Another short question on Rovelli's book

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The discussion centers on Carlo Rovelli's concept of the "timeless double pendulum" as presented in his book. Specifically, it clarifies that the phase space is two-dimensional, contrary to the expectation of four dimensions based on the two coordinates (a and b) and their corresponding conjugate momenta. Rovelli's definition of "relativistic phase space" diverges from the traditional understanding of phase space as the cotangent bundle of configuration space. The two-dimensionality arises from the parametrization of the phase space by the variables alpha and beta, as indicated in the evolution equation f(a,b,alpha,beta).

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nrqed
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On page 109 he does the example of the "timeless double pendulum".
He says that the phase space is two dimensional. I think I am getting confused with all the spaces he defined :biggrin:

Why 2?? I would have expected 4 since there are two coordinates, a and b, and their conjugate momenta.
 
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nrqed said:
On page 109 he does the example of the "timeless double pendulum".
He says that the phase space is two dimensional. I think I am getting confused with all the spaces he defined :biggrin:

Why 2?? I would have expected 4 since there are two coordinates, a and b, and their conjugate momenta.

It looks like his phase space "relativistic phase space" isn't simply the usual one we're familiar with (cotangent bundle of configuration space). Just a bit below the comment about dimension 2, he gives the evolution equation f(a,b,alpha,beta) and states that the phase space (space of ellipses in (a,b) space) is parametrised by alpha and beta hence 2 dimensional.
 

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