Inflation and Element Formation: Irreconcialble?

[aboro]

I added an "ago" to your quote. Did you mean to have one there? Yes. If not, then I do not understand the sentence. You did understand the sentence

The real situation in our expanding (not static) universe is similar to what I described above, except that the radius of our *observable* universe is even larger. It's some 46 billion light years, even though the age is only 13.7 billion years. The reason for this is that the universe is expanding.

But if I understand correctly from the Table Marcus included in post #2, it appears that the Universe started to decelerate when it was about 5.4 billion years old. Do we know what caused the deceleration to occur? How is this deceleration reconciled with what is today regarded by the cosmological community as an “expanding” universe?


Have you read the Cosmology FAQ thread on "faster than light" expansion? It's the fourth link I put in post #8.

I just did. Thanks for calling it to my attention. This subject is drop-dead interesting.

 

[marcus]

But if I understand correctly from the Table Marcus included in post #2, it appears that the Universe started to decelerate when it was about 5.4 billion years old. Do we know what caused the deceleration to occur? How is this deceleration reconciled with what is today regarded by the cosmological community as an “expanding” universe?

Hi Aboro, it seems to me now that I blundered when I posted that table. Too much unexplained info for now. I think Cepheid and some of the others are engaging very successfully with your questions and probably I should just be quiet ("too many cooks" what you don't need is more distraction! just keep focused on a single question and quiz people until you understand.) Probably best just to ignore the table in my post #2.

 

[marcus]

However…this is such an interesting thread that I simply cannot resist jumping in! I really like your question about the MAXIMUM in the D_then column! It doesn't mean the universe reaches a maximum size and then shrinks. D_then is not the size of the universe, it's more interesting than that.

We can classify galaxies by how much their light waves have been stretched by the time we receive them. That gives a handle on when it was they emitted the light which we are receiving from them today. D_thenis the distance that galaxy was back then when it emitted the light.

You noticed a MAXIMUM in the row labeled S=2.458, also labeled a=0.407 (this is just the reciprocal 1/S).
Let's round off for convenience and say S = 2.5, and a = 0.4.

If you see a galaxy with your telescope and you determine that its waves have been stretched by a factor of 2.5 then it emitted the light back when DISTANCES WERE 40 PERCENT what they are today. And the table tells you all kinds of stuff about that galaxy.
How far from our matter it was when it emitted the light (Dthen) and how far it is now (Dnow) and how fast it was receding then, and now, and HOW OLD the universe was at that that moment when the light was emitted.

{\scriptsize\begin{array}{|r|r|r|r|r|r|r|r|r|r|r|r|r|r|r|r|} \hline a=1/S&S&T (Gy)&R (Gly)&D_{now} (Gly)&D_{then}(Gly)&V_{now} (c)&V_{then} (c) \\ \hline 0.091&11.000&0.4726&0.7105&31.447&2.859&2.18&4.02\\ \hline 0.106&9.469&0.5920&0.8894&30.231&3.193&2.10&3.59\\ \hline 0.123&8.151&0.7414&1.1130&28.920&3.548&2.01&3.19\\ \hline 0.143&7.017&0.9284&1.3922&27.509&3.921&1.91&2.82\\ \hline 0.166&6.040&1.1621&1.7401&25.990&4.303&1.80&2.47\\ \hline 0.192&5.199&1.4542&2.1728&24.357&4.684&1.69&2.16\\ \hline 0.223&4.476&1.8185&2.7087&22.602&5.050&1.57&1.86\\ \hline 0.260&3.853&2.2723&3.3685&20.721&5.378&1.44&1.60\\ \hline 0.302&3.317&2.8355&4.1732&18.711&5.642&1.30&1.35\\ \hline 0.350&2.855&3.5313&5.1413&16.574&5.805&1.15&1.13\\ \hline 0.407&2.458&4.3851&6.2820&14.316&5.825&0.99&0.93\\ \hline 0.473&2.116&5.4225&7.5870&11.954&5.650&0.83&0.74\\ \hline 0.549&1.821&6.6657&9.0202&9.516&5.225&0.66&0.58\\ \hline 0.638&1.568&8.1292&10.5121&7.046&4.494&0.49&0.43\\ \hline 0.741&1.350&9.8148&11.9676&4.596&3.406&0.32&0.28\\ \hline 0.861&1.162&11.7095&13.2878&2.224&1.915&0.15&0.14\\ \hline 1.000&1.000&13.7872&14.3999&0.000&0.000&0.00&0.00\\ \hline 1.162&0.861&16.0138&15.2745&2.081&2.417&0.14&0.16\\ \hline 1.331&0.751&18.1309&15.8712&3.784&5.036&0.26&0.32\\ \hline 1.524&0.656&20.3179&16.3092&5.321&8.110&0.37&0.50\\ \hline 1.746&0.573&22.5554&16.6216&6.693&11.686&0.46&0.70\\ \hline 2.000&0.500&24.8287&16.8396&7.910&15.820&0.55&0.94\\ \hline \end{array}}

You are very observant, I believe, to have noticed that Dthen maximum in the S=2.5 row!
Of course it is not the size of the universe. It is the distance that a very special galaxy was from us at a very special moment (or more exactly that special class of galaxies whose light was emitted when distances were 40% of today's size and whose light arrives more reddish because wavelengths enlarged by factor S=2.5.)
Each row of table tells you about a different class of galaxies.

And if the row has S much bigger than 11 then it tells you not about light from stars and galaxies but about the heat-glow of hot gas that has not formed stars yet.

Aboro, did you notice the special row S=1 ?
That is the row for what we would see with no wave stretch at all. Where the light we receive today from something was emitted today and there is essentially no change in wavelength.
In other words S=1 denotes the PRESENT.

So naturally the distance is zero! Because we are seeing the thing as it is today. Dthen in that row equals Dnow, both distances are the same and both are zero.

 

[cepheid]

The real situation in our expanding (not static) universe is similar to what I described above, except that the radius of our *observable* universe is even larger. It's some 46 billion light years, even though the age is only 13.7 billion years. The reason for this is that the universe is expanding.

But if I understand correctly from the Table Marcus included in post #2, it appears that the Universe started to decelerate when it was about 5.4 billion years old. Do we know what caused the deceleration to occur? How is this deceleration reconciled with what is today regarded by the cosmological community as an “expanding” universe?

Hi aboro,

The universe has always been expanding: the separation between any two particular objects has always been increasing with time. When we say that the universe has been "decelerating" or "accelerating", what we mean is that the expansion has been "slowing down" or "speeding up." So, it is a statement about the rate of the expansion. In the beginning, the universe began expanding rapidly, but then that expansion slowed with time. In the relatively recent past, this trend reversed itself, and the outward expansion began to speed up.

EDIT: You asked what caused the deceleration to occur, initially. Although the physics of this is determined by General Relativity, a complicated theory, you can get some intuition for it even from high school level physics and the simpler gravitational theory of Newton. In Newtonian gravity, everything with mass exerts a force on everything else with mass, and we call this force gravity. So, if you take a bunch of objects and throw them outward away from each other in all directions, you would expect their outward motion to be slowed due to the mutual gravitational attraction of those objects. This is what cosmologists expected: that the expansion should be ever slowing down due to the mutual gravitational attraction of all the matter in the universe. In the mid 90s, astronomers discovered that this was not the case: it is actually speeding up. Newtonian gravity cannot explain this. It was a super shocking and unexpected discovery: like as if you threw your keys in the air, and instead of gravity slowing down their upward motion, that upward motion got faster and faster and the keys accelerated away from you, escaping. However, General Relativity can explain this, with something that can be fairly naturally added to the equations called "the cosmological constant."