Try to get your brain around this.

[BargeGazer]

Big Bang was 13.7 billion years ago but now the observable universe stretches up to 46.5 billion light years from us! Doesn't that mean it is expanding faster than the speed of lightt!!??

http://scienceblogs.com/startswithabang/2012/12/28/the-universe-beyond-our-reach

I need to think about this a bit more! Actually I think I need a chat with someone like Brian Cox!

David

[anthony]

There'll be better answers than mine and I have no confidence in my answer and I am sure that I am completely muddled but I think that early on inflation had a big role to play in this. Also I think that presently, as it is space that is expanding and the further away from us a region of space is, the faster it is receding from us. So, in effect space is (might be?) expanding faster than light travels.

I vaguely remember an analogy with a length of elastic band, mark several dots with pen equally spaced and stretch it evenly. Those dots further from the central portion will have moved further and faster than those closer to the centre despite the stretch being even.

Less sure about this bit - observable universe is the key in the statement. Light radiating out in all directions. Pick a point and that light will have travelled to the same degree in the opposite direction by the time it has reached us

Or something like that.

PS having said that, I can't get my brain round it!

[cantab]

Big Bang was 13.7 billion years ago but now the observable universe stretches up to 46.5 billion light years from us! Doesn't that mean it is expanding faster than the speed of lightt!!??

Yes. It's allowed because it's space itself that's expanding, and because no information is being sent faster than light.

[Photosbykev]

we are assuming that the speed of light is the fastest velocity possible based on our caveman knowledge of the universe.

[George Jones]

I, too, put it down to the expansion of space, but I have yet to work out a non-mathematical explanation with which I am happy. One attempted partial explanation:

Special relativity is the theory that prohibits speeds greater than the speed of light. Cosmology, however, is not governed by special relativity, cosmology is governed by the curved spacetime of general relativity, to which special relativity is a good *local* approximation. Because special relativity is a good local approximately, and because special relativity prohibits speeds faster than the speed of light, we will never see anything moving faster than the speed of light in our *local neighbourhood*. Stuff at the "edge" of the universe is not in our local neighbourhood, and thus is not governed by the laws of special relativity.

As an analogy, consider what happens on the curved surface of the Earth. Locally, a flat surface is a good approximation to the curved surface of the Earth. Locally, e.g., on your living room floor, you can lay down a nearly perfect grid. Try to lay down a perfect grid on a patch of the Earth's surface that is several hundred kilometres by several hundred kilometres. It can't be done. The properties of flat surfaces apply locally to the Earth, but not globally.

[Tiki]

Big Bang was 13.7 billion years ago but now the observable universe stretches up to 46.5 billion light years from us! Doesn't that mean it is expanding faster than the speed of lightt!!??

Yes. This implied superluminal velocity is an artefact of how distance is defined when used on a large scale. Cosmologists frequently use a measure called 'proper distance'. Special Relativity uses a locally defined and more intuitive concept of distance eg. a ruler.

[DaveGarland]

I've just noticed this thread after randomly coming across this on YouTube.

I was quite happy with the universe looking roughly 13 billion (ish) light years in all directions but now all this. To be honest I feel scrambled! Is this video correct in its theories? The narrator does sound a bit of a weird hippy type.

[JulianO]

I think the concepts in this film are broadly right, but they rather over cook the effects.

Inflation is currently the best answer to a number of questions, but it isn't the only answer. There are a lot of issues with inflation that haven't been tied down fully yet, so it is fairly mainstream, but still needs some things to be sorted out. Quite how much it inflated if inflation is true is also up for dispute, and it's possible in some areas of the universe it is still going on - which is one of the issues with it.

One of my issues with productions like this is they present everything as fact - when at best it is mostly "These are our best guesses currently".

[Ganymede12]

No thing can go faster than the speed of light. Nothing can go faster than the speed of light. Space isn't really a "thing" so It can travel as fast as it wants.

At least, that's my understanding of it!

[stevegaze]

There'll be better answers than mine and I have no confidence in my answer and I am sure that I am completely muddled but I think that early on inflation had a big role to play in this. Also I think that presently, as it is space that is expanding and the further away from us a region of space is, the faster it is receding from us. So, in effect space is (might be?) expanding faster than light travels.

I vaguely remember an analogy with a length of elastic band, mark several dots with pen equally spaced and stretch it evenly. Those dots further from the central portion will have moved further and faster than those closer to the centre despite the stretch being even.

Less sure about this bit - observable universe is the key in the statement. Light radiating out in all directions. Pick a point and that light will have travelled to the same degree in the opposite direction by the time it has reached us

Or something like that.

PS having said that, I can't get my brain round it!

Having the same problem lol. i look at he ring nebula and imagine this as the big bang with all the dust ,gas and debris moving away from the blast site,,as the ring moves away it starts forming into galaxies in all positions but still moving away from the blast at the same speed...and now we can see the light from these galaxies at different positions of the ring as it still moves away from the blast site.....if you imagine our local group at the top of the ring and we see galaxies out there at say 2 million upto 2 billion light years away then these galaxies maybe at 1 or 2 0clock or 10 or 11 0clock in the ring ....then we see light from 4 to 8 billion light years away ..these could be the galaxies at 3 to 5 oclock or 9 to 7 oclock in the ring .but the red shift would show these moving away faster than the closer galaxies but actually going the same speed ....then we find light from galaxies 13 billion light years away these would be at 6 oclock in the ring and red shift would show these the most distant and moving away faster.......thats it the white coats are coming to pick me up lol brain as gone