# Cosmological Principle

### Reference Material

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\begin{document} \section*{ The Cosmological Principle}

\begin{figure} \centering \includegraphics[width=6.5in]{universe.png} \caption{A cartoon map of the scales of structures in our universe.} \end{figure}

The {\bf Cosmological Principle} states that the universe is spatially {\it isotropic} (looks the same in all directions) and {\it homogeneous} (has constant density everywhere) on large scales. The {\bf Perfect Cosmological Principle} states that the universe is also {\it temporally} isotropic and homogeneous (a steady state universe). This is unlikely because it doesn't describe the Cosmic Microwave Background (CMB). The CMB and Hubble's Law are both provide evidence for isotropy and homogeneity.

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