Possibly stupid universe question

[RB Will]

I just read that the universe is about 13.7 billion years old and that the universe has a diameter of approx 90 billion light years.

My understanding is that things can't exceed the speed of light so if it all started with a Big Bang then even if everything expanded at the speed of light the diameter can only be 27.4 light years across unless at the point of the Big Bang the universe was already a considerable size.

So clever people help me out with this one, preferably with an explanation that does not need a physics degree to understand it

[FunkyNige]

Apologies for posting links, but these may be of use
https://en.wikipedia.org/wiki/Observable_universe#...
http://www.astro.ucla.edu/~wright/Dltt_is_Dumb.htm...

Essentially it doesn't really make sense to measure distances in light-years, the example the second link gives is
If an SR-71 blackbird flies over at Mach 3 and you hear the sound 30 seconds later, then answer to the question "How far away is it?" is clearly not 30 "sound seconds" or 10 km

[ewenm]

Inflation theory - at some point in the very early universe the whole universe expanded very rapidly (much faster than the speed of light).

[eldar]

We don't know what happened in the f1rst 10,000,000th of a second after big bang, so anything could have happened. Secondly the universe isn't a nice ball shaped thing. It appears to have lots of odd properties.

To really understand it you need an odd brain.

[stew-S160]

13.82GA years is current estimate.

Inflation/expansion. The observable universe would be 13.82GA year in any direction. We are not the center of the universe.

[hairykrishna]

RB Will said:

I just read that the universe is about 13.7 billion years old and that the universe has a diameter of approx 90 billion light years.

My understanding is that things can't exceed the speed of light so if it all started with a Big Bang then even if everything expanded at the speed of light the diameter can only be 27.4 light years across unless at the point of the Big Bang the universe was already a considerable size.

So clever people help me out with this one, preferably with an explanation that does not need a physics degree to understand it

The universe itself expanded 'faster than light speed'.

[300bhp/ton]

Also if everything is expanding, I think Brian Cox's words on Stargazing were "moving away from each other". How can 2 galaxies be on a collision course?

[Eric Mc]

For the same reason two cars can collide - or two pedestrians can bump into each other on the footpath.

At a local level, everything ISN'T rushing away from each other.

In cosmological terms, a group of nearby galaxies is "local".

[TwigtheWonderkid]

What is the universe expanding into?

[Eric Mc]

TwigtheWonderkid said:

What is the universe expanding into?

Not a relevant question.
It does not need to expand "into" anything.

[Getragdogleg]

Eric Mc said:

TwigtheWonderkid said:

What is the universe expanding into?

Not a relevant question.
It does not need to expand "into" anything.

Ok, to ask it in a different way, What is where the universe isn't but is going to be ?

[Rotaree]

Getragdogleg said:

Eric Mc said:

TwigtheWonderkid said:

What is the universe expanding into?

Not a relevant question.
It does not need to expand "into" anything.

Ok, to ask it in a different way, What is where the universe isn't but is going to be ?

I was wondering this too - what's outside the expanding universe?

[ewenm]

Rotaree said:

Getragdogleg said:

Eric Mc said:

TwigtheWonderkid said:

What is the universe expanding into?

Not a relevant question.
It does not need to expand "into" anything.

Ok, to ask it in a different way, What is where the universe isn't but is going to be ?

I was wondering this too - what's outside the expanding universe?

Nothing, the Universe is everything (by definition!). The Universe isn't an object expanding in static space, the space itself is expanding.

[Eric Mc]

As it expands, it creates its own space - and time.

[Hooli]

Rotaree said:

Getragdogleg said:

Eric Mc said:

TwigtheWonderkid said:

What is the universe expanding into?

Not a relevant question.
It does not need to expand "into" anything.

Ok, to ask it in a different way, What is where the universe isn't but is going to be ?

I was wondering this too - what's outside the expanding universe?

A bag of marbles, I've seen MIB.

[Rotaree]

ewenm said:

Nothing, the Universe is everything (by definition!). The Universe isn't an object expanding in static space, the space itself is expanding.

Nope, sorry, much as I"'d like to, I'm still not grasping the concept. I suspect there isn't going to be an easily graspable way of explaining this one!

[Eric Mc]

The expansion may be into other dimensional space/time - something us three dimensional beings find impossible to envisage.

I always think the analogy of the two dimensional inhabitants of Flatland finding it difficult to visualise a third dimension is the best way of trying to relate to this.

[Terminator X]

Rotaree said:

I was wondering this too - what's outside the expanding universe?

You need to banish such thoughts or else you head will explode.

TX.

[Evil Jack]

Eric Mc said:

The expansion may be into other dimensional space/time - something us three dimensional beings find impossible to envisage.

I always think the analogy of the two dimensional inhabitants of Flatland finding it difficult to visualise a third dimension is the best way of trying to relate to this.

That epidode of "The Cosmos", where Carl Sagan goes on to demonstrate hyper-cubes as being 'shadows' of 4 dimensional shapes was pretty much the most convincing proof I ever saw for the existence of dimensions beyond our understanding...

[davepoth]

Rotaree said:

ewenm said:

Nothing, the Universe is everything (by definition!). The Universe isn't an object expanding in static space, the space itself is expanding.

Nope, sorry, much as I"'d like to, I'm still not grasping the concept. I suspect there isn't going to be an easily graspable way of explaining this one!

Try it another way. The universe stays the same size, everything in it is getting smaller, relatively speaking.