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Q: Size of the universe ( Answered,   2 Comments )
Subject: Size of the universe
Category: Science > Astronomy
Asked by: drsparkmaker-ga
List Price: $10.00
Posted: 27 May 2004 11:36 PDT
Expires: 26 Jun 2004 11:36 PDT
Question ID: 352789
How many googles of atoms are there in the universe?
Subject: Re: Size of the universe
Answered By: thx1138-ga on 27 May 2004 12:52 PDT
Hello drsparkmaker and thank you for your question.

The simple answer is none! This is because "Google" is the name of a
company and not a word for a large number, however the name Google is
a play on the word Googol (see:
:// ) which IS a BIG number,
and I think this is the number you are refering to.  Yet again I'm
afraid to say that there are no googols of atoms in the universe, in
fact all the atoms in the universe come to less than one googol which
is 10 to the 100th power (1 followed by 100 zeros) see:

A googol is the number 10 to 100 (10 raised to the 100th power or 1
followed by 100 zeros=
A googol is much larger than the number of atoms in the Universe."

Also see:

"Googol and Googolplex

The mathematician Edward Kasner's 9-year-old nephew coined the names
googol for the number that is 1 followed by a hundred zeroes, 10100
and googolplex for 1 followed by a googol of zeroes, 10googol.

These numbers are very large and impossible to visualise. A googol is
larger than any known estimate of the number of atoms in the universe
and thus it would be physically impossible to write out the even
larger googolplex since there are aren't the atoms available to make
up the zeroes.

The human mind finds it difficult to comprehend such vast numbers. To
illustrate this, guess how long you think it would take to count from
one to a million, which is a mere 106, counting at a rate of one
number per second without a break. How long would it take to count to
a billion (US version) 109? Check your guesses by using a calculator
(think a for minute and should be clear how to do this)."

For a more scientific explanation:

"First of all, by "the universe" I'll assume we're talking 
about the _observable_ universe, which is necessarily much smaller
than the entire physical volume of space (which for all we know could
be infinite). The size of the observable universe is basically
spherical, with radius about equal to the "Hubble radius", d_H = c/H_0
~ 4e9 pc = 1e28 cm ~ ct_0 (where 0 denotes present values). In fact,
when you allow
for the expansion of the universe, the better value is more like 2d_H.
I hesitate to bother you with such factors, but we are after all going
to cube this. Anyway, the volume of
the observable universe is just that of a sphere with r=2d_H, or about
3e85 cm^3. The microwave background photons have T=2.728 K, and Planck
tells you that this gives n_gamma = 411 photons/cm^3, so there are
about 1e88 photons in the observable universe (not far from a googol
in some sense, though 12 orders of magnitude is not negligible, even
for astrophysics).

There are comparable numbers of each neutrino species. 
Finally, big bang nuke (that's me) sez that the baryon to photon ratio
in the universe is about n_b/n_gamma = 3e-10 (i.e., the photons and
nu's outnumber [but not outweigh]
the measley baryons by a hefty factor) so the baryon number of the
universe is about 3e78. So this is 21.5 or so orders of magnitdue off
from a googol, but in some sense it's not so far off."


For estimates regarding the number of atoms in the universe see:

"It seems, then, that the number of atoms in the Universe is at least
about 4e78, but perhaps as many as 6e79. I would suggest 1e79 as a
reasonable estimate. That is, 10 000 000 000 000 000 000 000 000 000
000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000

"By comparison, the total number of seconds that have elapsed since
the beginning of the universe is only about 1 followed by 17 zeros,
and the total number of atoms in the universe is equal to about 1
followed by 100 zeros"

Thank you for your question, and if you need any clarification of my
answer do not hesitate to ask before rating my answer.

Very best regards


Search strategy included:
googol "atoms in the universe"

"number of atoms in the universe"
Subject: Re: Size of the universe
From: iang-ga on 27 May 2004 15:44 PDT
illustrate this, guess how long you think it would take to count from
one to a million, which is a mere 106, counting at a rate of one
number per second without a break.

Wanting to give a group of primary school children some idea of how
long a billion years is, I asked them how long it would take to count
to a billion at the rate of one per second.  One kid immediately
answered "a billion seconds"!

Ian G.
Subject: Re: Size of the universe
From: neilzero-ga on 27 May 2004 18:16 PDT
The observable universe is now thought to be a sphere with a radius of
13.7 billion light years. Volume = 4/3 times 3.14 times r cubed = 4.19
times 2571 times 10^27 = 10,774 times 10^27 = about 10^31 cubic light
 Using 10^79 for the total number of atoms gives 10^ 48 atoms per
cubic light year. There are about 10 trillion kilometers in one light
year = 10^13. A cubic light year is 10^39 cubic kilometers; so there
are 10^9 (one billion) atoms per cubic kilometer on the average. If
that is correct there are lots more cubic kilometers with only a few
hundred atoms to make up for the very few cubic kilometers with
billions of billions of atoms such as the cubic kilometer just below
our feet. The billion billion = 10^18 is a wild guess.  Neil

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