[Harri (OP)]

As a non scientist I get all my information from popular science books and websites. And as such I take these as good places to get factual scientific information. I often read that particles can be in two separate locations at once. Of course particles in the plural suggests more than one particle so the fact that they can be in two separate locations at once isn't too surprising. It is when I read that 'a particle' can be in two separate locations at once I wonder if the statement is true and if it is at all helpful to describe it as such when discussing superposition? My initial reaction is to be in awe of such a possibility. But then if I think about it a bit more I ask would this be possible in spacetime? How could one particle occupy two places in spacetime?

[Halc]

I often read that particles can be in two separate locations at once.

This has certainly never been demonstrated, and while not denying it, I am unaware of a quantum interpretation which goes to far as to assert this.
So it sounds to me like poorly worded pop literature. I've no doubt that such statements are out there.
I might say that it is incoherent to talk about a particle being at a location (let alone more than one) at all. A particle is measured at a location, or it isn't. That's all we know for sure.

It is when I read that 'a particle' can be in two separate locations at once I wonder if the statement is true and if it is at all helpful to describe it as such when discussing superposition?

A cat being in superposition of dead and alive is not the same as saying it is both dead and alive. I think that's the disconnect not spelled out well in statements that word it otherwise.

How could one particle occupy two places in spacetime?

Spacetime is a different story. My hand is down. My hand is raised. Both these states are in spacetime, but in only one state at a particular time, where time is a chosen cross section of spacetime. That's the same as a highway 80 being in Chicago and New York at the same time. It's not a contradiction, it's just in those places at different locations along its length. A particle is similarly not a point (an event) in spacetime, but rather a worldline in spacetime. Being a line, it doesn't exist all in one place. This has nothing to do with superposition. It's a classic concept.

[Colin2B]

I often read that particles can be in two separate locations at once.

This has certainly never been demonstrated, and while not denying it, I am unaware of a quantum interpretation which goes to far as to assert this.

I’m not aware of one either. I think this is a misinterpretation of the solution to some wave equations where there is equal probability of 2 or even 4 solutions; that doesn’t mean those solutions exist simultaneously.

It is when I read that 'a particle' can be in two separate locations at once I wonder if the statement is true and if it is at all helpful to describe it as such when discussing superposition?

A cat being in superposition of dead and alive is not the same as saying it is both dead and alive. I think that's the disconnect not spelled out well in statements that word it otherwise.

Agreed, it’s a common misunderstanding of the Schrödinger’s thought experiment.

[Origin]

It is when I read that 'a particle' can be in two separate locations at once

Perhaps you are referring to the 2 slit experiments, where an electron passes through both slits?  This is not a particle being in 2 places at on time, this is a demonstration of the wave nature of an electron.  An electron is not a particle in the classical sense, so the 2 slit experiment does not say a particle is in 2 places at the same time.

[alancalverd]

A particle, by definition , can only be in one place at any instant. Problem is that the more accurately you know where it is, the less accurately you know how fast it is travelling or where it will be next. That's simple continuum physics leading to Heisenberg's indeterminacy principle.

Not to be confused with the Schrodinger interpretation which states that eg for an electron, all we know is the probability density distribution of finding it anywhere.

[geordief]

A particle, by definition , can only be in one place at any instant. Problem is that the more accurately you know where it is, the less accurately you know how fast it is travelling or where it will be next. That's simple continuum physics leading to Heisenberg's indeterminacy principle.

Is that an "existential **" situation(I mean ,is that just the way things behave) ?

...or is it a question of a limit of the powers of perception?

I am going to "guess" it is the former and not the latter as I have unconsciously assumed until now.

** bad choice of word,but I want to contrast the ways things actually work with the way we perceive them to do.

[Halc]

A particle, by definition , can only be in one place at any instant. Problem is that the more accurately you know where it is, the less accurately you know how fast it is travelling or where it will be next. That's simple continuum physics leading to Heisenberg's indeterminacy principle.

I want to contrast the ways things actually work with the way we perceive them to do.

The difference between science and philosophy is exactly this distinction. Science deals with what is measured, 'how we perceive them' so to speak. How things actually work, or 'what actually is' is metaphysics, which is philosophy: open to interpretation but impossible to know.
So a scientific statement would say that a particle can be measured at only one location at a given time. To assert that it can only be at one location at a time, or that it is even meaningful to discuss the location of a particle unmeasured, would be a metaphysical interpretation of the observations. I can for instance find at least two quantum interpretations that assign meaning to a particle having position despite lack of measurement, and the rest (dozen?) not. Those two interpretations (and not the others) would say that the particle definitely has some factual location and momentum, and Heisenberg's uncertainty is just an epistemological limit, as alan has worded it.

Not to be confused with the Schrodinger interpretation

There's such a thing as a 'Schrodinger interpretation'?

which states that eg for an electron, all we know is the probability density distribution of finding it anywhere.

That sounds like quantum theory, a scientific thing, not some metaphysical interpretation. It references what we can expect to measure instead of describing what is. That makes it a theory, not an interpretation.

[alancalverd]

The simple derivation of Heisenberg's indeterminacy principle is that if it were possible for the position and momentum of an electron to be defined simultaneously, the most likely place to find any electron would be glued to a proton, so all atoms would have diameters about 10⁵ times smaller than they do. Hence the Bohr model (orbiting electrons)  and deBroglie wavelengths, which consist with Δp.Δx = h. Note that this is an inherent indeterminacy, nothing to do with the uncertainty of a measurement - a persistent mistranslation that has baffled many a journalist.

Problem then arises that an orbiting charged particle loses energy in the form of electromagnetic radiation, but this is not observed, hence Schrodinger's fuzzy "probability cloud", which is consistent with observation.  I probably used "interpretation" loosely - apologies.

 

[Harri (OP)]

If I look down onto a football field and see a player, I can tell where his position is on the field and from his momentum I can see which direction he is going. If I look at the position of a particle in a 'field' why is it not possible to see which direction it is going due to its momentum?

[Halc]

If I look down onto a football field and see a player, I can tell where his position is on the field and from his momentum I can see which direction he is going.

Yes, a player is a classical thing and such things have position and momentum that can be simultaneously measured to considerable accuracy.
The classical properties start to drop off as you go smaller and smaller, to the point where intuitive things (like having an objective state, unmeasured, having a mass-density, etc.) vanish.

If I look at the position of a particle in a 'field' why is it not possible to see which direction it is going due to its momentum?

It's more like you know its momentum because you've measured its movement. And no, this cannot be done, because to measure its position accurately, you need to interact with it with a significant energy. It might as well have been kicked by a mule; it goes skittering off somewhere, momentum completely unmeasured.
The trick is to compromise.  A given proton in a cold diamond lattice is practically a classic thing with its position confined to the small wiggle-room of the elements of the crystal, and its average velocity is the same of that of the diamond. Not sure what the mean deviation from that velocity would for a proton in a carbon nucleus were you to measure it. It's not like anybody has actually measured the atom, let along a given proton. Only the diamond, so all measurements are indirect.

[alancalverd]

I've never liked the "bouncing photon measurement" approach because it tends towards "uncertainty" rather than "indeterminacy".

The simple fact is that to determine the player's momentum, which is a vector, he has to move so you know the direction of the vector. But now he has moved, he isn't where he was when he had that momentum, so you can't know both to an infinitesimal precision at any instant. Heisenberg proposed that the limit had a single value, and that turned out to be consistent with all our observations.

As with relativity, the derivation given by the inventor is a lot simpler than most of the "explanations" in the textbooks!

[Colin2B]

If I look down onto a football field and see a player, I can tell where his position is on the field and from his momentum I can see which direction he is going. If I look at the position of a particle in a 'field' why is it not possible to see which direction it is going due to its momentum?

Different example to add to what @Halc is saying:
Let’s say your friend is coming to visit you, gives a call as he’s leaving. You know it takes about half an hour, so after 15min he should be half way, but you don’t know. Your model has to include some randomness because of traffic, roadworks etc.
It’s similar with quantum objects, we can model them and we can predict where they probably are, but unless we measure we can’t be sure, and because we can’t see them directly there are problems with the measurements. As @Halc says a measurement can disturb the position of the particle unless we can confine it. There are ways of detecting the electric field of atoms so that researchers can build up some pretty amazing images of the structures and atomic bonds and take measurements from these, however the boundaries of the atoms are fuzzy due to the nature of the electron field.
(Some overlap with @alancalverd I see).

[geordief]

If I look down onto a football field and see a player, I can tell where his position is on the field and from his momentum I can see which direction he is going. If I look at the position of a particle in a 'field' why is it not possible to see which direction it is going due to its momentum?

Different example to add to what @Halc is saying:
Let’s say your friend is coming to visit you, gives a call as he’s leaving. You know it takes about half an hour, so after 15min he should be half way, but you don’t know. Your model has to include some randomness because of traffic, roadworks etc.
It’s similar with quantum objects, we can model them and we can predict where they probably are, but unless we measure we can’t be sure, and because we can’t see them directly there are problems with the measurements. As @Halc says a measurement can disturb the position of the particle unless we can confine it. There are ways of detecting the electric field of atoms so that researchers can build up some pretty amazing images of the structures and atomic bonds and take measurements from these, however the boundaries of the atoms are fuzzy due to the nature of the electron field.
(Some overlap with @alancalverd I see).

You seem to me to be be saying or implying that ,if measurements were finer and more efficient that the position and the momentum of a particle could be determined separately and not as a pair that are joined at the  hip


Suppose there was  a new particle  discovered  that was millions of times smaller than the electron and it was able to be manipulated  would this  allow us the disentangle the electron's momentum from its position or are these two properties simply two sides of the same coin?

Is there forever and intrinsically a limit to how close an approximation  there can be to a separation  of these two descriptions?

[yor_on]

It's open for interpretations, superposition. A entanglement can be seen as a superposition too and so can a two slit experiment. It also relates to whether you take HUP seriously or just assume that it is a result of us not 'knowing ' all parameters beforehand. It opens for a lot of interpretations. Myself I take HUP seriously and when it comes to particles it's about their 'wave nature'. If the same particles can exist in 'two places spatially'? I don't know, you have to measure/probe them directly to do that and once you've done it they no longer will be 'entangled', nor will they be 'super positioned'.

https://scitechdaily.com/quantum-superposition-record-2000-atoms-in-two-places-at-once/

the more interesting question is if you get 'work' out of it before measured, somehow? I don't think that's possible but I don't know.


syntax

[alancalverd]

You seem to me to be be saying or implying that ,if measurements were finer and more efficient that the position and the momentum of a particle could be determined separately and not as a pair that are joined at the  hip

Quite the opposite. If you know the position of a particle to infinitesimal precision, you have no information as to its momentum. People look different when they are running compared with standing still, but if you photograph a car with a very short flash, you can't tell whether it is moving forwards, backwards, or stationary Cameras have advanced to the point that you can now get "propellor disc blur" software so that photos of classic aircraft in flight look different from stationary models, but a true "snapshot" gives you no clue as to its speed.

So far, so intuitive. But intuition breaks down if you know that an electron is absolutely stationary, Heisenberg says in that case, you can have no idea where it is!

[geordief]

You seem to me to be be saying or implying that ,if measurements were finer and more efficient that the position and the momentum of a particle could be determined separately and not as a pair that are joined at the  hip

Quite the opposite. If you know the position of a particle to infinitesimal precision, you have no information as to its momentum. People look different when they are running compared with standing still, but if you photograph a car with a very short flash, you can't tell whether it is moving forwards, backwards, or stationary Cameras have advanced to the point that you can now get "propellor disc blur" software so that photos of classic aircraft in flight look different from stationary models, but a true "snapshot" gives you no clue as to its speed.

So far, so intuitive. But intuition breaks down if you know that an electron is absolutely stationary, Heisenberg says in that case, you can have no idea where it is!

Oh,it kind of "blinks" out of the realm of information when it is  stationary wrt the observer?

Or does it "fadeout" rather  the more relatively stationary it becomes?

And I suppose that applies to any object ,and not especially to an electron....

There is no principle involved , is there such  that at the quantum level it is impossible for any two objects to be  completely at rest wrt each other?

[Colin2B]

You seem to me to be be saying or implying that ,if measurements were finer and more efficient that the position and the momentum of a particle could be determined separately and not as a pair that are joined at the  hip

No, I’m not saying that, as Alan has explained very clearly.
What I’m saying is that the analogy @Harri was giving is inappropriate. There are two factors at work here, one is our state of knowledge of a particle because we can’t see it in the same way as looking at a player on a field. We see the player on the field because photons bounce off him and hit our eyes, those photons don’t move him or alter his momentum significantly, but they do if the player is an electron. One way we can detect an electron is to have it hit a detector eg phosphor screen, but then it’s stopped moving. Even if we use a speed gun on the player s/he has to move in order to get a doppler reading. These are the physical and practical problems.
The second problem is answered by Alan.
Reread Alan’s reply https://www.thenakedscientists.com/forum/index.php?topic=83459.msg659621#msg659621
There is an intrinsic limit to how accurately we can know these 2 properties at the same time and is quite different from the measurement problems already described. This is a limit set by the way the universe works. Reread both posts by Alan as he has put down very clearly what is an endless source of confusion to most non physicists, and unfortunately a few physicists!
For a large object like a ball kicked by a player the difference is so small that it is irrelevant around 10^-30m.

[Petrochemicals]

A cat being in superposition of dead and alive is not the same as saying it is both dead and alive. I think that's the disconnect not spelled out well in statements that word it otherwise.

But that is what it means to me Halc. But the cat is singular, in the same place

[Colin2B]

A cat being in superposition of dead and alive is not the same as saying it is both dead and alive. I think that's the disconnect not spelled out well in statements that word it otherwise.

But that is what it means to me Halc. But the cat is singular, in the same place

Why does it mean that to you? It didn’t to Schrödinger who intended it as an example of the absurdity of such an interpretation. The problem is that many people have misunderstood what he was trying to say.

[Petrochemicals]

A cat being in superposition of dead and alive is not the same as saying it is both dead and alive. I think that's the disconnect not spelled out well in statements that word it otherwise.

But that is what it means to me Halc. But the cat is singular, in the same place

Why does it mean that to you? It didn’t to Schrödinger who intended it as an example of the absurdity of such an interpretation. The problem is that many people have misunderstood what he was trying to say.

Because our actual actions of seeking definition render either answer if I am right in my understanding of it. It can be both alive and dead, 0 and 1.