Have you ever wondered how the world was created? In every civilization throughout time and throughout the world, there has always been an account of the creation of the world. Such discussions have always belonged to religion and philosophy. It might seen strange that astronomers, astrophysicists, physicists have now become involved in the discussion of the creation of the universe. Of course, if we think about it, it is not strange at all. Since physics is a study of the entire physical world; it is only natural that physics should try to say something about the world’s birth.
The story starts in 1923 when the American astronomer, Edwin Hubble, using the Doppler effect ( Apparent change in the frequency of waves by the motion of source or observer) for light, observed that all the galactic clusters, outside our own, in the sky were receding away from the earth. When we studied the Doppler effect we see that e.g when a train recedes from us frequency of its sound decreases ( we hear less sound) . A decreases in the frequency means that there is an increase in the wavelength. Similarly, a Doppler effect for light can be derived. In case of light waves the effect is same. That is, a receding source that emits light at a frequency f, is observed by the stationary observer to have a frequency f ‘, where f < f ‘. Thus, since the frequency decrease, the wavelength increase. Because long waves are associated with the red end of the visible spectrum (ROYGBIV), all the observed wavelengths are shifted toward the red end of the spectrum. The effect is called the cosmological red shift. Hubble found that the light from the distant galaxies were all red shifted indicating that the distant galaxies were receding from us.
It can, therefore, be concluded that if all the galaxies are receding from us, the universe itself must be expanding. Hubble was able to determine the rate at which the universe is expanding. If the universe is expanding now, then in some time in the past it must have been closer together. If we look far enough back in time, we should be able to find when the expansion began.
(Imagine taking a movie picture of an explosion showing all the fragments flying out from the position of the explosion. If the movie is run backward, all the fragments would be seen moving backward toward the source of the explosion.)
The best estimate f or the creation of the universe , is that the universe began as a great bundle of energy that exploded outward about 15 billion years ago. this great explosion has been called the Big Bang. It was not an explosion of matter into an already existing space and time, rather it was the very creation of space and time, or spacetime, and matter themselves.
As the universe expanded from this explosion, all objects became farther and farther apart. A good analogy to the expansion of spacetime is the expansion of a toy ballon. A rectangular coordinate system can be drawn on an unstretched balloon, locating three arbitrary points, A, b and C. The bloon is then blown up. As the balloon expands the distance between points A and B, A and C, and B and C increases. So no matter where you were on the surface of the balloon you would find all other points moving away from you. This is similar to the distant galaxies moving away from the earth.
If everything in the universe is spread out and expanding, the early stages of the universe must have been very compressed. To get all these masses of stars of the present universe back into a small compressed state, that compressed state must have been a state of tremendous energy and exceedingly high density and temperature. Matter and energy would be transforming back forth through Einstein’s mass-energy formula, E=mc2. Work done by particle physicists at very high energies allows us to speculate what the universe must have looked like at these very high energies at the beginning of the universe.
