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

Nigel G

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Stub Mandrel

Stub Mandrel

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50 minutes ago, andrew s said:

the universe does not, in current models the universe does not have a centre.

That's more or less my point. It's certainly true if the universe was infinite at conception.

 

51 minutes ago, andrew s said:

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?

I explored this elsewhere, all I could conclude is that 'now' doesn't really mean very much, all we can grasp on to is that the speed of light limit means you can't screw with causality. Probably (and there's always the Morphail Effect...)

 

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andrew s

andrew s

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19 minutes ago, Stub Mandrel said:

I explored this elsewhere, all I could conclude is that 'now' doesn't really mean very much

The best idea I found to define a cosmological "nows" was to define them as a series of times at which observers would measure the same temperature for the CMB. This is not very practical but doable in principle. This would work ok in regions where gravitational time dilation was negligible.

Regards Andrew

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andrew s

andrew s

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2 hours ago, Pippy said:

Do we even know what we actually mean by 'time' ?

 

You just want this thread to go on forever! I think operationally for working scientists it is perfectly well defined and measurable. However, if it exists or not, is an active topic in the foundations of science (and an ongoing philosophical topic). I am currently rereading Julian Barbour's "The End of Time" where he argues it is a illusion and replaces it with a version of the "Block Universe" where "time" is a path through a preexisting space which contains all possible pasts presents and futures.

As far as I know though Block Universes have not made any unique observable predictions. In this sense it is a bit like the various interpretations of QM where they all give the same answers.

Regards Andrew 

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Herzy

Herzy

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On September 12, 2016 at 02:30, 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.

I'll try to the answer these as I understand it. I may not be entirely correct, however, as what I'll answer is mainly from documentaries that tend to oversimplify things.

"the universe is 13.7 billion years old and the observable universe is 13.7 billion light years in diameter."

"The universe is 46 billion light years in radius, but could be infinite"

These are not contradictory. You have to be careful with the definition of observable universe and universe. If the universe is 13.7 billion years old, light could only have traveled 13.7 billion light years. That means that we can see in any given direction 13.7 billion light years. That is our observable universe - everything that we can observe. 

The actual size of the universe, however, can be estimated to about 46 billion light years (I believe that estimation comes from the rate of acceleration and the age).

As for Andromeda, it is getting closer due to local gravitational effects. Galaxies on average are getting farther apart.

Hope that helps somehow.

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Alien 13

Alien 13

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2 hours ago, andrew s said:

You just want this thread to go on forever! I think operationally for working scientists it is perfectly well defined and measurable. However, if it exists or not, is an active topic in the foundations of science (and an ongoing philosophical topic). I am currently rereading Julian Barbour's "The End of Time" where he argues it is a illusion and replaces it with a version of the "Block Universe" where "time" is a path through a preexisting space which contains all possible pasts presents and futures.

As far as I know though Block Universes have not made any unique observable predictions. In this sense it is a bit like the various interpretations of QM where they all give the same answers.

Regards Andrew 

I would be quite happy for this thread to go on forever it has certainly enlightened me, it is perhaps the questions where we dont have the maths or an answer that are important.

Alan

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Tiki

Tiki

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8 hours ago, Pippy said:

Do we even know what we actually mean by 'time' ?

 

On a trivial (and local) level, time is simply that which is recorded on your wrist-watch. On a global level however, to be able to cogently define time would quite possibly be equivalent to solving the deepest cosmological questions.

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andrew s

andrew s

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14 hours ago, SilverAstro said:

or was that in a parallel universe ?

I have never understood why a parallel universe. I assume its intention was to indicate it was in some way it alongside ours but not touching. If that is the case it was a poor choice as parallel lines can easily intersect in a curves space-time and while the best estimate is that our universe is indeed flat the "parallel" one might well not be.

Make your hair stand up thinking about cosmic car crashes.

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