Observation = interaction, question from a dummy

[CuriousCop]

TL;DR Summary

Could anyone advise if my understanding of this is basically correct? That on a quantum physicis scale, measurement or observation is equall to interaction. Please settle a friendly debate between coworkers.

Greeting all!

So I apologize if this has been explained to death and if so, please advise as I do not want to clog up the forums with the same questions over and over.
A little background first, a coworker and I routinely talk about astrophysics and quantum mechanics( yes, somewhere out there, two cops are parked side by side arguing and debating their understanding of astrophysics and quantum mechanics and theory, believe it or not, it's a beautiful world we live in isn't it!).
So, I have no classical education and am a lowly cop with an average intellect.
There is not choice under prefixes for Associates Degree( yes I know, it's sad, still working on my Bachelors, so I chose undergraduate degree but I still feel that you all should know I do not have a 4 year degree)
So please have patience and know that I am very thankful for any guidance any of you can provide.
On a quantum scale ( not sure of how you all speak about these things so I mean on the scale of quantum experiments, particles, wave functions ect), I understand the idea of a wave function being just that, until observed. When observed it appears to be a particle.
Now I know this has nothing to do with a "conscious observer" like most people peddling "wooo" would have people believe.
My question is, that at those scales, to observe anything experimentally would most likely involve bouncing some form of light or radiation (basically something from the e.m. spectrum) off of the wave function. This is then detected by some device to produce a readout or observable value.
Is this correct?
To lay persons like me, the concept of something appearing like a particle when observed is easily understood because one has to interact with the wave function.
I imagine it like dropping a pebble into a lake. The lake is the wave function, and when you throw a pebble into it( the pebble being a particle of light sent to detect somthing and provide observational information) then a point is produced where the pebble struck the water, appearing to be the particle.
I know that is extremely oversimplified and I apologize if I have this all wrong.
Are the only ways to observe somthing experimentally in quantum physics equall to interacting with the object or wave?

Any help with this would be appreciated. Thank you so much and I am loving the threads and ideas in this forum, even if most are over my head, it's still fun to think about and expand my kowledge.

-Hoyt

 

[CuriousCop]

I apologize, I just realized that this may be a better thread for the foundations forum, and if the mods would be so kind to move it. I apologize for the extra work you may have to do and will be more careful in the future.

 

[PeterDonis]

Are the only ways to observe somthing experimentally in quantum physics equall to interacting with the object or wave?

"Equal to" might not be quite right. All measurements are interactions, but not all interactions are measurements.

I just realized that this may be a better thread for the foundations forum

The basic question that I just answered above does not require adopting any particular QM interpretation, so it's ok here. But if you want to get into more detail about how "measurement" works in QM and how the various QM interpretations handle it, you could start a new thread in the foundations forum to discuss that.

 

[PeroK]

On a quantum scale ( not sure of how you all speak about these things so I mean on the scale of quantum experiments, particles, wave functions ect), I understand the idea of a wave function being just that, until observed. When observed it appears to be a particle.

A particle is always a particle. The wave function describes the dynamic properties of the particle, also known as its state. The wave function gives the probabilities of possible measurement outcomes: for example, for a measurement of position.

When you measure the position of a particle you get one of the possible outcomes, according to the probabilities defined by the wave function.

In general, in order to measure anything you must interact with it, at the quantum scale or not.

 

[CuriousCop]

That makes sense, I have never thought about it like that before but it absolutely makes sense. I appreciate the help!

The way I envision it is say all particles(oversimplified) are a bunch of tennis ball sized objects, and the wave function has a foundational lattice of some sort that is built of grids of tennis ball sized objects. Then you shoot a laser into it to observe it, the laser is made of light "particles " tennis ball sized. So these similar sized particles collide and thus you have interacted with the object that you are trying to observe, thereby fixing a point or particle as like sized objects or particles have interacted.
I know this is wrong on many levels and I say it purely as a metaphor for wrapping my head around things at that scale being so small, that things we normally wouldn't believe to be contaminating or interacting(other than reflection, refraction or absorption) do.
Is there a way that the wave function appearing to be a particle or point ( or probability point) is explained to baby( basic or intro) physicists students?
Just a normal guy trying to understand some incredibly awsome ideas and concepts. Thank you again for your reply!

 

[CuriousCop]

Ahhh I see. It has always been difficult to nail down whether the wave function was genuinely an area, in which the particle could be at probably points given certain values, or that the wave function was in essence just that, a wave or area that the particle is and is not all in the same. That the observation of a particle when measured is due only to the interaction of the measurement.

 

[PeroK]

Ahhh I see. It has always been difficult to nail down whether the wave function was genuinely an area, in which the particle could be at probably points given certain values, or that the wave function was in essence just that, a wave or area that the particle is and is not all in the same. That the observation of a particle when measured is due only to the interaction of the measurement.

A lot of popular introductions to QM focus on position, momentum and the HUP (Heisenberg Uncertainty Principle). This leads to metaphors or analogies that are largely pointless, because there are other dynamic variables that don't fit these metaphors at all.

The best example is quantum spin. If you measure the spin of an electron about a particular axis, you only ever get one value, although it can be positive or negative. In other words, when you measure the spin of an electron about a given axis you always get the same amount of spin, but it can be clockwise or anticlockwise.

For spin the wave-function becomes a much simpler "state vector". Essentially this state vector specifies a single number: the probability of getting clockwise spin (and hence also the probability of getting anticlockwise spin).

Now, you could try to imagine an electron spinning both ways at once. But, in general, it seems pointless to look for a classical analogy or metaphor. There are many other examples like this that convinced me when I was learning QM to ditch the classical analogies.

 

[EPR]

Pre-existing properties are problematic for QM(some theorems seem to rule out such) but... does the quantum world even exist? Bohr would say no, the minimal interpretation would say only statisics exist, but our human experience would say the quantum world exists.

 

[PeroK]

Pre-existing properties are problematic for QM(some theorems seem to rule out such) but... does the quantum world even exist? Bohr would say no, the minimal interpretation would say only statisics exist, but our human experience would say the quantum world exists.

It's very different to debate the existence of an electron than the existence of a definitive 3D spin. In one sense, it's only the dynamic properties of things that are subject to probabilities. The charge on an electron, say, is not governed by a probabilistic wave-function; nor is its mass.

Or, in a particle in a box or subject to harmonic oscillation, wave mechanics does not cast doubt, per se, on the existence of the particle, box or harmonic oscillator. And, if you put the oscillator in an energy eigenstate, then you have definite energy. What wave mechanics models is the likelihood of obtaining certain measurements of position, momentum, kinetic energy and potential energy etc.

 

[PeroK]

Pre-existing properties are problematic for QM(some theorems seem to rule out such) but... does the quantum world even exist? Bohr would say no, the minimal interpretation would say only statisics exist, but our human experience would say the quantum world exists.

Also, in my opinion, you present a false dichotomy between QM and "human experience". QM is designed to model the real world as accurately as possible, and to explain measurements. To some extent, of course, the macroscopic world has to be reconciled with QM.

Finally, QM above all is determined by experiment. The conclusions of QM are inherent in the observed phenomena, albeit on a microscopic scale. There are in effect no grounds to reject QM on the basis of experimental evidence or human experience. Quite the reverse: QM is fully supported by experiment.

 

[DarMM]

It's very different to debate the existence of an electron than the existence of a definitive 3D spin. In one sense, it's only the dynamic properties of things that are subject to probabilities. The charge on an electron, say, is not governed by a probabilistic wave-function; nor is its mass.

Or, in a particle in a box or subject to harmonic oscillation, wave mechanics does not cast doubt, per se, on the existence of the particle, box or harmonic oscillator. And, if you put the oscillator in an energy eigenstate, then you have definite energy. What wave mechanics models is the likelihood of obtaining certain measurements of position, momentum, kinetic energy and potential energy etc.

Just for your own interest, QFT places limits on the notion of particle. Field theoretic states cannot be understood in a particulate manner, except in the asymptotic future and past. Even in that limit the particle content is not objective, depending on the acceleration of the observer.

In QFT particles gain the same "indefiniteness" as Spin.