Current values for Friedman's scalar and its derivative?

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Discussion Overview

The discussion centers on the current values of Friedman's scalar, specifically the scale factor and its first derivative with respect to time, within the context of cosmology. Participants explore the implications of different conventions and the relevance of the Hubble parameter.

Discussion Character

  • Technical explanation, Conceptual clarification, Debate/contested

Main Points Raised

  • One participant asks for the current values of Friedman's scalar and its first derivative.
  • Another participant suggests that the scale factor ##a(t)## is convention-dependent, typically set to ##a(t_0) = 1## at the current time ##t_0##, and relates its derivative to the Hubble parameter ##H_0##.
  • A further inquiry is made regarding the current value of the Hubble parameter, emphasizing its dimensionality as a rate.
  • One participant provides a link to an external source for the Hubble constant but notes that the forum is not intended to serve as an encyclopedia.
  • Another participant reiterates the importance of ratios of the scale factor over time, indicating that ##a(t)## alone lacks meaning without context.

Areas of Agreement / Disagreement

Participants express differing views on the interpretation of the scale factor and its relevance, with no consensus reached on the specific current values or the best way to present them.

Contextual Notes

The discussion reflects varying conventions in cosmology regarding the scale factor and the Hubble parameter, with some assumptions about definitions and context remaining unaddressed.

exmarine
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What are the current values for Friedman's scalar and its first derivative with respect to time?

Thanks.
 
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Are you referring to the scale factor ##a(t)##. It depends on your convention. A typical convention is to choose ##a(t_0) = 1##, where ##t_0## is the current time. Its derivative is then directly given by the Hubble parameter ##H_0 = \dot a(t_0)/a(t_0) = \dot a(t_0)##.
 
Yes, what is the current value of the Hubble parameter? It should be some number per unit time?
 
exmarine said:
Yes, what is the current value of the Hubble parameter? It should be some number per unit time?
a(t) doesn't mean itself anything. The ratios of a(t) matters. Like a(t_0)/a(t_1)
 

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