Paul Dirac on Dimensionless Physical Constants and "Large Number Hypothesis"
Why Physics Stack Exchange recommends it
Physics Stack Exchange users link it as a primary source when discussing Dirac's views on dimensionless constants, the fine-structure constant, and the Large Number Hypothesis.
Recommended by 1 people across 1 different months, 2015 to 2023.
What it is
A short archival clip of Paul Dirac discussing dimensionless fundamental constants, such as the fine-structure constant and the electron-to-proton mass ratio. He also touches on his Large Number Hypothesis, which links the ratio of electromagnetic to gravitational force (about 10^39) to the age of the universe in atomic units. The clip is uploaded by the Muon Ray channel.
What people said
Recommends M06-2x · 2023-06 · Physics Stack Exchange · on “How does dimension work?”
Most of the physical properties are related explicitly or implicitly to a dimension space and a dimension time. A mesure of a position or a time is strongly relative to a frame of reference, this is a simple notion of relativity. There are scales $\gamma$ to convert an unit to another similarly to the change of a frame of reference. By adding the dimension, we can recognize the frame, the physical significance of the property. Normally most of the dimensions expressed as $L^x.T^x$ , with $x,y$ positive integers are invariant by addition (extensive). The acceleration contains $L.T^{-2}$ is intensive, the same for the velocity. As Antoin Roquentin said dimensionless quantities are interesting
Cites Omar Nagib · 2015-07 · Physics Stack Exchange · on “Is there a relation between $G$ and the age of the universe?”
Here is a recording [this video] of Paul Dirac, talking about dimensionless constants and their significance. He gives some examples of such constants(ratio of the masses of an electron to a proton, the fine-structure constant) and then touches upon the subject of the relative strength of electromagnetic force compared with that of gravity. He says, the ratio of the electromagnetic force to that of gravity is $10^{39}$. The age of the universe(which according to the estimation of their time is the "false" $18$ billion years), When expressed in atomic units of time, is also $10^{39}$. He believes this is more than a coincidence, and hence he developed a theory in which $G$ and the age of the unive
Cites peter · 2019-02 · Physics Stack Exchange · on “Is the fine-structure constant related to the size of the observable universe?”
This is a related speech by Dirac proposing a numerical relationship between the fine-structure constant and the age of the universe in "atomic units". His proposition involves time-varying G to reconcile constancy of the fine-structure constant with the time-varying age of the universe. [this video]
Cites ann marie cœur · 2021-03 · Physics Stack Exchange · on “Paul Dirac on Dimensionless Physical Constants and $\alpha\sim\frac{1}{137}$”
Paul Dirac gave his viewpoints on the dimensionless constant (click to see the youtube video) [this video] . For example, he mentioned the fine structure constant $$ \alpha\sim\frac{1}{137}. $$ It is not clear that whether Dirac gave this presentation before or after the invention of renormalization group. But Dirac said that "physicists think that there must be a reason for the the dimensionless fine structure constant to be this value instead of others: $ \alpha\sim\frac{1}{137}$ . At present, there is no satisfactory answer for this. But with the future development, people believe that the reason will be found." Is Dirac viewpoint still correct under the current modern physics view (in the 202
Cites Deschele Schilder · 2021-05 · Physics Stack Exchange · on “To calculate the ratio of the strength of the electromagnetic and gravitational force which mass is needed?”
Obviously, mass comes in elementary chunks, like all elementary charges (electric, color, and assumed weak). All elementary particles have an inherent mass. Unlike charges though, these masses are not rational multiples of one another (which is why I think they are not truly elementary, but that's another question). In calculating the ratio between the electric and gravitational force one usually calculates this by reference to two electrons. See for example this [LINK] question. The ratio, in this case, is about $10^{42}$ . Dirac used for this ratio a proton and an electron, which gives about $10^{39}$ . See this video [this video] , in which he explains his large number hypothesis: in Natural u