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cbsimkins
2010-Apr-01, 03:46 AM
Several years ago Stephen Hawking spoke on the universe as he saw it. One thing stuck in my mind in his explanation; that was his vision was not a constantly expanding universe as a balloon, the model I have heard of most often, but resembles more of a test tube with us currently on the curved, semicircular end. But the thing that puzzles me most is that the expansion model is a product of Doppler shift. As this represents only one dimension there is seemingly no evidence and therefore no consideration of the other two dimension, which could be present but not detected by the Doppler shift. So instead of Hawking's test tube it could also be any of several solid conical sections like a paraboloid or ellipsoid. There is to my knowledge no way to detect this, parallax at the limits of cosmic distances we can see does not work and even near objects where parallax will detect lateral movement does not exactly plot the trajectories of stellar objects. Is there any work being done to investigate the manner of the expansion or otherwise?

01101001
2010-Apr-01, 01:02 PM
Several years ago Stephen Hawking spoke on the universe as he saw it. One thing stuck in my mind in his explanation; that was his vision was not a constantly expanding universe as a balloon, the model I have heard of most often, but resembles more of a test tube with us currently on the curved, semicircular end.

Is this the model of which you speak?

http://map.gsfc.nasa.gov/media/060915/060915_CMB_Timeline26.jpg (http://map.gsfc.nasa.gov/m_ig/060915/)

If so, we're currently a good ways from the early inflation on the left, away from the curved bottom of the "test tube". We're at the rim at the right.

It's pretty much the shape it has to be to fit the data. A linear expansion, which would result in a conical shape, doesn't fit the data we have measured. We know not only how the speed of expansion affects object we observe, but we know how the effect varied over time, as we look backward in spacetime.

Swift
2010-Apr-01, 05:06 PM
Keep in mind that in the model that 01101001 showed, the long dimension is time, not one of the spatial dimensions. Only two of the spatial dimensions are shown. And I'm not even sure I'd call it a model (meaning an exact representation of the Universe), but more of a conceptional drawing.

IsaacKuo
2010-Apr-01, 07:06 PM
Only one of the spatial dimensions is shown. See the grid lines? They are representing a two dimensional space-time, with one dimension of time and one dimension of space.

cbsimkins
2010-Apr-23, 07:20 PM
That is basically the model. However his slide showed a more rounded origin. The question is the path of light in a fixed spatial frame.

Cougar
2010-Apr-23, 10:43 PM
But the thing that puzzles me most is that the expansion model is a product of Doppler shift.

Well, not exactly. Doppler shift results from the relative motion of things moving through space, while that concept of space is a fixed "background." With cosmic expansion, on the other hand, space is not static but expanding between the objects, which are not moving through space to any significant degree.


As this represents only one dimension there is seemingly no evidence and therefore no consideration of the other two dimension

A query: There is evidence of cosmic expansion no matter which direction we look. Doesn't this evidence expansion in all 3 dimensions?

Aik4on
2010-Apr-28, 07:20 AM
I'm not clear about what this represents, is it just the observable universe? Presumably the entire universe, including what we cannot see, could not have a shape, as such, as this would imply a 3D object expanding into some form of higher dimensional space?