Simple no-pressure cosmic model gives meaning to Lambda

[Jorrie]

Marcus, I will comment more fully later, but your Udays and especially light-Udays raise some concerns. A light-day has an established meaning in Physics and there is some confusion potential. Secondly, your Uday is a very long, non-cyclic time and perhaps a word that has such connotations would have been better; something like a Universal Time Constant. This specific one would not abbreviate well, because UT and UTC have already been established. Perhaps $U \tau$?

Us engineers are used to $\tau$ for time constants. :)

 

[Ken G]

Incidentally, I have a suggested minor change of form for your main equation for H(s). Instead of the coefficient 0.443, which occupies a somewhat arbitrary place, take its inverse cube root, which is 1.31, and place it under the s in your equation. Then 1.31 has the interpretation of "the stretch factor when the effective mass density of dark energy equals that of actual mass", so is a number that itself carries a meaning. Or, if you switch to a, take the inverse of 1.31 and that's the scale parameter when dark energy took over the lead. It's in the same spirit as your Uday parameter, just a meaningful scale for the stretch factor instead of a scale for the time parameter. I wouldn't recommend redefining the scale of s just to get a universal form for the equation, because s (or a) already has a unique meaning that relates directly to redshifts as you know, but this new form at least explicitly indicates the scale for s.

 

[marcus]

Marcus, I will comment more fully later, but your Udays and especially light-Udays raise some concerns. A light-day has an established meaning in Physics and there is some confusion potential. Secondly, your Uday is a very long, non-cyclic time and perhaps a word that has such connotations would have been better; something like a Universal Time Constant. This specific one would not abbreviate well, because UT and UTC have already been established. Perhaps $U \tau$?

Us engineers are used to $\tau$ for time constants. :)

Hi Jorrie, you could say that we don't have much NEED for a time unit name like Day or Universe Day because we can always talk around it and use a symbol for Hubble time, like 1/H_∞, or refer to the quantity as "our time unit 17.3 billion years".

Even if we do arrive at a unit name we like, we still might not make a lot of use of it. Might only need to use it occasionally.

Still, I'd like to try out some name. You've expressed reservations about Day and Uday. Maybe this other idea would work:

Aeon is a word associated with long spans of time. Roger Penrose has used that and I think also Paul Steinhardt may have used it. Anyway it is used.

So how about a magazine-style article on this simple version of the standard LambdaCDM where the title is

"From Aeon to Zeon"

The title would be just kidding, no need to discuss other people's "aeons", the whole point of the article (and this thread) is to explore introducing a time scale based on the cosmological curvature constant Λ and the eventual longterm distance growth rate H_∞ that we get from the curvature Λ.

In effect, the whole thing is about the zeon (whatever we happen to call it).

So the present age of expansion is 0.8 zeon, that's our way of saying "now".

And our distance unit is LZ instead of LY, or lz instead of ly.

And the current expansion rate is 1.2 per zeon, or more precisely 1.201 per zeon

and the longterm distance growth rate is 1 per zeon, which is our unit of expansion rate.

I hope that seems OK to you.

Also wondering how it sounds to Ken G, and others who might be reading the thread!

 

[Ken G]

I like the idea of using some version of "eon" for your time unit, you are talking about the single most fundamental long-time unit there is in our universe. Perhaps a "cosmological aeon", rather than aeon or zeon, because it could be abbreviated ca, not a or z. a is the scale parameter, z is redshift, and Z is metallicity, all important cosmological topics.

 

[Jorrie]

I like the idea of using some version of "eon" for your time unit, you are talking about the single most fundamental long-time unit there is in our universe. Perhaps a "cosmological aeon", rather than aeon or zeon, because it could be abbreviated ca, not a or z. a is the scale parameter, z is redshift, and Z is metallicity, all important cosmological topics.

Yea, what about "cosmaeon", still abbreviated ca and lca for distance? It is pronounced just like "cosmeon", but the latter is a trademark in the cosmetics industry. AFAIK, "Cosmaeon" has no established meaning. Aeon and Zeon both have known meanings, the latter in liturgy (http://en.wikipedia.org/wiki/Zeon_(liturgy)).

I'm busy with an article-style write-up, so maybe it could be titled "From Aeon to Cosmaeon".

 

[Ken G]

I do like cosmaeon. Perhaps a title like "How many eons in a cosmaeon?"