DRIVING THE EDGE OF UNIVERSE
Before the initial years of 19th century our knowledge about universe was limited to our galaxy'' Milky way'' or solar system .We did just know that this universe is all about milky way where our solar system is at the center of universe and surrounding stars are extended to boundary of universe , but there were some more curious ones like Hubble , not satisfied of that.
Till then most important physical theories of modern science so far had been introduced.(two of the major were general relativity and quantum mechanics)hence it should not have been pretty difficult for astronomers as far as space and time structure was concerned.
In order to analyse light ray coming from farther regions it was important to have a clear light ray which was very fainter due to the atmosphere . In order to neglect effect of earth's atmosphere it was crucial to establish an observatory high at the mountain and above the clouds and mists . That time an astronomer found a place to establish at an altitude of 5777ft in California. It was quite difficult to carry materials to mountain top,however, with tremendous effort the construction of observatory completed.Hubble telescope was put on in that observatory, which was at that time highest in the world .It took the images of night sky and got us some very surprising results.On its disc it appeared that our milky way is just one of the million million million million (one with 50 zeros) or more galaxies one with some 125 billion stars.It took us beyond our imagination of universe. If we multiply the no. of galaxies with no. of stars in each galaxy the product would be larger than total number of grains of sand on earth including all the beaches and desert.
Hubble kept alalysing those light rays from the distant stars ; mostly with spectra which bends light rays into its constituents colors as a prism does.Since a light ray is composed of with 7 colors of different wave lengths . In that red is longest and blue is smallest . Light from the galaxies to us reaches us through space . That travelling light ray of different wave lengths gets stretched when the emitting source gets away causing red wave length to appear more brighter and when the emitting source gets close the ray of light gets wrinkled making blue wave length appear more brighter. By these results Hubble noted something very surprising .He found that light ray of wave length red was getting more brighter and wave length of blue was getting fainter. This suggested that light rays are getting more stretched suggesting that emitting source is getting more distant . It proposed that galaxies were getting way in all direction . The galaxies being farther are moving more faster. It also suggested that ,since it is expanding it must had been very small if we go backward in time .This fact gave rise to modern universe defining theory called ''BIG BANG'' the beginning of time .
In past our universe would have been smaller than our galaxy,our earth even than an atom with infinite density. Scientist calculated that some 13 billions years before that very very hot ball of infinite density had a massive collision and in just in a trillion part of a second the universe would have expanded over a millions of light years and its must have dropped over 1/3 of initial still, it was just an idea which was proved by the detection of invisible infrared gama rays from all direction in space released by the galaxies formed in the very early year of universe . todays w-map telescope are not only enabling us to see very far in space but also make us see past in time as even rays of light of very distant galaxies take thousands of year to reach us.
Now, since we have understood the concept of origin of universe , lets move to the factors and phenomenas which have governed universe so far and presented the current universe we live in and we have dogmas about it.
Quantum mechanics has had a very major effect on origin of the universe and will affect further in fate of universe .
In order to explain this, it is necessary first to understand the general accepted theory of universe, according to what is known as the'' Big Bang Model'' This assumes that the universe is described by the Freedman's model, right back to the big bang (will be mentioned further).In such models one finds that as the universe expanded any matter or radiation in it kept getting cooler .[When the universe doubles in size its temperature drops by half] Since temperature is simply the measure of the average energy -or speed of particles, this cooling of universe would have a major effect on matter in it. At very high temperatures , particles would be moving so fast that they could escape any attraction towards each other due to nuclear or electromagnetic forces , as they cooled off one would expect particles that attract each other to clump together. Moreover , even the types of particles that exist in the universe would depend on the temperature . At high enough temperature particles have so much energy that whenever they collide many particle/antiparticle pair would be produced and although some of those particles anihalate on hitting antiparticles they would be produced more rapidly than they anihalate. At lower temperatures , however when colliding particles have less energy , particles/antiparticles pairs would be produced less quickly and anihalation would become faster than production .
At the big bang itself , the universe is thought to have had zero size , and so to have been infinitely hot. But as the universe expanded , the temperature of the radiation decreased , one second after the big bang it would have fallen to about 10 thousand million degrees. This is about thousand times the temperature at the center of the sun but the as high as this are reached in a hydrogen bomb explosion.At this time universe would have contained mostly photons , electrons and neutrinos (extremely light particles that are mostly affected by weak forces and gravity ) and their antiparticles together with some protons and neutrons . As the universe continued to expand and temperature to drop , the rate at which electrons/anti electrons pairs were being produced in collisions would have fallen below the rate at which they were being destroyed by anihalation , so most of the electrons and anti-electrons would have anihalated with each other to produce more photons leaving only a few electrons left over. The neutrons and anti-neutrons however would not have anihalated with each other because these particles intract with each other and other particles only very weakly. So, they should be still around today. If we could observe them , it would provide a good test of this very hot early stage of universe . Unfortunately , their energies now-days would be too low for us to observe them directly.
However , if neutrons are not massless ,but have a small mass of their own , we might be able to detect them indirectly; they could be a form of 'dark matter'with sufficient gravitational attraction to stop the expansion of universe and cause it to collapse again.
about one hundred seconds after the Big Bang , the temperature would have fallen to one thousand million degrees, the temperature inside the hottest stars. at this temperature protons and neutrons would no longer have sufficient energy to escape the attraction of strong nuclear force , and and would have started to combine together to produce nuclei of atoms of deuterium [heavy hydrogen], which contain one proton and one one neutron. the deutrium then would have combined with more protons and two neutrons , and also small amounts of a couple of heavier elements lithium and beryllium. One can calculate that in hot big bang model about a quarter of electron and proton would have been converted in helium nuclei , along with a small amount of heavy hydrogen and other elements and the remaining neutron would have decayed into protons which are the nuclei of oridinary hydrogen atoms.
This picture of a very hot early stage of universe was first put forward by scientist George Gamow in a famous paper written with his student Ralph Alpher . Gamow had quite a sense of humor - he pursued the nuclear scientist ''Hans Bethe'' to add his name to the paper to make a list of authors ''Alpher , Bethe, Gamow like first three letters of Greek alphabet '' alpha, beta, gama , particularly appropriate for a paper on the beginning of universe ! In this paper they made a remarkable prediction that radiation[in form of photons] from very hot early stages of universe should still be around today , but its temperature reduced to only few degrees above absolute zero(-273 degree ) c. It was this radiation that Penzias and Wilson found in 1965 .At the time wen Alpher,Bethe and Gamow wrote not much was known about reaction of protons and neutrons . Prediction made for the preposition of various elements in early universe were therefore rather inaccurate , but these calculations have been repeated in the light of better knowledge and now agree well with what we observe .It is moreover very difficult to explain in any other way that why should be helium in the universe . We are therefore fairly confident that we have the right picture of universe , at least back to about one second after the Big bang. Within only a few hours of Big bang , the production of helium and other elements would have stopped . And after that , for the next million year and so , the universe would have just continued expanding without anything much happening. Eventually once the temperature had dropped to a few thousand degrees , and electrons and nuclei no longer had enough energy to overcome electromagnetic attraction between them, and they would have started combining to form atoms. The universe as a whole must have continued expanding and cooling , but in region that were slightly denser than average the expansion would have slowed down by the extra gravitational attraction . This had eventually stopped expansion and caused those region to collapse again. However, they will be attracted by outside gravitational pull. It will cause them to rotate and as they collapse more they would spin faster and when they got enough small and attained faster enough rotation to balance gravity , they would be what we call them rotating galaxy. Other regions which did not happen to pick up rotation , would become a oval shaped object called elliptical galaxies . In these the region would stop collapsing because the individual parts of galaxies must be orbiting stably around its center , but the galaxy had no over all rotation. As the time went on hydrogen and helium in the galaxies would have broken into small clouds which contracted within it self by its own gravity which would led its atom to collide one another, the temperature of the gas would increase untill eventually it became hot enough to start nuclear fission reaction . These had converted hydrogen into more helium , and heat would given off to raise pressure and so stop the clouds from further contracting . They would remain in this state for a very long period as stars like our sun, burning hydrogen into helium and radiating the result energy as heat and light. More massive stars would need to be hotter to balance the gravitational attraction of their own , which would makevthe nuclear fission reaction proceed much more than they would use up in as little as a hundred million years. They would then contract slightly , and as they heated up further helium would begin to convert into heavier elements like carbon and or oxygen . This wouldn't release much energy although, so a crisis would occur.
What happens next is not completely clear , but these stars are pretended to collapse to a very denser state like neutron star,black hole or white dwarf. The outer regions of star may get blown off in tremendous explosion called super nova, which would outshine all the stars in the galaxy and would provide some of the raw materials for the next generation of stars . Our own sun contains about 2% of those heavier elements because it is a 2nd generation star , formed some five thousand millions year ago out of a rotating gas cloud containing the debris of earlier supernovas . Most of the gas in that cloud went to form the sun or got blown away to form the bodies that now orbit the sun like our earth.
Hope ,you must have enjoyed reading this and it has answered your most frequent questions about universe.
To be continued .......
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