Questions about a travelling electron

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In summary, the assumption that the electron is physically present between the emitter and the screen, when it is not interacting, can not be verified by any experiment.
  • #1
kipsate
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I have a question which I hope gives rise to a good discussion.

Imagine an electron source and a screen. An electron is emitted in the direction of the screen. While traveling towards the screen, the electron does not interact with any other force or particle (assuming that any interactions with virtual particles do not have a net effect on the electron). Then, the electron hits the screen and gets detected.

Common sense says that the electron has physically traveled through the space between the electron source and the screen. Also, it is assumed that when the electron does not interact, it is still physically present. But is there a way to prove this? There is no way to establish that the electron is actually present between the source and the screen without actually interacting with the electron.

Am I therefore correct when I state that the assumption that the electron is physically present between the source and the screen - where it does not interact - can not be verified by any experiment?

If the answer is "yes", then can't I just as well state that the electron was NOT physically present? That between any two interactions, an electron does not take up any space or time? Because that would be equally unverifiable.

Note that here, I am not stating that this is actually the case, but note that I am just observing that the common assumption that the electron (or photon) is physically present between two interactions is just that - an assumption, or, if you wish, a postulate, for which no experiment can be incepted to prove its veracity.

Or do I see it wrong?
 
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  • #2
Well unless the electron is transported (instantaneous teleport style) from the source to the screen, it is present during travel through the space between.

To prove this you could just move the screen closer and observe how long it takes between emission and interaction. The time would reduce and as such show that a 'journey' takes place for the electron.

I suppose you're looking at the argument of "there's no evidence showing it there and so we can't prove nor disprove it". But I don't think it quite works in this case.

EDIT: Quick thought, wouldn't an electron traveling produce a magnetic field? Just use that to monitor it moving through the space. No interaction required.
 
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  • #3
jarednjames said:
Well unless the electron is transported (instantaneous teleport style) from the source to the screen, it is present during travel through the space between.
Indeed. I am just noting that it is impossible to prove that the electron has actually physically traveled through the space between the emitter and the screen.

jarednjames said:
To prove this you could just move the screen closer and observe how long it takes between emission and interaction. The time would reduce and as such show that a 'journey' takes place for the electron.
This still does not prove that the electron was physically present between the emitter and the screen.

jarednjames said:
I suppose you're looking at the argument of "there's no evidence showing it there and so we can't prove nor disprove it". But I don't think it quite works in this case.
To be called science, a theory has to be http://en.wikipedia.org/wiki/Falsifiability" . I am arguing that the assumption that the electron is physically present when it is not interacting, is not falsifiable and therefore not scientific.

jarednjames said:
Quick thought, wouldn't an electron traveling produce a magnetic field? Just use that to monitor it moving through the space. No interaction required.

Detecting the magnetic field can only succeed by exchanging force carriers and thus interaction with the electron. So no, this would not help.

I can postulate that at the emitter, the electron disappeared from the observable universe only to reappear at the screen. This would be equally unfalsifiable, and therefore, not worse as a theory than the common one which says that the electron is physically present at all times between the emitter and the screen.
 
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  • #4
Ole Ulfbeck and Aag Bohr claimed that atomic scale objects do not exist at all.As an example they claimed that a click on a geiger counter is nothing more than a fortuitous event correlated with a radioactive substance.Any assumptions we make about unobserveable or unobserved features of events are unfalsifiable,they are models and models can be useful but they must conform to the observations that can be or are made.
 
  • #5
kipsate said:
Detecting the magnetic field can only succeed by exchanging force carriers and thus interaction with the electron. So no, this would not help.

If it has a magnetic field, we can detect it. Like I said, I don't see how this is a good example. Or am I missing something here, like an electron in motion not having an magnetic field? If so, please do explain how that works.

I would have said you'd be better off using nutrinos.
 
  • #6
jarednjames said:
If it has a magnetic field, we can detect it. Like I said, I don't see how this is a good example. Or am I missing something here, like an electron in motion not having an magnetic field? If so, please do explain how that works.
Yes, I'm afraid you're missing something. I'll try to explain.

The photon is the http://en.wikipedia.org/wiki/Force_carrier" for electromagnetism. Detecting the electron by detecting the magnetic field would require a photon exchange between your magnetic field detector and the electron.

It is true that the detection proves that the electron is present - after all the electron interacted with your magnetic field detector by exchanging a photon with it. But its detection does not prove that the electron was physically present between the time it left the emitter and just before the spot where you detected it. Although it may seem super obvious to conclude that the electron physically traveled the entire path between the emitter and the detector, this is still no more than an assumption, and even an unfalsifiable one at that.

The key here is to understand that I'm considering the electron in between two interactions. I might just as well postulate that in the time between two interactions, the electron is not physically present, and that it simply jumps from interaction to interaction. There is no way you can falsify that either.

Note that although I'm taking the electron here as an example, but I could have chosen a photon or any other fundamental particle.
 
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  • #7
If you have a wire and pass a current through it, it produces a magnetic field. You can use a gauss meter to detect said field. It doesn't have to touch any of the electrons to do so. Why would this be any different?

If your instrument is sensitive enough, the electron would pass through the sensor, sensor detects the magnetic field and the electron continues onwards.

You could place a series of sensors covering the entire path to detect the fields and track its movement.

I think I'll leave this one, not a fan of philosphy as it is.
 
  • #8
jarednjames said:
If you have a wire and pass a current through it, it produces a magnetic field. You can use a gauss meter to detect said field. It doesn't have to touch any of the electrons to do so. Why would this be any different?
A "magnetic field" is an illusion created by positive and negative charges in motion relative to each other. If you have negative charges only, you will have no "magnetic field".
http://physics.weber.edu/schroeder/mrr/MRRtalk.html

Also if the electron in question has a detectable effect in the device, the device WILL have an effect on the electron. On a macro scale, like detecting a bullet, the measuring devices effect on the subject can be so small that it is negligible and irrelevant to the experiment. This cannot be said about experiments on a quantum scale.

If your instrument is sensitive enough, the electron would pass through the sensor, sensor detects the magnetic field and the electron continues onwards.

You could place a series of sensors covering the entire path to detect the fields and track its movement.

I think I'll leave this one, not a fan of philosphy as it is.

Each time you "detect" the electron you have interacted with it in some way. In between interactions you can say nothing about what the electron is or isn't doing. Dr. Quantum will explain.

Or Dr. Idunno
http://www.youtube.com/watch?v=UXvAla2y9wc&feature=related

This is not philosophy, this is quantum mechanics.
 
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  • #9
jarednjames said:
To prove this you could just move the screen closer and observe how long it takes between emission and interaction. The time would reduce and as such show that a 'journey' takes place for the electron.

All you have done is to observe another electron. Moving the screen closer will not change the original experiment, as it already has finished.

In the double slit experiment you have to do the experiment over and over again, so the interference pattern appears. So, the question here is.. "Is there interference pattern if one and only one electron is allowed to go through the double slit?" You may say, there is. How can you prove it?

The fact is that you need many electrons to get the interference pattern. The same is valid for your experiment. You need many electrons to correlate their travel time to the distance they have to cover. Just as in the case with the interference pattern, your 'journey' does not exist for a single electron. At least not in physically meaningful way.
 
  • #10
Travelling electron, continued

I would now like to try to take this a step further.

For the discussion, let's now assume the following http://en.wikipedia.org/wiki/Axiom" :
"An elementary particle only exists in the observable universe at the instant moment it interacts. It exists at an infinitely small moment in time, at an infinitely small location."

Elementary particles like the electron have no internal structure and are considered to be http://en.wikipedia.org/wiki/Point_particle" . My interpretation of this is that an elementary particle does not take up any physical space.

Since everything in the observable universe consists of elementary particles, then it follows that all particles that exist in the universe do not take up any space. The aggregate volume of all elementary particles is zero.

Previously in this thread I have noted that no falsifiable claims can be made about the position of an elementary particle in the time between two interactions. The axiom now claims that in between two interactions, the particle was not present at all. A particle only manifests itself the instant moment it interacts, becoming part of the observable universe for an infinitely small amount of time, in an infinitely small amount of space.

To illustrate this further, consider again an electron source that fires an electron to a screen and that the electron will not interact (with any other particle or force) between the source and the screen. From the point of view of the electron, it will have a first interaction which causes it to be fired from the electron source towards the screen. Then, without having experienced any travel through space and without having experienced any passing of time, it will interact with (a particle of) the screen. From the point of view of an observer, an electron seems to have been traveling from the source to the screen and seems to have been present somewhere in between the space between the source and the screen in the time that passed between the two interactions. Assuming the axiom, the electron did not exist in the observable universe at all. It disappeared at the detector and reappeared at the screen.

For every elementary particle, the axiom says that it only exists in the observable universe when it interacts. It follows then, that the observable universe is a succession of momentary interactions that themselves do not take up any space or time.

Feedback welcome!
 
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  • #11
Unfortunately there is the gravity (and probably Higgs field). So, the particle has to interact very rapidly or even continuously. Now, the question is if the time is quantized.
 
  • #12
Upisoft said:
Unfortunately there is the gravity (and probably Higgs field). So, the particle has to interact very rapidly or even continuously. Now, the question is if the time is quantized.

Consider the double-slit experiment. Is it possible to extract information about the path of a single electron by introducing variations in the gravitational field for different paths?

Consider the following double-slit thought experiment. Imagine a standard set-up, with an emitter, two slits next to each other and a screen. Let us now place a super heavy mass half way the two slits and the screen, a little left of the center. See image below. The mass is placed in a position low enough such that the electrons will fly over it.

double-slit.gif


Fire a single electron. Observe where it hit the screen. Can we now deduce path information? After all, electrons flying over the mass will experience more gravity and end up on the screen in a slightly lower position than electrons that took a path further away from the mass. Does the height in which the electron hits the screen, tell us something about the path of a single electron?

Unfortunately, it doesn't. After all, the electron leaves the two slits at an unknown http://en.wikipedia.org/wiki/Inclination" . The fact that an individual electron hits the screen in a low position may either be caused by the gravitational force of the mass, or simply by its original inclination. We can't tell the difference. The only thing we will see, after firing many electrons, is an inference pattern that is bend downwards on the left part of the screen. But no path information of individual electrons can be revealed in this set up. The inference pattern remains.

This experiment would show that gravity does not collapse the wave function of a particle. Or in other words, going back to the topic of this thread, the path of the electron is not known between two interactions. Gravity does not cause interactions with the electron such that path information is revealed.

The above is topic of debate. Therefore, it is more correct to put in a second axiom:
"Gravity does not interact with an elementary particle such that it causes its wave form to collapse."

Feedback, again, welcome.
 
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  • #13
Well there is a problem. If the particle is not there before the collapse of its wave function how did it interact with the gravity field? What matters is that the interaction exists, therefore the particle also exists.
 
  • #14
Upisoft said:
Well there is a problem. If the particle is not there before the collapse of its wave function how did it interact with the gravity field? What matters is that the interaction exists, therefore the particle also exists.

Agreed. Note that all the time, I am carefully referring to some concept called the "observable universe" without having defined, so far, what that actually means. But allow me to explain that now.

I am saying that in between two interactions, an elementary particle disappears from the observable universe. I have argued that this is unfalsifiable. I did not state that the elementary particle disappears entirely, as that would not make any sense. In between two interactions, the particle must be represented somewhere, somehow. Also, as you point out, gravity is capable of interacting with it. But in between two interactions, there is not a single trace of the particle in the universe as we know it, as we can observe it. Hence the concept of the observable universe, the part of the universe that we are part of.

The axiom:
"An elementary particle only exists in the observable universe at the instant moment it interacts. It exists at an infinitely small moment in time, at an infinitely small location."

This implies that in between two interactions, the elementary particle is represented somewhere, somehow where it can not be accessed or interacted with. It implies the existence of an unaccessible "unobservable universe" where apparently elementary particles are somehow represented, and where the force of gravity interacts with the elementary particles.

Thoughts?
 
  • #15
Sounds just like David Bohm's implicate order if you are familiar with it

Also everyone is always going on about non locality but the issue of realism is much more interesting (ok they are both fascinating!, and related anyway)
 
  • #16
ferenan said:
Sounds just like David Bohm's implicate order if you are familiar with it

David Bohm basically proposed the existence of a http://en.wikipedia.org/wiki/Hidden_variable" (and will not).
 
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  • #17
kipsate said:
David Bohm basically proposed the existence of a http://en.wikipedia.org/wiki/Hidden_variable" (and will not).

Yes. But his views changed quite significantly over time. His view ended up being very holistic with the notion of the implicate order of a holographic nature of the universe where everything is intrinsically connected and the whole is contained even within a single particle. I don't think a hidden variable answer does justice to what his views became.
In this view the "existence" of the electron inbetween places is very questionable as it would be "folded" up in a higher dimension (if you don't mind the over simplified metaphor) along with everything else . Only to be unfolded at the time where it interacts from our point of view (and so can act non locally as it was/is in contact with all in the folded up realm). That seems very relevant to your discussion.
 
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  • #18
kipsate said:
I have a question which I hope gives rise to a good discussion.

Imagine an electron source and a screen. An electron is emitted in the direction of the screen. While traveling towards the screen, the electron does not interact with any other force or particle (assuming that any interactions with virtual particles do not have a net effect on the electron). Then, the electron hits the screen and gets detected.

Common sense says that the electron has physically traveled through the space between the electron source and the screen. Also, it is assumed that when the electron does not interact, it is still physically present. But is there a way to prove this? There is no way to establish that the electron is actually present between the source and the screen without actually interacting with the electron.

Am I therefore correct when I state that the assumption that the electron is physically present between the source and the screen - where it does not interact - can not be verified by any experiment?

If the answer is "yes", then can't I just as well state that the electron was NOT physically present? That between any two interactions, an electron does not take up any space or time? Because that would be equally unverifiable.

Note that here, I am not stating that this is actually the case, but note that I am just observing that the common assumption that the electron (or photon) is physically present between two interactions is just that - an assumption, or, if you wish, a postulate, for which no experiment can be incepted to prove its veracity.

Or do I see it wrong?



What do you mean by ''electron'' and what do you mean by ''travel''(I am expecting a satisfactory answer so that there'd be a possibility of answering your fundamental question)
 
  • #19
Maui said:
What do you mean by ''electron'' and what do you mean by ''travel''(I am expecting a satisfactory answer so that there'd be a possibility of answering your fundamental question)

I suppose this marks the arrival of the trolls?
 
  • #20
kipsate said:
I suppose this marks the arrival of the trolls?


You are not supposed to ask(or try to imagine) what an electron or other point particles are(or how they travel), as they are not particles, nor are they waves. The idea of movement is also a bit of a stretch and the question as posed reveals a classical mindset that doesn't fit the quantum 'hole'.
 

Related to Questions about a travelling electron

1. What is an electron?

An electron is a subatomic particle that carries a negative charge and is found in the orbitals around an atom's nucleus.

2. How does an electron travel?

An electron can travel in multiple ways depending on the context. In terms of atomic structure, electrons move in the orbitals around the nucleus of an atom. In terms of electrical current, electrons flow from a higher potential to a lower potential in a conductor.

3. Can an electron travel in a straight line?

No, electrons do not travel in a straight line. They follow a random path due to their interaction with other particles and their wave-like behavior.

4. What is the speed of an electron?

The speed of an electron can vary depending on its energy level and environment. In a vacuum, electrons can travel at about 2.2 million meters per second, but in a conductor, their speed is much slower due to collisions with other particles.

5. How does an electron's travel affect its charge?

The charge of an electron remains constant regardless of its travel. It always carries a negative charge of -1. The direction and speed of its travel may change, but its charge remains the same.

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