STUDY WITH ME | Quantum Measurement & Observables

The important ideas that I discuss:

1. At the limit of many quantum measurements, the average will always approach the classical result, even if individual experiments appear to violate the classical law. This is called the classical limit.

2. Quantum measurements are not as gentle as classical measurements. Sometimes measuring a quantum state can change the state for all future measurements.

3. Observers can change the state of quantum objects. Quantum states are reset by observation itself, though the point in the experiment when this occurs is still the subject of active debate.

Previous episodes:

#QuantumPhysics

[ericzeigler]

My granddaughter, Tallulah (3), asks me why Elsa from the cartoon movie is teaching maths. Her doll does bear a resemblance. Thanks for encouraging her interest in maths.

[jasonmenke]

You have inspired me to go back to school and continue my physics education.. I originally majored in physics but switched to another major because of several reasons. I have regreted it since as it was my main love. I was hesitant to go back but you have inspired me to go back and pursue my dream. Great videos about a topic true to my heart and you represent the topic very gracefully and as it should be communicated. Thank you!

[albertomolano]

I love this stuff, been reading about it for 2 years. Reality is crazy

[khoanguyen]

Thank a lot. I really like "study with me" series on quantum mechanics. I am looking forward to the new video on this topic.

[priyaarora]

I pursued commerce and only know about the name of subject- quantum physics...but I liked maths in school and somehow understood and loved this whole thing. U make things interesting tibees :) :)

[tombufford]

Certainly helps to have you with me when learning the very difficult topic. I will return latter as it is very difficult.

[xbrlinfinity]

Toby and Brilliant do an excellent job on this topic, very insightful and well explained.  A nice surprise at the end, "the x-component was never actually observed …." and what this says about the nature of measurement, forced choice, and information loss or preservation.  A challenge for us to come up with a complete and consistent model of what is happening that we understand personally.

[stephenpitylak]

Thank you again for taking the time to share your studies. I look forward to learning more.

[Nikkes]

It's nice to study with you, your voice soothes my soul :)

[Otonium]

I love his co-course. Good luck and much success.

[declankruppa]

Very interesting thanks. Near the 3 min mark you say air resistance and gravity on the neutron can be neglected. But all matter and even photons fall at the same rate in a gravitational field. So maybe the straight line path of the neutrons is just a sufficiently accurate approximation over short distances

[johnjohn-edqt]

Thank you for these videos. A lot of details that I poorly understood or that I have forgotten in *mumble mumble* years are a bit cleared. One thing that drove me nuts back in the day shows clearly at about 5:30.... It is not ANY magnetic field. the field is non-uniform, . In a uniform field, there is no force (unless there is something I am still missing)

[mikedavis]

Love you Tibees! Love your look and presence and voice and presentations I mean--I'm sure you're a great person too-...anyway...you know what I mean. :) Wonderful videos! Keep smart'n up YouTube! :) You would be a great professor...you could easily lead "flipped" classes, you already have a lot of material ready to go, and then just answer questions and lead discussions in class.

[MasamuneX]

If you have a polarizing filter aligned vertically and a second polarizing filter aligned horizontally. Placing a thir filter between the two will then allow light trough in a somewhat similar way to what you described except instead of spin its the polarization of light.

[TommyLikeTom]

The symbol you are using is called psi and it is also used to denote consciousnesses. It's quite interesting to see what else the symbol denotes on the Wikipedia page for the symbol psi.

[jasonmenke]

imagination = theory. theory = math. math = research. research = Tibees. Tibees = joy!

[xbrlinfinity]

Flipping the analyser (12:00 – 12:40) gave the answer "out the down channel".  This is identified diagrammatically as the channel towards the bottom of the page (see also the diagram 14:22). I (did) worry it should be the channel at the foot of the B field arrow on the diagram of the analyser box, which is the channel towards the top of the page; and where I thought the neutron would come out (south pole of magnetic moment being pushed away from stronger south pole of inhomogeneous magnetic field which is now at the bottom of the page). But I think we are just using different conventions for the same thing … I had seen the respective ends of the arrow as labelling the output ports (the arrowhead of the B field pointing to the spin-up port), but it is now apparent the bottom port is still to be read as the spin-down port.

[Juarqua]

The behaviour of the neutron in the experiment at about [4:00] reminds me of a ball that has been played/kicked with a spin. It seems to be a helpful analogy to at least some extent.

[Chaboo]

This has made me realise that the quantum realm is just that jump from maths to classical physics. It's the randomness that you see in mathematical asymptotes that end up averaging out and the way that there comes a point in which you can't measure something so small without completely disrupting it. Like, mathematically, those things are real things and we now see them.

Like, it's complicated and crazy but also not as crazy as the general publics perception of it seems to be.

But its just kinda cool that reality has in some ways been mapped by mathematics before humans even knew the quantum realm existed. Like limits in maths was discovered well before quantum mechanics, and it explains how quantum mechanics can be so random while at a larger classical scale there's nothing at all happening.

[sld]

Listening right now ; Good Lord, that takes me back 20 years, to the time I studied that in college. I'm getting old.