Cosmic Microwave Background Hamza Meel December 4, 2019 Cosmic - - PowerPoint PPT Presentation

Cosmic Microwave Background

Hamza Meel December 4, 2019

Cosmic Microwave Background

Table of Contents

History First Experimental Evidence Modern Observations The Universe Before Recombination An Orange Plasma Acoustic Waves Inhomogeneity Results in Anisotropy Power Spectrum Conclusion

Cosmic Microwave Background History

Table of Contents

History First Experimental Evidence Modern Observations The Universe Before Recombination An Orange Plasma Acoustic Waves Inhomogeneity Results in Anisotropy Power Spectrum Conclusion

Cosmic Microwave Background History First Experimental Evidence

• A. Penzias’ and R.Wilson’s Observation

◮ 1964 ◮ Super-sensitive microwave antenna. ◮ Noise that can’t be removed.

https://cosmology.education/images/holmdel_antenna.jpg

Cosmic Microwave Background History First Experimental Evidence

• A. Penzias’ and R.Wilson’s Observation

◮ 1964 ◮ Super-sensitive microwave antenna. ◮ Noise that can’t be removed. ◮ Matches R. Dicke’s predictions.

https://upload.wikimedia.org/wikipedia/en/c/cf/Robert_Henry_ Dicke.jpg

Cosmic Microwave Background History First Experimental Evidence

• A. Penzias’ and R.Wilson’s Observation

◮ 1964 ◮ Super-sensitive microwave antenna. ◮ Noise that can’t be removed. ◮ Matches R. Dicke’s predictions.

https://i.huffpost.com/gen/1853981/thumbs/

• -ROBERT-WILSON-PENZIAS-900.jpg

Cosmic Microwave Background History Modern Observations

Most Known Missions

◮ COBE (1989 - 1993)

https://science.nasa.gov/missions/cobe

Cosmic Microwave Background History Modern Observations

Most Known Missions

◮ COBE (1989 - 1993) ◮ WMAP (2001 - 2010)

https://www.nasa.gov/feature/ making-sense-of-the-big-bang-wilkinson-microwave-anisotropy-probe

Cosmic Microwave Background History Modern Observations

Most Known Missions

◮ COBE (1989 - 1993) ◮ WMAP (2001 - 2010) ◮ Planck (2009 - 2013)

http://www.esa.int/ESA_Multimedia/Images/2013/03/Planck_CMB

Cosmic Microwave Background History Modern Observations

First peak in the power spectrum measured by: ◮ Toco ◮ BOOMEranG ◮ MAXIMA

Cosmic Microwave Background The Universe Before Recombination

Table of Contents

History First Experimental Evidence Modern Observations The Universe Before Recombination An Orange Plasma Acoustic Waves Inhomogeneity Results in Anisotropy Power Spectrum Conclusion

Cosmic Microwave Background The Universe Before Recombination An Orange Plasma

An Artist’s Illustration of the Early Universe

Color calculated by http://www.vendian.org/mncharity/dir3/blackbody/

Cosmic Microwave Background The Universe Before Recombination An Orange Plasma

Characteristics of the Plasma

◮ Hot Plasma (> 3000 K) ◮ Opaque due to Thomson scattering and electromagnetic interactions.

Cosmic Microwave Background The Universe Before Recombination An Orange Plasma

Recombination

◮ Universe becomes cooler due to its expansion. ◮ 3000 K : Threshold for formation of hydrogen and helium.

Cosmic Microwave Background The Universe Before Recombination Acoustic Waves

Origin of Acoustic Waves

◮ The plasma is moved by two forces:

◮ Gravity (attractive) ◮ Radiation pressure (repulsive)

◮ Formation of a pressure wave, also known as acoustic wave.

Cosmic Microwave Background The Universe Before Recombination Acoustic Waves

Fundamental Problem

Why should gravity be important ?

Cosmic Microwave Background The Universe Before Recombination Acoustic Waves

Fundamental Problem

◮ Why should gravity be important ? ◮ Assuming the early universe to be uniform seems reasonable. ◮ Uniformity = ⇒ No potential wells = ⇒ No gravity

Cosmic Microwave Background The Universe Before Recombination Acoustic Waves

The Solution: Quantum Noise

◮ Early quantum noise amplified by Inflation ◮ It creates inhomogeneities at all scales

Cosmic Microwave Background The Universe Before Recombination Acoustic Waves

The Solution: Quantum Noise

◮ Early quantum noise amplified by Inflation ◮ It creates inhomogeneities at all scales = ⇒ Potential wells

Cosmic Microwave Background Inhomogeneity Results in Anisotropy

Table of Contents

History First Experimental Evidence Modern Observations The Universe Before Recombination An Orange Plasma Acoustic Waves Inhomogeneity Results in Anisotropy Power Spectrum Conclusion

Cosmic Microwave Background Inhomogeneity Results in Anisotropy

From Inhomogeneity to Anisotropy

◮ At Recombination, the sound waves freeze. ◮ Imagine being in a well.

• 1. The light that we observe is also from the well =

⇒ isotropy.

Cosmic Microwave Background Inhomogeneity Results in Anisotropy

From Inhomogeneity to Anisotropy

◮ At Recombination, the sound waves freeze. ◮ Imagine being in a well.

• 1. The light that we observe is also from the well =

⇒ isotropy.

• 2. Some part of the light we observe is now from a hill.

Cosmic Microwave Background Inhomogeneity Results in Anisotropy

From Inhomogeneity to Anisotropy

◮ At Recombination, the sound waves freeze. ◮ Imagine being in a well.

• 1. The light that we observe is also from the well =

⇒ isotropy.

• 2. Some part of the light we observe is now from a hill.
• 3. Well, hill, well.

Cosmic Microwave Background Inhomogeneity Results in Anisotropy

From Inhomogeneity to Anisotropy

◮ At Recombination, the sound waves freeze. ◮ Imagine being in a well.

• 1. The light that we observe is also from the well =

⇒ isotropy.

• 2. Some part of the light we observe is now from a hill.
• 3. Well, hill, well.
• 4. Well, hill, well, hill.

Cosmic Microwave Background Inhomogeneity Results in Anisotropy

From Inhomogeneity to Anisotropy

◮ At Recombination, the sound waves freeze. ◮ Imagine being in a well.

• 1. The light that we observe is also from the well =

⇒ isotropy.

• 2. Some part of the light we observe is now from a hill.
• 3. Well, hill, well.
• 4. Well, hill, well, hill.
• 5. Et caetera

◮ http://background.uchicago.edu/~whu/intermediate/brief.gif

Cosmic Microwave Background Power Spectrum

Table of Contents

History First Experimental Evidence Modern Observations The Universe Before Recombination An Orange Plasma Acoustic Waves Inhomogeneity Results in Anisotropy Power Spectrum Conclusion

Cosmic Microwave Background Power Spectrum

Definition

◮ Power spectrum of a signal is the Fourier transform of its magnitude squared. ◮ Multipoles l are used in place of wave-numbers k.

Cosmic Microwave Background Power Spectrum

Existence of Harmonics

◮ Inflation amplified noise to all scales. ◮ If a mode exists, its harmonics too.

Cosmic Microwave Background Power Spectrum

Extrema of Vibrations

◮ There exist a mode such that it only went through one compression.

Cosmic Microwave Background Power Spectrum

Extrema of Vibrations

◮ There exist a mode such that it only went through one compression. ◮ So there exist one who went through a compression and a relaxation, and so

• ne

Cosmic Microwave Background Power Spectrum

Extrema of Vibrations

◮ There exist a mode such that it only went through one compression. ◮ So there exist one who went through a compression and a relaxation, and so

• ne

◮ Baryons help compression but not relaxation.

Cosmic Microwave Background Power Spectrum

First Peak of the Power Spectrum

◮ The multipole moment l1 of the first peak depends on the curvature of the universe. ◮ The more negative the curvature, the higher is l1.

Three-Year Wilkinson Microwave Anisotropy Probe (WMAP*) Observations: Temperature Analysis, G.Hinsaw et al., The American Astrophysical Journal Supplement Series, 2007, https://doi.org/10.1086/513698

Cosmic Microwave Background Power Spectrum

First Peak of the Power Spectrum

◮ The multipole moment l1 of the first peak depends on the curvature of the universe. ◮ The more negative the curvature, the higher is l1. ◮ Measurements on CMB indicates a (nearly) flat universe.

Three-Year Wilkinson Microwave Anisotropy Probe (WMAP*) Observations: Temperature Analysis, G.Hinsaw et al., The American Astrophysical Journal Supplement Series, 2007, https://doi.org/10.1086/513698

Cosmic Microwave Background Power Spectrum

First Peak of the Power Spectrum

◮ The multipole moment l1 of the first peak depends on the curvature of the universe. ◮ The more negative the curvature, the higher is l1. ◮ Measurements on CMB indicates a (nearly) flat universe. ◮ We do not observe enough matter and dark matter to have a flat universe.

Three-Year Wilkinson Microwave Anisotropy Probe (WMAP*) Observations: Temperature Analysis, G.Hinsaw et al., The American Astrophysical Journal Supplement Series, 2007, https://doi.org/10.1086/513698

Cosmic Microwave Background Power Spectrum

First Peak of the Power Spectrum

◮ The multipole moment l1 of the first peak depends on the curvature of the universe. ◮ The more negative the curvature, the higher is l1. ◮ Measurements on CMB indicates a (nearly) flat universe. ◮ We do not observe enough matter and dark matter to have a flat universe. ◮ This missing energy is called dark energy.

Three-Year Wilkinson Microwave Anisotropy Probe (WMAP*) Observations: Temperature Analysis, G.Hinsaw et al., The American Astrophysical Journal Supplement Series, 2007, https://doi.org/10.1086/513698

Cosmic Microwave Background Power Spectrum

Second Peak of the Power Spectrum

◮ Odd peaks are enhanced by baryons. ◮ The ration of the two should yield the baryonic density. .

Three-Year Wilkinson Microwave Anisotropy Probe (WMAP*) Observations: Temperature Analysis, G.Hinsaw et al., The American Astrophysical Journal Supplement Series, 2007, https://doi.org/10.1086/513698

Cosmic Microwave Background Power Spectrum

Second Peak of the Power Spectrum

◮ Odd peaks are enhanced by baryons. ◮ The ration of the two should yield the baryonic density. ◮ We do not observe enough baryons. .

Three-Year Wilkinson Microwave Anisotropy Probe (WMAP*) Observations: Temperature Analysis, G.Hinsaw et al., The American Astrophysical Journal Supplement Series, 2007, https://doi.org/10.1086/513698

Cosmic Microwave Background Power Spectrum

Second Peak of the Power Spectrum

◮ Odd peaks are enhanced by baryons. ◮ The ration of the two should yield the baryonic density. ◮ We do not observe enough baryons. ◮ The missing baryons are called dark baryons.

Three-Year Wilkinson Microwave Anisotropy Probe (WMAP*) Observations: Temperature Analysis, G.Hinsaw et al., The American Astrophysical Journal Supplement Series, 2007, https://doi.org/10.1086/513698

Cosmic Microwave Background Conclusion

Table of Contents

History First Experimental Evidence Modern Observations The Universe Before Recombination An Orange Plasma Acoustic Waves Inhomogeneity Results in Anisotropy Power Spectrum Conclusion

Cosmic Microwave Background Conclusion

Discussed Topics

◮ The universe was originally a hot plasma. ◮ CMB is the snapshot of the acoustic waves of this plasma at Recombination. ◮ Its power spectrum gives us information about the geometry of the universe and the density of its constituents.

Cosmic Microwave Background Conclusion

What Next ?

◮ Polarization of the CMB ◮ Power spectrum at low l could help chose a suitable quantum gravity theory.

Loop quantum cosmology: From pre-inflationary dynamics to observations, A. Ashketar,

• A. Barrau, 2015, arXiv:1504.07559v2