What is Fine structure constant: Definition and 58 Discussions

In physics, the fine-structure constant, also known as Sommerfeld's constant, commonly denoted by α (the Greek letter alpha), is a fundamental physical constant which quantifies the strength of the electromagnetic interaction between elementary charged particles. It is a dimensionless quantity related to the elementary charge e, which denotes the strength of the coupling of an elementary charged particle with the electromagnetic field, by the formula 4πε0ħcα = e2. As a dimensionless quantity, its numerical value, approximately 1/137, is independent of the system of units used.
While there are multiple physical interpretations for α, it received its name from Arnold Sommerfeld, who introduced it in 1916, when extending the Bohr model of the atom. α quantifies the gap in the fine structure of the spectral lines of the hydrogen atom, which had been measured precisely by Michelson and Morley in 1887.

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  1. G

    I Fine Structure Constant - 10 steps

    An alternative method to calculate the fine structure constant as a function of the proton \ electron mass ratio. Equation 8 with the delta fudge factor gives the same value for alpha as equation 1 (test it yourself). Delta is close to zero, so if this approach is telling us something about...
  2. Adrian59

    A Feynman loop diagrams and Dyson series for anomalous magnetic moment

    Many authors appear to assert that they can derive the fine structure constant from a Feynman loop diagram(s) from first principles. Most recently a team from Japan lead by Aoyama (Aoyama, T., Kinoshita, T. and Nio , M. (2019). Atoms; vol. 7, (issue 1): pg 28) have attempted this. I have not...
  3. Conn_coord

    I Lectures on the Varying fine structure constant

    A University of Oxford and Cambridge Collaboration in 2014 produced a series of lectures "Cosmology and the constants of nature". John K Webb spoke on the topic of variations in the values of fundamental constants. Latest developments here. Who else is doing similar research?
  4. LCSphysicist

    How Does a New Lagrangian Term Affect the Fine Structure Constant?

    I am having some hard time to finding out where i should start. I remember see the strucutre constant arrising when we evaluate vertices on feynman diagrams for QED interactions... But i am too ignorant to know how to proceed..
  5. LarryS

    I Role of Fine Structure Constant in Q.E.D.?

    Why, in a nutshell, are there two coupling constants for the EM field, the fundamental electric charge, e, and the Fine Structure Constant? If a brief answer is not possible, can you recommend good literature on this subject? Thanks in advance.
  6. Auto-Didact

    A Quantization isn't fundamental

    This thread is a direct shoot-off of this post from the thread Atiyah's arithmetic physics. Manasson V. 2008, Are Particles Self-Organized Systems? The author convincingly demonstrates that practically everything known about particle physics, including the SM itself, can be derived from first...
  7. John Greger

    How Do You Identify Spectral Lines and Calculate Fine Structure Constants?

    Homework Statement The Ca spectrum below, recorded using a Fourier Transform Spectrometer (FTS), shows the resolved ##3d4s ^3D - 3d4p ^3D## multiplet. The wavenumbers and their relative intensities are given in the table. Identify all the lines and determine the fine structure constants in the...
  8. P

    I Calculating the fine structure constant in Feynman diagrams

    Griffith's Introduction to Elementary Particles, if I understand it correctly, states that in QED, the fine structure constant contributes less and less to the strength of the EM interaction as we add more and more vertices since the constant is so small (1/137). However, in QCD, since the...
  9. ohwilleke

    I Is there a fine structure constant running anomaly?

    Background The chart above, via Lubos Motl's blog which is standard in any textbook talking about supersymmetry, illustrates the running of the the inverse of the Standard Model (SM) and Minimal Supersymmetric Model (MSSM) coupling constants with energy scale for the electromagnetic force...
  10. T

    I Is the fine structure constant the biggest myth ever?

    The fine structure constant ##\alpha## is commonly cited as a very important quantity, because it gives the strengh coupling of the electromagnetic force. But it seems that the fine structure constant is not actually constant. It rather changes with the momentum of the (mediating?) particle and...
  11. S

    I Systematic Redshift: Exploring Mg II Uses

    Hi everyone, I am new to observations and observational terms! I am reading the paper "constraining the time variation of the fine-structure constant" by Srianand et. al in the section "constraining alpha with QSO absorption lines" there is a sentence saying "... rest wavelengths of MG II ...
  12. mikenw

    B Dipole pattern for Fine Structure Constant?

    Can someone describe for me the dipole pattern that was detected related to the fine structure constant? This thread talks about that pattern some. What I am trying to understand is how that dipole is oriented relative to the observer on Earth? Are we talking about a toroidal shape with a...
  13. J

    B Alpha is 1/137th of what? (Fine Structure Constant)

    Hi. With regard to the Fine Structure Constant, I have been trying to figure out the practical applications of the formula in nature but have had difficulty trying to discern what the 137 denominator in the equation represents. ie, it is 1 137th of what? Or, 137 whats? Is there a practical...
  14. TrickyDicky

    Fine structure constant meaning

    I admit that I have always seen this number as a simple proportionality constant relating other constants and units. But there is a long tradition attributing it all kinds of deep physical and even mystic significance, what do you think?
  15. P

    Quarks and the Fine Structure Constant

    In a recent online lecture it was said there is now known releationship between the masses of quarks. My online search seemed to back this up. My comparison suggests: Mcharm ≈ Mtop * fine Mup ≈ Mcharm * fine / 4 Mstrange ≈ Mbottom * fine * 3 Mdown ≈ Mstrange * fine * 7 (corrected for...
  16. E

    Relation of fine structure constant to splitting of spectral li

    Homework Statement Estimate the magnitude of the fine structure splitting in H-α in THzHomework Equations Rydberg -- R_y \left(\frac{1}{n_f^2}-\frac{1}{n_i^2}\right) = \Delta E The Attempt at a Solution This isn't really a request for solution help, and more a justification. I know that if...
  17. W

    Why is the fine structure constant what it is?

    This question occurred to me while working through some textbooks. Since it is dimensionless, its value can't be explained away saying it's because of the way we chose the units. Well it turns out I'm a 100 years late to this game. I found it's even more serious than I had realized. (And it...
  18. H

    Where did Epsilon go in the Fine Structure Constant Equation?

    Homework Statement e is charge epsilon is permittivity Homework Equations e^2 = 4\pi \epsilon GM^2 The Attempt at a Solution This is just a question really because I am a bit confused about something. Was reading up on the fine structure constant and apparently the fine...
  19. L

    Change in fine structure constant

    What would be the consequences of slightly changing the fine structure constant, i.e. changing the strength of the electromagnetic interaction - but not changing gravitation or the strong force? In the everyday world? You might imagine that the strength of chemical forces etc. would change...
  20. A

    Fine structure constant and energy scale

    Hi all, I have a rather naive question about the fine structure constant and the relationship between its value and the energy scale involved. I understand the idea of the a charge being 'screened' by vacuum polarization (i.e., electron-position pairs popping in and out of existence), and...
  21. L

    Questions about (potential) variations in the Fine Structure Constant

    I have read an amount of material on (potential) variations in the Fine Structure Constant. The majority of the material seems cautiously positive in declaring support for the potential variations, but I have a couple of question that you may be able to help me with. 1) Am I correct is...
  22. A

    Fine structure constant and perturbation theory

    Hi all, I have a question about perturbation theory and the fine structure constant. Consider an electron moving through the vacuum - this wil induce vacuum polarization, and (if I understand correctly) perturbation theory can be used to analyze the situation. My question is essentially: if...
  23. A

    Varying Fine Structure Constant and Vacuum Energy Density

    Hi all, I have a bit of a variation of a question I asked some time ago. Webb et al. continue to publish results which suggest that the fine structure constant may vary over space and time. I realize the results are controversial - what I'm wondering: If the fine structure constant...
  24. Dotini

    Does Fine Structure Constant Vary From Place to Place?

    http://www.swinburne.edu.au/chancellery/mediacentre/media-centre/news/2011/10/natures-laws-may-vary-across-the-universe One of the laws of nature may vary across the Universe, according to a study published today in the journal Physical Review Letters. One of the most cherished principles in...
  25. E

    Variations in the fine structure constant

    In http://arxiv.org/PS_cache/astro-ph/pdf/9803/9803165v4.pdf" the authors use (second paragraph) "Spectroscopic observations of gas clouds seen in absorption against background quasars" to search for variations in alpha. Is my understanding correct that A) The quasars are background and...
  26. A

    Varying Fine Structure Constant - Any recent results?

    Hi all, I was wondering if there have been any recent (i.e., in the last 10'ish months) results / articles which either support or refute the claim made by Webb et al. in the article "Evidence for spatial variantion of the fine structure constant"? http://arxiv.org/abs/1008.3907 Also...
  27. L

    Modifying the Fine Structure Constant to Incorporate Self-Energy Interactions?

    How do (e^2)/(4Pi x epsilon x Planck constant x speed of light) cancel to give one and make the fine structure constant dimensionless? thanks
  28. C

    QED Predictions of fine structure constant and g-factor

    Hi, I know QED is one of the most tested theories in all of science (and one of the most accurate) but I wanted to know if it disagreed at ALL with its predicted values of both http://en.wikipedia.org/wiki/Fine_structure_constant http://en.wikipedia.org/wiki/G-factor_(physics ) The thing...
  29. E

    Evidence for spatial variantion of the fine structure constant

    Webb et al wrote article "Evidence for spatial variantion of the fine structure constant". http://arxiv.org/abs/1008.3907. As I understand there exists direction where fine structure constant is the smallest and the opposite direction, where it is the largest. Do maybe these directions have...
  30. A

    Mass, fine structure constant & annihilation

    Hi, If the mass is very high and the fine structure constant very small, is it true particles of opposite charge can't annihilate? If yes. What has mass and fine structure constant got to do with annihilation?
  31. S

    About recommended fine structure constant value

    value of fine structure constant logarithmically depend upon momentum/energy scale. so what is exact energy/momentum scale corresponds to standard/recommended value of fine structure constant?
  32. A

    Variation of fine structure constant and spacetime?

    Hi all, I'm going to ask a naive question - hope that's ok. There's been a lot of recent discussion of the results from Webb et al. which indicate that the fine structure constant varies spatially. I realize the results are very controversial - I'm wondering, hypothetically, if these...
  33. Q

    Fine Structure Constant appears to vary across the distant sky

    I guess I don't have much to say about this other than it's pretty amazing if it's true and I wanted to bring it to everyone's attention here. http://www.sciencedaily.com/releases/2010/09/100909004112.htm http://arxiv.org/abs/1008.3907
  34. R

    Question about alpha, the fine structure constant

    I understand that it's been determined to have a very small value. At the same time, it is also true that gravity is incredibly weak compared to the other fundamental forces. What I'm wondering whether there might be some relationship between them?
  35. bcrowell

    Fine structure constant probably doesn't vary with direction in space

    The thread "Fine Structure Constant Varies With Direction in Space!" was locked because it didn't cite papers published in refereed journals. Actually all of this stuff has been published in refereed journals. The list of references below is cut and pasted from...
  36. S

    Fine Structure Constant Varies With Direction in Space

    Here's something profoundly earth-shaking: Thursday, August 26, 2010 http://www.technologyreview.com/blog/arxiv/25673/ A spatial variation in the fine structure constant has profound implications for cosmology -- What is going to have to be revised as a result of this discovery? What are the...
  37. W

    Fine structure constant increase with energy?

    Hi! Hope someone can help, I am currently studying an Open University course and I am a little confused by a statement in one of the textbooks. It says that the value of the fine structure constant increases with collision energy (in Electron/Positron annihilation). I am probably being...
  38. 1

    Help: Planck Scale and Fine Structure Constant

    Could someone explain the relationship between the FSC and the Planck Scale? What are they in relation to each other. I know what the Planck Scale is, and I even have a loose understanding of the FSC, but what of them in contrast and comparison? And how does the FSC affect QM, if at all...
  39. H

    What is the value of the fine structure constant at Planck energy?

    At low energy, the value is around 1/137.036. What is the value at the Planck energy? Is it listed somewhere? After all, the renormalization of the charge (as it is also called) is mentioned everywhere. But numbers are rare ... Hz
  40. Orion1

    Grand Unification Theory fine structure constant

    I am inquiring if anyone here is qualified to numerically demonstrate the solution to this equation? The equation is the Proton lifetime derived from the SU(5) Georgi-Glashow model listed in reference 1, eq. (19). SU(5) Proton lifetime: \tau_p \geq \frac{1}{\alpha_{(5)}^2} \frac{M_X^4}{m_p^5}...
  41. J

    Exploring the Inter-Relationship of Nature's Constants

    Hello all. I only have a few posts here so I am somewhat new to the forum. I have been reading a number of the posts though and I am favorably impressed by many of the responses. I am also somewhat new to LaTex so please forgive my mistakes with it. I am interested in learning more about the...
  42. S

    Fine structure constant -1/137

    A lot of scientists say that fine structure constant is still a mystery..one of them was Richard Feynmann...i know fine structure constant is a dimensionless constant and there are many dimensionless constant but why this fine structure constant takes special place?can anyone tell me why this...
  43. H

    What Is the Significance of the Fine Structure Constant 1/137?

    The dimensionless pure number 1/137 obtained from the bohr theory (e^2/2hc epsilon_0) is given a particular name 'The Fine Structure Constant'. What is the significance of this number? Why has this value a name?
  44. K

    The dimension of the fine structure constant

    Everyone "knows" that the fine structure constant (alpha) is a dimensionless number, but I am troubled by the fact that the Planck unit of resistance must be one - if that is true - and that strikes me as suspicious. I wonder if anyone can shed any light on this. I present the complete...
  45. T

    Smilga paper, in which he derives an estimate to the fine structure constant

    I've been trying to figure out this paper by W. Smilga: Spin foams, causal links, and geometry-induced interactions I don't have the knowledge and background to be able to determine whether his derivation of an estimate to the fine structure constant is interesting, or just a trick. I am...
  46. D

    The Calculated Value of the Fine Structure Constant From Gravitational Potential

    This paper conjectures a relation between the gravitational potential and the value of the Fine Structure Constant. Although a key constant in all electromagnetic quantum and quantum field theories, accept for some numerology manipulations, the value of the Fine Structure Constant is not...
  47. T

    What Are the Possible Changes in the Fine Structure Constant in the Past?

    Scientists are doing experiments to find any change in the Fine Structure constant in the past. It is dependent on the following constants. C (Velocity of Light) e (Charge of the electron) E0 (Permittivity of free space) h (plancks constant) Could you pls let me know which of the...
  48. E

    The Fine Structure Constant and Hawking Radiation

    Abstract. Theory of quantum gravity is still a mystery, as well as the derivation of fine structure constant and masses of elementary particles. (Fine structure constant is calculated from force between two elementary charges.) Possibility that elementary particles are black holes is offering...
  49. marcus

    New value for alpha, the fine structure constant

    alpha reciprocal new value is 137.035 999 710(96) (uncertainty 0.70 ppb) http://physicsweb.org/articles/news/10/8/1/1?rss=2.0 "The new value, based on the most precise measurements ever of the magnetic moment of the electron, has an uncertainty of 0.7 parts per billion. The new value is ten...