Zeno's Paradox & The Quantum Zeno Effect

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“A moving arrow is at rest.” This is obviously a nonsensical contradiction. But Zeno, a Greek philosopher famous for his metaphysical trolling, devised a paradox whose conclusion is just this. Here’s how it goes: if you look at an arrow flying through the air at any instantaneous snapshot in time, the arrow doesn’t travel any distance. If time is composed of an infinite number of these snapshots, and the arrow doesn’t move in any of them, then the arrow is at rest during the entirety of its flight. The moving arrow is at rest.

In fact, if we’re talking about a quantum arrow, there may be a way to freeze its motion simply by looking at it, through the aptly named quantum Zeno effect. The quantum Zeno effect predicts that certain quantum events - like the electrons moving between atomic energy levels, or the decay of atomic nuclei, can be frozen through the simple act of observation. I’m going to tell you about some very real experiments that claim to have demonstrated this phenomenon. But first, let’s see if the quantum Zeno effect can save us from being shot by a quantum arrow.

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Hosted by Matt O'Dowd
Written by Katie McCormick & Matt O'Dowd
Graphics by Leonardo Scholzer, Yago Ballarini, Pedro Osinski, Adriano Leal & Stephanie Faria
GFX Visualizations: Katherine Kornei
Directed by Andrew Kornhaber
Assistant Producer: Setare Gholipour
Executive Producers: Eric Brown & Andrew Kornhaber

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[jacquelinejohns]

Did you just describe Zeno's paradoxical ideas as 'trolling'? It all makes sense now.

[bierrollerful]

Kids: "Are we there yet? Are we there yet?"
Parents: "Stop quantum freezing the car!!"

[ayehavgunne]

I used to be a spacetime adventurer like you but then I took a quantum arrow to the knee. Because I blinked.

[hiccup.]

"If someone shoots a quantum arrow towards you, don't blink"
One of my favourite quotes

[seionne]

You got me there after "don't blink" lol

[misaki_live]

Spacetime is the best channel on this whole site. This series is amazing, and you're a great host, Matt! If I ever get around to getting higher education, I know what I'm studying!

[ThierryTiramisu]

0:20 metaphysical trolling. Quite badass, Zeno!

[skyebluesilly]

"We do a little metaphysical trolling"
-Zeno

[ScionVyse]

"Quantum Ouch" is my new favourite term.

[aluxt]

If the Quantum Zeno Effect plays a role in birds' ability to see magnetic fields, then does that mean (according to the Many-Worlds interpretation) there would be many, many worlds full of very, very lost birds?

[pauldacus]

4:59 Never let a Dr Who reference go to waste!

[PatricioHondagneuRoig]

0:20 "Metaphysical trolling". I love that way of putting it.

[ayehavgunne]

“So now you know why a quantum watched pot doesn’t boil. And it’s because you did watch.

Spacetime.”

[mjassims]

“Observing a quantum object; observing an image of a quantum object. These are the same” - Tower of Quantum Trials

[flensdude]

This reminds me of a poem attributed to Odin, chief god of all the Viking gods:

_A fifth spell, I know―_
_if I see shot with ill intent_
_an arrow, travelling in a fight;_
_it's incapable of flying too quickly_
_for me to stop it in its path_
_as long as I keep my eyes on it._

(Odin, Hávamál. Rough translation.)

_Þat kank fimta, _
_ef sék af fári skotinn_
_flęin í folki vaða, _
_flýgra svá stint, _
_at stǫðvigak, _
_ef hann sjónum of sék_

(Odin, Hávamál. Original poem.)

[vladdangel]

"observe" is such a cop out. If I'm blindfolded and my way of "observing" a baseball is by swinging a bat then yeah, some how when I observe a ball it travels away from me. This is the strange nature of observing baseballs in quantum mechanics.

[andrewgotlost]

I cant wait to watch this video 4 or 5 more times until I understand it.

[robertstrawser]

Love the weeping angel reference. Just had a creepy thought. If the weeping angels were creatures governed by quantum mechanics that means they should also be able to quantum tunnel into your room at night, while you’re sleeping, even if you have the door locked.

Pleasant dreams everyone… ;)

[Jeppelelle]

Will there be a video about the new potential discovery at CERN about the decay of beauty quarks? Would be awesome 👍

[thomasrichardson]

I know I will probably never get lucky enough to have my comment read, but here’s to hoping!!!! Matt, you and everyone else at SpaceTime are amazing. This show is my favorite part of the week because me and my daughter get to sit down and watch this show together, and now it has inspired her to pursue this field when she grows up. Keep up the good work and keep inspiring! Thanks.