Photon the smallest particle

  • #1
Hi can I ask a question please, is a photon the smallest particle known ? If it is then how do we know there isn't something smaller as the light would blind us from a smaller particle ?.
 

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  • #2
Orodruin
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In the Standard Model of particle physics, all elementary particles are point-like, i.e., without spatial extension.
 
  • #3
Orodruin
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Electron is the smallest particle in the universe if you are talking about size.
This is wrong. As I have already explained in this thread, all elementary particles are considered point-like in the Standard Model.
 
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  • #4
sophiecentaur
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This is wrong. As I have already explained in this thread, all elementary particles are considered point-like in the Standard Model.
Yes. The idea of 'extent' of a particle that can be considered as travelling at c is very questionable. In many ways, for instance, you could consider a photon as extending over all space until it actually interacts with some localised particle of structure. This is why Wave Theory is often a far batter way of studying EM radiation.

Avoid the 'little bullet' model of a photon!!
 
  • #5
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Avoid the 'little bullet' model of a photon!!
Avoid it for all particles. None of them behave like you would expect it from e. g. pool balls.
 
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  • #6
So the smallest particle is unknown then ?
 
  • #7
Orodruin
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The concept is not meaningful.
 
  • #8
sophiecentaur
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So the smallest particle is unknown then ?
If you want to play Top Trumps with fundamental particles then why not Google "Fundamental Particle Sizes"?
If you can think of smaller than Zero ??????
 
  • #9
How can you know if it's not observable ?
 
  • #10
davenn
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How can you know if it's not observable ?
the experiments and observations have been done with particle accelerators
have you heard of the LHC ? Large Hadron collider and other accelerators like it ?

try some googling as was suggested to you :smile:


Dave
 
  • #11
the experiments and observations have been done with particle accelerators
have you heard of the LHC ? Large Hadron collider and other accelerators like it ?

try some googling as was suggested to you :smile:


Dave
The CERN collider thingy majig in Switzerland yeah I've heard of this, don't know the exact workings of it though just the basics. They fire subatomic particles at eachother through tubes that are under the ground.

My questions simple what's the smallest particle ? Only answer I got was that all particles are at zero measurements ? Maybe we haven't invented a measurement small enough ?
 
  • #12
sophiecentaur
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The CERN collider thingy majig in Switzerland yeah I've heard of this, don't know the exact workings of it though just the basics. They fire subatomic particles at eachother through tubes that are under the ground.

My questions simple what's the smallest particle ? Only answer I got was that all particles are at zero measurements ? Maybe we haven't invented a measurement small enough ?
From your posts, I have to conclude that you just don't know enough about basic Physics to understand what is involved. It is 'Hard Stuff' and there is no shame in not knowing about things at this level. The present theory (which is what you are asking about) treats these particles as having no extent (zero size). Experimental evidence supports this. Your suggestion that we haven't invented a measurement small enough is outside the gamut of present knowledge but there is more to "no extent" than just not having small enough divisions on a ruler to measure them with. It is a meaningless concept.
Get into Google and you will see what we mean.
 
  • #13
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The OP is not listening. To repeat: the question is not meaningful unless "size" is defined differently than it being the distance between points. Often size is defined to be the energy possessed by the particle. Other definitions, such as its cross-section depend critically on which particle it is colliding with. Another definition is its range of influence, the distance in which it might interact with another particle. Before you say, "yeah, that's the one", you should know that all particles are waves, and waves have infinite extent. That is there is no cut-off beyond which a particle can't interact. OTOH, we can determine the probability that a particle interacts, and that (in simple cases) declines rapidly with distance. It's for this reason that drawings of electron orbitals/clouds around atoms and molecules are given a surface (a specific size), often chosen to be the surface inside of which for 90% of the time, the particle can be found in (or 75%, or any other arbitrary % - but if you set it much above 90% the shape gets enormous, impractical, and without much use - interpretation becomes quite difficult). On a very crude level, size is determined by either looking at something or by touching it (with some measuring device, perhaps). In the sub-microscopic world, light is just as "solid" as an electron or gluon, so all you can do to "determine" size is touch the particle with another.(a photon is a particle of light).Cross-section is a particle's "touching" size. Because our world is both quantum and relativistic, "size" as understood by the simple distance between points concept is meaningless. (But I've not explained why that is in this post). Note that 'touching size' depends on what you are touching it with. This definition means that a particle has many sizes, one for each particle that can 'touch' it. Note also that the distance between two points changes as the velocity of the observer changes. For the third time: size, as the OP means it, is not meaningful for sub-atomic particles.
 
  • #14
Surly there is a different way to interact with people than this prickly knee jerk reaction way, why would I be not listening ?? Maybe I am not understanding ?? This will be my last post on here as I clearly lack the knowledge to proceed in conversation about the subject.
 
  • #15
Wait I lied, I actually sent this post as a private message because I thought you very smart guys would think I was thick, ( clearly was right). The person I messaged wouldn't give me a answer just told me to write it in a post on here, last post I swear :) bye.
 
  • #16
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The CERN collider thingy majig in Switzerland yeah I've heard of this, don't know the exact workings of it though just the basics. They fire subatomic particles at eachother through tubes that are under the ground.

My questions simple what's the smallest particle ? Only answer I got was that all particles are at zero measurements ? Maybe we haven't invented a measurement small enough ?
I think it is important to note that you could be asking two very different questions:

1) According to current theories, what is the size of fundamental particles?

2) If we consider the experimental upper bounds, what is the smallest particle measured?

It seems like your question is 1), but it is possible that you meant 2).

According to theory, particles actually take up zero space. They have no physical size or volume. Every direct experiment tests to see if the particle takes up more or less space. For a silly example, if you have a net with one meter holes, a baseball will get through, but a net with one centimeter holes will not let a baseball through. Therefore, a baseball is less than a meter across and more than a centimeter across.

Every experiment has shown that fundamental particles are less than whatever size the experiment is checking. That along with theory leads physicists to conclude that particles do not take up any volume.

It is possible that someday an experiment will show that the electron has a radius greater than zero. If this happens, current theories have to change. So, the answer currently stands that fundamental particles take up no space.
 
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  • #17
sophiecentaur
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Maybe I am not understanding
This is true
My questions simple what's the smallest particle ? Only answer I got was that all particles are at zero measurements ? Maybe we haven't invented a measurement small enough ?
But you still seem to want there to be a simple enough answer but on your terms. There just isn't one.
The adverse reactions you have been getting are caused by your insisting that a simple answer exists, which is devaluing the whole of Physics.
 
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  • #18
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I'm wondering if the OP is thinking of photons in respect to two parallel plates excluding light vibrating normal to the plate surfaces with an peak to peak amplitude greater than the distance between the two plates; or even a fiber optic excluding all photons with an amplitude greater than the diameter of the fiber? That could be construed as saying a photon is too big to fit, or small enough to fit inside, even though we're not really talking about a solid object with physical dimensions.
 
  • #19
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One of your questions suggests you are really asking whether there is another layer down. The atom was once the "smallest" thing in models. Then the atom was modeled as built from "smaller" things. Physicists (for a while) settled on the "smaller" neutrons, electrons, and protons. Now they have (almost?) filled in the 17 even "smaller" things of the Standard model.

A Photon is one of the things in the standard model. If the question is whether physicists will someday decide there is a better model, and a photon is really two "smaller" things ... that can't be answered. I feel certain that in the future, we will know more than we know now. I do not know the things that we know that will be revised completely, and which things will remain in future models.

The answers have focused on the physical dimensions of the particles. And as stated, there is no "smallest" in the model. There also is not any "smallest" when measurements are made. And that is an incredibly compelling argument that there is no "smallest", with regard to physical dimensions.

Asking if physicists are just working with an incomplete set of facts currently ... I think everyone knows that, but it is not a productive question. What will we know when we know more? ... What if we learn one particle is smallest, which one will it be? ... you can't phrase that as a question that has an answer. The answer is what people are saying: "we know we don't know" any difference in the size of the fundamental particles.

So
is a photon the smallest particle known
has an answer of "no" with regards to physical size. Because we don't know the photon is the smallest. It is the same PHYSICAL SIZE as the others in theory, and in measurement.

It also has an answer of "no" with regards to the model of particles, because the current best model has 17 fundamental particles, which are the things that make up everything "larger".
 
  • #20
sophiecentaur
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I'm wondering if the OP is thinking of photons in respect to two parallel plates excluding light vibrating normal to the plate surfaces with an peak to peak amplitude greater than the distance between the two plates; or even a fiber optic excluding all photons with an amplitude greater than the diameter of the fiber? That could be construed as saying a photon is too big to fit, or small enough to fit inside, even though we're not really talking about a solid object with physical dimensions.
That is not a valid way to describe light. The Amplitude does not involve a Distance.
 
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  • #21
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Perhaps I could frame the question a bit differently. From my (naive) understanding, String Theory postulates that "elementary" particles are comprised of one-dimensional strings, vibrating in 11 (or more) dimensions. If that one dimension is spatial, strings are of the order of the Planck length, or 10^-35 m. Might that be considered the "size" of particles (at least according to the string model)?
 
  • #22
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Perhaps I could frame the question a bit differently. From my (naive) understanding, String Theory postulates that "elementary" particles are comprised of one-dimensional strings, vibrating in 11 (or more) dimensions. If that one dimension is spatial, strings are of the order of the Planck length, or 10^-35 m. Might that be considered the "size" of particles (at least according to the string model)?
MY even more naive understanding is that String Theory is generally purely theoretical and not yet at a point where it makes any sense. If someone can take the string theory starting point (and it seems little more than that right now) and come up with a meaningful theory that can unify gravity with the other forces, then it would be pretty nice.

I can't see using any string theory as a basis for size until it makes more sense as a descriptive model.
 
  • #23
russ_watters
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Wait I lied, I actually sent this post as a private message because I thought you very smart guys would think I was thick, ( clearly was right). The person I messaged wouldn't give me a answer just told me to write it in a post on here, last post I swear :) bye.
Though you may not be back to read this, I'd like to weigh in. I don't think people were being mean, but they were getting testy/impatient. People get testy/impatient when they feel like they aren't being listened to.

Sometimes you justo have to accept that you were barking up the wrong tree and accept the answers given instead of just repeating the same question over and over again as if you didn't see the answers.

Rather than just leave in a huff, we would prefer you try changing your approach and trying again.

The issue was not beyond you. It is simple: if we can detect zero size particles then particle size is not a limitation to what we can detect because you can't have something smaller than zero.
 
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  • #24
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String Theory is generally purely theoretical
I think that theoretical models are what we're talking about. The Standard Model says point (zero dimensional) particles. The string model says the Planck length. Experiments have not reached the level where either extent can be measured.
 
  • #25
Orodruin
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I think that theoretical models are what we're talking about. The Standard Model says point (zero dimensional) particles. The string model says the Planck length. Experiments have not reached the level where either extent can be measured.
The Standard Model has made a large number of testable predictions which have been verified. String theory has not. Even starting to compare their experimental status is doing the Standard Model an injustice. Please keep the thread on topic and B level.
 
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