B How Does Modern Particle Accelerator Energy Density Compare to the Big Bang?

[jeremyfiennes]

TL;DR Summary

How close to the Big Bang can modern particle accelerators get?

How many nanoseconds after the Big Bang was its energy density that achievable in modern particle accelerators?

 

[mfb]

In the range of many nanoseconds, but without a specific number - if you match the density you don't match the temperature and vice versa, and every collision is different.

 

[jeremyfiennes]

Thanks. I had however imagined that temperature and energy density were the same thing. What is the difference?

 

[mfb]

Roughly: Temperature is the energy per particle, density is how many particles you have per volume. [Here is a sketch of a phase diagram](https://en.wikipedia.org/wiki/File:Phases_of_Nuclear_Matter.JPG).

More detailed discussion - figure 11 has the profile for the early universe and dots corresponding to experiments. The x-axis is the "chemical" potential of baryons instead of density, but they are related quantities.

Proton-proton collisions can reproduce processes at higher energy but they don't reach thermal equilibrium so temperature and density become a bit ill-defined, but they can study what happens at higher temperatures.

 

[jeremyfiennes]

Thanks. From fig.11 I see that temperature is given in baryon-Mev, which is a unit of energy, rather than degrees C. So they are different ways of expressing the same thing?

 

[PeterDonis]

From fig.11 I see that temperature is given in baryon-Mev, which is a unit of energy, rather than degrees C. So they are different ways of expressing the same thing?

No. Energy per particle and energy density are not the same thing. Baryon-Mev is a unit of energy per particle; it's just Boltzmann's constant times degrees C (or more precisely degrees K). Expressing temperature in units of energy per particle instead of degrees is common in physics.

 

[jeremyfiennes]

Thanks. I thing energy-per-particle/temperature was what I was really after.