The collapse of the wave function?

[Jstar70]

TL;DR Summary

Are particles just telling us what time it is when the wave function collapses?

I never took any physics courses nor don't have a background in mathematics never the less I became very interested in quantum physics after reading Sean Carroll's book Something deeply hidden. One of the difficult things for me to wrap my head around was the concept of superposition and entanglement. When we think of superposition in the macro world in relation to the future this seems intuitive and natural. for example if i purchase 1 share of visa stock on the nyse at 196.64 i am unsure of the future state of it's value . The value in the future can only be in a state of superposition 200 or 190 are likely values, 0 or a million dollars unlikely values but possible, so there would be a bell curve of likely to unlikely values that the stock may have when the opening bell sounds. The bell curve of possible values collapses when the stock is sold at 9:30 am Monday morning. This is when the true value of the stock reveals itself (ie. 198.20). Its value changes from a cloud of possibilities to its true value because it was sold at a specific time. This kind of thing never happens in the macro world during our present, only the future. In the quantum world superposition does happen in the present . This got me thinking of the double slit experiment and how particles become entangled with the screen. when a particle is shot through the double slits it travels through as a wave, and only reveals itself to be a particle when it hits the screen. At that moment the screen and the particle become entangled and the wave function collapses. Doesn't that mean then that all the screen is doing is measuring time at that moment? Just like the opening bell at the nyse is a measurement of the value of my 1 share of visa at that specific time? Just as the particle is unsure of itself while it is moving forward in spacetime, and only reveals itself to be a particle of a certain value when measured at a very specific time as well?(ie. what time it hit the screen) How are time and entanglement related or are they? to me it seems like particles are telling us what time it is when they become entangled and reveal themselves to be particles. Does the wave function just mean things are moving and the collapse just mean things are not moving at that moment in time because we are trying to take a measurement?

 

[Jstar70]

is the Schrodinger equation just a measurement of quantum states while in motion and the Copenhagen interpretation just a measurement of a static quantum state?

 

[PeroK]

is the Schrodinger equation just a measurement of quantum states while in motion and the Copenhagen interpretation just a measurement of a static quantum state?

I'm not really able to make much sense of your posts. The Schrodinger equation is not a "measurement" in any sense.

when a particle is shot through the double slits it travels through as a wave, and only reveals itself to be a particle when it hits the screen.

Note that this is a popular-science attempt to explain QM and doesn't really describe what QM says. The particle is always a particle. Its dynamic properties are described by a wave-function, but the particle itself is not a wave.

 

[Isaac0427]

The first thing is about the book you cited. It's popular science-- not true, rigorous physics. Lots of what is in that book is misleading, or worse.

This got me thinking of the double slit experiment and how particles become entangled with the screen. when a particle is shot through the double slits it travels through as a wave, and only reveals itself to be a particle when it hits the screen. At that moment the screen and the particle become entangled and the wave function collapses. Doesn't that mean then that all the screen is doing is measuring time at that moment?

I don't think you've fully grasped the concepts you're talking about here. There is no entanglement going on in the double slit experiment. The particle can be thought of as in a superposition of going through the first slit and going through the second slit, and then these two possibilities interfere with each other. The screen measures where the particle is-- prior to hitting the screen, we only have a probability distribution to represent the particle. I don't know why you got entanglement mixed in with this, but that is probably a function of the book you used. Also, the screen is measuring the location of the particle, not the time.

How are time and entanglement related or are they? to me it seems like particles are telling us what time it is when they become entangled and reveal themselves to be particles. Does the wave function just mean things are moving and the collapse just mean things are not moving at that moment in time because we are trying to take a measurement?

Time and entanglement (as well as time and superposition) are not related as you are thinking of it. Nothing is measuring a time.

I think your problem with time is because you are confusing the stock market analogy (which is not really a good analogy) with the actual situation in quantum mechanics. Some people on here will disagree with my next statement, but I believe that Schrodinger's cat is actually a good analogy, as long as you accept that the state of the cat being dead or alive is truly non-existent until you open the box. It is inherently probabilistic before you open the box, it's not unknown.

is the Schrodinger equation just a measurement of quantum states while in motion and the Copenhagen interpretation just a measurement of a static quantum state?

This is a different issue altogether. Quantum mechanics has two parts-- the equations, and the interpretations. The Schrodinger equation describes the math of how quantum states evolve in time-- it has nothing to do with measurements. The interpretations of quantum mechanics deal with explaining what the quantum states mean, in terms of probabilities, measurements, etc. They're related, in the sense that the interpretations are explaining in physical terms the wavefunction, which is found by solving the Schrodinger equation.

 

[Jstar70]

Thanks for your reply, i am new to this and am looking to better understand the core concepts.

 

[Jstar70]

so i think it is obvious that i am a total noob at all this but in the double slit experiment the particle reveals its position when it hits the screen correct? before it hits the screen it can only be described by a probability distribution. my question is if the screen is sectioned off in a grid pattern a-z and 1-100 and the particle is shot through the double slit and it hits the screen at h-8, don't you also have to include the time it hit h-8 to more accurately describe its position? for example if I'm going to tell you where I'm going to be i have to say I'll be at starbucks at 4th and main at 11am to accurately describe where i am and when i'll be there?

 

[PeterDonis]

Moderator's note: Thread moved to QM interpretations forum.

 

[PeroK]

so i think it is obvious that i am a total noob at all this but in the double slit experiment the particle reveals its position when it hits the screen correct? before it hits the screen it can only be described by a probability distribution. my question is if the screen is sectioned off in a grid pattern a-z and 1-100 and the particle is shot through the double slit and it hits the screen at h-8, don't you also have to include the time it hit h-8 to more accurately describe its position? for example if I'm going to tell you where I'm going to be i have to say I'll be at starbucks at 4th and main at 11am to accurately describe where i am and when i'll be there?

The double slit experiment is only concerned with where the particle hits the screen, not precisely when. The time is not particularly relevant for this experiment.

In general, a particle's wave-function is a function of position and time: $\psi(\vec x, t)$. The modulus squared of this function $|\psi(\vec x, t)|^2$ is the probability density for finding the particle at position $\vec x$ at time $t$.

 

[Jstar70]

my point is that when those particles hit the screen is relevant because the image at the end becomes a flip book. The first shot is a picture of a particle frozen in time, that is why the image looks like a dot. when you shoot 1000 particles at the screen over a period of let's say a 5 minute period. the screen may be stationary in space but not time, its moving forward in time. at the end of the experiment you see what particles look like while they are in motion. in this case motion through time. just as you get when your flipping the pages in animated flip book. so don't particles act like waves only because they are moving through space time? The wave function only seems to collapse because your asking time to pause for a sec so you can look at it.

 

[atyy]

In quantum mechanics, the time of an event (such as when a dot appears on a screen) is gauged by a classical clock that is external to the quantum system. So time is running all the time, and does not pause during a measurement.

In the traditional double slit, the time that each dot appears on the screen is not relevant. However, the time of the event is important in other quantum mechanical applications with variants of the double slit, such as determining the Wigner function of the initial quantum state.

https://www.researchgate.net/publication/228595687_Measurement_of_the_Wigner_function_of_an_ensemble_of_helium_atoms
Measurement of the Wigner function of an ensemble of helium atoms
Kurtsiefer, Pfau, Mlynek
Nature 386:150-153 · March 1997

 

[PeroK]

my point is that when those particles hit the screen is relevant because the image at the end becomes a flip book. The first shot is a picture of a particle frozen in time, that is why the image looks like a dot. when you shoot 1000 particles at the screen over a period of let's say a 5 minute period. the screen may be stationary in space but not time, its moving forward in time. at the end of the experiment you see what particles look like while they are in motion. in this case motion through time. just as you get when your flipping the pages in animated flip book. so don't particles act like waves only because they are moving through space time?

The impact of a particle on the screen may leave a mark or may result in simply a number in a database. In either case, the data is not the particle. The particle is gone, disappeared or decohered into the macroscopic measuring apparatus. What you see on the screen (if anything) is an illuminated device that is part of the measuring apparatus. In fact, what you are actually seeing are many photons emitted from this device. The behaviour of this device is triggered by a particle impacting the screen in a certain area

The particles aren't stuck on the screen in some way!

The wave function only seems to collapse because your asking time to pause for a sec so you can look at it.

QM says nothing remotely like that.

 

[Jstar70]

Looks like I'm mixing my apples with my oranges. A consequence of trying to self educate. What is a good book to start with? I have a lot of reading to do if I hope to understand this stuff.
P.S. I wasn't suggesting the particles were stuck on the screen in any way, just that when the particle passes through the screen that is when and where its location are measured. just wondering if the "when" mattered or not, but I don't think I articulated myself very well. Thanks for the response.

 

[PeroK]

Looks like I'm mixing my apples with my oranges. A consequence of trying to self educate. What is a good book to start with? I have a lot of reading to do if I hope to understand this stuff.
P.S. I wasn't suggesting the particles were stuck on the screen in any way, just that when the particle passes through the screen that is when and where its location are measured. just wondering if the "when" mattered or not, but I don't think I articulated myself very well. Thanks for the response.

You could try this.

https://physics.mq.edu.au/~jcresser/Phys304/Handouts/QuantumPhysicsNotes.pdf

Other than that, Susskind's theoretical minimum has a good reputation.

https://www.goodreads.com/book/show/18210750-quantum-mechanics

 

[Minnesota Joe]

Looks like I'm mixing my apples with my oranges. A consequence of trying to self educate. What is a good book to start with? I have a lot of reading to do if I hope to understand this stuff.
P.S. I wasn't suggesting the particles were stuck on the screen in any way, just that when the particle passes through the screen that is when and where its location are measured. just wondering if the "when" mattered or not, but I don't think I articulated myself very well. Thanks for the response.

Other than that, Susskind's theoretical minimum has a good reputation.

https://www.goodreads.com/book/show/18210750-quantum-mechanics

I can second this recommendation @Jstar70 . Susskind has 3 in the series currently:

https://www.goodreads.com/book/show/13587145-the-theoretical-minimum

https://www.goodreads.com/book/show/18210750-quantum-mechanics

https://www.goodreads.com/book/show/33784507-special-relativity-and-classical-field-theory

He also has youtube lectures and lecture notes.

 

[Jstar70]

great! thanks a lot, looking forward to reading the material