Planck Toolkit introduction

Welcome to the Planck ‘toolkit’ – a series of short questions and answers designed to equip you with background information on key cosmological topics addressed by the Planck science releases. The questions are arranged in thematic blocks; click the header to visit the relevant topic, or use the links on the right hand side of the page.

Planck and the Cosmic Microwave Background
What is Planck and what is it studying?
What is the Cosmic Microwave Background?
Why is it so important to study the CMB?
When was the CMB first detected?
How many space missions have studied the CMB?
What does the CMB look like?
What is ‘the standard model of cosmology’ and how does it relate to the CMB?

The cosmic microwave background and inflation
How did the temperature fluctuations get there?
How exactly do the temperature fluctuations relate to density fluctuations?

The cosmic microwave background and the distribution of matter in the Universe
How is matter distributed in the Universe?
Has the Universe always had such a rich variety of structure?
How did the Universe evolve from very smooth to highly structured?
How can we study the evolution of cosmic structure?

Tools to study the distribution of matter in the Universe
How is the distribution of matter in the Universe described mathematically?
What is the power spectrum?
What is the power spectrum of the distribution of matter in the Universe?
Why are cosmologists interested in the power spectrum of cosmic structure?
What was the distribution of the primordial fluctuations?
How does this relate to the fluctuations in the CMB?

History of cosmic structure formation
How did seed fluctuations grow into today's cosmic structures such as galaxies and galaxy clusters?
How did the formation of structure effect the CMB?
How is the history of cosmic structure formation encoded in the CMB and power spectrum?

The effect of cosmic structure on the cosmic microwave background
Did the photons travel freely ever since the CMB was released?
What happens when the CMB photons encounter structure in the cosmic web?
Do the CMB photons encounter other particles along their way?

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