[tt] Sigma Xi: Michael J. Disney: Modern Cosmology: Science or Folktale?

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Michael J. Disney: Modern Cosmology: Science or Folktale?
http://www.americanscientist.org/template/AssetDetail/assetid/55839?&print=yes

But first:
The Chronicle of Higher Education Magazine & Journal Reader, 7.8.16
http://chronicle.com/daily/2007/08/2007081601j.htm

A glance at the current issue of American Scientist: Proof in the cosmos

For all the technological advancements that have helped improve the study 
of cosmology, the discipline continues to rest on "very flimsy 
observational support," writes Michael J. Disney, an emeritus professor of 
physics and astronomy at Cardiff University, in Wales.

The modern study of cosmology has, without a doubt, "taken a turn for the 
better," writes Mr. Disney. Yet many theories have "run into serious 
difficulties, which have been cured only by sticking on some ugly 
bandages." Sure, it's interesting, he says, "but is it, even in its modern 
guise, convincing?"

For example, experts once believed that the expansion of the universe was 
slowing. They were unable to determine the speed of that deceleration, 
though, because, as it turns out, the universe is actually expanding at an 
accelerating pace. However, "the physics responsible for this seeming 
acceleration is entirely unknown," says Mr. Disney, "and goes under the 
deliberately inscrutable name 'dark energy.'"

Mr. Disney is sure to point out that "expansion is a moderately 
well-supported hypothesis." However, finding more direct evidence for it 
"must be of paramount importance," he argues.

"Though cosmologists are strangely reluctant to admit it," he says, the 
discipline has often maintained a somewhat "negative significance" in the 
sense that it has often had to create new hypotheses to account for 
phenomena that have not, or cannot, be observed. Unfortunately, he writes, 
"a skeptic is entitled to feel that a negative significance, after so much 
time, effort, and trimming, is nothing more than one would expect of a 
folktale constantly re-edited to fit inconvenient new observations."
____________

Modern Cosmology: Science or Folktale?

Current cosmological theory rests on a disturbingly small number of
independent observations

Michael J. Disney

It appears that everybody is interested in cosmology. In one
anthropological study, every one of the more than 60 separate
cultures examined was found to have several common characteristics,
including "faith healing, luck superstitions, propitiation of
supernatural beings, ... and a cosmology." Apparently, to be human
is to care how the physical world came to be, whether it has
boundaries and what is to become of it. Modern cosmology is a highly
sophisticated subject funded by governments with hundreds of
millions of dollars a year. It is unquestionably interesting, but is
it, even in its modern guise, convincing?

click for full image and caption
Distant galaxies

The current Big Bang paradigm has it that the cosmos is expanding
out of an initially dense state and that by looking outward into
space, one can, thanks to the finite speed of light, look back to
much earlier epochs. This understanding owes much to two accidents:
astronomers' discovery of redshifts in the spectra of distant
nebulae and the fortuitous detection of an omnipresent background of
microwave noise, which is believed to be the remnant of radiation
from a hot and distant past. Set in the theoretical framework of
Einstein's general theory of relativity, such observations lead to a
model that makes predictions and can thus be tested.

Of late, there has been much excitement over precision measurements
of the cosmic background radiation and the discovery of very distant
galaxies of great antiquity. There is even talk of a "concordance
model" in which all of the observations come together to paint a
coherent picture of how the universe must be constructed.

It is true that the modern study of cosmology has taken a turn for
the better, if only because astronomers can now build relevant
instruments rather than waiting for serendipitous evidence to turn
up. On the other hand, to explain some surprising observations,
theoreticians have had to create heroic and yet insubstantial
notions such as "dark matter" and "dark energy," which supposedly
overwhelm, by a hundred to one, the stuff of the universe we can
directly detect. Outsiders are bound to ask whether they should be
more impressed by the new observations or more dismayed by the
theoretical jinnis that have been conjured up to account for them.

My limited aim here is to discuss this dilemma by looking at the
development of cosmology over the past century and to compare the
growing number of independent relevant observations with the number
of (also growing) separate hypotheses or "free parameters" that have
had to be introduced to explain them. Without having to understand
the complex astrophysics, one can still ask, at an epistemological
level, whether the number of relevant independent measurements has
overtaken and comfortably surpassed the number of free parameters
needed to fit them--as one would expect of a maturing science. This
approach should be appealing to nonspecialists, who otherwise would
have little option but to believe experts who may be far too
committed to supply objective advice. What one finds, in my view, is
that modern cosmology has at best very flimsy observational support.

A Short History of Cosmology

Almost a century ago, Einstein's general theory of relativity
posited that matter and energy could bend spacetime. This idea was
philosophically attractive because it removed the need to worry
about cosmic boundaries if the universe closed back on itself.

Unfortunately (or so Einstein then thought), general relativity
implied that the universe would have to either collapse or expand.
So in 1921 he found room in his theory for a new free parameter, the
so-called "cosmological constant," an arbitrary antigravity term
that would put a stop to all that. Ironically, the observers who
were examining faint nebulae (distant galaxies) at the time
discovered that their spectra were dramatically redshifted--hinting
that on its largest scale the universe was expanding after all.

In 1965 Arno Penzias and Robert Wilson stumbled accidentally onto
the cosmic background radiation, a microwave whisper arriving from
all directions of the sky. As cosmologists interpret it now, they
were observing optical radiation emitted by the gas of the universe
when it was hot (3,000 degrees Celsius), opaque and relatively young
(300,000 years old), redshifted through the enormous factor of a
thousand by subsequent cosmic expansion. They were looking into the
past with a vengeance and seeing the remnants of what astronomer
Fred Hoyle dismissively called the "Big Bang." From then on, the
expanding universe was accepted, usually without question, as a
natural explanation for the microwave background.

At the same time, astrophysicists sought to understand the origin of
the elements. It seemed that most had formed from the fusion of
pristine hydrogen inside stars and then had been expelled into
general circulation when those stars exploded as supernovae.
However, some of the lighter elements, in particular helium,
deuterium and lithium, would have had to form much earlier, during
the first minutes of the Big Bang. The theory of Big Bang
nucleosynthesis did a fair job of predicting the relative amounts of
most of these substances, lending more support to the notion of an
expanding universe.

Robert Dicke meanwhile noticed a worrying paradox in the Big Bang
model: Opposite sides of the cosmos look very much the same, even
though they had never been sufficiently close to equilibrate--indeed
they had never been sufficiently close for any kind of information
(which is limited to the speed of light) to travel between them.
This difficulty was virtually unadmitted until 1981, when Alan Guth
suggested a vague conceptual solution called "inflation": a slow
start to expansion, followed by a rapid acceleration. The necessary
causal contacts could then have taken place when the universe was
young but not yet flying apart too fast. If inflation actually
happened, sufficient stretching during that period of rapid
acceleration would have lowered the local curvature today so that it
would look flat to the observer, even if it wasn't so on a much
larger scale (just as the Earth looks flat to someone with a limited
horizon).

At about this time in Holland, Albert Bosma discovered that spiral
galaxies are spinning far too rapidly to be held together by the
mutual gravitational tugs of their observable contents. Astronomers
concluded that there had to be far more dark than ordinary, visible
matter around to keep galaxies (and galaxy clusters) together. Most
cosmologists welcomed the possibility of such dark matter, because
it might be lumpy enough to get the galaxies formed in the early
universe--another serious problem for theorists. The apparent
uniformity of the cosmic background radiation had cosmologists
struggling to figure out how the present uneven structure of
galaxies and clusters evolved out of such a smooth beginning.

They thus posited the existence of primordial "seeds" of unknown
origin, which somehow survived the early, hot era when radiation
would tear material things apart. Cosmologists argued that these
seeds would grow over time, finally collapsing into the galaxies
seen today. A type of dark matter that ignored radiation ("cold dark
matter") would be the ideal stuff for such seeds. It could condense
into lumps, thereafter dragging the much lesser amounts of ordinary
matter in afterwards, matter that would eventually light up as
stars. By the 1980s the theoreticians' universe was entirely
dominated by such invisible material.

Meanwhile, observations of distant supernovae in the late 1990s told
an astonishing, almost shocking, story. The results suggested that
the expansion, far from being slowed by gravitation, as was
expected, had instead accelerated. Moreover, this acceleration had
started only in comparatively recent times (7 billion years ago).
The physics responsible for this seeming acceleration is entirely
unknown and goes under the deliberately inscrutable name "dark
energy," which may or may not have something to do with Einstein's
cosmological constant.

The Significance of Cosmology

click for full image and caption
Timeline of cosmological theories

The currently fashionable concordance model of cosmology (also known
to the cognoscenti as "Lambda-Cold Dark Matter," or LCDM) has 18
parameters, 17 of which are independent. Thirteen of these
parameters are well fitted to the observational data; the other four
remain floating. This situation is very far from healthy. Any theory
with more free parameters than relevant observations has little to
recommend it. Cosmology has always had such a negative significance,
in the sense that it has always had fewer observations than free
parameters (as is illustrated at left), though cosmologists are
strangely reluctant to admit it. While it is true that we presently
have no alternative to the Big Bang in sight, that is no reason to
accept it. Thus it was that witchcraft took hold.

The three successful predictions of the concordance model (the
apparent flatness of space, the abundances of the light elements and
the maximum ages of the oldest star clusters) are overwhelmed by at
least half a dozen unpredicted surprises, including dark matter and
dark energy. Worse still, there is no sign of a systematic
improvement in the net significance of cosmological theories over
time.

Where Do We Stand Today?

Big Bang cosmology is not a single theory; rather, it is five
separate theories constructed on top of one another. The ground
floor is a theory, historically but not fundamentally rooted in
general relativity, to explain the redshifts--this is Expansion,
which happily also accounts for the cosmic background radiation. The
second floor is Inflation--needed to solve the horizon and
"flatness" problems of the Big Bang. The third floor is the Dark
Matter hypothesis required to explain the existence of contemporary
visible structures, such as galaxies and clusters, which otherwise
would never condense within the expanding fireball. The fourth floor
is some kind of description for the "seeds" from which such
structure is to grow. And the fifth and topmost floor is the
mysterious Dark Energy, needed to allow for the recent acceleration
of cosmic expansion indicated by the supernova observations. Thus
Dark Energy could crumble, leaving the rest of the building intact.
But if the Expansion floor collapsed, the entire edifice above it
would come crashing down. Expansion is a moderately well-supported
hypothesis, consistent with the cosmic background radiation, with
the helium abundance and with the ages inferred for the oldest stars
and star clusters in our neighborhood. However, finding more direct
evidence for Expansion must be of paramount importance.

In the 1930s, Richard Tolman proposed such a test, really good data
for which are only now becoming available. Tolman calculated that
the surface brightness (the apparent brightness per unit area) of
receding galaxies should fall off in a particularly dramatic way
with redshift--indeed, so dramatically that those of us building the
first cameras for the Hubble Space Telescope in the 1980s were told
by cosmologists not to worry about distant galaxies, because we
simply wouldn't see them. Imagine our surprise therefore when every
deep Hubble image turned out to have hundreds of apparently distant
galaxies scattered all over it (as seen in the first image in this
piece). Contemporary cosmologists mutter about "galaxy evolution,"
but the omens do not necessarily look good for the Tolman test of
Expansion at high redshift.

In its original form, an expanding Einstein model had an attractive,
economic elegance. Alas, it has since run into serious difficulties,
which have been cured only by sticking on some ugly bandages:
inflation to cover horizon and flatness problems; overwhelming
amounts of dark matter to provide internal structure; and dark
energy, whatever that might be, to explain the seemingly recent
acceleration. A skeptic is entitled to feel that a negative
significance, after so much time, effort and trimming, is nothing
more than one would expect of a folktale constantly re-edited to fit
inconvenient new observations.

The historian of science Daniel Boorstin once remarked: "The great
obstacle to discovering the shape of the Earth, the continents and
the oceans was not ignorance but the illusion of knowledge.
Imagination drew in bold strokes, instantly serving hopes and fears,
while knowledge advanced by slow increments and contradictory
witnesses." Acceptance of the current myth, if myth it is, could
likewise hold up progress in cosmology for generations to come.