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Author Topic: How old is the Universe?  (Read 30138 times)

Offline Bill S

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How old is the Universe?
« on: 13/04/2015 03:36:40 »
How old is the Universe?  That seems like an easy question to answer.  It’s 13.7 billion years, or close to. 

Where do we measure that time from?  That’s another easy one: now.

Relativity tells us there is no universal now, all we can identify is the spacetime event that is “here and now”.  So,  what do we mean when we say that we measure back from now?  Any reference frame that is in motion relative to ours will identify a different here and now.  Every part of the Universe is in motion relative to every other part, and the faster that relative motion, the greater will be the discrepancy between the measurement of here and now with respect to each part.

We are assured that the more distant (from us) parts of the Universe are moving away from us at speeds faster than c.  What can we say about the measurement of here and now in those areas?  All these areas are parts of the Universe.  If we can’t identify a “present” for them, how can we say how their “present” relates to the start of the Universe from their perspective?

We could assume that any measurement taken from any part of the Universe would show that the Big Bang occurred at 13.7 billion years before that local “present”, but what does that actually mean?  Is our measurement of the age of the Universe just a feature of our particular location in spacetime?
« Last Edit: 13/04/2015 03:39:37 by Bill S »


 

Offline jccc

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Re: How old is the Universe?
« Reply #1 on: 13/04/2015 15:32:22 »
no one has the answer. how could one has an answer that is absolute?

how big is the universe? seems most of us agreed it is infinite.

if space is infinite, time should be infinite.

as we can wonder and ask why, we are somehow infinite.

we stand here and now trying to reach out, to learn, to become infinite.

oh, life, thank you.
 

Offline ScientificSorcerer

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Re: How old is the Universe?
« Reply #2 on: 13/04/2015 19:55:20 »
Who's to say that the big bang was the beginning? Big bangs could simply be the result of gravity eventually bringing everything to a single spot called a singularity then exploding. Big bangs could have happened an infinite amount of times. in a never ending loop. (look up big crunch theory)

The only thing standing in the way of such an idea is "dark energy theory" which is almost certainly the result of gravity waves persisting to this day from when all the mass in the universe (singularity) was suddenly converted into energy during the big bang.   these waves are far larger then any galaxy and far larger then we can perceive with our telescopes  that's why we think there is such a thought that there actually is something called dark energy.  we have no Idea that we are on the tale end of a huge gravity wave.

space could be infinite but there is a perceivable diameter of space occupied by matter and light. If the big bang did occur 13 billion years ago that simply means that light could only travel 13 billion light years in any direction giving you the radius of the universe (with light in it).
« Last Edit: 13/04/2015 20:05:29 by ScientificSorcerer »
 

Offline Bill S

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Re: How old is the Universe?
« Reply #3 on: 14/04/2015 12:26:03 »
SS, you make points that are valid in themselves, but may not be relevant to the OP.  It really makes no difference if the BB was the start of "everything" or just a point along the way.  The significant question of the OP was: if we cannot identify a generalised present for the Universe, how can we identify any point in the past with universal validity?

I had hoped we might tackle this point before moving on to the next, which would be to ask if it might be reasonable to make a case for our living in an atemporal cosmos in which time is just a local "illusion" that is necessary in order to make intelligent life possible.
 

Offline PmbPhy

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Re: How old is the Universe?
« Reply #4 on: 14/04/2015 16:18:17 »
How old is the Universe?  That seems like an easy question to answer.  It’s 13.7 billion years, or close to. 

Where do we measure that time from?  That’s another easy one: now.

Relativity tells us there is no universal now, all we can identify is the spacetime event that is “here and now”.  So,  what do we mean when we say that we measure back from now?  Any reference frame that is in motion relative to ours will identify a different here and now.  Every part of the Universe is in motion relative to every other part, and the faster that relative motion, the greater will be the discrepancy between the measurement of here and now with respect to each part.
That time refers to cosmological time, i.e. the time read on a particular clock in co-moving coordinates. See http://en.wikipedia.org/wiki/Comoving_distance
 

Offline Bill S

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Re: How old is the Universe?
« Reply #5 on: 14/04/2015 21:45:32 »
Pete, what you say is absolutely right.  However, your Wiki link contains the following:

Quote
Although general relativity allows one to formulate the laws of physics using arbitrary coordinates, some coordinate choices are more natural (easier to work with). Comoving coordinates are an example of such a natural coordinate choice.

This makes it clear that co-moving coordinates and, consequently, cosmological time are arbitrary concepts.  Even without getting into things like the anthropic principle, it is obvious that the potential to make sense of the Universe is a sine qua non of the development of intelligent life.  Thus, such arbitrary coordinates are very valuable to cosmologists and astronomers.  However, we should not forget that they are chosen precisely to fit our 3+1 dimensional cosmology. 
We are still left with the question: If relativity prevents us from identifying an absolute present, can there be any way of absolutely relating any past point to any later point in such a way that it can be universally valid?
Wouldn't relativity always insist that such relationships appeared to be different (indeed, were different) when observed from different reference frames?
 

Offline PmbPhy

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Re: How old is the Universe?
« Reply #6 on: 14/04/2015 21:59:23 »
Quote from: Bill S
Pete, what you say is absolutely right.  However, your Wiki link contains the following:
Quote
Although general relativity allows one to formulate the laws of physics using arbitrary coordinates, some coordinate choices are more natural (easier to work with). Comoving coordinates are an example of such a natural coordinate choice.
Okay. I certainly agree with that.

Quote from: Bill S
This makes it clear that co-moving coordinates and, consequently, cosmological time are arbitrary concepts.
I disagree with that though. The concept itself is far from being arbitrary since it has a solid meaning independent of anything outside of itself. The only thing arbitrary about it is the choice of coordinates. It's the particular set of coordinates that are arbitrary, not the concept of coordinates itself.

Quote from: Bill S
If relativity prevents us from identifying an absolute present, can there be any way of absolutely relating any past point to any later point in such a way that it can be universally valid?
Yes.

Quote from: Bill S
Wouldn't relativity always insist that such relationships appeared to be different (indeed, were different) when observed from different reference frames?
No. Not always. It depends on the events and the coordinate system used.
« Last Edit: 15/04/2015 01:49:29 by PmbPhy »
 

Offline jeffreyH

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Re: How old is the Universe?
« Reply #7 on: 15/04/2015 01:04:45 »
There are no global fixed coordinates and no global fixed time. If you are asking if time dilation matters then yes it does. Intelligent life that arose in orbit very near to a black hole may well see the beginning of the universe to be at at totally different point in time. That however is a very special situation. Within a galaxy time dilation at a remote distance from the central black hole will be insignificant. Unless you count close orbits around neutron stars. However it is unlikely that intelligent life would exist there. So I think we have a good handle on the age of the universe.
 

Offline PmbPhy

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Re: How old is the Universe?
« Reply #8 on: 15/04/2015 04:20:49 »
Quote from: jeffreyH
There are no global fixed coordinates and no global fixed time.
I don't understand that response. What do you mean by "fixed/coordinates" and "fixed time"?

Quote from: jeffreyH
If you are asking if time dilation matters then yes it does. Intelligent life that arose in orbit very near to a black hole may well see the beginning of the universe to be at at totally different point in time. That however is a very special situation. Within a galaxy time dilation at a remote distance from the central black hole will be insignificant. Unless you count close orbits around neutron stars. However it is unlikely that intelligent life would exist there. So I think we have a good handle on the age of the universe.
Yes. But that doesn't mean that all observers can't agree on a particular age for the universe. That age is the one determined by observers who are at rest in co-moving frames. An observer can tell that he's in such a frame by examining the cosmic microwave background and make sure that it looks the same in every direction that you look in. Then all observers can agree exactly on what those observers agree on. Nothing like this happens in special relativity though.
 

Offline yor_on

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Re: How old is the Universe?
« Reply #9 on: 16/04/2015 17:13:49 »
The universe we measure on should be around http://www.slate.com/blogs/bad_astronomy/2013/03/21/age_of_the_universe_planck_results_show_universe_is_13_82_billion_years.html

That doesn't tell you what it 'is', or how it come to exist though.
 

Offline yor_on

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Re: How old is the Universe?
« Reply #10 on: 16/04/2015 17:18:22 »
It's really simple Bill if you accept the definitions we use. That the universe is a homogeneous and isotropic 'place'. If that is true that age will be the same everywhere you go, using the same measurements, and it really means that the universe we measure on is 'infinite'. Find this to be wrong and I will get a bigger headache than I already have accepting it :)
 

Offline jeffreyH

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Re: How old is the Universe?
« Reply #11 on: 17/04/2015 00:22:24 »
Quote from: jeffreyH
There are no global fixed coordinates and no global fixed time.
I don't understand that response. What do you mean by "fixed/coordinates" and "fixed time"?

There isn't a universal background time that runs at the same rate for all observers and spatial coordinates are also not universal.
 

Offline Bill S

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Re: How old is the Universe?
« Reply #12 on: 17/04/2015 01:32:52 »
Quote from: Pete
I disagree with that though. The concept itself is far from being arbitrary since it has a solid meaning independent of anything outside of itself.

My bad wording.

Quote
The only thing arbitrary about it is the choice of coordinates

Surely it is the coordinates that form the basis of any calculations, and if they are selected arbitrarily, then the calculations that arise from them, although they may be of great value within their specified parameters, cannot be other than arbitrary in nature, and therefore cannot be extrapolated beyond the specific.

Quote
Quote
Wouldn't relativity always insist that such relationships appeared to be different (indeed, were different) when observed from different reference frames?
No. Not always. It depends on the events and the coordinate system used.

Could you give an example of the sort of thing you mean.
 

Offline Thebox

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Re: How old is the Universe?
« Reply #13 on: 17/04/2015 02:01:14 »
How old is space?
 

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Re: How old is the Universe?
« Reply #14 on: 17/04/2015 05:37:44 »
How old is space?
???...No, this cannot be real. I hope you were not serious when you wrote this... I hope this is a joke.
« Last Edit: 17/04/2015 05:43:57 by Jasper Hayden »
 

Offline jccc

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Re: How old is the Universe?
« Reply #15 on: 17/04/2015 06:03:55 »
How old is space?

good question. all things are within space, if things have age, so does space.

how old is now? pretty old i say.
 

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Re: How old is the Universe?
« Reply #16 on: 17/04/2015 06:58:54 »
How old is space?

good question.
Is this sarcasm? If not, then would you mind explaining how this is a good question?
 

Offline jccc

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Re: How old is the Universe?
« Reply #17 on: 17/04/2015 09:30:40 »
How old is space?

good question.
Is this sarcasm? If not, then would you mind explaining how this is a good question?

all matters/things are within this boundless box we called space. surely a good question. space is bigger and older then big bang is for sure.
 

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Re: How old is the Universe?
« Reply #18 on: 17/04/2015 09:40:37 »
How old is space?

good question.
Is this sarcasm? If not, then would you mind explaining how this is a good question?

all matters/things are within this boundless box we called space. surely a good question. space is bigger and older then big bang is for sure.

"http://en.wikipedia.org/wiki/Universe", quote from Wikipedia: 'The Universe is the totality of existence.'.
Unless of course Wikipedia is cheating with me, I believe 'totality; includes space. Since 'How old is universe' is already answered (Within the framework of logical and fundamental deductions) asking 'How old is space?' is just really just... Redundant;
We don't even know what's beyond Universe's edge... You cannot say it's a 'Boundless box'. The logic you are using to describe space can be used to mention many other possible theories which are merely speculations.
The reason why I'm arguing with you on this is because, 'The Box' always asks very feeble questions and your answers only encourage him. You should rather tell him to read some physics and philosophy books.
« Last Edit: 17/04/2015 09:46:53 by Jasper Hayden »
 

Offline Thebox

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Re: How old is the Universe?
« Reply #19 on: 17/04/2015 13:53:02 »
How old is space?

good question.
Is this sarcasm? If not, then would you mind explaining how this is a good question?

all matters/things are within this boundless box we called space. surely a good question. space is bigger and older then big bang is for sure.

"http://en.wikipedia.org/wiki/Universe", quote from Wikipedia: 'The Universe is the totality of existence.'.
Unless of course Wikipedia is cheating with me, I believe 'totality; includes space. Since 'How old is universe' is already answered (Within the framework of logical and fundamental deductions) asking 'How old is space?' is just really just... Redundant;
We don't even know what's beyond Universe's edge... You cannot say it's a 'Boundless box'. The logic you are using to describe space can be used to mention many other possible theories which are merely speculations.
The reason why I'm arguing with you on this is because, 'The Box' always asks very feeble questions and your answers only encourage him. You should rather tell him to read some physics and philosophy books.

If how old space is a redundant question then may Newton's sword slice through it, and may the space-time of space also be slashed by Newton's sword into matter time in a space.   Science wants to insist on a space-time, then science should be able to answer my question, how old is space?   

The Universe age is matter in a period of space, space and matter make the universe but are two separate dependent issues.

So, how old is space?

Is space immortal so age is redundant, and time is redundant?
« Last Edit: 17/04/2015 13:54:37 by Thebox »
 

Offline Bill S

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Re: How old is the Universe?
« Reply #20 on: 17/04/2015 21:50:06 »
Quote from: yor_on
It's really simple Bill if you accept the definitions we use. That the universe is a homogeneous and isotropic 'place'. If that is true that age will be the same everywhere you go, using the same measurements, and it really means that the universe we measure on is 'infinite'.

I accept that cosmology needs the definitions of homogeneity and isotropy, and that we probably have no concrete evidence that this is not the case. 

Quote
If that is true that age will be the same everywhere you go

That makes sense, but the measurement made from each place must be made from the local “now”.  Relativity says that “now” here and “now” elsewhere are not synchronous.  It must, surely, follow that the start of the Universe as seen from different places differs in the same way when viewed from any given reference frame.

Is it my imagination, or is this thread degenerating into a competition so see who can “nest” the most quotes? :)
 

Offline jccc

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Re: How old is the Universe?
« Reply #21 on: 17/04/2015 21:55:14 »
i want to invite thebox to become my science brother. my light sword is  sharper than newtons.
 

Offline Ethos_

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Re: How old is the Universe?
« Reply #22 on: 17/04/2015 22:04:18 »
i want to invite thebox to become my science brother. my light sword is  sharper than newtons.
Now that would be a pair, jccc and The Box. I think you'll enjoy each others company!
 

Offline jccc

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Re: How old is the Universe?
« Reply #23 on: 17/04/2015 22:10:25 »
i want to invite thebox to become my science brother. my light sword is  sharper than newtons.
Now that would be a pair, jccc and The Box. I think you'll enjoy each others company!

i hold you, he kicks you?
 

Offline Bill S

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Re: How old is the Universe?
« Reply #24 on: 17/04/2015 23:02:43 »
Alice and Bob have a specimen of uranium, and the ability to date it with extreme accuracy.  It has been dated at 20 million years.  They break it in half.  Bob stays on Earth with one half while Alice goes on a trip at close to the speed of light.  When Alice returns Bob’s half is dated at 20m+20 years, while Alice’s is dated at 20m=5years.  Is that accurate reasoning?
 

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Re: How old is the Universe?
« Reply #24 on: 17/04/2015 23:02:43 »

 

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