Among
the many mysteries scientists cannot solve, two of them involve
gigantic asymmetries that scientists cannot explain. The first such
asymmetry is what is called the matter/antimatter asymmetry. Scientists
believe that when two very high-energy photons collide, they produce
equal amounts of matter and antimatter, and that when matter collides
with antimatter, it is converted into high-energy photons. Such a
belief is based on what scientists have observed in
particle accelerators such as the Large Hadron Collider, where
particles are accelerated to near the speed of light before they
collide with each other. But such conclusions about matter,
antimatter and photons leads to a great mystery as to why there is
any matter at all in the universe.
Let
us imagine the early minutes of the Big Bang about 13 billion years
ago, when the density of the universe was incredibly great. At that
time the universe should have consisted of energy, matter and
antimatter. The energy should have been in the form of very high
energy photons that were frequently colliding with each other. All
such collisions should have produced equal amounts of matter and
antimatter. So the amount of antimatter should have been exactly the
same as the amount of matter. As a CERN page on this topic says, "The Big Bang should have created equal amounts of matter and antimatter in the early universe." But whenever a matter particle touched
an antimatter particle, both would have been converted into photons.
The eventual result should have been a universe consisting either of
nothing but photons, or some matter but an equal amount of
antimatter. But only trace amounts of antimatter are observed in the
universe.
It
would be incredibly inconvenient if matter and antimatter were
equally distributed. So much energy is released when matter makes
contact with antimatter that if there were trace amounts of
antimatter lying about, you'd have “oops, someone blew up Europe
because he stepped on a tiny piece of antimatter” situations all
over the place.
The
asymmetry of matter and antimatter (the fact that matter and
antimatter do not exist in equal amounts) reminds us of the fact that
the Big Bang theory is not quite a successful theory, in the sense of
making only predictions that match reality. We read in the popular
press triumphalist talk like the statement below by cosmologist Ethan
Siegel:
This
picture is part of what’s known as the hot Big Bang, and it makes a
whole slew of predictions. Each one of these predictions, like a
uniformly expanding Universe whose expansion rate was faster in the
past, a solid prediction for the relative abundances of the light
elements hydrogen, helium-4, deuterium, helium-3 and lithium, and
most famously, the structure and properties of galaxy clusters and
filaments on the largest scales, and the existence of the leftover
glow from the Big Bang — the cosmic microwave background — has
been borne out over time.
Siegel
here fails to mention that the Big Bang theory predicts a universe
with either equal amounts of matter and antimatter, or all energy and no matter (which is what would result from all the matter combining with antimatter). That
is a gigantic prediction of the theory that does not match reality.
We don't patch up this problem by adding the “cosmic inflation”
speculation to the Big Bang theory, as that also predicts a universe
with either no matter or equal amounts of matter and antimatter. So
rather than engaging in such triumphalist talk, our cosmologists
should be saying, “There must have been something far more going on
at the beginning than we understand.”
Every
several years we hear about some type of result (typically
preliminary) which we are told may hold an answer to the mystery of
matter/antimatter asymmetry. But such results don't hold up over
time. The latest report of a promising preliminary result came in
2017, but by 2018 news stories were throwing cold water on such
results, saying they did nothing to explain the mystery of
matter/antimatter asymmetry.
There's
another gigantic mystery involving asymmetry that scientists don't
understand: the mystery of homochirality. Chemicals such as amino
acids and sugars can be either left-handed or right handed. A left
handed amino acid looks like a mirror image of the right-handed amino
acid. Homochirality is the fact that in living things essentially all amino
acids are left-handed, and all sugars are right-handed. But when such
things are synthesized in a laboratory, or experimentally produced in
experiments such as the Miller-Urey experiment, you see equal amounts
of left-handed and right-handed amino acids or equal amounts of
left-handed and right-handed sugars.
A left-handed amino acid and its right-handed counterpart
Based
on the fact that it is just as easy for left-handed amino acids to
form in the laboratory as right-handed amino acids, and just as easy
for left-handed sugars to form in the laboratory as right-handed
sugars, we would expect for there to be a symmetry in the handedness
of amino acids, with an equal amount of left-handed and right-handed
amino acids. We would also would expect a symmetry in the handedness
of sugars, with equal amounts of left-handed sugars and right-handed
sugars. But what we see is an asymmetry, with living things having only
left-handed amino acids and right-handed sugars.
I
can give an analogy for why homochirality is such a mystery. Let us
imagine a stack of cards. On one side is a particular word.
And
on the other side is the mirror image of that word.
Now,
let us imagine someone tosses this stack of cards into the air, and
the cards randomly arrange into a long, elaborate instruction. Let us
also imagine that all of the cards show only one side: the side with
the intelligible word, and not the side with the mirror image of that
word.
We
would have two great problems in explaining such a thing. The first
would be that this elaborate set of instructions had formed randomly.
The second problem would be explaining how all the cards had landed
in a way so that all of the regular words had appeared, without any
of the mirror image words appearing. A similar problem comes with
explaining the origin of life. We have to explain not merely the
“organization explosion” in which huge amounts of functional
information appeared, but also the fact of all the amino acids being
left-handed and all the sugars being right-handed. The fact of this
homochirality greatly compounds the problem of explaining the origin
of life.
There
was in the news recently a goofy news story on this topic,
which stated the following:
Homochirality,
or one-handedness, plays a key role in cellular chemical reactions,
and all living organisms (that we know of) contain the ‘left-handed’
molecules. Scientists aren’t sure why this is, but some believe the
answer may have something to do with the molecules’ cosmic origin.
In 2016, researchers found propylene oxide, a chiral molecule, in
Sagittarius B2, which is a massive molecular gas cloud roughly 25,000
light years from Earth, near the center of our Milky Way Galaxy. The
findings suggest that the chiral molecules necessary for life may
have come from space, particularly from star-forming regions.
This
is hardly helpful in explaining the mystery of homochirality. What we
want to know is why sugars and amino acids display homochirality, and
the fact of a “chiral molecule” of the biologically irrelevant
propylene oxide modecule does nothing to explain that. The existence
of a chiral molecule does not explain homochirality, just as the
existence of a two-sided penny does not explain 300 consecutive coin
flips that were all heads rather than tails. The problem isn't the
existence of chiral molecules (molecules that can be left-handed or
right-handed). The problem is why in living things we see only
left-handedness in amino acids and right-handedness in sugars.
A
much better article about homochirality is “The Origin of
Homochirality” in the Chemistry World magazine. The article points
out why homochirality is necessary for living things, saying, “No
homochirality, no life.” The article says that according to a
London chemist, “understanding homochirality is still completely
unresolved.”
It
would seem that once we consider homochirality, we need three miracles for life to appear from non-life. The first miracle is just
for you to get all of the genetic information needed for life to
begin, at least 160,000 DNA base pairs arranged in just the right way (with also the proteins that correspond to such a genome).
The second miracle is for you to have homochirality, so that all of
the amino acids have the same handedness, and all of the sugars have
the same handedness. The third miracle is for the genetic code to
originate, a complex symbolic system of representations in which
particular combinations of nucleotides represent particular amino
acids. Similarly, it would be a triple miracle if your 2-year-old in
America were to start speed typing well-written how-to books in French. The first
miracle would be that he could understand enough to write
how-to-books, the second miracle would be that he could write in
French, and the third miracle would be that he could do speed typing
on a keyboard.
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