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kevin1981
2011-Nov-27, 04:08 AM
Matter is either a solid, liquid or gas. But recently i got told on this board that Atomic "particles" are not solid, so what
are they ?

People say, matter is not solid, so an Electron is not solid. But an Electron exists, however small, so why is it not
solid ? And if it is not solid, what is it ?

Delvo
2011-Nov-27, 05:23 AM
The words "solid", "liquid", and "gas" are descriptions of how large numbers of atoms behave as a group. If the group behaves one way, it's a solid; if the group behaves another way, it's a liquid; if the group behaves another way, it's a gas. Such words can't apply to individual particles because an individual particle can't do what groups of them do.

cjameshuff
2011-Nov-27, 05:55 AM
Stated another way, a bulk material can be solid, liquid, or gas, depending on the strength of the forces between the molecules of the material, the temperature (the amount of energy in random vibrations of those molecules), and the pressure (which packs the molecules in tighter than they otherwise would be and changes the relationship between the first two. They aren't terms that apply to individual atoms or subatomic particles. A particle is a particle, a tiny excitation of quantum fields, and isn't a solid, liquid, or gas.

Paul Beardsley
2011-Nov-27, 07:51 AM
Further to the two replies (which I thought were well put), consider an army, which is made up of soldiers, or a congregation, which is made up of worshippers. A single soldier is not an army; a single worshipper is not a congregation.

It is sometimes convenient, when teaching children, to describe atoms as like tiny billiard balls, or the insides of atoms as miniature solar systems. This is a useful fiction, because it gives people a working idea of what is going on, but it is a fiction. As Richard Feynman put it (heavily paraphrased), you begin with the solar system model of the inside of the atom, then you realise that it is actually more like a cloud, so you work with that idea for a while, then you realise that the cloud analogy isn't true either, and in fact the best analogy is... no analogy, because the inside of the atom does not resemble anything in our experience.

kevin1981
2011-Nov-27, 02:51 PM
Okay thanks. So the solid, liquid and gas states are when there are billions of Atoms together, which make up a material, got it.

I think i know why everything looks solid to us, it is because of the EM forces between Electrons, this is correct yes ?

I know an Electron is described as a one dimensional point particle, with no inner structure. But i am finding it hard to understand why it is not
solid, what is it ?

I am trying to visualize it too, maybe this is a hindrance ?

Noclevername
2011-Nov-27, 03:06 PM
Okay thanks. So the solid, liquid and gas states are when there are billions of Atoms together, which make up a material, got it.

I think i know why everything looks solid to us, it is because of the EM forces between Electrons, this is correct yes ?

I know an Electron is described as a one dimensional point particle, with no inner structure. But i am finding it hard to understand why it is not
solid, what is it ?

I am trying to visualize it too, maybe this is a hindrance ?

It's not a point but a cloud of probable locations. Not really something we can visualize; a lot of quantum physics is that way.

kevin1981
2011-Nov-27, 04:22 PM
It's not a point but a cloud of probable locations

Is that the same with all Atomic particles. I am just trying to understand how matter is not solid at a fundamental level.

AndreH
2011-Nov-27, 04:40 PM
Is that the same with all Atomic particles. I am just trying to understand how matter is not solid at a fundamental level.

I think it would be honest to say we do not know what particles really "are". Even though , as mentioned above it is helpful in some cases to visualize them as small har balls or as cloudes or other helpful analogies. These analogies, referred to as "models" help to understand the behaviour of the particles.
For example the "hard ball" model addinfg some forces between the balls helps to understand the behaviour of gases and there properties.But that does not mean atoms "are" really hard balls.
In fact there is a big part of the scientific community who will tell you we can never know what things really "are, we only can hope to find theories which describe the behaviour and make it possible to predict the outcome of interactions correctly. This is the point were the boundary between physics and phillosophy lies.

Feynman who was quaoted before also said: " I think I can safely say no one understands quantum mechanics"

kevin1981
2011-Nov-27, 05:33 PM
In fact there is a big part of the scientific community who will tell you we can never know what things really "are"

Observer dependance, the only way to really tell would be to look at the universe objectively, but we can not do that. I am learning,
maybe slowly, but i am learning !

Still, anybody else ? How is fundamental matter not actually solid ?

ravens_cry
2011-Nov-27, 06:25 PM
According to this (http://www.teachersdomain.org/resource/phy03.sci.phys.matter.atoms/) (watch the video, it's fascinating), the reason why matter doesn't clip through each other like a buggy video game is because the electrons of the atoms of one surface repel the electrons in the atoms of the other surface.
Either that, or someone forgot to turn idclip back on.:p

AndreH
2011-Nov-27, 06:28 PM
Observer dependance, the only way to really tell would be to look at the universe objectively, but we can not do that. I am learning,
maybe slowly, but i am learning !

Still, anybody else ? How is fundamental matter not actually solid ?

Ok, let's pretend for a moment we could know what a particle really "is". What we perceive as solid in normal live is the sum of all forces of one piece of bulk matter (e.g. a wall) when interacting with another piece of bulk matter (e.g. your forehead).
In the microscopic world we also only see the interaction of the forces which we attribute to the particles. So for an electron to "bounce off" from another electron it does not to be solid, it is enough that it interacts via the Coulomb force with the other particle.
As for the question how or by what this force is carried....we are back to the problem of "can we know it at all".

cjameshuff
2011-Nov-27, 06:44 PM
Still, anybody else ? How is fundamental matter not actually solid ?

Solid matter consists of materials where the component molecules are held in fixed positions relative to the neighboring atoms by intermolecular forces, thermal vibrations being insufficient to pull them loose and allow free movement. There isn't anything analogous with individual atoms or subatomic particles, they don't have anything like a solid phase (or a liquid or gas one).

kevin1981
2011-Nov-27, 09:30 PM
So an Electron is an individual piece of sub atomic matter that can be fired one at a time, but it is not solid. I find that unsatisfactory. (Only because if it is not solid, what is it?)

AndreH
2011-Nov-27, 10:13 PM
So an Electron is an individual piece of sub atomic matter that can be fired one at a time, but it is not solid. I find that unsatisfactory. (Only because if it is not solid, what is it?)
Bold mine
so we are back to "we do not know". And yes it is unsatisfactory to me, too. I just learned to live with it:(

kevin1981
2011-Nov-27, 10:24 PM
:confused:

cjameshuff
2011-Nov-27, 10:48 PM
So an Electron is an individual piece of sub atomic matter that can be fired one at a time, but it is not solid. I find that unsatisfactory. (Only because if it is not solid, what is it?)

A subatomic particle. That's what it is. "Solid", "liquid", and "gas" are characteristics of large collections of atoms, they are not applicable to individual atoms or subatomic particles. Particles don't have surfaces, yet don't flow like gases. You can't even pin them down to an exact location, and any definition of a specific size is an arbitrary choice for a given purpose, the best you can generally do is the scale of the internal structure, if any. They form interference patterns, they go into bound states with distinct energy levels instead of circling around in continuously variable orbits like planets. Some of them will go right through others, while other combinations interact strongly or annihilate to form more particles. Matter at that scale behaves quite differently, and it's a mistake to try to apply terms that only have meaning at more familiar scales.



Bold mine
so we are back to "we do not know". And yes it is unsatisfactory to me, too. I just learned to live with it:(

No, "we don't know" is not the answer. It implies that it could be solid, but that we don't know if it is. We do know, it's a particle. We lack common everyday experience with individual particles to give us a firm grasp on their nature, but that doesn't mean we don't know what they are like.

Shaula
2011-Nov-27, 11:17 PM
In poker you can have a wide range of hands. Flush, Straight, Full house being examples of this. Each behaves differently in the game.

Now I take one card from the pack. Is it a flush? A straight? A full house? It is none because those are behaviours/properties of five-card hands. The terms are just not applicable to a single card.

Now swap out the hands for states of matter and card for particle. Do you see what we are saying? Solid, liquid, gas are all ways of describing the way collections of particles behave. They are simply not applicable terms to an individual particle.

kevin1981
2011-Nov-27, 11:29 PM
Do you see what we are saying? Solid, liquid, gas are all ways of describing the way collections of particles behave. They are simply not applicable terms to an individual particle.

Yes, i understand that now and it is very helpful. But i still find it weird that particles are individual but are not solid. It seems there is
no straight forward answer to my question. (I know, quantum mechanics is weird!)

Delvo
2011-Nov-28, 12:45 AM
I think you need to find another word or phrase to describe what you're asking. If you've got it down that a single particle can't literally be an object that's defined as a group of them, then you're apparently expressing an analogy; there's something you expect the two different things to have in common, some way in which you expect them to be similar/comparable, even though they are different in other ways.

In what way would you expect a particle to be at all like a solid? Is it that you picture them as having shapes that don't change? Is it that, when you picture particles colliding, you think of them bouncing off instead of splashing and mixing? Is it that you picture the volume inside them as completely filled, with no gaps? What is it about the traits of solid objects that you expect to find in particles?

kevin1981
2011-Nov-28, 02:06 AM
What is it about the traits of solid objects that you expect to find in particles?

Actually, i think i have been thinking about it a little wrong. The particles themselves do not make up the solid world we see, it is the
electromagnetic forces between electrons. Is that correct?

Though coming back to individual particles, they are real physical entities. I see them as tiny points with no inner structure. If they are
real then they must have a size.

I just can not understand that if they are not solid then what state are they in :/

kevin1981
2011-Nov-28, 03:02 AM
Or is it, simply, they are quantum particles. They are not solid, but we do not know how to describe them
using modern language ?

Shaula
2011-Nov-28, 06:36 AM
We can describe them using modern language and describe them using maths - they are quantum particles. We can describe their properties in terms of probabilities and mathematics very well. What we cannot do is simply translate these properties to something easier to put into more colloquial English. Language just has too many traps and assumptions built in.

You are forgetting that particles are also waves. Something that behaves like a little billiard ball sometimes, like a water wave at other time and like a fuzzy cloud at other - it doesn't behave like any form of bulk matter (Bose Einstein Condensate maybe) we are familiar with.

The particles have the properties which generate the forces that interact to give us a feeling of 'solidity' when we bring two bulk collections of matter together (my hand and the table). You cannot point at one or the other and say "that is solid, that is what makes things solid". Sorry, it is a bit of a brain bender!

Bobunf
2011-Nov-28, 07:33 AM
Humans do not have the brains to visualize atomic and sub-atomic particles. This is not surprising since such an ability would not have contributed to fending off tigers, finding edible fruit or reproducing. Humans also can't visualize four dimensional objects for similar reasons. Humans are able to describe both in mathematical terms, and we find such descriptions extremely useful. Analogues like clouds, waves, particles or hairy balls are not as useful.

Thus, rather than describe a four dimensional hypersphere as a hairy ball, it's more useful to say that the formula for a four dimensional hypersphere is x1^2+x2^2+x3^2+x4^2=r^2. I have no idea what a hypersphere would look like; perhaps no humans do. But from the formula, I can you what it's shadow would look like, what the 3 dimensional volume of its surface would be {(2*pi^2)*r^3}, and lots of other useful stuff. Thinking of it as a hairy ball won't get me very far in answering any questions about it, and a hypersphere is certainly not a hairy ball.

Same thing with electrons. The mathematics can tell us how it will behave. Thinking of it as a cloud, wave, or particle won't.

Give up on the analogues and use the math. Humans just do not have the tools to intuit at an atomic or sub-atomic level.

It would be easier for a blind person who never had sight to intuit about colors. He has the tools for that task, just not the experience.

PraedSt
2011-Nov-28, 07:52 AM
Though coming back to individual particles, they are real physical entities. I see them as tiny points with no inner structure. If they are real then they must have a size.If you really want to confuse yourself, ask yourself what a string (http://en.wikipedia.org/wiki/String_%28physics%29) is. :)

Jens
2011-Nov-28, 08:14 AM
Actually, i think i have been thinking about it a little wrong. The particles themselves do not make up the solid world we see, it is the
electromagnetic forces between electrons. Is that correct?


In a way, yes, because although it's weird to think of this way, we can't really see electrons or protons or any of that stuff. We can only see photons. So our whole image of the world is just a pattern created by how photons strike our eyes.

Another thing, is that although this is not really a good analogy, you can think of the way an airplane's propeller appears to be a solid sphere whereas in reality the propeller blades themselves only occupy a small portion of the what we actually see.

Paul Beardsley
2011-Nov-28, 09:29 AM
Kevin, you've demonstrated how useful it is when someone asks a seemingly simple (but actually quite deep) question, clearly listens to the answers, asks follow-up questions, and so on. This is so refreshing after having sat through several recent threads where someone makes a wrong assertion and then ignores key questions and counter-evidence.

It's also made me rethink the nature of matter, which I found fascinating.

As regards language, I think the problem is that the word "solid" has many figurative meanings. My parents' marriage is as solid as ever; the prosecution have presented a solid case, and so on. Plus it's only natural to think of a proton as like a billiard but smaller, rather than the completely different thing that billiards are made from.

Shaula, I prefer your poker/card analogy to my army/soldier analogy.

AndreH
2011-Nov-28, 09:55 AM
snip.....


No, "we don't know" is not the answer. It implies that it could be solid, but that we don't know if it is. We do know, it's a particle. We lack common everyday experience with individual particles to give us a firm grasp on their nature, but that doesn't mean we don't know what they are like.

bold mine:
this is exactly what I mean by we "don't know". We have a formalism to describe their behaviour, to predict the outcome of experiments and also make use of the predicted properties (Laser would be an example).
If you define this as "knowing what they are" than you are right. My interpretation of the bolded sentence above is "we don't know".

BTW: We don't know does not necesarrily imply they could be "solid". If we know they are not "solid" in the way a wall is solid this is knowing what they not are.
But I said before TMO we crossing the line to phillosophy at this point. (Discussing the "real" nature of things).

Paul Beardsley
2011-Nov-28, 10:12 AM
I wouldn't use the phrase "we don't know" here. What else is there to know besides their behaviour?

Strange
2011-Nov-28, 11:56 AM
Actually, i think i have been thinking about it a little wrong. The particles themselves do not make up the solid world we see, it is the electromagnetic forces between electrons. Is that correct?

I think that is a good mental model for the "solidity" of objects in the every-day world. And, because it is about "the forces between them" it clearly doesn't apply to a single electron.


Though coming back to individual particles, they are real physical entities.

I'm sure there are some who would debate endlessly about the meaning and relevance of the terms "real", "physical" and "entities". Not me though...


If they are real then they must have a size.

Not necessarily. That may be true of macroscopic objects but, as already agreed, the solidity and size of an atom comes about from the forces and other quantum mechanical effects. For example, electrons have to maintain a certain distance from the nucleus (and this distance relates to the energy of the elctron). Also, only two electrons can occupy the same state (energy level). This means that where there are more than two electrons in an atom, they have to be "stacked up" at increasing distances from the nucleus (as Atomic Orbitals (http://en.wikipedia.org/wiki/Atomic_orbital)). This distribution of electrons is what gives the atom a certain size (which is still rather fuzzy). And then the interactions between atoms is what gives "stuff" its solidity (or liquidity, or gassity).

This all works equally well if you treat the electrons as zero-sized points, as it is the quantum rules and forces which determine their spacing and hence the space occupied by bulk materials.

You might want to google the scanning tunneling microscope, which allows us to "see" individual atoms by interacting with and measuring these forces.


I just can not understand that if they are not solid then what state are they in :/

They are what they are, is the only mental model that works for me. They are not "like" (not even analogous to) anything in our normal experience.

Each particle could be thought of as the collection of properties that define it, brought together in a single point (a consistent set of "deformations" of all the fields involved, perhaps). This relates to the playing card analogy earlier: in the same way that a playing card has properties of suit, color and number, a particle has properties like charge, spin, etc.

AndreH
2011-Nov-28, 01:30 PM
I wouldn't use the phrase "we don't know" here. What else is there to know besides their behaviour?

As I said before this crosses the limit to phillosophy (and also the limit of my ability to express things correctly in English). Just let me try to explain what I mean: "Behavior" is a property attributed to something. It is not the same as that something itself.
So for my personal view we do not know what they "really are". This implies I assume there is a underlying "real nature" of things. We may just not be able to get knowledge about them in principle. As I said we are entering into phillosophy, definitions of words etc. We should not go down that road I believe (or at least maybe not in this thread).
It is just that I personally have never accepted that knowing how something behaves is the same then knowing what it is. I hope I did not confuse kevin1981 too much, because I agree with you this was a positive example how a discussion should work.

Swift
2011-Nov-28, 02:00 PM
Though coming back to individual particles, they are real physical entities. I see them as tiny points with no inner structure. If they are real then they must have a size.

Electrons and their relatives can be described as point particles with no inner structure. But this would not be a good description of protons and neutrons. They do have a size (there have been measurements of them) and they are made of even smaller particles (quarks) so they do have a structure, though I don't think I would call them "solids".

By the way (completely off topic), but what the heck is your new avatar? :D

kevin1981
2011-Nov-28, 02:18 PM
Kevin, you've demonstrated how useful it is when someone asks a seemingly simple (but actually quite deep) question, clearly listens to the answers, asks follow-up questions, and so on. This is so refreshing after having sat through several recent threads where someone makes a wrong assertion and then ignores key questions and counter-evidence.

Thanks Paul and AndreH for your comments. I am here to learn and have an inquisitive nature. I like to know how things work, especially
in nature. There are obviously many people on this board who have a much better, deeper, understanding about these subjects than me.
So i take the answers i get seriously and trust there judgement.

I am not too sure where to go now as i do not want to keep repeating myself. It would seem to me that the question of, is fundamental
matter solid, is a tricky question.
The answer seems to be, no, it is not. The solid world we see is due to interaction of forces. We can not really think of them as very tiny
snooker balls because that is a misinterpretation. What ever they really are is outside of our every day common experience so trying to
make sense of them or visualize them is all ways going to come up short. It is rather unsatisfactory, but that is the way it is.

kevin1981
2011-Nov-28, 02:22 PM
By the way (completely off topic), but what the heck is your new avatar? :D

haha I was hoping for that sort of reaction ! It is a smiling pumpkin !

AndreH
2011-Nov-28, 02:39 PM
BTW: Here is maybe a helpful link to a Wikipedia page. It is concerning the so called "Copenhagen interpretation" of QM. As you see, physicists have been struggling with the philosphical implications of QM since the very beginning. As you may notice from my posts, I have never liked this interpretation but everything is pointing into the direction it is maybe all we will ever have.
http://en.wikipedia.org/wiki/Copenhagen_interpretation

Jeff Root
2011-Dec-07, 09:02 PM
I disagree that the quantum world is counterintuitive. What is
intuitive is what you are accustomed to. I've been hearing and
reading about quantum mechanics my entire life, and the rules
which describe quantum interactions seem natural to me. They
make sense to me-- as I interpret them. Some interpretations
of QM do not make sense or seem natural to me. I'd say that
those interpretations are either wrong or misleading.

In the thread which led to this one, I said that a fundamental
particle is its properties. Same as Strange said here in post 29.
An electron is the properties of an electron, which are centered
on a location which your intuition makes you want to think of as
the electron itself. That location is just a location, nothing more.

The assertion that an electron is a cloud of probabilities is an
interpretation which I think is not wrong, but very misleading.
If you understand it, it makes perfect intuitive sense. If you
misunderstand it-- which is almost unavoidable-- it is crazy.
Absurd. Ridiculous. Complete nonsense. Although learning
the math necessary to be able to work out quantum calculations
is beyond my ability, I understand the ideas sufficiently for them
to make sense to me, so I know it can make sense to you, too.

I reject the notion that we can't describe quantum behavior in a
way that makes sense, is meaningful, and is explanatory. I think
the idea that quantum behavior is beyond comprehension is a
consequence of it being so different from classical physics that
it seemed that way to people accustomed to classical physics,
and the idea hasn't yet died out. Most people have such a
superficial knowledge of QM that they have not developed an
intuitive feel for it. That is, they don't understand it yet, so they
generally misunderstand it, and the interpretation they have is
nonsensical. Nonsense often makes people lose interest. But
it also often makes people wonder, and ask good questions.

-- Jeff, in Minneapolis

Shaula
2011-Dec-07, 09:24 PM
Some interpretations of QM do not make sense or seem natural to me. I'd say that those interpretations are either wrong or misleading.
Wow. This is not meant in a nasty way but that is a hugely egotistical thing to say. "Any interpretation that doesn't seem natural to me is wrong". No. It may not be useful to you but to someone else it might be a perfectly valid interpretation that they can use and reason from. Sorry but that is true. You are not the arbiter of right and wrong when it comes to QM!

Jeff Root
2011-Dec-07, 10:32 PM
Shaula,

I'll repeat what I said to someone in a PM on November 17:
Don't assume that the mainstream disagrees with you or that
you disagree with the mainstream. It is more likely a difference
in perception or description than a difference in the physics.

Do you feel that intuitive understanding of advanced physics
ideas must necessarily always be wrong?

Don't assume that because that question is ironic, it isn't
serious. I ask it in earnest.

Do you disagree with the example I gave, that the assertion
that an electron is a cloud of probabilities is an interpretation
which is not wrong, but is very misleading?

-- Jeff, in Minneapolis

Jeff Root
2011-Dec-07, 11:07 PM
Shaula,

I just came across a good example of a misleading
interpretation in another thread in which you participated.
It is a good example because it is very simple. You agreed
with Cougar, Strange, and Grey that the term "halo" is
misleading as applied to the dark matter associated with
a galaxy. However, cjameshuff (whose comments I almost
always agree with strongly) opined that it sounds like the
perfect word for it to him. I agree with you that "halo" is
misleading. I would speculate that cjameshuff doesn't see
it as misleading because his image of what constitutes a
halo is different from mine and yours.

-- Jeff, in Minneapolis

Shaula
2011-Dec-08, 05:53 PM
My point was that you are not the yardstick of QM. You may not like or feel comfortable with an interpretation - but to make the bold statement you made about things not being right if you didn't like them is too much.

I genuinely think that most intuitive pictures are fine if they are used where they are applicable. A huge swathe of bad physics comes about because people take an analogy that is intuitive and then try to reason with it outside where it is applicable. Ten minutes of maths is enough to show they are wrong but because for many people mathematical explanations are less intuitive than pure word ones they will cling to the verbal explanation. So short version: Intuitive models of advanced physics always fail somewhere. But they are perfectly valid if they are applied correctly and within their own limitations.

AndreH
2011-Dec-08, 06:24 PM
......snip.... I said that a fundamental
particle is its properties. Same as Strange said here in post 29.
An electron is the properties of an electron, which are centered
on a location which your intuition makes you want to think of as
the electron itself. That location is just a location, nothing more.

We could argue a lot on that. I would insist that the properties cannot be the thing itself. But that that would not lead anywhere. To me it sounds as if you have found an explanation that you can live with. That is completely fine. But it does not mean for other'S it is the same.



....snip..... Although learning
the math necessary to be able to work out quantum calculations
is beyond my ability, I understand the ideas sufficiently for them
to make sense to me, so I know it can make sense to you, too.
I reject the notion that we can't describe quantum behavior in a
way that makes sense, is meaningful, and is explanatory. I think
the idea that quantum behavior is beyond comprehension is a
consequence of it being so different from classical physics that
it seemed that way to people accustomed to classical physics,
and the idea hasn't yet died out. Most people have such a
superficial knowledge of QM that they have not developed an
intuitive feel for it. That is, they don't understand it yet, so they
generally misunderstand it, and the interpretation they have is
nonsensical. Nonsense often makes people lose interest. But
it also often makes people wonder, and ask good questions.

As I mentioned the one or other time, it is a while since I got my degree, and today doing the math for therotical physics is completely beyond me. But at some point in my studies I could solve simple (one dimensional) wave functions. Calculate things as tunneling, partial reflection and other stuff (the Alonso Finn study book has some very good exercises). I could do operator equations to determin things like from which to which state an atom can go and so on.
I could explain what outcome the double slit experiment has and what happens if you know which way a photon (or electron goes) etc.
In other words: I could do the math, and new how to apply it in which situation on that level described above.
But I never found an intuitive way to understand what is going on. Being able to do the math or explain the outcome of an experiment never really satisfied me. At that point I subscribed to the "shut up and calculate" fraction and left the rest to the phillosophers.
Sad but true.

AndreH
2011-Dec-08, 06:29 PM
My point was that you are not the yardstick of QM. You may not like or feel comfortable with an interpretation - but to make the bold statement you made about things not being right if you didn't like them is too much.

I genuinely think that most intuitive pictures are fine if they are used where they are applicable. A huge swathe of bad physics comes about because people take an analogy that is intuitive and then try to reason with it outside where it is applicable. Ten minutes of maths is enough to show they are wrong but because for many people mathematical explanations are less intuitive than pure word ones they will cling to the verbal explanation. So short version: Intuitive models of advanced physics always fail somewhere. But they are perfectly valid if they are applied correctly and within their own limitations.

I totally agree with that statement. The electron "cloud" model e.g. helps at some point a lot to understand chemistry. It is the same with all models. Hard balls for atoms in a gas, depicting potentials as hills and valleys and the particles as small balls rolling around and so on.

Jeff Root
2011-Dec-09, 03:17 AM
My point was that you are not the yardstick of QM.
I think you mean that I'm not the person who decides what
QM says and does not say.

I can agree with that. But if I do, I will add that nobody holds
the job of deciding what QM says and does not say.

On the other hand, I can disagree. If I do, I will add that it
is everyone's job to decide what QM says and does not say.
Anyone posting anything about QM here on BAUT or
anywhere else necessarily does so. You are doing it when
you tell me that I can't or shouldn't do it.



You may not like or feel comfortable with an interpretation -
but to make the bold statement you made about things not
being right if you didn't like them is too much.
I didn't say such a thing, anyway. That is the second time
you misrepresented what I said. I'll grant that your version
isn't very different from what I actually said, but it is different.
What I actually said:



Some interpretations of QM do not make sense or seem
natural to me. I'd say that those interpretations are either
wrong or misleading.
Since I did not specify what interpretations I was referring
to, you have no way of assessing whether my assessments
of them are right or wrong.

The one example I gave was of something which I explicitly
said I think is not wrong, but is very misleading. So you have
no idea what I am talking about and no idea what you are
talking about when you object to my assessments of "some
interpretations of QM" being "wrong". You also have no idea
what my assessments are based on or how they are arrived
at, in contradiction to your repeated assertion that they are
based on my not liking them.



I genuinely think that most intuitive pictures are fine if they
are used where they are applicable.
And I do not think that. I think it is not a matter of an
interpretation being applicable or not being applicable.
I think it is a matter of the interpretation working or not
working.

In effect, I do not distinguish between a theory and a
correct interpretation of that theory. In my opinion they
are one and the same.

I want to reply to what you said next, but not today, and
not in this thread. So I'm skipping to ...



Intuitive models of advanced physics always fail somewhere.
1) Why?

2) What about physics which isn't "advanced"?

-- Jeff, in Minneapolis

Shaula
2011-Dec-09, 07:01 AM
I don't want to get into a fight on this but you said:

Some interpretations of QM do not make sense or seem natural to me. I'd say that those interpretations are either wrong or misleading.
From this statement the implication is that your criteria for assessment is the 'naturalness' or 'sense' in an interpretation. If that is not the case and all you are saying is that by pure coincidence the set of all misleading or wrong interpretations (as agreed by consensus in the mainstream) happens to be identical with the set of all interpretations you don't like then I retract my comments.


In effect, I do not distinguish between a theory and a correct interpretation of that theory. In my opinion they are one and the same.
OK, disagree totally there. A theory is a predictive framework constructed in a logical language to allow for internal self-consistency checks. An interpretation is a way of relating the modelled entities to common experience in order to allow our minds to better grasp and manipulate them. Which is why interpretations are not unique and theories can be shown to be unique or transformations of one simpler statement of the theory.

1) Because they use non-rigorous models of a system to try to make predictions about it. And to be fair theories also fail if used outside their remit. Interpretations just tend to cover bits of theories and so fail multiple times within the domain a theory works in.
2) I don't really know where you draw the line, but I'd say yes. As soon as you start dealing with things by assigning them mental models which are not fully representative of them then you have an interpretation that will fail. Gas molecules don't behave like billiard balls. The only difference with the physics of the macroscopic is that generally the entities we are modelling are actually very similar to the entities we use in our heads to interpret them. So a billiard ball does act like a billiard ball.

Jeff Root
2011-Dec-09, 06:31 PM
Some interpretations of QM do not make sense or seem
natural to me. I'd say that those interpretations are either
wrong or misleading.
From this statement the implication is that your criteria for
assessment is the 'naturalness' or 'sense' in an interpretation.
If that is not the case and all you are saying is that by pure
coincidence the set of all misleading or wrong interpretations
(as agreed by consensus in the mainstream) happens to be
identical with the set of all interpretations you don't like then
I retract my comments.
Not one extreme or the other, but somewhere between.

It is not a coincidence. What I don't like is an interpretation
which is wrong (or misleading). To the extent that I have a
good understanding of the physics, a good interpretation
(one which works) will make sense and seem natural to me,
and a bad interpretation will not. Obviously that does not
work when my understanding of the physics is wrong, and
detecting when my physics might be wrong is not an entirely
separate issue.

But when I do understand the physics correctly, then any
correct interpretation of it will naturally tend to make sense
and seem natural. If an interpretation does not make sense
and does not seem natural, then either I do not understand
the physics or the interpretation is either wrong or misleading.




In effect, I do not distinguish between a theory and a
correct interpretation of that theory. In my opinion they
are one and the same.
OK, disagree totally there. A theory is a predictive framework
constructed in a logical language to allow for internal self-
consistency checks. An interpretation is a way of relating the
modelled entities to common experience in order to allow our
minds to better grasp and manipulate them. Which is why
interpretations are not unique and theories can be shown to
be unique or transformations of one simpler statement of the
theory.
My assertion is essentially that if an interpretation says
something different from what the theory says, then it is not
a correct interpretation of the theory.





Intuitive models of advanced physics always fail somewhere.
1) Why?
1) Because they use non-rigorous models of a system to
try to make predictions about it.
I see no reason for a correct interpretation of a theory to
make predictions different from predictions made by the
theory. If predictions made by the interpretation do not
match those made by the theory, then the interpretation
is wrong.



And to be fair theories also fail if used outside their remit.
A correct interpretation would fail in the same ways that
the theory fails.



Interpretations just tend to cover bits of theories and so
fail multiple times within the domain a theory works in.
If an interpretation covers only part of a theory, then it
should accurately cover that part of the theory. It will
be a correct interpretation of that part of the theory and
should never be asserted to represent the whole theory.

For example, the interpretation of economic theory that
rarity of a commodity determines its value is correct as
far as it goes, but obviously is far from complete. Rarity
is only one factor in the determination of value. It would
be silly to think that rarity was the only factor.




2) What about physics which isn't "advanced"?
2) I don't really know where you draw the line, but I'd say
yes. As soon as you start dealing with things by assigning
them mental models which are not fully representative of
them then you have an interpretation that will fail. Gas
molecules don't behave like billiard balls. The only
difference with the physics of the macroscopic is that
generally the entities we are modelling are actually very
similar to the entities we use in our heads to interpret
them. So a billiard ball does act like a billiard ball.
A description of gas molecules which likens them to
billiard balls is an analogy, not an interpretation of a
theory. I agree that analogies always fail. A correct
interpretation of a theory should never fail except
where the theory itself fails.

-- Jeff, in Minneapolis

Shaula
2011-Dec-09, 06:45 PM
Well if your interpretation is something that follows the mathematical model exactly then fine, it will fail with the theory. I've just never seen anyone reasoning from an interpretation alone who got the same results as the models did. YMMV.