Presuppositions of Standard Model?

In summary, the lambda-CDM model predicts a nearly flat spatial curvature at scales larger than the the scale of homogeneity of the universe. This is based on various parameters that are fit to observational data, such as the average density of baryonic matter. There is no assumption of perfect homogeneity or flatness, but rather these are constraints derived from combining data from different sources. The current observations show that the spatial curvature is within error bars of zero, but this may change if new data is considered. Overall, the predictions of the lambda-CDM model are impressive and independent of presuppositions of flatness.
  • #1
skippy1729
The lambda-CDM model predicts a nearly flat spatial curvature at scales larger than the the scale of homogeneity of the universe. The calculation of many of its parameters depend on the cosmic distance ladder which in turn depend on many observational techniques and statistical comparisons.

My questions are:

1. Have all of these myriad calculations been done in a manner which does not presuppose a nearly flat spatial universe?

2. Many of the observations leading to both the lambda-CDM model and the cosmic distance ladder are taken at distances far below the scale of homogeneity where no assumption of nearly flat curvature can be made (voids and filaments, for example). How has this been taken into consideration?

All of the predictions of these models are impressive but have they been shown to be independent of presuppositions of flatness?

Any references to this topic would be appreciated.

Skippy
 
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  • #2
ΛCDM models don't assume flatness. They have various parameters that are fit to the data, like the average density of baryonic matter, etc. One of the outputs is the average spatial curvature. This curvature just happens to be within error bars of zero based on current observations. They also don't assume perfect homogeneity. When you see graphs of the intensities of multipole moments, with fits to the model, that model is clearly not assuming homogeneity, because otherwise the intensities of all the multipole moments (beyond l=0) would be zero.
 
  • #3
bcrowell said:
ΛCDM models don't assume flatness. They have various parameters that are fit to the data, like the average density of baryonic matter, etc.

Wouldn't these average densities calculated from observational data be different if the actual curvature was nonzero?
 
  • #4
skippy1729 said:
Wouldn't these average densities calculated from observational data be different if the actual curvature was nonzero?

Certainly. But there is no assumption that the curvature is zero, and there is no assumption that the average densities are such as to cause zero curvature.
 
  • #5
bcrowell said:
Certainly. But there is no assumption that the curvature is zero, and there is no assumption that the average densities are such as to cause zero curvature.
Well, to be a bit pedantic, it isn't always assumed that the spatial curvature is zero. Often it is assumed to be zero, simply because the particular observation in question isn't sensitive to the curvature.

You only get a strong constraint on the curvature if you combine very far-away observations (e.g. CMB observations) with nearby observations (e.g. the distribution of galaxies, supernovae). And when we combine near data with far data, spatial curvature is constrained to be zero to within about 1% of the total energy density of the universe.
 

Related to Presuppositions of Standard Model?

What is the Standard Model?

The Standard Model is a theoretical framework in physics that describes the fundamental particles and forces that make up the universe. It is currently the most successful and widely accepted theory to explain the behavior of subatomic particles.

What are the presuppositions of the Standard Model?

The presuppositions, also known as the underlying assumptions, of the Standard Model include the existence of fundamental particles, the existence of fundamental forces, and the concept of symmetry in nature.

How are the presuppositions of the Standard Model tested?

The presuppositions of the Standard Model are tested through experiments using particle accelerators and other high-energy physics techniques. The results of these experiments can either confirm or challenge the assumptions of the Standard Model.

Is the Standard Model a complete theory?

No, the Standard Model is not a complete theory. It does not include gravity, dark matter, or dark energy, which are all important components in our understanding of the universe. Scientists are currently working on theories that can incorporate these missing pieces.

What are the practical applications of the Standard Model?

The Standard Model has been incredibly successful in predicting and explaining the behavior of subatomic particles. It has also led to the development of technologies such as medical imaging and particle accelerators. Additionally, the study of the Standard Model has advanced our understanding of the universe and has the potential to lead to new discoveries and technologies in the future.

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