What is Particles: Definition and 1000 Discussions

In the physical sciences, a particle (or corpuscule in older texts) is a small localized object to which can be ascribed several physical or chemical properties such as volume, density or mass. They vary greatly in size or quantity, from subatomic particles like the electron, to microscopic particles like atoms and molecules, to macroscopic particles like powders and other granular materials. Particles can also be used to create scientific models of even larger objects depending on their density, such as humans moving in a crowd or celestial bodies in motion.
The term 'particle' is rather general in meaning, and is refined as needed by various scientific fields. Anything that is composed of particles may be referred to as being particulate. However, the noun 'particulate' is most frequently used to refer to pollutants in the Earth's atmosphere, which are a suspension of unconnected particles, rather than a connected particle aggregation.

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  1. Luca_Mantani

    A How to determine if 2 particles come from the same process

    Hi, I am studying the Higgs discovery and I've got a doubt. One of the process used to discover Higgs is the decay H -> γγ in 2 photons. At LHC there are detectors of photons that can measure energy and momentum of them. So if you measure the energy and the momentum of both, you can calculate...
  2. M

    Deriving perfect fluid energy tensor from point particles

    Homework Statement For a system of discrete point particles the energy momentum takes the form T_{\mu \nu} = \sum_a \frac{p_\mu^{(a)}p_\nu^{(a)}}{p^{0(a)}} \delta^{(3)}(\vec{x}-\vec{x}^{(a)}), where the index a labels the different particles. Show that, for a dense collection of particles...
  3. zdroide

    I Is there a real need for a theory of everything (ToE)?

    I been studying quantum field theory and standard model lately. I not see how a unified theory could fit between quantum field and special or general relativity. One being for big objects and the other for microscopic one. In fact, standard model not seem to be all proven. Many particles are not...
  4. M

    Temperature & kinetic energy of particles in solid vs gas

    Consider the internal energy of a gas and solid (different materials) both at the same temperature, which material has the larger potential energy and why? Do they also both have the same kinetic energy? Finally is the definition of temperature as the average kinetic energy of the particles only...
  5. M

    Deriving perfect fluid energy tensor from point particles

    Homework Statement [ For a system of discrete point particles the energy momentum takes the form T_{\mu \nu} = \sum_a \frac{p_\mu^{(a)}p_\nu^{(a)}}{p^{0(a)}} \delta^{(3)}(\vec{x}-\vec{x}^{(a)}), where the index a labels the different particles. Show that, for a dense collection of particles...
  6. K

    Use a bubble chamber photo to find collision/decay particles

    Homework Statement Problem #13 on the attached picture (I can't retype a bubble diagram) Homework Equations I honestly have no clue. I know I'm not supposed to say this because I'm supposed to read my textbook first, but this is not covered at all in my textbook, this is a unit my teacher...
  7. dschwie

    Gravity and massless particles

    Just finished reading Sean Carroll's "The Higgs Boson and Beyond". I would be grateful if someone could explain how gravity, which I understand to be a function of mass, can interact with massless particles as evidenced by the phenomenon of gravitational lensing. I understand that gravity is a...
  8. Salvador

    Charged particles through various B field shapes quesion

    Hi, first of all I wan to ask a few simple questions , when we move a piece of wire perpendicular to a uniform magnetic field like between the faces of two magnets facing N-S we get a current either one or the other way in the wire , yet when we would shoot an electron beam the same path as the...
  9. ChrisVer

    Admissions Can Networking Help You Land a PhD in Experimental Astroparticle Physics?

    I wanted to ask something that should have been asked in the past... What are the chances to find a PhD in Astroparticle Physics [Experimental] if you have done something with LHC/ATLAS at your masters, mainly associated to data analysis and not hardware? Thanks.
  10. Arsen

    Fluid Dynamic. Force on particles in carrying fluid (liquid)

    Good day to all! I have a question : We have a flowing fluid ( liquid ) with known pressure, flow in the pipe ( pump is pumping it). There are some spherical microparticles in the liquid, let's say 10-15 microns. I want to create force to stop them moving! Will the pressure force be in the form...
  11. M

    Quantum Mechanics-Spin State for Identical Particles

    Consider a system of two identical spin-1 particles. Find the spin states for this system that are symmetric or antisymmetric with respect to exchange of the two particles. (Problem 13.3, QUANTUM MECHANICS, David H. McIntyre) I know that for bosons, the total wavefunction should be symmetric...
  12. P

    A Where are the Higgs particles?

    I've been reading Jim Baggott's book "Higgs -- The Invention and Discovery of the 'God Particle' "and have a rather elementary question, easily answered, I'm sure, by folk that contribute to this forum: is the Higgs only associated with the inner machinations of other 'elementary' particles, or...
  13. nomadreid

    I 2 particles created around event horizon: out or inside?

    The question is simple, and I have checked the "similar discussions" and googled, but I still come out with various replies. I also know that experimental evidence that could back up the selected choice would be tricky, not to say impossible. But at least according to theory: the entangled...
  14. A

    I The Higgs and virtual particles

    I have been reading the Quantum Diaries here http://www.quantumdiaries.org/2011/03/25/an-idiosyncratic-introduction-to-the-higgs/ and in discussing the Higgs and the LHC experiment he says "The general problem is this: at the LHC, we’re smashing protons into one another. The protons are each...
  15. F

    B Entangled Particles: Understanding the Interaction

    Pardon me for asking a very simple question, but this is something that I'm confused about. If we have a pair of entangled particles, and we measure the state of one of the particles, then the state of the other particle becomes fixed instantaneously. But what if we have three entangled...
  16. KarminValso1724

    B Can different types of particles be entangled with one another ?

    For example, can an electron and a photon become entangled?
  17. twistor

    A What would happen if only gravitons existed?

    This is a somewhat weird question, but here it goes: What would happen if there were only gravitons? Would some other kind of particle appear in the Universe sooner or later? Would there be any chance for mass to appear in such a Universe (assuming that the graviton is a massless particle)...
  18. B

    B Disentanglemt of a system of particles

    Is it possible for an entangled system of particles to be disentangled at a distance, without making them interact directly with each other?
  19. KarminValso1724

    B Could dark energy just be caused by virtual particles

    The tital pretty much explains it all? Why would this be impossible or not explain everything?
  20. B

    Heat Capacity of Distinguishable Particles

    Homework Statement A system of N distinguishable particles, each with two energy levels. The lower energy level has energy equal to zero, and the higher energy level has energy ##\epsilon##. The higher energy level is four fold degenerate. Calculate the heat capacity. Homework EquationsThe...
  21. newjerseyrunner

    B What causes recombination of virtual particles?

    In a situation like this: What causes the particle/antiparticle pair to recombine? They obviously will have opposite charge, is there a virtual photon being exchanged between them that's omitted from Feynman diagrams? That would imply that it's mathematically irrelevant, I know than these...
  22. B

    I Identical particles distinguished by their trajectory?

    Hello. It is said that if we exchange two electrons, we can't tell which is which. Identical mass, charge, etc. So if I hold two electrons, one in each hand, and someone switched them, I wouldn't be able to know. But one way to distinguish particles is their trajectory. If I have a very long 1D...
  23. P

    I Why is there a space between two particles of a dipole

    If you consider an electric dipole, why is it that there is any space between the two particles at all? If both particles of opposite sign attract to each other with equal magnitude, shouldn't they just stick together?
  24. KarminValso1724

    B If all particles were different sizes, would the speed of light stay the same

    For example, if photons were the size of galaxies, would they still move at the speed of light?
  25. K

    Charged particles moving through a magnetic field

    Homework Statement A collection of charged particles move through a magnetic field at an angle to the field lines. Calculate the velocity of the particle if it is an electron moving at 30 degrees to the magnetic field of strength 3.4mT, causing it to experience a force of 4.7x106-18N Homework...
  26. O

    A De Broglie Wavelength - Compound Particles, Particle Systems

    Can someone describe the physical processes which distinguish between separate and single particles when dealing with a collection of particles in the context of the De Broglie wavelength? The De Broglie wavelength is inversely proportional to the momentum of a "particle". Assume "separate"...
  27. S

    A few questions about charged particles

    I understand the basic forces moving charges experience in magnetic fields. I dont; however, understand how these these charges would interact with particles uninfluenced by the magnetic field. 1. If a charged particle is moving perpendicular to a uniform magnetic field, it will follow a...
  28. G

    B How do beta particles remove electrons?

    Hello all, I'm just learning about beta decay and the emission of beta particles. I have come to an understanding that this is ionising radiation because it has the ability to remove electrons and turn the molecules it interacts with into ions. I've looked on the Internet for this information...
  29. P

    Moment of inertia of a collinear system of particles

    Homework Statement Landau&Lifshitz Vol. Mechanics, p101 Q1 Find the moment of inertia of a collinear set of molecules Homework Equations I=sum m_i*(r_i^2) The Attempt at a Solution r_i= r_i'-r_cm where r_cm=sum m_i*r_i/sum m_i I=sum m_i r_i^2 I= 1/M sum m_i m_j (r_i' - r_cm)^2 I=1/M sum m_i...
  30. L

    B Uncovering the Truth: Non-Dualistic Particles Revealed

    Hello, could you please help me with this question? What particles do NOT have a dualistic character? Thank you for your answer.
  31. heartshapedbox

    Gravitational Force of Particles

    Homework Statement There are three particles; 1) 26kg at 12i-hat 2)13kg at -5j-hat 3)13 kg at 5j-hat A) What is the gravitational force on the 26kg mass due to the 13kg mass at -5j-hat Homework Equations F= GMm/r^2 The Attempt at a Solution A) IN COMPONENTS; Y Component...
  32. V

    What home based solvent might dissolve unknown molecular particles?

    What home based solvent might dissolve an unknown electron microscope seen insoluble particles ? There are some sort of unknown insoluble particles in our water. Does anyone know of any home remedy acid solution (baking soda and vinegar) that might dissolve these particles ? Please keep in...
  33. Allen_Wolf

    B Were all the particles or matter one?

    Were all the particles or matter a single particle in the beginning? If so were all forms of energy and and matter one single unit?
  34. R

    I Differential number of particles in Fermi gas model

    I'm practicing for the Physics GRE, and came across a question that has me stumped. "In elementary nuclear physics, we learn about the Fermi gas model of the nucleus. The Fermi energy for normal nuclear density (ρ0) is 38.4 MeV. Suppose that the nucleus is compressed, for example in a heavy ion...
  35. Ranku

    I Virtual Particles: Inflation vs Present Universe

    Are virtual particles of the false vacuum during inflation indistinguishable from virtual particles of the true vacuum of the present universe?
  36. D

    Thermodynamics Particles in Water

    Homework Statement A column of water contains fine metal particles of radius 20 nm, which are in thermal equilibrium at 25°C. If there are 1000 such particles per unit volume at a given height h0 in the water column, how many particles would be found in the same volume 1.0 mm higher than h0...
  37. A. Neumaier

    Insights Misconceptions about Virtual Particles - Comments

    A. Neumaier submitted a new PF Insights post Misconceptions about Virtual Particles Continue reading the Original PF Insights Post.
  38. D

    Thermodynamics study questions

    THIS WAS MOVED FROM ANOTHER FORUM, SO THERE IS NO TEMPLATE. HOWEVER, THE OP DID SHOW SOME EFFORT Hello, I have been having troubles beginning these two problems given for exam prep. Was wondering if anyone could give guidance on where to begin. Problem 1: A cylinder with adiabatically...
  39. C

    How many 0.3 micron particles in 0.1L volume of room air?

    Hello all, I wanted to say thanks to everyone on this forum who dedicate their personal time to enlighten so many like myself. I am a fan of physics and consider myself a student for life. I recently bought an Indoor Air Quality (IAQ) sensor/monitor to test my air purifier and as expected...
  40. E

    Simple harmonic motion of particles

    Homework Statement Two particles are executing simple harmonic motion of the same amplitude A and frequency ω along the x-axis. Their mean position is separated by distance X0 (X0 > A). If the maximum separation between them is (X0 + A), the phase difference between their motion is My answer...
  41. A. Neumaier

    Insights The Physics of Virtual Particles - Comments

    A. Neumaier submitted a new PF Insights post The Physics of Virtual Particles Continue reading the Original PF Insights Post.
  42. F

    B Quantum to Classical Particles: Understanding the Entropy Limit

    I have heard that identical distinguishable classical particles having different ''statistics''.It is the limit of quantum case.Then we mix many parts(cells) of identical gases, the total entropy increases.I can not derive this limit from quantum particles to classical particles(please help...
  43. amyy

    Massive particles are relativistic particles if their speed....

    Homework Statement Massive particles are relativistic when their kinetic energy is comparable to or greater than the energy corresponding to their rest mass. (This condition implies that their speed is close to the speed of light.) But what does the comparable mean? Is it that the particle...
  44. Q

    B Does retrocausality only apply to subatomic particles?

    It seems that historical events are the same every day. If the future affected the past wouldn't history books change everyday by themselves? Is it possible that history does actually change but we don't realize it because our memories change too?
  45. entropy1

    B Number of entangled particles in nature

    I understand that we can create entangled particles in the lab. But how many (non-locally) entangled particles (such as photons/polarisation or electrons/spin) exist in free nature?
  46. KarminValso1724

    B Does quantum mechanics explain why subatomic particles behave the way they do?

    For example, general relativity relates the behavior of gravity the the deformation of spadetime. But does quantum mechanics explain why particles behave the way they do? Or does it only explain how processes such as entanglement work not why they occur.
  47. T

    I Ratio of abundance of sub-atomic particles in the universe?

    I was wondering if there is a current hypothesis about the quantities of which matter particles were created? I'm not completely au fait with the standard model, but I've seen the picture...
  48. heartshapedbox

    Collision of Two Particles: Conservation of Momentum and Final Velocities

    Homework Statement A particle of mass 5.0kg travels initially with a velocity of 8.0mˆı and then interacts with a particle of mass 6.0kg which was initially at rest. After the interaction the 5.0kg mass travels at a speed of 4.0m/s along a direction which makes an angle of 53◦ with the x-axis...
  49. E

    I Energy of a number of particles

    Hello! It is sometimes useful to find the average energy of a certain number N of particles contained in a box of volume V. In order to find this quantity, the total energy is required and then divided by N. The result is E_{average} = \displaystyle \frac{1}{N} \sum_{n = 1}^{N} \left| a_n...
  50. S

    I Spin states for two identical 1/2 particles - Confused :s

    Im having trouble with my thought process for spin states of a system of two electrons Using Total Spin 'S' and Total spin mag quantum numbers 'MS' as state ket |S MS> My textbook states... " Three Symmetric Spin states Triplet spin stats for twin identical spin -1/2 particles | Up Up> = |S...
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