by Lucy Hawking
“He’s at the Large Hadron Collider … ,” said George slowly as the true horror of the situation became clear to him. “At a meeting of the Order of Science to Benefit Humanity. Every single full-member of the Order will be there. They’ve been asked to come together.”
“That’s it!” cried Reeper. “That’s where they are going to use the bomb! They’re going to use it to destroy the Collider, and not just Eric, but all the leading physicists in the world!”
“But … but … but how could they know that the Order of Science is having a meeting?” gasped George.
“I have long suspected that the Order contains a mole,” said Reeper, speaking quickly now. “One of the scientists in TOERAG must also be a member of the Order of Science. He or she must have betrayed the Order to TOERAG.”
“And that person definitely isn’t you?” asked George fiercely.
“I’m not even a member of the Order,” said Reeper sadly. “So it couldn’t be me. My membership was revoked many years ago and I was not allowed to rejoin. It is someone else, someone really dangerous.”
“Why are you trying to help Eric now?” wondered George.
“George,” said Reeper, “I know you don’t have a high opinion of me. But believe me, what I love above all else is science. I can’t just stand by and, after all these centuries of work, see it extinguished by idiots who are acting out of greed or prejudice. I joined TOERAG to try to stop them. That’s why I’m here.”
George’s head was spinning. Could Reeper really be telling the truth? If so, this would be the first time he wasn’t concealing some deadly trick, intended to exterminate Eric and even up the score. He looked over at Reeper … but something had happened to him while George was absorbed in his thoughts. He seemed to be fading, disappearing into the blackness of the Andromeda galaxy around him.
PARTICLE COLLISIONS
If there were no forces, particles colliding inside machines like the LHC would come out the same as they went in. Forces allow fundamental particles to influence each other in collisions (even to change into different particles!) by emitting and absorbing special force-carrying particles called gauge bosons.
Physicists can represent a collision by using Feynman diagrams. Such diagrams show the ways in which it is possible for particles to scatter off each other. One Feynman diagram is one part of describing such a collision and the diagrams need to be summed up for a complete description of a single collision.
Here is the simplest kind, in which two electrons approach, exchange a single photon, and then continue on their way. Time goes from left to right, the wiggly line is a photon, and the solid lines show the electrons (marked as e). This diagram includes all the cases where the photon travels up to down or down to up (which is why the wiggly line is drawn vertically):
More complicated processes have more than one virtual particle in more complex Feynman diagrams. For example, here is one with two virtual photons and two virtual electrons:
An infinite number of many diagrams are needed to fully describe each kind of particle reaction, though thankfully scientists can often obtain very good approximations by only using the simplest ones. Here’s one that could represent what might happen at the Large Hadron Collider when protons collide! The letters u, d, and b are quarks; while g shows gluons:
“George,” said Reeper urgently. “We have less time than I thought.”
“What’s happening to you?”
“I’m not real.” Reeper was talking very fast now. George could no longer see his outline—only small triangles of reflected starlight on his shiny helmet and boots. “I am a computer-generated avatar of myself. It was the only way I could meet you. When I couldn’t find Pooky or Eric or Cosmos, I broke into your house and secretly left a re-router downstairs. Through that re-router, I used Pooky to send myself here and open the portal remotely to transport you.”
“Why don’t you avatar yourself to the Collider and tell them?” cried George. “Why me?”
“I cannot get to the Collider!” said Reeper, his voice distorting. “I will not be able to escape them again.”
“What about the quantum mechanical bomb?” cried George.
“There’s a way! I’m not a complete fool! I made an observation! Pooky sent you a code …”
“What! How do I use Pooky’s code? How do I defuse the bomb?”
But the only reply George got was a faint whisper through his voice transmitter: “George …”
And with that, the Universe around him fell silent. In front of him, where Reeper had stood, the silvery tunnel had opened up once more, pulling him forward into its river of light.
He twisted and turned at unimaginable speed across the Universe, flying quintillions of miles from Andromeda back to our own Galaxy, the Milky Way, which is made up of matter and dark matter—that mysterious dark substance that surrounds us but which we can’t see, feel, or hear. As he traveled, a thought flew into his brain—I have been to the dark side, he said to himself . I have been to the dark.
THE LATEST SCIENTIFIC THEORIES
THE DARK SIDE OF THE UNIVERSE
One of the simplest questions we can ask is: What is the world made of?
Long ago, the Greek Democritus postulated that everything is made of indivisible building blocks he called atoms. And he was right—and over the past two thousand years we have filled in the details.
All the stuff in our everyday world is made of combinations of the ninety-two different types of atoms: the elements of the periodic table—hydrogen, helium, lithium, beryllium, boron, carbon, nitrogen, oxygen, and all the way up to uranium, number ninety-two. Plants, animals, rocks, minerals, the air we breathe, and everything on Earth is made of these ninety-two building blocks. We also know that our Sun, the other planets in our Solar System, and other stars far away are made of the same ninety-two chemical elements. We understand atoms very well, and are masters at rearranging them into all kinds of different things, including my favorite, French fries! The science of chemistry is all about building different things with atoms, a kind of “Lego with atoms.”
Today, we know there is a whole lot more out there than just our Solar System—a mindbogglingly large Universe, with billions of galaxies, each made of billions of stars and planets. So what is the Universe made of? Surprise—while our Solar System and other stars and planets are made of atoms, most of the stuff in the Universe is not; it is made of very strange stuff—dark matter and dark energy—that we do not understand as well as atoms.
THE LATEST SCIENTIFIC THEORIES
First the numbers: In the Universe as a whole, atoms account for 4.5%, dark matter for 22.5%, while dark energy comes in at 73%. An aside: Only about one in ten of those atoms is in the form of stars, planets, or living things, with the rest existing in a gaseous form too hot to have made stars and planets.
Let’s begin with dark matter. How do we know it is there? What is it? And how come we don’t find it on Earth or even in our Sun?
We know it is there because the force of its gravity holds together our Galaxy, the Andromeda galaxy, and all the other big structures in the Universe. The visible part of the Andromeda galaxy (and all other galaxies) sits in the middle of an enormous (ten times larger) sphere of dark matter (astronomers call it the dark halo). Without the gravity of the dark matter, most of the stars, solar systems, and everything else in galaxies would go flying off into space, which would be a very bad thing.
At the moment we don’t know exactly what the dark matter is made of (not unlike Democritus, who had an idea—atoms—but didn’t have the details). But here is what we do know.
Dark matter particles are not made of the same parts that atoms are (protons, neutrons, and electrons); it is a new form of matter! Don’t be too surprised—it took nearly two hundred years to identify all the different kinds of atoms, and over the course of time, many new forms of atomic matter were discovered.
Because dark matter is not made of the same pieces as atoms, it is pretty mu
ch oblivious to atoms (and vice versa). Moreover, dark matter particles are oblivious to other dark matter particles. A physicist would say that dark matter particles interact with atoms and with themselves very weakly, if at all. Because of this fact, when our Galaxy and other galaxies formed, the dark matter remained in the very large and diffuse dark matter halo, while the atoms collided with one another and sank to the center of the dark halo, eventually forming stars and planets made almost completely of atoms.
The “shyness” of dark matter particles, then, is why stars, planets, and we are made of atoms and not of dark matter.
Nonetheless, dark matter particles are buzzing around our neighborhood—at any given time there is about one dark matter particle in a good-sized tea cup. And this is key to testing this bold idea. Dark matter particles are shy, but can occasionally leave a telltale signature in a very, very sensitive particle detector. For this reason, physicists have built large detectors and placed them underground (to shield them from the cosmic rays that bombard the surface of the Earth) to see if dark matter particles really do comprise our halo.
Even more exciting is creating new dark matter particles at a particle accelerator by turning energy into mass, according to Einstein’s famous formula, E = mc2.
The Large Hadron Collider in Geneva, Switzerland, the most powerful particle accelerator ever built, is trying to create and detect dark matter particles.
And satellites in the sky are looking for pieces of atoms that are created when dark matter particles in the halo occasionally collide and produce ordinary matter (the reverse of what particle accelerators are trying to do).
If one or more of these methods are successful—and I hope that at least one will be—we will be able to confirm that something other than atoms makes up the bulk of the matter in the Universe. Wow!
And now we are ready to talk about the biggest mystery in all science: dark energy. This is such a big puzzle that I am confident it will be around for one of you to solve. Solving it might even topple Einstein’s theory of gravity, General Relativity!
We all know that the Universe is expanding, having grown in size for the past 13.7 billion years after the Big Bang. Since Edwin Hubble discovered the expansion more than eighty years ago, astronomers have been trying to measure the slowing of the expansion due to gravity. Gravity is the force that holds us to the Earth, keeps all the planets orbiting the Sun, and is generally nature’s cosmic glue. Gravity is an attractive force—it pulls things together, slows down balls and rockets that are launched from Earth—and so the expansion of Universe should be slowing down due to all the stuff attracting all the other stuff.
In 1998 astronomers discovered that this simple but very logical idea couldn’t be more wrong ; they discovered that the expansion of the Universe is not slowing down, but instead it is speeding up. (They did this by using the time-machine aspect of telescopes: Because light takes time to travel from across the Universe to us, when we look at distant objects we see them as they were long ago. Using powerful telescopes—including the Hubble Space Telescope—they were able to determine that the Universe was expanding more slowly long ago.)
How can this be? According to Einstein’s theory, some stuff—stuff even weirder than dark matter—has repulsive gravity. Repulsive gravity means gravity that pushes things apart rather than pulling them together, which is very strange indeed!) It goes by the name of dark energy and could be something as simple as the energy of quantum nothingness or as weird as the influence of additional space-time dimensions! Or there may be no dark energy at all, and we need to replace Einstein’s Theory of General Relativity with something better.
THE LATEST SCIENTIFIC THEORIES
Part of what makes dark energy such an important puzzle is the fact that it holds the fate of the Universe in its hands. Right now, dark energy is stepping on the gas pedal and the Universe is speeding up, suggesting that it will expand forever, with the sky returning to darkness in about one hundred billion years.
Since we don’t understand dark energy, we can’t rule out the possibility that it will put its foot on the brake at some time in the future, perhaps even causing the Universe to recollapse.
These are all challenges for the scientists of the future—you, maybe?—to explore and understand.
Michael
Chapter Thirteen
Eric was standing in the main control room at the LHC, in front of the CCTV screens that showed ATLAS, 100 meters (328 feet) below in its cave, one of the gargantuan detectors at the Large Hadron Collider. ATLAS was the largest of its kind ever built, a colossal piece of engineering that dwarfed the tiny human beings who had created its mighty bulk. But entry to the mile-long tunnels housing the accelerator, and the huge man-made caves housing ATLAS and the other detectors, was now forbidden, and all the doors were sealed. No one was allowed into that part of the underground complex while the LHC was running.
According to the official schedule, the start of the great experiment—complete with politicians pressing a red button—was still weeks away. This was meant to be the dress rehearsal, a time when the scientists could work out whether they had thought of everything and could sort out their last technical problems before the experiment began for real. However, everything had gone so well that the trial run was now indistinguishable from the real thing. The proton beams were already circling in opposite directions through the tunnels more than eleven thousand times per second, creating six hundred million collisions per second, and ATLAS was reading the collision data.
The Large Hadron Collider (LHC)
CERN
In 1990 a
CERN scientist, Tim
Berners-Lee, invented the
World Wide Web as a way of
allowing particle physicists
to share information
easily—now the Web is an
everyday tool for many
people!
CERN—properly known as the European Organization for Nuclear Research—is an international particle physics laboratory on the border of France and Switzerland.
Founded in 1954, CERN has been operating colliders for more than fifty years now as part of its research into fundamental particles.
In 1983, the Super Proton Synchrotron (SPS) collided protons and antiprotons (the antimatter version of the proton) together and discovered the W and Z particles, which carry the weak nuclear force. The SPS is built inside a circular tunnel 7 kilometers (4.3 miles) in circumference, and today feeds protons to the LHC.
In 1988, after three years of digging, a new 27-kilometer (17-mile)-circumference circular tunnel 100 meters (328 feet) underground was completed to house the Large Electron-Positron collider (LEP). The LEP collided electrons with positrons (the antimatter version of the electron).
In 1998, work began on digging the detector caverns for the LHC. The LEP was turned off in November 2000 to make way for this new collider in the same tunnel.
The LHC was fully turned on for the first time in September 2008.
THE LHC
This is world’s largest particle accelerator.
Two beam pipes run along the 27-kilometer (17-mile) circular tunnel of the LHC, each carrying a beam of protons, traveling in opposite directions. It’s like a huge electromagnetic racetrack!
Inside the pipes, almost all the air has been pumped out to create a vacuum like there is in outer space, so that the protons can travel without hitting air molecules.
The core of the
LHC is the most
lifeless place on
Earth!
Because the tunnel is curved, more than 1200 powerful magnets around the tunnel bend the protons’ course so that they don’t hit the walls of the pipe. The magnets are superconducting, which means they can generate very large fields with very little loss of energy. This requires them to be cooled with liquid helium down to -456 degrees Farenheit (-271 degrees Celsius)—colder than outer space!
All in all, there
are around
9,300
magnets at the
LHC.
At full power, each proton will perform 11,245 laps of the ring per second, traveling at more than 99.99% of the speed of light. There will be up to six hundred million head-on collisions between protons per second.
As well as protons, the LHC is also designed to collide lead ions (nuclei of lead atoms).
THE GRID
With about one megabyte of data per collision, the LHC detectors produce too much data for even the most modern storage equipment. Computer algorithms select only the most interesting collision events—the rest, more than 99% of the data, are discarded.
Even so, the data from collisions at the LHC in one year is expected to be fifteen million gigabytes (which would fill seventeen thousand PCs with a two-hundred-gigabyte hard drive each). This creates a massive storage and processing problem, especially since the physicists who need the data are based all over the world.
The storage and processing is shared by sending the data rapidly over the Internet to computers in other countries. These computers, together with the computers at CERN, form the worldwide LHC Computing Grid.
The Detectors
The LHC has four main detectors situated in underground caverns at different points around the circumference of the tunnel. Special magnets are used to make the two beams collide at each of the four points along the ring where the detector caverns are situated.
ATLAS is the biggest particle detector ever built. It is 46 meters (151 feet) long, 25 meters (82 feet) high, 25 meters (82 feet) wide, and weighs 7,000 metric tons (15,432,359 pounds). It will identify the particles produced in high-energy collisions by tracing their flight through the detector and recording their energy.
CMS (Compact Muon Solenoid) uses a different design to study similar processes to ATLAS (having two different designs of detector helps to confirm any discoveries). It is 21 meters (69 feet) long, 15 meters (49 feet) wide, and 15 meters (49 feet) high, but weighs more than ATLAS at 14,000 metric tons (30,864,716 pounds).
