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

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Discussion Overview

The discussion revolves around the comparison of energy density in modern particle accelerators to that of the early universe shortly after the Big Bang. Participants explore the relationship between energy density, temperature, and particle interactions, focusing on theoretical and conceptual aspects.

Discussion Character

  • Exploratory
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • One participant inquires about the specific time after the Big Bang when energy density matches that achievable in modern particle accelerators.
  • Another participant notes that while energy density can be matched, temperature does not correspond directly, as each collision in particle physics is unique.
  • A participant expresses confusion about the distinction between temperature and energy density, prompting further clarification.
  • It is explained that temperature refers to energy per particle, while energy density pertains to the number of particles per volume, with a reference to a phase diagram for further context.
  • Discussion includes the observation that proton-proton collisions can achieve higher energy levels but do not reach thermal equilibrium, complicating the definitions of temperature and density.
  • Clarification is provided that baryon-MeV is a unit of energy per particle, and while it relates to temperature, it is not the same as expressing temperature in degrees Celsius.
  • A participant acknowledges that their interest lies in the relationship between energy per particle and temperature.

Areas of Agreement / Disagreement

Participants demonstrate a lack of consensus on the precise relationship between energy density and temperature, as well as the implications of particle collisions in this context. Multiple views on the definitions and their interrelations are presented.

Contextual Notes

The discussion highlights the complexity of relating energy density and temperature, indicating that definitions may depend on specific contexts and assumptions. The relationship between baryon-MeV and temperature is noted to be nuanced.

jeremyfiennes
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TL;DR
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?
 
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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.
 
Thanks. I had however imagined that temperature and energy density were the same thing. What is the difference?
 
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.
 
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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?
 
jeremyfiennes said:
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.
 
Thanks. I thing energy-per-particle/temperature was what I was really after.
 
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