What is Constants: Definition and 486 Discussions

A physical constant, sometimes fundamental physical constant or universal constant, is a physical quantity that is generally believed to be both universal in nature and have constant value in time. It is contrasted with a mathematical constant, which has a fixed numerical value, but does not directly involve any physical measurement.
There are many physical constants in science, some of the most widely recognized being the speed of light in vacuum c, the gravitational constant G, the Planck constant h, the electric constant ε0, and the elementary charge e. Physical constants can take many dimensional forms: the speed of light signifies a maximum speed for any object and its dimension is length divided by time; while the fine-structure constant α, which characterizes the strength of the electromagnetic interaction, is dimensionless.
The term fundamental physical constant is sometimes used to refer to universal-but-dimensioned physical constants such as those mentioned above. Increasingly, however, physicists only use fundamental physical constant for dimensionless physical constants, such as the fine-structure constant α.
Physical constant, as discussed here, should not be confused with other quantities called "constants", which are assumed to be constant in a given context without being fundamental, such as the "time constant" characteristic of a given system, or material constants (e.g., Madelung constant, electrical resistivity, and heat capacity).
Since May 2019, all of the SI base units have been defined in terms of physical constants. As a result, five constants: the speed of light in vacuum, c; the Planck constant, h; the elementary charge, e; the Avogadro constant, NA; and the Boltzmann constant, kB, have known exact numerical values when expressed in SI units. The first three of these constants are fundamental constants, whereas NA and kB are of a technical nature only: they do not describe any property of the universe, but instead only give a proportionality factor for defining the units used with large numbers of atomic-scale entities.

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  1. Danielk010

    How do you solve for multiple constants given the wave functions at the boundary?

    From my understanding, you can equate ψ1(x) and ψ2(x) at the boundary of x = a, so I plugged in the values of a into x for both equations and I got ψ1(x) = 0 and ψ2(x) = ## (a-d)^2-c ##. I am a bit stuck on where to go from here.
  2. mister i

    B Exploring the equivalences between mass, time and length

    We know that in the universe we can establish an equivalence between length and time through a constant (the speed of light): l = ct and talk about length in units of time (light-years). But, by playing mathematically with the dimensions of M, L and T and the constants G and c we can see...
  3. T

    I cannot work out constants a and b --

    75 = (1.5 x 10^-3)a + (1.5 x 10^-3)b 105 = (3 x 10^-3)a + (3 x 10^-3)b
  4. S

    I Arguments leading to the speed of light as a dimensionless constant

    I once read (though I don’t remember where) that in the same way that you talk about a dimensionless ratio between Y and X in ordinary space, you can conceive of c as a dimensionless ratio between T and X in spacetime. Do you know where I can find a reliable treatment of that idea? As...
  5. ermia

    Finding Constants: Potential and Field Analysis

    I have wrote all feilds and potentials and I want to find the constants. My first question is " when we say in the a<x<2a the potential is V(x)" then the potential in the a is V(a) or V(0) ( cause it is 0 in our new area) ? Second one is " when I want to write the gausses law for the point x=a I...
  6. G

    B Can physical constants be different in other galaxies?

    I've learned that some cosmological observations do not match with theoretical predictions leading to the hypothesis of dark matter or dark energy. Do you know references which discuss if instead the explanation could be that physical constants slowly vary in space? This seems conceptually...
  7. D

    I Elastic Constants for Natural Rubber

    Hi, Looking for the Elastic Constants for any rubber-like material such as Natural Rubber. It can be inorganic or organic. The constants I am looking for take the form of a fourth-rank tensor. I only need the first order elasticities, not the zeroth or higher (not Cij or Cijklmn.. just Cijkl)...
  8. M

    Find the constants ## A ## and ## B ##

    Proof: Observe that \begin{align*} &li(x)=\int_{2}^{x}\frac{dt}{\log t}\\ &=[\frac{t}{\log t}]_{2}^{x}-\int_{2}^{x}t(\frac{1}{\log t})'dt\\ &=\frac{x}{\log x}-\frac{2}{\log 2}-\int_{2}^{x}t(-\frac{1}{t\log^2 t})dt\\ &=\frac{x}{\log x}+\int_{2}^{x}\frac{dt}{\log^2 t}-\frac{2}{\log 2}\\...
  9. barryj

    I Uncovering the Mystery of Calorie Constants

    When calculating calories of a food.. It is sort of well known that carbs have 4 cal/gram, protein has 4 cal/gram and fat has 9 cal/gram. I wanted to do an experiment to determine these constants 4,4,and 9 I looked at soup, peanut butter, and a protein mix to get the values from the labels per...
  10. J

    I Bubble universes and physical constants

    Hello, couple of questions about bubble universes and the physical constants. I understand in an eternal inflation scenario universes bubble off the original during the inflation phase. Firstly, according to this theory, does the new universe creation only happen at an early inflation phase of a...
  11. PaulDiddams

    B Quadratic with simple meaningful intuitive constants

    Ever made a simple model that fits a quadratic function? Tweaking the a, b and c constants to fit new observed data is a bit of a pain. When I was a grad. student I came up with the following simple quadratic rearrangement that uses the intercept (Yo) and the values of x and y that define the...
  12. H

    I Propagation of uncertainty with some constants

    Hi, I have a value ##100 \pm 0.1## and a function ##\frac{V}{E} = \frac{1}{\sqrt{1 + (\omega r c)^2}}## and I would like to find the uncertainty. Where r = 1000 and c = ##5 \cdot 10^{-8}## are constants. However, I'm not sure to understand how. Here's what I think and did. Since I multiply the...
  13. L

    I Number of integration constants

    If we have system of 3 ordinary differential equation in mechanics and we have two initial condition ##\vec{r}(t=0)=0## and ##\vec{v}(t=0)=\vec{v}_0 \vec{i}##. If we somehow get \frac{d^2v_x}{dt^2}=-\omega^2v_x then v_x(t)=A\sin(\omega t)+B\cos(\omega t) Two integration constants and one initial...
  14. D

    I Usage of First Order Elastic Constants in Soft Body Equations

    Hi, I have some soft body equations that require first order elasticity constants. Just trying to figure out the proper indexing. From Finite Elements of Nonlinear Continua by J.T. Oden, the elastic constants I am trying to obtain are the first order, circled below: My particular constitutive...
  15. skywalker

    I More info on HT/HD shielding constants?

    I was wondering how they measured or calculated these differences? I don't know what they refer to, but assume theyre scattering Hydrogen with Tritium or Deuterium to measure the difference of something. https://physics.nist.gov/cgi-bin/cuu/Results?search_for=shielding+difference
  16. S

    Constants in scalar and vector potentials

    We have a scalar potential $$\Phi(\vec{r})=\frac{q}{4\pi\epsilon_0} \left( \frac{1}{r} - \frac{a^2\gamma e^{-\gamma t}\cos\theta}{r^3}\right)$$ and a vector potential $$\vec{A}(\vec{r})=\frac{a^2qe^{-\gamma t}}{4\pi\epsilon_0r^4}\left(3\cos\theta\hat{r} + \sin\theta\hat{\theta} \right) .$$ how...
  17. L

    Engineering System Constants for Perfect Gas

    Q) I have to explain the relationships between system constants for a perfect gas. Hi can somebody explain this to me. I am kind of confused what this means and where to start and what to do. Also not 100% sure what a perfect gas is.
  18. K

    How to represent this absolute value inequality with constants?

    see attached image, it asks to repesent it in x-graph constant "a" isn't conditioned. Do I need to separate it into a few cases of the constant a and represent each in one x-graph?
  19. V

    I Dimensionless vs. dimensional "constants"

    [Moderator's note: Spin off from another thread due to topic change.] This is a weird argument to me. We can define metric units, but pretty much everything is defined by something else that we measure. Certainly their are unitless scalar "constants", but they are still basically defined by...
  20. Heisenberg_white

    Measure Planck's constant without universal constants

    I am not getting any ideas to solve this without the universal constants. The method that I want to use invloves the speed of light, which is a universal constant.
  21. P

    I Varying dimensional universal constants

    If Planck constant h and light speed constant c were (very) different, would we notice it? (I know we can change units and make h and c take any numerical value we like. But let‘s stick with one set of units.) I assume rulers, clocks, coupling constants, all dimensionless constants would...
  22. I

    I About fundamental constants and vacuum

    Does it not raise question to be able to build two parameters with the same dimension and order of magnitude of two fundamental constants from five parameters (other fundamental constants and measured properties)? $$\sqrt{10\frac{\left(\varepsilon_0 e^{-2}\right)^3\left(k_B T\right)^4}{\rho_c}}...
  23. E

    Normalisation constants with ladder operators

    The previous part was to show that ##a_+ \psi_n = i\sqrt{(n+1)\hbar \omega} \psi_{n+1}##, which I just did by looking at$$\int |a_+ \psi_n|^2 dx = \int \psi_n^* (a_{-} a_+ \psi_n) dx = E+\frac{1}{2}\hbar \omega = \hbar \omega(n+1)$$so the constant of proportionality between ##a_+ \psi_n## and...
  24. jk22

    I Exploring Cosmological Constants

    Can we explain the cosmological constant in this way ? The Einstein tensor is derived from the Ricci tensor and one property is that, like the stress-energy tensor, its covariant derivative shall vanish. Since the covariant derivative of the metric vanishes it can be added to the EFE as...
  25. chwala

    Finding constants of a quartic equation

    ##4x^4+Ax^2+11x+b##≡##(x^2-x+2)(ax^2+mx+d)## ≡##ax^4+(m-a)x^3+(d-m+2a)x^2+(2m-d)x+2d## ##a=4## ##m-a=0, m=4## ##d-m+2a=A## ##2m-d=11## ##2d=b## ##A=1##, ## B=-6 ## is that correct?
  26. A

    Determine the constants a,b,c, and d

    So are my constants a=-1/4, b=0, c=3, and d=0?
  27. V

    Exploring Hooks Law & Oscillation-Method Spring Constants

    During an experiment, using Hooks law resulted in a spring constant of 7,8N/m while for the oscillation-method the constant was 8,6N/m. Could someone help me to clarify whay they differ and which vlsue is the correct one.
  28. tomdodd4598

    I Renormalisation and running of the φ^3 and other coupling constants

    Hey there! I am still rather new to renormalising QFT, still using the cut-off scheme with counterterms, and have only looked at the φ^4 model to one loop order. In that model, we renormalise with a counterterm to the one-loop four-point 1PI diagram at a certain energy scale. Do I simply, in...
  29. Admiralibr123

    I DEs - Constants in Exercises: Why Not in General Forms?

    I have just started out with ODE's and in none of the general form in the classification have I seen a term with no variable but some questions do have constants in the exercise. I am just confused as to why are they not in general forms. Are they redundant? Do they not contribute anything to...
  30. D

    IEC 60890 - Heat Rise Calculations

    When designing a panel, it is imperative that you keep the components inside at a temperature which they can operate optimally at; allowing the air temperature to go above this limit can cause component failure and fire. To assist with calculating the air flow required to keep the components...
  31. JD_PM

    Get all possible constants of motion given an explicit Hamiltonian

    I do not understand the following sentence (particularly, the concept of extra symmetry): 'If all ##\alpha^i## are the same, then there is extra symmetry and corresponding constants of motion'. OK so let's find the Lagrangian; we know it has to have the form: $$L(q, \dot q) = T(q, \dot q) -...
  32. usm4nq

    B Who set the values of Physics Constants?

    Hello, I am writing a blog post about Physics Constant. I recently found out how you can find out the Constant of Proportionality. and had an idea that all the Physics Constants were Constants of Proportionality. but I have no idea how to confirm this because there are so many. so I don't know...
  33. G

    I Values of the coupling constants

    I am heavily confused about the coupling constants. I primarily refer to this source https://www.physicsmasterclasses.org/exercises/keyhole/en/projects/running_alphas.html , but other sources were not able to lift my confusion either. First, in the figure, the scales appear as quite failed. The...
  34. A

    I Constants at the end of the Frobenius method

    I'm having a hard time grasping the concept of reducing the two recursive relations at the end of the frobenius method. For example, 2xy''+y'+y=0 after going through all the math i get y1(x) = C1[1-x+1/6*x^2-1/90*x^3+...] y2(x) = C2x^1/2[1-1/3*x+1/30*x^2-1/630*x^3+...] I know those are right...
  35. C

    I Are physical constants 'constant' axiomatically, or is there a theory?

    I can see why it would be pretty illogical to speculate that physical constants change over time, but is there more to it than just being 'illogical' to assume otherwise? Is it axiomatic in physics to presume certain physical constants are constant, because otherwise stuff like atoms and things...
  36. M

    Find psi(x,t) when psi(x,0)= Ae^(-x^2/a^2) and A, a are real constants

    EQ 1: Ψ(x,0)= Ae-x2/a2 A. Find Ψ(x,0) So I normalized Ψ(x,0) by squaring the function, set it equal to 1 and getting an A I. A=(2/π)¼ (1/√a) B. To find Ψ(x,t) EQ:2 Ψ(x,t)= 1/(√2π) ∫ ∅(k) ei(kx-ωt)dk --------->when ω=(ħk2)/2m and integral from -∞ to +∞ EQ 3: ∅(k)= 1/(√2π) ∫ Ψ(x,0)...
  37. T

    Finding the spin-orbit coupling constants of an Alkai transition?

    The set of quantum numbers for the 4p orbital is: 4, 1, {-1,1}, +-1/2 (n,l,m,s) The set of quantum numbers for the 4d orbital: 4,2,{-2,2},+-1/2 Hence we can calculate DeltaE for the 4p sub levels for j=1+- 1/2 And for the 4d sub levels as j=2+-1/2. Giving four total values for Delta E as: C_4p...
  38. JamesBennettBeta

    Values of constants in power-law fluid relation

    NO TEMPLATE, MISPLACED HOMEWORK Summary: What are the values of constants in power-law fluid relation when the fluid behaves as an ideal fluid, a Newtonian fluid and a non-Newtonian fluid? τ = A(du/dy)^n +B Where A, B and n are constants that depend upon the type of fluid and conditions...
  39. J

    I Finding Normalization Constants for a Set of Energy Eigenstates

    I do not know what I'm doing wrong but I'm working on the problem of finding the normalization constants for the energy eigenstate equation for a 1D plane wave that is traveling from the left into a potential barrier where E < V at the barrier. This is from Allan Adams' Lecture 12 of his 2013...
  40. M

    Lame's Constants: Definition & Proof

    what are lame's constants for material? their definitions? their proof "if exist"?
  41. F

    I Big Bang and physical constants

    Were the universal physical constants already in place at the instant of the BB? Things like Planck's constant, the speed of light, the various mass of particles, the various force values. Was it possible that the early universe ( the first couple of billionths of a second or so) existed without...
  42. S

    Gas Solubility in water - constants, and calculations

    I can measure O2, Co2, TGP, and temperature, Want to calculate the rest gases, so N2, and Ar in my water. There for i bulit up an axcel table. So i get to the point to calculate Bunsen contans on different Temperature. I have this calculation: ln(β)=exp(A1 + A2*(T/100) + A3*ln(T/100) +...
  43. E

    MHB Solve My Constant Problem: Integral Sign + -2

    I don’t understand how the second (-2) (in front of the integral sign) gets into the equation. Can you please help me?
  44. A

    Spring constants from the physical dimensions of a spring

    I’d like to know if anyone has formulas for calculating the spring constant (k) of coil springs, from their physical dimensions. I bought a coil spring, suspended a 0.6 kg mass to it, observed its oscillation period at very close to 0.6 seconds, and so believed the spring constant “k” to be...
  45. R

    A Different gauge coupling constants

    Hi all, I am sure I am missing something really elementary, but I would really appreciate someone pointing it out to me. So, if we consider the situation in abelian gauge symmetry, say for fermion matter ψ, of charge q. The transformation law for ψ is, ψ→ψ' = e[- i q θ(x)] ψ. We then have to...
  46. Y

    Automotive Motor constants at high current

    Hi, This is a general question: Do the motor constants KV and KT stay constant at high current? Thanks
  47. Dave1212

    Calculating equilibrium constants Keq

    Homework Statement 2Fe(s) + 3Cl2(g) ⇔ 2FeCl3(s)[/B] Keq = 53.25 [CL2(g)] = ?M Answer = [0.2658M] Homework Equations Keq = (cC)(dD)/(aA)(bB) The Attempt at a Solution Keq = [Cl2]3 53.25 = (Cl2)3 I’m confused because I feel like I need more to work with in this question. It seems like I...
  48. evinda

    MHB Convergence and existence of constants

    Hello! (Wave) Let $m$ be a natural number. I want to check the sequence $\left( \binom{n}{m} n^{-m}\right)$ as for the convergence and I want to show that there exist constants $C_1>0, C_2>0$ (independent of $n$) and a positive integer $n_0$ such that $C_1 n^m \leq \binom{n}{m} \leq C_2 n^m$...
  49. S

    Finding effective spring constants

    Homework Statement a) Consider 2 springs, connected in series. If they have different spring constants k1 and k2 then what is the effective spring constant for the double spring system? Give a convincing argument for your formula. You may assume that the mass of the springs is negligible. b)...