Dark matter is:
In article , "Phillip Helbig (undress to
reply)" writes:
In one notation (unfortunately, there are several)
Omega_M + Omega_Lambda + Omega_K = 1
or
Omega + lambda + Omega_L = 1
Above line should be
Omega + lambda + Omega_K = 1
Hence Omega + lambda = 1 if the universe is flat.
Yes, different notation schemes can be confusing, on the other hand
understanding them can help one learn other things.
In the scheme above,
Omega_K := 1 - Omega - lambda
or
Omega_K := 1 - Omega_M - Omega_lambda
One can also find
Omega_K := Omega_M + Omega_lambda - 1
or
Omega_K := Omega + lambda - 1
i.e. the sign of Omega_K is opposite.
I prefer the latter, since then Omega_K (or K, in some notation) has the
same sign as k, the curvature constant in the Friedmann equation.
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