Does a particle really try every possible path?

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In quantum physics, particles can theoretically occupy any position in the universe, but they don't literally "try" every possible path. Instead, their behavior can be described using probability calculations that account for all potential paths, with nearby paths reinforcing the likelihood of certain outcomes. The concept of the path of least action suggests that particles tend to take the most efficient routes, leading to the highest probability of being found near their previous positions. The double-slit experiment illustrates that particles behave as if they take all possible paths, but this is a mathematical representation rather than a literal one. Overall, the initial confusion surrounding quantum mechanics diminishes when understanding that while all paths are possible, most are highly improbable.
  • #91
Joel A. Levitt said:
Requested Reference Re: Recent experimental demonstrations of the FTL transmission of information between entangled entities --

Challenging preconceptions about Bell tests with photon pairs
Authors: V Caprara Vivoli, P Sekatski, J -D Bancal, C C W Lim, B G Christensen, A Martin, R T Thew, H Zbinden, N Gisin, N Sangouard
Journal: Phys. Rev. A 91, 012107 (2015)

You are seriously misunderstanding this paper if you believe that it suggests that FTL information transfer is possible. It is discussing some of the mathematical niceties around the well-known fact that spacelike-separated measurements of entangled pairs will demonstrate non-local correlations; it says nothing to challenge the equally well-known fact that these correlations cannot be used to transmit information.
 
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  • #92
Joel A. Levitt said:
Would you please provide a more detailed response to "How do you define PARTICLE?"

Loosely it's an excitation in a quantum field. The sense that is meant is made rigorous in books on Quantum Field Theory.

Quantum Field Theory is notoriously difficult and challenging, usually requiring a course in advanced Quantum Mechanics.

However books have started to appear at that can be tackled with less preparation:
https://www.amazon.com/dp/019969933X/?tag=pfamazon01-20

Suitable preparation would be Susskinds text:
https://www.amazon.com/dp/0465036678/?tag=pfamazon01-20

It ends where the QFT book starts at the harmonic oscillator.

Thanks
Bill
 
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  • #93
Joel A. Levitt said:
Peter Donis:
Would you please provide a more detailed response to "How do you define PARTICLE?"

PeterDonis is using the generally accepted definition that you will find in any textbook on quantum field theory. Two that I recommend are https://www.amazon.com/dp/0521670535/?tag=pfamazon01-20 (challenging, to put it gently) and Quantum Field Theory for the gifted amateur (like the title says, suitable for someone who has made it through an undergraduate physics degree program).
 
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  • #94
Nugatory said:
You are seriously misunderstanding this paper if you believe that it suggests that FTL information transfer is possible. It is discussing some of the mathematical niceties around the well-known fact that spacelike-separated measurements of entangled pairs will demonstrate non-local correlations; it says nothing to challenge the equally well-known fact that these correlations cannot be used to transmit information.
Any measurement of one of a pair changes its state and therefore the state of the other. This is the FTL transmission of information. Unfortunately, it isn't all that useful, because the prior state of the second member wasn't known.

It is to be noted that we both have avoided using the word particle. I assume that this is because we both know that this word was originated from our macro sensory experience and is only some sort of metaphor when applied to almost all quantum phenomena. It's unfortunate that the use of this word confuses so many. This is also the case when, in discussion with the general public, the Schrödinger-motivating elements of classical mechanics are introduced without detailed explanation.

By the way, all three volumes of Weinberg's "The Quantum Theory of Fields" are available in relatively inexpensive soft cover.

A second matter, you wrote to me, " You are talking too much and listening too little." Having spent almost 50 years as a frequently published applied physicist and having successfully nurtured 7 PhD candidates, I find this amusing. You seem to believe that this site is you very own sandbox. Forgive me for intruding.

Bye!
 
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  • #95
Joel A. Levitt said:
Any measurement of one of a pair changes its state and therefore the state of the other.

Entangled particles do not have a state for each particle - that's part of what entanglement means.

What the measurement does is break entanglement and when that is done we see the outcomes are correlated.

Locality in QM is a bit different - its the so called cluster decomposition property:
https://www.physicsforums.com/threads/cluster-decomposition-in-qft.547574/

It does not apply to correlated system. Entangled particles are correlated so locality doesn't apply.

Thanks
Bill
 
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  • #96
it is a matter of probability of being in a location, some are much more likely than others...
 
  • #97
When we say that a particle "tries" every path, we don't mean that it actually has a choice at the given point in time. What it means is that we don't know which path it will take because we don't know the actual events that cause the particle being where it is now.
This is called a probabilistic model. The opposite (or rather its perfect form) is a deterministic model.
 
  • #98
double slit seems to act like an OR gate. look at the truth table for an OR gate.
 
  • #99
If this idea makes sense, then it's rather a "quantum or gate". That's the very point of the discussion of the double-slit experiment! The particle distribution behind the double slit is not the naive sum of the particle distribution behind each single slit, but there's an interference term. In the former days this was taken as a hint for what the physicsts called "wave-particle duality", which is a highly misleading concept, but in this case it's a good buzz word to describe what's really happening in the mathematical description of particles going through a double slit: It shows some analogy to the behavior of classical waves (no matter which ones you consider, e.g., water waves or the electromagnetic field/light) running through openings.

Of course, the meaning of the waves is quantum theory completely different from the classical analoga: It describes a probability amplitude. Shooting a single particle through a double slit will never result in an extended interference pattern at the detection screen but a single point. You cannot predict with certainty, where such a particle will hit the screen, but shooting many single particles through the double slit, however, reveals a distribution resembling the interference pattern of waves' intensity. Mathematically the analogon is quite direct: The probability amplitude is described by the Schrödinger equation which leads to wavelike solutions, and its modulus squared is the probability distribution where the particle will hit the screen.
 
  • #100
vanhees71 said:
If this idea makes sense, then it's rather a "quantum or gate". That's the very point of the discussion of the double-slit experiment! The particle distribution behind the double slit is not the naive sum of the particle distribution behind each single slit, but there's an interference term. In the former days this was taken as a hint for what the physicsts called "wave-particle duality", which is a highly misleading concept, but in this case it's a good buzz word to describe what's really happening in the mathematical description of particles going through a double slit: It shows some analogy to the behavior of classical waves (no matter which ones you consider, e.g., water waves or the electromagnetic field/light) running through openings.

Of course, the meaning of the waves is quantum theory completely different from the classical analoga: It describes a probability amplitude. Shooting a single particle through a double slit will never result in an extended interference pattern at the detection screen but a single point. You cannot predict with certainty, where such a particle will hit the screen, but shooting many single particles through the double slit, however, reveals a distribution resembling the interference pattern of waves' intensity. Mathematically the analogon is quite direct: The probability amplitude is described by the Schrödinger equation which leads to wavelike solutions, and its modulus squared is the probability distribution where the particle will hit the screen.
can the double slit be thought of as a 'phase filter'. the distance between the slits determans what phases it will filter?
 
  • #101
An electron is a quanta meaning it can behave like a wave or particle, this was first observed in the micro-slit experiment, search it, it is really interesting. Basically, if you have a point A and point B, the electron would theoretically takes every possible path from point A to point B.
 
  • #102
As stressed before, an electron is one quantum (formally it's a one-particle Fock state). This means it's neither a classical particle nor a classical wave but can only described by quantum theory. There's no simpler way to describe it that is entirely correct. The wave-like and particle-like properties are only consistently described by quantum theory, and you cannot describe it in some simpler way.

You cannot say, the electron takes a certain way or that it takes every possible path at once. What you calculate with the Schrödinger equation or, equivalently, with the path integral is a socalled propagator, which is a mathematical description how the state (a highly abstract mathematical object) evolves in time, given the state at some initial time and the interactions (forces) of the particle with the experimental setup (in this case with the double slits). The result is a probability distribution that the electron makes a mark on the detection screen. You an make this probability distribution visible by performing the experiment very often with the same initial state of each electron and the same experimental setup. All we can say is that up to know the predictions of quantum theory are confirmed by the so made observations. You cannot expect more from the natural sciences than such a successful description of objectively observable facts about (certain aspects of) nature. Particularly, it never answers and also never aims to answer the question, "what's really going on". The reason is, that you cannot even precisely define, what you mean by this question. It's highly subjective, depending on your personal experience in life. It takes time to get used to the very unfamiliar way of thinking when it comes to the realm of nature requiring quantum theory to describe it. The intuition is due to quite abstract ideas, and you can only grasp its meaning by looking at it in different applications to get a kind of intuition for these highly abstract ideas.
 
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  • #103
vanhees71 said:
As stressed before, an electron is one quantum (formally it's a one-particle Fock state). This means it's neither a classical particle nor a classical wave but can only described by quantum theory. There's no simpler way to describe it that is entirely correct. The wave-like and particle-like properties are only consistently described by quantum theory, and you cannot describe it in some simpler way.

You cannot say, the electron takes a certain way or that it takes every possible path at once. What you calculate with the Schrödinger equation or, equivalently, with the path integral is a socalled propagator, which is a mathematical description how the state (a highly abstract mathematical object) evolves in time, given the state at some initial time and the interactions (forces) of the particle with the experimental setup (in this case with the double slits). The result is a probability distribution that the electron makes a mark on the detection screen. You an make this probability distribution visible by performing the experiment very often with the same initial state of each electron and the same experimental setup. All we can say is that up to know the predictions of quantum theory are confirmed by the so made observations. You cannot expect more from the natural sciences than such a successful description of objectively observable facts about (certain aspects of) nature. Particularly, it never answers and also never aims to answer the question, "what's really going on". The reason is, that you cannot even precisely define, what you mean by this question. It's highly subjective, depending on your personal experience in life. It takes time to get used to the very unfamiliar way of thinking when it comes to the realm of nature requiring quantum theory to describe it. The intuition is due to quite abstract ideas, and you can only grasp its meaning by looking at it in different applications to get a kind of intuition for these highly abstract ideas.
Excellent!
 
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  • #104
brianhurren said:
can the double slit be thought of as a 'phase filter'. the distance between the slits determans what phases it will filter?

Thinking back to when I was into electronics I would say no.

I have noticed a pattern in your posts - trying to reduce things like the double slit to something else. It can't be done - QM is QM - its analogous to just one thing - QM. The wave particle duality is an attempt at such an analogy left over from the early days of QM - but it's wrong. In popularisations and beginning texts so students can get an initial grasp they do such things, but as you advance they are abandoned. Personally I am not a fan of that method - I would prefer facing it head on from the start as an extension of probability:
http://www.scottaaronson.com/democritus/lec9.html

But I must emphasise my background is applied math and that's how someone like me imbued with the spirit of mathematical modelling would approach it. Those into physics normally take the route of building intuition by a semi-historical approach.

Thanks
Bill
 
  • #105
Joel A. Levitt said:
Excellent!

As usual.

I have learned so much from reading Vanhees posts.

Thanks
Bill
 
  • #106
phinds said:
Yeah, I think that way too. My logic is that if you move the wall a bit closer, you still get an interaction. Move it a bit closer and you still get an interaction. And so forth. So clearly it's THERE in some sense.

The mistake would be to connect the dots between all those interactions and think that you have found even one path that the particle took on the way to the wall when it was farthest away. There's no path, there's nothing until you get an interaction, but I'm agreeing w/ you that it is in some sense there even if that is undefined and not useful in practice.
From a non-physicists (but interested layman) point of view. It appears from this and other threads that it serves little purpose in using common language to describe QM. It appears to be only describable using mathematics. Our language serves only to misdirect or mislead when attempting to explain how particles/waves move or what their state is when they are not moving. Using language that describes states or motions we understand in our macro universe, we appear not be able to describe the state or motion of Q particles/waves. As a previous message says, concerning the journey between outset and arrival of a particle or wave, the theory is 'silent' about it. If there is no theory concerning the route taken from A to B, and no evidence to show which path is taken (does it take one of an infinite number, does it take all possible paths), then what evidence exists to show that a wave or particle arriving at a detector is the same wave or particle that left the source? If a wave or particle does not indeed travel (in the conventional sense) between two points in space, then the source and detector have a messenger between them, and so the discussion then moves to how the messenger communicates or travels. The difficulty is how do mathematicians translate their language into meaningful and unambiguous spoken language.

AD2004
 

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