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What is an electron?

  1. Apr 18, 2005 #1
    Does it have a radius or not? If yes, then what is it? If no, then why does it (seemingly) not curve space-time to the point where it's discontinuous at the electron's center (an infinate potential)? If the answer isn't a yes or no, what is the probability distribution of radii as a function of radial distance? What is the substance that makes up the electron? Is it a group of matter waves bounded by one unit of charge? if it's made of three quarks, how does that work? what forces hold the quarks together, do they have charge or mass? How much empty space is in the electron, if any? If it's a point, is it infinately dense? if it's infinately dense, wouldn't it have infinate mass, and infinate gravity? How does the standard model make such a daft claim that the electron is a point?
  2. jcsd
  3. Apr 18, 2005 #2


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    Not in the classical sense, no. There is no concept of precise size in quantum mechanics.
    It doesn't have zero size, either. There is no concept of precise size in quantum mechanics.
    The electron is fundamental.
    I have no idea what this even means, so I guess the answer is no.
    An electron is not made of three quarks. An electron is fundamental.
    The strong force. They have both charge and mass.
    There is no concept of precise size in quantum mechanics.
    It generally doesn't. The electron is described by a wavefunction, which can be used to find a probability distribution for its detection or interaction.

    - Warren
  4. Apr 18, 2005 #3


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    Classical Radius of Electron

    Obviously, this isn't a direct measurement, nor is such a thing likely to be possible, but I'd guess this is about the best answer you're going to get that actually gives you a number. At least this will dispel your notion that the electron is thought of as a point particle.
  5. Apr 18, 2005 #4
    I find all this confusing as well.

    If there is no concept of precise size in QM then why do we think of electrons as being very small? Or does non-locality mean that we don't? If electrons are fundamental then would it correct to say that electrons are made out electrons? Did all the electrons in existence emerge fully formed from the initial singularity? This seems to be implied but seems to make no sense.
  6. Apr 18, 2005 #5
    thats interesting lose your name, I've never ran acroos anything like this before.

    Is there really no concept of size in qm? what about the Bohr radius? is that not a size, and won't it usually stay the same? Do you mean that particles have no size? or do you mean that we can't make a precise enough measurement of a particle's size? I understand that the uncertainty principle puts limitations on the things we can know about particles, but it doesn't make the idea of size invalid. Can't size be a sharp observable, while momentum and/or location are fuzzy? Actually that last question just doesn't make sense to me, I never thought the uncertainty principle applied to the size of a particle.
  7. Apr 18, 2005 #6


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    You can make statements like "there is a probability x that a particle will be detected inside some volume V," but that's about as close as you can get to the concept of size. Particles do not have distinct boundaries in quantum mechanics, because quantum mechanics represents particles with wavefunctions, and wavefunctions do not (generally) have sharp boundaries.
    The Bohr radius has units of length, but it cannot be interpreted physically as the actual size of anything.
    As I said, the concept of size is tricky in quantum mechanics. There is no "size" operator. The best you can do is to draw a map showing the probability of detecting the particle in each volume unit in space, and then declaring that the "size" of the particle is the volume in which there's a 90% of detecting it. But, therein lies the rub: should you consider the volume in which there's a 90% chance to detect it? Or a 99% chance? Or a 99.9% chance? There's no "definition" of size.
    We can't, but that's because particles just don't really have "sizes" in quantum mechanics. They don't have sharp edges.
    Location and size are intimately tied together. If location is a "fuzzy" variable, size must be, also.
    It doesn't, directly. The uncertainty principle results mathematically from the failure of two observables to commute. Since there is no observable for size, there's no uncertainty relation for it, either.

    - Warren
  8. Apr 18, 2005 #7


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    When you have many particles, as in a macroscopic object, there is a certain volume inside of which all these particles are extremely likely to be found. This is the everyday notion of size. For a single fundamental particle like an electron, the probability distribution is much more smeared out, and there are no sharply defined boundaries. Still, it is very localized, with a vanishingly small chance of finding it a few cm away, so we can still safely consider it small. Like many macroscopic concepts, there is no obvious microscopic correlate of size.
    Last edited: Apr 18, 2005
  9. Apr 19, 2005 #8
    ok, the size is indeterminate. What about the composition? what is it made of?
  10. Apr 19, 2005 #9
    if you say matter and charge, then is charge evenly distributed (or embeded) in the mass?
  11. Apr 19, 2005 #10
    what is meant by fundamental? it can't be cut in half? How can it not be cut in half, and at the same time, be the composition of two different things (mass and charge)? As far as I understand, something that is the composition of two things is not fundamental. Are matter waves not only composed of mass, but also charge? Is the matter wave not just the thing that causes the observation of mass, but also the observation of charge? Keep in mind, wave functions are all based on matter waves, those waves are what the wave functions describe, one such arrangement of matter waves (described by the wave functions) happens to be an electron... So I guess my main question is, in the invention of matter waves, were they given the property of both mass and charge, or just mass?
  12. Apr 19, 2005 #11
    A wise man once said, re: quantum mechanics:

    "Do not keep saying to yourself, if you can possibly avoid it, 'But how can it be like that?' because you will get 'down the drain' into a blind alley from which nobody has yet escaped. Nobody knows how it can be like that."

    Sounds like you're headed down that alley.
  13. Apr 19, 2005 #12


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    An apple is both red and round. Can you cut an apple into two pieces, one red and one round?

    - Warren
  14. Apr 20, 2005 #13
    Hmm. I see what you mean but apples are not usually considered fundamental. To say that something is fundamental means, to me, that it cannot have parts. A thing that has no parts cannot have extension according to Leibnitz. If electrons are fundamental and Leibnitz was right then perhaps it's to be expected that their extension is indeterminate.

    Infidel - I've seen that quote before but can't remember who said it. Can you remember where it comes from?

    One very naive question. If an electron has a 50% chance of occupying a particluar volume of space does this mean that 50% of its mass and charge is somewhere else? Or does it have no mass and charge when it's not in that position? Or is this not a sensible question?
  15. Apr 20, 2005 #14
    thats a great question... I think. But then again, I'm headed down an alley of some sort, so don't take my support seriously.

    back to my question that hasen't been answered yet:

    So I guess my main question is, in the invention of matter waves, were they given the property of both mass and charge, or just mass?
  16. Apr 20, 2005 #15
    I understand what you mean Chroot. Suppose I built a couple of identical miniature houses out of legos, in that case, the smallest and most fundamental unit of "lego house" is one of the entire houses and nothing less, but that shouldn't stop our understanding of what the little houses are made from. We most definately shouldn't make a rash statement like "lego houses are indivisible," does that mean that "lego houses" existed during the big bang?

    Here's a wierd concept: what if at the center of every particle, there is an extremely large and possibly infinate potential (because it's a point, and doesn't have a surface to touch, so if two electrons get close enough, they can push each other away with the force of a supernova for example, because the coulomb force is inversly proportional to the square of the distance between two point charges). And this potential is a multiply connected space with the big bang. All black holes are multiply connected to the big bang... all particles too. All particles are like tiny windows to the big bang, but the size of the windows are proportional to the energy of the particle (it's momentum). Somehow these tiny windows can coellece into a black hole, which is a much bigger window. Perhaps a black hole is like a huge Bose_Einstienien condensate and behaves just like a particle, but on a maco scale... So all particles are visible because light quanta are too big to fall into their tiny singularities, so the photons are able to bounce off, but not from a black hole, because it's singularity is much bigger. So if all matter is actually just multiply connected spaces to the big bang, then matter itself is imaginary (just in our heads) and the only thing that exists is space, all tied in knots and flowing through and within itself like a giant mobius strip. That would mean that the big bang is continuously occurring, and we only percieved it as an instant because our observable universe that we are familier with today has been moving along with us the whole time (it along with us, has we passed through the point of big bang) so it looks like it was an event that occured once in the past.
  17. Apr 20, 2005 #16


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    I simply mean that mass and charge are not "parts" of the electron, they are characteristics. That an object has more than one characteristic does not make it composite, at least not in the physical sense.
    This doesn't make the slightest bit of sense to me (you are perhaps misusing terms like 'multiply connected" and "potential"), and frankly this sort of speculation is not permitted on this site.

    - Warren
  18. Apr 20, 2005 #17
    Not just photons can move through the multiply connected space at the center of a black hole, but also matter, as long as the singularity radius is larger than the average radius of any particle. The influx of energy being pulled by central forces towards the singularity must be equal to or greater than the uniform energy-density in the big bang. In other words, the "pressure" (or energy-density) at the edge of the radius (event horizon) of any particle can't be less than the energy-density of the big bang or else the pressure of the big bang would push it's way through every particle, and all particles would behave the opposite way (negative would be positive). Pressure is related to the area of the singularity (average radius), because it's in units of force per unit area. So if a small enough area (approaching a point in size) is defined as the area of the singularity (or, area of the open window to the big bang), then any ammount of energy distributed on this area can equal or exceed the pressure in the big bang.
  19. Apr 20, 2005 #18
    Speculation is the reason for epistomology.

    I may not arrange words in the way you like, but I just want to communicate this idea to other people. If it only makes sense to me, is it because I'm the only one willing to entertain this thought? I guess I'm special.

    How can I better explain this idea... I've already explained that when two particles get close enough to each other, thier electric field energy-density can seemingly have no limit if they have no radii. right?

    So, using general relativity, (which states that the curvature of space-time is dependant on the ammount of energy present per unit volume) then if there exists an infinate energy-density, space-time will be discontinuous (it will be curved so much that it's in a state that we define as a "singularity").

    note: particles must have radii, at least a probability distribution of possible radii, and the average radius must be small enough to produce black hole like effects (an infinate potential energy isn't needed, but a very large one is needed).

    (keep in mind, I haven't taken any classes on cosmology or general relativity, so I'm not sure if I'm using these words the way cannonical physicists use them (all I know is that somehow a black hole produces a singularity without using an infinate ammount of energy), please do me a favor and see these words the way I'm using them and not the way they are exactly defined)

    Here's the big jump I make, and is why this is a wierd concept: I define this "singularity" as being "multiply connected" to the "singularity" at the big bang. I'm viewing the big bang as kind of a "reverse black hole" (or, a black hole that is viewed backward in time), so in that sense, it does have a "singularity" from which there is an outflux of energy, and at the center, there exists a constant energy-density. This energy density must be equal to or less than the maximum energy-density in the center of every known particle and "macro particle" (if we want to define all particles as multiply connected to the big bang). Viewing things this way, we know that every particle has a total potential energy (from it's mass, charge, momentum, spin, distance from a central force, etc.), so their radius must then correspond to an area that allows that specific particle's energy to be distributed (over the area in a cross-section of in a mannor that equals or excedes the pressure in the big bang. perhaps photons are the only particles that have the property where the two pressures are equal, and somehow because of this they don't have mass.
  20. Apr 20, 2005 #19


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    Particle probability distributions do not have a well-defined radius. Where do you strike a radius in a bell curve?
  21. Apr 20, 2005 #20
    well, the best I can do to bridge the gap you see is say that it's not a point and it doesn't have a radius. It's somewhere in between a point and sphere. due to the wave-particle duality of nature, so I simply regard this distribution as the overall radius.
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