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The Cosmic Microwave Background Università degli studi di Napoli Federico II Viviana Gammaldi Matr. 242/011 Contents •The Big Bang Theory •The Cosmic Microwave Background • The experiments (COBE, WMAP, PLANK) The Big Bang theory The Big Bang theory postulates that ~ 14 billion years ago, the portion of the universe we can see today was only a few millimeters across: we can see remnants of this hot dense matter as the now very cold cmb radiation which still pervades the universe as a uniform glow across the entire sky. The Big Bang theory rests on: •General Relativity: gravity is supposed to be a distortion of space and time itself . • The Cosmological Priciple: the universe is homogeneous and isotropic when averaged over very large scales. The Big Bang theory Given the GR and the CP, the distortion of space-time, due to the gravitational effects of this matter can only be positively or negatively cuved or flat. About the dynamics of the universe, it started from a very small volume with an initial expansion rate: a key question is whether or not the pull of gravity is strong enough to ultimately reverse the expansion and cause the universe to collapse back on itself (Big Crunch). The Big Bang theory There are free parameters of Big Bang model that must be fixed by observations of our universe: • the geometry of the universe ΩK (open, flat or closed); •the Hubble constant H0; •the overall course of expansion q, past and future, which is determined by the fractional density of the different types of matter in the universe : •Radiation Ωr •Baryonic matter Ω B, •Dark Matter Ω DM •Dark energy ΩΛ Tests of the Big Bang theory The Big Bang Model is supported by important observations: Expansion: 1917 Einstein invetend a Cosmological costant Λ 1929 The Hubble’s expansion law is v = Hd. 2001 WMAP satellites results show: H = 71.9 −+22..67 kms −1Mpc −1 Light elements: The Big Bang nucleosynthesis: it is in good agreement with observations. Elements heavier than lithium are all synthesized in stars. Elements heavier than iron are produced both in super-giant stars and in the explosion of a supernovae Tests of he Big Bang theory •CMB: observed in 1965 by Penzias and Wilson. The CMB radiation is very cold, only 2.725 K, thus this radiation shines primarily in the microwave portion of the electromagnetic spectrum. The uniformity is the reason to interpret the radiation as remnant heat from the Big Bang. The CMB photons easily scatter off of electrons: this produces a blackbody spectrum of photons, according to the Big Bang theory. The Big Bang theory The behavior of CMB photons moving through the early universe is analogous to the propagation of optical light through the Earth’s atmosphere: we can look through the air out towards the clouds, but can not see through the opaque clouds. Cosmologists studying the CMB radiation can look through much of the universe back to when it was opaque: a view back to 400,000 years after the Big Bang. This wall of light is called the surface of last scattering . Beyond Big Bang cosmology The Big Bang model is not complete: • The flatness problem: a universe as flat as we see it today would require an extreme fine-tuning of conditions in the past; • The horizon problem: distant regions of space in opposite directions, assuming standard Big Bang expansion, they could never have been in causal contact with each other: the uniformity of the CMB temperature tells us that these regiions are in thermal equilibrium; • The monopole problem: Big Bang cosmology predicts that stable ”magnetic monopoles” should have been produced in the early universe. However, magnetic monopoles have never been observed; • The origin of the structure problem: the universe is omogeneous and hisotropic only on large scales, while on small scales there are a lot of anysotropies, such as stars an galaxies. Beyond Big Bang cosmology The Inflation Theory proposes a period of exponential expansion of the universe prior to the more gradual Big Bang expansion and offers solutions to these problems : • The flatness problem: the surface of the Earth appear flat to you, even though it is still a sphere on larger scales. Inflation stretches any initial curvature of the 3-dimensional universe to near flatness; • The horizon problem: distant regions were actually much closer together prior to Inflation than they would have been with only standard Big Bang expansion. • The monopole problem: Inflation allows for magnetic monopoles to exist as long as they were produced prior to the period of inflation. During inflation, the density of monopoles drops exponentially; • The origin of the structure problem: prior to inflation quantum fluctuation in the density of matter on microscopic scales expanded to astronomical scales during Inflation: the higher density regions condensed into stars, galaxies, and clusters of galaxies Beyond Big Bang cosmology While gravity can enhance the tiny fluctuations seen in the early universe, it can not produce these fluctuations. Different theories to produce the primordial fluctuations make very different predictions about the properties of the CMB fluctuations. The inflationary theory predicts that the largest temperature fluctuations should have an angular scale of one degree, while the defect models predict a smaller characteristic scale. WMAP indicates that the inflationary model is more likely. However, the Big Bang theory successfully explains the ”blackbody spectrum” of the CMB radiation. Beyond Big Bang cosmology •When cosmologists first looked at the microwave sky, they noticed it was nearly uniform. •As observations improved, they detected the dipole anisotropy. •1992, COBE satellite made the first detection of fluctuation : one part of the sky has a temperature of 2.7251 K , while another part has a temperature of 2.7249 K. Two main sources for the fluctuations: • Emission from the Milky Way; • Fluctuating emission from the edge of the visible universe; • There is also residual noise Temperature of the microwave sky in a scale in which Blue is 0K and Red is 4K: Green is because T=2.725K Blue -> 2.721K Red -> 2.729K The ”yin-yang” pattern is the dipole anisotropy that results from the motion of the Sun relative to the rest frame of the CMB. CMB after the dipole anisotropy has been subtracted. Red is 0.0002K hotter than the cold regions (Blue) The CMB anisotropies Before z*≈103 the tightly coupled system of photons, electrons and protons behaved as a single gas: photons pression resists gravitational compression of the fluid sets up acoustic oscillations. Further, the compressions heated the gas and the rarefactions cooled it. At z*,of recombination, about 380,000 years after the Big Bang, the photons were no longer scattered, so they traveled through space. Photons released from hotter, denser areas were more energetic than photons emitted from rarefied regions, so the pattern of hot and cold spots induced by the sound waves was frozen into the CMB: we call these fluctuations primary anisotropies, while a secondary anisotropies can also be generated between recombination and the present. The CMB anisotropies At z*,, denser areas of matter coalesced into stars and galaxies under the attractive influence of gravity. Inside the horizon, acoustic, Doppler, gravitational redshift and photon diffusion effects combine to form a seemingly complicated spectrum of primary anisotropies: Considering the component contributions individually reveals the spectrum and the cosmological parameters. Secondary effects may provide important clues for the process of structure formation. From inflaction to recombination The inflation provides a physical mechanism for triggering the primordial sound waves and all the structure in the universe, through inflaton: quantum fluctuations in the provide initial disturbances that are approximately equal on all scales, that become fluctuations in the energy density in the primordial plasma. Because inflation produced the density disturbances all at once moment, the phases of all the sound waves were synchronized. Consider blowing into a pipe that is open at both ends: the fundamental frequency of the sound corresponds to a wavelenght with maximum air compression at the mouthpiece end minimum compression (maximum rarefaction) at the end piece. But the sound also has a series of overtones corresponding to wavelengths that are integer fractions of the fundamental wavelength.. From inflaction to recombination The sound waves in the early universe oscillating in time instead of space. Assume that a certain region of space has a maximum positive displacement, that is maximum temperature, at inflation. As the sound waves propagate, the density of the region will begin to oscillate. The wave that causes the region to reach maximum negative displacement exactly at recombination is the fundamental wave of the early universe. The overtones have wavelengths that are integer fractions of the fundamental wavelength: they cause smaller regions of space to reach maximum displacement, either positive or negative, at recombination. The angular power spectrum Plotting the magnitude of the temperature variations against the sizes of the hot and cold spot providing a map of temperature variations across the whole sky (a). Taking an angular decomposition of the fluctuations in multipole space l, proportional to the inverse angle (l=100≈θ=1° ), we get the angular power spectrum of CMB anisotropies ∞ l . m m f (θ , φ ) = ∑ ∑ Cl Yl (θ , φ ) l =0 m = −l The series of peaks supports the inflation, but the sound waves should have nearly the same amplitude on all scales. The power spectrum shows a drop-off in the magnitude of temperature variations after the third peak, because a wave cannot propagate if its wavelength is shorter than the mean free path of the particles. The angular power spectrum The position of that first peak in the power spectrum of the anisotropies depend sensitively on the spatial curvature of the universe. As the curvature decreases the peaks move to higher multipole l while preserving their shape; dark energy makes the universe flat despite a sub-critical density of matter. The CMB reveals the angular size of the most Intense temperature variations and knowing the distance CMB photons have traveled before reaching Earth with the classic test of spatial curvature it’s possible estimate the geometry of the universe: the universe obeys the laws of Euclidean geometry and must be very close to spatially flat, and so the average matter density is close to the critical density ρ0=10-29gcm−3. The angular power spectrum The next thing we would like to know is the exact breakdown of the universes matter and energy. Gravity can enhance or counteract sonic compression and rarefaction. Both ordinary matter and dark matter supply mass to the primordial gas. At recombination the fundamental wave is frozen in a phase where gravity and sonic motion have worked together to raise The radiation temperature in the troughs (blue) and lower the temperature at the peaks (red) (up). At smaller scales, the first overtone is caught in the opposite phase, gas pressure is trying to expand the plasma (blue arrows), while gravity tries to compress it (white arrows). This tug-of-war decreases the temperature differences, which explains why the second peak in the power spectrum is lower than the first. The angular power spectrum Comparing the heights of the two peaks, cosmologists can gauge the relative strengths of gravity and radiation pressure. The Baryon density Ωbh2 make the first acoustic peak much larger than the second. The more baryons the more the second peak is relatively suppressed. Baryons constitute about 5% of the critical density today, in agreement with the number derived from studies of light element synthesis in the infant universe. An abundance of cold dark matter was needed to keep the gravitational-potential wells sufficiently deep. By measuring the ratios of the heights of the first three peaks, researchers have determined that the density of cold dark matter ΩDMh2 constitutes ~21% of the critical density. Notice also that the location of the first peak in particular changes as we change the DM density. The angular power spectrum These calculations of matter and energy leave ~74% of the critical density unspecified, so theorists have posited the dark energy: most of the universe today is composed of invisible dark matter and dark energy, both seem to be coincidentally comparable in energy density today. Another mysterious component, the inflaton, dominated the very early universe and seeded cosmic structure. The energy densities of DM and DE, as measured from the CMB, are in striking accord with these astronomical observations. The angular power spectrum The existence of DE also predicts additional phenomenain the CMB,like the so-called the integrated Sachs-Wolfe effect, causes large-scale temperature variations in the CMB. The amount of DE needed to produce the large-scale temperature variations is consistent with the amount inferred from the acoustic peaks and the distant supernovae: the ISW effect could become an important source of information about dark energy. In 1968 Silk predicted (by MCS) that radiation should gain a small but known polarization: on the small scales photons can travel with relatively few scatterings, so they retain directional information that is imprinted as a polarization of the CMB. The value misured by WMAP was in agreement with predictions: WMAP also detected polarization on larger scales that was caused by scattering of CMB photons after recombination. The next investigations Measurements of the CMB have dramatically strengthened the case for the simplest models of inflation. Another exciting possibility is that we could learn about the physics of inflation by determining the energy scale at which it took place: inflation created fluctuations in the space-time itself, that is gravitational waves, whose amplitude is proportional to the square of the energy scale at which inflation took place. Measurements of the Sunyaev-Zeldovich effect allows galaxy clusters to be identified during the crucial period, about five billion years ago, when dark energy began to accelerate the expansion of the universe. The second phenomenon, gravitational lensing, happens when CMB photons pass by a particularly massive structure that distorts the pattern of temperature and polarization variations. The degree of lensing reveals the amplitude of the mass density fluctuations associated with these structures. The next investigations To conduct these investigations of inflation and dark energy, however, researchers will need a new generation of CMB telescopes. In may 14th 2009 the European Space Agency (ESA) launched the PLANCK spacecraft. The higher resolution and lower noise of the Planck satellite allows it to measure further out into the series of acoustic peaks and so gather more information from them. Notice however that both experiments have the same errors at low multipoles. So I’ll analyze now the main experiments about the CMB, and the huge improvement that the researcher made in this field. COBE:Cosmic Background Explorer The COBE satellite was developed by NASA’s Goddard Space Flight Center launched November 18, 1989 to measure the diffuse infrared and microwave radiation from the early universe. A gold-colored sun shield Cylindrical metal tank. Painted on the side of the rocket are the triangular ”Delta” logo and the COBE logo 3 wings of solar panels: they fitted up next to the satellite sides when the wings were folded for launch. The bottom section COBE:Cosmic Background Explorer COBE carried three instruments: • DIRBE: Diffuse Infrared Background Experiment to search for the cosmic infrared background radiation (CIB) in the range from 1 to 1000 µm. The primary aim is to conduct a search for an isotropic CIB radiation and to measure its energy distribution. Secondary objectives include studies of foreground astrophysical sources. The observational approach is to make absolute brightness maps of the full sky at ten wavelengths from 1.2 to 240 µm and to map linear polarization at 1.2, 2.2, and 3.5 µm. The emission from stars and dust in the Galactic plane (horizontal feature) and light scattered and emitted by dust in the solar system (S-shape). The zodiacal (emission from the solar system dust, strongest at 25 µm , but also in evidence in the 100 µm image and to a lesser degree at the longer wavelengths) and Galactic emission must be precisely modeled and subtracted in order to detect the relatively faint CIB. COBE:Cosmic Background Explorer • DMR: Differential Microwave Radiometer maps the cosmic radiation sensitively. The CMB was found to have intrinsic ”anisotropy” for the first time, at a level of a part in 100,000. Each antenna has a 7 degree (FWHM) beam, giving an effective angular resolution of 10 degrees. These tiny variations in the intensity of the CMB over the sky show how matter and energy was distributed when the Universe was still very young. • FIRAS: Far Infrared Absolute Spectrophotometer compares the spectrum of the CMB radiation with a precise blackbody. It is a polarizing Michelson interferometer operated differentially with an internal reference blackbody, and calibrated by an external blackbody having an estimated emissivity of better than 0.9999. It covers the wavelength range from 0.1 to 10 mm in two spectral channels separated at 0.5 mm and has approximately 5% spectral resolution. FIRAS measured a nearly perfect blackbody spectrum of the CMB with a temperature of 2.725 +/- 0.002 K. COBE:Cosmic Background Explorer The COBE cryogenics, propulsion and Fluid Systems Branch Components are: • Spacecraft propulsion module • Infrared bolometers: The FIRAS and DIRBE instruments on COBE require these long wavelength infrared detectors: COBE has bolometers with sensitivity more than an order of magnitude better than required. A bolometer is a device for measuring the energy of incident electromagnetic radiation. It consists of an ”absorber” connected to a heat sink (area of onstant temperature) through an insulating link. The result is that any radiation absorbed by the absorber raises its temperature above that of the heat sink: the higher the energy absorbed, the higher the temperature will be. Temperature change can be measured directly or via an attached thermometer. COBE:Cosmic Background Explorer • Flight helium dewar: The COBE dewar was a 660 liter liquid helium cryostat. It provided a stable 1.4 Kelvin environment for the two cold instruments, FIRAS and DIRBE. The first phase of the COBE science mission came to an end on Friday, September 21, 1990, after 306 days of cryogenic operations as the last of the superfluid helium contained within the dewar was consumed. •Test dewars: The COBE test dewar is a cylinder 10 to 12 feet high, a few feet in diameter. The label ”COBE ITD” identifies the test dewar. • Dewar Vent Line Analysis: The sensitivity of the FIRAS and DIRBE detectors is highly dependent on their operating temperature. The vent analysis correlated well with on-orbit conditions, confirming other dewar temperature data and lifetime predictions. The analysis was performed by Code 713 (now Code 552). WMAP :Wilkinson Microwave Anisotropy Probe The WMAP satellite was launched on 30 June 2001, from Florida. A (94 cm diameter x 33 cm length x 0.318 cm thick) gamma-alumina cylindrical shell provides low thermal conductance between the warm spacecraft and the cold instrument components. Deployed sun shield (5 m in diameter) keeps the spacecraft and instrument in shadow for all nominal science operations. The Observatory is 3.8 m tall and its mass is 836 kg. Large passive radiators are connected directly to amplifiers at the core of the radiometers. WMAP :Wilkinson Microwave Anisotropy Probe The WMAP mission is designed to determine the geometry, content, and evolution of the universe via a 13 arcminute FWHM resolution full sky map (>95%) of the temperature anisotropy of the CMB radiation: the WMAP mission characteristics are: • ≈ 2° angular resolution • Accuracy on all angular scales > 0.2° • Minimally correlated pixel noise • Polarization sensitivity • Accurate calibration (< 0.5% uncertainty) • An overall sensitivity level of ∆Trms< 20µK per pixel • Systematic errors limited to < 0.5% of the random variance on all angular scales WMAP :Wilkinson Microwave Anisotropy Probe The choice of orbit, sky-scanning strategy and instrument/spacecraft design were driven by the goals of uncorrelated pixel noise, minimal systematic errors, multifrequency observations, and accurate calibration. To minimize systematic errors WMAP has: • Symmetric differential design: two sky signals, from directions separated by ~141°, are reflected via two nearly identical back-to-back primary reflectors towards two nearly identical secondary reflectors and into 20 feed horns, 10 in each optical path. The off-axis Gregorian design allows for a sufficient focal plane area, a compact configuration that fits in the Delta-rocket fairing envelope. The principal focus of each optical path is between its primary and its secondary mirror. The Gregorian telescope is a reflecting telescope: the primary mirror collects the light and brings it to a focus before the secondary mirror where it is reflected back through a hole in the centre of the primary. WMAP :Wilkinson Microwave Anisotropy Probe • Rapid large-sky-area scans: the ideal scan strategy would be to instantaneously scan the entire sky. Practical constraints limit the scan rate. For a space mission, increasing the scan speed rapidly becomes expensive. It is possible to assess the quality of a sky scanning strategy by computer simulations. • L2 orbit to minimize contamination from Sun, Earth, and Moon emission and allow for thermal stability: to minimize thermal and electrical variations the solar arrays maintain a constant angle relative to the Sun of 22.5°± 0.25° during CMB anisotropy observations at L2. •Multiple independent channels: MAPs Microwave System consists of ten 4-channel differencing assemblies, each of which receives two orthogonally polarized signals from a pair of feeds. The signals are combined in a way such as there are 20 statistically independent signal. WMAP :Wilkinson Microwave Anisotropy Probe •5 frequency bands to enable a separation of galactic and cosmic signals: Four physical mechanisms that contribute to the galactic emission are synchrotron radiation, free-free radiation, thermal radiation from dust. There are three approaches that can be used. I) to scale and subtract to the MAP existing galactic maps. II) to form linear combinations of the multi-frequency MAP. III) to determine the Spatial and/or spectral properties of each one. All three of these techniques were employed with some degree of success with the COBE data. Those techniques also generally reduce extragalactic contamination. The most affected MAP pixels should be masked and not used. Hot gas in clusters of galaxies will also contaminate the maps by shifting the spectrum of the primary anisotropy to create a SunyaevZeldovich decrement in the MAP frequency WMAP :Wilkinson Microwave Anisotropy Probe • Passive thermal control with a constant Sun angle for thermal and power stability: there are three major objectives of the thermal sign of MAP. I) to keep all elements of the Observatory within nondestructive temperature ranges. II) to passively cool the instrument front-end microwave amplifiers and reduce the microwave emissivity of the frontend components to improve sensitivity. III) to minimize all thermal variations during the nominal observing mode. • Precision temperature sensing at selected instrument locations: there are precision platinum resistance thermometers (PRTs) at various locations to provide a quantitative demonstration of thermal stability at the submillikelvin level. The information from these sensors is invaluable for making a quantitative assessment of the errors and could be used to make error corrections in the ground data reduction pipeline. The design is to make these corrections unnecessary and to use the sensor data only to prove that thermal variations are not significant. WMAP :Wilkinson Microwave Anisotropy Probe • Main beam pattern measured accurately in-flight: Jupiter serves as the source for beam pattern measurements in-flight. Beam patterns were measured in an indoor compact antenna range at the Goddard Space Flight Center and the far-sidelobes were measured between rooftops at Princeton University. • Control of beam sidelobe levels to keep the Sun, Earth, and Moon levels <1µK: Those emission can contaminate the Raw data by entering the instrument via the sidelobes of the beams. A source of external emission is the dipole signal induced by MAP’s motion with respect to the Sun: this effect is treated as a calibration error. • Calibration determined in-flight: the instrument is calibrated in-flight using observations of the CMB dipole and of Jupiter. Despite the in-flight amplitude calibration, it was necessary to provide provisional calibration on the ground to characterize various aspects of the instrument to assure that all requirements would be met. Observations of Jupiter and other celestial sources provide an in-flight pointing offset check relative to the star tracker pointing. The pointing directions of the feeds were measured on the ground using standard optical alignment techniques. WMAP :Wilkinson Microwave Anisotropy Probe In the first release of WMAP data (February 2003), only the temperature data and analyses from the first year of operations at L2 were provided: •Data from the first three years of spacecraft operations at L2 are made available. •Polarization analysis, maps, and time-ordered data are made available. •The temperature analysis and maps are improved. •The error analysis was improved. •The map-making algorithm was changed. Much more information and data was provided in the second release (March 2006): •Data from the first five years of spacecraft operations at L2 are made available. •The temperature and polarization analysis and maps are improved. •The error analysis was improved. •The calibration algorithm was improved. •The beam maps were improved. WMAP :Wilkinson Microwave Anisotropy Probe The following CMB anisotropy observables should be seen within the context of the simplest form of inflation theory (a single scalar field with adiabatic fluctuations): • an approximately scale-invariant spectral index of primordial fluctuations n≈1; • a flat Ω0 = 1 geometry, which places the first acoustic peak in the CMB fluctuation spectrum at a spherical harmonic order l=220; • no vector component (single scalar field, although vector modes could be introduced with late-time defects); • Gaussian fluctuations with random phases; • a series of well-defined peaks in the CMB power spectrum, with the first and third peaks enhanced relative to the second peak; • a polarization pattern with a specific orientation with respect to the anisotropy gradients. WMAP :Wilkinson Microwave Anisotropy Probe The main cosmological parameters measured by WMAP are: If these numbers are fixed to match an observed temperature spectrum, then the properties of the polarization fluctuations are nearly completed specified, particularly for l > 30. If the polarization pattern is not as predicted, then the primordial fluctuations can not be entirely adiabatic. PLANCK surveyor PLANCK is the first European mission to study the birth of the Universe, it has been carried into space on 14 May 2009 in Kourou, French Guiana: • 4.2 metres high and has a maximum diameter of 4.2 metres, with a launch mass ~ 1.9 tonnes. • systems for power generation and conditioning • data handling and communications, together with the warm parts of the scientific instruments • payload module. that is the telescope, •the optical bench, with the parts of the instruments that need to be cooled, the sensitive detector units, and the cooling systems. PLANCK surveyor The PLANCK telescope is an off-axis tilted Gregorian design with a primary mirror measuring 1.9 x 1.5 m and with an aperture of 1.5 m diameter. The 1.1 x 1.0 m secondary mirror focuses the collected light onto the two scientific instruments: • LFI (Low Frequency Instrument), an array of radio receivers using high electron mobility transistor mixers: The LFI is designed to produce measurements of the microwave sky in the frequency range 27 to 77 GHz ; • HFI (High Frequency Instrument), an array of microwave detectors using spider bolometers equipped with neutron transmutation doped germanium thermistors: The HFI is designed to produce Measurements of the diffuse sky radiation in the frequency range 84 GHz to 1 THz; The measurements made by the two instruments will be combined to produce a full-sky map of the anisotropies with unprecedented precision. The off-axis angle of the telescope design allows the system to minimize the polarization effects introduced by the telescope. The function of the baffle is to shield the detectors from thermal radiation originating within the optical enclosure. PLANCK surveyor PLANCK has been carried into space by an Ariane 5 ECA together with Herschel, an IR space telescope. After launch, PLANCK will reach its operational orbit L2 located 1.5 million kilometres away from the Earth. The spacecraft will be operated in a Lissajous orbit around the L2 point with an average amplitude of about 400000 km. Orbits about L2 are dynamically unstable. Planck will use its propulsion system to perform orbit maintenance manoeuvres. Planck has a nominal operational lifetime of fifteen months from the end of the Calibration and Performance Verification Phase. The Mission Operations Centre is located at ESA’s European Space Operations Centre in Germany. For communication with the spacecraft two deep space antennas in Australia and Spain will be used. The PLANCK science planning in Spain. The data processing and the operations centre for the HFI Instrument are both located in France, whereas those for the LFI instrument are located at the Osservatorio Astronomico di Trieste,Italy. PLANCK surveyor The key objectives of PLANCK are as follows: • Measurement of CMB anisotropies with a temperature resolution (∆T/T) of the order of 10−6 (astrophysical limit set by small scale fluctuations in foreground emission) at all angular resolutions greater than 10 arcminutes; • Test inflationary models, specifically the determination of the spectral index of the primordial fluctuation spectrum to high precision and the detection of a component of the CMB anisotropies induced by primordial gravitational waves; • Measurement of the amplitudes of structures in the CMB with physical scales between 100 and 1000 h−1Mpc, that have sizes comparable to the voids and filaments observed in the galaxy distribution today to establish a consistent theory of the formation of cosmic structure and shed light on the nature of the dark matter; PLANCK surveyor • Detection of characteristic signatures in the CMB created by topological defects, such as cosmic strings and textures, generated at a phase transition in the early Universe; • Measurements of the Sunyaev-Zeldovich effect: PLANCK will detect this effect providing information on the physical state of the intracluster gas and on the evolution of rich clusters, these measurements can also be combined with spatially resolved X-ray observations to estimate the Hubble constant H0; • Using the high sensitivity of PLANCK’s sub-millimetre bolometer channels, it will be possible to disentangle the frequency dependent Sunyaev-Zeldovich effect in rich clusters of galaxies from temperature differences caused by their peculiar motions, providing powerful tests of theories of structure formation and information on the mean mass density of the Universe. Summary In this seminary I showed an overview of the cosmological standard model of the Big Bang, with a particullary research on one of its tests: the CMB. I showed the main features of the CMB and the way to understending them and the other way round to deducing the cosmological parameters from the experimental data. Finally I showed the three main experiments on the CMB, their results and improvement: The Cosmic Background Explorer (COBE), launched in 1989, determined that the CMB exhibits anisotropies at a level of 10-5 and angular resolution of 10° and showed that the CMB spectrum matched that of a black body with a temperature of 2.725K. The Wilkinson Microwave Anisotropy Probe (WMAP), launched in 2001, made measurements of the CMB enabling the creation of a map of the anisotropies with 45 times the sensitivity and 33 times the angular resolution on the COBE DMR mission. PLANCK, launched in 2009, has been designed to have 10 times better sensitivity to temperature variations of the CMB and more than 50 times the angular resolution of the COBE spacecraft.