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Erwin Schrödinger.

Erwin Schrödinger, one of the fathers of quantum mechanics, is famed for a number of important contributions to physics, especially the Schrödinger equation, for which he received the Nobel Prize in Physics in 1933.

Photograph from Science Source

Melody Kramer

National Geographic

Published August 12, 2013

His feline paradox thought experiment has become a pop culture staple, but it was Erwin Schrödinger's work in quantum mechanics that cemented his status within the world of physics.

The Nobel prize-winning physicist would have turned 126 years old on Monday and to celebrate, Google honored his birth with a cat-themed Doodle, which pays tribute to the paradox Schrödinger proposed in 1935 in the following theoretical experiment.

A cat is placed in a steel box along with a Geiger counter, a vial of poison, a hammer, and a radioactive substance. When the radioactive substance decays, the Geiger detects it and triggers the hammer to release the poison, which subsequently kills the cat. The radioactive decay is a random process, and there is no way to predict when it will happen. Physicists say the atom exists in a state known as a superposition—both decayed and not decayed at the same time.

Until the box is opened, an observer doesn't know whether the cat is alive or dead—because the cat's fate is intrinsically tied to whether or not the atom has decayed and the cat would, as Schrödinger put it, be "living and dead ... in equal parts" until it is observed. (More physics: The Physics of Waterslides.)

In other words, until the box was opened, the cat's state is completely unknown and therefore, the cat is considered to be both alive and dead at the same time until it is observed.

"If you put the cat in the box, and if there's no way of saying what the cat is doing, you have to treat it as if it's doing all of the possible things—being living and dead—at the same time," explains Eric Martell, an associate professor of physics and astronomy at Millikin University. "If you try to make predictions and you assume you know the status of the cat, you're [probably] going to be wrong. If, on the other hand, you assume it's in a combination of all of the possible states that it can be, you'll be correct."

Immediately upon looking at the cat, an observer would immediately know if the cat was alive or dead and the "superposition" of the cat—the idea that it was in both states—would collapse into either the knowledge that "the cat is alive" or "the cat is dead," but not both.

Schrödinger developed the paradox, says Martell, to illustrate a point in quantum mechanics about the nature of wave particles.

"What we discovered in the late 1800s and early 1900s is that really, really tiny things didn't obey Newton's Laws," he says. "So the rules that we used to govern the motion of a ball or person or car couldn't be used to explain how an electron or atom works."

At the very heart of quantum theory—which is used to describe how subatomic particles like electrons and protons behave—is the idea of a wave function. A wave function describes all of the possible states that such particles can have, including properties like energy, momentum, and position.

"The wave function is a combination of all of the possible wave functions that exist," says Martell. "A wave function for a particle says there's some probability that it can be in any allowed position. But you can't necessarily say you know that it's in a particular position without observing it. If you put an electron around the nucleus, it can have any of the allowed states or positions, unless we look at it and know where it is."

That's what Schrödinger was illustrating with the cat paradox, he says.

"In any physical system, without observation, you cannot say what something is doing," says Martell. "You have to say it can be any of these things it can be doing—even if the probability is small."

59 comments
Hector Caban
Hector Caban

The paradox involved in the thought experiment known as Schrodinger's Cat is not as many seem to think simply that the status of the cat (dead or alive) cannot be known until an observation is made. If this were the case the whole thing would be downright silly.  However, the explanation offered in the article is so poor I am not surprised so many people misunderstand it. 

Tawny Hadouken
Tawny Hadouken

Hm... I didn't know the idea behind the hypothetical experiment was simply that one can not know the state of the cat until it is observed. That doesn't sound all that amazing to me. I mean, isn't that obvious? O.o


I always thought it had more to do with the idea that particles may behave differently when observed as to when not observed, and thus with this theory in mind, the cat is in two states, one without an observer and one with, which might mean that even if the radioactive material was triggered and the cat died, it might not be so until somebody observed this and thus changed the behavior of the particles.


See, now that I'm hearing it was just about 'Oh, you can't know until you observe, thus anything else is just a guess', I'm just like 'wow, why did I think Schrodinger's Cat was so cool?' :/

Ed Lau
Ed Lau

Largo, is your DP photoshopped? You look like a white Obama. The resemblance is uncanny. 

Karyn Fletcher
Karyn Fletcher

It just goes to show no matter smart you are can not know for sure what is in your present until you unwrap it ;)=)..........

Henry Norman
Henry Norman

Calling this "though experiment" a paradox is nonsense. I agree with Stephen Hawking's "When I hear about Schrödinger's cat, I reach for my gun"... The only thing undetermined is our knowledge (of the state of the cat), and if any "wave form collapses" at all when we open the box, would be the brain wave representing that knowledge. ES himself devised the gedankenexperiment to point out the absurdity of the notion that opening the box would have any influence as to the biological status of the cat.

Ian Wilson
Ian Wilson

"Those who think they understand quantum mechanics, clearly do not understand quantum mechanics."  There is more to know, lot's more.  But for arguments sake it could be like an imaginary number i.  i for those who are new to the math is the square root of -1.  i * i is -1 so you tally up the i's until they wouldn't have mattered anyway, or leave them in and have a useless answer, until it comes to matter in another equation...

Largo Lagg
Largo Lagg

The paradox is that we don't know if Schrodinger was right or wrong.  

Therefore, I can say with Schrodinger-like certainty that he is wrong.

Sounds like smoking weed's cat to me.

Lynn Mann
Lynn Mann

Let's step out of theory and into reality.

1. Any cat owner knows if you stick a cat in a box (that's if you can get the cat in the box in the first place) OH YOU'LL KNOW if it's dead or not. 

2. If you can't hear the wretched animal howl, scratch, crashing into the walls, ... then the box is very well insulated and doesn't have air holes and you won't need to wait long before you know the cat IS dead.

Paradox? :-)

Ray Bobbitt
Ray Bobbitt

The point of the paradox is not that the cat is alive, dead or both but:

1 - That in order to use any of the possible outcomes of the experiment in a mathematical description, we must use a method that contains ALL of the possible outcomes, as if all possibilities were co-existent.

2 - That by measuring for the answer, we have destroyed all other possibilities except for the one that we observed.  For example, if we agree that light is a stream of photons from an energy source how would we measure it?  The two of us might place a sensor on the light amd measure it's intensity.  Now lower the light down to one photon.  I put my instrument in the path and check my reading.  I see 1 photon, but my instrument must absorb that photon to measure it.  You disagree with my findings because from your position there are none to measure.  We can repeat the experiment but never agree on the outcome.

Don't worry, after our argument we went for a beer and discussed half full, half empty.


Last Curmudgeon
Last Curmudgeon

that's it?  that's the brilliant observation?  please say you're kidding.  please say there's more to the paradox than admitting you don't know until you look.  that's as brilliant as peek-a-boo!  this is where the kid says the emperor has no clothes.  a genius comes running in the door and says believe it or not, i don't know until i look!  the paradox here is that so many people have been amazed at finding out they don't know, either.

Chris Meyering
Chris Meyering

I consider myself a smart and reasonable man with a good a comprehension of Science, Math and Logic. But these Titans of Intelligence are on a whole other level, I would love to sit back and watch their thought processes unfold on a TV screen...wouldn't that be something.

Craig Busse
Craig Busse

What the cat paradox does is point up a critical weakness in quantum theory: it does not explain anything about the process by which the wave function, (the superimposed quantum states of any object be it photon or cat), "collapses" into a singular observable. It happens somewhere along the way to an observation but the theory is silent on just exactly where. I believe physicists are hoping that an eventual theory of quantum gravity will shed light on this mystery.


Reid Barnes
Reid Barnes

Quantum theory assumes Einstein's general theory of relativity, and he challenged quantum theory saying, God does not play dice. Yet if Einstein was right about general relativity, subsequent scientific developments apparently show his challenges to quantum theory are wrong—IF he was right about general relativity.  But what if Einstein was wrong about general relativity, because it is flawed by self-contradicting non-Euclidean geometry, and right about dice? Check out this Facebook Note:  https://www.facebook.com/notes/reid-barnes/not-the-god-particle-the-god-field-if-you-must-call-it-that/519767374742508

Clinton Weir
Clinton Weir

"if there's no way of saying what the cat is doing, you have to treat it as if it's doing all of the possible things—being living and dead—at the same time"

So you have to both feed it AND bury it in the backyard?  It seems like the latter will collapse its wave function, rendering the former unnecessary.

Clinton Weir
Clinton Weir

"if there's no way of saying what the cat is doing, you have to treat it as if it's doing all of the possible things—being living and dead—at the same time"

So you have to both feed it AND bury it in the backyard?  It seems like the latter will collapse its wave function, rendering the former unnecessary.

Ronny DeGumbia
Ronny DeGumbia

Run a can opener next to the box, you'll know if the cat is alive :p

Wang Chung
Wang Chung

What's not explained here is that by making an observation, you are in-fact changing the state of the particle. In order to see something so small, we have to shine it with a laser, therefore the observation has altered its state. We can never make a true observation of a quantum particle, because we don't have the means to do so without disturbing it.

Steve Traynor
Steve Traynor

This question is like the one about how if a tree falls in the woods and nobody is around to hear it, does it make a sound? A human being doesn't have to be present for an event to occur. The cat is dead when he is dead and most likely he was the first to know.

Ron Britvec
Ron Britvec

In my physics the condition of the cat is "unknown" and the location of the cat is "unknown" and the existence of the cat is "unknown".  If we could see into the box without opening it we could likely answer all three "unknown" questions, ditto if we opened the box.  I think all other answers come under the heading of conjecture, speculation, or what we common people call "guessing." 

R G
R G

So I have a simplistic "solution" to Schrödinger's cat that I'm sure is wrong and dismissible on several counts... or totally misses the point but I just don't know how or why...

Add to the box a detector of organic decay. Say it takes 48 hours for a dead cat to decay sufficient to be detected.

Without opening the box it is possible to know that the cat died 48 hours ago and has been dead ever since.





Barm Krauesen
Barm Krauesen

"Schrödinger developed the paradox, says Martell, to illustrate a point in quantum mechanics about the nature of wave particles."

Yes.  His point was that the current understanding was false.  At the time, the interpretation of Young's double slit experiment was that light was both a wave and a particle, but not at the same time, and it depended on how you observed it.  Schrödinger came up with this thought experiment to show that it was false.  Mathematically, he's right.  It is perfectly valid math to come to a paradox, to demonstrate that either the assumptions or the logic that got you there was false.

It is one of the best known theories because most people recognize how ridiculous it is.  But, he intended it to be ridiculous, to show how ridiculous the current theory on light was.  Since the average person correctly recognizes the ridiculousness of the statement, anybody championing this theory as serious obviously has less of a scientific mind than the average person.  Way to go, National Geographic.  Maybe you should go back to reporting on soft science?

Frank Shore
Frank Shore

Schrodinger's Cat favorite soliloquy:  "To be or not to be, that is the question."


Schrodinger's Cat  

      Wanted 

Dead and Alive


Schrodinger's cat proves Hugh Everett's MWI of QM.  The wave-function does not collapse.  The universe is a 5-D hypersphere with the BB at the center.  Use Riemann geometry and Minkowski space.  This follows Hartle & Hawking's NBP.

My AOL email address: advanpropcons

michael

Becker Head
Becker Head

Dr. Sheldon Cooper (Big Bang) had the best explanation of Schrodingers paradox.

charles currie
charles currie

The paradox explains the paradox of a collapsing wave function which was needed to explain the misguided interpretation of the results of the double-slit experiment.  It was needed for the sake of continuity, not for a proper explanation. It was about as useful as "spooky action at a distance" or the need to create space-time.

Bill Skywatcher
Bill Skywatcher

Similar to "nothing is good or bad, but thinking makes it so"...nothing is real or unreal, but observing makes it so.

Kaylan Orben
Kaylan Orben

@Hector Caban  I agree.  I have seen explanations of this experiment that have several variables that are not discussed here. I have found that it makes the experiment difficult to explain, as well as understand, which is why it ends up getting over simplified. 

Doug L
Doug L

@Ray Bobbitt and after the second pitcher discussed something about angels and pin heads (or maybe pinheads)

Thomas Wolken
Thomas Wolken

@Last Curmudgeon 

The point is that the cat is neither alive nor dead...it is 'undecided" if you will. Now this particular case is impossible because the wave function would have already collapsed, but in the double slit experiment the photons shot through the slits exist in a state of all probable possibilities unless it is observed which slit the photons go through, at which point the photon 'decides' on only one of the possibilities. The quantum eraser experiment strongly indicates that this is really because of the ability to know which slit the photons go through, and not simply direct interference from measuring.

Ramon Joslin
Ramon Joslin

@Chris Meyering Go to CBS, and watch the hit comedy The Big Bang Theory.  It won't enlighten you on the conundrum about Schrodinger's cat, but it would fulfill part of your desire RE: sitting back and watching their thought processes unfold on a TV screen, and laugh out loud while you're doing it.  The character known as Sheldon could go toe-to-toe with Erwin Schrodinger.  Of course, debating Quantum physics with Sheldon would make ES reach for a gun (refer to the post by Henry Norman).

charles currie
charles currie

@Reid Barnes The flaw of the double slit experiment is that you don't go looking for a particle result with wave tools.

Melody Kramer
Melody Kramer

@Wang Chung Right -- this is stating that it's prior to observation -- that's why it's in an and/or state. 

Thomas Wolken
Thomas Wolken

@Steve Traynor 

At the macro level that's generally true, but on the quantum level events don't just "occur"...there really are indeterminate states. The quantum eraser experiment is a pretty significant demonstration of that.

Melody Kramer
Melody Kramer

@Steve Traynor As a wise man named @pontoondock said on Twitter "There ought to be a range of Schrodinger’s Cat Food. Half the price but a 50-50 chance of the tin being empty." 

Mark Decyk
Mark Decyk

@Ron Britvec If you can see into the box without opening it, you collapse the superposition.  As @le jardin noted below, the issue is not the box, which is just a symbol for not being able to observe the actual state of the cat, but rather the information about the cat, however obtained.

Several people have noted that this isn't about the cat at all... the cat is a familiar Newtonian object, and does not exhibit quantum behaviours (although I am deeply suspicious about where my socks have all vanished to)... so why do we care?

Quantum computing exploits entanglement, where the state of the ambiguous particle can be inferred from the observing a related "entangled" particle (which does not collapse superposition) rather than the observation of the particle itself (which would).  It's a neat trick that lets us sneak a peek at quantum states.

Where this becomes useful is the idea that if you develop a problem where y=f(x) and make x a 'quantum' input, you can solve the thing once for all possible values of x, instead of repeatedly and sequentially solving for individual values.  The number of x's you can solve at once depends on how complex a superposition you can establish (or the number of 'qubits' in your quantum processor).

I'm describing this stuff as though it were simple (it isn't) and as though such a computer was easy to use (it isn't).  As I write, I feel confident that I know what I'm talking about here, which in this space is a SURE sign that I'm confused... so caveat emptor.


Steve Johnson
Steve Johnson

@R G or just use X-ray to see if its moving or not :)

just saying that its just an example he used.

le jardin
le jardin

@R G It's not opening the box per se that's the problem.  You wouldn't have to open the box at all if you just had a camera in there either.  The point is, you're making an observation.  Whether it's 48 hours or 48 microseconds after the event is irrelevant: it is at that point that the wavefunction collapses.

Reid Barnes
Reid Barnes

@charles currie @Reid Barnes Isaac Newton made a determination that light is a particle (which he called a corpuscle) not a wave by observing refraction patterns in consecutively placed crystals.

R G
R G

@le jardin @R G  But the observation (at which time the wavefunction collapses) actually confirms that something happened 48 hours earlier, 48 hours before the observation and the collapse  that you mention even occurs.

In the case of  a camera taking a picture ("click" – observation – waveform collapses), if  it shows a decomposed cat carcass with a weeks worth of putrefaction, well, the cat's already been dead for 7 days. What non-observed event collapsed the waveform 7 days earlier and killed the cat?

Thomas Wolken
Thomas Wolken

@R G @le jardin

The thing about the quantum world is an observation really can retroactively collapse a wave function. Schrodinger's Cat is impossible because the cat would not exhibit quantum effects, but on the quantum level this can actually happen. Read about the quantum eraser which essentially uses a slightly later observation to change a measurement that had technically already been done.

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