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Old February 14th 17, 06:18 AM posted to sci.astro.research
Phillip Helbig (undress to reply)[_2_]
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Default Cosmic Energy Budget, vs time

In article ,
writes:

Questions (below) relate to total energy (sum of terms) in this paper:

In the paper, "The Cosmic Energy Inventory" Fukugita / Peebles, They
created a list of all known forms of energy within the universe today.


Always good to mention the date, or a full reference.

(They said, "We present.............at the present epoch".........which
I take to mean, correct me if wrong, they are listing all forms of
energy that exist within the entire modern (co moving with us)
universe.)


Newer papers might have better data. (There is an old joke to plot the
Hubble constant as a function of time, seeing it decline from 600 in
1930 to 100 in 1980, then extrapolating that it would become negative
before 1990. The joke doesn't work anymore, because the decline has
levelled off and the current value is probably close to the true value.)

Neutrinos = 0.00126
Baryon Rest Mass
Warm Intergalactic plasma = 0.045
Intracluster plasma = 0.0018
Main Sequence Stars spheroids and bulges, disks and irregulars
0.0015 + 0.00055 = 0.00205

These 4 components combined constitute 0.05011.


At any rate, this 100% of known stuff (5% if we were to include dark
stuff) must total to the same value no matter what age of the universe I
consider, right?


To the extent that mass is conserved. Of course, they are talking about
mass fractions, not absolute numbers.

In other words, section 7 is post stellar radiation. section 6 is post
stellar nuclear binding energy.


Yes, but how much energy is released by fusion during the lifetime of a
star? 1% of the rest mass or something like that. Negligible at the
precision you have here. Ditto for radiation from starlight. (Almost
all photons are CMB photons, by the way.)

And the energy associated with those two categories must have originally
been associated with the section 3, baryon rest mass.

ie, fusion energy release reduced baryon mass and increased radiation
and nuclear binding energy. But the total energy (if I sum all of the
forms in addition to these 3) at previous epochs of our universe would
be the same as the total today, Right?


Right. Again, energy density. And in comoving coordinates. Everything
gets thinner as the universe expands (except the cosmological constant,
which is why it is called the cosmological constant).

In other words, 100% of this 5% of stuff we know about, has always been
and always will be, 100%. The quantity of energy in each category may
shuffle around a little, but the total will remain unchanged.


Right.

So if I want to make a plot of this inventory as a function of age of
the universe, then I should make certain to track the sum of the
individual components to make sure they always sum to 100% of what 100%
is today, Right?


Right.

However, to a very good approximation, the energy density in radiation
and neutrinos is negligible and always has been, except in the very
early universe, and will be even more negligible in the future.