The Particle at the End of the Universe: How the Hunt for the Higgs Boson Leads Us to the Edge of a New World by Sean Carroll Page A
Authors: Sean Carroll
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answer is that their mutual electromagnetic repulsion does indeed push them apart, but it is overwhelmed by the strong nuclear force. Electrons don’t feel the strong force (just like neutrons don’t feel electromagnetism), but protons and neutrons do, which is why they can combine to make atomic nuclei. Only up to a point, however. If the nucleus gets too big, the electric repulsion just becomes too much to take, and the nucleus becomes radioactive; it may survive for a while, but eventually it will decay into smaller nuclei.
Antimatter
Everything you see around you right now, and everything you have ever seen with your own eyes, and everything you have ever heard with your ears and experienced with any of your senses, is some combination of electrons, protons, and neutrons, along with the three forces of gravity, electromagnetism, and the nuclear force that holds protons and neutrons together. The story of electrons, protons, and neutrons had come together by the early 1930s. At that time, it must have been irresistible to imagine that these three fermions were really the fundamental ingredients of the universe, the basic Lego blocks out of which everything is constructed. But nature had some more twists in store.
The first person to understand the basic way fermions work was British physicist Paul Dirac, who in the late 1920s wrote down an equation describing the electron. An immediate consequence of the Dirac equation, although one that took physicists a long time to accept, is that every fermion is associated with an opposite type of particle, called its “antiparticle.” The antimatter particles have exactly the same mass as their matter counterparts, but an opposite electric charge. When a particle and an antiparticle come together, they typically annihilate into energetic radiation. A collection of antimatter is therefore a great way (in theory) to store energy, and has fueled much speculation about advanced rocket propulsion in science-fiction stories.
Dirac’s theory became a reality in 1932, when American physicist Carl Anderson discovered the positron, the antiparticle of the electron. There is a tight symmetry between matter and antimatter; a person made of antimatter would undoubtedly call the particles of which they were made “matter,” and accuse us of being made of antimatter. Nevertheless, the universe we observe is full of matter and contains very little antimatter. Exactly why that should be so remains a mystery to physicists, although we have a number of promising ideas.
Anderson was studying cosmic rays, high-energy particles from space that crash into the earth’s atmosphere, producing other particles that eventually reach us on the ground. It’s like you’re using the air above you as a giant particle detector.
To create images of the tracks of charged particles, Anderson used an amazing technology known as the “cloud chamber.” It’s an apt name, as the basic principle is similar to that of the actual clouds we see in the sky. You fill a chamber with gas that is supersaturated with water vapor. “Supersaturated” means that the water vapor really wants to form into droplets of liquid water, but it won’t do it without some external nudge. In a regular cloud, the nudge typically comes in the form of some speck of impurity, such as dust or salt. In a physicist’s cloud chamber, the nudge comes when a charged particle passes through. The particle bumps into the atoms inside the chamber, shaking loose electrons and creating ions. Those ions serve as nucleation sites for tiny droplets of water. So a passing charged particle will leave a trail of droplets in its wake, much like the contrail created by an airplane, lingering evidence of its passage.
Anderson took his cloud chamber, wrapped in a powerful magnet, up to the roof of the aeronautics building at the California Institute of Technology, or Caltech, and watched for cosmic rays. Obtaining the properly supersaturated vapor
Antimatter
Everything you see around you right now, and everything you have ever seen with your own eyes, and everything you have ever heard with your ears and experienced with any of your senses, is some combination of electrons, protons, and neutrons, along with the three forces of gravity, electromagnetism, and the nuclear force that holds protons and neutrons together. The story of electrons, protons, and neutrons had come together by the early 1930s. At that time, it must have been irresistible to imagine that these three fermions were really the fundamental ingredients of the universe, the basic Lego blocks out of which everything is constructed. But nature had some more twists in store.
The first person to understand the basic way fermions work was British physicist Paul Dirac, who in the late 1920s wrote down an equation describing the electron. An immediate consequence of the Dirac equation, although one that took physicists a long time to accept, is that every fermion is associated with an opposite type of particle, called its “antiparticle.” The antimatter particles have exactly the same mass as their matter counterparts, but an opposite electric charge. When a particle and an antiparticle come together, they typically annihilate into energetic radiation. A collection of antimatter is therefore a great way (in theory) to store energy, and has fueled much speculation about advanced rocket propulsion in science-fiction stories.
Dirac’s theory became a reality in 1932, when American physicist Carl Anderson discovered the positron, the antiparticle of the electron. There is a tight symmetry between matter and antimatter; a person made of antimatter would undoubtedly call the particles of which they were made “matter,” and accuse us of being made of antimatter. Nevertheless, the universe we observe is full of matter and contains very little antimatter. Exactly why that should be so remains a mystery to physicists, although we have a number of promising ideas.
Anderson was studying cosmic rays, high-energy particles from space that crash into the earth’s atmosphere, producing other particles that eventually reach us on the ground. It’s like you’re using the air above you as a giant particle detector.
To create images of the tracks of charged particles, Anderson used an amazing technology known as the “cloud chamber.” It’s an apt name, as the basic principle is similar to that of the actual clouds we see in the sky. You fill a chamber with gas that is supersaturated with water vapor. “Supersaturated” means that the water vapor really wants to form into droplets of liquid water, but it won’t do it without some external nudge. In a regular cloud, the nudge typically comes in the form of some speck of impurity, such as dust or salt. In a physicist’s cloud chamber, the nudge comes when a charged particle passes through. The particle bumps into the atoms inside the chamber, shaking loose electrons and creating ions. Those ions serve as nucleation sites for tiny droplets of water. So a passing charged particle will leave a trail of droplets in its wake, much like the contrail created by an airplane, lingering evidence of its passage.
Anderson took his cloud chamber, wrapped in a powerful magnet, up to the roof of the aeronautics building at the California Institute of Technology, or Caltech, and watched for cosmic rays. Obtaining the properly supersaturated vapor
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