Can you unscramble a scrambled egg?

In summary, the article discusses the story of the landmark SG Experiment and its interesting twists, as well as contemporary reactions to the results. The conversation then shifts to the possibility of doing a S-G experiment with a uniform magnetic field and the potential differences in the input and output beams. The questions of whether the reasoning is correct and if there is an experiment to distinguish the two situations are raised. The response suggests that the splitting and recombining of beams does not unscramble the electrons, rather it scrambles them. An experiment is proposed using polarizing filters to demonstrate this concept. Ultimately, the response summarizes the main points of the conversation and highlights the bizarre nature of quantum mechanics.
  • #1
Swamp Thing
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Here is a fascinating article about the story of the landmark SG Experiment.

http://www.physicstoday.org/vol-56/iss-12/p53.html [Broken]

There are some interesting twists to the tale, but I won't spoil them for you.

Some contemporary reactions to the results:-
http://www.physicstoday.org/vol-56/iss-12/captions/p53box1.html [Broken]

Cheers,
S.T.
 
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  • #2
Question about SGE

What if we do a S-G experiment with a uniform magnetic field?

Each atom will still have to "decide" to point up or down, only we won't be able to tell them apart at the output of the apparatus because there will be no vertical deflection. Now, is this not a different situation from the input beam? At the input, (if I understand correctly) each atom is essentially "unpolarized" i.e. in a 50-50 superposition of both states. At the output, we have a 50-50 mixture where each individual atom is definitely "up" or "down".

My questions:
(a)is the above reasoning correct

(b) if so, is there an experiment that we can do to distinguish a beam that has been "combed out" by a uniform magnetic field, from a beam that has not passed through any field.
 
  • #3


Originally posted by Swamp Thing
What if we do a S-G experiment with a uniform magnetic field?

Each atom will still have to "decide" to point up or down, only we won't be able to tell them apart at the output of the apparatus because there will be no vertical deflection. Now, is this not a different situation from the input beam? At the input, (if I understand correctly) each atom is essentially "unpolarized" i.e. in a 50-50 superposition of both states. At the output, we have a 50-50 mixture where each individual atom is definitely "up" or "down".

My questions:
(a)is the above reasoning correct

(b) if so, is there an experiment that we can do to distinguish a beam that has been "combed out" by a uniform magnetic field, from a beam that has not passed through any field.

I'm not a QM guru, so this won't be very specific:

Let's say we have a beam of electrons that's been polarized s.t. all spins are pointing up at orientation 0. Then if we slap a detector at an angle of θ to 0, then the probability of getting an electron with spin up orientation θ is cos(θ/2)2.
The probability for the other orientation from the 'combed pair' is cos((π-θ)/2)2=sin(θ/2)2
So, along any orientation, you would still get a 50-50 distribution of spins since you get .5*(sin2+cos2) probability of spin up.

So the splitting and recombining does not unscramble the electrons. In fact it scrambles them. You can do the following:

Let's say we've got a beam of electrons that is all spin-up in orientation 0. Now, if we split it into beams along orienation π/4, and then recombine it, we will get a beam with a 50-50 orientation split along spin orientation 0.
 
  • #4
Oh, there's a nice easy experiment for you to check this.
It takes 3 polarizing filters and a light source.

Take the two polarizing filters, and line them up so their polarization is perpendicular. You should get almost no light coming through.

Now, if you put the third filter between them, you'll get *more* light coming through from before.

Analagous experiments are , I believe, possible with birefringent materials such as calcite, which can act as a beam splitters instead of eliminating a particular polarization.
 
  • #5


Originally posted by NateTG
So the splitting and recombining does not unscramble the electrons. In fact it scrambles them. You can do the following:

Let's say we've got a beam of electrons that is all spin-up in orientation 0. Now, if we split it into beams along orienation π/4, and then recombine it, we will get a beam with a 50-50 orientation split along spin orientation 0.
I'm not exactly sure what you are saying, but you can certainly recombine the exit beams of a SG magnet by putting them through a second (reversed) SG. If you can maintain the coherence of the beams, you will not be able to distinguish the final beam from the original: it will be in its original pure state. That's (part of) what's weird about this stuff.
 

What is the Stern Gerlach Experiment?

The Stern Gerlach Experiment is a physics experiment that was first conducted in 1922 by Otto Stern and Walther Gerlach. It demonstrated the quantized nature of angular momentum in atomic systems, which laid the foundation for the development of quantum mechanics.

How does the Stern Gerlach Experiment work?

In the experiment, a beam of neutral silver atoms is directed into a non-uniform magnetic field. The atoms are deflected by the field, and their paths are observed on a screen. The results show that the atoms are deflected into two distinct paths, indicating that their magnetic moments are quantized in either an "up" or "down" state.

What is the significance of the Stern Gerlach Experiment?

The Stern Gerlach Experiment was the first experiment to demonstrate the quantization of angular momentum in quantum systems. It provided strong evidence for the existence of electron spin and paved the way for the development of quantum mechanics, which has revolutionized our understanding of the microscopic world.

What are the implications of the Stern Gerlach Experiment?

The Stern Gerlach Experiment showed that the properties of particles at the atomic level are discrete and cannot be explained by classical physics. It also laid the foundation for the concept of superposition, where particles can exist in multiple states simultaneously, leading to the development of technologies such as quantum computing.

How has the Stern Gerlach Experiment been used in other areas of research?

The principles of the Stern Gerlach Experiment have been applied in various fields, including nuclear physics, particle physics, and quantum information. It has also been used to measure the magnetic moments of other particles, such as protons and neutrons, and has been used to study the structure and behavior of complex molecules.

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