What is Model: Definition and 1000 Discussions

A model is an informative representation of an object, person or system. The term originally denoted the plans of a building in late 16th-century English, and derived via French and Italian ultimately from Latin modulus, a measure.
Representational models can be broadly divided into the concrete (e.g. physical form) and the abstract (e.g. behavioural patterns, especially as expressed in mathematical form). Of particular importance in the modern context, conceptual models are central to philosophy of science, as almost every scientific theory effectively embeds some kind of model of the physical or human sphere.
In commerce, a model might instead reference a specific version or configuration of a product offering, rather than functioning as a representation of something else.
In taxonomic settings (e.g. biology, architecture, art) a model is sometimes a particular instance of a set of related entities (species, built structures, artistic compositions) chosen as a convenient reference point around which to build discourse; such a model is almost always chosen to typify some central tendency of the group, exemplify the group's defining characteristic, or reify the group's historical lineage.
Kinds of models include:

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  1. bland

    I Why isn't the Goldstone boson on the Standard Model map?

    They seem to have something to do with Z or W particles, maybe, and they have something to do with mediating weak iso spin, I think, and they may be related to the Higgs field. But they don't have a box dedicated to them on the Standard Model of particle physics. Can someone tell me why this is...
  2. I

    A Combining model uncertainties with analytical uncertainties

    This is my problem : it all starts with some very basic linear least-square to find a single parameter 'b' : Y = b X + e where X,Y are observations and 'e' is a mean-zero error term. I use it, i find 'b', done. But I need also to calculate uncertainties on 'b'. The so-called "model uncertainty"...
  3. agnimusayoti

    How to model a function of a box's volume using Lagrange multiplier methods

    I started to understand how to apply Lagrange multiplier methods. But, for problem like this, I have difficulty to build the function to describe the volume that will be maximized. For the second question, I know from the example (in ML Boas) that ##V=8xyz## becase (x,y,z) is in the 1st octant...
  4. P

    A Translating/encoding a continuous variable model into a qubit model

    I've read these two pages that discuss going from qubit to continuous variable - https://arxiv.org/abs/quant-ph/0008040 and https://arxiv.org/abs/1907.09832 . I'm curious if anyone knows some papers that discuss going the other way around? I.e. qubitizing a continuous variable model? Any insight...
  5. E

    3D model of an RBMK reactor refueling machine

    I made this 3D model of the RBMK-1000 nuclear reactor central hall about 3 years ago. But I did not model the fuel handling machine. Recently I decided to complete it by modeling the fuel handling machine.
  6. P

    A How to see if a cosmological model is flat?

    The RW metric reads $$ds^2 = -dt^2 + a^2(t) \Big( \frac{dr^2}{1-kr^2} + r^2 d\theta^2 + r^2 sin(\theta)^2 d\phi^2 \Big)$$ The value of k determines the model is flat/open/closed. But say if we have a model on a completely different form, with no explicit k-dependence. How would I determine if...
  7. MathematicalPhysicist

    How to derive Eq. (4.26) from Eq. (4.25) in Birger Bergersen's book (Maier-Saupe model)

    The dictators at physics.stackexchange want to close my post that I post here. I hope someone can help me with this question, I want to compute this by hand, without Computer algebra software, mainly because I don't know which syntax to use for Mathematica (if you know the syntax, can you give...
  8. M

    A Seeking the Standard Model in E8 plus Supersymmetry

    This is just a quick alert regarding a paper today https://arxiv.org/abs/2005.03048 Exceptional Unification of Families and Forces Alfredo Aranda, Francisco J. de Anda, Stephen F. King [Submitted on 6 May 2020] This work considers the remarkable suggestion that the three families of quarks and...
  9. F

    Bohr Model - Absorbing a Photon with Enough Energy to Ionize the Atom

    I just want to confirm something. You need about 13.6 eV of energy to ionize a hydrogen atom in the ground state. Can the atom absorb a photon with 15 eV of energy? I think it can. This would free the electron, and the freed electron would move off with a kinetic energy of 15 minus 13.6 eV...
  10. S

    Problem with PMSM motor model in Simulink

    Good afternoon, I have developed a Vector Control for a PMSM motor in Simulink using Simscape Electrical but my motor is not spinning. I have tried applying various speed values but nothing happens. I am applying a step signal from 0 to 300 but the motor speed still doesn't move. My error...
  11. J

    Entanglement on the Many Worlds model

    Entanglement's non-locality ('spooky action at a distance') depends on the instantaneous collapse at all points in space of the entangled particles' common wave function. The Many Worlds model has no wave function collapse. Does it also have no entanglement?
  12. Auto-Didact

    A The Wolfram Model & Wolfram Physics Project

    As seen in the video above, ten years ago Stephen Wolfram teased a computational physics program which he simply called 'Physics'; some of this work was outlined in his magnum opus "A New Kind of Science". A few days ago he has finally given a huge update of this in his blog...
  13. H

    I Right chiral vs left chiral electrons in the standard model

    Sometimes I hear particle physicists refer to left/right chiral electrons as different particles that are 'mixed' by the mass term. Maybe I misunderstood entirely, but if there is even a handwavy sense in which this is the case, clarifications would be appreciated. In high energy collisions...
  14. Saptarshi Sarkar

    I Query regarding Fermi Gas model

    I was reading an introductory text on nuclear models and came across the Fermi Gas model. I understand that the depth of the potential well of the proton should be less than the depth of the potential well of the neutron due to the Coulombic repulsion between the protons. But I did not...
  15. F

    Deriving the Adjoint / Tangent Linear Model for Nonlinear PDE

    I am trying to derive the adjoint / tangent linear model matrix for this partial differential equation, but cannot follow the book's steps as I do not know the math. This technique will be used to solve another homework question. Rather than posting the homework question, I would like to...
  16. G

    I Solving the Paradox: A Dynamical Model of Disease Spread

    I'm considering a dynamical model of the scenario of a disease spreading across the population, modelling the number of cases, and there's a mathematical puzzle which I'd like to solve. It's kinda different from the S-I-R model, and its also a crude model. First, we consider two numbers, NT...
  17. P

    Partition Function for Spin-1 One Dimensional Ising Model

    $$H=-J\sum_{i=1}^{N-1}\sigma_i\sigma_{i+1}$$ There is no external magnetic field, so the Hamiltonian is different than normal, and the spins $\sigma_i$ can be -1, 0, or 1. The boundary conditions are non-periodic (the chain just ends with the Nth spin) $$Z=e^{-\beta H}$$...
  18. Janus

    AT-AT Model V2.0: Improved Design and Detailing in Blender

    A bit over two years ago I began using Blender on a more regular basis for doing 3-D modeling. One of the first models I did was of an AT-AT from the Star Wars movies. This is the result: In the time since, I've honed my skills some, learned a bit more about Blender, and picked up a couple...
  19. M

    Problem with the friction model in an Abaqus simulation

    Hello, I have faced a weird problem and would really appreciate any comments. Assume a 2D model e.g. an axisymmetric model, meshed with quad, linear, and reduced integration elements. As you now if a model contains contact, we will get "CSHEAR1" and "CSHEAR2" in outputs. Assuming that the...
  20. G

    I Evaluating Accuracy of Dynamic Model for Spreading Disease

    I'm trying to dynamically model the scenario of a disease spreading across the population, modelling the number of cases, and I would love to hear your feedback. It's kinda different from the S-I-R model, and its also a crude model. First, we consider two numbers, NT and NA. NT is the total...
  21. E

    B Predator-prey model of a virus

    I was trying to put together a basic mathematical model for the Coronavirus and happened to stumble across the predator prey model; if ##x## is the number of humans and ##y## is the number of Covid-19 viruses, then $$\frac{dx}{dt} = ax-bxy$$ and $$\frac{dy}{dt} = cxy - dy$$ I took the reciprocal...
  22. Weran

    I Newtonian stable universe model

    I was discussing a problem related to Einstein's universe model. As we all know its an unstable equilibrium. So a small fluctuation in the density would result in an either expanding or contracting universe. However, I read that "There are static and stable solutions in Newtonian gravity...
  23. tomdodd4598

    I Form of the Standard Model: Higgs-Fermion Yukawa Coupling

    Hey there, I was looking at the Higgs sector of the standard model, particularly its coupling to the fermions: ##\mathscr{L}_{ yukawa }=-\sum _{ a,b=1 }^{ 3 }{ \left( { Y }_{ ab }^{ u }{ \bar { Q } }_{ a }{ \hat { \varepsilon } }_{ 2 }{ H }^{ \dagger }{ u }_{ b }+{ Y }_{ ab }^{ d }{ \bar { Q }...
  24. ZapperZ

    I Ptolemaic Model of the Solar System

    OK, this is more on history of astronomy than anything else. I hope someone has an insight on how they were thinking of things back then. The Ptolemaic model of the Solar system, i.e. the Geocentric model, placed Venus inside the sun's orbit around the earth. And to account for the retrograde...
  25. patrykh18

    Numerically simulating stellar pulsation using a "one zone" model

    The question is taken from An Introduction to Modern Astrophysics by Carroll and Ostlie. I did manage to do the entire question and plot the relevant graphs but I just want to to investigate a bit more. For example I want to look at how the graph would like in the case of the Sun. I don't know...
  26. Twigg

    Physical Intuitions for the k-epsilon Turbulence Model

    Hey all! I am trying to understand the terms in the source-side of the k-epsilon transport equations. My only reference on this so far has been the wikipedia article (in my defense, it's not in Landau! the gospel has forsaken me :cry:). If you have a reference that goes into gory detail on the...
  27. J

    Comp Sci Modeling the queues at a college restaurant

    So far, I have implemented the code below, using Java Priority Queues and Maps. I tried to identify each customer by the time they came in (ranging from 360 and onwards) and their grades. However, this is my first time using priority queues and maps, and I am not very sure if I'm doing things...
  28. PeterDonis

    A Exploring Rotating Lepton Model for Hadron Masses

    I just came across a 2016 paper [1] that claims to have computed reasonably accurate masses for hadrons using what it calls a "rotating lepton model" and "the relativistic Newton equation". An earlier 2001 paper by two of the same authors [2] appears to be the first introduction of the general...
  29. weningth

    A Deriving the Callan-Gross Relation via the Parton Model

    I want to derive the Callan-Gross relation from the parton model but I am having some problems obtaining the textbook result. I am following M.D. Schwartz: Quantum Field Theory and the Standard Model (pp.672, 675, 678). Starting from the hard scattering coefficient obtained from the partonic...
  30. SteadyStater

    I DDO 68: A Young Galaxy Supporting the Steady State Theory

    Young Galaxy Comes to the Rescue of an Old Theory The Steady State Theory of the universe has taken on a new lease of life with the discovery in 2014 of galaxy DDO 68, a dwarf galaxy 39 million light years away which, based on its structure, appearance and composition, appears to be relatively...
  31. J

    How Does the Ising Model Apply to Lattice Gas Systems?

    Hi everyone, even before addressing the following points I have a serious issue in understandig the text of the Exercise.My idea was to model this system with a lattice gas. Given that each site can host 2 atoms I have 3 possibilities for each site: I'll call'em ##S_{11} S_{00}## and ##...
  32. M

    Engineering Find the output resistance in a amplifier (MOSFET) small-signal model

    I have to solve a problem related with an 'invented' (non-real) MOSFET working in its saturation region (amplifier). I have solved all the questions, but I'm unable to get the last one. Basically, I need to determine the output resistance of the amplifier as a function of other given 4...
  33. K

    Exploring the Ray Model for Radio Waves: Does it Apply to Longer Wavelengths?

    I have never seen ray model of light being considered for radio waves, or waves of larger wavelengths. I have a feeling that this model does not apply to them. Am I right?
  34. Frigus

    B Quantum mechanical model of an atom

    We say that principal quantum number tells us the average distance from the nucleus, so the sub shells of some principal quantum number say 3 has 3 sub Shells 0,1,2 and in 3p sub shell their will probability of finding the electron near the nucleus which doesn't mean electron will find in region...
  35. P

    A Why is there no distance-measure in the standard model?

    The standard answer: “In GR, only average density matters.” That is what Friedmann’s equations (1) say—mathematically—but he does not derive that conclusion. He starts with it. Friedmann does not start with a messy, real-world model of the universe, one that has fractured into galaxy clusters...
  36. Adesh

    Putting a slab of some material just after the slits in Young's model

    If I put a slab of some material whose refractive index is \mu and width is D, in front of slits in Young's Double Slit model, then In the figure you can see that I have placed the slab just after the slits. So, when rays going to come out of the slab they will bend away from...
  37. T

    I Dispersive approximation (limit) in the Jaynes-Cummings Model

    I wanted to know what is understood as the dispersive approximation (or limit) in the context of the Jaynes-Cummings model for one mode of the field.
  38. E

    3D model I made of the Three Mile Island control room

    This took roughly two months to complete from start to finish. Link to imgur album so that the full-size photos can be viewed. Rendered in 4K.
  39. T

    Crane Arm Model using beam theory

    Can a Bernoulli or Timoshenko model be reasonable for a crane arm, on ships? Yes, the arm might have a truss element, yes there is a hydraulic force to lift the arm (or cables). But to some extent, can one model the crane arm as one of a simple beam (either Timoshenko or Bernoulli -- and...
  40. S

    A Standard Model and number of fundamental forces

    Just a curious question, is there a limit within the standard model on how many fundamental forces there can be? I have some familiarity with particle physics/QFT(not quite mastery obviously otherwise Id probably be able to answer this myself) and the thought popped in my head when reading about...
  41. E

    Here is an interactive 360 degree panoramic photo of a 3D model I made

    Here is an interactive 360 degree panoramic photo of a 3D computer model I made of the RBMK-1000 nuclear reactor central hall. The refueling crane is a work-in-progress. https://www.artstation.com/artwork/A9BAJm
  42. J

    Forward kinematics model using DH parameters in MATLAB

    5 links (thus 6 frames) and corresponding theta, alpha, d and a values are all given. However, I'm not sure how to start coding the DH parameters to derive a forward kinematics model. I know that I'll have to use matrix operators, but do I just put in the values of the 4 factors mentioned above...
  43. G

    A Debye Model Q&A: Interpreting Expression & Link to Einstein's

    Hi all, I have trouble understanding some ideas relating to the Debye model. In my text (Oxford Solid State Basics by Steven Simon, page 11), it was stated that Debye wrote the following expression ⟨E⟩=3∑→kℏω(→k) [nB(βℏω(→k))+12] What was not stated was the meaning of this expression. The only...
  44. L

    Engineering How do I model a Thorium Reactor thermal system?

    Hi, I'm working on a project for a thermal fluids design class in which a theoretical Thorium reactor is to be designed and modeled, and I'm a little bit at a loss for how to start analyzing the problem. I know the system will have 4 fluid systems: an enriched FLiBe system connected via HX to...
  45. T

    What is the Correct Way to Plot a 2D Ising Model Temperature Chart?

    Hi, I've been given a homework to do based on 2D Ising model. Ive already read plenty of articles bout 2d ising model but I'm not fairly certain about some things. I got to do a chart similar to the one I attached. Correct me if I am wrong, but on the Y axis, I have to put average of...
  46. lelouch_v1

    I Quark Model Families and Masses

    Consider the pseudoscalar and vector meson family, as well as the baryon J = 1/2 family and baryon J = 3/2 family. Within each multiplet, for each particle state write down its complete set of quantum numbers, its mass, and its quark state content. Furthermore, for each multiplet draw the (Y...
  47. L

    MATLAB Gaussian process and climate model in Matlab

    I'll admit I am very new to Gaussian processes, but from what I know a Gaussian process is completely determined by a mean vector E(Y(θ)) and a covariance function Cov[Y(θ1), Y(θ2)]. E(Y(θ)) is given, and we have the correlation, which is just the covariance divided by Var(θ1)*Var(θ2).The...
  48. Physyx

    How to model a rocket equation from the derivative of momentum?

    I am using the derivative of momentum (dp/dt) with Newton’s 3rd Law with the gravitational force of Earth. F - [Force of gravity on rocket] = dp/dt F - (G * m_e * m_r / r2 ) = v * dm/dt + ma F = Force created by fuel (at time t) G = Gravitational Constant m_e = Mass of Earth m_r = Mass of...
  49. E

    3D model I created of the largest steam locomotive ever built

    Here is a 3D model (blender 2.8) I created of the Chesapeake And Ohio Allegheny 1601 steam locomotive, which remains today the largest locomotive ever built.
  50. I

    The Nearly Free Electron Model

    This is a multi-part problem. I'm having trouble getting started. Any insights would be greatly appreciated. Prompt: To start off with, I think I'm finding the notation confusing. Specifically I'm not sure what U_200 refers to. Some thoughts: I know that both the potential, and the periodic...
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