Our ideas on v_rec/c column added to J's calculator

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Discussion Overview

The discussion revolves around the potential addition of a 9th column to Jorrie's cosmic history calculator, specifically focusing on the recession speed history of a representative galaxy at Hubble distance. Participants explore the implications of this addition, considering its educational value and the complexity it may introduce for beginners.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants suggest that a 9th column could enhance understanding of recession speed, which is often misunderstood as a galaxy's inertia rather than a result of cosmic expansion.
  • Others argue that recession speed can be easily calculated using existing columns, implying that the addition may not be necessary.
  • There is a proposal for an instruction manual to accompany the calculator, providing users with the formulas used, which could aid in understanding the calculations involved.
  • One participant emphasizes the need to clarify that recession speed relates to the change in separation between stationary observers in the cosmic microwave background (CMB) frame, rather than ordinary motion.
  • Another point raised is the importance of tracking a single representative galaxy's recession speed over cosmic history, suggesting that this could provide valuable insights into the expansion of the universe.
  • Participants discuss the mathematical representation of recession speed, debating whether to label it as "recession speed," "vrec/c," or "Rnow da/dT," each with different implications for user understanding.

Areas of Agreement / Disagreement

Participants express a mix of opinions regarding the necessity and utility of the 9th column. While some see value in its addition for educational purposes, others believe it may complicate the calculator unnecessarily. The discussion remains unresolved, with no consensus on the best approach.

Contextual Notes

There are uncertainties regarding the impact of adding a 9th column on user comprehension, as well as the potential need for additional explanatory materials to accompany the calculator. The discussion also highlights the complexity of accurately conveying the concept of recession speed to beginners.

  • #31
yeah I was thinking of having 3 examples provided it doesn't make the manual too long.
 
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  • #32
Mordred said:
yeah I was thinking of having 3 examples...
Good. From my experience writing first-draft material, I'd urge not to worry about too long and include stuff. Let the editor shorten it by making cuts as he or she wishes.

Exercises are good. I hope you already have 3 picked out. But if you include more and some aren't used in the main manual the others can go into a "supplemental exercises" PDF file attachment. You never know how useful that might be. Let's write down any ideas for exercises we have.

That magic "deja vu" date, when everybody's recession speed was (once before) just the same as what it is today, I think was around year 3 billion. We could use Jorries "tablemaker" to find out the answer more precisely.
 
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