Picturing the history of the world's expansion

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Discussion Overview

The discussion focuses on the visualization of the scale factor function, which describes the history of the universe's expansion based on observational data. Participants explore different ways to conceptualize the shape of this curve, including both technical and humorous comparisons.

Discussion Character

  • Exploratory
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants propose various shapes for the scale factor curve, including a straight line, exponential growth, a convex ramp, and a humorous anatomical comparison.
  • One participant suggests that the curve could be described as a "convex-then-concave ramp" or a "tilde ramp," emphasizing the curve's characteristics at different times.
  • Another participant notes that the real curve starts out vertical at time zero, indicating an infinite slope and rapid expansion, before becoming convex and then concave.

Areas of Agreement / Disagreement

Participants express differing views on how to visualize the scale factor curve, with no consensus on a single description. The humorous anatomical comparison adds a light-hearted element to the discussion, but the technical aspects remain contested.

Contextual Notes

Participants reference specific characteristics of the curve, such as its behavior at time zero and the presence of an inflection point, without resolving the implications of these features.

Who May Find This Useful

This discussion may be of interest to those exploring cosmology, the expansion of the universe, or the visualization of mathematical functions in a conceptual context.

The universe's expansion curve is most like:

  • a straight-line ramp (steady expansion rate)

    Votes: 0 0.0%

  • an exponential growth curve (increasing rate)

    Votes: 2 66.7%

  • a convex ramp (decreasing slope)

    Votes: 0 0.0%

  • silhouette of a woman's breast down to the nipple

    Votes: 1 33.3%
  • Total voters
    3
marcus
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The scale factor function (they write it R(t) or a(t)) gives the history of the expansion of the universe, as calculated from observational data. The slope at any moment is the expansion rate at that moment. Which of these best describes how you picture this curve?

1. straightline ramp (constant expansion rate)
2. exponential growth (increasing slope)
3. convex ramp (positive but decreasing slope)
4. silhouette of a woman's breast down to the nipple

http://nedwww.ipac.caltech.edu/level5/March03/Lineweaver/Figures/figure14.jpg

the solid dark line is the curve giving the best fit to current astronomical data
 
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4. silhouette of a woman's breast down to the nipple

Oh, LOL!

And so, would it then be best to describe some of the slopes as "perkier" than the others? LOL! :0)
 
Originally posted by Nacho
Oh, LOL!

And so, would it then be best to describe some of the slopes as "perkier" than the others? LOL! :0)

It was a conversation with you in "Newton's" cosmological constant thread that sparked the particular idea so I have to share credit with you on it, and this discussion of the shape of the scale-factor curve in general.
 
Well?

Is everybody scared off by the anatomical comparison?

Would you rather the curve were described as a

"convex-then-concave ramp"?

afterthought: or maybe a "tilde ramp"?

the tilde symbol has the right kind of hump-then-dip, like a horizontal version of the ESS curve, so, if you make an upwards-sloping tilde, it looks about right.

the real curve starts out at time zero essentially vertical---infinite slope, and is convex and rounds off, then has an inflection point and becomes concave. being vertical at time zero (a time when expansion was very rapid) is essential to the shape
 
Last edited:
you only get one of these per 1,000 posts, marcus. :wink:
 
Originally posted by Phobos
you only get one of these per 1,000 posts, marcus. :wink:

Yes, we have to keep it on the up and up!
I believe in fact that she is wearing a low-cut evening gown.
So everything is perfectly proper after all.

BTW Phobos, how about doing us a favor and responding to
Shadow's question in the Astronomy QA game. I believe Shadow
is a comparative newcomer and he just posted a nice one. I'm
refraining from answering because its time for some other people to get involved, with fresh interests.
 
Last edited:

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