It is generally agreed that the age of the U is roughly 13.8 Gy.
How did they determine that? does it come from Friedman equation and/or by experimental data?
Can it be determined without a theoretical model, at all?
Thanks

It is generally agreed that the age of the U is roughly 13.8 Gy.
How did they determine that? does it come from Friedman equation and/or by experimental data?
Can it be determined without a theoretical model, at all?
Thanks
It can't be calculated theoretically; it depends on a number of parameters. The main ones are the density of normal (baryonic) matter, cold dark matter, and radiation (including both photons and neutrinos), a cosmological constant and the Hubble constant.
Age of the universe  Wikipedia, the free encyclopediaMeasurements of the cosmic background radiation give the cooling time of the universe since the Big Bang, and measurements of the expansion rate of the universe can be used to calculate its approximate age by extrapolating backwards in time.
Lots more detail on that page...
Thanks Strange, I had read that article, but there is something that I do not understand:
The main factor is 1/H_0 , which is mofified by a factor F (which is only fractional)
I do not see the relation between H_0 and the age of U. Can you tell me why the should be related at all?
Suppose we say that the current value is correct and that the age of the U is 10 times grater: 144 Gy. What can disprove that?
Thanks!
The Hubble parameter is the relationship between distance and time. At a very simple level, you can think of this describing a graph of the distance between two points (any two) versus time. This is a straight line and, as you go back in time, there is a point where the distance is zero. That is treated as time 0.
The model is somewhat more complex than that, taking into account various other factors such as the energy density. Ultimately it is a solution to the equations of GR.
The only way that the universe could be much older is if that straightline relationship no longer holds at some point in the past; e.g. the universe started out large and old, and then started expanding. If there were such a "static" period then it would have to be before the evidence we have that is consistent with expansion. So for example, the CMB in this model is dated at about 380,000 years after t0. So the universe has been expanding since at least that time. But there is a lot more evidence (that I don't fully understand) which is consistent with the model back to a fraction of a second after t0.
The other way the age could be wrong is if the current model is completely wrong. But the model is consistent with all observations and no one has yet come up with a better one.
Haha, as we like to say in science, we can never be proven right, only proven wrong :P
It doesn't matter. In your words, "1 cm" or "the distance between you and any object" (*). Just pick a distance and plot a graph of how it changes over time as represented by the Hubble factor. You will get a straight line that intercepts the x axis at some point. Call that t0. It will be about 13.8 billion years before now.
(*) Obviously, in reality, the points need to be far enough apart to be affected by expansion. But for this simple mathematical exercise, that is irrelevant.
It seems you are taking for granted 2 factors:
 that all points where in the same place at t0 and that
 the rate is 1/D every second, so, over time, 1cm has grown by ...+1/2+1/3...+1/n.
This is not stated by the theory,
 at BB(t0): we do not know the dimension of U, space may have already been infinite, it says
 H might have had any value , why can't it be (1)+ 1/10^18 from the beginning?
What is the evidence that T cannot be 140 Gly?
The radius of the visible universe being 46 Gly would mean that average velocity of expansion has been 1/3 C, which is more realistic than 3 C
That is a conclusion  look at the graph you have plotted. (You have done that, haven't you?)
That is based on observation. (Actually it is now known not to be constant; expansion started accelerating at some point.) the rate is 1/D every second
See the posts above.What is the evidence that T cannot be 140 Gly?
Only if the objects at the edge of the universe had travelled at a constant velocity, rather than a constant expansion.The radius of the visible universe being 46 Gly would mean that average velocity of expansion has been 1/3 C, which is more realistic than 3 C
I have not, I have deduced by your propositions. But that is not true. You are saying that at BB all energy/matter was in 1 cm.
where did you learn that?
That is not true, too.That is based on observation.
the only real observation is redshift, all the rest is model dependent.
I was asking, please tell me from what/where in the model you deduce that expansion rate is (roughly of course) 1/D
Last edited by whizkid; June 27th, 2014 at 06:14 AM.
There are many observations. Red shift was one of the first. There are also things like the temperature of the CMB, the relative proportions of hydrogen, helium and lithium isotopes, and may other things. Obviously the interpretation of these is model dependent  we are after all talking about science which is all about building models and testing them. In this case the model existed before any of the observations were made; they were all found to be consistent with the model. The model has, of course, been adjusted based on the evidence. Currently it is the only accepted model because it is the only one that fits all the data. People are constantly trying different models but so far no one has come up with a better one.
But this is not an area I know a huge amount about so perhaps you should study this: Ned Wright's Cosmology Tutorial
(Then in future you can answer my questions!)
[QUOTE=Strange;576177]All the elements you mention are interpreted through the model, exactly like redshift.
I have studied thoroughly that (and even better calculator) and I'll be glad to answer any your question,
But I am enquiring about the model, if you know, tell me where it is said or how you deduce that the espansion rate must be 1/D. Why should it be like that in the first place? Is all that in friedman equation?
do you get that from Ned Wrights?
Can you discuss Friedman?
Of course they. As you have extensively studied these things, you must either understand why the model is the best one we currently have or you must have an alternative model that you can publish in a peerreviewed journal.
I don't have any more time to waste on this. I suggest you take your questions to the Cosmoquest forum. There are people there with a lot more expertise than me (including many professionals in the field) who will be able to give you far better answers than I can.
Your response is irrational, Strange. I have not said it is not the best model or that there is a better model.
I asked you only if you are able to discuss Friedman equations.
if you are not, I asked if you know the relation between time and espansion rate, and how you decide its development over time.
If you have not time, it is another story!
btw, I tried to register at your site, but at a random question "the colour of the big spot of Jupiter" I answered "red" and they refused to register me as they said it is wrong. Is that normal?
Sorry, but all of your threads turn into "I don't understand it so it must be wrong." That may not be your intention but that is how it comes across.
No. Markus Hanke is one of the few people on this forum who understands the math behind these things.I asked you only if you are able to discuss Friedman equations.
Because all the evidence is consistent with a model based on a constant expansion rate.if you are not, I asked if you know the relation between time and espansion rate, and how you decide its development over time.
Not my forum. I have no idea why that should happen; there may be a bug in the registration system. You could try contacting one of the moderators.btw, I tried to register at your site, but at a random question "the colour of the big spot of Jupiter" I answered "red" and they refused to register me as they said it is wrong. Is that normal?
That's not fair, Strange, I always recognize I do not understand, (when I don't)
I am not asking for maths, just for the concepts of the FLRW metric and how these translate into conjectures about age, size and distances of the U.
Just answer what you know, than , hopefully, Marcus will complete:
In the F equations the spacetime curvature ds (LHS) depends on (RHS) matter, density and pressure, right?
The same LHS element is referred to as
...derived from field equations. is the Hubble parameter,
is that right? if so:
what has H to do with spacetime curvature?
H just says that 1 cm becomes 1cm+ 1/10^17 cm next second, it is the derivative of space ds/dt, which is valid for any object with velocity moving in Euclidean space, ds/dt = v/D, or not?
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