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Schrödinger's Cat

It appears there's hope, quantum cat lovers!
Physicists can predict the jumps of Schrödinger's cat (and finally save it)

Yale researchers have figured out how to catch and save Schrödinger's famous cat, the symbol of quantum superposition and unpredictability, by anticipating its jumps and acting in real time to save it from proverbial doom. In the process, they overturn years of cornerstone dogma in quantum physics.

The discovery enables researchers to set up an early warning system for imminent jumps of artificial atoms containing quantum information. A study announcing the discovery appears in the June 3 online edition of the journal Nature.

Schrödinger's cat is a well-known paradox used to illustrate the concept of superposition -- the ability for two opposite states to exist simultaneously -- and unpredictability in quantum physics. The idea is that a cat is placed in a sealed box with a radioactive source and a poison that will be triggered if an atom of the radioactive substance decays. The superposition theory of quantum physics suggests that until someone opens the box, the cat is both alive and dead, a superposition of states. Opening the box to observe the cat causes it to abruptly change its quantum state randomly, forcing it to be either dead or alive.

The quantum jump is the discrete (non-continuous) and random change in the state when it is observed.

The experiment, performed in the lab of Yale professor Michel Devoret and proposed by lead author Zlatko Minev, peers into the actual workings of a quantum jump for the first time. The results reveal a surprising finding that contradicts Danish physicist Niels Bohr's established view -- the jumps are neither abrupt nor as random as previously thought. ...

FULL STORY: https://www.sciencedaily.com/releases/2019/06/190603124621.htm
 
I'd just hoped that when its nine lives were exhausted, we could get back to simple physics again. :thought:
 
I've always felt that Schrödinger's cat is one of those illustrations that causes more confusion than it resolves, rather like the "butterfly's wings causing a hurricane" analogy for chaos theory.

You put a cat in a box and there is a mechanism which may or may not activate. If it activates, the cat dies; if it doesn't activate, the cat lives.

Until you open the box, you do not know whether the cat is alive or dead and, therefore you do not know whether the mechanism has activated or not.

If you posit that the mechanism is activated by a single particle decaying, then you do not know whether the particle has decayed until you open the box.

The analogy breaks down when it is then suggested that the cat is "neither alive nor dead" and that opening the box to check somehow "causes" the cat to die.

If this were a real situation, we would say, "We do not know if the cat is alive or dead until we check."

If we needed to make a decision about something else that depended on the status of the cat, but we were unable to open the box, we would assess the probability as best we could.

Example: if the cat is alive, we can use it to get rid of the mouse. It the cat is dead, we'll need to buy a mousetrap. Best guess is it's 50/50, so there is a 50% chance we need to spend £5 on a mousetrap. We'll allow for that when planning our domestic budget.

Of course, the analogy of S's C was intended to say something profound about events at a quantum level, where there is a serious argument that the act of observation may cause something to happen.

My own thought: a blind man cannot find intact windows by throwing bricks. The act of detecting the intact window breaks it. The act of observation changes the state of the thing observed. This is how it really is at a subatomic level.

We can only observe things by bouncing things off them (e.g. electrons) or by extracting energy from them in some way with our measuring equipment. A blind man can detect a battleship by throwing a piece of gravel at it, because the effect of the gravel is negligible. A scientist cannot pinpoint the position of a subatomic particle by bouncing another subatomic particle off it, because that immediately moves the particle being observed.

Therefore, the scientist says, "The particle may be there. If we check, we will either get a yes or a no, but the very act of checking will change its position. Therefore, we can only work on the basis that there is an X% probability that it is there."
 
Glass half full/half empty:

It depends if you prefix "half" with words such as "only" or "still".

Optimist: the glass is half full. The glass is only half empty. The glass is still half full.

Pessimist: the glass is half empty. The glass is only half full. The glass is still half empty.

It also depends what's in the glass. "This wine's awful but my glass is half full."

My personal bugbear: "There was an empty bottle of milk on the worktop." If it is empty, it isn't a bottle of milk.
 
I'm probably oversimplifying...but I always thought the idea was...

There's a cat in a soundproof box.

You can't see it or hear it so it could be dead, or it could be alive.

So, until you have evidence either way, the cat is both alive and dead.
 
I'm probably oversimplifying...but I always thought the idea was...
There's a cat in a soundproof box.
You can't see it or hear it so it could be dead, or it could be alive.
So, until you have evidence either way, the cat is both alive and dead.

It's not really about the cat ...

The non-observability of the cat in the box is peripheral to the point of the thought experiment. The cat is simply an indicator for whether the event at issue (particle decay) has or has not occurred.
 
It's not really about the cat ...

The non-observability of the cat in the box is peripheral to the point of the thought experiment. The cat is simply an indicator for whether the event at issue (particle decay) has or has not occurred.
More to the point is that the cat is there to demonstrate the absurdity of quantum mechanics' implications. If the atom of radioactive material is in a state both decayed and not decayed, because it isn't being observed and nor are its effects, including those on the cat, then the cat must also be in a state both alive and dead. Since this is a ridiculous situation, something, Erwin Schrodinger felt, must be up with our interpretation of the evidence of particle physics.

So, until you have evidence either way, the cat is both alive and dead.
It's important to realise though that the randomness, the wave function, of subatomic particles isn't some mathematical convenience for modeling their behaviour. It's a real, physical thing. A single particle's probability wave can be separated, and the two waves can interfere with one another. So the cat could be both alive and dead until observed.
 
I've always understood it... and this is just the interpretation that makes sense to me... that the cat in question is both alive and dead because both of those possibilities exist as separate timelines - universes - and it's only when the observer looks, that they move into one or other of these universes, and hey presto the cat is either alive or dead in that timeline.

Every action creates a new reality, and all that.


And anyway, it's not a cat, it's a zebra. ;)
 
I've always understood it... and this is just the interpretation that makes sense to me... that the cat in question is both alive and dead because both of those possibilities exist as separate timelines - universes - and it's only when the observer looks, that they move into one or other of these universes, and hey presto the cat is either alive or dead in that timeline.

Every action creates a new reality, and all that.

I think that's fine. I suspect we become immediately causally connected to quantum systems once we view them. Which means particles are disconnected from our experience enough for us to be able to detect them as possibilities until we take a close look.
And anyway, it's not a cat, it's a zebra. ;)
Black with white stripes, or white with black stripes? Or simultaneously both until observed.
 
I do wish people would stop referring to 'Schrödinger’s cat '.

It's just an exercise in sophistry.

No normal person would use 'dead and alive'. They would use 'dead or alive', which fits Schrödinger’s theory quite well.

As I have mentioned elsewhere, my car is either outside my house, or it isn't. No way can it be both at the same time.

And, of course, I resolve the problem by looking.

INT21 (or is it ?).
 
I do wish people would stop referring to 'Schrödinger’s cat '.

It's just an exercise in sophistry.

No normal person would use 'dead and alive'. They would use 'dead or alive', which fits Schrödinger’s theory quite well.

As I have mentioned elsewhere, my car is either outside my house, or it isn't. No way can it be both at the same time.

And, of course, I resolve the problem by looking.

INT21 (or is it ?).
A friend of my Mum's drove her Merc into her house by mistake. It was half in, half out.
Not her fault, apparently. Mercedes admitted responsibility for a clutch failure in a new car.
 
I do wish people would stop referring to 'Schrödinger’s cat '.

It's just an exercise in sophistry.

No normal person would use 'dead and alive'. They would use 'dead or alive', which fits Schrödinger’s theory quite well.

As I have mentioned elsewhere, my car is either outside my house, or it isn't. No way can it be both at the same time.

And, of course, I resolve the problem by looking.

INT21 (or is it ?).

Schrödinger used the cat analogy as a way out pointing out the absurdity of Quantum Mechanics. Your car (electron) is either outside your house or it isn't, it can't be in two places at the same time but there can be an equal probability of it being outside your house or not. By looking out of the window (measuring the position of an electron) you have changed the phenomena by observing it.
Extrapolate to Quantum computers, switch is either on or off or on and off or not on and not off

Forgotten my point ...
 
catschr.gif
 
I'm not sure I agree with some of the premises in this new study which claims to outline a means for observing the famous cat without (theoretically) forcing it to be in one or the other state. Then again - maybe I'm just not getting the point ...
Physicists Can Finally Peek at Schrödinger's Cat Without Killing It Forever

There may be a way of sneaking a peak at Schrödinger's cat — the famous feline-based thought experiment that describes the mysterious behavior of subatomic particles — without permanently killing the (hypothetical) animal.

The unlucky, imaginary cat is simultaneously alive and dead inside a box, or exists in a superposition of "dead" and "alive" states, just as subatomic particles exist in a superposition of many states at once. But looking inside the box changes the state of the cat, which then becomes either alive or dead.

Now, however, a study published Oct. 1 in the New Journal of Physics describes a way to potentially peek at the cat without forcing it to live or die. In doing so, it advances scientists' understanding of one of the most fundamental paradoxes in physics. ...
FULL STORY: https://www.livescience.com/schrodingers-cat-can-be-peeked-at.html
 
Here's more info and an access link for the published article to which the Live Science item above refers ...

The role of system–meter entanglement in controlling the resolution and decoherence of quantum measurements
Abstract

Measurement processes can be separated into an entangling interaction between the system and a meter and a subsequent readout of the meter state that does not involve any further interactions with the system. In the interval between these two stages, the system and the meter are in an entangled state that encodes all possible effects of the readout in the form of non-local quantum correlations between the system and the meter. Here, we show that the entanglement generated in the system–meter interaction expresses a fundamental relation between the amount of decoherence and the conditional probabilities that describe the resolution of the measurement. Specifically, the entanglement generated by the measurement interaction correlates both the target observable and the back-action effects on the system with sets of non-commuting physical properties in the meter. The choice of readout in the meter determines the trade-off between irreversible decoherence and measurement information by steering the system into a corresponding set of conditional output states. The Hilbert space algebra of entanglement ensures that the irreversible part of the decoherence is exactly equal to the Hellinger distance describing the resolution achieved in the measurement. We can thus demonstrate that the trade-off between measurement resolution and back-action is a fundamental property of the entanglement generated in measurement interactions.

SOURCE (With Access To Full Article):
https://iopscience.iop.org/article/10.1088/1367-2630/ab4451
 
In the quantum world, uncertainty reigns – or is it all in the mind?

Source: newscientist.com
Date: 11 December, 2019

Schrödinger's dead-and-alive cat embodies the uncertainty of the quantum world. But whether parallel realities truly exist is a question less of science than belief.

HEISENBERG is speeding down the autobahn when a police officer pulls him over. “Do you know how fast you were going? 150 kilometres an hour!” the cop tells him. “Great,” Heisenberg replies, “now I’m completely lost.”

The joke is a pretty fair summary of Werner Heisenberg’s notorious quantum uncertainty principle. This says that certain pairs of properties in the quantum world can never be known simultaneously with perfect accuracy – the speed (or momentum) of something and its position, say. Measure one precisely and you know nothing about the other.

The uncertainty principle is more than a curiosity. Among other things, it allows a latitude in particles’ states and positions that explains the radioactivity that ultimately powers the sun and the fluctuations that gave rise to all matter in the early universe.

https://www-newscientist-com.cdn.am...-uncertainty-reigns-or-is-it-all-in-the-mind/
 
One aspect of the Schrödinger's Cat problem concerns the issue of whether quantum effects (and attendant wave function uncertainties) pertain only to atoms and particles at the nano-scale versus larger 'macro-scale' objects (such as a cat) as well.

A team of researchers propose a method for testing whether wave function collapse (and elimination of uncertainty) might be possible at this macro-scale.
Could Schrödinger’s cat exist in real life? Our research may soon provide the answer

Have you ever been in more than one place at the same time? If you’re much bigger than an atom, the answer will be no.

But atoms and particles are governed by the rules of quantum mechanics, in which several different possible situations can coexist at once.

Quantum systems are ruled by what’s called a “wave function”: a mathematical object that describes the probabilities of these different possible situations.

And these different possibilities can coexist in the wave function as what is called a “superposition” of different states. For example, a particle existing in several different places at once is what we call “spatial superposition”.

It’s only when a measurement is carried out that the wave function “collapses” and the system ends up in one definite state.

Generally, quantum mechanics applies to the tiny world of atoms and particles. The jury is still out on what it means for large-scale objects.

In our research, published today in Optica, we propose an experiment that may resolve this thorny question once and for all. ...

FULL STORY: https://theconversation.com/could-s...r-research-may-soon-provide-the-answer-147752
 
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I've always understood it... and this is just the interpretation that makes sense to me... that the cat in question is both alive and dead because both of those possibilities exist as separate timelines - universes - and it's only when the observer looks, that they move into one or other of these universes, and hey presto the cat is either alive or dead in that timeline.

Every action creates a new reality, and all that.
This is how I also see it (except that both timelines are not created by the action, they already exist, but our perceptions are limited by our entropy-driven perception of 'time passing)

The idea that reality 'collapses' has caused more confusion that it has solved. You do not change the universe; you move to the place where it is changed.

Or, more accurately, you experience the sequence of events where it is changed.
 
Anyone who says you cannot be in more than one place at once has never delivered pizza...
 
The box business is about the moment of observation. When you open the box the cat hasn't either died or not- it's the act of observing the cat which makes this happen.

I think the cat analogy is a little poor, meself.
I do understand the theory but thinking about poisoning pussycats didn't help me any.
Hi. I am reading Jenny Randles' book 'Time Storms' and I enjoyed the first part relating actual/supposed cases of 'time' (freaky electromagnetic) storms but now I am on to the physics part and I don't understand a word! Not the bit about astronauts ageing more slowly if they could travel faster than light speed and not this new bit about observation causing things to happen.

Obviously Schrödinger's cat is already either dead or not when the observer opens the box. I don't understand how anyone can say the poor moggy is simultaneously both until it's opened. Similarly, a tree falling in an empty forest does indeed make a sound if no-one and no creature is there to hear it: the tree landing creates vibrations.

I am still reading the book but mostly staring at the page thinking, 'Eh?'

If anyone can suggest a really, really simple and patronising book or maybe podcast or YouTube video on the topic, I'd be grateful!
 
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