How do you visualise particles?

[james mccue]

I'm struggling to keen my mind open when visualising fundamental particles. I've only been reading about quantum/particle physics for 3-4 years so I'm very much a beginner.

(if I remember rightly) Heisenberg liked to describe things in maths and Feynman preferred visual models, I'm swinging toward the Feynman camp.

I've read a lot of literature that particles are not dimensionless points. Why can we not think of them as such?

Why can particles not be points of energy in space which (depending on the amount of energy in the point) cause space to fold around them? Then it's more logical to see how they give rise to fermions and bosons depending on the nature of the folding and interaction between the folds.

How do you visualise particles and their interactions?

 

[malawi_glenn]

What you mean by "visualising particles" ? Define it.

It depends on what "camp" you belong to. The answer is different depening if you are asking a high energy physicsists or a string theorist.

Feynman approach is just that his diagram-method makes it easier to structurize your calculations in a nice way.

You idea that they are points of energy in space etc, how can you measure why that is more logical than for instance string theory description of particles? There is a reason for why string theory has the structure it has, it tries to embrace all known physics and what we know that physical laws must obey. Your suggestion is just a "science fiction guessing" with fancy physical words.

Sorry, but arguing in the way that "why can't particles be made out of small tiny cheese balls" does not prove that they are cheese balls, just because no one can't disprove you. Science must make positive, testable, claims.

 

[james mccue]

thanks for the response, its very interesting.

I was not trying to make any scientific claims. While reading about particle physics I imagine models in my head and I want to reduce my misconceptions so I can understand things more fully. I am hoping to open a discussion to find out how the (clearly extremely learned) users of this forum think about physics.

sorry if it came across wrong :)

 

[malawi_glenn]

So how do define "visualise" particles?

You can also try to search for old threads, this is one of the most frequent quetions here ; "what is a particle?"

The most fundamental answer, as I almost alaways give - since it is very honest, is that a particle is a particle. Then particle has certain properties, which there exists coherent physical theories and models in order to describe them.

For a high energy physicsits, an elementary particle is just a point with no extension in space, no internal structure. But for a string theorist, a particle is something like a string attached to a brane which vibrates

The difference between certain "crackpot" theories and models, is that string theory is not an "intutive game of guessing", it is a serios attempt to give a unified picture of physics-> As you might know, there are some serious "flaws" in physics, one of them is the incompatibility of Quantum mechanics and gravity.

There was also quite recent an interesting thread about epistemology in physics, "do you sometimes have the feeling.. " or something like that was the name of it.

Since you are quite new here, take your time to search for old threads, and perhaps take a look in our tutorial session, where some nice links to teaching material can be found.

 

[jal]

Hi malawi_glenn!

The most fundamental answer, as I almost alaways give - since it is very honest, is that a particle is a particle. Then particle has certain properties, which there exists coherent physical theories and models in order to describe them.

For a high energy physicsits, an elementary particle is just a point with no extension in space, no internal structure. But for a string theorist, a particle is something like a string attached to a brane which vibrates

If I might add a comment ... Since a point has only position and location then it is not restricted by the Planck Scale (minimum length).

As a result, different models are required when considering a "particle" or a "point".

 

[atyy]

Why can particles not be points of energy in space which (depending on the amount of energy in the point) cause space to fold around them?

There is a concept of "energy bubble", but it is from high energy quantum physics. In that theory, a particle is a type of energy bubble with well defined "properties" and that is "on the mass shell". The concept of energy causing space to warp is from the classical theory of general relativity. The relationship between the two theories being currently researched.

Veltman, Facts and Mysteris in Elementary Particle Physics, World Scientific 2003. See chapter 6:
http://books.google.com/books?id=CNCHDIobj0IC&printsec=frontcover#PPA161,M1

 

[james mccue]

Thanks guys this helps a great deal.

When I say visualise I mean to imagine as a visual model. I'm just trying to get an idea of how you guys picture particles and interactions. Surely everyone doesn't think in maths?! :)

that is "on the mass shell". [/url]

What does that mean?

 

[||spoon||]

...(if I remember rightly) Heisenberg liked to describe things in maths and Feynman preferred visual models...

Think you mean Julian Schwinger, not Heisenberg.

-Spoon

 

[malawi_glenn]

Thanks guys this helps a great deal.

When I say visualise I mean to imagine as a visual model. I'm just trying to get an idea of how you guys picture particles and interactions. Surely everyone doesn't think in maths?! :)




What does that mean?

Well then we use feynman diagrams, if you are asking a high energy physicsist. Particles are lines in space and times and interaction between particles are described as "virtual particle" exchange. This tool was invented by Feynman, in order to help one to structurize the calculations -> at each point where lines meet (called vertex) certain things must be conserved and so on.

http://en.wikipedia.org/wiki/Feynman_diagram

Mathematical formalism is the only way we can describe particles (well everything that is governed and dominated by quantum mechanics) is by using the language of physics -> Math. Same thing for strings, they exists in 10spatial dimension, now how do you draw that on a sheet of paper? ;-)

"Off mass shell"

Is another way of saying that the particle does not obey the "rule":
$$E^2 = (pc)^2 +(mc^2)^2$$, i.e the general formula for $$E = mc^2$$.
They can do that during a small time interval, so that this uncertainty rule is not violated:
$$\Delta E \Delta t \sim \hbar/2$$.
Particles can thus violate the rule E^2 = p^2 + m^2, but only during a short time that $\Delta E \Delta t \sim \hbar/2$ is fullfilled.

 

[malawi_glenn]

Hi malawi_glenn!


If I might add a comment ... Since a point has only position and location then it is not restricted by the Planck Scale (minimum length).

As a result, different models are required when considering a "particle" or a "point".

Jal, there are many different interpretations on what the Planck length resembles.

 

[Naty1]

One of many issues is that "particles" sometimes appear as "particles" and sometimes appear as fields/waves... think of the double slit experience. Quantum field theory and the Schrodinger wave equation give two different perspectives from a field/wave viewpoint, quantum mechanics sees discrete particles,but bigger than Planck length, and string theory as, well, strings..maybe membranes.

So you get to pick, then haggle which is "best" !...until you realize it's rather imprecise in many respects "down there" no matter what ...maybe a result of quantum uncertainty and anamolies like wave particle duality, Heisenberg uncertainty over position/memontum as well as energy/time...I'm getting a headache thinking about all the confusion...

Lee Smolin says in THE FABRIC OF THE COSMOS: "The overarching lesson that has emerged from scientific inquiry over the last century is that human experience is often a misleading guide to the true natrue of reality."

"we know much, we understand little"

 

[malawi_glenn]

particles as in "tiny billiard balls". For a particle physicsists, a particle is a particle - it has the properties of a classical tiny billiard ball, and the properties of a wave such as light. Just as light both as wave and "billiard"-particle properties.

 

[Chaste]

I always thought they were ball-like or spherical shapes.. somehow that's what education has gotten that into us.

 

[malawi_glenn]

I always thought they were ball-like or spherical shapes.. somehow that's what education has gotten that into us.

That is due to pictures "showing" nuclear decays etc.

http://education.jlab.org/glossary/betadecay.gif

 

[smallphi]

The quantum particles are excited states of the quantum field so I imagine them as some kind of soliton ripples propagating on the surface of a lake (which visualizes the quantum field). The ripple is a parcel of specific energy and momentum.

 

[TimeDependent]

Seriously, nobody here has answered the question adequately. If you can't explain it to your grandmother, you don't understand it!

Without leaving the domain of conventional physics, we should consider the wave-particle duality, the Heisenberg uncertainty principle, and de Broglie wavelength concept.

A point-like particle, in reality, has a certain amount of room to move - within the Planck scale - as shown by Heisenberg. This means we don't actually have a point, but a radius.

Now, since there is such a thing as the de Broglie wavelength of any particle, insisting that every particle can be mapped as a thing of a specific wavelength and interacting as such under the correct type of observation, we can in fact model a fundamental particle as follows (now we're talking quarks, leptons, and gauge bosons, and everything else is built up from this in a complex way):

A particle should be seen as a "wavicle"; that is, we have a wave that is confined within a given radius. To model a reaction in one plane, we *could* treat it as a circle with a squiggle inside it, or it might be seen as a squiggly loop. Those aren't quite billiard balls, as they allow wave interactions *as well*. Either is good for the purpose of this question.

For first and second order interactions, we can even use this to try and predict scattering patterns and use mathematical perturbation to correct anomalies as we go.

Smallphi, that kind of talk is why we're not able to sell string theory to the rest of the physics world.

Those of you who referred to Feynman diagrams are certainly on the correct path, but the actual diagrams can be tailored to whatever particle description you're using.

If you want to learn something properly, TEACH it. You will have to answer questions you ought to know, clarify models, and argue against other ideas - and maybe you'll even have to admit sometimes, that you don't know.

 

[malawi_glenn]

What it the wave composed of "TimeDependent"? The wave is "what"? According to mainstream QM the wave is a wave of probability density.

A wave confined within a given radius, is that testable? Is that what current knowledge from a experimental point of view tells us?

It would be very kind of you, prove the theorem above: "A point like particle can move within the Planck scale".

The use of feyman diagram is a beautiful way to "illustrate" a reaction, so that it can be printed within a popular science book with the feeling that "this is what physicsists really are using", but physicsits are using the diagram in another sense - to structureize their calculations, which is contains the physics.


i) Why don't you understand something if you can't explain it to your grandmother? There is no such criterion in the mainstream philosophies of epistemology. The problem of understanding might lay within my grandmother, who don't have enough background knowledge to understand the things I am talking about. Then of course I can always, as popular science books do, start to describe things in a non-mathematical sense and compare with daily life observations.

But what if it is impossible to explain things which are described by mathematics and counter-intuitive in a non mathematichal and intuitive way? Classical and ordinary day life experience explanations on quantum physics will always fail to give the same description as the language of physics - math - will do.

By swiching language I immediately loose information. It's like going from CD to MP3...

ii) Having the idea that one KNOWS what a particle REALLY is, is like giving a statement that one have 100% correct description of god or anything else which is beyond of our ordinary day life experiences. What a particle "is" depends on who you ask, which then of course, needs to have a coherent use of his/her particle concept.

 

[TimeDependent]

Don't use quotation marks on a name, malawi glenn. You sound like you're getting rather too personal about the argument.

The wave, the 'squiggle' as i refer to it, is normally seen as a wave of probability density, indeed, but this is not fundamentally proven, depending on the interpretation of quantum mechanics used. It could, in fact, be a string, if one wished to consider it thus.

By within the Planck scale, i mean that dt*dE=h/2pi. This gives us a maximum radius for the probability density under measurement of any type.

By switching language, i *may* lose information if I'm not careful, but the point is to try and explain something -without losing the basic point- in simple language. The idea of teaching one's grandmother is based on a quote from Einstein anyway, and no doubt his grandmother *did not* have any physics background. This is actually the point - you have to explain it as simply as possible, but no more so.

Wave-particle duality is the commonly accepted (Standard Model) theory, and whilst modified under string theory is not outright rejected by it.

The interactions, however, often are not intuitive, but there are specific examples which one can mentally examine in a non-mathematical way.

At any rate, particles are not quite billiard balls.

 

[malawi_glenn]

I do it all the time, its a nice way to show that "TimeDependent" is your name.

Now "dt*dE=h/2pi" is not Heisenberg.. calling it Heisenberg uncertainty relation is a bit wrong.
https://www.physicsforums.com/showthread.php?t=230693&highlight=demystifier

Now do a full calculation to obtain the Planck scale, should be a trivial calculation.

Some things require advanced fancy math, that is my point. And just because he is Einstein, doesn't mean that we should take his word as standard. Physics have no prophets. Einstein beleived in locally hidden variables, "God Dont Play Dice", should we abandon the probibalistical description of nature just because that quotation? Einstein also lived in a world which is quite different then ours, we are dealing with quantum mechanics severel times each day - transistors etc. For Eistein, these things where quite new and spooky.

Thus describing a particle as a "wave confined within a radius" you leave the particle concept open to many different interpretations; "what is the wave?" - and how do you tell what interpretation which is plausible?

I can give you a quote from Bohr: "If you think you have understood quantum mechanics, you have not understood Quantum mechanics"

Now try to examine a QED interaction mentally, NO mathematics at all, I am waiting.

 

[||spoon||]

I don't think the OP was asking whether particles ARE waves or classical particles. I think the OP simply wished to know, when you think about particles whilst problem solving does it help at all to THINK of them as a wave or a classical particle or something else all together?

The OP was not after a scientific answer, simply a point of view.

I can give you a quote from Bohr: "If you think you have understood quantum mechanics, you have not understood Quantum mechanics"

Also i believe that was R. Feynman.

-Spoon

 

[malawi_glenn]

My teacher in nuclear physics said it was "Bohr",

Feynman said "It is safe to say that nobody understands quantum mechanics. "

 

[||spoon||]

I know Bohr DID say:

"Those who are not shocked when they first come across quantum theory cannot possibly have understood it."


But who said what and when is trivial, the main point of my post was that i think the OP only wanted an opinion on whether visulaisng particles in certain ways helps when solving problems, not the specifics about the science behind what a particle ACTUALLY is. Yet that seems to be the direction the thread is taking.

 

[malawi_glenn]

The thread took that direction since the OP also incooporated hiw "model" of particles as energy bubbles.

I think it was the post of "Naty1" (#11) which started to describe the particle-wave duality, a post which I added that what "Naty" meant with particles was classical particles, i.e tiny billiard balls. A particle in the particle-physics camp is something else then a tiny billiard balls. Then "Chaste" came and said that he had always thoght of particles as tiny billiard balls. Then "smallphi" said what "particles are" (in the model of quantum field theory - just one of different models)

Then finally, "TimeDependent" started to lecture all of us, since he has the absolute truth of what a particle is and that a person who can't explain things to his/her grandmother, he has not understood it. Quite high-stomached...

 

[TimeDependent]

Do you know, I agree with both those last five replies on most points? You may use quotation marks as you please, "malawi glenn", despite how it may look. Neither you nor anyone else had answered the question adequately to that point, and you've mistaken me greatly.

I offered a point of view on how one can visualise a particle. The conclusion that should be drawn is that you can view it as a wave, or as a nearly-infinitesimal point, depending on what's required. Feynman diagrams are good for dealing with reactions, but not enough information necessarily. You may actually be required to make a decision on what a particle is, based on further understanding, and guess what? We don't know. A plausible definition is based on a testable (usually confirmed) theory.

However, time-energy uncertainty actually *does* give us length scales. 3-space and time are *directly* interchangeable. I did not call *this* equation *the* Heisenberg uncertainty principle, but mentioned that it is based on that; I acknowledge and agree that there are various equations by which we interpret quantum mechanical uncertainty.

It is safe, indeed, to say that i do not understand well enough how, in real terms, operator functions and wavefunctions interreact, beyond their mathematical interpretations, in most circumstances. A *qualified* statement, due to the fact that, relativistically, one cannot intuitively determine, for example, lepton decay, without a frame of intertial reference to tell if it's a real or virtual process.

I did not call Einstein a prophet, nor would i dare to, despite his brilliance in describing special relativity with little more than pythagoras' theorem. I intend to bring to your attention that you must answer the question directly, because what had been said was either insufficient or unintelligible. You had a couple of days before i logged in on the debate.

You think i have a high stomach, "malawi glenn"? At least give me the dignity of attempting right-of-reply to apologise for being a little too strong. I started typing when there was only your *first* response. Don't whine about it. Nonetheless, i intentionally left some room for interpretation in my description as I'm well aware that *noone* has a 100% proof of anything, ever.

I'm sorry you took my response the wrong way, but i got no sense of how to visualise a particle from what you said previously. I therefore substituted my own.

 

[malawi_glenn]

You offering of what a particle is has aldready been presented in this thread.

Post #2 "It depends on what "camp" you belong to".

Since the OP said that the answers he had gotten so far was good, then I don't think you should judge for him by saying that all answers so far have been insuficent.

 

[james mccue]

Thanks for these responses guys, this kind of thing you generally can't read about in regular literature! It's helping me understand a great deal more.

If you can't explain it to your grandmother, you don't understand it!

I'm a big fan of this concept :) I teach physics across the 11-18 age range which requires simple explanations. My students would never learn anything if I tried to teach them atomic structure using quarks and gluons! They have to be given the basics first. Malawi has a good point in saying it's dumbing down from the actual reality, it is. But then once you've understood the basics you can take another look and develop your understanding.

That's what I joined this forum for, hoping that I can get some help to understand particle physics :) I do read a lot of literature, but this only helps so much. Special Unitary Groups, for instance, I can't find an explanation that doesn't have me confused with maths I don't understand! Will keep reading but may eventually have to ask you guys.

many thanks :)

 

[malawi_glenn]

Oh, here a good resource for you for learning particle physics from a particle physicsits point of view:

http://arxiv.org/abs/0810.3328

Me and my friend who is phd student in hadronphysics really love this text.

One can then discuss what "basics" of gluons and quarks is of course ;-) We was taught the bohr model of the atom in high school, because that was what we could graps then. And our teacher was really good at teaching, it made me want to study physics at university. But when going to university and finding out that the bohr model "is false" really chocked me. That is why one must stress that our simple models and analogies with our daily life experience can't provide the "truth" (where truth in this sense is contemprorary quantum physics).

Sure everybody can explain to their grandmother that an atom is a small ball in the middle with electrons orbiting around it like planets around the sun - but is it true?

Is it even true at the level at 1%

How do we judge what is a good analogy or not when we are going from on set of formalism to another? (this is a quite dense philsophical problem, which I have discussed a lot with my friends who study philosophy).

SU(n) IS math hehe... so don't be dissapointed ;-) But you can think of this as rotation in 3-space, but the rotations in particle physics is in abstract spaces such as colour space etc.

 

[jal]

How do I visualize particles?

Perfect Symmetry vs. broken symmetry (CPT)

1. First I realize that what we “see” is an interpretation of what is achieved by experiments
2. Experiments can only “see” a confined proton, neutron, size of approx. 10^15. The interpretations are the QED of the Standard model .
3. At a smaller scale, QCD, inside the proton, models are still being developed, and tested against the results of experiments. If a physical minimum length, (ie. Planck scale), is applied as a condition, then LQG, Lattice QCD etc. which all use a minimum length, would be a more accurate description and you can only get to a 4-Manifold, A3 lattice, a cube.
4. Experiments at high pressure and density have produced a liquid of quark gluon, which is not confined, which can be modeled as a perfect liquid and maybe as perfect symmetry.

For high school students, read my blog and see if there is anything there that you want to use.
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~~~ Since I am learning, I reserve the right to change my mind. ~~~~
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