Quantum Technology

[Aranfan]

So in my philosophy class my professor said that Quantum Mechanics was not reflective of anything we experience in real life. I figure the best way to prove him wrong is to give him a list of technologies that wouldn't work if Quantum Theory were just scientists making shit up as they go along. Unfortunately my google-fu has failed me. Could SD.net provide me a list of technology that we use today that works only because of Quantum Mechanical weirdness?

[Duckie]

well, there's 2 answers here:

1) We don't often experience the Strong Nuclear Force, but without it pretty much nothing we recognize would exist. Everything we have depends on Quantum Mechanics because Quantum Mechanics is part of the universe, even if we don't experience it.

But the most commonly cited Quantum Mechanical Device is:
2) Transistors; more reading
Transistors and knowledge of how they work depend upon Quantum Mechanics, or so I am told (I am no physicist)

[Terralthra]

I have a feeling that the philosophy professor is using "quantum mechanics" here as a stand-in for "things about physics that are unintuitive to me."

It's hard to give a specific example without knowing what parts of quantum mechanics he finds to be unrelated to everyday life. Lasers, MOSFETs, diodes in general, transistors, MRIs, fluorescent bulbs, and electron microscopes all rely on quantum mechanical effects.

EDIT: What he may mean is that quantum mechanical effects tend to operate on scales that humans can not perceive directly, and so may seem unrelated to everyday life. If that's what he means, he's sort of correct, but direct perception and perceived relation to everyday events are not the determiner of actual relation.

[Ryan Thunder]

Quantum Physics isn't bullshit, its just incredibly unintuitive most of the time. Shit just doesn't act the way you'd expect it to at that level, because that's where the classical physics that many poor idiots people already struggle with break down.

And that's why I'd like to stay as far away from it as possible, in a context where my GPA is at stake.

[Feil]

He's talking out of his ass. Flash memory works entirely on quantum tunneling of electrons; it is impossible using classical electrical theory. So are transistors, as mentioned above, which in turn means that every chip in every computer ever is a quantum mechanical device that cannot function according to classical theory. Light switches cannot function according to classical theory: they require quantum tunneling to explain why they work. Quantum electrodynamics is required to explain the function of TV and computer monitors.

[Gil Hamilton]

So in my philosophy class my professor said that Quantum Mechanics was not reflective of anything we experience in real life. I figure the best way to prove him wrong is to give him a list of technologies that wouldn't work if Quantum Theory were just scientists making shit up as they go along. Unfortunately my google-fu has failed me. Could SD.net provide me a list of technology that we use today that works only because of Quantum Mechanical weirdness?

Point to a fluorescent light and tell him to be quiet.

[Zixinus]

Ahem.

[Akhlut]

It's not technology, per se, but the way the periodic table is arranged is due to quantum mechanics. And it was arranged that way before anyone knew about such things, so, that seems to be a rather strong proof of its existence.

I forgot why that is precisely (a professor explained it to me outside of class about 4 years ago, so, I'm only hazy on why it is relevent), but, as I recall, it is due to the valence electron shells and their interactions, hence the arrangment into rows.

[Fingolfin_Noldor]

Tell him that unless he's a Physics graduate, he is not qualified to talk about Quantum Mechanics.

Next, tell him that without Quantum Mechanics, no computer would exist.

Next, you might want to google a picture of say a Magneto Optical Trap, or a Bose Einstein Condensate. These things can be fairly big, and you could see them with naked eye.

[Starglider]

Ahem.

Is QM actually necessary for nuclear weapons? I'm certainly no expert on this, but I got the impression that it would be possible to do the necessary design calculations using just the old liquid drop nucleus model (and hence that the device itself could work with classical physics only).

[Zixinus]

old liquid drop nucleus model

Does the liquid drop model explain nuclear fission and what happens if you slit a nucleus?

[Starglider]

Does the liquid drop model explain nuclear fission and what happens if you slit a nucleus?

Yes. It's a primitive but workable way of calculating nuclear binding energies.

[Kuroneko]

The liquid drop model is not entirely classical. The spin correction term contributes (negatively) about 15% to the total binding energy of U-235, and neglecting it makes the prediction off by almost that amount.

[Zixinus]

The liquid drop model is not entirely classical. The spin correction term contributes (negatively) about 15% to the total binding energy of U-235, and neglecting it makes the prediction off by almost that amount.

Did they use that correction when actually making the first nuke or the later nukes? How significant is that 15% correction?

Yes. It's a primitive but workable way of calculating nuclear binding energies.

I doubt the professor knows that.

[Kuroneko]

How significant is that 15% correction?

Well, for U-235, the spin correction term is a bit under 15%. For barium-141, one of the fissile products of U-235, however, neglecting it gives an error of almost 200%.

Did they use that correction when actually making the first nuke or the later nukes?

I don't know much of what was actually involved in project, but I expect that the relevant binding energies in particular could have been, and no doubt were, measured experimentally. But it doesn't matter much if that particular formula was used or not--regardless of how much come have been done by experimental stamp collecting once the project was underway, it's unlikely that they would've been in a position to even start it without QM.

[Ariphaos]

Specifically, the doping arrangements for electrical transistors require PDEs that originate from quantum mechanics. Was a long time ago and our professor showed us one when discussing the composition of semiconductors - but I've never done them. The quantum tunneling demon is also rearing its head again, and it may be more intractable this time around as process size continues to shrink.

It may be more pertinent, though, to start with the two-slit experiment and delve into the construct of the human eye.

[Aranfan]

I talked to Professor Clouser again, and he clarified that he thinks Quantum Theory comes from failures in other theories as opposed to observation of the outside world. My response was that I didn't see a difference. He does think that Quantum Mechanics is reflective of the real world.

[Surlethe]

My time is brief, but as a short point, note for him that quantum mechanics - in particular, QCD - is the most precisely predictive science humans have ever created. I was at a seminar last Thursday, and the professor delivering it showed an experiment where QCD predicted the results to within observation tolerances over seven orders of magnitude.

[Terralthra]

I talked to Professor Clouser again, and he clarified that he thinks Quantum Theory comes from failures in other theories as opposed to observation of the outside world. My response was that I didn't see a difference. He does think that Quantum Mechanics is reflective of the real world.

How would we know there are failures in other theories without having observed those theories not matching up with observing the outside world? His distinction makes no sense.

[Kuroneko]

My time is brief, but as a short point, note for him that quantum mechanics - in particular, QCD - is the most precisely predictive science humans have ever created.

That title would be taken by QED rather than QCD, but your point remains. QED is easier to calculate in (among several reasons) because photons do not carry charge and the coupling constant is a lot smaller (and stays constant).

How would we know there are failures in other theories without having observed those theories not matching up with observing the outside world? His distinction makes no sense.

Perhaps it's a claim that QM is made of patches to other theories and was mostly postdictive rather than predictive. That would make sense, but still be wrong. Although it's true that much of the early development of QM was the result of trying to match already known experimental results, QM has also made plenty of genuinely new predictions.