Is our Universe 13.7 billion years old ? I'm not quite convinced

[cloudsweeper]

1 hour ago, andrew s said:

 

Firstly division by zero (in modern mathematics) is not an allowed operation i.e. does not produce a number. 

 

Exactly - and that is why when you state it, you get an undefined quantity, namely infinity.

[cloudsweeper]

1 hour ago, DRT said:

It is relatively easy to comprehend an infinity of integers as most people are able to grasp the fact that there is no way of reaching an upper or lower limit where one would have to stop adding or subtracting 1. An infinity of integers therefore (to me) seems to be a relatively simple and intuitive way of describing the concept whether it be an infinite number of things or an infinite space.

The "between x and y" thing is counter intuitive and therefore difficult to understand as it is trying to describe a space that has no limits by placing limits around it. Whilst that might work for mathematicians in their endeavors to do things with one or more infinities it does not mean much to a non-mathematician who might be trying to imagine what a real life infinity looks or feels like.

 

I personally don't have a problem with infinite divisions between limits, but I think maybe we are swapping between different notions of infinity here - infinite sets, and infinite space.  What I do have difficulties with is imagining infinite space.  And strangely, non-infinite space is also perplexing.  With spatial considerations, we are getting into extra dimensions and curvature of space - truly counterintuitive notions!

Doug.

[Pippy]

4 minutes ago, cloudsweeper said:

Exactly - and that is why when you state it, you get an undefined quantity, namely infinity.

oooo this sounds very much like we still have a problem with our numbering system.

Bare in mind that it wasn't really that long ago that '0' was first introduced into our numbering system.

[SilverAstro]

57 minutes ago, Pippy said:

oooo this sounds very much like we still have a problem with our numbering system.

Bare in mind that it wasn't really that long ago that '0' was first introduced into our numbering system.

'Our' , ,well come to think,  it aint all that long that 'we' have had a numbering system.

 

[SilverAstro]

2 hours ago, andrew s said:

DRT > The idea that there was no period of time before the big bang just seems nonsensical to me.

That's fine by me you can hold what opinion you like but just to be clear the currently accepted model of cosmology does have a start point to space and time. It may well be wrong and you right - possibly time will tell.

oh the wit ! V.good chortle.

the currently accepted model of cosmology may well say that about space&time but that does not mean that space&time did have a beginning at a moment in time at the BB * even in this currently accepted model it is accepted that it is unknown (sorry to nit pick) because the current model says nothing about that moment between the supposed start ( nearly used another word, but best not cos that will set off all sorts of bells in the mods dept. !) and a few somethings later, cant call them moments in time (because time was in the process, ha haaa, of being begun) , just before,, Andrew will correct me, the Planck time is it called or the Planck interval ? That time before which the current model and our present understanding says nothing about, can not say anything about, we have no physics able to say if it was a chocolate eclair or a singularity before then The use of the word singularity is just a fancy way of saying we dont know.

* in fact the BB gets very wooly in these sorts of discussion about when it banged, did it go off before that Planck time or after the Planck time, hand in your homework tomorrow at the latest.

 

[Stub Mandrel]

It depends whether time exists and space lies within it, or if time is a property of space.

[DRT]

I love the idea of the universe being a chocolate eclair just before the big bang.

1 hour ago, cloudsweeper said:

I personally don't have a problem with infinite divisions between limits, but I think maybe we are swapping between different notions of infinity here - infinite sets, and infinite space.  What I do have difficulties with is imagining infinite space.  And strangely, non-infinite space is also perplexing.  With spatial considerations, we are getting into extra dimensions and curvature of space - truly counterintuitive notions!

You have nailed it. I am definitely thinking about infinite space, not infinite divisions, and I think these are completely different concepts.

Non-infinite space gives me the same problem as finite time - i.e. what exists outside it?

Space time curvature just gives me a sore head.

[SilverAstro]

would this help :

Where the Y axis is the 4th of spacetime (I'm not going to try to draw the other 3 space ones, GingaDin ) and CT, clocktime, is our perception of time and how our clocks measure it in the current standard model.

The tangent is how we are supposing our current model is interacting with spacetime. This 13.7byear "start" thingumy is only an intercept. The shape of the curve is as speculative as anything else 'before' the BB.

The trouble is "words", or "worms" as TwoR's would have said, because really I should have folded my bit of paper at -13.7 and hidden the lefthand bit at 90deg behind, so that it would seem not to exist, but then it would not have photographed very well    Any similarity to S. Hawking's' jTime is in your imagination, honest.

 

 

[SilverAstro]

PS I should have added  that the two diverging bits of graphs to the right of the contact at Now is in the realms of Andrew's "only time will tell"

[andrew s]

1 hour ago, SilverAstro said:

Andrew will correct me

No he won't I have given up.

However, I agree with your comments on the exact point at which space time did or did not begin and that singularity means we don't know. I was being to lax in my statement.

 The whole idea of time is not well understood as I mentioned before. I am currently reading up on it to bore you all a a later date.

As to the asserted different concepts of infinity (sets,  space...) I just don't know how to add more without more mathematics than I care to recall or the protagonists would like.

This is not a strop I have enjoyed the debate but all good things come to an end and I have my father of the bride speech to write.

Good luck with the debate.

Regards Andrew

 

 

[cloudsweeper]

1 hour ago, DRT said:

I love the idea of the universe being a chocolate eclair just before the big bang.

You have nailed it. I am definitely thinking about infinite space, not infinite divisions, and I think these are completely different concepts.

Non-infinite space gives me the same problem as finite time - i.e. what exists outside it?

Space time curvature just gives me a sore head.

One way of attempting to envisage curved spacetime is to consider the principle that light travels in a straight line.  When light passes close to a massive star, it appears to bend towards that star (gravitational lensing), and we can still consider that the light is travelling in a straight line! - it is the space/time that is actually curved.

Doug.

[SilverAstro]

41 minutes ago, andrew s said:

No he won't I have given up. Oh !  Why? have I needed to be corrected that often ! Heheee

and I have my father of the bride speech to write. Argh ! Now that is much (infinitely?) more difficult than all this Universe stuff  

Good luck   & you

 

[Herzy]

7 hours ago, DRT said:

For the record, I think the answer to the question in the title of this thread is no. I have yet to see any convincing argument that time had a beginning, therefore the universe is of infinite age.

Do you believe in the multiverse theory? That's rhe one where the Big Bang was caused by something outside of our universe and that there are universe popping up everywhere there.. It's a little out there but I get where your coming from. I don't understand how there can be no time. One thing we can be sure of is the fact that the Big Bang did happen.

[Herzy]

6 hours ago, DRT said:

I love the idea of the universe being a chocolate eclair just before the big bang.

You have nailed it. I am definitely thinking about infinite space, not infinite divisions, and I think these are completely different concepts.

Non-infinite space gives me the same problem as finite time - i.e. what exists outside it?

Space time curvature just gives me a sore head.

I think that a good way to think of space time curvature is to imagine your on the surface of a sphere. The sphere is finite yet there is no wall at the end of it. A sphere can also expand. A sphere is a 2dimmensional world that is curved through a higher dimension. For us, you would just add one dimension to the equation. That's what I've always read snyways.

[DRT]

4 hours ago, andrew s said:

This is not a strop I have enjoyed the debate but all good things come to an end and I have my father of the bride speech to write

Thank you for the debate, Andrew - I have also enjoyed it.

I do not envy your next task - very best of luck with that and I hope the day goes well

 

[DRT]

3 hours ago, Herzy said:

The sphere isn't finite

I completely understand that spheres can expand otherwise ping-pong balls and footballs would be the same size. But any given sphere has a finite area, so in at least one sense a sphere is finite.

I think this could go on for a while

 

[Herzy]

13 minutes ago, DRT said:

I completely understand that spheres can expand otherwise ping-pong balls and footballs would be the same size. But any given sphere has a finite area, so in at least one sense a sphere is finite.

I think this could go on for a while

 

SORRY! I meant it IS finite. Typo.

[Nigel G]

Tonight on bbc4 at 10.30 horizon,  how big is our Universe , 

I must watch , 

[Nigel G]

After watching Horizon I'm even more confused ☺

Quotes from horizon,  The Universe IS 13.7 billion years old , our observable universe is 13.7 billion light years. 

The Universe IS 46 billion light years to the edge but could be infinite ?? The infinite they were suggesting is infinite distance not infinite amount of numbers within 46 billion LYs

Space is expanding at an accelerated rate, EVERYTHING is getting further away ? How comes Andromida is getting closer then?

A very interesting programme but a few contradictory quotes which only tells me that they don't have a clue to the size of our Universe which surely means they haven't a clue how old it is, if it is infinite the time its been here must be infinite. 

Still non the wiser ☺ I'll just have to find out myself  ☺☺. I might need a bigger scope. 

Nige.

[Nigel G]

25 minutes ago, Nigel G said:

 I'll just have to find out myself 

I've cracked it.  Having my morning tea I had a Einstein moment. 

Here's my theory. ..... The Universe is 1 x 1 x infinity,  the Universe is a very big 1

 Finally we know the truth.  Case closed ☺☺☺☺

[Alien 13]

The second part of that Horizon program "how small is the universe" is even weirder suggesting the real universe is actually smaller than an atom.

Alan

[cloudsweeper]

39 minutes ago, Nigel G said:

After watching Horizon I'm even more confused ☺

Quotes from horizon,  The Universe IS 13.7 billion years old , our observable universe is 13.7 billion light years. 

The Universe IS 46 billion light years to the edge but could be infinite ?? The infinite they were suggesting is infinite distance not infinite amount of numbers within 46 billion LYs

Space is expanding at an accelerated rate, EVERYTHING is getting further away ? How comes Andromida is getting closer then?

A very interesting programme but a few contradictory quotes which only tells me that they don't have a clue to the size of our Universe which surely means they haven't a clue how old it is, if it is infinite the time its been here must be infinite. 

Still non the wiser ☺ I'll just have to find out myself  ☺☺. I might need a bigger scope. 

Nige.

The 46 bn ly thing (courtesy of Wiki):

The best estimate of the age of the universe as of 2015 is 13.799±0.021 billion years^[5] but due to the expansion of spacehumans are observing objects that were originally much closer but are now considerably farther away (as defined in terms of cosmological proper distance, which is equal to the comoving distance at the present time) than a static 13.8 billion light-yearsdistance.^[8] It is estimated that the diameter of the observable universe is about 28.5 gigaparsecs (93 billion light-years, 8.8×10²⁶ metres or 5.5×10²³ miles),^[9] putting the edge of the observable universe at about 46.5 billion light-years away.^[10][11]

 

As for Andromeda - as I understand it, that is just a "local", gravitational effect.  Doesn't alter the much larger scale recession effect.

Doug.

 

[Stub Mandrel]

To me it's all greatly confused because people :

• Assume we are at the centre of the universe (we are at the centre of the observable universe but a moments thought makes it obvious that we are very unlikely to be at the real centre, in which case it is almost certainly bigger than the observable universe without recourse to any esoteric thinking).
• People confuse radius and diameter. If the furthest object we can see if 'x' away, the diameter of the observable universe is 2x.

How is anyone to understand the more complex ideas when these two basics are not properly addressed in simplified explanations?

[andrew s]

1 hour ago, Stub Mandrel said:

To me it's all greatly confused because people :

• Assume we are at the centre of the universe (we are at the centre of the observable universe but a moments thought makes it obvious that we are very unlikely to be at the real centre, in which case it is almost certainly bigger than the observable universe without recourse to any esoteric thinking).
• People confuse radius and diameter. If the furthest object we can see if 'x' away, the diameter of the observable universe is 2x.

How is anyone to understand the more complex ideas when these two basics are not properly addressed in simplified explanations?

Neil, the difficulty is that the concepts are difficult and subtle. While, I would agree we should not confuse diameter and radius the rest not so easily resolved.

For example while we are at the centre of our observable universe (to a very good approximation - we do orbit the sun.) the universe does not, in current models the universe does not have a centre.

Knowing how far away something is depends on when you measure it. Defining the when in cosmology is difficult or at least has multiple options. As an example do we mean the distance at the time of emission of the light we receive or where it will have moved to when we receive it?

To unambiguously resolve these issue requires terms and concepts most are not familiar with. Terms like proper-time, co-moving observer, metric expansion, gravitationally bound and so on as well as the ideas of the possible topology of space-time i.e. open or closed, finite or infinite.

No excuse I suppose but as this tread shows it is not easy. 

Regards Andrew.

PS I wish I had never discussed points on a line! I was just trying to get across the idea of bounded and unbounded and that something can be infinite and always expanding. Oh well try harder next time.

[andrew s]

I came across this post by Peter Donis on Physics Forum which I think is very clear and avoids the issue I raised above.

I have made some cosmetic changes to make it readable after cutting and pasting. Op in italics.

"the universe is 13.7 billion years old
Yes.

Which means light that reaches us NOW has traveled 13.7 billion light years
No. You are trying to apply intuitions that don't work in an expanding universe.

Let me describe in more detail what happened to light emitted 13.7 billion years ago that is just reaching us now. For simplicity, I'll assume the "light" is actually CMB radiation, because it gives a nice round number for how much the universe has expanded since then. The CMB radiation was emitted when the universe was about 300,000 years old, so it was emitted 13.7 billion years ago to very good accuracy. (Also, light emitted any earlier would not reach us anyway because the universe was not transparent to light until the time of CMB emission.)

At the time of CMB emission, a point in the universe that emitted CMB light that we, on Earth, are just receiving now (call this point P) was about 46 million light-years away from where Earth would have been if it had existed at that time (obviously it didn't, but we can trace back the spatial position of the Earth to that time).

At the current instant of time, 13.7 billion years from the time of CMB emission, when we are just receiving CMB light emitted from point P, point P itself is about 46 billion light-years away from Earth. That is because the universe has expanded by a factor of about 1000 since the time of CMB emission.

What happened in between was two things: the light emitted from point P in the direction of Earth traveled towards Earth; and the universe expanded. The two effects worked against each other; you can think of it, heuristically, as the light having to "swim upstream" against the universe's expansion in order to reach Earth. That's why the travel time of the light is not equal to either the time it would take light to travel the distance between P and Earth at the time of CMB emission (46 million years) or the time it would take light to travel the distance now between P and Earth (46 billion years), but something in between (13.7 billion years).

As for what distance the light "actually" traveled, there isn't really a well-defined answer. In an expanding universe, "distance" only has meaning at a single instant of time; for objects that take a lot of time to travel, there is no unique way to tell what distance they have traveled. The only really meaningful quantity is the travel time."

Regards Andrew