Dark Energy & Age of Universe

[clpratt]

If Dark Energy is increasing the expansion rate of the universe (ie. Expansion rate is not constant) wouldn't that effect the Hubble "constant", Red shift with time, and our current estimates of the age of the universe?? It was nearly 15 years ago, there was some debate whether the universe was 20 billion years old, or 8.5 billion plus a host of estimates between these two figures. Improvements in the measuring the hubble constant resulted in a midway figure of around 13.6 -13.8 billion years. Is it time to tweak the age estimate again?

[Chris Peterson]

If Dark Energy is increasing the expansion rate of the universe (ie. Expansion rate is not constant) wouldn't that effect the Hubble "constant", Red shift with time, and our current estimates of the age of the universe?? It was nearly 15 years ago, there was some debate whether the universe was 20 billion years old, or 8.5 billion plus a host of estimates between these two figures. Improvements in the measuring the hubble constant resulted in a midway figure of around 13.6 -13.8 billion years. Is it time to tweak the age estimate again?

No. The age of the Universe isn't determined by the Hubble parameter alone. The formula used also includes a function whose value depends on the cosmological density factors (which includes the effect of dark energy or a cosmological constant). These values have been measured, and the resulting scale value is around 0.99. That means that the effect of expansion has barely tweaked the Hubble parameter, which is why using it alone yields a close value for the age of the Universe. But more accurate calculations do utilize the more complex formula. So the current 13.6-13.8 billion year age remains solid in spite of recent observations of an increasing rate of expansion.

[harry]

G'day from the land of ozzzzzzzz

You said

So the current 13.6-13.8 billion year age remains solid in spite of recent observations of an increasing rate of expansion.

Do you think this is a phase or pure origin of all or part of?

How do you expalin the evoltion of galaxies and mergers and super cluster of galaxies in this short period of time?

Not to mention the phase change in star formation

[Chris Peterson]

So the current 13.6-13.8 billion year age remains solid in spite of recent observations of an increasing rate of expansion.

Do you think this is a phase or pure origin of all or part of?

How do you expalin the evoltion of galaxies and mergers and super cluster of galaxies in this short period of time?

I'm not sure exactly what you're asking. The beginning of the Universe was an instantaneous event, which happened 13.7 ± 0.1 billion years ago. That doesn't mean that the Universe sprang into existence in its present form.

Galaxy formation and evolution is, of course, an area of active research. The currently best supported theory argues that the Universe initially consisted almost entirely of H, He, and dark matter. Fluctuations in dark matter density caused accelerated clumping, and the first galaxies, or large groups of stars, were developing by 500 million years. Galaxies grew by accretion, a process that continues to this day.

[harry]

G'day Chris

You said

The beginning of the Universe was an instantaneous event, which happened 13.7 ± 0.1 billion years ago. That doesn't mean that the Universe sprang into existence in its present form.

Galaxy formation and evolution is, of course, an area of active research. The currently best supported theory argues that the Universe initially consisted almost entirely of H, He, and dark matter. Fluctuations in dark matter density caused accelerated clumping, and the first galaxies, or large groups of stars, were developing by 500 million years. Galaxies grew by accretion, a process that continues to this day.

From one point or evenly spread?

I know the BBT like the back of my hand. I just want to know where you are coming from.

[harry]

G'day Chris

This maybe of interest in reading

http://arxiv.org/abs/0809.2404
Accretion onto Seed Black Holes in the First Galaxies

Authors: Milos Milosavljevic, Volker Bromm, Sean M. Couch, S. Peng Oh
(Submitted on 14 Sep 2008)

Abstract: The validity of the hypothesis that the massive black holes in high redshift quasars grew from stellar-sized "seeds" is contingent on a seed's ability to double its mass every few ten million years. This requires that the seed accrete at approximately the Eddington-limited rate. In the specific case of radiatively efficient quasiradial accretion in a metal-poor protogalactic medium, for which the Bondi accretion rate is often prescribed in cosmological simulations of massive black hole formation, we examine the effects of the radiation emitted near the black hole's event horizon on the structure of the surrounding gas flow. We find that the radiation pressure from photoionization significantly reduces the steady-state accretion rate and renders the quasiradial accretion flow unsteady and inefficient. The time-averaged accretion rates are a small fraction of the Eddington-limited accretion rate for Thomson scattering. The pressure of Ly-alpha photons trapped near the HII region surrounding the black hole may further attenuate the inflow. These results suggest that an alternative to quasiradial, radiatively efficient Bondi-like accretion should be sought to explain the rapid growth of quasar-progenitor seed black holes.

[Chris Peterson]

From one point or evenly spread?

I don't understand the question.

[harry]

G'day Chris

I think it is better that you explain your version of the BBT.

[clpratt]

We seem to be drifting off topic here. Chris' first response seems most cogent. If the current formula for calculating the age of the Universe is barely affected by the increased rate of expansion related to Dark Energy now, 13.7 billion years after the creation of the universe; then as expansion continues to increase in rate, will the calculations using the current model still be close in say, another 13.7 billion years??

I don't think any of us will still be around to hold you to any response you may give.

[Chris Peterson]

I think it is better that you explain your version of the BBT.

I don't think so. Since I don't do original research in this area, I depend on my scientific training only for evaluating the quality and reasonableness of other people's work. And my opinion is that the lambda-CDM model is doing a pretty good job of explaining our observations (and that is not my version of the BBT). While I recognize that this is work in progress, and many questions remain, I do think it is likely that the theory is broadly correct.

[Chris Peterson]

If the current formula for calculating the age of the Universe is barely affected by the increased rate of expansion related to Dark Energy now, 13.7 billion years after the creation of the universe; then as expansion continues to increase in rate, will the calculations using the current model still be close in say, another 13.7 billion years?

Yes. Just to be clear, what I was pointing out is that there are two formulas that can be used. The full expression giving the age of the Universe is

t = 1/H0 * f(e1, e2, e3, ...)

where f is a scaling function depending on the energy densities of the different types of energy making up the Universe. Right now, f evaluates to something like 0.99, so we can leave it out and simply use t = 1/H0 to get an age that is accurate within our measurement uncertainties. Given a long enough time, f will change enough that 1/H0 by itself won't be accurate. But H0 itself presumably won't change, nor will our ability to perform accurate calculations (assuming we have the ability to accurately measure the energy density components).

[astrolabe]

Hello Chris,

So the current 13.6-13.8 billion year age remains solid in spite of recent observations of an increasing rate of expansion.

Do you think this is a phase or pure origin of all or part of?

How do you expalin the evoltion of galaxies and mergers and super cluster of galaxies in this short period of time?

I'm not sure exactly what you're asking. The beginning of the Universe was an instantaneous event, which happened 13.7 ± 0.1 billion years ago. That doesn't mean that the Universe sprang into existence in its present form.

Galaxy formation and evolution is, of course, an area of active research. The currently best supported theory argues that the Universe initially consisted almost entirely of H, He, and dark matter. Fluctuations in dark matter density caused accelerated clumping, and the first galaxies, or large groups of stars, were developing by 500 million years. Galaxies grew by accretion, a process that continues to this day.

Fluctuations?

[Chris Peterson]

Fluctuations?

Not sure of the question. "Fluctuations" means that the density of the very early Universe wasn't perfectly uniform. That's the only thing required for structure to evolve. As to why it wasn't uniform, that's still a matter of debate. There are some interesting ideas, but we need better observations to settle the question.

[astrolabe]

Hello Chris,

The second half of your reply was what I was looking for. Thanks. It seems you did get the question indeed.

BTW Happy New Year to you and the Forum!