- 4501 - PARTICLE ACCELERATORS - smashing atoms together?
--------------- 4501
- PARTICLE ACCELERATORS
- smashing atoms together?
-
- What do we learn by smashing atomic
particles together? It turns ot that
much of what physicists know about the fundamental laws of nature has come from
building machines to bash particles together.
-
- Physicists began developing particle
colliders in the wake of revelations that there was more to the universe than
atoms. Ernest Rutherford glimpsed inside the atom in one of the earliest
proto-collider experiments in 1909.
-
- Rutherford
and his student put some radioactive material behind a lead shield with
a hole in it, so that a stream of alpha particles (now known to be helium
nuclei) could shoot through the hole. When they pelted a thin gold foil with
this beam of particles, they observed that one in 20,000 bounced straight
backward.
-
- Rutherford likened it to an artillery
shell reflecting off a sheet of tissue paper. The physicists had discovered
that the gold atoms were mostly empty space, but that the alpha particles were
occasionally scattering off the atoms’ dense, positively charged nuclei.
-
- Two of Rutherford’s students, John Cockcroft
and Ernest Walton, went on to assemble and operate the first proper particle
collider in 1932. They used an electric field to speed up protons and slam them
into lithium atoms with enough energy to break the lithium atoms in two,
splitting the atom for the first time.
-
- In the following decades, physicists built
a parade of increasingly capable particle colliders. They increased the density
of the projectile particles, added superconducting magnets to steer them
better, and bought themselves more runway by designing circular colliders. To
produce more violent fireworks, they smashed together beams of particles
circulating in opposite directions.
-
- Many of the technological innovations came
in pursuit of higher-energy collisions for generating richer varieties of
particles. All the matter you’ve ever seen or touched is made up of just three
lightweight, fundamental particles: electrons and two types of quarks. Nature
allows more than a dozen heavier elementary particles to exist as well, but
only for a flash before they transmute into light, stable ones.
-
- To learn what massive particles can exist,
physicists leverage the interchangeability of matter and energy discovered by
Albert Einstein, expressed in his famous equation, E = mc^2. By generating more
energetic collisions, they see heavier particles pop out.
-
- Another way to think of it is that
higher-energy collisions push deeper into the subatomic world. All quantum
particles have wavelike properties, or wavelengths. And their wavelengths
determine what they can interact with.
-
- Sound waves can get around walls because
they’re meters long while light waves get stopped by anything larger than their
wavelength of a few hundred nanometers. The incredibly tiny waves involved in
high-energy collisions are sensitive to equally tiny quantum obstacles. In this
way, higher energies let physicists explore the rules of reality at smaller and
smaller scales.
-
- The energy of particle collisions increased
10 times every six to eight years for the better part of a century, nearly
matching the pace of Moore’s law for computer chips. That progress culminated
in the construction of the Large Hadron Collider (LHC) in Europe, a circular
underground track 27 kilometers in circumference that crashes protons together
at energies some 20 million times higher than what Cockcroft and Walton used to
split the atom.
-
- It was at the LHC in 2012 that physicists
discovered the Higgs boson, a heavy particle that gives other fundamental
particles mass. The Higgs was the final missing piece of the Standard Model of
particle physics, a set of equations that accounts for all known elementary
particles and their interactions.
-
- The LHC has seen no sign of the particles
predicted by supersymmetry, and in 2016 proponents of the theory conceded a
bet, acknowledging that our universe is not supersymmetric in the simple way
they had thought. The same year, a hint of a new particle turned out to be a
statistical mirage, and physicists had to confront the fact that the LHC
probably won’t uncover any new phenomena beyond the particles of the Standard
Model.
-
- Without hints pointing to the existence of
heavier particles that could be conjured up in higher-energy collisions, the
case for building another, even bigger multibillion-dollar particle collider is
hard to make. Some insist it’s worth doing because there’s still plenty to
investigate about the Higgs boson, which might hold clues about any heavier
entities beyond the LHC’s reach.
-
- A proposal to construct a next-generation
collider in Japan has stalled. Europe is mulling a 100-kilometer successor to
the LHC, but if approved and funded, it will take so long to build that today’s
grad students will be long retired before it switches on.
-
- American particle physicists got some
optimistic news last December when a government panel supported studying the
prospects of a muon collider. Muons are bulkier versions of electrons that
would pack more punch in collisions, while lacking the substructure of protons,
so that a relatively small muon collider could achieve clean, high-energy
collisions.
-
- A bleeding-edge muon collider could fit
into the footprint of an existing facility, the Fermi National Accelerator
Laboratory in Illinois, and so could conceivably be built more quickly and
affordably. The catch is that muons decay in a few microseconds, and the
technology required to create and control narrow beams of them doesn’t exist
yet. Still, if the project goes forward, proponents hope that such a device
could be operational around the time today’s kindergartners start getting their
doctorates.
-
- In the meantime, physicists have little
choice but to come up with alternative experiments and novel ways of piecing
together the clues that colliders have already given them.
-
-
June 18, 2024 PARTICLE
ACCELERATORS - smashing atoms together? 4501
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“Jim Detrick” -----------
--------------------- --- Wednesday, June 19,
2024
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