Alex McColgan
speaker
29,301 appearances
104 recordings
1 series
first heard Nov 2024
last heard 2d 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 — 68 in all, peaking in Aug 2026 with 11.
Appearances
Now, this may sound fairly straightforward, but it's not.
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The reason being that even in the sun, getting two protons to react to form deuterium, the first step of the reaction, is far from easy.
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Firstly, in order to fuse, the protons must get extremely close to each other, around 10%.
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10 to the power minus 15 meters apart.
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That is so, the strong nuclear force, the force that holds protons and neutrons together in the nucleus of an atom, kicks in, and they are drawn together.
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However, for two positively charged protons, getting this close means overcoming an immense amount of electrostatic repulsion.
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So much so, that even the kinetic energy provided by the extreme conditions at the heart of
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where protons are travelling around 500 km per second, is wildly insufficient.
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In fact, protons have only around 1,000th of the kinetic energy they require to overcome this barrier.
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It turns out, the only reason the Sun is able to sustain fusion at all is because quantum effects come into play.
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Now, you may remember that according to quantum physics, protons don't just act as particles, they also act as waves.
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This wave behavior means that in 10 to the power 28 proton-proton interactions, the protons can overcome this energy barrier, getting close enough that the strong nuclear force pulls them together.
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This is called quantum tunneling.
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But even when protons are drawn together this way,
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There is yet another effect to contend with.
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The force that mediates the conversion of one of the protons into a neutron is the weak force, which, because it is controlled by the massive W boson, is very inefficient.
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This leads to the more likely product of the proton-proton reaction being a proton pair, which immediately decays back into single protons.
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Together, these effects mean that the rate of proton conversion in our star is extremely slow.
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On average, a proton will wait 10 billion years before undergoing fusion.
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Indeed, the only reason the proton-proton reaction proceeds at all is because there are a heck of a lot of protons in the Sun.
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Showing 1801–1820 of 29,301 · page 91 of 1466
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