This paragraph displays genius of Feynman. No equations or laws, just defining the problem in a better way, with making reasonable assumptions or ruling out possibilities, and he reached an equation. Pure delight!  **Figure 1:** *The dashed line represents an element of Volume $dV$, the black dots represents the stars. The solid line depicts the trajectory of a cosmic ray inside that element of volume when it is scattered by a star.* Consider a set of stars (dipoles) distributed inside an element of volume $dV$. We assume that all the stars are: - non-absorbing: we consider the CRs have sufficient energy to collide with the star to be negligeable - non-capturing: the set of these type of orbits is negliegeable compared to all the other orbits Thanks to these assumption we know that all particles entering the distribution of matter will emerge at infinity, thus we have summing over all the possible directions $R'$ we can write: \begin{eqnarray*} \int F(R,P;R',\infty) \, dR' = 1 \end{eqnarray*} We want to find the intensity of particles in the direction $R$ at point $P$: $I_p(R)$. Considering a beam of particles at infinity with constant intensity $$I_{\infty}(R') = I_{\infty}$$ (independent of R') and taking into account that the probability of following any route is equal to the probability of following the reverse route we can write that: \begin{eqnarray*} I_p(R) &=& \int F(R',\infty;R,P)I_{\infty}(R') \, dR' \\ &=& I_{\infty} \int F(R,P;R',\infty) \, dR' \\ &=& I_{\infty} \end{eqnarray*} We can conclude that the intensity in any direction at any point $P$ is the same and the distribution is isotropic at $P$ if it is isotropic at infinity. **This paper is Feynman's first published work.** The first official scientific publications by Richard Feynman first appeared in 1939 in the Physical Review. He published two papers as an undergraduate student: - "The Scattering of Cosmic Rays by the Stars of a Galaxy", co-written with Manuel Vallarta - ["The Forces in Molecules"](http://faculty.washington.edu/miller/51816/Feynman.pdf), Feynman's senior thesis This paper was published in 1939 in his final year as an undergraduate at the Massachusetts Institute of Technology (MIT). Feynman and his Professor Manuel Vallarta were investigating whether cosmic rays came from inside or outside the galaxy by studying their scattering by the magnetic fields of the galaxy's stars. Their result is simple and straightforward but their reasoning is very clever: they stated that the probability of a particle’s emerging from a clump of scattering matter in a certain direction must be equivalent to the probability of an antiparticle's taking the reverse path. (like an anti-particle going backwards in time) Feynman went on to receive his Bachelor's degree from MIT and attained a perfect score on the graduate school entrance exams to Princeton University in physics.  *1939 - Picture of Richard Feynman at the Princeton Library* Feynman and Vallarta found that the **net effect of the scattering of cosmic rays by stars was zero.** They have shown that that the intensity of cosmic rays is isotropic and thus the magnetic fields of the stars are unable to contribute anything to the solution of the problem whether or not cosmic rays come from beyond our galaxy. If cosmic rays seem to come from all directions, it is not because the stars are interfering and disguising their original orientation.