“Dark matter is hard to see - that’s what makes it dark matter - so to
look for it,
you need to think of something clever that no one has tried before”.
If all of that Dark Matter that we cannot actually see, but that the
physicists say is out there, is not really out there, then this will mean that some
basic laws of physics and astronomy will need to undergo ‘a seismic re-assessment’.
Brendan Cole has recently written about a new scientific attitude regarding
dark matter (http://www.sciencealert.com/physicists-just-debunked-one-of-the-most-promising-dark-matter-candidates):
Physicists just debunked one of the most promising
candidates for dark matter
Any progress is good.
BRENDAN COLE
27 APR 2016
You probably
know that just 15 percent of the known Universe is made up of matter that we
can actually see. The majority of the Universe - some 85 percent of it - is made up of
dark matter and dark energy
- two phenomena that are currently 100 percent unknown to science, despite the best
efforts of researchers worldwide.
But now,
thanks to a paper authored by over
100 physicists... well, it’s still unknown, but it’s just a little
less unknown than it was before, because one of the top candidates for dark
matter has pretty much been debunked.
The kind of
matter that makes up everything we’ve ever seen in the Universe, from tiny
quarks to massive galaxies, is only 15 percent of the matter that’s actually
out there. The rest is known enigmatically as dark matter, because we can't see
it and no one knows what it is, but we’re almost positive that it’s out there,
unless we have to seriously rethink our
understanding of the laws of gravity - the force that governs
everything in the known Universe.
There are
some scientists out there doing this kind of rethinking, but most agree that
dark matter has to be something. They just disagree about what that
something actually is. The leading contender is a class of
Weakly Interacting Massive Particles, or WIMPs.
But there are other possibilities with exciting names like axions, axion-like
particles, and supersymmetric particles.
Now, thanks
to the Fermi Large Area Telescope, the array of possibilities is starting to
thin out.
Axions were first proposed in 1977
to resolve a problem in quantum chromodynamics - the theory of how quarks
interact with one another. Later, when they were developing string theory over
the next 10 or 20 years, they noticed some particles showing up in it that
looked a lot like axions.
Physicists
are famously good at naming things, so they called these exciting new particles
axion-like particles, or ALPs.
It wasn’t
long before they realised that axions and ALPs might also make good candidates for dark matter.
When the Big Bang created all of the light and matter in the Universe, it
should have also created a whole bunch of axions and ALPs - if they exist. But
if they do, these particles probably would’ve congregated right where see
evidence of dark matter.
Dark matter
is hard to see - that’s what makes it dark matter - so to look for it, you need
to think of something clever that no one has tried before. And scientists
hadn’t really tried looking at gamma rays, so these researchers looked at gamma
rays.
Every once in
a while, you’d expect an axion or ALP to run into a bit of regular matter, which should
send a gamma ray out into space with a specific energy. These gamma
rays would then be visible to modern telescopes like the Fermi Large Area
Telescope (LAT).
Different
models of ALPs predict different numbers of them in the Universe: some models
say that all of the dark matter could be ALPs, others say that they make up
only a tiny fraction of it. These different models predict different amounts of
gamma rays, so you can use the number and kind of gamma rays observed to test
the different models of ALPs.
That’s a
bunch of steps, but it’s exactly what a team of 102 scientists has done in a
recent paper in Physical Review
Letters.
They used six
years of LAT data on the galaxy NGC 1275 (another very creative name), and
checked to see if the observed gamma rays matched some popular models where
ALPs make up about 5 percent of the dark matter in the Universe. If these ALP
models were right, that would still leave 80 percent of the mass in the
Universe unexplained. But you have to start somewhere with these things.
It looks like
we’ll have to start somewhere else. The team simulated galaxies with and
without the ALPs and then they checked the results of these simulations against
those six years of observations. They found that the ALPs don’t seem to predict
the observed gamma rays any better than the model without them.
And in
science, if you have two hypotheses that perform equally well, you get rid of
the one with more stuff in it. In this case, you get rid of the one with those
ALPs.
There’s still
a big range of possibilities to explore for LAT and for future gamma-ray
telescopes. The most obvious one that the researchers mention is a model where
ALPs make up all dark matter, not just 5 percent of it. But testing this model
is going to take some time.
So it’s
possible that in the next few years, we’ll discover what makes up all of the
dark matter in the Universe. Or we’ll discover what doesn’t make it up. Either
way, that’s pretty exciting.
[End of quote]
According to US author Robert Sungenis, however, there may a more
simple alternative, the return to a non-Copernican cosmological model, a
biblical or Geocentric Universe (http://loveforlife.com.au/content/10/03/03/new-evidence-earth-center-universe-dark-energy-or-geocentrism-modern-science-crossr):
Dark Energy or Geocentrism?
Modern Science at a Crossroads
By Robert A. Sungenis, Ph.D.
10th December 2008
The most significant scientific evidence that is
challenging Copernican cosmology hails from that gathered by astronomers
themselves. In short, they are increasingly confronted with evidence that
places Earth in the center of the universe. In a paper written by three
astrophysicists from Oxford in 2008 evidence for the centrality of the Earth
was the simplest explanation for the practical and mathematical understanding
of the universe, far superior to the forced invention of “Dark Energy” to
support the Copernican model. ScienceDaily put it in simple terms for the
layman:
Dark energy is at the heart of one of the greatest
mysteries of modern physics, but it may be nothing more than an illusion,
according to physicists at Oxford University. The problem facing
astrophysicists is that they have to explain why the universe appears to be
expanding at an ever increasing rate. The most popular explanation is that some
sort of force is pushing the acceleration of the universe’s expansion. That
force is generally attributed to a mysterious dark energy. Although dark energy
may seem a bit contrived to some, the Oxford theorists are proposing an even
more outrageous alternative. They point out that it’s possible that we simply
live in a very special place in the universe – specifically, we’re in a huge
void where the density of matter is particularly low. The suggestion flies in
the face of the Copernican Principle, which is one of the most useful and
widely held tenets in physics. Copernicus was among the first scientists to
argue that we’re not in a special place in the universe, and that any theory
that suggests that we’re special is most likely wrong. The principle led
directly to the replacement of the Earth-centered concept of the solar system
with the more elegant sun-centered model. Dark energy may seem like a stretch,
but it’s consistent with the venerable Copernican Principle. The proposal that
we live in a special place in the universe, on the other hand, is likely to
shock many scientists.
With the same vigor as Edwin Hubble, recently deceased
astrophysicist, Hermann Bondi, had also tried to stem the tide of geocentric
cosmology by stating in his 1952 book, Cosmology (published by Oxford’s rival,
Cambridge University Press) “the Earth is not in a central, specially favored
position.” Bondi hadn’t proved this view; rather, it was merely a scientific
presupposition, a foundation from which to interpret all the data that
telescopes were gathering, known simply as the “Cosmological Principle” or what
is sometimes called the “Copernican Principle.” There was also a second
principle at work, what we might call the “Einsteinian Principle,” that is,
that the universe obeyed the Special and General Relativistic equations of
Albert Einstein. In this model, the universe has been expanding since the Big
Bang 13.5 billion years ago. Based on both the Copernican and Einsteinian
principles, a grid to measure the universe’s expansion was invented by three
physicists, which became known as the “Friedmann-Walker-Robertson (FRW) metric,”
but the expansion is only possible, as Clifton, et al say,
…if a fraction of r is in the form of a smoothly
distributed and gravitationally repulsive exotic substance, often referred to
as Dark Energy. The existence of such an unusual substance is unexpected, and
requires previously unimagined amounts of fine-tuning in order to reproduce the
observations. Nonetheless, dark energy has been incorporated into the standard
cosmological model, known as LCDM.
Clifton then shows that the tweaking required to get the
Dark Energy model working is wholly unnecessary if one simply rejects the first
principle of cosmology, the Copernican principle:
An alternative to admitting the existence of dark energy
is to review the postulates that necessitate its introduction. In particular,
it has been proposed that the SNe observations could be accounted for without
dark energy if our local environment were emptier than the surrounding
Universe, i.e., if we were to live in a void. This explanation for the apparent
acceleration does not invoke any exotic substances, extra dimensions, or
modifications to gravity – but it does require a rejection of the Copernican
Principle. We would be required to live near the center of a spherically
symmetric under-density, on a scale of the same order of magnitude as the
observable Universe. Such a situation would have profound consequences for the
interpretation of all cosmological observations, and would ultimately mean that
we could not infer the properties of the Universe at large from what we observe
locally.
Within the standard inflationary cosmological model the
probability of large, deep voids occurring is extremely small. However, it can
be argued that the center of a large underdensity is the most likely place for
observers to find themselves. In this case, finding ourselves in the center of
a giant void would violate the Copernican principle, that we are not in a
special place…
New Scientist wasted no time in laying out
the cosmological and historical implications of this study:
It was the evolutionary theory of its age. A
revolutionary hypothesis that undermined the cherished notion that we humans
are somehow special, driving a deep wedge between science and religion. The
philosopher Giordano Bruno was burned at the stake for espousing it; Galileo
Galilei, the most brilliant scientist of his age, was silenced. But Nicolaus
Copernicus’s idea that Earth was just one of many planets orbiting the sun –
and so occupied no exceptional position in the cosmos – has endured and become
a foundation stone of our understanding of the universe. Could it actually be
wrong, though? At first glance, that question might seem heretical, or
downright silly….And that idea, some cosmologists point out, has not been
tested beyond all doubt – yet.
When we add to this the fact that no one has ever found
physical evidence of the much needed Dark Energy to make the
Copernican/Einsteinian model work, it is clear that current cosmology is merely
a desperate attempt to avoid the simplest solution to the data – a geocentric
universe. As one commentator put it: “Astronomers will find it hard to settle
that troubling sensation in the pit of their stomachs. The truth is that when
it comes to swallowing uncomfortable ideas, dark energy may turn out to be a
sugar-coated doughnut compared to a rejection of the Copernican principle.” New
Scientist shows why even the sugar-coated phase gives astronomers a queasy
feeling in their stomachs:
This startling possibility can be accommodated by the
standard cosmological equations, but only at a price. That price is introducing
dark energy – an unseen energy pervading space that overwhelms gravity and
drives an accelerating expansion. Dark Energy is problematic. No one really
knows what it is. We can make an educated guess, and use quantum theory to
estimate how much of it there might be, but then we overshoot by an astounding
factor of 10120. That is grounds enough, says George Ellis…to take a hard look
at our assumptions about the universe and our place in it. “If we analyse the supernova
data by assuming the Copernican principle is correct and get out something
unphysical, I think we should start questioning the Copernican principle….
Whatever our theoretical predilections, they will in the end have to give way
to the observational evidence.”
So what would it mean if…the outcome were that the
Copernican principle is wrong? It would certainly require a seismic
reassessment of what we know about the universe….If the Copernican Principle
fails, all that goes that [the Big Bang] goes out the window too….Cosmology
would be back at the drawing board. If we are in a void, answering how we came
to be in such a privileged spot in the universe would be even trickier.
Actually, it’s not really that “tricky.” As Robert
Caldwell of Dartmouth College said in remarking on the crossroads that modern
cosmology finds itself: “It would be great if there were someone out there who
could look back at us and tell us if we’re in a void.” The truth is, Someone
has already told us that the Earth was in a privileged spot, many years ago in
a book, oddly enough, called Genesis ….
