3.33 Sspd_chapter 1_part 13_ constituent particles of solid state  (Page 14/14)

How did the uniform, featureless Big Bang explosion evolve into the galaxies and stars we see today?

13.7Gya Big Bang occurred. Explosion is uniform and featureless. During the inflationary phase of expansion matter is still uniformly distributed.

300,000 years after the Big Bang, COBE satellite show huge wispy cloud of matter, 500 million light years in length and larger, beginning to condense - this is verified by the discovery of ripples of matter in deep space.

The first galaxies must have formed at about 200 million years after the Big Bang.

Today 13.7 billion years later, stars and galaxies have evolved out of the ripple of matter.

In 1993, right on the cue, came the news from NASA that ripples in the Cosmic Background Radiation of exactly the right size had been detected –Dr. George Snout, the leader of the COBE team, announced at a meeting of the American Physical Society in Washington, what he described as evidence for the birth of Universe.

To refine the CMB radiation pattern studies, in 2001 Wilkinson Microwave Anisotropy Probe was launched (WMAP). This is in a circular orbit around Sun with semi-major axis a= + 1.5×10 ⁶ km.

In February 2003, the image of the infant cosmos only 400,000yrs old was received. The results from WMAP reveal that the CMB temperature variations follow a distinctive pattern predicted by cosmological theory: the hot and cold spots fall in characteristic sizes .The image of infant cosmos is shown in Figure 1.75.

Figure 1.75. The image of the infant COSMOS as taken by Wilkinson Microwave Anisotropy Probe and the Big Bang time line.

Hot spots (colored red) in the background radiation are the images of compressed, dense plasma in the cooling universe, and the cold spots ( colored blue) are the signatures of rarefied region of gases.

WMAP give the following picture of the Universe:

1. 4% ordinary matter;
2. 23% exotic matter- the dark matter made up of an-as-yet-undetected-particle;
3. the remaining 73% is dark energy which is causing repulsion and hence accelerating the expansion rate of the Universe.

The age of the Universe is exactly pinned down at 13.7Gy±100,000yrs.

H, Hubble Constant, is exactly 71km per sec per megaparsec.

Universe’s shape is exactly flat, neither closed nor open. This means the density mass density is exactly at the critical mass density.

After 10 ^-6 second the temperature falls below 10 ¹³ K, equivalent to 1 GeV, the quarks get confined into nuclear particles. This Quark-Nucleon Phase Transition. Two kinds of nuclear particles are created: hadrons which are Fermions and gluons which are Bosons.

Protons and neutrons are hadrons. Mesons are gluons.

After 10 ^-4 second, temperature fell below 10 ¹² K, equivalent to 100MeV. This provided the condition for the stable formation of nuclii of Hydrogen, Helium and Lithium. At this point the mass density of the Universe was 10 ¹⁴ gm/cc and this is the nuclear density also.

At the time of Quark-Nucleon Phase Transition, some quarks got decoupled and must exist as relic quarks in a given mass abundance. This mass abundance is the same as that of gold but till date no free quark has been detected.

From 10 ^-6 second to 10 ¹³ second, temperature falls from 10 ¹³ K (equivalent to 1GeV) to 4000K(0.3eV). At this energy level the photons are not energetic enough to maintain the ionized plasma. The primitive form of ionized H and He and traces of ionized Lithium transform into neutral H ₂ , He and traces of neutral Li. Once the matter neutralizes, energy present in form of electro-magnetic energy gets decoupled and starts cooling with continued expansion of the Universe and today it fills up the Universe as all pervasive 3Kelvin CMB ( cosmic microwave background radiation).

We have already described that detection of CMB by WMAP has helped reveal the heterogeneity which must have been present in the matter density distribution which eventually led to the formation of Super-Clusters, Clusters, Galaxies and Solar Systems.

Our Solar System is 4.56 Gy old. It belongs to Milky Way Galaxy which is 10Gy old and is third generation galaxy. This Milky Way belongs to a cluster of galaxies known as Local Group. Local Group in turn belongs Virgo Cluster which in turn belongs to Virgo Super Cluster.