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Asked by rohitmkiller to Adam, Geoff, Rob, Sheila, Suzie on 15 Mar 2011 in Categories: Space.
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Geoff McBride answered on 14 Mar 2011:
I like this sort of question. There’s a pretty good book called ‘Big Bang’ by Simon Singh. He puts it rather nicely. The Big Bang wasn’t an explosion in space it was an explosion of space, it wasn’t an explosion in time it was an explosion of time. Some don’t agree BBC Horizon ‘What is Reality’ had some interesting views.
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Robert Simpson answered on 14 Mar 2011:
This is a confusing topic, so this may be a confusing answer.
Imagine a balloon with a grid drawn on it, If you imagine blowing up that balloon, there is always the same amount of balloon, and the same number of squares on the grid, but it is being stretched out as you fill it with air. If there were objects sitting on the grid (e.g. galaxies) then they aren’t moving but rather they are stretched apart with the grid itself. They remain the same number of grid spaces apart from each other all the time.
This is why there is no ‘centre’ of the universe. Where is the centre of the balloon? There isn’t one as part of the grid. The balloon expands into the third dimension that you and I can see, but which a balloon had no concept of.
Similarly, if you were a two-dimensional creature that lived on the balloon and asked where the edge of the balloon was, you can see that the question doesn’t necessarily make any sense. The edge of the balloon is outside of the balloon and so you can never detect or comprehend it. If the Universe is expanding into something then presumably the universe has an ‘edge’ but what that would be is beyond the universe itself.
If the Universe has no edge and is infinite, which is how I understand things to be, then we are dealing with infinity and that gets really weird. Think of the Universe as a grid of length infinity and width infinity. The part of the universe nearest you in easy to ‘measure’ you have 1,2,3,4,5,6 and so on, out to infinity, in each direction. If the Universe stretches out to be twice as big your local part becomes 2,4,6,8,10,12 and so on instead and this goes out to… well its still infinity. Actually its infinity x infinity, which is… infinity. So the universe got twice as big and is still infinite. There is nothing beyond the grid of numbers because it is infinitely long.
I have a feeling I’ve confused myself here so I hope this helped. there are some excellent books about infinity and also a great book called the ‘Book of Nothing’ by John Barrow, which is very mind-bending but not too hard to grapple with. I read it as a teenager and although parts passed me by, it mostly made sense.
Phew – that was a long one…
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Adam Tuff answered on 14 Mar 2011:
This is a question even I don’t think I, nor anyone else could answer – the answer though could depend on one crucial fact – does the universe have edges? If it doesn’t, and it is infinite, then the question of where are the edges is meaningless. We can radiation – photons, from very early in the universe, coming from the far reaches of space, but even though these were created early in the universe’s existance, we cannot see what is beyond it, and we will never be able to. If this is the case, I don’t think we will ever be able to find out. Good question!
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Sheila Kanani answered on 14 Mar 2011:
As far as I see it, the universe sort of makes the space it expands into, so I don’t think there is a set volume for it. That is a bit of a head-spinny idea I know! Think of it like the surface of a balloon stretching rather than expanding.
Not sure if this will help or not:The latest ideas on the fate of the universe (as far as I know) are still:
1) Ever expanding
2) The big crunchThe evolution of the universe is determined by a struggle between expansion and the pull (or push!) of gravity. The current rate of expansion is measured by the Hubble Constant, while the strength of gravity depends on the density and pressure of the matter in the universe.
If the pressure of the matter is low, as is the case with most forms of matter we know of, then the fate of the universe is governed by the density.
If the density of the universe is less than a critical density, then the universe will expand forever. Gravity might slow the expansion rate down over time, but for densities below the critical density, there isn’t enough gravitational pull from the material to ever stop or reverse the outward expansion. This is also known as the “Big Chill” or “Big Freeze” because the universe will slowly cool as it expands until eventually it is unable to sustain any life.
If the density of the universe is greater than the critical density, then gravity will eventually win and the universe will collapse back on itself, the so called “Big Crunch”. In this universe, there is sufficient mass in the universe to slow the expansion to a stop, and then eventually reverse it.
Recent observations of distant supernova have suggested that the expansion of the universe is actually accelerating or speeding up which implies the existence of a form of matter with a strong “negative” pressure. This strange form of matter is also sometimes referred to as the “dark energy”.
We believe that unlike gravity which works to slow the expansion down, dark energy works to speed the expansion up. If dark energy exists, and plays a significant role in the evolution of the universe, then in all likelihood the universe will continue to expand forever.
There is a growing consensus among cosmologists that the total density of matter is equal to the critical density, so that the universe is spatially flat. Approximately 3/10 of this is in the form of “non-baryonic” dark matter, while the remaining 7/10 is thought to be in the form of “dark energy”. If this is true, then dark energy is the major driving force behind the fate of the universe and it will expand forever exponentially.
I quite like the idea of a Big Crunch, because then there could be a new Big Bang and it can all start again! This theory is called the Big Bounce 🙂
What do you think is going to happen?
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Suzie Sheehy answered on 15 Mar 2011:
This is always a question which blows my mind a little bit. It’s hard to ask “what” it’s expanding into though, because it is just expanding. The Universe that we know contains all the space that we know about, and that itself is expanding. That could be wrong, but we just don’t know.
If you think of a way to find out, let me know!
Comments
rohitmkiller commented on :
Thank you all so much for your comments: it’s been a real eye-opener into the theories of this really interesting topic of space.
Thanks Geoff for the reference to the book which I shall aim to look into, and thanks Robert for you answer which makes a fair amount of sense 🙂
Sheila, I think it’s really quite interesting to know about the effects of dark energy – something which I didn’t know a lot about, so thank you. I think, so far looking at the theories you have all put so far, I believe that there will come a stage of the ‘Big Crunch’ and that as I think one theory has been put forward elsewhere, that maybe the Universe we know is in fact park of a ‘multi-verse’ (if that’s the correct term!) and there is continual creation, expansion and collapsing of universes over billions of years; but as Adam said, maybe we’ll never know!
Sheila commented on :
Np Rohit, this is what we’re here for!
Suzie commented on :
Rohit, on my profile page there is a link to a song called “multiverse” that a friends’ band recorded in honour of my work. Check it out! (in the “what would you do with the money?” section)