Microwaves, observing universe

The entire observable universe, of which the Earth is a veiy tiny part, contains matter m the form of stars, planets, and other objects scattered in space, such as particles ol dust, molecules, protons, and electrons. In addition to containing matter, space also is filled with energy, part of it in the form of microwave radiation. 

To date, researchers have identified more than 100 different molecules, composed of up to 13 atoms, in the interstellar medium [16]. Most were initially detected at microwave and (sub)millimetre frequencies, and the discoveries have reached far beyond the mere existence of molecules. Newly discovered entities such as difhise mterstellar clouds, dense (or dark) molecular clouds and giant molecular cloud complexes were characterized for the first time. Indeed, radioastronomy (which includes observations ranging from radio to submillunetre frequencies) has dramatically changed our perception of the composition of the universe. Radioastronomy has shown that most of the mass in the interstellar medium is contained in so-called dense... 

The primordial Li abundance was sought primarily because of its ability to constrain the baryon to photon ratio in the Universe, or equivalently the baryon contribution to the critical density. In this way, Li was able to complement estimates from 4He, the primordial abundance of which varied only slightly with baryon density. Li also made up for the fact that the other primordial isotopes, 2H (i.e. D) and 3He, were at that time difficult to observe and/or interpret. During the late 1990 s, however, measurements of D in damped Lyman alpha systems (high column-density gas believed to be related to galaxy discs) provided more reliable constraints on the baryon density than Li could do (e.g. [19]). Even more recently, the baryon density has been inferred from the angular power spectrum of the cosmic microwave background radiation, for example from the WMAP measurements [26]. We consider the role of Li plateau observations post WMAP. 

Interrogating the light from stars and the absorption features of atoms and molecules in-between requires some fairly complicated optics in the form of a telescope. However, the telescopes are not restricted to the parts of the electromagnetic spectrum that you can see but use radiation from microwaves to gamma rays to observe the Universe. There is too much to learn about the optics or even adaptive optics of telescopes to be discussed here but there are some properties of telescopes that we must know because they are important for the identification of atoms and molecules. We shall discuss three telescope considerations the atmosphere, the spatial resolution and the spectral resolution. 

In 1988, Riis et al. [52] observed a direction-dependent anisotropy of light in the direction of the apex of the 2.7 K microwave background radiation in the universe. These data are consistent with nonzero photon mass. The upper bound on photon mass was estimated as mT 10-65g. A compilation of laboratory data [53] established that the photon mass should not exceed 10-24 eV or even 10 26 eV. 

As far as we can see into the Universe, we don t observe any primordial antimatter. Within the limits of our present observational horizon the Universe is seen to contain only matter and no antimatter. The presence of cosmic antimatter would lead to observable traces of annihilation however the measurements of the extragalactic 7 ray flux indicate an absence of annihilation radiation, and the microwave background spectrum lacks a corresponding distortion. These findings preclude the existence of a significant amount of antimatter within tens of Megaparsecs, which is the scale of super-clusters of galaxies. 

Shortly after the Cosmic Microwave Background (CMB) was discovered, the first anisotropy in the CMB was seen the dipole pattern due to the motion of the observer relative to the rest of the Universe (Conklin, 1969). After confirmation by Henry, 1971 and by Corey and Wilkinson, 1976 the fourth discovery of the dipole (Smoot et al., 1977) showed a very definite cosine pattern as expected for a Doppler effect, and placed an upper limit on any further variations in Tcmb Further improvements in the measurement of the dipole anisotropy were made by the Differential Microwave Radiometers (DMR) experiment on COBE (Bennett et al., 1996 and by the Wilkinson Microwave... 

The isotropic microwave background radiation, observed in the vacuum, has the same wavelength distribution as a black body, which shows that the universe is closed, like a cavity, rather than open and expanding. 

The major selling point of standard cosmology is the observed isotropic microwave background radiation, with black-body spectrum. In a closed universe it needs no explanation. Radiation, which accumulates in any closed cavity, tends, by definition, to an equilibrium wavelength distribution according to Planck s formula (Figure 2.5). 

Cosmic microwave background radiation The uniform background radiation in the microwave region of the spectrum that is observed in all directions in the sky. Its discovery added credence to the big bang model of the universe. 

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