Alex McColgan
speaker
27,837 appearances
101 recordings
1 series
first heard Nov 2024
last heard 11 Sep
Alex McColgan’s voice in public audio — every appearance, attributed to the second.
Trend
recordings per month · last 12 monthsRecordings per month over the last 12 months — 65 in all, peaking in Aug 2026 with 11.
Appearances
Meanwhile, a British physicist, who was also destined to win a Nobel, had been developing a description of electrons that would fit nicely within the framework of quantum field theory.
voice-verified
His name was Paul Dirac.
voice-verified
By 1928, Dirac had realised that in order to describe electrons as quantum fields in a way that was physically consistent with special relativity,
voice-verified
they had to be part of a larger mathematical structure, later known as a Dirac spinner, that inevitably gave rise to both positively and negatively charged versions of the same particle.
voice-verified
In this way, Dirac had predicted the existence of positrons before Anderson had even built the cloud chamber that would detect them four years later.
voice-verified
What's even more incredible is that electrons aren't the only fundamental particle to come in a two-for-one Dirac spinner package.
voice-verified
Other particles of matter, like the quarks that make up protons and neutrons, each have their own anti-quark counterparts.
voice-verified
These antiquarks can come together to form antiprotons and antineutrons, which can then bond with positrons to form anti-atoms and anti-molecules.
voice-verified
You could make a whole planet out of antimatter, and from the outside, it would look quite similar to an ordinary planet made of ordinary matter.
voice-verified
But if antimatter were too similar to matter, if the only difference were the sign of its charge, then it would be impossible to explain why our universe contains so much of one and so little of the other.
voice-verified
This cosmic mystery, known as the baryonic asymmetry of the universe, sent physicists on a decades-long quest to try and find as many differences as they could between matter and antimatter.
voice-verified
That quest lives on today, spearheaded by particle colliders at CERN that are capable of producing, trapping, and studying both positrons and antiprotons.
voice-verified
But, before we talk about these experiments, let's try to summarise what we already know about the properties of antimatter.
voice-verified
When studying antiparticles in isolation, experiments have confirmed with ever greater precision that their intrinsic properties, namely their masses, are exactly the same as for ordinary particles.
voice-verified
And when studying how antiparticles are affected by electromagnetic forces, experiments have again found that they behave the same exact way as ordinary particles, except with the opposite electric charge, just as Anderson had observed in his cloud chamber.
voice-verified
But, electromagnetism is just one of the four fundamental forces of nature, alongside gravity and the weak and strong nuclear forces.
voice-verified
And as physicists began to better understand the weak force in the 1950s and 60s, they realised that particles and antiparticles are actually affected by it quite differently.
voice-verified
The first surprise was that ordinary particles could only feel the weak force if they were left-handed, and antiparticles could only feel it if they were right-handed.
voice-verified
The concept of handedness, or chirality, is subtle and difficult to conceptualise for particles with mass,
voice-verified
But a loose analogy can be drawn with a particle's helicity, which describes whether a particle is spin up or spin down along its direction of motion.
voice-verified
Showing 1541–1560 of 27,837 · page 78 of 1392
← Previous
Next →