Fine-structure constant

The fine structure constant is a dimensionless physical constant that indicates the strength of the electromagnetic interaction. It was introduced in 1916 by Arnold Sommerfeld to describe the splitting ( fine structure ) of spectral lines in the spectrum of the hydrogen atom, therefore it is also called Sommerfeld constant or Sommerfeld fine- structure constant.

It is the electromagnetic coupling constant. That is, it describes the probability that an interaction- of the electromagnetic interaction, a photon of an electrically charged elementary particles, for example, an electron coupling. Thus, the fine structure constant, determines the rate of physical processes, such as light emission and the magnitude of the repulsive or attractive forces between the charged particles.

Value

Its value is in accordance with current measurement accuracy:

Where the bracketed numbers indicate the estimated standard deviation of the mean corresponding to the last two digits before the brackets.

The fine structure constant depends according to the elementary charge and the Planck 's constant and the reduced quantum of action together on the speed of light and the electric field constant

Herein is the reciprocal of from the quantum Hall effect very precisely determinable by - Klitzing'schen elemental resistance ohms. So this return value must be due only with a well- known factor, multiplied, where, as mentioned, is the precisely defined speed of light in vacuum and also precisely defined the so-called vacuum permeability.

Comparison of the fundamental forces of physics

Direct the strength of the electromagnetic interaction only with gravity can be compared, since both forces obey the same law of distance: the strength of the force decreases with the square of the distance from.

Pressing the size specified by the gravitational constant strength of gravity between two protons, ie heavier elementary particles (compared to eg electrons) in a dimensionless as the fine structure constant number of, we obtain a value of

Comparing this value with the fine structure constant, which indicates the strength of the electric repulsion between the two protons, one sees that the electromagnetic interaction stronger by a factor of roughly than the gravitation ( hierarchy problem).

The strong interaction has an energy-dependent (, runny ') coupling constant. The comparison value for the force between two nucleons in the nucleus is

Comparing the decay rates of strong and weak decays, we obtain a coupling constant of the weak force

Temporal consistency

The answer to the question of whether the fine structure constant is unchanged or varied in time since the Big Bang, is of considerable theoretical interest. Previous considerations and measurements have so far significantly demonstrate no change.

Experiments and measurements for this purpose can be carried out in very different time scales:

• Laboratory experiments, such as atomic clocks can limit the relative temporal variation of α at most 10-16/Jahr.
• The observation of absorption lines of quasars improve this accuracy by one to two orders of magnitude, the treatment of systematic errors but is difficult and so far both significantly positive and zero results were published. A final analysis of all data is still pending.
• The observation of primordial nucleosynthesis expands the null result at times immediately after the Big Bang from, but with larger error bars.
• The Oklo natural reactor and the isotope distribution in meteorites were also used for estimates.

Energy dependence

In elementary particle physics, the fine structure constant also depends on the energy. Thus, in the mass of the Z boson (91 GeV ) the fine structure constant. The interaction is screened by electron-positron pairs out of the vacuum exist for a short time (see vacuum fluctuation ). The particles get closer at higher energies and thus there is between them less electron-positron pairs which shield the interaction.

In all conventional applications, for example in spectroscopy, the energies are typically only a few eV, so that the energy dependence is negligible.

Occurrence in physics

• Fine structure splitting in atoms.
• Spectral absorption of a graphene layer.

Quotes

" It has been a mystery ever since it what Discovered morethan fifty years ago, and all good theoretical physicists put this number up on Their wall and worry about it. "

" Since it was discovered over fifty years ago, it is a mystery, and all good theoretical physicists to hang this number on the wall and rack their brains about it."

References and evidence

• Physical constant
• Quantum physics