schroedingers cat

[Loklorien s'Ilancy]

i by no means possess a particularly scientific mind, but there are a few things in the world of science that do interest me. schroedingers cat being one of them. i think i first read about it in a magazine in high school, and its just kinda stuck with me since then, and every now and then i read as much as i can about it. now i know that the term schroedingers cat basically refers to a compilation of "superposed states", but i remember finding a site in particular where a group of scientists actually are conducting the experiment - putting a cat into a box and sealing it. let me tell you the emails they got werent the kindest. as far as i know, that apsect of the theory is just that - a theory; not meant to actually be carried out. if i find the site again, ill post the link.

but anyways, i was reading through some more schroedingers cat stuff, and found this. i know its old, but i still thought it was neat.

http://physics.nist.gov/News/Update/960528.html

[Charley]

I love that stuff :cool

[Darth Viscera]

NIST? National Institute of Science and Technology is right outside my house, 200 meters away. They dig lots of holes in the ground.

[Daiquiri Van-Derveld]

Maybe theyre burying the cats ;)

[Figrin D'an]

Schroedinger's Cat was one of favorite subjects of my physical chemistry professor in college. We spent way too much time analyzing the concept and breaking it down from different points of view.

It's a interesting subject... I just had a lifetime's fill of it in that class. :x

[Darth Viscera]

Originally posted by Daiquiri Van-Derveld
Maybe theyre burying the cats ;)

Well if this is true, then it's a bunch of mass graves that can each hold 100,000 cats.

The idea of that is rather disturbing to me. I hope they're just burying nuclear waste from their reactor (they must have one-it's a LARGE facility that spans several cities) or something.

[Loklorien s'Ilancy]

Posted by: chroot

A quantum system is very delicate. A system that is in a superposition of states will collapse into a stationary state on its first interaction with the outside world. That means it takes only one little photon, or one happenstance atom to come nearby and disrupt the system and collapse its wavefunction.

It's hard enough to isolate a microscopic object from other objects to observe its quantum properties. It's absolutely impossible to isolate a macroscopic object.

The common example is a playing card. If you balance a perfect playing card very precisely, exactly on its edge, it should actually fall to both the left and right simultaneously. The reason it doesn't, of course, is that there are billions of jiggling atoms inside it, all "measuring" the others, and there are air molecules and photons of heat radiation and so on all interacting with it from the external world. The action of all this is called "decoherence." The reason we don't observe quantum phernomena macroscopically is because it's impossible to isolate a macroscopic system well enough to protect its fragile wavefunction.

The only way to get macroscopic quantum behavior is at very low temperatures, where the thermal jiggling and radiation are diminished. Low temperature liquid helium, for example, becomes superfluid -- a sort of macroscopic quantum playground with billions of atoms all in the same quantum state, moving together without viscosity. Superconductors are another macroscopic quantum playground, but the slides are different colors.

- Warren

now this i found interesting - im pretty sure i understood it in that basically, to see a quantum phenomenon, the molecules making up something have to be supercoold in order for said something to exhibit a quantum reaction

is that right?

[Figrin D'an]

Pretty much, yeah.

Subatomic particles are always in motion, and because of the nature of their motion, it's impossible to simultaneously know an atom's position and velocity. That's called the Heisenberg Uncertainty Principle. The one way to limit the motion (not stop completely, but almost) is to drop the temperature as close to absolute zero as possible (0 Kelvin, or -273.15 C). At such low temperatures, the quantum energy levels (every atom has multiple energy states it can achieve) are very low, and their behavior becomes a close to an "ideal" system as possible.

So... when those subatomic particles aren't moving around much, the atoms don't move, and in a controlled system with as few external factors as possible, it's possible for, say, a liter of helium to behave like a single atom of helium, and we can actually see the wavefunction in action.

And, what's really cool, is that the wavefunction measured in those kinds of experiments actually matches the wavefunction that we can predict mathematically.

[Pierce Tondry]

I love this stuff!

If one were to read "Dirk Gently's Holistic Detective Agency" by Douglas Adams they would find small mention of this principle included in the book. It's what got me hooked on these kinds of principles.

[Loklorien s'Ilancy]

And, what's really cool, is that the wavefunction measured in those kinds of experiments actually matches the wavefunction that we can predict mathematically.

why is it that they cant be predicted? too low?

[Ryan Pode]

Originally posted by Darth Viscera
They dig lots of holes in the ground.

Digging holes builds character.

[Figrin D'an]

Originally posted by s'Ilancy
why is it that they cant be predicted? too low?


I'm not sure what exactly you mean... it's possible to predict and write the wavefunction for particle behavior mathematically. It's just that under "normal" conditions, we can't actually observe the behavior on a large scale. (Like that section that you quoted, the wavefunction is too easily affected by things like molecular motion, heat, etc.)

That's why these experiments are so cool. We've been able to write equations for wavefunctions for a long time, but it was always difficult to see if they stood up to experimental results. As technology has progressed, we're finding that a lot of the theories that guys like Schroedinger, Heisenberg and Feynman developed are being backed up with physical evidence.


Just for kicks, I thought I would repost this section from one of Michio Kaku's books, entitled "Beyond Einstein." It's a great read if you want to learn about the history of quantum mechanics and the search for a Unified Field Theory. Anyway, here's what he says about the famous Schroedinger's Cat thought experiment:



'Although scientists have never seen a violation of quantum mechanics in the laboratory (but they have seen plenty of confirmations), the theory continually violates "common sense." The notions introduced by quantum mechanics are so novel that Erwin Schroedinger devised a clever "thought experiment" in 1935 that captured it's apparent absurdity.

Imagine a bottle of poison gas and a cat trapped in a box, which we are not allowed to open. Obviously, although we cannot peer into the box, we can say that the cat is either dead or alive. Now imagine that the bottle of poison gas is connected to a Geiger counter, which can detect radiation from a piece of uranium ore. If a single uranium nucleus disintegrates, it releases radiation, which sets off the Geiger counter, which in turn breaks the bottle and kills the cat.

According to quantum mechanics, we cannot predict with certainty when a single uranium nucleus will disintegrate. We only can calculate the probability of billions upon billions of nuclei disintegrating. Therefore, to describe a single uranium nucleus, quantum mechanics assumes that it is a mixture of two states - one where the uranium nucleus is inert, the other where it has decayed. The cat is described by a wave function that contains the possibilities that it is both dead and alive. In other words, we must assume statistically that the cat is a mixture of two states.

Of course, once we are allowed to open the box and take a measurement, we can determine with certainty whether the cat is dead or alive. But before we open the box, according to probabilities, the cat is statistically in the nether state of being dead and alive. If that isn't weird enough, the very act of opening the box decides whether the cat is dead or alive. According to quantum mechanics, the measurement process itself determines the state of the cat. To make matters worse, quantum mechanics also implies that objects do not exist in a definite state (e.g., dead or alive) until the are observed.

Enstein was disturbed by the implications of quantum paradoxes such as Schroedinger's cat. "No reasonable definition of reality," he wrote, "could be expected to permit this." He, like Newton before him, believed in an objective reality, holding that the physical universe exists in a precise state independent of any measuring process.

The introduction of quantum mechanics opened a hornet's nest of philosophical ideas that have been buzzing around ever since.'

- Michio Kaku, Beyond Einstein, Pages 45-46

[Loklorien s'Ilancy]

Schroedinger, Erwin! Professor of physics!
Wrote daring equations! Confounded his critics!
(Not bad, eh? Don't worry. This part of the verse
Starts off pretty good, but it gets a lot worse.)
Win saw that the theory that Newton'd invented
By Einstein's discov'ries had been badly dented.
What now? wailed his colleagues. Said Erwin, "Don't panic,
No grease monkey I, but a quantum mechanic.
Consider electrons. Now, these teeny articles
Are sometimes like waves, and then sometimes like particles.
If that's not confusing, the nuclear dance
Of electrons and suchlike is governed by chance!
No sweat, though--my theory permits us to judge
Where some of 'em is and the rest of 'em was."
Not everyone bought this. It threatened to wreck
The comforting linkage of cause and effect.
E'en Einstein had doubts, and so Schroedinger tried
To tell him what quantum mechanics implied.
Said Win to Al, "Brother, suppose we've a cat,
And inside a tube we have put that cat at--
Along with a solitaire deck and some Fritos,
A bottle of Night Train, a couple mosquitoes
(Or something else rhyming) and, oh, if you got 'em,
One vial prussic acid, one decaying ottom
Or atom--whatever--but when it emits,
A trigger device blasts the vial into bits
Which snuffs our poor kitty. The odds of this crime
Are 50 to 50 per hour each time.
The cylinder's sealed. The hour's passed away. Is
Our <smallfont color={hovercolor}>-Censored-</smallfont> still purring--or pushing up daisies?
Now, you'd say the cat either lives or it don't
But quantum mechanics is stubborn and won't.
Statistically speaking, the cat (goes the joke),
Is half a cat breathing and half a cat croaked.
To some this may seem a ridiculous split,
But quantum mechanics must answer, "Tough @#&!
We may not know much, but one thing's fo' sho':
There's things in the cosmos that we cannot know.
Shine light on electrons--you'll cause them to swerve.
The act of observing disturbs the observed--
Which ruins your test. But then if there's no testing
To see if a particle's moving or resting
Why try to conjecture? Pure useless endeavor!
We know probability--certainty, never.'
The effect of this notion? I very much fear
'Twill make doubtful all things that were formerly clear.
Till soon the cat doctors will say in reports,
"We've just flipped a coin and we've learned he's a corpse."'
So saith Herr Erwin. Quoth Albert, "You're nuts.
God doesn't play dice with the universe, putz.
I'll prove it!" he said, and the Lord knows he tried--
In vain--until fin'ly he more or less died.
Win spoke at the funeral: "Listen, dear friends,
Sweet Al was my buddy. I must make amends.
Though he doubted my theory, I'll say of this saint:
Ten-to-one he's in heaven--but five bucks says he ain't."


found this on another message board, got a good laugh out of it :D

[Wei Wu Wei]

How incredibly odd. So essentially, due to quantum mechanics, we can have an undead cat walking the earth o.o;

[Loklorien s'Ilancy]

not really. the way it works, is that there is both a dead AND a live cat sitting in a box at the same time. if i understand things right

*hic*

[Pierce Tondry]

Up until you open the box, that is correct.

[Wei Wu Wei]

Then the whole thing mushes together and the cat becomes either alive, or dead.

[Pierce Tondry]

We scientifically minded like to call it "waveforms resolving". =p

[Lilaena De'Ville]

There was a great bit about this in "The Last Hero" by Terry Pratchett - I'll copy it out. It's hilarious. :D

[Figrin D'an]

Think of it as two sides of one infinitely thin coin. You can flip the coin, and it will either come up heads or tails. However, until you actually flip the coin, there is no way to know for sure what the result will be. We can write a mathematic expression on the probability of one result opposed to the other, but nothing more concrete.

On top of that, consider that the manner in which the coin is flipped, as well as external factors (wind, contact with another object, etc.) may affect the result.

As such, before and during the act of being flipped, the only way to describe the coin's final state is as a mixture of both heads and tails. And even then, we can't be sure that the result won't tainted.



A bit simplistic an analogy, but it works for the most part.

[Lilaena De'Ville]

"I don't stand for cruelty to cats."

:p

[Pierce Tondry]

Fig, did you ever read "Dirk Gently's Holistic Detective Agency" by Douglas Adams? I ask because your description is very similar to the one presented in the book.

And no, Fett, you cannot make a joke about offering Holly a chair.

[Figrin D'an]

Originally posted by Pierce Tondry
Fig, did you ever read "Dirk Gently's Holistic Detective Agency" by Douglas Adams? I ask because your description is very similar to the one presented in the book.


That's one of the few Douglas Adams books that I never read. I've read all the "Hitchhiker" books.

I remember that analogy being used by one of my professors, so maybe that's where he got it.

[Figrin D'an]

Here's a really awesome story that kind of ties into this discussion.

http://www.cnn.com/2004/TECH/science/01/28/matter.new.reut/index.html


Like I mentioned before, when you cool atoms and subatomic particles to near absolute zero, the quantum energy level drops and becomes uniform, behaving like one really big particle.

Well, that's what the researchers did here with fermions, which are the uber-tiny particles that make up subatomic particles like protons, neutrons and electrons. The result was a previously undiscovered state of matter.

This is way, way cool. I knew they had done this with bosons several years ago, but this has major practical application possibilities if it can be made to behave in similar manner at a higher temperature.