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How old is the universe?





barmstonian
13.7 billion years old according to http://en.wikipedia.org/wiki/Cosmological_time.

But with my very vague (mis?) understanding of relativity, I keep wondering how the early universe's strong gravitational fields and fast expansion affects the calculations.

Is there anybody out there who can get to grips with the Lorentz equations (or whatever else comes into play) on this?

Does being next to (or part of) something infinitely dense (at the moment of the big bang) affect the "perception" of the passing of time? If so, is this taken into account by the 13.7 billion year calculation.

I'd be very interested if someone could shed some light on all this.

Cheers,
B.
SonLight
Cosmologists estimate the age of the universe according to the factors they observe, but there are many uncertainties. One crude estimate would be to measure the apparent speed of expansion today, and assume the universe began as long ago as it would have taken for the universe to expand from a point to its present size at the present velocity. I believe that would give about 20 billion years, according to current estimates of the Hubble constant.

Of course no one thinks the universe has expanded at the same rate. Cosmologists do consider the gravitational influence which is expected to have slowed down expansion from a higher rate in the past. There is also considerable uncertainty in the Hubble constant, since calculating it requires making a lot of assumptions.

I'm sure cosmologists do take strong gravitational fields, relativistic corrections to Newtonian laws of motion, and probably even some effects of quantum theory into effect. In some cases, though, they may need to use models which cannot be fully verified. For examplle, the inflationary hypothesis seems to allow for arbitrary and large changes in the expansion. I think no one even tries to guess the elapsed time prior to the end of the last inflationary period.

As far as working out the details of various theories, you would have to study a lot of math to understand them.
mulejudo
Very Happy
Thank you sonlight for this well done synthesis. However all of this is in the straight line of actual scientific hypotheses, which is : make it simple. This big bang story is still very puzzling from other non-scientific or para scientific questions.
- What was there before the initial spark ?
- Where did the energy come from ?
- If today science believes in forever ongoing expansion of the universe then there will be a point where everything is so diluted in space it will be almost equivalent to nothing. Is this "nothing" state somwhat the answer to the first question ?
- If it is we would then rather have to look at the universe as a cyclic engine.
- But then when did it start ?
So back to square one.
Of course all of the previous considers only one universe. How about a multiverse ?
But it all leads to the ab initio question. What started it ? Did it start ? Was it there all along ?

On a clear night watching the stars it's nice to think of all that.

Rolling Eyes
ocalhoun
By that you must mean the time since the big bang...

But, the way I see it, the big bang happened within the universe, it didn't start the universe.

The universe is the entirety of all space and time, right? So, it must include the time before that.
Bikerman
ocalhoun wrote:
By that you must mean the time since the big bang...

But, the way I see it, the big bang happened within the universe, it didn't start the universe.
Not really. The observable universe started at the BB. Whether there was something before that or not is moot.
Quote:
The universe is the entirety of all space and time, right? So, it must include the time before that.
But according to BB theory there was NO time before that.
metalfreek
Age of universe is about ten or twenty thousand million years (1 or 2 with ten zeros after it) after bib bang.
Bikerman
metalfreek wrote:
Age of universe is about ten or twenty thousand million years (1 or 2 with ten zeros after it) after bib bang.

Well, the current best estimate (using the WMAP data) is 13.7 billion years.
_AVG_
I think that the Universe is 15.6 billion years old (I saw it on some History Channel Programme recently)

Philosophically and aesthetically, I believe that the Universe is static and infinite.
Bikerman
_AVG_ wrote:
I think that the Universe is 15.6 billion years old (I saw it on some History Channel Programme recently)
Well, you can believe the History Channel (the programme could have been an old one) or you can believe the latest up to date estimates.
The WMAP data gives an age of (13.73 ± 0.12) × 10^9 years.*
Quote:
Philosophically and aesthetically, I believe that the Universe is static and infinite.
So you think that the Hubble red-shift data we observe is not indicative of an expanding universe then? I'd be most interested to see how you explain the data away.

* http://en.wikipedia.org/wiki/Age_of_the_universe#Age_based_on_WMAP
ocalhoun
Bikerman wrote:
Whether there was something before that or not is moot.

Why?
Gagnar The Unruly
Supposedly, no information 'survived' the big bang, so it literally doesn't matter.
Bikerman
ocalhoun wrote:
Bikerman wrote:
Whether there was something before that or not is moot.

Why?

Well, because we currently have no way to know. The universe we inhabit started at the Big Bang. It is possible that the big bang was 'caused' by a collision of 'membranes' in an 11th dimension, which brought about our spacetime ('M-Theory'). This is not, as yet, what I would call science because we cannot test it.

If we find evidence for extra dimensions (and there is a very remote possibility that the LHC could do so - I would say perhaps one in a thousand) then we can begin to think about what might have come 'before' the BB, because we will have some good evidence that M-Theory could be correct. Until that time it is just speculation and the point, as I said, remains moot.
ocalhoun
^Well, just because we can't know doesn't mean we can't speculate about it.
I suppose we don't know enough about the nature of time to really say if it 'started' then.

Perhaps something like this... I assume that when the big bang went 'bang', it expanded roughly equally in all directions, right? Perhaps it did exactly the same thing in the time dimension as it did in the others, and an identical universe is playing out in... well, I guess you'd call it a mirror image of time as we know it, going backwards in time from our perspective, but forwards in time from the perspective of that half of the universe.
Bikerman
ocalhoun wrote:
^Well, just because we can't know doesn't mean we can't speculate about it.
I suppose we don't know enough about the nature of time to really say if it 'started' then.

Perhaps something like this... I assume that when the big bang went 'bang', it expanded roughly equally in all directions, right? Perhaps it did exactly the same thing in the time dimension as it did in the others, and an identical universe is playing out in... well, I guess you'd call it a mirror image of time as we know it, going backwards in time from our perspective, but forwards in time from the perspective of that half of the universe.

Nono. The Big Bang created spacetime, not space. Spacetime expands, not just space. There was no time dimension before BB - that's the point. Relativity describes time quite adequately. We still have questions about the exact nature of time, for sure, but we are pretty sure that, whatever the exact nature of time is, it started at the BB.

Direction is a tricky concept when talking about the BB because it implies a point of reference - we talk about directions relative to a point. In this case it would be wrong to imagine a point in space 'exploding' in every direction. There was no 'point' at which the BB occurred - how could there be? Imagine blowing-up a balloon. At what point on the balloon did the balloon start inflating? The question makes no sense, yes?
ocalhoun
^Well, no we can't have a point of reference 'before' it happened, but I would think of the point everything was expanding away from as the reference point, automatically becoming the center of the universe, since there is nothing else out there.

I'm just looking at what happened in all the other (observable) dimensions and speculating that time is not an exception.
Indi
ocalhoun wrote:
^Well, no we can't have a point of reference 'before' it happened, but I would think of the point everything was expanding away from as the reference point, automatically becoming the center of the universe, since there is nothing else out there.

I'm just looking at what happened in all the other (observable) dimensions and speculating that time is not an exception.

There is no reference point. The dimensions are not expanding "away" from anywhere, they are expanding.

This is hard to imagine in 3D (or 4D!!!) but really easy to picture in 2D. Imagine the surface of a balloon that is being blown up. Put evenly spaced dots all over its surface, then blow it up some more. What happens? Every point looks like the centre. No matter which point you take as your reference point, every point around you is moving way from you at the same rate. There is no centre of expansion... or every point is the centre of expansion.

Now the next logical question is: "Does that mean the spacetime dimensions are finite and closed, like the two spatial dimensions on a balloon surface?" Answer: "Dunno." The dimensions of the universe may be closed and finite, or they may be open and infinite. The result would be the same. (FYI, M-theory says closed and finite.)

Time is the same way. It is not expanding "from" a point, it is expanding. There's no reference point... or every point is the reference point. You can look at it either way.
Socioed
I've always been very interested in this and it is one of the unexplainable phenomenons of life. :'(
profbis
This in my opinion is unanswerable question. There is no science to answer this question. The universe is big. In the Universe, there are several galaxies. Our sun is among one of those galaxies. Look at the stars in the sky, how many can you see? So, is each star is like one Sun, how many planets could there be? Universe is wayyyyy to big to determine it age.
Bikerman
profbis wrote:
This in my opinion is unanswerable question. There is no science to answer this question. The universe is big. In the Universe, there are several galaxies. Our sun is among one of those galaxies. Look at the stars in the sky, how many can you see? So, is each star is like one Sun, how many planets could there be? Universe is wayyyyy to big to determine it age.

There is plenty of science to answer this question. The universe is indeed big. There are more than several galaxies - there are several hundred billion.
What we do is use large telescopes to look at very distant galaxies. It turns out that the further away a galaxy is, the faster it is moving away from us. We can measure that speed using something called 'redshift' (the light changes colour towards the red end of the spectrum when something is receding, and towards the blue end when something is approaching - like the siren on a police car changing tone as the car passes you).
Now, if we 'turn back time' then obviously the galaxies are all rushing together, rather than flying apart.* By taking careful measurements and applying Einstein's theory of General Relativity, it is possible to calculate when everything would have been in a single 'point' - the Big Bang. Wind-forward again and we can calculate how big the universe is from that time.

* In fact the galaxies are not really rushing apart - the space between the galaxies is expanding.
yagnyavalkya
The dark energy may give us the answer to this question
here is an article I read which try's to draw a relationship with dark energy and the age of the universe
"Quantum mechanics together with general relativity leads to the Károlyházy relation and a corresponding energy density of quantum fluctuations of space–time. Based on the energy density we propose a dark energy model, in which the previous termage of the universenext term is introduced as the length measure. This dark energy is consistent with astronomical data if the unique numerical parameter in the dark energy model is taken to be a number of order one. The dark energy behaves like a cosmological constant at early time and drives the previous termuniversenext term to an eternally accelerated expansion with power-law form at late time. In addition, we point out a subtlety in this kind of dark energy model"
Ref: Rong-Gen Cai 2007 A dark energy model characterized by the age of the Universe Physics Letters B
Volume 657, Issues 4-5, 6 December 2007, Pages 228-231
tamilparks
how its billion years, now we are only 2008 years? i am wondering how its calculated? is it true?
saratdear
tamilparks wrote:
how its billion years, now we are only 2008 years? i am wondering how its calculated? is it true?

2008 means 2008 A.D. There is B.C years before that, and honestly, we started counting years when the early human had the required knowledge about months and years, right?
nilsmo
There were years before year 1 (those are the BC years saratdear mentioned). Year 1 was an arbitrary point in time; it does not relate to when time started.
barmstonian
nilsmo wrote:
There were years before year 1 (those are the BC years saratdear mentioned). Year 1 was an arbitrary point in time; it does not relate to when time started.

In the time before 'year zero' (in fact, there was no year zero - it went from 1BC to 1AD, which means you've got to be careful with calculating time periods across the two eras...) a lot of people wondered what the years were counting down to ....

On the issue of 'before the big bang' there's an interesting article in Scientific American http://www.sciam.com/article.cfm?id=big-bang-or-big-bounce about loop quantum gravity which suggests theories that avoid the big bang singularity, and points to not only time before the big bang, with similar physics, but even ways of detecting information that survived the big bang. That would mean the age of the universe does not have to be measured from the big bang, but could be extended back before it, even infinitely.

I think this is only one of many theories out there trying to come up with something more fundamental than quantum mechanics and relativity (e.g. all the string theory flavours) but maybe one day soon, something will turn out to agree with both QM and relativity as well as explain dark matter / energy and be able to deal elegantly with singularities (or maybe avoid them) and thus shed some light on the beginning (or phase change) of the universe.
ocalhoun
barmstonian wrote:

In the time before 'year zero' (in fact, there was no year zero - it went from 1BC to 1AD, which means you've got to be careful with calculating time periods across the two eras...) a lot of people wondered what the years were counting down to ....

Did they really use BC reckoning at that time? Or was that time measurement just imposed on history when it was invented? It seems unlikely to me that when people were making their first primitive dating systems that they would make the years count down, while everything else counted up.
Jinx
*facepalm*

Ok, folks - There have been many different calendars, and numerous "start"dates, usually based on some significant event in the culture using that calendar. The Gregorian, Mayan, Hebrew, ect... calendars all have different start dates.

Gregorian: this is the year 2008 AD
Hebrew: the year is 5769
The Julian Day is: 2454752.5
By the Islamic calendar, this is the year 1429
As the Mayans reckoned it this would be the year 12.19.15.13.10
To the Persians this would be the year 1387
In India it's only 1930
And according to Unix systems the date and time is: 1223856000

None of which have any meaning whatsoever when dealing with cosmic scales of time.
barmstonian
ocalhoun wrote:
barmstonian wrote:

In the time before 'year zero' (in fact, there was no year zero - it went from 1BC to 1AD, which means you've got to be careful with calculating time periods across the two eras...) a lot of people wondered what the years were counting down to ....

Did they really use BC reckoning at that time? Or was that time measurement just imposed on history when it was invented? It seems unlikely to me that when people were making their first primitive dating systems that they would make the years count down, while everything else counted up.

lol
riyadh
just use the Hubble's law equation (v=Hd) to estimate the age of the universe
rshanthakumar
Time zero or the moment of big bang is not the time when the universe was born. But before that, it is better to define what is universe. Which one are we referring to as universe? Is the space that houses all the galaxies and the space where the big bang really happened, if at all it did? If that is the case, then the space existed even before big bang. It was just that the big bang happened in this universe.

Now this is free space and this continued to exist even beyond the time zero. So what was the age of the universe. Do we go by the 'pulsating universe' theory, there is no end to the existence of the universe. It keeps expanding and contracting and it would keep oscillating this way. For how long...? God only knows!
barmstonian
rshanthakumar wrote:
Which one are we referring to as universe? Is the space that houses all the galaxies and the space where the big bang really happened, if at all it did?

Conventional wisdom has it that the time and space that comprises our universe were created in the big bang. So it's not like the universe "before" the big bang was like an empty room that an explosion took place in, filling it with an expanding mess of matter. It's more like the big bang created the room itself and all that was in it. You may be tempted to ask 'what's outside the room' type questions, but if time and space (the non-time dimensions) were created at the time of the big bang, asking such questions is meaningless and a failure to get outside our human, every-day life perspective.

B.
pll
The question for me is : What was before the Universe?
If it was entirely created by the big bang how did some kind of particles collisioned ?
SonLight
pll wrote:
The question for me is : What was before the Universe?
If it was entirely created by the big bang how did some kind of particles collisioned ?


Surely the Universe did not begin at the time of the Big Bang. We cannot make any predictions about what it was like before that, but all our experience suggests that the total amount of mass/energy was the same beforehand.

It is common to speak of time and the Universe "beginning" when the big bang occurred. I think that is an improper way to speak scientifically, as the most reasonable (though highly speculative) hypothesis is that the Universe had collapsed to a single point, and some principle we know nothing about caused it to expand again. I think of the big bang in a somewhat naive way, as a black hole with the ability to release its content under special conditions (perhaps contracting to Heisenberg's quantum size has something to do with it). Time would be dramatically affected by the collapse, but it should be conceivable to define a time continuum through the event, even though there is no possibility of "recording" the event, so it appears that any details preceding the beginning of the expansion will remain forever unknown.
Bikerman
SonLight wrote:
pll wrote:
The question for me is : What was before the Universe?
If it was entirely created by the big bang how did some kind of particles collisioned ?


Surely the Universe did not begin at the time of the Big Bang. We cannot make any predictions about what it was like before that, but all our experience suggests that the total amount of mass/energy was the same beforehand.
Err...this is based on what exactly? If you figure that the curvature of spacetime is -ve energy and that mass/energy is +ve energy then add the two: -1+1=?
Quote:
It is common to speak of time and the Universe "beginning" when the big bang occurred. I think that is an improper way to speak scientifically, as the most reasonable (though highly speculative) hypothesis is that the Universe had collapsed to a single point, and some principle we know nothing about caused it to expand again. I think of the big bang in a somewhat naive way, as a black hole with the ability to release its content under special conditions (perhaps contracting to Heisenberg's quantum size has something to do with it). Time would be dramatically affected by the collapse, but it should be conceivable to define a time continuum through the event, even though there is no possibility of "recording" the event, so it appears that any details preceding the beginning of the expansion will remain forever unknown.
Nope - you have it totally wrong. The BB does not state that the universe 'collapsed to a single point'. That implies that there was a universe to collapse. The BB theory postulates that the universe started with a single 'point' that expanded (and is still expanding). The singularity at the BB is not comparable with a Black Hole.
SonLight
Bikerman wrote:
SonLight wrote:
pll wrote:
The question for me is : What was before the Universe?
If it was entirely created by the big bang how did some kind of particles collisioned ?


Surely the Universe did not begin at the time of the Big Bang. We cannot make any predictions about what it was like before that, but all our experience suggests that the total amount of mass/energy was the same beforehand.
Err...this is based on what exactly? If you figure that the curvature of spacetime is -ve energy and that mass/energy is +ve energy then add the two: -1+1=?


It is surely possible that there is negative energy, and that it exactly balances the positive energy of the Universe, leaving a total mass/energy content of zero to be conserved. I assume the negative energy content is based on the cosmological constant idea. Einstein originally set the value of that to produce a steady-state universe, but we know that can't be. Maybe you can enlighten us about current models, and under what conditions negative energy would be equal to positive energy. Even if we assume zero net energy, we have a problem with causation. It appears that a whole universe can spring into being with no effort and no reason. Perhaps we are protected against that happening arbitrarily by the existence of the current Universe? I see that you do agree that total mass/energy is likely to be conserved.

Bikerman wrote:
Quote:
It is common to speak of time and the Universe "beginning" when the big bang occurred. I think that is an improper way to speak scientifically, as the most reasonable (though highly speculative) hypothesis is that the Universe had collapsed to a single point, and some principle we know nothing about caused it to expand again. I think of the big bang in a somewhat naive way, as a black hole with the ability to release its content under special conditions (perhaps contracting to Heisenberg's quantum size has something to do with it). Time would be dramatically affected by the collapse, but it should be conceivable to define a time continuum through the event, even though there is no possibility of "recording" the event, so it appears that any details preceding the beginning of the expansion will remain forever unknown.
Nope - you have it totally wrong. The BB does not state that the universe 'collapsed to a single point'. That implies that there was a universe to collapse. The BB theory postulates that the universe started with a single 'point' that expanded (and is still expanding). The singularity at the BB is not comparable with a Black Hole.


I surely don't claim to have it right! We are clearly speculating here, in an area where we can hardly do an experiment to distinguish between possibilities. I assume conservation of mass/energy and causation are still valid at and prior to the big bang. We have perhaps reached beyond the limits of what should be called science, since we cannot test our hypotheses anymore. The Black Hole analogy is clearly a very loose one. Can we deduce anything about the immediate result of the Big Bang by applying quantum theory at the time when the Universe was as small as the minimum qauntized dimension?
easysolution
By that you must mean the time since the big bang...
Bikerman
SonLight wrote:
It is surely possible that there is negative energy, and that it exactly balances the positive energy of the Universe, leaving a total mass/energy content of zero to be conserved. I assume the negative energy content is based on the cosmological constant idea. Einstein originally set the value of that to produce a steady-state universe, but we know that can't be. Maybe you can enlighten us about current models, and under what conditions negative energy would be equal to positive energy. Even if we assume zero net energy, we have a problem with causation. It appears that a whole universe can spring into being with no effort and no reason. Perhaps we are protected against that happening arbitrarily by the existence of the current Universe? I see that you do agree that total mass/energy is likely to be conserved.
Yes, I agree that conservation is probably the best model we have and therefore we should stick with it. Remember, however, that quantum physics allows a 'borrowing' of energy on very small timescales so long as the energy is eventually 'paid back'. That is what we mean by a quantum fluctuation.
As for the idea of gravity as negative energy - I refer you to the post in this forum on the 'origin of the universe' that I made a while ago. It should illustrate the principle...
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