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Cosmo calculators and tabulators a primarily about the PAST expansion history and they give learners hands-on understanding by being able to vary the model parameters and see change. That's good. I sometimes notice a difference here at PF between how posters with mainly verbal understanding think and how those do who also have some of the quantitative feel you get from playing with an equation model of the cosmos or with one of the online interactive models.
However the murky talk about "dark energy" and all that is essentially about a FUTURE leveling off of the declining Hubble expansion rate, to about 60 km/s per Mpc. Or if you like about the plateauing of its reciprocal, the Hubble time, at about 16.3 billion years. And this adds a very interesting feature to our universe, which has to do with the FUTURE--namely the CEH (cosmic event horizon).
I'm not sure of its exact estimate right now, somewhere between 15 and 16 Gly. It is gradually converging to 16.3 Gly. So let's say it is now "around 16" billion lightyears.
This is a very interesting thing. If a galaxy is NOW less than ~16 Gly from us and we send them some light TODAY the light will eventually get there. Though if the galaxy is very close to the 16 Gly limit it could take a very very long time to reach them. The closer it is to the limit the longer it will take, because given the expansion of distances going on it can just barely make it, traveling at the speed of light.
However if the galaxy is NOW beyond the ~16 limit and we send them a flash today it will never get there.
And it works both ways. We see lots of galaxies out there which are farther than 16 Gly. In fact most of the galaxies you can see with a telescope are farther than that. But if something happens TODAY in one of those galaxies we will never see it. They are beyond the current event horizon and they cannot now send us a message that will ever reach us.
So that is an interesting feature of the universe which basically has to do with this plateauing of the Hubbletime at 16.3 Gly and involves future time. Can a cosmo tabulator give us hands-on experience with future expansion as well as experience with our universe's past expansion history?
You'd have to be able to play around with the Hubbletime parameters (ie. with the two expansion rate parameters) and see how the distances change. Namely the distance NOW to the galaxy we want to send light to, and the distance THEN to the galaxy when the light finally gets there (despite all the expansion that will have been happening).
Does anyone know of an online resource like this, or have any ideas? It could be helpful for people learning about cosmology, and kind of neat actually
However the murky talk about "dark energy" and all that is essentially about a FUTURE leveling off of the declining Hubble expansion rate, to about 60 km/s per Mpc. Or if you like about the plateauing of its reciprocal, the Hubble time, at about 16.3 billion years. And this adds a very interesting feature to our universe, which has to do with the FUTURE--namely the CEH (cosmic event horizon).
I'm not sure of its exact estimate right now, somewhere between 15 and 16 Gly. It is gradually converging to 16.3 Gly. So let's say it is now "around 16" billion lightyears.
This is a very interesting thing. If a galaxy is NOW less than ~16 Gly from us and we send them some light TODAY the light will eventually get there. Though if the galaxy is very close to the 16 Gly limit it could take a very very long time to reach them. The closer it is to the limit the longer it will take, because given the expansion of distances going on it can just barely make it, traveling at the speed of light.
However if the galaxy is NOW beyond the ~16 limit and we send them a flash today it will never get there.
And it works both ways. We see lots of galaxies out there which are farther than 16 Gly. In fact most of the galaxies you can see with a telescope are farther than that. But if something happens TODAY in one of those galaxies we will never see it. They are beyond the current event horizon and they cannot now send us a message that will ever reach us.
So that is an interesting feature of the universe which basically has to do with this plateauing of the Hubbletime at 16.3 Gly and involves future time. Can a cosmo tabulator give us hands-on experience with future expansion as well as experience with our universe's past expansion history?
You'd have to be able to play around with the Hubbletime parameters (ie. with the two expansion rate parameters) and see how the distances change. Namely the distance NOW to the galaxy we want to send light to, and the distance THEN to the galaxy when the light finally gets there (despite all the expansion that will have been happening).
Does anyone know of an online resource like this, or have any ideas? It could be helpful for people learning about cosmology, and kind of neat actually
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