A Watched Quantum State Doesn’t Change. Is the Zeno Effect Real?

The quantum Zeno effect is that, if you observe a quantum state it won’t change. Is this a real effect? What does it mean and when does it apply? I have answers.

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#science #physics

[nycbearff]

Please, Dr. Hossenfelder, do a video on what "observation" and "looks at" and "measure" mean in quantum mechanics. Obviously the universe didn't start acting differently when physicists were invented and started measuring things - non human quantum interactions must also have these same effects. What are they?

[thomasjgallagher]

At age 12 (a long time ago, now), I disproved "a watched pot never boils". I'm not sure why I haven't received notice from the Nobel folks just yet, but I reckon the physics prize is wide open now.

[DataIsBeautifulOfficial]

I'm no quantum physicist, but this explains why my downloads freeze when I watch them.

[mw-thov]

What hasn't been made clear is what are the special circumstances in a quantum system that constitutes its "memory" and results in the "Zeno effect"?

[fast_harmonic_psychedelic]

If you're checking state 2, you're doing something to it, and preventing that particle from going there. Measuring state 2 involves using a device that has some kind of current, which generates an electromagnetic field, which alters the local charge field in the experiment. but its not just a mathmatic field of numbers or some immaterial ether -- its a field of real photons with spin which effect the path of the particle not with magic or memory or time travel - but through physical bombardment.

[VolkerHett]

The pot alone is not the problem, you need milk, too! Watched milk will not boil but look in the other direction for a second and your in for a long cleaning session on your induction stove!

[OolTube]

The "memory" you're talking about is basically the particle being reset by the measuring interaction. I'm pretty sure you could do that with radioactivity, too, but then you'd need a measuring device that can actually interact with the particle without destroying it, and at those energies and such a small scale that's just not an option.

[doubletribble-yt]

1:40 - "just check that the particle is not in state two" - well that is still interacting with the particle, so yeah, there's no such thing as measurement independence when working with quantum effects. I don't understand what's different here than just saying that an observation is an interaction, and an interaction effects the state of the system.

[mskiptr]

This sounds perfectly in line with the measurement apparatus getting entangled with the experiment during the measurement. Before the measurement the particle is in a superposition of state 1 and 2. After measuring it once, the whole setup is now in the superposition of (1, we've measured 1) and (2, we've measured 2).

Now if we only consider the first part of the superposition, after a while it will shift to a superposition of (1, we've measured 1) and (2, we've measured 1) and if we measure it once more, we will again get a superposition of (1, we've measured 1 and 1) and (2, we've measured 1 and 2).

The "paradox" occurs because 1) as you said in the video, the probability density of the state changing starts at 0 and only increases after the measurement and 2) our measurement apparatus is not isolated from our bodies and so we're getting entangled with the "almost certainly 1" states as they are measured (or the wave function collapses, if that's how you prefer to think about it).

[renocence]

This is it right here, this is what I love so much. I love hearing the explanation of sa topic such as the zeno effect followed by "confirmed by experiments many times" . I get to sit comfortably in my new knowledge. I get that so rarely these days from the world.

[dguy]

But the states aren't "places". If you're watching a particle to see if it's in state 2, but the particle is in state 1, you're still interacting with that particle.

[Chad.Commenter]

Petition to make physicists stop using words like "observing" and "looking at" in context of explaining Quantum Mechanics to regular audiences. Just say "interacting", or "literally bombarding it with other particles" to make it all less spooky. You people are never simply looking at something anymore than a tree is looking at a car wrapped around it next to the highway.

[kevinberg]

Around 1:48 you're still interacting with the system even if you're only checking where the particle isn't. Claiming this is weird is akin to placing a detector at only one slit in a double-slit experiment, then acting surprised you have a clump pattern behind both slits.

[Zeeraha]

If you shortly observe the system for the state 2, you observed it and influenced it, resetting the "timer". It would only be the strange if you expect some particle ending up at some isolated position, and particle never gets there because you frequently check if the particle is there.

As for the prison guard and prisoner analogy, it would be like if the prison guard is checking outside of the prison if the prisoner is trying to escape. And strangly, he never tries to escape because guard is looking outside, but the prisoner cannot know if the guard is looking outside. It would only be strange if quantum systems would behave like that.

[pierluigimartini]

"watching" a radioactive decay is diffrent than "watching" an ultracold lattice gas (the paper mentioned) -- if by "watching" a radioactive decay we mean looking at a Geiger counter. The Geiger counter goes off *after* the decay has already happened, it doesn't interact with the radioactive atom. But "watching" the ultracold gas does involve interacting with it. If we had some way of measuring the state of the radioactive atom directly, then we could perhaps have a zeno effect (or anti-zeno effect .. speeding up the decay).

[byronwatkins]

"Looking" is an interaction with the particle that causes it to become exactly one of the two allowed states. After we look, the wave function can mix the known state with the other state at a certain rate. When we look again, the mixed state will again become exactly one of the two allowed states and the two probabilities for the two states are directly determined by how much of "the other" state got mixed into the wave function. A short time interval between observations means it is VERY probable that the state will not change and shorter intervals results in more certainty that the state will not change. It is only after a long interval that the probability of changing becomes significant.

[mrmouse]

my question is: are we sure that when we observe if the 2nd state wasn't reached, we aren't also interacting with the 1st state?
Like for example, checking the 2nd state 'fills it in' which makes it impossible for the quantum whatnot in the 1st state to move.

[xthesayuri]

How is that surprising?

The particles are described by probability distributions. Every time we observe it we reset the particles distribution. The longer we don't look the more uncertain we are about it's position or state or whatever it is we are measuring, and the higher the chances that it switches to another state. Therefore the more often we measure its state the more certain we are about its state.
Every observation causes a wave collapse.

[FrancisFjordCupola]

You can watch pots boil. Just need enough heat to melt them first.

[joelt]

This literally sounds like a software program. That if you aren't actively utilizing a module it will kill its process, then when you go to look it reinitialize (with the random effect being described). No it doesn't make sense at all that when you look at something that it behaves differently than when you don't. That defies all reasoning of the physical universe. That does sound natural at all. That sounds artificial. Either we have this *really* wrong, or this points to a higher power.