13 Things That Don't Make Sense (6 page)

The crowing was over observations of a massive collision between two clusters of galaxies, known collectively as the Bullet
Cluster. Observing the outcome of the collision, astronomers had found that dark matter had separated from normal matter.
They inferred this from the way that light bent around a seemingly empty area of space. One of Einstein’s great successes
was to show that mass and energy distort the very fabric of the universe. Any radiation—be it light or X-rays—traveling through
space dotted with massive stars and planets will therefore follow a curved path rather than a straight one. So when NASA’s
Chandra telescope recorded light bending around empty space, with no visible matter in the vicinity, it seemed like a slam
dunk for dark matter and a poke in the eye for the troublemakers who claim there’s no need to invoke dark matter, pixie dust,
or magic space blancmange (as one satirist decided to call it) to explain the universe.

The press release put the mainstream case majestically. “A universe that’s dominated by dark stuff seems preposterous, so
we wanted to test whether there were any basic flaws in our thinking,” said Doug Clowe of the University of Arizona at Tucson,
and leader of the study. “These results are direct proof that dark matter exists.”

Except that they’re not, exactly. They are, the press release later concedes, simply “the strongest evidence yet that most
of the matter in the universe is dark.”

The release went on to gasp that some have had the gall to doubt the existence of dark matter. They could no longer, apparently.
“Despite considerable evidence for dark matter, some scientists have proposed alternative theories for gravity where it is
stronger on intergalactic scales than predicted by Newton and Einstein, removing the need for dark matter. However, such theories
cannot explain the observed effects of this collision.”

It was all over for modified gravity theories, you’d think. Except it seemed that no one had actually asked the modified gravity
people whether their theories could or couldn’t explain the observed effects of the collision. In fact, no one had even checked
the archive of papers where physicists routinely post their latest results and theories.

Two months before the triumphant NASA announcement, researchers looking at Bekenstein’s relativistic MOND theory had taken
a glance at the Bullet Cluster. Their paper, playfully titled “Can MOND take a Bullet?” and published in a well-respected
peer-reviewed astronomy journal, makes interesting reading. There was nothing in the Chandra observations that contradicted
relativistic MOND, it argued. Milgrom’s reaction was also intriguing. We heard the same claims three years ago, he said; the
MOND community has had plenty of time to digest the matter, to discuss it at conferences, and to let the authors know how
MOND explains it, “but they don’t seem to listen.” In McGaugh’s view, the Bullet Cluster is difficult for MOND to explain
without invoking some unseen matter, but there’s no need for anything exotic. The presence of some neutrinos (which are known
to exist, are difficult to detect, and make up some small fraction of the dark matter in the standard theory) might be enough
to explain the observations. Plus, McGaugh points out, we know that the kinds of particles we are made of—they are called
baryons
—make up 4 percent of the cosmos, but we’ve only ever directly detected one tenth of the baryons that are known to exist.
Maybe these “dark baryons” are involved in the Bullet Cluster?

MOND, accompanied by neutrinos and dark baryons, wasn’t even the only alternative. Nine days after the NASA press conference,
the Canadian physicist John Moffat posted his response on the archive. His modified gravity theory, he said, could also explain
the Chandra observations without invoking any dark matter.

Moffat is one of those rarest of scientists: he is self-taught, having left Paris as a penniless artist, and yet has risen
to occupy senior academic positions. His story reads like a fairy tale: In 1953, at the age of twenty, he wrote a letter to
Einstein, expounding on some implications of the great man’s ideas. Einstein wrote back, impressed with Moffat’s work and
understanding, and started to open doors for the young man. By 1958 Moffat had a PhD from Trinity College, Cambridge—without
ever earning an undergraduate degree.

Not that luck has always been on Moffat’s side. His unconventional genius led him to work on unfashionable ideas, and in science
fashion matters. He had his biggest idea—that the speed of light might have been different in the past—around a decade too
early. Though Moffat only managed to publish it in an obscure journal in the early 1990s, the idea came to the forefront of
physics ten years later. Even then, Moffat had to kick up a fuss before he got any proper recognition.

And he is still kicking up a fuss—but now in the realm of dark matter. Moffat’s explanation for the flat rotation curves of
galaxies is called, rather inelegantly but at least unpretentiously,
MOG. Modified Gravity
—that’s it. But according to Moffat, MOG’s slight adjustment to Newtonian gravity, making it a little stronger than normal
at large distances, explains the Chandra observations.

Maybe dark matter is there; maybe it is not. There are alternatives, and any neutral observer has to say the dark matter issue
has not yet been resolved. So far, we’ve waited more than sixty years to find out what is causing those strange galactic rotations,
and it is possible that none of us alive today will ever find out the truth about dark matter. Maybe we’ll know tomorrow.
Until we do, though, as Adam Riess pointed out, we can’t be sure about dark energy.

NOT
that the dark energy researchers are twiddling their thumbs. NASA, the National Science Foundation, and the U.S. Department
of Energy have commissioned a group of physicists to find the best way forward for exploring the dark energy enigma, and in
September 2006 the Dark Energy Task Force issued their report. Most of their conclusions recommended an “aggressive program”
of experiments and astronomical observations that will help us make sense of it all. What is most intriguing, though, is that,
besides all the program recommendations, the chair of the task force quietly recommended another way to approach the dark
energy issue. What we really need, says Edward “Rocky” Kolb, is another Einstein.

Kolb suggested that dark energy might be solved by winding physics back eighty-five years. Part of the problem, he says, might
be the assumptions theorists made in the 1920s in order to find solutions to Einstein’s equations (the solutions are, essentially,
mathematical descriptions of the universe). They assumed that the universe was
isotropic
, that is, pretty much the same, whichever way you looked at it.

If it’s not too peculiar a notion, imagine standing inside a blueberry muffin and looking around. The blueberries surround
you left, right, up, and down; whichever way you look, there’s no appreciable difference in how they are distributed throughout
the muffin. Our view from inside the universe appears to be the same. Sure, if we look one way in the solar system or the
Milky Way, we’ll see certain familiar features that aren’t there if we look the other way. Once we look beyond our local region,
however, the universe seems the same wherever we look.

But is it? We don’t know for sure. There are rumblings among astronomers that measurements of the cosmic microwave background
radiation, the echo of the big bang, are showing hints that the universe is not isotropic and some cosmologists are suggesting
there is good reason to consider bringing back a concept dismissed at the end of the nineteenth century: the
ether
, a ghostly entity that makes it easier for light and particles to move through the universe in one direction rather than
another. Either scenario would invalidate the assumption of isotropy. At the moment, we don’t have enough information to know
anything for sure, but it is clear that, to get closer to the truth about the missing universe, what we really need is a theory
that doesn’t make the assumption. Only with that theory in place can we be sure we haven’t led ourselves into error.

It’s easier said than done. Put bluntly, we are not yet clever enough to describe the universe without making those—possibly
catastrophic—simplifying assumptions. It’s not an impossible puzzle, as far as we know. It’s just that we stand without the
required insight—we can’t yet do the math. We are like the generation before Einstein. But one day, Kolb says, someone will
work out how to solve Einstein’s equations without the crippling assumptions of isotropy, and that person might then throw
out something interesting, something like an explanation for dark energy. On that day, the inaccessibility of the landscape
of universes—if such a thing exists—would no longer have any bearing on our understanding of the cosmos.

IT’S
certainly something to look forward to. For the moment, however, all we can do is be Slipher-conservative and declare with
confidence that there is more to the universe than we currently know. The cosmos is still ripe for investigation.

Who knows what surprises it has in store? Especially since dark energy and dark matter are not the only hints that there are
things out there waiting to be brought into the canon of physics. There are reasons to doubt, for example, that what we call
the laws of physics necessarily apply everywhere in the universe—or that they were applicable to every time in its history.
That would surely change our view of the universe’s evolution. Before heading off down that trail, though, we should first
examine the tale of two spacecraft, launched in the 1970s. They are currently leaving our solar system—but on a very slightly,
and mysteriously, different course than the one with which they were programmed. Perhaps the Pioneer anomaly can tell us what’s
wrong with our cosmos.

2

THE PIONEER ANOMALY

Two spacecraft are flouting the laws of physics

I
saac Newton offers hope to every underachiever. He was born prematurely, a runt among newborns who, according to his mother,
could be “put in a quart mug.” At his school he was among the poorest performers. Then, at the age of twenty-three, he came
up with the
universal theory of gravitation.
There is a force between any two bodies, it said, that is “directly proportional to the product of their masses and inversely
proportional to the square of the distance between them.”

Though it might seem simple, it is, quite literally, rocket science. Everything we launch into space is governed by this inverse
square law because rocket scientists have to apply it to understand how their craft will move through the gravitational fields
of the planets and moons of our solar system and—as in the case of the Pioneer probes—beyond.

By rights, the Pioneer 10 and 11 space probes should no longer be of interest to anyone. Launched in the 1970s, they are now
far beyond the edge of our solar system, drifting silently out into the void. The last contact we had with Pioneer 10 was
on January 10, 2003, when a weak signal made it back to Earth. It is now nearly 8 billion miles away, past the orbits of Neptune
and Pluto, and we will not hear from it again because it no longer has any power left with which to send out a signal. The
probe’s next significant moment will come in 2 million years, when, according to calculations based on the gravitational law
that Newton developed just over three centuries ago, it will hit the star Aldebaran in the constellation Taurus.

However, the Pioneer probes hint that the law might be wrong, or at least wrong for those particular calculations. For the
probes are drifting off course. In every year of travel, the probes veer eight thousand miles farther away from their intended
trajectory. That is not much when you consider that they cover 219 million miles a year; whatever is causing the drift is
around 10 billion times weaker than the Earth’s pull on your feet. Nonetheless, it is there, and casting doubt over the universality
of one of Newton’s greatest achievements.

The idea that the Pioneer probes threaten the known laws of physics is almost universally derided—even by the people trying
to make sense of the anomaly. The fact that is seldom appreciated, though, is that NASA explicitly planned to use them as
a test of Newton’s law. The law failed the test; shouldn’t we be taking that failure seriously?

IN
1969, when most eyes were on the Apollo moon landings, John Anderson was focused on the Pioneer probes. As principal investigator,
he had the job of making sure they would do everything they should—that is, observe the outer planets. It dawned on Anderson,
however, that they could do more.

As spacecraft, the Pioneer probes are unique. Every other craft has the means of checking its orientation and trajectory—by
triangulating its position with certain stars, for example. If the mission scientists find the craft has strayed, they can
fire rocket thrusters to correct any drift. Pioneer 10 and 11, on the other hand, were going to keep themselves stable using
the same trick that keeps a child’s spinning top upright: they were going to spin their way through space. The spin provides
a force that fixes the top’s orientation; on Pioneer, the spin meant the mission scientists wouldn’t have to worry about firing
any thrusters to keep the craft on track.

Anderson realized that, since they were traveling under the influence of gravity alone, the Pioneer trajectories would provide
a perfect test of gravity’s nature. He submitted a proposal to NASA to use the probes for this purpose as well as their main
mission, the investigation of Jupiter and the outer solar system. The NASA authorities agreed it would be a good test, and
funded the extra experiments.

The first Pioneer probe was launched from Cape Canaveral on March 2, 1972. Pioneer 11 went up on April 5, 1973. Another seven
years passed, years in which Richard Nixon resigned, Saigon fell, and Margaret Thatcher became prime minister of Britain.
And then John Anderson noticed something odd.

Through all the years of their journey, the instruments on board the Pioneer probes had been sending back their readings to
Earth. In 1980, the trajectory readings stopped making sense: both spacecraft, it seemed, were being pulled toward the Sun.
Anderson talked to a few astronomers within his team about the anomaly, but he didn’t go public because he couldn’t explain
it. Then, in 1994, he took a phone call from a physicist based at the Los Alamos National Laboratory in New Mexico.

Michael Martin Nieto was on a mission to find out just how reliable our gravity theories were. Whenever he came across other
physicists, he would ask them what seemed like a dumb question: Can we still predict the motion of things using Newton’s inverse
square law if they lie outside our solar system? Eventually, he spoke to someone on Anderson’s team, who said it might not
be such a dumb question—and that he should ask John Anderson’s opinion. Nieto made the call.

“Well, there is this Pioneer thing,” Anderson said.

Once he had picked himself up off the floor, Nieto began to talk widely about the issue. Which is how Slava Turyshev got the
Pioneer bug.

Turyshev has the distinction of being the first Soviet scientist to be employed at NASA’s Jet Propulsion Laboratory (JPL)
in Pasadena, California. When he came across Nieto’s story, he had been invited over to do some work on his specialist subject,
Einstein’s general theory of relativity, the equations that describe how matter and energy shape the universe. He was only
supposed to be in California for a year, and he thought that would be plenty of time to sort out this Pioneer nonsense. Fifteen
years later, he is still there—and heading the investigation into the anomaly.

IF
he had followed his first love, Slava Turyshev would have ended up an engineer, not a theorist specializing in general relativity.
He grew up in a remote region of the Altai Mountains in what is now Kazakhstan; Turyshev’s childhood was spent within viewing
distance of the cosmodrome at Baikonur, the place where human spaceflight began. It was from here that Yuri Gagarin had been
hurled into space in 1961. This was the 1970s, and the Soviets had become expert in spaceflight. From the balcony of his family
home, the young Turyshev would watch in awe as the needle-sharp rockets pierced the sky. On treks up into the mountains, he
and his father would sometimes come across shattered metal debris. He knew exactly what it was; he had watched the second-stage
rockets being jettisoned in a cloud of gas a couple of minutes after launch, and falling back to Earth like Lucifer expelled
from heaven.

Inspired by the Soviet space program, he and his friends began to make their own rockets. Turyshev, now in his forties, is
proudest of “Ultraphoton,” a two-stage rocket he built with his cousin. It was seven feet tall and was powered by a homemade
gunpowder charge: sulphur scraped from scavenged matches. A glass Christmas tree bulb provided a suitable container for the
charge; the ignition spark came courtesy of a 4.5-volt battery at the end of a one-hundred-foot length of wire. The launch
was spectacular, he says. The heartbeat of his passenger—the young Turyshev’s pet mouse—must have gone off the scale.

Everything was shaping up for Turyshev to become a space engineer. But when he was sixteen, someone showed him the equations
for Einstein’s general theory of relativity. And that was that. Somehow building rockets suddenly seemed a childish passion;
the warp and weft of space and time, the mysterious fabric on which planets and people played out their dramas, seemed a far
more fitting object for his attention.

By 1990 Turyshev had equipped himself with a PhD in astrophysics and theoretical gravity physics from Moscow State University.
Three years later, he left for California.

TURYSHEV
first came into the Pioneer project as the fixer—the cleaner. Like Harvey Keitel’s character in
Pulp Fiction
, he was there to clear up the mess after people had done something stupid. Something stupid, in this context, was to have
forgotten to factor in some subtle but important aspect of general relativity, Einstein’s gravitational theory, in the planning
of the Pioneer missions. But, to his surprise, Turyshev couldn’t find anything wrong. And that is how his ongoing obsession
with solving the Pioneer problem began.

Anderson, Nieto, and Turyshev all think they must have missed something. They don’t want to rewrite the laws of physics; they
want to leave Newton and Einstein alone. The trouble is, a massive analysis has failed to find anything on the spacecraft
that could be causing it to drift off course. In 2002 they published a fifty-five-page paper together, going through everything
they could think of to explain the drift. Nothing fit. And that was after Turyshev’s cleaning job that checked every possible
tiny effect of general relativity. Which came after Anderson’s decade-long solo effort to find the problem. Something is pulling
on the Pioneer probes with a tiny—but constant—pull. And, after nearly thirty years, it remains a mystery.

That is why, in several places around the world, researchers are watching the Pioneer probes fly all over again. It was Turyshev’s
idea to gather all the flight data from the Pioneer probes and write them into a computer program: Pioneer, the simulator.

It is a hugely demanding project. To understand why, think back to what information technology was like in 1973. Dot matrix
printers are still new—and pretty cool. Bill Gates is still at Harvard; he hasn’t yet come up with the Diskette Operating
System and dropped out to form a little company called Microsoft. That’s still two years away. The first eight-inch floppy
diskette drive had been invented just two years earlier. Which means that the Pioneer craft, designed in the 1960s, would
store most of its data on the old-style punch cards. The mission data that aren’t on punch cards are on rudimentary magnetic
tape, coded in various programming languages that are the computer industry’s version of ancient Latin.

Turyshev’s problems don’t stop there. NASA doesn’t exactly archive all its mission data with loving care. These are records
of when a thruster fired, or in what direction a spacecraft was pointing at 2:30 a.m. on a cold Friday morning in the early
1970s—they are hardly critical data. Unless, of course, the data challenge the laws of physics. But who knew that was going
to happen?

No one at NASA, obviously. Turyshev eventually found most of the Pioneer trajectory data—four hundred reels of magnetic tape
recording the computer’s logs of the missions’ paths through space—in a pile of cardboard boxes under a staircase at JPL.
The tapes had suffered decades of neglect, heat, and humidity, but colleagues helped him restore the data and rerecord them
onto DVD. Next, he went in search of the records from the on board instruments that would reveal every move and spin of the
Pioneer probes. He eventually found them at NASA Ames, in Moffett Field, California: sixty filing cabinets’ worth of instrument
readouts. They had been earmarked for imminent destruction.

The administrators at Moffett Field needed the space the filing cabinets were taking up, and were about to dump them in a
landfill. Outside, in the parking lot, the first dumpster was waiting to be filled. In a moment of passion, Turyshev told
them the discs were too important to throw away; he would rent a truck and take them away himself. The administrators were
impressed and let the discs stay. They are now on DVD too. And all these data have been distributed to interested parties
around the world. The refly of the Pioneer probes is going to be a global effort.

EVERYONE
involved in the refly thinks the solution to the mystery will be something onboard the craft. After all, it wouldn’t take
much—just 70 watts of heat, for instance, could explain everything. As the heat radiation escapes, Newton’s equal and opposite
reaction would push the probe in the other direction.

The probes do indeed carry a source of heat: the probes’ radioactive plutonium generators that power the crafts’ electrical
systems. When the probes were launched, these generators, stuck on long booms at the side of the craft so as to minimize any
radiation damage, produced 2,500 watts of heat. Even now, they could produce 70 watts.

They could. But if they did, it would push the probes in the wrong direction. The generators are mounted at the side of each
craft. To produce the anomalous acceleration toward the Sun, they would need to be mounted on the front.

There’s a long litany of ideas like this—plausible mechanisms that have all been ruled out after careful examination. The
software has all been checked, too; there are no faults that would result in a false reading of the trajectory or a slight
shove off course. A fuel leak could do the trick, but it would have to be one that happened on both craft, in exactly the
same way, and was not picked up by the internal instruments on either craft.

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