# Thread: real age of Universe?

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## real age of Universe?

From what point is the age of the Universe calculated? It is now thought to be 15Billion years old. But counting from what? The Big Bang?
Ok, fine, but did time begin at the point the BB started, or did time exist before?
If the universe existed before it went bang, then it's far older than 15B years. Imagine if the matter that went bang was
in existence 25Billion years, and then, due to some force or action, it went boom. Thus, the thing we call universe has
actually existed 40B years.

For all we know, the universe existed in a steady unbanged state 70Trillion years, or as little as 10 minutes. Perhaps even, the
matter came into being and the Big Bang occurred immediately. Thus, either there was something for a (long or short) period
of time, or there was nothing at all before the BB.

But, if there was no universe before the BB, then what was there, how long did it exist, are there others?

2. Originally Posted by Gomar
...did time begin at the point the BB started, or did time exist before?
We don't know if time or anything existed before the so-called big bang. If you run the expansion backwards, everything runs together at some point. That is the point where we start counting time. Whether time existed before that, we don't know.

By the way, our current estimate of our universe's age is 13.7 billion years, with a remarkably small uncertainty of 1%.

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The Big Bang theory describes the evolution of the visible universe from a hot dense state that existed about 14 billion years ago. Before that state none of our models can predict what was happening. Since everything we sense came from that hot dense state it makes sense to say that the age of our observable universe is 14by.

All of your questions are essentially answered by the same reply: No one knows because our physical models have broken down by that point. Scientists are working on making better models in the hope that we can answer those questions but for now any answers given are speculation.

4. Originally Posted by Gomar
But, if there was no universe before the BB, then what was there, how long did it exist, are there others?
The problem is, if there was "something" before the hot dense state we call the big bang, where did that "something" come from. And
then what produced the something before the 2nd "something", and so on...

This is how i see it: Before the big bang, there was no space, time, or energy, complete nothingness. For no apparent
reason the universe spontaneously sprung into existence. Why and how nobody knows, it just happened.

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well when i listen to cosmologists these days, i rarely hear anyone suggest there was nothing before the big bang. They al have their ideas - its just providing evidence thats a tad tricky.
Intuitively i do quite like the cyclic models. Penrose for example suggests when the universe reaches maximum entropy it is essentially the same state as existed before the big bang...so it can pop off again. But you can take your pick from any number of ideas

6. It's a tricky one !

7. Originally Posted by Gomar
From what point is the age of the Universe calculated? It is now thought to be 15Billion years old. But counting from what? The Big Bang?
Ok, fine, but did time begin at the point the BB started, or did time exist before?
If the universe existed before it went bang, then it's far older than 15B years. Imagine if the matter that went bang was
in existence 25Billion years, and then, due to some force or action, it went boom. Thus, the thing we call universe has
actually existed 40B years.

For all we know, the universe existed in a steady unbanged state 70Trillion years, or as little as 10 minutes. Perhaps even, the
matter came into being and the Big Bang occurred immediately. Thus, either there was something for a (long or short) period
of time, or there was nothing at all before the BB.

But, if there was no universe before the BB, then what was there, how long did it exist, are there others?
The matter in our universe has not been in existence for more then 13.75 billion years according to current models. When you get close to the big bang matter did not exist just energy. So the age of the universe for all intensive purposes is how long the matter has been in existence. The big bang starts from a pre existing state and time may or may not have existed as we know it.

A good analogy is like asking how old a kangaroo is. Generally you'd give the Kangaroo's age from the moment it was born. The way a Kangaroo's reproductive system works there is almost always a fertilised embryo in a form of stasis. If the kangaroo doesn't give birth for 3 years then we don't add that 3 years to the Joey's age even though it was in existence that entire time. Like wise we don't add the 9 odd months before you where born to your age. Nor do we add the number of years your mother was at the time you where conceived to your age because the egg you came from is just as old as your mother.

Essentially the questions you are asking have possible answers but they are not testable at the moment thus no way to distinguish between different possible states before the big bang.

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Originally Posted by Shaula
Scientists are working on making better models in the hope that we can answer those questions but for now any answers given are speculation.
Of course, there is nothing wrong with speculation. All scientific models begin with some degree of speculation.

Originally Posted by mutleyeng
When I listen to cosmologists these days, I rarely hear anyone suggest there was nothing before the big bang. They all have their ideas - it’s just providing evidence that’s a tad tricky.
Cyclical models certainly postulate a time before the Big Bang; but not all models are cyclical. Although I don’t subscribe to the Hartle-Hawking “no-boundary” hypothesis, it is an example of a no time before the Big Bang model.

Originally Posted by WayneFrancis
The big bang starts from a pre existing state and time may or may not have existed as we know it.
It depends on how we define the Big Bang. If it was the beginning of expansion, then there may have been a pre-existing state, even if our current physics describe that state as a singularity.
If the Big Bang is defined as the beginning of everything, then the notion of a pre-existing state is meaningless, since time is part of the everything.

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Of course, there is nothing wrong with speculation. All scientific models begin with some degree of speculation.
And the go on to make testable predictions. That is the bit that a lot of people doing the speculation seem to stop just before

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Originally Posted by amensae
Cyclical models certainly postulate a time before the Big Bang; but not all models are cyclical. Although I don’t subscribe to the Hartle-Hawking “no-boundary” hypothesis, it is an example of a no time before the Big Bang model.
.
Yes but i wasnt talking about no time, i was talking about the hypothetical state of absolute nothing that kevin raised.
Ive got a lot of problems with absolute nothing.

11. I "like" cyclical models, in that I sort of wish one of them were real, but it really just doesn't look that way, because there's no sign of anything that's going to cause our current iteration of such a cycle to ever lead to another one. It's just headed toward everything drifting farther and farther apart forever in the dark.

On the issue of not knowing what came before the Big Bang, it's a little bit more drastic than that: we can't even really describe the universe at the moment of the Big Bang. Whatever is the smallest unit of time you're working with, you have to start/stop at 1 of that unit, the shortest instant after it you can handle, because at 0, you'd end up doing mathematically naughty or useless things like dividing or multiplying everything by infinity or zero. Every answer that way ends up infinity, zero, or undefined, which doesn't make sense or convey any information.

Also, since acceleration and gravity affect the speed of the flow of time, not all parts of the universe are equally old. I've read once that we live in one of the parts of the universe where the least time has passed since the Big Bang, and in others it's been up to about 18 billion years.

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but you dont need the universe to change direction to have cyclical models.
Am i the only one that dosnt think that 13.7 ga seems all that old? of all the numbers we use when talking about the universe, that always strikes me as being the blink of an eye

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Originally Posted by mutleyeng
Yes but I wasn’t talking about no time, I was talking about the hypothetical state of absolute nothing that kevin raised.
Fair enough. I was focusing on the “before” rather than the “nothing”.

I’ve got a lot of problems with absolute nothing.
Agreed. The very fact that we exist would appear to render the concept of absolute nothingness meaningless.

Am I the only one that doesn’t think that 13.7 ga seems all that old? Of all the numbers we use when talking about the universe, that always strikes me as being the blink of an eye
Indeed. I need to brush up on my Bayesian analysis, but it does appear to be a VERY brief period of time. Unless we are the statistical anomaly that happens to live at the very beginning of an extremely long-lived universe, then the universe won’t be around, or is not going to be hospitable for life, for very much longer– a few trillion years at the most, give or take an aeon.

14. Originally Posted by amensae
Of course, there is nothing wrong with speculation. All scientific models begin with some degree of speculation.

Cyclical models certainly postulate a time before the Big Bang; but not all models are cyclical. Although I don’t subscribe to the Hartle-Hawking “no-boundary” hypothesis, it is an example of a no time before the Big Bang model.

It depends on how we define the Big Bang. If it was the beginning of expansion, then there may have been a pre-existing state, even if our current physics describe that state as a singularity.
If the Big Bang is defined as the beginning of everything, then the notion of a pre-existing state is meaningless, since time is part of the everything.
It seems the latter is what most lay people equate with the big bang but when I see scientist in the field discuss it with other scientists they talk more in the former.

Models inherently being with some pre-existing assumptions. An initial state so to speak. Moving the big back to before our current models can deal with only emphasises that they break down at that point. Even with the cyclical models or even multi-verse models our big bang model works as a subset and currently anything before it is currently not testable.

15. Originally Posted by Delvo
...

Also, since acceleration and gravity affect the speed of the flow of time, not all parts of the universe are equally old. I've read once that we live in one of the parts of the universe where the least time has passed since the Big Bang, and in others it's been up to about 18 billion years.
Really? Do you have any links or articles I can read on that? We aren't in a significantly deep gravity well here. I don't see how we'd even have experience .001% less time then a point far from any gravitational influence that would slow down our time by 25%. Even factoring SR effects I don't see how that kind of gap could be bridged.

16. Originally Posted by mutleyeng
but you dont need the universe to change direction to have cyclical models.
Am i the only one that dosnt think that 13.7 ga seems all that old? of all the numbers we use when talking about the universe, that always strikes me as being the blink of an eye
all that old for what? What do you need more time for given what we see in the universe?

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i wasnt suggesting that i saw anything in the universe that i think required more time... just it dosnt strike me as being old.
when i hear people say the universe is 13.7ga...i think, wow, is that all

18. Originally Posted by mutleyeng
i wasnt suggesting that i saw anything in the universe that i think required more time... just it dosnt strike me as being old.
when i hear people say the universe is 13.7ga...i think, wow, is that all
I have to agree. Given how much longer we thing the universe will go on it is very young. Given how long some stars lives are the age is still very young. But to me 13.75 billion years is still a VERY long time

19. Originally Posted by mutleyeng
13.7ga...i think, wow, is that all
It must be all the billionaires around these days. There never used to be ANY.

13 billion years is one heck of a long time! Consider the length of time that humans have even existed, which is, very roughly speaking a few million years. Consider 10 times that duration. Then consider 10 times that duration. Then take that entire duration and multiply it by 10 again. Then take that resultant huge expanse of time and triple or quadruple it. That gets us somewhere around the age of the Universe.

Or let's say the typical lifespan of a human is 100 years. The age of Universe is 130 million times longer than that.

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Originally Posted by Cougar
Or let's say the typical lifespan of a human is 100 years. The age of Universe is 130 million times longer than that.
wow, is that all?
see what i mean!

Yes i appreciate all of that of course, but this is a whole universe we are talking about.

21. Originally Posted by Cougar
Or let's say the typical lifespan of a human is 100 years. The age of Universe is 130 million times longer than that.
Or to make it feel like an even shorter length of time , one might consider how long it is since the dinosaurs became extinct - 65 million years. That time has only passed 200 times or so since the Big-Bang!

But seriously, I feel most of us don't really appreciate how long 1 million years is, let alone a billion years.

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When I read about some of the possible fates of the universe, say the heat-death for example, the aeons involved completely boggle my brain. On those scales, the universe seems very young.

Usually though, I have in the back of my mind that the optimum epoch for star formation in the Milky Way is already behind us, and that most of the galaxies in the observable universe are already ancient structures. When you compare our mere thousands of years of 'history' with the billions of years evolution of the universe, and billions of light-years of it's extent, I do wonder if we will ever encounter life like us...

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'Time' couldn't really exist before the big bang, to define time you need a point of reference to measure from, if something has 'always' been there, there is nothing to measure. The only point of reference we have to measure anything is the big bang, our human sense of 'time' (our 'reality' if you will) can only be measured from this event.

24. Originally Posted by mutleyeng
wow, is that all?
see what i mean!

Yes i appreciate all of that of course, but this is a whole universe we are talking about.
Would you expect something different for "part of the universe"?

25. Originally Posted by speedfreek
But seriously, I feel most of us don't really appreciate how long 1 million years is, let alone a billion years.
I would have to agree with you there ! I on the other hand, have thought about this question a few times because i have tried
to get a sense of evolutionary time scales.

I think of it like this. You have 100 years. Then you have 1000 years. Then you have 2000 years. Then 5000 years. Then 10,000 years, that is a long time.

Then there is 50,000 years. Then add another 10,000 years to that and you get 60,000 years. Then you add another 40,000 years
to the 60,000 years you already have and you end up with 100,000 years. 100,000 years is an awfully long time.

Then you get 200,000 years. Then you get 210,000 years. Then you get 220,000 years. Then you get 250,000 years. Then double that 250,000 years and you end up with 500,000 years. We are only at 500,000 years, half a million. Hopefully you are beginning to see my point !

Now I could go through it all again but i will not. So lets just double up that 500,000 years and we get to 1 million years.

1 million years is a long time. Now what about 1,100,000 years. 1,200,000 years. Then 1,500,000 years. Then double that to 3,000,000 years. Then add another 2,000,000 years to the 3,000,000 years we already have and you get 5,000,000 years !

Five million years is a very long time indeed. Then we double that 5,000,000 years to get 10,000,000 years !

Now we are talking. Now we take that 10 million and times it by 10 to get 1 billion.

1 billion is a huge number when really thought about, in my opinion.

The universe is 13.7 billion years old, a lot can happen over that time frame. A lot has happened..

26. Originally Posted by kevin1981
Five million years is a very long time indeed. Then we double that 5,000,000 years to get 10,000,000 years !

Now we are talking. Now we take that 10 million and times it by 10 to get 1 billion.
Heh, sorry but you missed quite a big bit there. You need 100 times 10 million to get 1 billion. So take your whole post up to the 10 million point and do it 100 times over to get a real feel for it!

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Originally Posted by Cougar
By the way, our current estimate of our universe's age is 13.7 billion years, with a remarkably small uncertainty of 1%.
That 1% uncertainty depends upon certain things being true, which we cannot be certain of, as it does explain further down. I know a professor of astrophysics at a leading UK university who would just laugh at the hubris of anyone claiming such certainty of knowledge of anything in cosmology. Despite WMAP apparently narrowing the uncertainty in our knowledge of the age of the universe, amusingly, our uncertainty in the value of the Hubble constant still remains much wider.

28. Originally Posted by speedfreek
Heh, sorry but you missed quite a big bit there. You need 100 times 10 million to get 1 billion. So take your whole post up to the 10 million point and do it 100 times over to get a real feel for it!
Oh yes, thanks ! Shame i made a mistake but you get the idea, 13.7 billion years is a long time !

29. Originally Posted by Ivan Viehoff
That 1% uncertainty depends upon certain things being true, which we cannot be certain of, as it does explain further down.
It sounded like there was only one assumption, that the universe is flat, which is a model parameter. Otherwise, WMAP has been able to determine the density, composition, and expansion rate of the universe to a pretty darn high degree of accuracy. If the universe is a little non-flat one way or the other, then the age estimate will be a little different.

Originally Posted by Ivan Viehoff
Despite WMAP apparently narrowing the uncertainty in our knowledge of the age of the universe, amusingly, our uncertainty in the value of the Hubble constant still remains much wider.
Actually, isn't WMAP's age accuracy claim based in part on its accurate determination of Hubble's constant?

Heck, it wasn't long ago that our best age estimate was "between 10 and 20 billion years." Now it's pretty clearly between 13 and 14 billion years, which squares well with the ages of the oldest stars. I think that level of accuracy is pretty impressive.

30. Originally Posted by Ivan Viehoff
Despite WMAP apparently narrowing the uncertainty in our knowledge of the age of the universe, amusingly, our uncertainty in the value of the Hubble constant still remains much wider.
It is only a bit wider. Riess et al. (2011) updated their estimate of the Hubble constant, incorporating new supernova data along with an extensive calibration with Cepheid data from the updated WFC3 camera on Hubble. Their measure is independent of WMAP and gives a value of 73.8 +/- 2.4 km s-1 Mpc-1. The 7 yr WMAP gives a value of 71.0 +/- 2.5 km s-1 Mpc-1.

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