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andrah
2010-Feb-15, 11:13 PM
Hello
can someone tell me why when explaining about the universe scientists tend to showthe universe as a sphere or globe? Is it simply because it is easier for us to comprehend in this manner or is there an actual scientific reason for this portrayal?
If there is no scientific reason for this portrayal, does the universe have a shape? I dont understand why it would have a shape at all.
I watched the BBC Horizon program about Infinity, the inflation theory of our universe made sense to me, but Im not sure that it was because of the way it was demonstrated by blowing a ball up!
Many thanks
Andrea

IsaacKuo
2010-Feb-15, 11:20 PM
Mostly, it's just a convenient analogy. However, the observable universe is limited by the age of the universe and how far light could have moved during that time. As such, the observable universe is roughly spherical. That doesn't mean there isn't anything beyond the edge, it just means that light from beyond the edge hasn't reached us yet.

andrah
2010-Feb-15, 11:33 PM
Thank you. OK, yes I understand about what we can actually see and there not necessarily being an edge (doesnt that depend on whether you believe the universe is infinite or not;). Is what we can observe spherical because we are viewing from a ball or because of our instruments and the way in which we view, I still dont know why what we view is spherical unless it is because of our 'field of vision'. Sort of like only being able to see so far out to sea because of the curve of the Earth.

01101001
2010-Feb-16, 12:30 AM
Is what we can observe spherical because we are viewing from a ball or because of our instruments and the way in which we view, I still dont know why what we view is spherical unless it is because of our 'field of vision'.

It's because the universe has existed only for some 13.7 billion years and no matter which direction we look the most distant things we see appear to be the same distance away, (nearly) 13.7 billion light years (look-back distance). That most distant stuff defines a sphere: a set of points that are all at the same distance from us.

Wikipedia: Observable universe (http://en.wikipedia.org/wiki/Observable_universe)

andrah
2010-Feb-16, 01:05 AM
Thank you for the answer and the Wikipedia link...I am a biologist and do not use wikipedia but Im hoping the info you sent me is pretty accurate.
I really didnt understnd what was meant by 'observable universe'...I was taking it far too literally.
Lots of reading to do I think! and I feel like a fool now.
Thank you tho

Jeff Root
2010-Feb-16, 01:14 AM
In addition to what Ones and Zeros says, the visible part of the Universe
looks spherical simply because anything that surrounds you and doesn't
have a visible surface or edge looks like the inside of a sphere. When
you look at the blue daytime sky you are seeing light from all distances
ranging from right in front of your eyes to almost a thousand miles away
(just above the horizon). It gives the impression of the inside of a dome.
The night sky is similar: You see stars at all different distances, but they
are much too far away to detect the different distances, so they look
like they are all on the inside of a gignormous dome.

Considering the Universe beyond what we can see with our eyes, but can
see with telescopes, the main reason to consider it as appearing spherical
is just that we are accustomed to thinking of it that way from having seen
the night sky with our own eyes. It doesn't actually *look* spherical,
except that the limit of what we can see due to decreasing brightness
with increasing distance defines a sphere around us. Nomatter where you
go, you are always at the center of the visible Universe! (As long as a
wall of some kind doesn't get in the way.)

-- Jeff, in Minneapolis

Cougar
2010-Feb-16, 04:09 PM
...can someone tell me why when explaining about the universe scientists tend to showthe universe as a sphere or globe? Is it simply because it is easier for us to comprehend in this manner or is there an actual scientific reason for this portrayal? ... does the universe have a shape?

Sometimes a spherical balloon is used as an analogy of the expanding universe. It is important to note, however, that the balloon analogy focuses only on the two-dimensional surface of the balloon as representing the entire universe. The two-dimensional surface of a balloon has directions north-south and east-west, but no up and down! Dropping out the up-down dimension just makes it easier to picture and get an idea of what's going on.

The surface of a sphere also illustrates a "universe" that is finite but unbounded. No edge! The geometry of the universe, at least that which we can see, appears to be flat - Euclidian. (That's 3-dimensional "flat".) The topological shape of the universe, however, is another story and is unknown, AFAIK. I recommend Janna Levin's How the Universe Got Its Spots.

JustAFriend
2010-Feb-17, 07:43 PM
Which is more easier to imagine:

a googleplex polyhedron with multidimensional extensions

or just say "here's a sphere 50 billion light-years across..."

...sometimes ya just gotta let the picky things go......

cosmopaul67
2010-Feb-17, 08:55 PM
I think that the balloon surface analogy is misleading too; espacially when cosmologists also assert that the topology of spacetime appears flat, or is curved, or closed... :confused:

I always prefered to think of the universe as a baking loaf of raisin bread, with the yummy raisins representing the matter of galaxies (which don't expand) and the bread dough as spacetime. But now it looks like we live in a multi-verse sized pan of hot-cross buns all rising and baking at different rates due to the baker not sifting and mixing the dough thoroughly enough and adding bags and bags of nuts to the recipe in the form of dark matter, and accidently dumping way, way too much baking powder in the form of dark energy... !

...All in all, these buns seem really hard to swallow, but in lieu of any other tasty treats, we just have to suffer with them for the time being ... :)

caveman1917
2010-Feb-20, 02:53 AM
In addition to what Ones and Zeros says, the visible part of the Universe
looks spherical simply because anything that surrounds you and doesn't
have a visible surface or edge looks like the inside of a sphere. When
you look at the blue daytime sky you are seeing light from all distances
ranging from right in front of your eyes to almost a thousand miles away
(just above the horizon). It gives the impression of the inside of a dome.
The night sky is similar: You see stars at all different distances, but they
are much too far away to detect the different distances, so they look
like they are all on the inside of a gignormous dome.

There seems to be a perspective which takes this a step further http://en.wikipedia.org/wiki/Holographic_principle

If i understand it correctly, it states that we can actually consider the universe to be 'painted' on the inside of this sphere, in this case the cosmological horizon.

01101001
2010-Feb-20, 03:15 AM
http://en.wikipedia.org/wiki/Holographic_principle

If i understand it correctly, it states that we can actually consider the universe to be 'painted' on the inside of this sphere, in this case the cosmological horizon.

It's part of the non-theory of strings, so don't expect it to offer much explanatory power. And I'm not sure you noticed, though you reproduced them, the quotes around the word 'painted'.


In a larger and more speculative sense, the theory suggests that the entire universe can be seen as a two-dimensional information structure "painted" on the cosmological horizon, such that the three dimensions we observe are only an effective description at macroscopic scales and at low energies.

That sort of paint-like mapping isn't something likely to define the spherical shape of the observable universe. Simple geometry suffices for that. The article speaks of a much different sort of seeing there.