Flat Universe?

[mikey32shaw]

I was hoping someone could shed a little light on this for me please. After listening to a podcast recently they were saying we live in a flat universe.

What I was wanting to know is what is the definition of flat there talking about. Is it flat like a piece of paper with stars and planets sat on the same horizontal line? Or flat as in we are in a circular shoe box that has a little depth to it so stars could be above at below by a small amount?

Hope the question made sense.

Mike

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[JulianO]

Its the former - a bit like living on a plane, or on a sphere like the Earth. In a flat universe triangles have 180 degrees and parallel lines neither diverge or converge.

Its possible for the universe to be any shape - but being flat is an oddity - as there are many ways to be on a sphere, and many ways to be on the opposite (a saddle shape). Being in a flat universe is fairly unlikely, which is why inflation or a similar mechanism is required.

[Mr Flibble]

The key is to let the glue 'breathe' for about 5-10 mins before applying the patch. Then when you pump it up you shouldn't have any inflation problems. Sorry, I couldn't resist

[Knight of Clear Skies]

I struggled to understand this for quite a while. This is the most readable explanation of the flatness problem and how inflation theory solves it I've come across:

http://scienceblogs.com/startswithabang/2013/04/12/inflation-dark-energy-and-the-physics-of-spacetime/

Hope that is some help.

[laowho]

The Wilkinson Microwave Anisotropy Probe has also measured and found a flat universe. As for inflation, I think Guth should get the Nobel...the implications coming out of it--whichever particular model--are profound and spectacular...truly mind-bending. But I know what you mean...whether it's the surface of a sheet of paper, a sphere or a saddle, it's still hard to conceptualize, to map Euclidean geometry onto the real world.

[impactcrater]

THE Universe is not flat . It has been established that it is shaped like a Vuvuzela . That is, like a long thin trumpet.....this fits the models best for our understanding of what we see and how it appears gravity 'runs downhill'....

[JulianO]

THE Universe is not flat . It has been established that it is shaped like a Vuvuzela . That is, like a long thin trumpet.....this fits the models best for our understanding of what we see and how it appears gravity 'runs downhill'....

I don't think that agrees with the latest Planck findings. Do you have a reference for this?

[ollypenrice]

THE Universe is not flat . It has been established that it is shaped like a Vuvuzela . That is, like a long thin trumpet.....this fits the models best for our understanding of what we see and how it appears gravity 'runs downhill'....

I need to know more about this!

Olly

[saken]

Well, this is my first post on this forum and I hope you find it useful:

I can't tell what does it mean if the universe geometry is flat, but whatever it means it's possible we live in a flat universe.

However it's not quite probable, as for the universe to be flat, it requires an exact amount of mass to comply with a specific density.

"If the average density of the universe exactly equals the critical density so that Ω = 1, then the geometry of the universe is flat: as in Euclidean geometry, the sum of the angles of a triangle is 180 degrees and parallel lines continuously maintain the same distance. Measurements from Wilkinson Microwave Anisotropy Probe have confirmed the universe is flat with only a 0.4% margin of error."

http://en.wikipedia.org/wiki/Ultimate_fate_of_the_universe#Flat_universe

This briefly explains this concept of universe geometry related to density:

http://csep10.phys.utk.edu/astr162/lect/cosmology/geometry.html

Hope this was useful =]

[Ronnie67]

We live in a lopsided universe: That has been a lesson that cosmologists have learned from examining the detailed structure of the radiation left over from the Big Bang. Now, two cosmologists show that the data are consistent with a universe that is curved slightly, similarly to a saddle. If their model is correct, it would overturn the long-held belief that the cosmos is flat.

On a large scale, precision measurements of the cosmic microwave background (CMB) by NASA’s Wilkinson Microwave Anisotropy Probe provided the first hints of an asymmetry in 2004. Some experts wondered whether the finding was a systematic error that would be corrected when the NASA probe’s successor, the European Space Agency’s Planck spacecraft, mapped the CMB again with higher precision. But the Planck results, announced earlier this year, confirmed the anomaly.

To explain those results, Andrew Liddle and Marina Cortês, both at the University of Edinburgh, UK, have now proposed a model of cosmic inflation—a hypothetical period of rapid expansion right after the Big Bang in which the universe grew by many orders of magnitude in a small fraction of a second.

The simplest theory of inflation holds that the universe is flat and that its expansion is driven by a single quantum field called the inflaton. In their model the inflaton has two roles: it triggers hyperexpansion and generates the tiny density fluctuations that enlarged to become the seeds of galaxies.

[JulianO]

The Planck findings are consistent with a flat universe. Their actual figures are -0.1 +/- 0.62 - with a value of 0 being flat and anything else being curved in one direction or another with higher numbers being more curved. 0.1 is pretty close to zero, and with a margin of error of 0.62, 0 fits easily in that range. So its pretty clear the evidence points at a flat universe so far. You can see the full results here - but to summarise from their conclusions.

In summary, there is no evidence from Planck for any departure from a spatially flat geometry. The results of Eqs. (68a) and (68b) suggest that our Universe is spatially flat to an accuracy of better than a percent.

The article by Liddle and Cortes is a hypothesis. It may turn out to be real, but there are countless papers on this subject every month, each showing how a given model might fit the data. So its possible their model might turn out to be right, but as far as I'm aware it has no consensus as yet.

[impactcrater]

i base my statements on the lovely and stimulating article which appeared in a magazine called 'science illustrated' , formally 'australian science illustrated' issue 20, 21 november 2012. page 68. 

reading it again i see that there are two concepts which are 'degree of flatness' and 'shape of the universe' and they are not the same and even knowing the universe is flat does not tell you what shape it is !!! some possibilities are a torus (flat universe, and apparently this is the simplest topology) , a Poincare dodecahedron (bent positively) and a Picard horn which is like a vuvuzela (negatively bent).

this is a lot to get your head about and is certainly beyond me....but I really like the idea that we may be sitting in a 'hall of mirrors' and thinking we are seeing a lot of stuff in the distance and are really just looking at varied reflections of the same things....it even makes you feel comologically less lonely.

[Ant F]

 I think Guth should get the Nobel...the implications coming out of it--whichever particular model--are profound and spectacular...truly mind-bending. But I know what you mean...whether it's the surface of a sheet of paper, a sphere or a saddle, it's still hard to conceptualize, to map Euclidean geometry onto the real world.

nahh only war mongers get nobel prizes

[cosmiquery]

My understanding is that gravity distorts space, making it not flat ("positive"), and dark energy distorts it the opposite way ("negative") . Our universe appears to have just enough dark energy to balance gravity, so that when you add them together you get zero which corresponds to space being (overall) flat.

[Ronnie67]

Curvature and energy density are very closely related in cosmology: you measure the expansion rate (which allows you to calculate the Universe's critical density), you measure the energy density, and then you compare those two to determine the curvature. As far as our measurements can tell, the actual average energy density of the Universe, including dark energy is indistinguishable from the critical density, and that’s why our Universe's curvature is indistinguishable from flat.