 6 inches! 
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
... antennas.2.11
The formula for a single dish is identical with f = 1. 
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
... Earth.2.12
Actually L2 is a point of unstable equilibrium, but the spacecraft can be made to `orbit' around L2 with little expenditure of fuel. 
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.