[clueless (OP)]

I saw the above, to me great SF series 'Devs'. I'm a bit puzzled though; not that good a science. But I'm sure someone here can alleviate my confusion.

1. Apparently, if you can inhibit decoherence, macroscopic superposition IS impossible; considering Everett interpretation. However, since we are built by quants or small particles, that exist in many states before observed, if we consider, for example, a human being not as a whole, but as countless little quants or particles that make him up, that are in many states before observed directly, isn't it true that a human being, or the Moon for that matter, IS susceptible to macroscopic superposition after all, and not just to classical state/mechanics, regardless of his/its size? Of course, if the man is observed as a collection of many particles, instead of as a macroscopic living object, that is to say, if you consider a man's particles that make him up, you might somehow produce a result known as macroscopic superposition? If so, is it possible to resurrect a dead Schrodinger's cat into a living one in a blink of an eye, if you somehow inhibit decoherence and you have an advanced computer, direct access to quantum fluctuations, superposition and many states of the cat?

2. While I'm watching a human being without a microscope or nanoscope, just using my eyes, I'm not watching particles he is made of, not directly. Instead, I am watching the man as a whole, say focusing on his face, which is to say, particles inside of him or quants ARE in the state of flux or quantum superposition, for my eyes don't have microscopic zooming ability? So, the man is not in a state of macroscopic superposition as a whole, but his particles are in a state of quantum superposition for they are not observed directly? Must I zoom all the way to the man's particles to turn quantum mechanics into classical mechanics, on a subatomic level, so that the system (for all particles in question) chooses one classical state out of many quantum states, considering countless particles that make this man up, observing him with or without a zooming ability? Or simply by looking at the man (as a whole) his particles that make him up revert from quantum superposition to a classical, one state? If it is the former, the man truly is in a state of quantum flux on a quantum level nearly all the time, or indirectly maybe even in a state of macroscopic superposition because of his quantum particles, electrons etc. that make him up, until not him as a whole, but all of his particles are directly observed with a zooming scanning ability? So, the man is in a state of classical mechanics (observed as a whole) but also in a state of superposition (on a quantum level) at the same time?! Or, this observed man is in a classical state as a whole, and his particles as well, that make him up, because it is enough to observe the man as a whole to render not just his outside, but also all of his particles inside that make him up on a subatomic level? Aw. My mind is foggy on this one.

[alancalverd]

Sir Arthur Eddington remarked that the student of physics must become accustomed to having his common sense violated five times before breakfast, and if he disappeared through the floorboards and rematerialised in the room below, he would not consider it magic but merely a single observation of an extremely rare phenomenon.

The harder you zoom, the less your object will behave like classical mechanics. You have a pretty good idea of how an ant nest, a beehive, or a flock of birds works, but you'd have a hard job to predict where an individual animal will be in 10 seconds' time.   

The test of quantum mechanics is whether, if you average over a very large number of particles, you end up with classical physics and chemistry. (Yes!) Same for relativity: if v << c, do you get the flight of an artillery shell?  (Yes!) But there's no way you could predict the behavior of a single particle from a mesoscopic observation.  At its simplest, the argument all comes down to Heisenberg: if subatomic particles behaved like cannonballs, the atom would collapse and we wouldn't be here to ask the question.

[clueless (OP)]

Maybe you can't develop a prediction algorithm for a bee's next direction of flight. But, what if you could? What if you could "know" or "choose" a state, like the bee's next position, be it clairvoyance or, less likely, applied macroscopic superposition? Isn't that playing God, possibly blasphemy or just advancement of science, or destiny, determinism, some kind of quantum computer and a labyrinth, a simulation in which we are all trying to solve countless puzzles, where determinism negates free will, to such extent that You think that you have a choice and that you're thinking about the bee and its movements, at the moment, but in fact you are being operated all the time like a puppet by the greatest puppeteer: destiny/superdeterminism? In particular, since we can't control our thoughts, our thoughts might be borrowed radio transmissions from a hidden  radio transmitter. Or am I talking out of my ear?   

[alancalverd]

Back to Heisenberg. There's no point in asking "what if you could" because the universe wouldn't be as it is if you could!

Simple case: a mesoscopic projectile (cannoball, billiard ball...). The only way we can determine its speed is to measure the elapsed time between two points. That gives us the average speed between A and B, but we can only assume its velocity was constant during that period. The longer the distance and hence the longer the elapsed time, the more accurately we can calculate the average but the less we know about its position at any point in that interval. 

All the principle of indeterminacy suggests is that there is a limit to the overall determinacy of the product of momentum and position, and when we look at the structure of an atom  we can get a very good idea of what that limit is.

[varsigma]

Macroscopic is getting blurry these days. The first mechanical qubit has been manufactured it's basically a small vibrating wire; "small enough" that it can be in a superposition of vibrational modes.

So when is a bunch of particles "small enough" so that you can observe this superposition and what the hell does it mean that a physical wire can be vibrating in two modes?

Physicists like Heisenberg and Schrodinger both had to conclude that a single particle like an electron in a Hydrogen orbital, was "too small" to be described classically. Schrodinger finally worked out a solution for the orbitals of a single electron and began to seriously doubt his result.

It seems that "small enough" collections (systems) of particles are allowed to do this, over small distances, and "get away with it". Only recently has technological development allowed us to look at it more closely. There is ample evidence that "distinct particles" are a bit of an illusion, only something we can talk about if we're a long way away.

Oops, perhaps I should add that we have to have these small systems well away from heat, so low temperatures for massive particles is the ticket (not needed for massless particles who get a free ride).
 And that, in a roundabout way, introduces a kind of dual view--we are a long way from the distances we need to see and the systems are a long way from having a significant "temperature".

[varsigma]

I guess there is a corollary to all that we know about what we can do with superposition of all those particles, is that a human or a cat is a collection which is "not small enough".

Or we could extrapolate our notion of measurement to say something like, measuring the superpositions of a large system of particles is roughly equivalent to the complexity of the system. We are highly complex systems, so we will need a really large computer for this problem. About the size of the solar system.

[alancalverd]

We have seen interference fringes caused by the superposition of buckyballs so the deBroglie wave model certainly applies to medium-size molecules. In principle, anything can be "small enough" to have an associated wave function but once you get beyond a few dozen rigidly-bound atoms that function is too complicated to produce a predictable effect.

[varsigma]

Another comment about being able to measure superpositions. You can't.

Measurement means the state isn't in a superposition any more--it necessarily destroys or annihilates it.
But, simulating a large collection of particles on a quantum computer might be a thing one day.

Even so, any outputs will be classical information, because we can't measure quantum information. The reason we can't is, the equipment does that. So the double slit in a quantum interference experiment 'measures' something that we can't, and will never be able to, unless we don't need any interference.

Measurement is the seemingly weird thing. It plays with our ideas of what space and time really are.

[clueless (OP)]

Thanks for all Your comments, input.

"Even so, any outputs will be classical information, because we can't measure quantum information. The reason we can't is, the equipment does that. So the double slit in a quantum interference experiment 'measures' something that we can't, and will never be able to, unless we don't need any interference."

Speaking of human consciousness, I take it a very smart and self-aware future robot, he (his consciousness) could measure quantum information directly w/o any "problems"; as though artificial life bypasses certain limitations or differences that apply to relationship between classical and quantum. 

[alancalverd]

No. "Measurement" always implies interaction, which necessarily alters the state of the measurand. Bouncing a few photons off a brick wall doesn't make a lot of difference to the height of the wall, but bouncing one photon off an electron puts the electron in a new state.

[varsigma]

No. "Measurement" always implies interaction, which necessarily alters the state of the measurand. Bouncing a few photons off a brick wall doesn't make a lot of difference to the height of the wall, but bouncing one photon off an electron puts the electron in a new state.

?. An electron that interacts with a pair of small slits is making a difference to . . . what?
It makes a difference to what we measure, by counting particles at later times. We assume that the equipment is unchanged by measurements.

Which is a kinda vague thing like---the equipment has essentially infinite degrees of freedom, but the small particles, such as electrons, don't. There is some sort of confinement--an invariant, in there somewhere.

ed. sorry I'm reading what I just posted and having a bit of a chuckle.
Since, I've assumed that I can get real physical particles to interact with a pair of slits without causing any damage to any equipment--it doesn't age. Nor do the particles I want to count. But to do that I need to age a device, because it will have to change irreversibly if I want to 'store information'. Or rather if I need to erase any of this information, there will be an aging process, necessarily.
l
How this can be overcome if we ever try to store human consciousness or whatever, I couldn't possibly comment.

[alancalverd]

An electron that interacts with a pair of small slits is making a difference to . . . what?

The electron, mostly.

[varsigma]

Quote from: varsigma on Yesterday at 18:10:49

    An electron that interacts with a pair of small slits is making a difference to . . . what?

The electron, mostly.

But that isn't something you can claim without measuring something, and then saying it's different.

[alancalverd]

You can compare the diffraction pattern from a wide slit, with that from a narrow slit. It's pretty obvious that the photon, electron or whatever  has interacted significantly with the edges of the narrow slit and hardly at all with those of the wide slit, and there's nothing else in the apparatus.

[varsigma]

You can compare the diffraction pattern from a wide slit, with that from a narrow slit. It's pretty obvious that the photon, electron or whatever  has interacted significantly with the edges of the narrow slit and hardly at all with those of the wide slit, and there's nothing else in the apparatus.

Yes, I would say that more or less sums up a few things about quantum particles interacting with other, erm, particles.

Everything except the electrons or whatever, is classical, or has classical dimensions. And you can demonstrate by altering the width of an aperture, that you can control this interaction, classically. You have the beginnings of an operator algebra.

[varsigma]

Interference with fixed-width diffraction slits isn't something that lends itself to designing a quantum computer, but the principles do have to be something you can "carry over".

You can "enrich" the situation, of starting with diffraction gratings, various different types of input beam, and deduce that "dimensions" at the classical level for the apparatus or equipment, depend on "sizes" for the particles in each beam.
You can't use an optical diffraction system with electrons, for instance.

So the engineering of these gratings tells you something about the inputs. It also tells you this information has a classical basis--the equipment.

Now you can make things "richer" by for instance, including a fixed magnet if you have charged particles--something photons are not--to see what this does. All the equipment has to be classical and controllable, at least to an "on or off" level.

Enriching diffraction for photons, could be say, using polarization filters.

You develop an algebra of operations, with different kinds of interaction. Unless you can store some information about the photons or electrons,  as they interact with your equipment, you must conclude it's unknown, and quantum information sneaks past what you think is a nice, logical setup. Everything looks nice and linear, you can ask yes/no questions, etc.