Alex McColgan
speaker
28,638 appearances
102 recordings
1 series
first heard Nov 2024
last heard 5d ago
Alex McColgan’s voice in public audio — every appearance, attributed to the second.
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recordings per month · last 12 monthsRecordings per month over the last 12 months — 66 in all, peaking in Aug 2026 with 11.
Appearances
With that in mind, physics is still an experimental science at its core, and we can't know for sure whether matter and antimatter obey the same laws of gravity unless we check for ourselves.
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The physicists at CERN set out to do just that,
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motivated not only by the baryonic asymmetry of the universe, but also by a few speculative papers suggesting that the cosmological properties of dark matter and dark energy could be more easily explained if antimatter were to have a negative gravitational charge, or to put it simply, if antimatter were to fall up rather than down.
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There are several ongoing experiments at CERN testing the gravitational properties of antimatter, including Aegis, G-bar and Alpha.
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Today we will focus specifically on a key experiment coming out of the Alpha group that was published in the journal Nature this past September.
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After decades of assumptions, this experiment has brought us real-world data on the gravitational acceleration of antimatter on Earth's surface.
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But before we show you the results, let's take a moment to appreciate just how intricately this experiment was designed in order to isolate and measure the effects of gravity.
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The first step in the experiment is to secure a beam of several million positrons per second emitted from a radioactive isotope of sodium.
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Most of these positrons end up colliding with ordinary matter in the experiment, causing miniature explosions in which positrons and electrons annihilate each other and release a small burst of energy in the form of light.
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but a small fraction of the positrons survive as they are guided through the experimental apparatus, where they are cooled by low pressure gases and trapped by electric and magnetic fields.
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But observing the effects of gravity on these positrons would be nearly impossible.
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Their masses are so small that the tiny force of gravity felt by each particle is overshadowed by even the smallest fluctuations in the surrounding electromagnetic fields.
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That's why this collection of positrons is merged with a separate container of antiprotons, where they bond and form neutral antihydrogen atoms that are much less responsive to stray electromagnetic fields.
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And where did the antiprotons come from?
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Suffice it to say that they were produced by firing ordinary protons into a block of metal really, really fast.
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Yes, physics is awesome like that.
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Once the anti-hydrogen atoms are created, they behave like tiny, weak magnets that can remain trapped by complicated arrangements of external magnetic fields.
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Now, this magnetic interaction is weak enough that it no longer overwhelms the gravitational effects that we are trying to measure.
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The chamber containing these antihydrogen atoms is nearly a vacuum.
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There are just about 200,000 atoms of ordinary gas per cubic centimetre, compared to a typical atmospheric density of 20 quintillion atoms per cubic centimetre.
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Showing 1581–1600 of 28,638 · page 80 of 1432
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