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 ...
Only when you observe the moon does it come into being in one place. All other possibilities become zero. So in this part of quantum mechanics, human observation really does change things!OK... what happens when TWO or more people see it at the same time? then what???
e=mChode2 suck at String Theory...
I was waiting for that question, and I knew you would ask it! It is night. You are inside and cannot see the moon. So the moon "exists" everywhere it possibly could be, including in the sun.
I am outside. I am observing the moon. It is where I see it, and nowhere else.
So where is the moon? Some physicists say it's where I, the actual observer, see it. Others say that your interpretation is equally valid, and so the question can have no definite answer.
With large objects it does not matter. For you, the moon is everywhere, but it is most probably in its normal orbit, where I see it. For you, the chances of it being anywhere else are real, but very low. So you wouldn't complain too much about my observation.
But as objects become smaller, the chances of a far-away observation increases. If the moon were the size of an electron, there would be a decent chance that it would be observed in the sun, then an instant later past Mars, then an instant later in its normal orbit.
Weird stuff. As I mentioned earlier, Einstein could not accept it. And that's one reason he made almost no useful contributions to science in the last 25 years of his life.
It appears the question is how does the electron know what you are measuring for and why does the electron show up for the test exactly how you want to measure it? Why does the electron want to please the tester? Could it somehow be communicating with us?
You’re welcome. Thanks for pinging your mob over here. :)
“In science, the term observer effect refers to changes that the act of observation will make on a phenomenon being observed. This is often the result of instruments that, by necessity, alter the state of what they measure in some manner. A commonplace example is checking the pressure in an automobile tire; this is difficult to do without letting out some of the air, thus changing the pressure. This effect can be observed in many domains of physics.
The observer effect on a physical process can often be reduced to insignificance by using better instruments or observation techniques.
Historically, the observer effect has been confused with the uncertainty principle.[1][2]”
http://en.wikipedia.org/wiki/Observer_effect_%28physics%29
Once we have measured the system, we know its current state and this stops it from being in one of its other states.[3] This means that the type of measurement that we do on the system affects the end state of the system. An experimentally studied situation related to this is the quantum Zeno effect, in which a quantum state would decay if left alone but does not decay because of its continuous observation. The dynamics of a quantum system under continuous observation is described by a quantum stochastic master equation known as the Belavkin equation.[4][5][6]
An important aspect of the concept of measurement has been clarified in some QM experiments where a small, complex, and non-sentient sensor proved sufficient as an "observer"—there is no need for a conscious "observer".[7]
A consequence of Bell's theorem is that measurement on one of two entangled particles can appear to have a nonlocal effect on the opposite particle. Additional problems related to decoherence arise when the observer too is modeled as a quantum system.
The uncertainty principle has been frequently confused with the observer effect, evidently even by its originator, Werner Heisenberg.[1] The uncertainty principle in its standard form actually describes how precisely we may measure the position and momentum of a particle at the same time — if we increase the precision in measuring one quantity, we are forced to lose precision in measuring the other.[8] An alternative version of the uncertainty principle,[9] more in the spirit of an observer effect,[10] fully accounts for the disturbance the observer has on a system and the error incurred, although this is not how the term "uncertainty principle" is most commonly used in practice."
Please ping me to the Quantum Mechanics / pix of cats in boxes threads!
Fascinating questions. Delightful even. And fun to think about. But sadly, it would take someone well above my pay grade to answer them.
Awww, had a collapse of the wave function?
Thanks for the ping!
LOL!!! pretty much...
Now, this is an interesting parallel to the question... When you take the pressure of a tire, air escapes, so the pressure you get is different from the pressure that was in it before you measured it.
there you go... better check it again to see how much air you let out to check it! repeat as necessary 8^)
Above my pay grade too FReeper. I heard about another experiment with two paired electrons. Forgive me my recall isn’t what it used to be but the basics are this, the spin of one electron was altered and the paired electron immediately reflected the change. The communication was far faster than the speed of light and the scientista performing the experiment concluded that everything appears to be interconnected and that when something happens the entire universe is aware of the event. Now that is an impressive idea.
this description reminds me of manuevring board solutions when doing shipboard operatons - using vectors on speed and position measurement to determine future states of speed and position
Is that Navy talk?
Disclaimer: Opinions posted on Free Republic are those of the individual posters and do not necessarily represent the opinion of Free Republic or its management. All materials posted herein are protected by copyright law and the exemption for fair use of copyrighted works.