Originally posted by RJHinds
I used to be able to do calculus when I was in college. That has been 40+ years ago. I can't remember exactly how I would do this problem now. But sometimes when I see something done that I haven't done in a long time, it refreshes my memory.
However what you never studied, and know nothing of, are the internal workings of a star.
And the first step of solving this 'problem' is not maths it's physics.
You need to know what physical processes you are trying to model and how they work before you can create an equation to solve.
I am not entirely sure what you mean when you say this because you are not clear...
... That is because the mass of the sun is made of 75% hydrogen and as we move back in time the sun would have had more
hydrogen to fuse and an increased mass. So the mass-energy conversion rate would be increasing every second as the mass increases
with time. ...
So I will give you a very basic explanation of how stars on the main sequence actually work and we can move on from there.
Stars are formed by giant collapsing clouds of gas made of hydrogen and helium (with small amounts of other elements
generated inside other stars) the ratio of hydrogen to helium left over from the big bang is predicted to be, and is observed as,
a ratio of about 74:26 hydrogen to helium.
As the clouds of gas collapse the pressure increases and they heat up
(basic physics that you as an 'engineer'
aught to know and understand) converting gravitational potential energy into heat.
They also rotate faster as they collapse to conserve angular momentum.
The gas collapses and collapses down under the immense gravitational pull of it's own weight.
The heat energy being generated however acts to hold up and slow this collapse.
As the gas gets denser and denser it becomes harder and harder to lose heat so the centre of this cloud gets very hot.
Eventually this spinning ball of (now plasma and degenerate matter) gets hot enough and the pressure gets high enough
at it's core to start fusing hydrogen atoms together to form helium.
The extra energy generated by the fusion stops the further collapse of the star and it enters dynamic equilibrium where the
outward push of the energy generated by the fusion exactly balances the inward pressure of the stars mass and it's consequent
gravitational attraction.
http://en.wikipedia.org/wiki/Solar_core#Equilibrium
As time goes on the fusion in the core reduces the amount of hydrogen and increases the amount on helium in the stars core.
This effect increases the closer you get to the centre of the core as that is where the temperature and pressure are highest
and correspondingly where the fusion rate is also highest.
Thus over time the energy output of the centre of the core diminishes as hydrogen gets rarer and thus the chances of hydrogen
atoms colliding and fusing reduces.
This reduction in energy output causes the stars core to contract as the energy output ceases to match the inward pressure from
gravity.
As the core contracts it heats up, expanding the volume in which fusion can happen and increasing the energy output by increasing
the fusion rate to again match the inward pressure.
Thus as the star ages it's core contracts and heats up burning through it's hydrogen faster and faster.
As it does so the increased temperature of the core causes the outer layers of the star to expand thus making the external size
and luminosity of the star increase with time.
As no fusion happens in the outer layers of the star the hydrogen/helium content stays
roughly as it was at formation with the
only the hydrogen:helium ratio in the core significantly changing.
This is why the wiki article talks about "
Photospheric composition (by mass)". http://en.wikipedia.org/wiki/Sun#Core
This is the composition of the photosphere, the bit we can see, not the core where fusion happens. And basically is the composition
of the gas cloud that the star
(and the rest of the solar system, including us) came from.
So as you can see, stars get larger over their lives and get brighter over their lives and do not shrink.
Even though they do lose (a trivial amount) mass over that lifetime.
It gets more complicated when a star leaves the main sequence but our sun has not done that yet and wont for about 5 billion more years.
Thus the sun will have been smaller and dimmer and not larger and brighter in the distant past and thus it is not an argument against an
old earth/universe and certainly isn't an argument against evolution.
So will you concede that the fact that the sun presently loses appx 4.26E9 Kg of mass per second in fusing hydrogen into helium
does not mean that the sun would have been large enough to engulf the earth 4 and a half billion years ago when it had first formed?
And that therefore this is not an argument against an old earth or an old universe and thus is also not an argument against evolution?
I am not asking you to accept the blindingly obvious fact of evolution and an ancient earth/universe.
I am just asking you to concede that you have not presented here in this thread an argument or evidence that contradicts or refutes an
ancient earth/universe or consequently evolution.
Note:
It doesn't matter if you think that if this matter was analysed closer and that calculations were done in more detail that you might be able
to prove that the sun would have engulfed the earth in the past if it were really as old as we say it is.
I am asking you to concede that you have NOT YET produced an argument or evidence in this thread that demonstrates that you are right.
Evolution is Dead
09 Jun '12 23:483 edits
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