I really like this version:
http://www.einsteins-theory-of-relativity-4engineers.com/beta_3/cosmocalc_code_2012.htm
so I changed over to it, in my signature, from the older one:
http://www.einsteins-theory-of-relativity-4engineers.com/cosmocalc_2010.htm
Visually the new one "beta 3" is handsome.
I like the blue info button texts (pedagogically they add a lot)
I really like the "time for a one percent increase" entry.
The URL for the new version says "beta 3", is it this "beta 3" version which will now become the official one? If so, I'm delighted.
If not, would you be willing to leave "beta 3" online at that address, so that I can keep that in my signature and work with that?
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I'm worried because the "beta 3" apparently didn't go in. When I click on the older link I don't get that one. BTW it's not vanity

You didn't need to mention me in the acknowledgments, although it was kind. Quite apart from acknowledgments, I like the new version because it's got considerably more appeal and pedagogical value!
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You asked about the choice of Y in this thread, where I'm experimenting with different ways to present the Friedmann model to beginners. No special reason. Could be J and J
∞ instead of Y and Y
∞. Or Q, or W.
It would be cumbersome to write T
H or T
Hubble. Gum things up with subscripts. I just want a single letter for the Hubble time 1/H, and it could be any letter that is not too closely associated with something else. E or M or V or P would not be good. I just picked Y without thinking much about it. Let's see how the basic differential equation looks with different letters.
Y' = (3/2)[ 1 - (Y/Y
∞)
2], where Y is the current value of the Hubble time 1/H.
J' = (3/2)[ 1 - (J/J
∞)
2], where J is the current value of the Hubble time 1/H.
Q' = (3/2)[ 1 - (Q/Q
∞)
2], where Q is the current value of the Hubble time 1/H.
Do you have any preference? or ideas about choice of symbol? The more I think about it the more I like Y. It reminds me of the letter T, the usual symbol for an interval of time, but with the arms raised a little. It's easy to remember that it stands for a really important longish interval of time (at least for me.)
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I like the "1% Hubble time" quantity we were talking about. A lot. It is the time needed for distances to grow by 1% (at their current growth speed.) That is a good handle on distance growth for beginners to get hold of.
Picture the world containing a lot of stationary observers (or objects) and a whole bunch of distances between them. Each distance is growing according to how big it is--in proportion to its current size. At a speed that is proportional to its current length.
I think that is how to picture expansion, and saying "1% Hubble time" to beginners inculcates that picture. It plants the right seed in their minds, when you say "time needed for distances to grow by 1%, at the present rate".
The picture planted is not of MOTION but of growth like in a bank account. It is so important to get that right, at the start.
So then we move on from there. Currently the 1%Y is 139 My which means 1/139% growth in a million years. And 1% of the eventual Y, denoted Y
∞, is 163 My which means 1/163% growth in a million years.
And the Y time itself is increasing according to this simple differential equation:
Y' = (3/2)[ 1 - (Y/Y
∞)
2] which if we plug in current values 139 and 163 gives
Y' = (3/2)[ 1 - (139/163)
2] = (3/2)[ 1 - 0.728] = 0.41
So we even have a handle on how rapidly the Hubble time has been growing recently and will be growing in the immediate future. Great! And nobody has, so far, had to look at a Megaparsec, or 8πG, or imagine galaxies zooming (thru space ) at km/s, or some kind of "dark energy" pushing on the galaxies so they will zoom faster thru space

We are talking about an enormous avoidance of fallacious mental garbage and clutter, basically just by including this "1% Hubble time" idea and letting beginners get familiar with it. Have you to thank in part. Thanks

