2 slit experiment again

krd

If you drop a pebble in a still lake - and watch the ripples. That is precisely the same process.

And before you come back and tell me I'm wrong, I want you to think about it.

boffinwannabe

well not much to think about here. One is a wave formed of molecules, the other is a probability wave that exists/doesnt exist in every possible state until the information of its precise location or speed could become available. At that point it collapses into a single state which cannot be known because its inherently uncertain. Some states being highly more probable than others depending where they are on that wave. This is why our world appears so certain, the uncertainty is so small that we cant see it, the smaller you go the larger the uncertainty.

krd

Okay.....and what are molecules made of?

You know, I asked you to think about this. And you didn't.

boffinwannabe

perhaps i did and you didnt think about the reply long enough because the reply wasnt the one you wanted. If you have a point to make it would be easier to just come right out and say it rather than ask me a series of questions we both know the answer to.

swhite44

Wannabe, how can simply 'knowing the position' of something change its structure?
Sounds like you accept the theory so firmly you reject experimentation to confirm or disprove it! Classic dogmatist.
What's the point of testing if the Earth is round when everybody knows it's flat?!

krd

No...I don't have the answer to it.

But, the ripples when you through a stone in a still pond - those waves are due to the underlying wave nature of the fundamental particles beneath. Probability distributions in themselves do not explain the wave nature.

boffinwannabe

the maths describes whats going on, it doesn't tell us why, thats philosophy. Im interested in the maths and the picture of quantum mechanics that describes to us. Knowing the position does not change the structure, there is no structure. Knowing gives us a single state from every possible state.
I accept the theory in as far as its the best one we have at this point. Its the way it appears to be till disproven. At some point you have to decide what for you seems the most likely 'way it is', based on th best science available to you. So if you do not accept what most scientists today take as the most likely correct theory can i ask why and if you actually accept anything?
is not Classic dogmatist. its the science as it stands today, not quite sure why you resort to a classic defence that actually says nothing at all.
The point of testing is to substantiate what we know, to see if it stands testing, and to delve into the realms of the unknown. The point of testing to see if the earth is flat is that you would find your theory doesnt standup to testing.

boffinwannabe

yes im afraid it does. its the Schrödinger equation and feynmans every possible path.
quantum mechanics doesnt make sense but it works. How can something be in more states than one at the same time? Its beyond our logic but its the way it is.

Nugatory

KRD, unless and until you can show some way of using the "underlying wave nature of the fundamental particles" to predict the height and speed of these ripples from the initial displacement of the water.... No one will be able to take you seriously.

Classical mechanics gives us a mathematically convincing explanation for these ripples, an explanation that allows us to calculate and predict the their size, speed, and propagation as we vary the size and weight of the stone, the density, viscosity, and surface tension of the liquid. This explanation is supported by enormous amounts of experimental evidence and convincingly contradicted by none. And this explanation has nothing to do with the "underlying wave nature of the fundamental particles" - indeed, it doesn't even have any particles in it.
You don't have to accept or agree with this existing base. But if you are not aware of it, it's going to be hard for you to either build on it or replace it with something better.

swhite44

Boffin "The point of testing is to substantiate what we know, to see if it stands testing, and to delve into the realms of the unknown. The point of testing to see if the earth is flat is that you would find your theory doesnt standup to testing."

I thought you were saying 'there's no point testing the theory, because the theory is right'.

boffinwannabe

no i didnt say that.

swhite44

You're right, I can't find what gave me that idea, I must have misread something!

krd

I'm not disputing any of this. But these are observations. Measuring weight, density, viscosity, and surface tension, will tell you the weight, density, viscosity. It doesn't explain these things. With more observations you'll be able to make predictions about the ripples different stones will causes. It doesn't answer the fundamental question of why the waves are happening in the first place. It's just taken too much for granted they should be happening at all.

Nugatory

The classical explanation of water waves starts with Newton's laws, then works from them through a series of very convincing mathematical steps to conclude that water waves must happen when surface of the water is disturbed, and provides a detailed quantitative explanation of their behavior. I'm really not sure what you see as being "taken for granted" in this process; certainly no one who has actually done this, perhaps in the second year of a serious undergraduate physics program, will feel like something is being taken for granted - it is hard work.

Nor am I clear on what what could be a more "fundamental" explanation. If you're objecting to the definitions of mass, energy, force, momentum that we use in this explanation or looking for an explanation of WHY Newton's laws work, that's a fair objection. There are serious unanswered questions here; they may belong more to philosophy than physics, but they're valid questions nonetheless.

But when you say things like:
you aren't raising these questions - you're just showing that you are not completely familiar with what we already do know about ripples in water. This matters for two reasons:

1) It's near impossible to build on or improve our understanding of the world if you don't know what you're building on and improving. It's tough to have a sensible discussion of fundamental unanswered questions if you don't have a clear understanding of which questions are answered, how far those answers go, and which taken for granted premises they depend on, and exactly how that dependency works. (As a practical matter, people who have done the studying and hard work are unlikely to take your ideas seriously if you haven't - this may appear to be a form of intellectual snobbery, but in fact it's a necessary defense mechanism).

2) Understanding, really understanding, at a mathematical level, the description of the world that physics provides is one of the most rewarding, empowering, fascinating, cool, addictive, stimulating, and just plain FUN experiences in life. The difference between qualitative hand-waving and the real thing is like the difference between looking at a picture of a delicious meal and actually preparing and eating the meal.

boffinwannabe

well said!

QuasiParticle

Suppose we are shooting electrons through a double slit. Just behind the double slit we are firing photons perpendicularly to obtain information through which hole the electrons pass (electrons scatter light so we can look to see through which hole the electron travelled). Farther we have a detection screen for the electrons. One guy is looking at the scattered light at the double slit, another guy is at the detector screen. The which-hole information is not recorded anywhere but in the observer's mind. When the first guy observes the scattered light, obviously no interference pattern is observed at the screen.

What happens when we leave the detection light at the double slit on, but the guy observing it closes his eyes. Does the other guy at the screen notice a difference in the pattern of the detected electons? Can he infer by looking at the distribution of electrons whether the first guy has his eyes open or closed?

In the latter case we are not gathering information through which hole the electrons pass, but we are still disturbing the system with the photons. The inability to obtain both interference and which-path information is more fundamental than simply disturbing it with our measurement equipment. As boffinwannabe put it: