13 things that do not make sense
19 March 2005
Michael Brooks
1 The placebo effect
Don't try this
at home. Several times a day, for several days, you induce pain in
someone. You control the pain with morphine until the final day of the
experiment, when you replace the morphine with saline solution. Guess
what? The saline takes the pain away.
This
is the placebo effect: somehow, sometimes, a whole lot of nothing can
be very powerful. Except it's not quite nothing. When Fabrizio
Benedetti of the University of Turin in Italy carried out the above
experiment, he added a final twist by adding naloxone, a drug that
blocks the effects of morphine, to the saline. The shocking result? The
pain-relieving power of saline solution disappeared.
So
what is going on? Doctors have known about the placebo effect for
decades, and the naloxone result seems to show that the placebo effect
is somehow biochemical. But apart from that, we simply don't know.
Benedetti
has since shown that a saline placebo can also reduce tremors and
muscle stiffness in people with Parkinson's disease (Nature Neuroscience,
vol 7, p 587). He and his team measured the activity of neurons in the
patients' brains as they administered the saline. They found that
individual neurons in the subthalamic nucleus (a common target for
surgical attempts to relieve Parkinson's symptoms) began to fire less
often when the saline was given, and with fewer "bursts" of firing -
another feature associated with Parkinson's. The neuron activity
decreased at the same time as the symptoms improved: the saline was
definitely doing something.
We have a lot to
learn about what is happening here, Benedetti says, but one thing is
clear: the mind can affect the body's biochemistry. "The relationship
between expectation and therapeutic outcome is a wonderful model to
understand mind-body interaction," he says. Researchers now need to
identify when and where placebo works. There may be diseases in which
it has no effect. There may be a common mechanism in different
illnesses. As yet, we just don't know.
2 The horizon problem
OUR
universe appears to be unfathomably uniform. Look across space from one
edge of the visible universe to the other, and you'll see that the
microwave background radiation filling the cosmos is at the same
temperature everywhere. That may not seem surprising until you consider
that the two edges are nearly 28 billion light years apart and our
universe is only 14 billion years old.
Nothing
can travel faster than the speed of light, so there is no way heat
radiation could have travelled between the two horizons to even out the
hot and cold spots created in the big bang and leave the thermal
equilibrium we see now.
This "horizon
problem" is a big headache for cosmologists, so big that they have come
up with some pretty wild solutions. "Inflation", for example.
You
can solve the horizon problem by having the universe expand ultra-fast
for a time, just after the big bang, blowing up by a factor of 1050 in 10-33
seconds. But is that just wishful thinking? "Inflation would be an
explanation if it occurred," says University of Cambridge astronomer
Martin Rees. The trouble is that no one knows what could have made that
happen.
So, in effect, inflation solves one
mystery only to invoke another. A variation in the speed of light could
also solve the horizon problem - but this too is impotent in the face
of the question "why?" In scientific terms, the uniform temperature of
the background radiation remains an anomaly.
3 Ultra-energetic cosmic rays
FOR more than a decade, physicists in Japan have been seeing
cosmic rays that should not exist. Cosmic rays are particles -
mostly protons but sometimes heavy atomic nuclei - that travel
through the universe at close to the speed of light. Some cosmic
rays detected on Earth are produced in violent events such as
supernovae, but we still don't know the origins of the
highest-energy particles, which are the most energetic particles
ever seen in nature. But that's not the real mystery.
As cosmic-ray particles travel through space, they lose
energy in collisions with the low-energy photons that pervade
the universe, such as those of the cosmic microwave background
radiation. Einstein's special theory of relativity dictates that
any cosmic rays reaching Earth from a source outside our galaxy
will have suffered so many energy-shedding collisions that their
maximum possible energy is 5 × 1019 electronvolts.
This is known as the Greisen-Zatsepin-Kuzmin limit.
Over the past decade, however, the University of Tokyo's
Akeno Giant Air Shower Array - 111 particle detectors spread out
over 100 square kilometres - has detected several cosmic rays
above the GZK limit. In theory, they can only have come from
within our galaxy, avoiding an energy-sapping journey across the
cosmos. However, astronomers can find no source for these cosmic
rays in our galaxy. So what is going on?
One possibility is that there is something wrong with the
Akeno results. Another is that Einstein was wrong. His special
theory of relativity says that space is the same in all
directions, but what if particles found it easier to move in
certain directions? Then the cosmic rays could retain more of
their energy, allowing them to beat the GZK limit.
Physicists at the Pierre Auger experiment in Mendoza,
Argentina, are now working on this problem. Using 1600 detectors
spread over 3000 square kilometres, Auger should be able to
determine the energies of incoming cosmic rays and shed more
light on the Akeno results.
Alan Watson, an astronomer at the University of Leeds, UK,
and spokesman for the Pierre Auger project, is already convinced
there is something worth following up here. "I have no doubts
that events above 1020 electronvolts exist. There are
sufficient examples to convince me," he says. The question now
is, what are they? How many of these particles are coming in,
and what direction are they coming from? Until we get that
information, there's no telling how exotic the true explanation
could be.
4 Belfast homeopathy results
MADELEINE Ennis, a pharmacologist at Queen's University,
Belfast, was the scourge of homeopathy. She railed against its
claims that a chemical remedy could be diluted to the point
where a sample was unlikely to contain a single molecule of
anything but water, and yet still have a healing effect. Until,
that is, she set out to prove once and for all that homeopathy
was bunkum.
In her most recent paper, Ennis describes how her team looked
at the effects of ultra-dilute solutions of histamine on human
white blood cells involved in inflammation. These "basophils"
release histamine when the cells are under attack. Once
released, the histamine stops them releasing any more. The
study, replicated in four different labs, found that homeopathic
solutions - so dilute that they probably didn't contain a single
histamine molecule - worked just like histamine. Ennis might not
be happy with the homeopaths' claims, but she admits that an
effect cannot be ruled out.
So how could it happen? Homeopaths prepare their remedies by
dissolving things like charcoal, deadly nightshade or spider
venom in ethanol, and then diluting this "mother tincture" in
water again and again. No matter what the level of dilution,
homeopaths claim, the original remedy leaves some kind of
imprint on the water molecules. Thus, however dilute the
solution becomes, it is still imbued with the properties of the
remedy.
You can understand why Ennis remains sceptical. And it
remains true that no homeopathic remedy has ever been shown to
work in a large randomised placebo-controlled clinical trial.
But the Belfast study (Inflammation Research, vol 53, p
181) suggests that something is going on. "We are," Ennis says
in her paper, "unable to explain our findings and are reporting
them to encourage others to investigate this phenomenon." If the
results turn out to be real, she says, the implications are
profound: we may have to rewrite physics and chemistry.
5 Dark matter
TAKE our best understanding of gravity, apply it to the way
galaxies spin, and you'll quickly see the problem: the galaxies
should be falling apart. Galactic matter orbits around a central
point because its mutual gravitational attraction creates
centripetal forces. But there is not enough mass in the galaxies
to produce the observed spin.
Vera Rubin, an astronomer working at the Carnegie
Institution's department of terrestrial magnetism in Washington
DC, spotted this anomaly in the late 1970s. The best response
from physicists was to suggest there is more stuff out there
than we can see. The trouble was, nobody could explain what this
"dark matter" was.
And they still can't. Although researchers have made many
suggestions about what kind of particles might make up dark
matter, there is no consensus. It's an embarrassing hole in our
understanding. Astronomical observations suggest that dark
matter must make up about 90 per cent of the mass in the
universe, yet we are astonishingly ignorant what that 90 per
cent is.
Maybe we can't work out what dark matter is because it
doesn't actually exist. That's certainly the way Rubin would
like it to turn out. "If I could have my pick, I would like to
learn that Newton's laws must be modified in order to correctly
describe gravitational interactions at large distances," she
says. "That's more appealing than a universe filled with a new
kind of sub-nuclear particle."
6 Viking's methane
JULY 20, 1976. Gilbert Levin is on the edge of his seat.
Millions of kilometres away on Mars, the Viking landers have
scooped up some soil and mixed it with carbon-14-labelled
nutrients. The mission's scientists have all agreed that if
Levin's instruments on board the landers detect emissions of
carbon-14-containing methane from the soil, then there must be
life on Mars.
Viking reports a positive result. Something is ingesting the
nutrients, metabolising them, and then belching out gas laced
with carbon-14.
So why no party?
Because another instrument, designed to identify organic
molecules considered essential signs of life, found nothing.
Almost all the mission scientists erred on the side of caution
and declared Viking's discovery a false positive. But was it?
The arguments continue to rage, but results from NASA's
latest rovers show that the surface of Mars was almost certainly
wet in the past and therefore hospitable to life. And there is
plenty more evidence where that came from, Levin says. "Every
mission to Mars has produced evidence supporting my conclusion.
None has contradicted it."
Levin stands by his claim, and he is no longer alone. Joe
Miller, a cell biologist at the University of Southern
California in Los Angeles, has re-analysed the data and he
thinks that the emissions show evidence of a circadian cycle.
That is highly suggestive of life.
Levin is petitioning ESA and NASA to fly a modified version
of his mission to look for "chiral" molecules. These come in
left or right-handed versions: they are mirror images of each
other. While biological processes tend to produce molecules that
favour one chirality over the other, non-living processes create
left and right-handed versions in equal numbers. If a future
mission to Mars were to find that Martian "metabolism" also
prefers one chiral form of a molecule to the other, that would
be the best indication yet of life on Mars.
7 Tetraneutrons
FOUR years ago, a particle accelerator in France detected six
particles that should not exist. They are called tetraneutrons:
four neutrons that are bound together in a way that defies the
laws of physics.
Francisco Miguel Marquès and colleagues at the Ganil
accelerator in Caen are now gearing up to do it again. If they
succeed, these clusters may oblige us to rethink the forces that
hold atomic nuclei together.
The team fired beryllium nuclei at a small carbon target and
analysed the debris that shot into surrounding particle
detectors. They expected to see evidence for four separate
neutrons hitting their detectors. Instead the Ganil team found
just one flash of light in one detector. And the energy of this
flash suggested that four neutrons were arriving together at the
detector. Of course, their finding could have been an accident:
four neutrons might just have arrived in the same place at the
same time by coincidence. But that's ridiculously improbable.
Not as improbable as tetraneutrons, some might say, because
in the standard model of particle physics tetraneutrons simply
can't exist. According to the Pauli exclusion principle, not
even two protons or neutrons in the same system can have
identical quantum properties. In fact, the strong nuclear force
that would hold them together is tuned in such a way that it
can't even hold two lone neutrons together, let alone four.
Marquès and his team were so bemused by their result that they
buried the data in a research paper that was ostensibly about
the possibility of finding tetraneutrons in the future (Physical
Review C, vol 65, p 44006).
And there are still more compelling reasons to doubt the
existence of tetraneutrons. If you tweak the laws of physics to
allow four neutrons to bind together, all kinds of chaos ensues
(Journal of Physics G, vol 29, L9). It would mean that
the mix of elements formed after the big bang was inconsistent
with what we now observe and, even worse, the elements formed
would have quickly become far too heavy for the cosmos to cope.
"Maybe the universe would have collapsed before it had any
chance to expand," says Natalia Timofeyuk, a theorist at the
University of Surrey in Guildford, UK.
There are, however, a couple of holes in this reasoning.
Established theory does allow the tetraneutron to exist - though
only as a ridiculously short-lived particle. "This could be a
reason for four neutrons hitting the Ganil detectors
simultaneously," Timofeyuk says. And there is other evidence
that supports the idea of matter composed of multiple neutrons:
neutron stars. These bodies, which contain an enormous number of
bound neutrons, suggest that as yet unexplained forces come into
play when neutrons gather en masse.
8 The Pioneer anomaly
THIS is a tale of two spacecraft. Pioneer 10 was launched in
1972; Pioneer 11 a year later. By now both craft should be
drifting off into deep space with no one watching. However,
their trajectories have proved far too fascinating to ignore.
That's because something has been pulling - or pushing - on
them, causing them to speed up. The resulting acceleration is
tiny, less than a nanometre per second per second. That's
equivalent to just one ten-billionth of the gravity at Earth's
surface, but it is enough to have shifted Pioneer 10 some
400,000 kilometres off track. NASA lost touch with Pioneer 11 in
1995, but up to that point it was experiencing exactly the same
deviation as its sister probe. So what is causing it?
Nobody knows. Some possible explanations have already been
ruled out, including software errors, the solar wind or a fuel
leak. If the cause is some gravitational effect, it is not one
we know anything about. In fact, physicists are so completely at
a loss that some have resorted to linking this mystery with
other inexplicable phenomena.
Bruce Bassett of the University of Portsmouth, UK, has
suggested that the Pioneer conundrum might have something to do
with variations in alpha, the fine structure constant (see "Not
so constant constants", page 37). Others have talked about it as
arising from dark matter - but since we don't know what dark
matter is, that doesn't help much either. "This is all so
maddeningly intriguing," says Michael Martin Nieto of the Los
Alamos National Laboratory. "We only have proposals, none of
which has been demonstrated."
Nieto has called for a new analysis of the early trajectory
data from the craft, which he says might yield fresh clues. But
to get to the bottom of the problem what scientists really need
is a mission designed specifically to test unusual gravitational
effects in the outer reaches of the solar system. Such a probe
would cost between $300 million and $500 million and could
piggyback on a future mission to the outer reaches of the solar
system (www.arxiv.org/gr-qc/0411077).
"An explanation will be found eventually," Nieto says. "Of
course I hope it is due to new physics - how stupendous that
would be. But once a physicist starts working on the basis of
hope he is heading for a fall." Disappointing as it may seem,
Nieto thinks the explanation for the Pioneer anomaly will
eventually be found in some mundane effect, such as an unnoticed
source of heat on board the craft.
9 Dark energy
IT IS one of the most famous, and most embarrassing, problems
in physics. In 1998, astronomers discovered that the universe is
expanding at ever faster speeds. It's an effect still searching
for a cause - until then, everyone thought the universe's
expansion was slowing down after the big bang. "Theorists are
still floundering around, looking for a sensible explanation,"
says cosmologist Katherine Freese of the University of Michigan,
Ann Arbor. "We're all hoping that upcoming observations of
supernovae, of clusters of galaxies and so on will give us more
clues."
One suggestion is that some property of empty space is
responsible - cosmologists call it dark energy. But all attempts
to pin it down have fallen woefully short. It's also possible
that Einstein's theory of general relativity may need to be
tweaked when applied to the very largest scales of the universe.
"The field is still wide open," Freese says.
10 The Kuiper cliff
IF YOU travel out to the far edge of the solar system, into
the frigid wastes beyond Pluto, you'll see something strange.
Suddenly, after passing through the Kuiper belt, a region of
space teeming with icy rocks, there's nothing.
Astronomers call this boundary the Kuiper cliff, because the
density of space rocks drops off so steeply. What caused it? The
only answer seems to be a 10th planet. We're not talking about
Quaoar or Sedna: this is a massive object, as big as Earth or
Mars, that has swept the area clean of debris.
The evidence for the existence of "Planet X" is compelling,
says Alan Stern, an astronomer at the Southwest Research
Institute in Boulder, Colorado. But although calculations show
that such a body could account for the Kuiper cliff (Icarus,
vol 160, p 32), no one has ever seen this fabled 10th planet.
There's a good reason for that. The Kuiper belt is just too
far away for us to get a decent view. We need to get out there
and have a look before we can say anything about the region. And
that won't be possible for another decade, at least. NASA's New
Horizons probe, which will head out to Pluto and the Kuiper
belt, is scheduled for launch in January 2006. It won't reach
Pluto until 2015, so if you are looking for an explanation of
the vast, empty gulf of the Kuiper cliff, watch this space.
11 The Wow signal
IT WAS 37 seconds long and came from outer space. On 15
August 1977 it caused astronomer Jerry Ehman, then of Ohio State
University in Columbus, to scrawl "Wow!" on the printout from
Big Ear, Ohio State's radio telescope in Delaware. And 28 years
later no one knows what created the signal. "I am still waiting
for a definitive explanation that makes sense," Ehman says.
Coming from the direction of Sagittarius, the pulse of
radiation was confined to a narrow range of radio frequencies
around 1420 megahertz. This frequency is in a part of the radio
spectrum in which all transmissions are prohibited by
international agreement. Natural sources of radiation, such as
the thermal emissions from planets, usually cover a much broader
sweep of frequencies. So what caused it?
The nearest star in that direction is 220 light years away.
If that is where is came from, it would have had to be a pretty
powerful astronomical event - or an advanced alien civilisation
using an astonishingly large and powerful transmitter.
The fact that hundreds of sweeps over the same patch of sky
have found nothing like the Wow signal doesn't mean it's not
aliens. When you consider the fact that the Big Ear telescope
covers only one-millionth of the sky at any time, and an alien
transmitter would also likely beam out over the same fraction of
sky, the chances of spotting the signal again are remote, to say
the least.
Others think there must be a mundane explanation. Dan
Wertheimer, chief scientist for the SETI@home project, says the
Wow signal was almost certainly pollution: radio-frequency
interference from Earth-based transmissions. "We've seen many
signals like this, and these sorts of signals have always turned
out to be interference," he says. The debate continues.
12 Not-so-constant constants
IN 1997 astronomer John Webb and his team at the University
of New South Wales in Sydney analysed the light reaching Earth
from distant quasars. On its 12-billion-year journey, the light
had passed through interstellar clouds of metals such as iron,
nickel and chromium, and the researchers found these atoms had
absorbed some of the photons of quasar light - but not the ones
they were expecting.
If the observations are correct, the only vaguely reasonable
explanation is that a constant of physics called the fine
structure constant, or alpha, had a different value at the time
the light passed through the clouds.
But that's heresy. Alpha is an extremely important constant
that determines how light interacts with matter - and it
shouldn't be able to change. Its value depends on, among other
things, the charge on the electron, the speed of light and
Planck's constant. Could one of these really have changed?
No one in physics wanted to believe the measurements. Webb
and his team have been trying for years to find an error in
their results. But so far they have failed.
Webb's are not the only results that suggest something is
missing from our understanding of alpha. A recent analysis of
the only known natural nuclear reactor, which was active nearly
2 billion years ago at what is now Oklo in Gabon, also suggests
something about light's interaction with matter has changed.
The ratio of certain radioactive isotopes produced within
such a reactor depends on alpha, and so looking at the fission
products left behind in the ground at Oklo provides a way to
work out the value of the constant at the time of their
formation. Using this method, Steve Lamoreaux and his colleagues
at the Los Alamos National Laboratory in New Mexico suggest that
alpha may have decreased by more than 4 per cent since Oklo
started up (Physical Review D, vol 69, p 121701).
There are gainsayers who still dispute any change in alpha.
Patrick Petitjean, an astronomer at the Institute of
Astrophysics in Paris, led a team that analysed quasar light
picked up by the Very Large Telescope (VLT) in Chile and found
no evidence that alpha has changed. But Webb, who is now looking
at the VLT measurements, says that they require a more complex
analysis than Petitjean's team has carried out. Webb's group is
working on that now, and may be in a position to declare the
anomaly resolved - or not - later this year.
"It's difficult to say how long it's going to take," says
team member Michael Murphy of the University of Cambridge. "The
more we look at these new data, the more difficulties we see."
But whatever the answer, the work will still be valuable. An
analysis of the way light passes through distant molecular
clouds will reveal more about how the elements were produced
early in the universe's history.
13 Cold fusion
AFTER 16 years, it's back. In fact, cold fusion never really
went away. Over a 10-year period from 1989, US navy labs ran
more than 200 experiments to investigate whether nuclear
reactions generating more energy than they consume - supposedly
only possible inside stars - can occur at room temperature.
Numerous researchers have since pronounced themselves believers.
With controllable cold fusion, many of the world's energy
problems would melt away: no wonder the US Department of Energy
is interested. In December, after a lengthy review of the
evidence, it said it was open to receiving proposals for new
cold fusion experiments.
That's quite a turnaround. The DoE's first report on the
subject, published 15 years ago, concluded that the original
cold fusion results, produced by Martin Fleischmann and Stanley
Pons of the University of Utah and unveiled at a press
conference in 1989, were impossible to reproduce, and thus
probably false.
The basic claim of cold fusion is that dunking palladium
electrodes into heavy water - in which oxygen is combined with
the hydrogen isotope deuterium - can release a large amount of
energy. Placing a voltage across the electrodes supposedly
allows deuterium nuclei to move into palladium's molecular
lattice, enabling them to overcome their natural repulsion and
fuse together, releasing a blast of energy. The snag is that
fusion at room temperature is deemed impossible by every
accepted scientific theory.
That doesn't matter, according to David Nagel, an engineer at George
Washington University in Washington DC. Superconductors took 40 years to
explain, he points out, so there's no reason to dismiss cold fusion.
"The experimental case is bulletproof," he says. "You can't make it go
away."
|
