Calculate number microstates? Why not include acceleration?

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    Acceleration Microstates
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Discussion Overview

The discussion centers on calculating the number of microstates in a system of indistinguishable particles within a 3D box, exploring the relevance of including various physical parameters such as position, velocity, and acceleration in this calculation. The conversation spans classical and relativistic statistical mechanics, examining the implications of these frameworks on the description of particle states.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant suggests that microstates can be represented by lists of positions and velocities, questioning the exclusion of acceleration from this representation.
  • Another participant argues that the state of the system is fully described by the canonical coordinates (position and momentum), which uniquely determine the system's location in phase space.
  • A different viewpoint emphasizes that in Newtonian statistical physics, the state is defined by coordinates and their first derivatives, while higher derivatives are determined by equations of motion.
  • One participant notes that in relativistic theory, the interactions of particles cannot be described by ordinary differential equations, which complicates the inclusion of acceleration.
  • It is mentioned that acceleration can be derived from forces acting on particles, while velocity is treated as a free parameter.
  • Another participant points out that in classical relativistic statistical mechanics, the states are defined by 4-positions and 4-momenta, with constraints that differ from the Newtonian case.
  • One participant contends that for interacting particles in relativistic theory, the state cannot be solely specified by positions and momenta due to the complex nature of forces involved.
  • A later reply suggests pausing the discussion on relativity to focus on the original question, which was posed in a more elementary context.

Areas of Agreement / Disagreement

Participants express differing views on the necessity of including acceleration in the calculation of microstates, with some advocating for its inclusion based on classical mechanics, while others argue against it, particularly in the context of relativistic theory. The discussion remains unresolved regarding the implications of these differing frameworks.

Contextual Notes

The discussion highlights the limitations of applying classical mechanics to relativistic scenarios and the assumptions involved in defining particle states. There is an acknowledgment of the complexity introduced by interactions among particles, particularly in relativistic contexts.

llisuhrtgslir
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I want to calculate the number of microstates in a system for, say, n indistinguishable particles in a 3D box. Some examples I see just represent one microstate as a list of positions. Other examples use a list of positions and a list of velocities (translational and rotational). And if you're supposed to use position and velocity, why not acceleration too? I can maybe see why you wouldn't use "jerk" and fifth derivatives of position and so on.
 
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Because the state of such is system is completely described by the canonical coordinates of the particles. Specifying the position and momentum of all the particles uniquely locates it in phase space.
 
llisuhrtgslir said:
I want to calculate the number of microstates in a system for, say, n indistinguishable particles in a 3D box. Some examples I see just represent one microstate as a list of positions. Other examples use a list of positions and a list of velocities (translational and rotational). And if you're supposed to use position and velocity, why not acceleration too? I can maybe see why you wouldn't use "jerk" and fifth derivatives of position and so on.

Those examples work within Newtonian statistical physics, where the state of many-particle system is specified by stating coordinates and their first derivatives. Higher derivatives are then determined by the equations of motion.

This is not valid in relativistic theory, where the interaction of the particles is no longer describable by such ordinary differential equations.
 
The acceleration on each particle is calculated from the force on the particles, which you can determine from a snapshot of the system, whereas the velocity is just a free parameter.
 
Jano L. said:
This is not valid in relativistic theory, where the interaction of the particles is no longer describable by such ordinary differential equations.

States of individual particles of a system in classical relativistic stat mech are given (in flat space-time) by the phase space of 4-positions and 4-momenta with the latter constrained to lie on the mass hyperboloid so it isn't much different from the Newtonian case.
 
Only if the particles are non-interacting. State of a system of interacting particles in relativistic theory is not specified by their positions and momenta only, because forces acting on them cannot be functions of the positions and momenta only.
 
Let's wait for the OP to come back before going into the intricacies of relativity theory. As the question was posed, no relativity theory was needed, so let us keep it nice and elementary.
 

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