The Big Bang Theory Is Probably True

I. The Homogeneity of the Universe "A major prediction of the Big Bang is that the universe is homogeneous. At small scales, just as in the solar system, this is obviously not true, but if we look at the largest scales of the universe, this is true. As an example, consider the plot below showing galaxies from the Las Campanas Redshift Survey. Each dot represents a galaxy (about 20,000 in the total survey) where they have measured both the position on the sky and the redshift and translated that into a location in the universe": [1] An even stronger case for the homogeneity of the universe can be made in the Cosmic Microwave Background Radiation (CMBR), in that it is virtually homogeneous and isotropic: [2]The CMBR is isotropic (the same) to roughly one part in 100,000, further confirming universial homogeneity. This spectrum has been redshifted by the expansion of the universe, and today corresponds to approximately 2.725 K. [3][4] II. Galatic Evolution The above information leads into my second point. Populations of stars have been aging and evolving, meaning that distant galaxies appear very different from nearby galaxies because of the effects of the speed of light. Further, galaxies that formed relatively recently appear markedly different from galaxies formed at similar distances from Earth but shortly after the Big Bang. Observations of star formation, galaxy and quasar distributions and larger structures agree well with Big Bang simulations of the formation of structure in the Universe. [5][6]III. Abundance of Elements "Using the Big Bang model, it is possible to calculate the concentration of helium-4, helium-3, deuterium, and lithium-7 in the Universe as ratios to the amount of ordinary hydrogen. The relative abundances depend on a single parameter, the ratio of photons to baryons. The measured abundances all agree at least roughly with those predicted from a single value of the baryon-to-photon ratio. The agreement is excellent for deuterium, close but formally discrepant for 4He, and off by a factor of two 7Li; in the latter two cases there are substantial systematic uncertainties. Nonetheless, the general consistency with abundances predicted by Big Bang nucleosynthesis is strong evidence for the Big Bang, as the theory is the only known explanation for the relative abundances of light elements, and it is virtually impossible to “tune” the Big Bang to produce much more or less than 20–30% helium. Indeed there is no obvious reason outside of the Big Bang that, for example, the young Universe (i. e. , before star formation, as determined by studying matter supposedly free of stellar nucleosynthesis products) should have more helium than deuterium or more deuterium than 3He, and in constant ratios, too. "[7][8][9] Here is a graph showing the abundance of elements in the universe (abundance versus atomic number): [10]Notice how the abundancies roughly decrease asymptotically as the atomic numbers of the various elements go up. This further confirms the predictions of the Big Bang Theory with regards to the abundance of elements in the universe. IV. The Integrated Sachs-Wolfe Effect "In addition to the Sunyaev-Zel’dovich effect, photons from the CMBR can also be subtly affected by the Integrated Sachs-Wolfe effect. The basis for this effect is gravitational redshift, one of the most basic predictions from GR and first demonstrated experimentally by Pound and Rebka in 1960. The basic idea is that, as photons enter a gravitational potential well, they pick up extra energy and when they exit they lose energy. Hence, scientists refer to photons “falling into” and “climbing out of” gravitational wells. As CMBR photons pass through the foreground large scale structure, they pass through many such gravitational wells. If the depth of the well is static (or rather if the depth of the well is increasing at the same rate as the expansion of the universe), then the net energy change is zero. All of the energy they gained falling in is lost climbing out. However, if the universe contains dark energy (or has an open geometry), then the universe expands faster than the gravitational wells around massive objects can grow. As a result, the CMBR photons do not lose all of the energy they gained falling into the potentials. This makes the CMBR look very slightly hotter in the direction of these potentials, which also contain the highest concentrations of galaxies. Following the release of the WMAP data, studies measured this effect using galaxies selected in a number of different ways. The signal-to-noise in any one of the measurements was not very large. However, taken together (and combined with the WMAP observation that the geometry of the universe was best fit by a flat universe), they provide significant evidence that this effect is real and is best explained by the standard Lambda CMD model of BBT. "[1][11][12] V. Hubble's LawHubble's Law states that v = H0D where v is the recessional velocity of the galaxy or other distant object, D is the comoving distance to the object, H0 is Hubble's Constant, measured to be 70.4 (errors +1.3, -1.4) km/s/Mpc The only plausible explanation for this is the expansion of the universe, which we are currently experiencing. It is one of the cornerstones of the Big Bang Theory, and very much helps prove it. [13][14][7]VI. Stellar AgeThese last two points grow out of previous points. If the BBT were to be true, there should be no stars older than approximately 13.5 billion years. The oldest stars known fit nicely into this model: "The globular cluster NGC 6397, Panquini found an age of 13.4 billion years, plus or minus 800 million years. Other studies like Krauss and Hansen obtained similar results with related methods: 12.2 and 12.1 billion years, respectively, with errors on order 1 to 2 billion years. "[1][15][16]In addition, we should see differeniations in different stellar generations. Stars create the denser materials. If so, newer stars should have more metallicity the younger they are. This is indeed observed. [17]Generally, the youngest stars, the extreme Population I, are found farther in and intermediate Population I stars are farther out, etc, as shown here: [18]This organization is observed in galaxies throughout the universe, and is another important proof of the BBT. VII. Time Dilation in Supernova Brightness CurvesThe basic idea of an expanding universe is the notion that the distance between any two points increases over time. One of the consequences of this effect is that, as light travels through this expanding space, its wavelength is stretched as well. In the optical part of the electromagnetic spectrum, red light has a longer wavelength than blue light, or redshifting. The longer light travels through expanding space, the more redshifting it experiences. Therefore, since light travels at a fixed speed, BBT tells us that the redshift we observe for light from a distant object should be related to the distance to that object. Since the wavelength and frequency for a given photon are related inversely through the speed of light, which is a constant, it is obvious that as the wavelength increases the frequency must decrease. Likewise, if light from a distant galaxy varies with time (like we would expect for Cepheid variable stars or pulsars), then the time between these events is stretched (remember, frequency is inversely related to time). Thus, if we observe this galaxy from Earth, we will see a slower variation than an observer in that distant galaxy and the ratio between those times will be exactly equal to one plus the redshift of the galaxy. [1]"While observing this time dilation with stars in distant galaxies is difficult, we can test it using supernova in those galaxies. Type Ia supernovae, in particular, are known to have a characteristic signature, increasing in brightness rapidly and then slowly fading away over the course of several weeks. This signature varies somewhat depending on the exact chemical composition of the star before it undergoes its supernova explosion, but with careful monitoring we can compensate for this effect. This aspect was key to the supernovae measurements that gave the earliest indication of the existence of dark energy and has been the subject of many papers. These papers make it clear that correcting for the effects of redshift time dilation is critical for understanding the data. In particular, Goldhaber rules out a "no time dilation" model at 18 standard deviations. "[1][19]Here is a plot of the findings: [1]Overall, this time dilation helps prove the expanding universe, and therefore the Big Bang Theory. Sources[1]: . http://www.talkorigins.org...[2]: Weinburg, S. The First Three Minutes: A Modern View Of The Origin Of The Universe. [3]: Spergel, D. N. et al. (2006). "Wilkinson Microwave Anisotropy Probe (WMAP) Three Year Results: Implications for Cosmology. "[4]: . http://arxiv.org...[5]: . http://arxiv.org...[6]: Bertschinger, E. (1998). "Simulations of Structure Formation in the Universe". [7]: . http://en.wikipedia.org...[8]: Kolb, E. ; Turner, M. (1988). The Early Universe. [9]: . http://arxiv.org...[10]: Croswell, Ken (February 1996). Alchemy of the Heavens. [11]: . http://arxiv.org...[12]: S. Boughn and R. Crittenden, A Correlation Between the Cosmic Microwave Background and Large-scale Structure in the Universe. Nature 427 (2004) pp. 45. [13]: . http://dx.doi.org...[14]: . http://lambda.gsfc.nasa.gov...[15]: . http://arxiv.org...[16]: L. M. Krauss and B. Chaboyer, Age Estimates of Globular Clusters in the Milky Way: Constraints on Cosmology. Science 299 (2003) pp. 65[17]: . http://arxiv.org...[18]: . http://en.wikipedia.org...[19]: . http://arxiv.org...