# The size of the universe



## MolotovCocktail (Mar 10, 2007)

Just how big do you think the universe really is? I read somewhere that its radius was estimated to be 130 billion light years across, which of course is much bigger than what can be observed.


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## j d worthington (Mar 10, 2007)

Atomika said:


> Just how big do you think the universe really is? I read somewhere that its radius was estimated to be 130 billion light years across, which of course is much bigger than what can be observed.


 
Well, Wiki's article on the universe had this to say about it:

Universe - Wikipedia, the free encyclopedia

However, there is strong disagreement. NASA has this on the subject:

Measuring the Size of the Universe

but with a stipulation about this being the "visible universe", which may not be anywhere near the total of the "physical universe":

Inflation for Beginners

And, for things a bit more simply stated:

Physics 110 Universe Age and Size

And this one takes it in graduated numbers, to help visualize and grasp:

http://physics.ucsd.edu/~tmurphy/phys10/universe.pdf

Answer: it all depends on how large a percentage of the total universe the visible universe is, how widely dispersed the remainder is, whether it curves back on itself in one of the various models... there is no single number for the all the various possibilities, even if we had a total for the amount of material in the entire universe, and its dispersion, if we have a universe that curves back on itself in the trumpet shape that's now being proposed, then by one measurement, it would be simply from the "small end" to the "large"... but that leaves out the fold back -- and there may be several of those, for all we know. It may even fold and then refold, like a staircase turns and then returns as one goes up levels... all without going "up" of course... but it's the only way we can visualize it.

Let me put it to you this way: In *Rocket Ship Galileo*, one of the characters asks another "how fast they're going"... well, it depends on what is meant: acceleration? In relation to everything else, which is also moving? etc. In other words... there is no simple answer, because it would depend on the frame of reference of the question.


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## catchmetwenty2 (Mar 26, 2007)

this is what i think about the universe:

there are juts 2 universes, parallel to each other, one is god, one is our universe. when we die, it is a trigger that sends us to the other universe, god.  i also think if we were to try to reach the outside of the universe, it wouldnt happen. i think that the universe has a mirror effect. you know when you put two mirrors next to each other htey go on forever. i think the same thing with the universe


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## mosaix (Mar 26, 2007)

j. d. worthington said:


> Well, Wiki's article on the universe had this to say about it:
> 
> Universe - Wikipedia, the free encyclopedia
> 
> ...



Thanks for the links JD.


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## j d worthington (Mar 26, 2007)

You're welcome...


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## The Ace (Mar 26, 2007)

Big enough ?


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## PTeppic (Mar 26, 2007)

Too big?


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## Talysia (Mar 26, 2007)

The size of the universe?  I doubt I'll find out in my lifetime, nor in many lifetimes.  All I know is that it's much bigger than anything I can comprehend.


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## Admiral Ryouhei (Apr 9, 2007)

as far as I can remember the universe is said to be expanding AT or FASTER than the speed of light since... THE BEGINNING, supposedly(spl?)

I'd assume it's expanding at FTL rates, but HOW BIG?

dunno, that's like asking a blind guy on a perfectly round/smooth sphere how big the sphere is when its the size of the earth

to know how big you'd have to know at what speed it started expanding from planck length and actually, how long it's been, but since time is relative, you can't really answer that

why? because gravity slows time around it, IF time exists, so then, something farther out is actually traveling faster according to your standpoint than it normally would be if there was no gravatic interference

so, the existence of matter ruins your whole question because space and time (if it exists as a dimension and not as some abstract) are distorted

so, yeah, the answer is: bigger than you think it is but smaller than it should be

idk


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## Chupacobra (Apr 13, 2007)

Surely the Universe is exactly the size of one universe?

How could it be anything else?


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## mosaix (Apr 13, 2007)

Chupacobra said:


> Surely the Universe is exactly the size of one universe?
> 
> How could it be anything else?



How big is that then?


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## chrispenycate (Apr 13, 2007)

The only convenient unit to measure it in (Parsecs are far too small) is UWs (universe widths) and, surprise, surprise it's exactly one universe by one universe by one. Very mystic that it should come out so precisely, no?


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## mosaix (Apr 13, 2007)

chrispenycate said:


> The only convenient unit to measure it in (Parsecs are far too small) is UWs (universe widths) and, surprise, surprise it's exactly one universe by one universe by one. Very mystic that it should come out so precisely, no?



Yeah, Chris but what good is a unit of measure that varies from one moment to the next?

But, I admit, that it is very spooky indeed that even thought the unit of measure does vary it should remain, nonetheless, extremely accurate.


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## Chupacobra (Apr 14, 2007)

mosaix said:


> How big is that then?


 
Exactly one universe in width and the same again in height.

It's the only one we've got, so questions about its size are a bit meaningless. By asking how big something is you are implying that it has an edge...something that you can measure from. By definition, the universe is everything, and therefore it cannot have edges.


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## mosaix (Apr 15, 2007)

In New Scientist this week they think that the have discovered that the Universe is mellon shaped rather than sperical.

Now a shape implies edges to me and mellon shaped means that it is a different size in one direction than it is in the other. And the use of the word size implies measurement..........

Also it's expanding of course so it's bigger than it used to be, so questions about size are certainly not meaningless.


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## Chupacobra (Apr 15, 2007)

mosaix said:


> Now a shape implies edges to me and mellon shaped means that it is a different size in one direction than it is in the other. And the use of the word size implies measurement..........


 
Did the NS article give any idea on what might be on the other side of the edge?


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## daisybee (Apr 16, 2007)

I always thought that the term universe pretty much covered everything, so how can it have a size? If we are part of a system that exists inside/outside something bigger -then we would rename our chunk of space and still label the entire thing universe wouldn't we? Therefore we couldn't possibly measure it because -if there is no such thing as nothing- then the term universe will be used for whatever is beyond our edge. Right?


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## chrispenycate (Apr 16, 2007)

It is possible to have something which is unbounded, but not infinite, where any point in three dimensional space can equally well be considered as the centre from which all is expanding. Such a space would have no edges, but it would have a size.
If (as seems most likely at present) the universe is expanding at the speed of light (where photon is, there is spacetime) and has been doing so since the Big Bang, then all we need is the age of the universe, and there's your radius in light years (lots, to an order of magnitude) It is, however, strange that they consider the form assymetric - I assume they have reasons for that.
Basically, it's not worth walking towards the edge, because even if it weren't receding at light speed it's also the edge youre walking away from.


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## daisybee (Apr 16, 2007)

So if it is constantly expanding then at most we could only calculate the size of the universe at a given point in history, or possibly predict the size it would be in x years time? Doesn't it get confusing trying to work out the size of something that can also be defined in light years?  Do we want to know the size of the universe or the amount of time held within it?


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## mosaix (Apr 16, 2007)

Chupacobra said:


> Did the NS article give any idea on what might be on the other side of the edge?



Nothing obviously. Everything in the Universe is this side of it.


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## Admiral Ryouhei (Apr 18, 2007)

I think a good explaination for the edge of the universe is: it's everywhere and nowhere, hence you are always at and can never reach the edge

but.. does that mean the universe is more like a wall between that which is in and that which is out? and how does 3-dimensions fit into the wall?


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## chrispenycate (Apr 18, 2007)

It's not anything as defined as nothing, just as the "edge" is its own other side. You can't fly to the edge of the universe, because wherever you are is the centre, and the limits are equidistant either side of you. You can't have emptiness where there is no spacetime, no interval; and when spacetime comes into existence (except there is no "when" because there is no time to have "when" in) then it's universe, seamlessly fitting into the space between galaxies.

The traditional model is this infinitely small, infinitely elastic balloon. No, the big bang isn't when I burst it; this time we're going for a big puff.

All the matter, energy, dark matter - the entire three dimensional continuum - is mapped onto the skin of the balloon. As it's infinitely small there isn't much elbow room so a first puff, and the seething dot can stabilise down into particles, and atoms, and nebuli, and stars and galaxies. (that _was_ a big puff) An ant on the surface of the balloon can only receive information along the rubber, so Occam's razor tells him it's flat, and light travels in straight lines, but, from outside we can see that it's curved and, if I keep on blowing, the entire surface is expanding, but not developing any edges - there's no rubber outside the surface.
We only need to add one more dimension, and the surface becomes volume - but since all matter and energy is within that volume, which is expanding at a considerable rate, and all information reaches us through that matter and energy, we are totally incapable of detecting the curvature, or imagining the situation in which that curviture exists; we're just not wired for it.
Clear? No?

*_lets go of universe which blblblbs out over heads  of audience_*


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## Chupacobra (Apr 19, 2007)

chrispenycate said:


> we're just not wired for it.
> Clear? No?


 
Very much so, and thanks for a very clear explanation.


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## matt-browne-sfw (Jul 20, 2007)

Admiral Ryouhei said:


> as far as I can remember the universe is said to be expanding AT or FASTER than the speed of light since... THE BEGINNING, supposedly(spl?)
> 
> I'd assume it's expanding at FTL rates, but HOW BIG?
> 
> ...



I found this puzzling too. If the age of the universe is 13.7 billion years and we assume a nuch larger "diameter" of the universe, this could only work if superluminal speed is possible, couldn't it? Well, it's important to understand the concept of the comoving distance (which is a bit tricky),

see Comoving distance - Wikipedia, the free encyclopedia

The fascinating aspect is that wherever you go in the universe, you're not closer to the "edge". The radius stays the same. Many believe it's *46.5 billion light-years...

*


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## matt-browne-sfw (Jul 21, 2007)

chrispenycate said:


> It's not anything as defined as nothing, just as the "edge" is its own other side. You can't fly to the edge of the universe, because wherever you are is the centre, and the limits are equidistant either side of you. You can't have emptiness where there is no spacetime, no interval; and when spacetime comes into existence (except there is no "when" because there is no time to have "when" in) then it's universe, seamlessly fitting into the space between galaxies.
> 
> The traditional model is this infinitely small, infinitely elastic balloon. No, the big bang isn't when I burst it; this time we're going for a big puff.
> 
> ...



A perfect explanation! To understand how the universe's age of 13.7 billion years does not contradict a radius of 46.5 billion light years given the speed of light limitation, the concept of the "comoving distance" is very helpful.

See Comoving distance - Wikipedia, the free encyclopedia


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## matt-browne-sfw (Jul 25, 2007)

Test Post.

Funny, this thread doesn't show up in my User Control Panel.

One more try...


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## Naryaló S dú (Jul 27, 2007)

We'll never know since the universe is expanding at an incomprehensible rate.


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## Interference (Aug 27, 2007)

From the front of your finger to the back of your finger - the long way.


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