Introduction to our discussion of “Just Six Numbers”
Let me begin by discussing what the book is not about.
It is well known that our existence here on Earth would have been
impossible, if our Solar System were even slightly different than
For example, everyone knows that if the Earth were even a little (by
astronomical terms) closer to the Sun than it is, then the surface of the
planet would be too hot for us to live on it.
And if the Earth were even a little further away from the Sun than it
is, then the surface of the planet would be too cold for us to
live on it.
And if the orbit of the Earth were a little more elliptical (instead
of the near-perfect circle that it is), then there would be times
of the year when the planet is too hot for us to survive on it, or
there would be times of the year when the planet is too cold for
us to survive on it, or both.
If the Earth did not rotate, but kept one side always facing the Sun
and one side facing away from the Sun (as one side of the Moon is
always facing us, and its other side is always facing away
from us), then again we could not exist, because the side of the
planet facing the sun would be too hot to support life, while the
side facing away from the sun would be too cold to support life.
This is also the reason why the Sun cannot be colder than it is.
If the Sun were colder than it is, but we were closer to it, so that
the average temperature on Earth would be the same,
then, at that distance from the Sun, the tidal forces would be
greater, and the rotation of the Earth would stop after only a few
hundred million years, with its rotational period equal to its year length
(just as the Sun has slowed the rotation of Mercury, so that its rotational
period is now equal to ⅔ of its year length).
Half of the planet would be too hot to support life, and half would be
And if the sun were hotter than it is (but we were further away
from it, so that the average temperature on Earth would be the same), then it would not last
long enough for life to evolve on Earth.
Before the necessary billion of years or so for evolution to take
place had elapsed, the sun would
already have burnt out.
If the Earth were even a little smaller than it is (like, e.g., Mars)
then its gravity would not be strong enough for it to hold on to
its atmosphere, and we could not exist.
If the Earth were larger than it is, than organisms of our size and
complexity could not exist on land, they would be crushed by
gravity, nor could there be the vascular plants on which we feed.
We need the iron-nickel core at the center of the Earth, even though
it is 8000 miles away from anything that lives, and without it, we
could not survive.
The iron-nickel core produces the magnetic field that protects us from
the charged particles that are constantly streaming out at us from
the Sun (the “solar winds”) and pouring down on us
from outside of our Solar system (the “cosmic rays”),
which would otherwise be fatal to all life.
This is also why the Earth cannot be smaller and denser than it is;
if the Earth were smaller than it is, but denser, so that its surface
gravity were the same, its surface area would be greater relative
to its volume and its core would therefore cool more quickly.
After a few billion years, it would no longer have a liquid outer
core, and without a liquid outer core flowing around a solid inner
core made of a suitable ferromagnetic material, there is no
magnetic field, and no protection from the solar winds and cosmic rays.
Earth would be a dead planet.
We need the Moon, exactly where it is, two hundred forty thousand miles
away from us, and without it, we could not exist.
Without the Moon to stabilize the Earth's axis, the Earth's axis would
wobble much more than it does, and much more quickly than it does.
Climates would change more rapidly, and the changes would be greater.
There would be no time for organisms to evolve to adapt to their
climate, because climates would not be stable long enough for
that to happen.
Maybe there could be chemosynthetic bacteria on the ocean floor near
volcanic vents, where the conditions do not depend on the climate
at the surface,
but there could be no complex and delicately-balanced ecosystems on
the surface, such as we now have, and such as produced our species.
We need the gas giants in our outer solar system, hundreds of millions
of miles away from us, and without them, there could be no life on
Jupiter and Saturn and Uranus and Neptune are our solar system's
vacuum cleaners, pulling the debris of the solar system toward
themselves instead of letting it fall on us.
If we didn't have the gas giants in our outer solar system,
asteroids and comets would be falling on the Earth every million years
or so, periodically sterilizing our planet.
None of this even begins to discuss the complexity of life itself.
The only thing that has been mentioned so far is the necessary but not
sufficient conditions for life — the prerequisites, without with,
life would be impossible.
But even with those conditions, the arrival of life is not inevitable,
quite the contrary, the complexity of a single procaryotic cell is
beyond human understanding, and a pismire, to the poet, is miracle
enough to stagger sextillions of infidels.
All of this, as I said, is well known, and it is interesting, but none of it is amazing.
Maybe the odds of a solar system giving birth to complex life are a
billion to one, or ten billion to one, or a hundred billion to
one, or a trillion to one.
But there are billions and billions of stars in our galaxy, and there
are billions and billions of galaxies in the universe, so it is
not amazing if there is life in one of them.
It is like being amazed that someone won the lottery.
True, the odds of winning the lottery may be a hundred million to one,
but there are a hundred million people who bought tickets, so it
does not amaze me that Shlomo Pipik won the lottery.
If it had not been Shlomo Pipik, it would have been someone else.
in higher mathematics, “billions and billions” is a unit
of quantity that can be abbreviated as “1 Sagan”.
You can apply metric prefices to this term, so “millions and
millions” is 1 milliSagan (mS), “thousands and
thousands” is 1 microSagan (μS), and “trillions
and trillions” is 1 kiloSagan (kS).)
In Just Six Numbers, the author discusses something else, and
something far less well known.
He does not discuss the conditions on and around Earth that
made life possible.
Everyone already knows that.
Rather, he discusses the conditions of the universe that made
the universe possible.
That is a far different thing, and it is a far more amazing thing,
because there are not billions and billions of universes, there is
only one that we know of, and the laws of physics, the fundamental
properties of the one universe that exists, are so well-tuned — they
have to be so well-tuned — that it is utterly amazing
that the universe exists, and the more we know, the more amazed we
Thus (and this is one that I knew about before I read the book), if
the strong nuclear force were slightly, ever so slightly, stronger than
it is, then a nucleus of two protons would be stable, and there
would be no hydrogen.
And if the strong nuclear force were only slightly weaker than it is,
then even an alpha particle would not be stable, and there could
be only hydrogen.
There is no reason — none that we know of, anyway — why
the strong nuclear force should be exactly as strong as it is, but
if it were not, the universe as we know it could not exist.
That was one of the better-known ones, and, like me, you may have
known about it before you read the book.
Just Six Numbers explained other things to me, though, that I
had never thought about before, but once I thought about them, I
saw how amazing they were.
For example, although it is obvious once someone has explained it to
you, prior to reading the book I had never given any thought to
the need for a precise level of non-uniformity in the early
But clearly it was necessary, and without it, nothing in our universe
If the early universe had been completely uniform, then the late
universe would be equally uniform, and, billions of years later,
there would be nothing in the universe but thinly diffused gas,
the same everywhere.
Gravity would never have brought about stars and galaxies, because, if
you were a hydrogen atom, the hydrogen atom on your left would be
no closer or further away from you than the hydrogen atom on your right.
The pull of gravity would be equal in every direction, and therefore,
there would be no reason for hydrogen atoms to come together here
rather than there.
So there would be no stars, there would be nothing at all, just
uniform, diffuse gas.
But if the early universe had been too non-uniform, then
gravity-created objects would be larger, and they would have formed sooner,
before the universe had expanded much, and in a short
time, all the matter in the universe would be aggregated into
immensely massive black holes, and again, there would be nothing.
So it is with the other numbers in this book.
These six numbers are not the only unexplained dimensionless constants
we know about.
For example, we have no explanation for why a proton is exactly
1836.152672 times as massive as an electron.
But we also have no reason to think that the existence of the universe
depends on this number having the precise value that it does, that
the universe could not exist if electrons were heavier (in fact,
there are heavier electrons — there are muons and
tau particles, together with their associated neutrinos, although they
are not stable, no one knows exactly why).
The “Six Numbers” chosen by the author are quantities
whose values have to be what they are, and if they were not, the
universe could not exist.
That these numbers have to be precisely what they are, in order for
the universe even to exist, is not seen, neither by the author of
the book nor by the man who recommended it to you, as proof of
a supernatural Creator (although, for another
take on these matters, the reader is referred to http://tinyurl.com/y9k733g).
In fact, the author of the book, who surely knows his topic better
than anyone, is a non-believer.
But awe and reverence are different emotions, and you can be
overwhelmed by the former, without feeling the latter.
That is why I recommended the book, and I look forward to hearing what
you have to say, when we meet to discuss it.
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