🚀 go-pugleaf

>>   I find particularly amusing the assumption that you
>> "know" the number of atoms in the universe, and that

>Of course they know how many atoms there are in the universe.  It's science,
>and everyone knows that science has never been wrong.  I mean, we always
>knew the world was round.  That stuff about people thinking that the world
>was flat is just propaganda.  Yeah right.
>
>I wonder that too.  How science can tell us things like how many atoms there
>are in the universe, and that the earth is 4.5 billion years old, or 14
>billion, or 20 billion (all of which I've heard expressed here).  I think

It doesn't tell us how many atoms there are.  It approximates (with
significant error) how many there are.  If I asked you how many atoms
of iron are in an engine block could you figure it out?  If the answer
is no I'd be quite concerned.  You take the volume of steel, determine
how much of the steel is iron (about 99% for a low-carbon ductile
steel), then multiply by the average density of the steel (7.87
grams/cc), to get the mass (if you didn't already have this) then
using Avagadro's number (6.02 x 10^23 atoms / mole) you can find out
exactly how many atoms there are in the engine block.  Big deal.

So, if you could do something similar for the universe, i.e., find an
average density (which has been approximated as 3 x 10^(-31) grams per
cubic centimetre for regular matter, and 1 x 10^(-29) grams per cubic
centimetre for regular plus dark matter.  We'll assume just regular
matter for now).  So, if you have the density, and if you have the
approximate volume of the universe (radius of the universe is about 15
billion light years (since the big bang happened about 15 billion
years ago, and the fastest objects [usually quasars] are moving at
nearly the speed of light [based on their redshifts]).  So, if you
have the volume of the assumed spherical universe (4/3 pi * r^3) times
density, you get total mass.  Since the universe is 90% hydrogen, you
can assume a molecular weight of 1.00794 grams/mole  and from this you
can then find how many atoms there are in the universe.  Although this
value might be weighted for the 9% of matter that is helium to give a
better answer of 1.2671 grams/mole  as the molecular weight.  

Notice that there were several "about"s throughout that paragraph, as
I stated before, it's an approximation, it could probably be off by an
order of magnitude or more.  The point is the calculation of the
number of atoms was almost trivial!  Does it still seem complicated
and unfathomable to you?  Probably not.

Again I must restate what I told you in another message.  Just because
you don't understand something, that doesn't mean it isn't true.  

Incidentally, as to the other stuff you said in that paragraph at the
top, the earth is estimated to be ABOUT 4.5 billion years old.  The
*14-15* billion is approximately the age of the UNIVERSE.  *20*
billion was an older estimate for the age of the universe, back before
there was as much data as there is now.  Again, these are estimates,
but I'm sure they're at least the right order of magnitude.  Not 6,005
years old.  

- Bill