- #1
Davide82
- 33
- 0
Hi.
First of all I apologize because I already posted this topic in the "Homework & Coursework Questions > Advanced Physics" but since it exquisitely concerns astrophysics and it is not getting many answers, I believe it's better to post it here. If a moderator wants to merge the two conversation, I would be glad.
I am studying the evolution of the universe.
In particular, I am reading the history of the universe happening just under a temperature of 100 MeV.
At this time, it is said that neutrons and protons are present along with some other particles: electrons, positrons, photons, neutrinos and anti-neutrinos.
They say the reactions which maintain kinetic equilibrium are:
[tex]e^- + e^+ \longleftrightarrow \gamma +\gamma[/tex]
[tex]e^\pm + \gamma \longleftrightarrow e^\pm + \gamma[/tex]
while the reactions which are responsible for both kinetic and chemical equilibrium are:
[tex]e^- + e^+ \longleftrightarrow \nu + \bar\nu[/tex]
[tex]\nu + e^- \longleftrightarrow e^- + \nu[/tex]
[tex]n + \nu_e \longleftrightarrow p + e^-[/tex]
[tex]n + e^+ \longleftrightarrow p + \bar\nu_e[/tex]
[tex]n \longleftrightarrow p + e^- + \bar\nu_e[/tex]
I am wondering why reactions such as:
[tex]p + e^+ \longleftrightarrow p + e^+[/tex]
[tex]p + e^- \longleftrightarrow n + \nu_e + e^+ + e^-[/tex]
are not taken into account.
First of all I apologize because I already posted this topic in the "Homework & Coursework Questions > Advanced Physics" but since it exquisitely concerns astrophysics and it is not getting many answers, I believe it's better to post it here. If a moderator wants to merge the two conversation, I would be glad.
I am studying the evolution of the universe.
In particular, I am reading the history of the universe happening just under a temperature of 100 MeV.
At this time, it is said that neutrons and protons are present along with some other particles: electrons, positrons, photons, neutrinos and anti-neutrinos.
They say the reactions which maintain kinetic equilibrium are:
[tex]e^- + e^+ \longleftrightarrow \gamma +\gamma[/tex]
[tex]e^\pm + \gamma \longleftrightarrow e^\pm + \gamma[/tex]
while the reactions which are responsible for both kinetic and chemical equilibrium are:
[tex]e^- + e^+ \longleftrightarrow \nu + \bar\nu[/tex]
[tex]\nu + e^- \longleftrightarrow e^- + \nu[/tex]
[tex]n + \nu_e \longleftrightarrow p + e^-[/tex]
[tex]n + e^+ \longleftrightarrow p + \bar\nu_e[/tex]
[tex]n \longleftrightarrow p + e^- + \bar\nu_e[/tex]
I am wondering why reactions such as:
[tex]p + e^+ \longleftrightarrow p + e^+[/tex]
[tex]p + e^- \longleftrightarrow n + \nu_e + e^+ + e^-[/tex]
are not taken into account.