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Ele Willoughby, PhD

Happy birthday Chien-shiung Wu (1912-1997), who came up with a truly beautiful experiment to test whether the weak force conserves parity (whether beta decay would be the same if reflected in the mirror)! In my print on the left I show Wu in her lab & a schematic diagram of her experiment. On the right I show her reflection, as in the mirror, & the mirror reflection of the experimental set-up & the shocking result, that 🧵1/n

Linocut print of Chien-shiung Wu in indigo wearing a lab coat and holding a schematic diagram of her famous violation of parity experiment (in blue and indigo) on the left side. The right side shows the mirror image except in the schematic diagram. The left side schematic shows a C shaped electromagnet open to the left. The top is labeled S, the bottom is labeled N and the middle is wrapped in wire drawn as a circuit diagram schematic with parallel lines to indicate a power source and left arrow on top wire, right arrow on bottom. Between the poles of the magnet is a big blue dot to designate Cobalt-60 with many tiny dots as beta-decay electrons, the majority going downwards to N pole. On the right, everything is flipping except most electrons go upwards (and and N and S poles are flipped).
May 31, 2024, 12:09 PM·Public
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Ele Willoughby, PhD

the reaction is not the mirror opposite.⁠

⁠In 1956, theoretical physicists Lee & Yang pointed out that no one had checked to make sure that the weak force, which controls beta decay in radioactive materials, also conserves parity. Lee convinced the brilliant experimentalist to test this.⁠
⁠
Wu did a subtle & technically difficult experiment with her collaborators which is shown schematically in the print. She took Cobalt-60 (shown as the cobalt blue sphere in the box), which is radioactive.🧵2/

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Ele Willoughby, PhD

Its neutrons spontaneously give off electrons & become protons. The electrons are the tiny blue dots. On the left, we see that the Co-60 in an electromagnet (a wire wrapped metal horseshoe with a source of power). Because of the spiral-wrap of the wire, we know that the North pole of the magnet will be on the bottom (you can figure this out by mimicking the curl of the wire with the fingers of your right hand & look at the direction your thumb points). It turns out that the emitted electrons 🧵3/

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Ele Willoughby, PhD

are given off preferentially towards the N pole. ⁠
⁠
Next, she reversed the set-up as in the mirror. On the right you see the horseshoe & wire spiral reflected. If you use your right hand to check the direction of the magnet field, you'll see that it is the opposite way; the N pole is now on the top. It turns out that the electrons are preferentially emitted upwards toward the N pole. 🧵4/5

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Ele Willoughby, PhD

Thus, beta decay IS NOT the same in the mirror! Wu showed that a "Law" of physics did not hold! This result was staggering & shocked the physics world. Lee and Yang won the Nobel prize for their theoretical work. Many physicists thought Wu should have been included in this win.⁠

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🧵5/5

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