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Re: Cosmology



In a message dated 2/14/01 11:03:52 PM Eastern Standard Time,
David_Bowman@GEORGETOWNCOLLEGE.EDU writes:

<< I noticed that Bob Zannelli and I have two different definitions of the
CC. Bob calls the Cosmological Constant A, and I (& many authors) call
it capital lambda which I have denoted by [LAMBDA]. But it seems that
these two symbols are not merely two different names for the same
quantity. AFAICT the relationship between these 2 different CCs is:

A =[LAMBDA]/3

With this mapping Bob's equations and mine agree. Otherwise, they don't.
>>
Dave in my text books the cosmological constant is represented with a symbol
that is a capital A without the horizontal part (I believe this is the
capital version of lambda). However I am not sure about the factor of 3
difference. The exact equation for the force due to the cosmological constant
in my book is F=A*R*M*(C^2) using my symbol for CC.
The equation I list is the one that is expressed in terms of the square of
the velocity of expansion. (da/dt)

((da/dt)^2)*(1/((a^2)*(c^2))+k/(a^2)-A=8*pi*G*p/(3*(c^4))

However in Guth's paper he uses the following equation

R(t)=-4*pi*G/(3*C^2)*[ U(t)+3*p(t)]*R(t)+(1/3)*A*(c^2)*R(t) where

R(t) is the scale factor
U(t) is the energy density
p(t) is the mass density
each as a function of time of course and
A the cosmological constant which is really represented as capital
lambda.

I used the first equation because it is easy to solve and get the exponential
result. In the second equation we have lambda being multiplied by 1/3. I hope
this makes sense.

Bob Zannelli