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Schrodinger's cat is probably dead - Comments

keyfeatures's Avatar Comment 1 by keyfeatures

Not sure I get the point of the story. Is it to illuminate the probabilistic nature of the universe?

However if we have more information on events leading up to the current point we could know with certainty if the cat had snuffed it or not. I presume the probability is assigned simply due to lack of knowledge about what has happened to, or is going on with, the cat? i.e. it is not actually impossible to determine if the cat is alive or dead but if my observations up to that point are limited I have to resort to probability.

In addition we know the cat has not lived or died randomly but as the result of specific events. We just don't know what specific events have occurred in the box - has the capsule broken or has the cat had a heart attack? I'd be willing to bet for sure that the cat hasn't turned into a dog or disappeared into thin air. Not sure what odds William Hill would give me on that one.....

Mon, 06 Jun 2011 18:25:07 UTC | #634855

DocWebster's Avatar Comment 2 by DocWebster

Schrodinger offered up this cat idea to illustrate the excessive navel gazing that was rampant in quantum physics at the time. Whether chance is weighted towards life or death is irrelevant compared to the idea that observing the answer has little effect on what the answer really is.

Mon, 06 Jun 2011 19:32:24 UTC | #634923

healthphysicist's Avatar Comment 3 by healthphysicist

No...observing the answer is the answer at a particular point in time.

It may not be the answer of the past or the future due to the probabilistic nature of the quantum world.

Mon, 06 Jun 2011 20:40:46 UTC | #634968

ccw95005's Avatar Comment 4 by ccw95005

Comment 1 by keyfeatures :

Not sure I get the point of the story. Is it to illuminate the probabilistic nature of the universe? However if we have more information on events leading up to the current point we could know with certainty if the cat had snuffed it or not. I presume the probability is assigned simply due to lack of knowledge about what has happened to, or is going on with, the cat? i.e. it is not actually impossible to determine if the cat is alive or dead but if my observations up to that point are limited I have to resort to probability.

The idea is that because of quantum uncertainty there's no way that having more information about events leading up to it would allow you to figure out whether the cat is alive or dead without looking. (I believe that it was a random radioactive decay that would somehow either kill the cat if it occurred - or not.) But I have to admit that I never quite saw the point of the story, other than the fun of saying that until observed, the cat should be considered both alive and dead. But Schrodinger posed the thought experiment almost as a joke, I believe - to show the absurdity of things existing in more than one state before observation. I don't remember anything about there being an equal chance of alive or dead, but I could be wrong. Maybe his cat can explain further.

Mon, 06 Jun 2011 21:13:45 UTC | #634988

Steve Hanson's Avatar Comment 5 by Steve Hanson

You're over thinking it. It was used to illustrate a point. Consider quantum entanglement, for instance, and you'll see what I mean.

Mon, 06 Jun 2011 21:21:34 UTC | #634996

raytoman's Avatar Comment 6 by raytoman

My understanding is that there are more people alive today than ever died. In fact, this has been true for a few decades. One could therefore argue that one has a better than 50:50 chance of living forever!

You can "prove" almost anything with numbers.

What you say about the cat makes sense.

BTW, I personally remember when the worlds population was first stated to have reached 2 billion. It's more like 7 billion today.

Mon, 06 Jun 2011 22:01:40 UTC | #635019

keyfeatures's Avatar Comment 7 by keyfeatures

We can at least assume the cat was alive before it was dead and that once it is dead it can't become alive again. Or does quantum theory even deny that?

Mon, 06 Jun 2011 22:03:28 UTC | #635021

Schrodinger's Cat's Avatar Comment 8 by Schrodinger's Cat

Comment 4 by ccw95005

I don't remember anything about there being an equal chance of alive or dead, but I could be wrong. Maybe his cat can explain further.

Yes, Schrodinger's original paper states...

"The psi-function of the entire system would express this by having in it the living and dead cat (pardon the expression) mixed or smeared out in equal parts. "

http://www.tu-harburg.de/rzt/rzt/it/QM/cat.html

My main point in posting this thread was that all too often that alleged 'equality' leads to a lot of quantum woo that completely leaves out other factors such as entropy.

For example, most of you have probably seen the scam referred to as 'Quantum Jumping'. This scam is based upon the supposed 'equality' of all the alleged multiple worlds, as if moving from one to another was simple, and completely leaves out other physics factors, including entropy.

Similarly there are other quantum woo hypotheses based upon a contested philosophical idea known as quantum suicide. Quantum siuicide ( a thesis partly developed by Max Tegmark ) posits a basis for a possible 'quantum immortality'. It's just a thought experiment, as with Schrodinger's cat, but that has not stopped a good deal of quantum woo writers from making use of it.......and once again with no consideration for entropy. Quantum immortality clearly defies other laws of physics.

Mon, 06 Jun 2011 22:16:01 UTC | #635028

AtheistEgbert's Avatar Comment 9 by AtheistEgbert

I'm pretty sure the thought experiment was all an excuse for Robert Anton Wilson to write a silly trilogy.

Mon, 06 Jun 2011 22:23:46 UTC | #635034

Schrodinger's Cat's Avatar Comment 10 by Schrodinger's Cat

Comment 7 by keyfeatures

We can at least assume the cat was alive before it was dead and that once it is dead it can't become alive again. Or does quantum theory even deny that?

As I mentioned in the opener, the thing that stops the cat coming back to life again is entropy......without which one could 'ressurect' the cat ! It's not hard to see why some of the more religious of the quantum woo writers latch on to the 'equality'.

Mon, 06 Jun 2011 22:25:12 UTC | #635036

healthphysicist's Avatar Comment 11 by healthphysicist

S. Cat -

I think you are really misapplying the concepts here.

The story is just a metaphor for how bizarre quantum mechanics is.

The cat lives in the macro-world, and is not subject to quantum mechanics.

If one plays the game of the metaphor, then once the cat is in the box, entropy is maximum (ie, maximum disorder, no state of reality is known) for that system.

That doesn't mean the cat's atoms have scrambled...it's just a metaphor.

Mon, 06 Jun 2011 23:31:31 UTC | #635066

Nikolovn's Avatar Comment 12 by Nikolovn

Actually, there are many examples of the Schrodinger's cat. Neutrino oscillation is similar effect. We know what kind of neutrino leaves the Sun, and we know what kind of neutrino we detect on the Earth. They are different. Another example is the double slit experiments with a single photon (or any particle). On the screen we obvserve diffraction, which means photon has passed trough both slits as a wave. Additional example is mass of the quarks. If you have "up" and "down" quark, and if you assume chiral symmetry of QCD Lagrangian, both quarks have same mass = 0. So, "up" and "down" are degenerate. Wave function of a neutral pseudo-scalar pion particle is 50% |"up"X"anti-up>+50%|down"X"anti-down">. Such kind of quantum configuration decays via annihiliation, and neutral pion decays to two photons. There can be an additional 3rd photon, if you consider pion as finite size object, than piont-particle. That means: pion is a density distribution, which automatically has mean radius. Pion has average sizes calculated from the density distribution. And if pion has a dipole moment, or quadrupole moment, there will be an additional photon transition. Probabilistic language of the Quantum Mechanics can be expressed as density distributions. Then, we can calculate the observables by averaging (and minimizing/optimization). Same story with the radioactive decay. The main observable is the average life time. The experssion of the life time is not random. It is an exact mathematics. However, the observables have meaning of average, because of the density distribution.

In the case of the cat, density distribution has values "tailing" 50/50, because beta decay has continuum spectrum. However, if we choose gamma discrete spectrum, you can set up the detector to trigger only a specific gamma line, with specific energy. Doing so, you can change little bit the probablitity to 60/40 or something else. Is there something wrong with QM here? The anwer is no, because you have information for the gamma-ray energy from an observation, and you use that information to select what do you want to observe. So, QM works.

Comment 4 by ccw95005 :

Comment 1 by keyfeatures :

Not sure I get the point of the story. Is it to illuminate the probabilistic nature of the universe? However if we have more information on events leading up to the current point we could know with certainty if the cat had snuffed it or not. I presume the probability is assigned simply due to lack of knowledge about what has happened to, or is going on with, the cat? i.e. it is not actually impossible to determine if the cat is alive or dead but if my observations up to that point are limited I have to resort to probability.

The idea is that because of quantum uncertainty there's no way that having more information about events leading up to it would allow you to figure out whether the cat is alive or dead without looking. (I believe that it was a random radioactive decay that would somehow either kill the cat if it occurred - or not.) But I have to admit that I never quite saw the point of the story, other than the fun of saying that until observed, the cat should be considered both alive and dead. But Schrodinger posed the thought experiment almost as a joke, I believe - to show the absurdity of things existing in more than one state before observation. I don't remember anything about there being an equal chance of alive or dead, but I could be wrong. Maybe his cat can explain further.

Tue, 07 Jun 2011 00:50:04 UTC | #635093

Ignorant Amos's Avatar Comment 13 by Ignorant Amos

Comment 12 by Nikolovn

No idea what that all means, but it read poetically. Wish really I was clever enough to grasp a bit of it, am off to bed with a warm feeling inside all the same.

Tue, 07 Jun 2011 00:59:32 UTC | #635098

Nikolovn's Avatar Comment 14 by Nikolovn

Just a few examples how QM probabilistic langauge works. I know, it isn't clear so much. Ok, let's consider neutrino oscillation. We know, what kind of neutrino leaves the Sun, we know the probability to oscillate from kind neutrino to another. Somewhere between Sun and Earth, neutrino wave function is exactly 50/50, similar to half-dead &h alf alive. It is a classical problem for physics students during their Quantum Mechanics class.

Comment 13 by Ignorant Amos :

Comment 12 by Nikolovn

No idea what that all means, but it read poetically. Wish really I was clever enough to grasp a bit of it, am off to bed with a warm feeling inside all the same.

Tue, 07 Jun 2011 01:42:45 UTC | #635113

Misfire's Avatar Comment 15 by Misfire

Cool.

Tue, 07 Jun 2011 02:04:25 UTC | #635121

yvrous's Avatar Comment 16 by yvrous

Why would Schrödinger not put 9 Geiger counters in the box to completely kill the poor cat or not kill the lucky cat?

Tue, 07 Jun 2011 02:37:09 UTC | #635127

ZenDruid's Avatar Comment 17 by ZenDruid

What I need to know is how the playing cards and Havana cigars got into that box.

Tue, 07 Jun 2011 02:53:21 UTC | #635129

ccw95005's Avatar Comment 18 by ccw95005

Comment 8 by Schrodinger's Cat :

Yes, Schrodinger's original paper states...

"The psi-function of the entire system would express this by having in it the living and dead cat (pardon the expression) mixed or smeared out in equal parts. " http://www.tu-harburg.de/rzt/rzt/it/QM/cat.html

Maybe I'm missing the point here, but wouldn't the chance of radioactive decay occurring depend on the amount of radioactive material? Big amount, 90% probability; small amount, 10% probability. The more radioactive isotopes, the more quantum options, right?

Tue, 07 Jun 2011 03:05:43 UTC | #635133

Schrodinger's Cat's Avatar Comment 19 by Schrodinger's Cat

Comment 11 by healthphysicist

I think you are really misapplying the concepts here.

The story is just a metaphor for how bizarre quantum mechanics is.

I think you've missed that my whole point was that the metaphor is mis-applied......as a lot of quantum woo and other junk depends on that mis-application.

Tue, 07 Jun 2011 04:01:49 UTC | #635143

Schrodinger's Cat's Avatar Comment 20 by Schrodinger's Cat

Comment 18 by ccw95005

Maybe I'm missing the point here, but wouldn't the chance of radioactive decay occurring depend on the amount of radioactive material? Big amount, 90% probability; small amount, 10% probability. The more radioactive isotopes, the more quantum options, right?

Yes, the thought experiment relates to equal probability after a specific interval of time, such that there's a 50/50 chance of one of the atoms having decayed within that period. More radioactive material doesn't alter the 50/50 probability.....it just shortens the period of time in which that state exists.

Tue, 07 Jun 2011 04:13:11 UTC | #635146

jac12358's Avatar Comment 21 by jac12358

Hey, why are you killing your namesake?

I think your point is much ado about nothing. When people say the cat has a 50/50 change of being dead or alive, what they REALLY mean is that the cyanide capsule has a 50/50 chance of being broken due to the quantum event that triggers it. The dead cat is a side effect of that purely to make the illustration more... dramatic. It would never have caught on if it were called "Schrodinger's Cyanide Capsule."

Though for fun, one might offset your "death by other means" entropy idea by suggesting that PERHAPS the cat is somehow immune to the cyanide, or the dose it too low, or something goes mechanically wrong and the glass vial doesn't break even though the quantum event should have led to that. Just saying.

Tue, 07 Jun 2011 05:03:52 UTC | #635151

keyfeatures's Avatar Comment 22 by keyfeatures

Comment 12 by Nikolovn :

Actually, there are many examples of the Schrodinger's cat. Neutrino oscillation is similar effect. We know what kind of neutrino leaves the Sun, and we know what kind of neutrino we detect on the Earth. They are different. Another example is the double slit experiments with a single photon (or any particle). On the screen we obvserve diffraction, which means photon has passed trough both slits as a wave. Additional example is mass of the quarks. If you have "up" and "down" quark, and if you assume chiral symmetry of QCD Lagrangian, both quarks have same mass = 0. So, "up" and "down" are degenerate. Wave function of a neutral pseudo-scalar pion particle is 50% |"up"X"anti-up>+50%|down"X"anti-down">. Such kind of quantum configuration decays via annihiliation, and neutral pion decays to two photons. There can be an additional 3rd photon, if you consider pion as finite size object, than piont-particle. That means: pion is a density distribution, which automatically has mean radius. Pion has average sizes calculated from the density distribution. And if pion has a dipole moment, or quadrupole moment, there will be an additional photon transition. Probabilistic language of the Quantum Mechanics can be expressed as density distributions. Then, we can calculate the observables by averaging (and minimizing/optimization). Same story with the radioactive decay. The main observable is the average life time. The experssion of the life time is not random. It is an exact mathematics. However, the observables have meaning of average, because of the density distribution.

In the case of the cat, density distribution has values "tailing" 50/50, because beta decay has continuum spectrum. However, if we choose gamma discrete spectrum, you can set up the detector to trigger only a specific gamma line, with specific energy. Doing so, you can change little bit the probablitity to 60/40 or something else. Is there something wrong with QM here? The anwer is no, because you have information for the gamma-ray energy from an observation, and you use that information to select what do you want to observe. So, QM works.

Thanks (I think!). The key bit (at least the bit I truly grasp given it's a while since I did GCSE physics) is that bit in bold. The observables are random but the expression is not. i.e. reality is not an average. The cat cannot be alive or dead. The particle cannot be there and not there. However the observables mean there are points at which we must assume that to be the case. Please tell me it is so because otherwise I'm going to have to wade through more quantum soup before my worldview can rest a little.

Tue, 07 Jun 2011 06:01:12 UTC | #635165

keyfeatures's Avatar Comment 23 by keyfeatures

Comment 19 by Schrodinger's Cat :

Comment 11 by healthphysicist

I think you are really misapplying the concepts here.

The story is just a metaphor for how bizarre quantum mechanics is.

I think you've missed that my whole point was that the metaphor is mis-applied......as a lot of quantum woo and other junk depends on that mis-application.

FWIW I thought it was an excellent point well made. I'm not sure why quantum mechanics are seen as bizarre. They don't seem that bizarre at all. It's the interpretation by some that is bizarre - and the cat tale drives that home. The entropy addition makes sense and suggests at least a way in which we can know which direction of travel we are going (in time).

Tue, 07 Jun 2011 06:13:27 UTC | #635169

reebus's Avatar Comment 24 by reebus

I submit that Schrödinger's cat was 100 % alive when it wrote the above article XD. What does what Susskind said recently about 'many worlds' and 'multiverse' being equivalent. Does that have a bearing on this question? I mean how do we know that entropy in this universe isn't offset with respect to the cat in another universe? Ok I admit it, i dont' know what the heck i'm saying lol. Just showing i'm awake ha ha

Tue, 07 Jun 2011 06:38:13 UTC | #635176

Rawhard Dickins's Avatar Comment 25 by Rawhard Dickins

It could just be stunned.

Tue, 07 Jun 2011 08:35:45 UTC | #635211

aball's Avatar Comment 26 by aball

There seems to be a lot of mistunderstanding here about the meaning of the Schrodinger's Cat thought-experiment. Using something familiar to all of us (a cat), this experiment demonstrates how bizzare the quantum world is by leading us to a seemingly rediculous conclusion.

In this case, the conclusion is that until an observation is made, the cat is neither dead nor alive. It only adopts one of the states dead or alive when someone opens the box and looks inside. This is not the same thing as saying there is a 50% chance that the cat is dead inside the un-opened box (and 50% that it is alive). And in fact, subtle statistical studies can differentiate between these two interpretations (although using boring things like electrons, not cats!). In quantum mechanics the cat is really in a mixed dead/alive state until you open the box.

Tue, 07 Jun 2011 08:39:52 UTC | #635213

AtheistEgbert's Avatar Comment 27 by AtheistEgbert

Comment 26 by aball :

In this case, the conclusion is that until an observation is made, the cat is neither dead nor alive.

Presumably, the cat is a blind cat. Or since it's a cat and not a human, it's not part of the science game.

Tue, 07 Jun 2011 10:48:17 UTC | #635257

KenChimp's Avatar Comment 28 by KenChimp

Erwin's thought experiment was meant to point out two things: The absurd implications of the Uncertainty Principle, and that no matter what we choose to believe, quantum mechanics does have some effect on our nice, stable, predictable, deterministic macro world.

There have been recent experiments to further demonstrate both points, including one experiment involving the manufacture of a structure of carbon nanotubes with one end comprised of one such tube, the other end comprised of an increasing number of attached tubes making part of the structure visible at about the width of a human hair.

The structure was suspended in a vacuum enclosure, super cooled, and energy was introduced to the end which was a single nanotube. The experimenters hoped to prove that quantum fluctuations are indeed exhibited in the 'macro' world. And the experiments were successful in this.

http://scholar.google.com/scholar?q=experiments+with+nanotubes+and+quantum+strangeness&hl=en&as_sdt=0&as_vis=1&oi=scholart

Tue, 07 Jun 2011 12:00:44 UTC | #635287

aball's Avatar Comment 29 by aball

@KenChimp

Thanks for the link. This sounds really interesting. I'm going to check this out.

Tue, 07 Jun 2011 12:12:18 UTC | #635292

kriton's Avatar Comment 30 by kriton

From a physics perspective, "observation" (such as looking at the cat) is just a series of interactions between photons, electrons, ions, and all the different molecules that make up our eyes and brains.

So if we are talking about a real cat in a box, opening the box and looking into it would not change some "quantum wave function of the cat" or something like that, right? The quantum state of everything in the box is what it is regardless of wether we open it or not.

If an atom has decayed, and emitted a particle (alpha/beta/gamma), and this particle has interacted with something, then whatever wave function of this decay must already have collapsed. The particle can not have both interacted and not interacted.

The wikipedia article on Schrödinger's cat (under "Copenhagen interpretation") says

Analysis of an actual experiment found that measurement alone (for example by a Geiger counter) is sufficient to collapse a quantum wave function before there is any conscious observation of the measurement.

But any interaction should be pretty much the same as a measurement, should it not?

Tue, 07 Jun 2011 12:59:30 UTC | #635319