# fizinfo AT lists.kfki.hu

**Subject:**
ELFT HÍRADÓ

## List archive

**From**: Szeminárium koordinátor <sem-admin AT szfki.hu>**To**: SZFI Szeminárium <seminar AT szfki.hu>,Fizinfo <fizinfo AT lists.kfki.hu>**Cc**: Fizinfo <fizinfo AT lists.kfki.hu>**Subject**: [Fizinfo] Szemináriumok - Seminars: Varró Sándor**Date**: Thu, 10 Dec 2020 06:26:01 +0100 (CET)**Authentication-results**: smtp2.kfki.hu (amavisd-new); dkim=pass (1024-bit key) reason="pass (just generated, assumed good)" header.d=szfki.hu

SZFI SeminarVarró SándorWigner FK SZFI, ELI-ALPSNotes on black-body radiation

and stimulated emissionTuesday, 15 December 2020, 10:00, video conference,

https://letsmeet.wigner.hu/szeminariumThe study of the physical bases of

stimulated emission and black-body radiation have been closely related from

the very beginning. We feel it justified to devote some time for their joint

analysis, in particular, in the present year, when we celebrate the 60th

anniversary of the invention of the LASER (Light Amplification by Stimulated

Emission of Radiation). Moreover, one should also keep in mind that in the

course of his work on black-body radiation, Planck discovered the elementary

quantum of action h just 120 years ago. In the present talk, though we shall

highlight some moments in the development of the laser during the past 60

years, the emphasis shall be put on the fundamental aspects. Our purpose is

on one hand to discuss some lesser known historical facts concerning the

stimulated emission of radiation as appeared in the works of Planck (1911)

and Einstein (1916). On the other hand, we present our recent results; a new

phenomenological derivation of the entropy of a Planckian oscillator, and the

building up of its connection with the fractal dimension of the relative

frequencies of the excitation of a Bohr atom in thermal equilibrium. In the

first part of the talk, we summarize Einstein’s famous derivation (1916) of

the Planck formula for black-body radiation, in which he introduced the

concept of stimulated emission. Then we discuss Planck’s so-called second

theory (which have been worked out earlier, in 1911) and show that it already

implicitely contained the process of stimulated emission (besides the

zero-point energy and the so-called Bose distribution). On the basis of

critiques by Landé (1925) and Heitler (1925) of Einstein’s derivation we draw

attention to the correct interpretation of the so-called ‘A and B

coefficients’. In the second part of the talk, we show that if we map the

relative frequencies of the excitations of a two-level system to the unit

interval, then the Planck entropy is directly connected to the

(temperature-dependent) Hausdorff dimension of the set of excitations

represented in this interval. Finally, we shall go back to the very

beginnings, and consider Planck’s interpolation formula for the entropy,

which resulted in the first correct expression for the spectral density of

the black-body radiation 120 years ago. We will show that by relaxing the

phenomenological scaling law for the ‘degree of irreversibility’ introduced

by Planck, it is possible to derive this entropy formula, without any

apparent quantization. Minden érdeklődőt szívesen látunk! - Everyone

is welcome to attend.Róbert Juhászsem-admin AT szfki.hu

**[Fizinfo] Szemináriumok - Seminars: Varró Sándor**,*Szeminárium koordinátor, 12/10/2020*

Archive powered by MHonArc 2.6.19+.