Skip to comments.Physicists scoop information from Schrodinger's cat box [Quantum Mechanics]
Posted on 01/22/2014 2:53:50 PM PST by ETL
In a paper published in the current issue of the scientific journal Nature Communications and titled "Direct measurement of a 27-dimensional orbital-angular-momentum state vector," a team of physicists led by the University of Rochester's Mehul Malik describe how they circumvented a basic principle of uncertainty that requires that some states of a quantum system must be understood poorly if other states are to be understood well.
Determining a quantum state, such as the position of an electron or the momentum of a photon, is tricky, to say the least. That's because subatomic particles behave nothing at all like billiard balls, orbiting moons, or any other kind of object with which we humans are remotely familiar.
A photon, for instance, sometimes acts like a wave, diffracting, interfering, and scattering, as all good waves ought to. Yet sometimes it will also behave like a particle, for instance by bashing into an electron or by traveling with ease through a vacuum.
According to our current understanding, things at the quantum scale can exist simultaneously in these two modes, both as localized particles, with distinct measurable states, and as spread-out probabilistic waves, with multiple contradictory states.
One consequence of this "wave-particle duality" is that it imposes a fundamental limit on how much we can know about the universe. An unobserved electron, say scientists, exists as a wave of mutually contradictory states. As the German physicist Werner Heisenberg first pointed out in 1927, taking a measurement of one state, say, the electron's position, and you irreversibly alter its momentum, and vice versa. In the parlance of quantum physicists, the "wavefunction" of a system's probabilities "collapses" into a specific state when you observe it.
If the quantum-mechanical model sounds bizarre, that's because it is.
(Excerpt) Read more at csmonitor.com ...
"Confusion about the Uncertainty Principle It's very common for the uncertainty principle to get confused with the phenomenon of the observer effect in quantum physics, such as that which manifests during the Schroedinger's cat thought experiment. These are actually two completely different issues within quantum physics, though both tax our classical thinking.
The uncertainty principle is actually a fundamental constraint on the ability to make precise statements about the behavior of a quantum system, regardless of our actual act of making the observation or not. The observer effect, on the other hand, implies that if we make a certain type of observation, the system itself will behave differently than it would without that observation in place."
not being argumentative, but like i said above, isn't sight passive?
kinda like the difference between active and passive SONAR is how i am looking at it, or is that a bad analogy
"The observer effect refers to situations in science where the act of observing a system has an impact on the system being observed. Checking pressure in a tire, for example, is done by causing a release of air which, in turn, causes a slight change in the tire pressure. This is a classic example. Scientists (especially psychologists) have to be especially careful when planning their research methods to avoid interfering with the results they intend to get.
In the realm of quantum physics, there's a more powerful form of the observer effect, as exhibited by the Schroedinger's Cat thought experiment and the quantum double slit experiment. It appears that in cases like these, the very act of making the measurement doesn't just modify the system, but actually results in fundamentally different physical behaviors within the system.
Yes. The effects are there even if a human is not observing the situation.
Suppose that a free electron is sitting on a lab table. And the overhead lights are on. Particles of light will "bounce" off the electron and cause the electron to shift around. It's like how throwing balls at a cardboard box will cause the box to shift around.
So a human does not cause the uncertainty in where the electron really is. The human just notices the uncertainty.
that is why i ask if he is using the words interchangeably when they really are not interchangeable
one is active the other is passive like active vs passive SONAR
or am i missing something?
thx for putting up with me here
Death to all misplaced apostrophes!!
Schroedinger’s girlfriends would make an interesting study, too.
Well, to be honest, I'm actually a little annoyed with you. You promised that you would be asking stooooopid questions, yet all you've been doing is asking great ones! And if you don't cut it out...
Variation on the cat experiment: instead of a cat, the physicist stuffs one of his grad students into the box. Does the grad student observing his own state collapse the wave function only from his own viewpoint, with his state being a wave function from the viewpoint of the physicist until he opens the box?
And if the grad student, upon being stuffed in the box, has vowed to kill the physicist if he survives the box, is the physicist's existence a wave function until the head of the department opens the lab door to check on him?
One theory is that events that will happen in the future (the observation), have effect on the past; so the act of observation is somehow already bound up with the future observed state. (Not a very coherent explanation, I know.)
A good, and highly readable, book on the weirdosity of quantum events is "In Search of Schrödinger's Cat".
I would just call campus security.
Now, to drive you a bit crazy, I'll add one more thing.
As I said in a previous post, a human does not cause the uncertainty in where an electron really is. The uncertainty is caused by the light-electron interactions.
The human just notices the uncertainty.
So where is the electron? It is exists somewhere within its movement blur. Right? Wrong! It exists everywhere within its movement blur. It exists everywhere it possibly could be.
And the same goes for every object. So let's suppose it's night, and you are inside, far from any window. Where is the moon?
It is everywhere it could possibly be! Could the moon have been struck by a meteor and fallen into the sun? Possibly. So "part" of the moon's "existance" really is in the sun.
Only when you observe the moon does it come into being in one place. All other possiblities become zero. So in this part of quantum mechanics, human observation really does change things!
This was all stated mathematically by Schrodinger. And it's so weird that Einstein refused to believe in any of it. Experiments have since proved that Schrodinger was right and Einstein was wrong.
Another great book by John Gribbin is The Matter Myth which he co-wrote with my favorite science author, Paul Davies.
Schrodinger’s Kittens and the Search for Reality: Solving the Quantum Mysteries - by John Gribbin
All are wonderfully written for the intermediate level reader. These two guys really have a knack for making the complex comprehensible.