Models Definition and 369 Threads

Several years ago, I posted about this paper, which claimed to be able to eliminate the need for dark energy by performing cosmological simulations differently, basically intercnaging the order of calculating the expansion rate and the average density. One quote from that paper is, "The...

String theory, being such a theoretically successful theory as it is but with no experiment to single it out as THE model among alternatives, Im left to wonder, which models can be excluded? Are there essential no-go theorems regarding the physics of a theory for QG? Im aware of the...

I know that ##\dot e_{gen} = \frac {R_{e}i^2} {\pi r^2 L}## the thing is I don't know the value of i. I didn't write it, but another thing that the problem asks is to determine the flow of electric current. The model I came up with using heat generation due to electrical current is $$ \frac...

I found this interesting discussion here in Physics Forums (https://www.physicsforums.com/threads/are-all-symmetries-in-physics-just-approximations.1005038/) where the topic of all symmetries being approximate is discussed Is there any model (for instance, some type of spacetime metric or...

Why do almost all people not think that neural networks are the mathematical model of intelligence? I briefly explain what I understand: -A neuron is a mathematical object that takes numerical inputs from other nearby neurons, applies a nonlinear function (combining the input with numbers...

I am reading Goldrei's book: "Propositional and Predicate Calculus: A Model of Argument", Chapter 4: Predicates and Models. I need help in understanding Goldrei's answer to Exercise 4.5 (a) ... Exercise 4.5 together with Goldrei's solution reads as follows: Can someone please explain exactly...

Hello, Models can be linear and nonlinear and I just learned that a "linear model" is not just a model where the dependent variable ##Y## is connected to independent variables ##X## raised to the 1st power... The model is called "linear" because the coefficients/parameters are not raised to...

I was reading a paper by J.M.C Montanus which was published in <low quality journal reference removed> in which he claims under AEST the new gravitational dynamics and electrodynamics are reformulated in close correspondence with classical physics, and subsequently leads to the correct...

This graph shows ##H## as a function of time related to the L-CDM model. Do we (@Jorrie) have similar graphs e.g. for ##\Lambda=0##; ##k=-1## critical, ##\Lambda=0##; ##k=0## open, ##\Lambda=0##; ##k=+1## closed? That would be great, thanks in advance.

https://www.quantamagazine.org/physics-experiments-spell-doom-for-quantum-collapse-theory-20221020/ Experiments Spell Doom for Decades-Old Explanation of Quantum Weirdness Physical-collapse theories have long offered a natural solution to the central mystery of the quantum world. But a series of...

I am not cooking up a torture device or a weapon. In fact, I have been spending time with skeletal models. I just want to be able to create the ability to perceive pain. Even if I were to try to work this out myself and get some kind of answer that relates to physics, how would I know for sure...

I thought this paper might be of interest to those who are interested in how large language models such as GPT-3 pose various hazards. From the abstract: It is quite long but particularly attractive because it gives advice on how to read it for those who can only afford a minute or 10...

Hi! so its me again. After previous problem already solved now i ran into another problem. now about BURN card. its said need model? what kind of model? I tried using .84c for all my material but doesn't seems to work! heres my code if anyone wants to try :-( c TWR-P...

Let ##(M_i)_{i\in I}## be a multiverse of models of ZFC. By that I mean: Each ##M_i## is a well-founded model of ZFC. ##(I,\leq_I)## is a partially ordered set, and whenever ##i\leq_I j##, there is an embedding ##\tau^j_i:M_i\rightarrow M_j## such that the image of ##M_i## is a transitive...

This is for my graduate EM Theory class. My background is physics/optics, so I was able to understand when we solved maxwells eqs. for waves propagating between parallel conducting plates, but that lead into the lumped element circuit model of transmission lines which I don't understand. I've...

Hello there, If we have M/M/C/K = M/M/2/2 (where note that the first M stands for memoryless arrival times for the packets (thus described by a Poisson process(lambda)), the second M stands for memoryless service times (i.e. described by an exponentially distributed(mu)), the number 2 for C...

I attached a Jpeg with my attempted solution but I´m not sure if I´m on the right way... I hope for a correction in my calculations

As of today, there are plenty of time machine mathematical models based on general relativity theory (warp drives, wormholes), but few ones based on quantum physics. However, back in 2010, Seth Lloyd wrote: "quantum mechanics supports a variety of counter-intuitive phenomena which might allow...

Angel and Kareem had some stickers. Angel had 5 times as many stickers as Kareem. After Angel gave 36 stickers to Kareem, both of them had an equal number of stickers. How many stickers did they both have altogether

I need help with how to use bar models with these kinda stuff. Thanks

Cyclic models for reference. I will take simple Big Bounce as an example of what I have in mind. In Big Bounce there periods of expansion and periods of contraction which result in a never-ending series of Big Bangs. However if Universe is infinite in extent this would require infinite amount...

The following figure shows observed distance modulus (µ) vs. redshift (z) data (references of data sources are available): How well do cosmological models, such as ΛCDM and models based on non-expanding universe, explain these observed data? For explanation of terms, please see, Type Ia...

There are some mathematical models (eg Delany-Bazley) to calculate impedance of porous materials and these formulas give complex impedance values as a result. But I could not find any model to be used for seafloor (underwater ground modeling) or I don't know if existing models may be used. I...

Hi, I am a mechanical student. I would like to ask are those drying kinetic equations for food drying applicable in drying a paperboard? Thankyou :)

I have seen that many posters here seem to be very knowledgeable about the man made climate "emergency". So someone can surely point out a reference where all the sources of uncertainties for at least one specific model are provided with an estimate of their values (for examples, uncertainties...

I am reading Planck 2015 results. In particular, I focused on "Power law potentials" subsection. The issues I have are 1. I do not understand why the validity of the model can be determined by the value of the ##B## mode. 2. Why the ##B## mode values ##\ln B = −11.6## and ##\ln B = −23.3## for...

Hi, I was recently reading about spectral estimation with parametric methods, and specifically auto-regressive models. I came across the statement: "An AR(p) model can provide spectral estimates with p/2 peaks" and I was wondering why this was the case. I do apologize if this is the wrong forum...

Can someone point out to a resource where would be provided a list and description of the constants/parameters used in modern climate models. And the values used with their uncertainties. (PS: I know that any question related to global warming tends to trigger some people, I was called dumb...

In cosmology, CMB tells a lot about which cosmological model can be acceptable or not. For instance we know that, whatever the cosmological model we use ##\theta_*## parameter will be always the same. Is there any other parameters that is listed in this picture is **model-independent** ?(i.e...

Some physicists (like John A Wheeler, Holger B Nielsen or Ilya Prigogine) have proposed that all the laws of physics (including the most fundamental ones) emerged from a primordial chaos (for example, in the case of Wheeler, he proposed that laws of physics emerged from an initial random and...

Thinking of the common language notion of "entropy" as "uncertainty", how can running a simulation based on a probability model implement entropy increasing? After all, the simulation picks definite outcomes to happen, so (intuitively) there is less uncertainty about the future as definite...

I have the impression (I've not actually researched the matter) that some online weather services publish data from weather stations set up by amateurs. Do any organizations incorporate such data in their weather prediction models? I'd think that using such data would involve a sophisticated...

Hi everybody, Academic papers in mechanical engineering use often lumped-element (or lumped-parameter) models such as a typical quarter car model. However, books about the (mechanical) engineering design methodologies (such as by authors Dieter, Shigley, or Pahl-Beitz) seem to not mention this...

Hello, I understand that CAD models (stl files) suitable for 3D printing must be "watertight" and not leaky in the polygon mesh. By analogy, if we filled the model with water, the water would not leak...This concept of watertightness means that there are no unintentional holes between the...

Who can share the primary sources where material models are formulated: Ludwik, Holomon, Swift, Wok, Ludwikson, Hill and others?

A detailed discussion of measurement in the Stern-Gerlach experiment can be given in the POVM setting; see this post.

I am developing my own project called orbital flight simulator myself. I was looking for some IAU rotational model about all planets (Sol solar system) through the Internet and my books but was unable find any information. Does anyone have good books or information (tables and algorithms like...

I have a question about the history of cosmology, hope its okay to ask here. Who was the first person since Einstein's Gr to point out a singularity in cosmology? I know Freidman talked of an expanding universe and Lematire a primeval atom. But were there any explicit mentions of the density of...

https://www.sciencemag.org/news/2020/03/mathematics-life-and-death-how-disease-models-shape-national-shutdowns-and-other This shows how policy can be informed about differing effects of control policies in different environments. One of the bleak aspects of UK choices is shown as a graph...

[url="https://www.physicsforums.com/insights/3-possible-models-for-why-uranus-spins-on-its-side/"]Continue reading...

I need to predict an upcoming rogue wave or analyse old rogue wave events using simple probability models and real-time data for a physics high school project.

I think the C_V for van der waals gas will be larger than ideal gas since it‘s a more precise description. However, for the relationship I cannot come up with a specific equation.

Given a balanced chemical equation, can we predict using computer models the maximum power of the chemical reaction? Thanks.

I am reviewing and comparing a wide range of mathematical models that are being applied to a specific realm of wildlife biology. For the comparison of these models, and to weigh advantages/disadvantages of different aspects with regard to application, I need to characterize each model. As I do...

Can we say that a universe with a radiation density (only) exists only in near a Big Bang time, and not a Big Crunch? Since it gets much smaller as time passes. For example in here: http://www.nat.vu.nl/~wimu/Varying-Constants-Pictures/Time-Scale-Universe.jpg We have different cosmological...

Molecules don't really look like this with clearly defined objects and outlines. Remember that in the double slit experiments, we can't even model what happens between measurements, like how the electron behave between emitter and detector. So what is the best model to describe them? How...

Hello everyone! Recently I saw this paper: https://arxiv.org/pdf/1304.4801.pdf ("Any nonlocal model assuming “local parts” conflicts with relativity " by Antoine Suarez). He mentions standard experimental configuration with beam-splitters and detectors. Then he distinguishes possible models...

Both Stephen Wolfram and nobel laureate Gerard 't Hooft think that the universe is a Cellular Automata. As far as I know, 't Hooft developped a series of frameworks to build different models of Cellular Automata and Wolfram also proposed a framework where network nodes could produce different...

Let's consider a simple scenario in Maxwell-Boltzmann statistics: 6 identical but distinguishable particles, and 9 quanta of energy, 9 indivisible units, to be distributed among the particles.The first model is like that of the wheels on a combination lock, or should I say "permutation lock"...

I am familiar with non-Bayesian methods for calculating best fit values of various parametric models, but I have not had any experience with cosmological models calculations. My understanding is that these models have five parameters: H0, Ωr, Ωm, Ωk, ΩΛ, and the last four satisfy the constraint...