So whats this i hear about a flat cosmological model of the universe?

[Zolar V]

http://wmap.gsfc.nasa.gov/

 

i stumbled across a new (to me at least) idea, that being the universe is flat.

wtf?

when did this happen.

[Martin]

http://wmap.gsfc.nasa.gov/

 

i stumbled across a new (to me at least) idea, that being the universe is flat.

wtf?

when did this happen.

 

No big deal. "flat" is technical parlance for not being curved.

 

Not being curved means for instance that whatever triangle you construct with lightrays will have angles add to 180 degrees.

 

Or for instance it means that the volume of a ball increases as the cube of the radius. (assuming we are talking about a 3D space.)

 

For an ordinary 3D space like we live in to be nearly "flat" just means it has the geometry that you are taught to expect in 9th grade or highschool---with 180 degree triangles and all that.

 

In fact space is NOT exactly flat. It has local bumps and hummocks.

what NASA is talking about is LARGE SCALE AVERAGE geometry. and even that we do not know to be exactly flat. All the WMAP data showed is that it was NEARLY so. Even if you only look large scale and ignore the local humps like around the sun, we still don't know exactly flat.

 

You ask "when did this happen?" "when did we find this out?" :-D

 

Well we've always known that over small distances, in and around our solar system locale, the geometry was nearly flat.

 

But measuring the large scale curvature, over billions of lightyears, is quite challenging. So we didn't know for a while. Evidence has been building up for either zero curvature, or maybe a very slight positive curvature (so that very large triangles would add to very slightly more than 180 degrees.) The WMAP spacecraft has been taking data for something like 8 years. Other methods involve counting galaxies within larger and larger volumes. The work goes on, the estimates get more accurate. It is still not finally settled.

Edited March 15, 2010 by Martin

[Zolar V]

So your saying the universe is flat then?

so all i was taught about the big bang, and how it universally expanded in a spherical shape is technically wrong.

[toastywombel]

So your saying the universe is flat then?

so all i was taught about the big bang, and how it universally expanded in a spherical shape is technically wrong.

 

Who taught you that?

[StringJunky]

It puzzles me too. If the Universe has a flat geometry what overall shape does it have if we could, hypothetically, look at the whole Universe from a distance based on current data? How would a computer model view its outward appearance?

[Zolar V]

no idea.. i dont really think its flat

 

i think our idea of its flat is similar to our idea of the world being flat

we may see correlations in data but they might be wrong correlations

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Who taught you that?

 

old ass school books?

[StringJunky]

no idea.. i dont really think its flat

 

i think our idea of its flat is similar to our idea of the world being flat

we may see correlations in data but they might be wrong correlations

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old ass school books?

 

The curvature in the space time geomtry is so slight and beyond the limit of our capabilities that it's measurably negligible leading us to think it's flat, as in an infinite Universe, when in reality it might be curved-A curved line would appear flat over an infinite distance from our point of view wouldn't it..is that the kind of idea you are getting at?

[Zolar V]

That makes perfect sense. i actually was lying in bed and thought of the same type of concept, less all the fancy terms . but i also added a little bit to it. That being that we may lie on the outside edge of the boundary of the universe, so we wouldn't receive any data from beyond that edge making it seem as though there is nothing above us or relatively speaking, below us. Or there could be trillions more planets/galaxies all around us but we cant see due to their photons getting absorbed into a something that blocks our view of them.

[Martin]

So your saying the universe is flat then?

 

No. Please read my post.

 

so all i was taught about the big bang, and how it universally expanded in a spherical shape is technically wrong

 

I don't know what you were taught, or what you understood from reading old-ass textbooks.

 

I said we do not know. Each year the data gets a little better and we measure the large scale curvature better and narrow down the estimate.

 

There is a 95% errorbar for the curvature that roughly speaking looks like

[0.99, 1.01]

where if it were to turn out to be exactly =1, the curvature would be zero and space would be, on average, at large scale, flat.

 

But if it should turn out to be 1.01 that would mean positive curvature and space would have the overall largescale shape of a 3D hypersphere.

That is, something analogous to the 2D surface of a balloon.

 

The standard model, the cosmo model that essentially everyone uses, includes both these cases, just by varying one or two key numbers that you plug in. The U can be infinite volume or it can be finite volume, but in either case NEARLY flat.

 

And according to the standard cosmo model there is no OUTSIDE space that the world is "expanding into". As in the balloon example, there is no inside of the balloon or room outside, only the 2D surface. All existence is concentrated on the 2D surface. But that is just an analogy for the 3D hypersphere where all existence is concentrated---there is no inside or outside of it. You couldn't "get outside" and look.

 

Nor could you in the infinite volume, perfectly flat, case.

 

In standard cosmo there is no outside edge. Matter is uniformly distributed thoughout space and has always been so. There is no boundary. There is no explosion of matter outwards into surrounding empty space.

You could read the mso.anu.edu article in my sig if you want more clarification. The file starts with one blank page so scroll down.

Edited March 16, 2010 by Martin

[Airbrush]

I like your explanation above Martin, I can follow it and it clarifies the balloon analogy and other things so well.

 

If the U is infinite, does that mean it is flat?

 

There is a H U G E difference between an infinite universe and a finite one. Infinity is so far beyond any finite number that the difference between the two is, literally, infinite.

 

Zolar V: "That makes perfect sense...we may lie on the outside edge of the boundary of the universe, so we wouldn't receive any data from beyond that edge making it seem as though there is nothing above us or relatively speaking, below us. Or there could be trillions more planets/galaxies all around us but we cant see due to their photons getting absorbed into a something that blocks our view of them."

 

It wouldn't matter where we are in the universe, we wouldn't receive any data from beyond our visual horizon which is the Cosmic Microwave Background Radiation, which is about 50% further away that the furthest visible galaxy or quasar.

 

Martin can explain this better, but if there was something absorbing photons, and thus "blocking our view" we would know about it. Right now cosmologists believe we can see all the way out to the first galaxies that formed after the Dark Ages which was the period of time from when matter cooled to darkness until it came together in clumps to form the first stars.

 

Questions for anyone. How long did the Dark Ages last? Did the Dark Ages begin exactly when the u first became transparent to photons or microwaves?

Edited March 17, 2010 by Airbrush