Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: PRisoNR on 04/08/2012 04:10:35
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I can't find agreement on the the size (volume) of an elementary particle. Some argue any measurement is only the size of the area around the particle, but that the particle itself is figuratively non-physical being zero volume. So when they say an atom or such is 99.999999% empty space, wouldn't it really be 100%
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Quantum theory tells us that all particles also act like waves. It is possible to measure the wavelength of a wave, but the wavelength depends on the energy of the particle.
To see very small things, we use an electron microscope. To see finer details, we increase the voltage of the electron gun, which increases the energy of the electrons, and reduces their wavelength. This changes the "size" and "volume" of the electron.
Waves do spread out (like ripples from a pebble dropped in a pond), and so there is no hard "edge" to an elementary particle - there is just a region where there is a vanishingly small probability of finding the particle.
Particle physicists who collide particles with each other can calculate an effective area for the particles, by knowing the physical area of the beam, the number of particles in the beam, and the probability that particles will collide or pass on by without "shattering". But this size depends on the energy of the particle accelerator.
The size of a Uranium nucleus is approximately 1 "barn": http://en.wikipedia.org/wiki/Barn_%28unit%29
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To confuse matters - all elementary particles can be considered point particles - that is to say they are treated mathematically as having no extension in any dimension. That is not to say they are localised to a point - the Heisenburg uncertainty means that even a non-dimensional point particle fills a volume!
If an elementary particle was found not to be a point particle the search would immediately start for the sub-structure and sub-particle - ie it would stop being elementary
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The concept of solidness, when thinking about particles is generally missunderstood. The vacuum of space is filled with energy, the so-called fabric. The shape and degree of freedom this energy takes form the familiar particles we all understand as fundamental. One example which most everyone can mentally visualize is the structure we see in weather systems. The tornado for example, is created thru the circular motion and force of moving air currents. Likewise, fundamental particles are really only somewhat localized energy currents within the fabric of space/time. Truly, there is nothing really solid about particles. Their presence is only an attribute of the geometry energy takes to maintain a shape and particular volume dictated by all the surrounding energetic influences.
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Even if elementary particles are considered to have zero size, when they form part of an atom, they sit in defined (quantised) energy levels.
The Pauli Exclusion Principle prevents two electrons from having exactly the same orbits in an atom. This means that as you move from smaller atoms like hydrogen to heavier atoms like uranium, the extra electrons must go into higher energy levels, which tend to be further from the nucleus.
This means that the uranium atom takes up more space than a hydrogen atom, even though the components of each atom could be considered to have zero volume (from a certain point of view).
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Even if elementary particles are considered to have zero size, when they form part of an atom, they sit in defined (quantised) energy levels.
Consider the fact that all particles of matter are constructed entirely of energy. But determining the "size" of energy makes absolutely no sense unless it has formed a shape in the fabric of space/time. To say "particles have zero size" is very misleading. The energy that particles are made of has "zero size" but particles do have volume. And because this volume will vary according to the energy state we find the particle in, it's size/volume is questionable and therefore strictly indefinite.
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To confuse matters - all elementary particles can be considered point particles - that is to say they are treated mathematically as having no extension in any dimension. That is not to say they are localised to a point - the Heisenburg uncertainty means that even a non-dimensional point particle fills a volume!
I'm going to nitpick a bit... The uncertainty principle just says that if we know the momentum of a particle with any accuracy, it must fill a volume. But if we don't have a clue about the momentum of a particle, it could take up zero volume. In other words a particle could exist at a perfect point of zero volume for an instant--we'd just have no clue which direction it went after that measurement.
Theoretically it is possible for a particle to really take up no volume. In reality, we'll never measure this because it would take a perfect detector to do so.
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Theoretically it is possible for a particle to really take up no volume.
This reality has it's foundation in the fact that particles can also exit in wave form. Personally, I've never liked the notion of the "particle" perse. I realize I may get a little static because of that remark. Nevertheless, all "particles" are nothing more than (Localized orbital energy flux)....E=mc^2
Let's have a little thougt experiment:
With weather systems, water saturated air represents itself in many different ways according to the temperture differential associated with varing air masses. Granted, it's not that simple when we consider the "particle". But it is however a similar situation. "Particles" don't exist without the energy they are composed of. That is to say; If we remove the energy associated with the "particle", are we left with some obscure point in space we could claim as fundamental? IMHO the answer would be a resounding NO!
There are no such things as points in space/time devoid of energy we could claim to be "particles" However, energy has the ability and propensity to become localized in various orbital fashions resulting in the so-called "particles" we deem as fundamental.
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Loose-nukes - let's keep this mainstream -Cheers.
JP - damn hadn't thought of that! How about this - a completely unknown momentum does not preclude speeds and energies that would lead to decay and/or other particle formation; thus we must have an idea of the momentum....
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Loose-nukes - let's keep this mainstream -Cheers.
I understand my friend.
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@loose_nukes: Particles are not "purely" energy, and you cannot freely convert matter into energy and then into some other form of matter.
As well as the momentum, particles have other properties like electric charge, matter/antimatter & spin. These are conserved by most nuclear interactions (although some interactions involving the weak nuclear force can violate them, see http://en.wikipedia.org/wiki/CP_violation).