Infinite Stars But Sky Is Dark

                                     

 Despite huge number of twinkling and bright stars, sky looks dark. It appears intriguing and unexplainable. But this is not the actual situation. In order to simplify the matter, it would be prudent to understand the stars, galaxies and the rays of light. Sun, in our galaxy called Milky Way, is a moderate star. However there are stars bigger, heavier and radiating more energy  in the galaxies. A galaxy is a cluster of stars. There are 100000000000 or 10 raised to the power eleven stars in a galaxy or Milky Way. There are 100000000000 or ten raised to the power eleven galaxies in the universe . 

               Milky Way

That makes 10 raised to the power 22 (or twenty two zeros proceeding one) stars in this universe. This is a very huge astronomical figure. But despite such large  number shining stars, there is darkness in the sky at night. Why is it so? I am not considering the reflection from moon which lit the sky at night. 

2. The probable answer would be that these stars are distantly situated and can not contribute to illumination of sky. But what stops light rays from huge number of stars from illuminating the sky? That may seem a bit technical question. To understand this , it would be better, to know in brief, the law governing these heavenly bodies. Hubble, an astrophysicist, gave the world law of recession of heavenly bodies. This law states, heavenly bodies recede from each other with velocity directly proportional to its distance. That means, as the distance will increase, the velocity increases. This velocity at the most can tend to reach that of light as per Einstein. Einstein stated that maximum achievable velocity is velocity of light and nothing can surpass this velocity. That means maximum achievable velocity for cosmological bodies would be velocity of light. It is obvious if the bodies  were moving with the velocity of light, the Rays from these would not be able to reach us. We thus can not see these. We can only see or detect those cosmological bodies whose velocity are less than that of light. Such galaxies which have velocities less than that of light, will fall in the universe visible to us. With the passage of time as velocities of such bodies tend to approach that of light, these would be out of our visible universe and beyond our detection. Visible universe is, therefore, losing those bodies whose velocities get increased to that of light with passage of time.

3. It is an admitted fact that ordinarily, all stars emit light rays, but these rays travel huge distances to reach earth. The distances traversed by the rays can be judged from the fact that rays take 4.67 years to reach here from our neighbouring nearest star Alpha Centauri. Stars situated even more distantly also exist in galaxies and these may take thousands of years for the rays to reach here. The journey of the rays from the source stars is not easy and smooth. The rays after emission from the stars pass through intervening some massive and some moderate stars. The rays when near the gravitating massive stars, get bent or attracted to the star and lose a part of their energy. 

Red Shifting Due To Massive Body

These thus get red shifted. In addition, the relative receding motion between the star and the sun also causes a red shift.To understand the red shift, it is submitted that a ray of light can be split into light of seven colours . This splitting can be done by glass prism or spectrometer. These colours of light denote its energy bands. These seven colours can be remembered by the word, ‘VIBGYOR’ where V stands for violet, I for indigo, B for blue, G for green, Y for yellow, R for red Rays of light. That is the energy of the rays from their colours, violet to red is in descending order. When rays are deflected towards gravitating heavy star, their energy get decreased and the rays are shifted towards red band in spectrum. This deflection of light rays due to the gravitating star is similar to that in optical lens and gives rise to the image of the star causing confusion in the location of the real star. This phenomenon is called gravitational lensing. In addition to this , the relative motion between the source star and the sun on account of recession, also causes an appreciable amount of red shift due to Doppler’s effect. Because of high red shifting, the rays fall in infra red zone and are too weak to illuminate the sky.   

4. As submitted above, the rays traverse large distances, these pass through intergalactic gases, dust etc. That causes absorption of the rays and this further weaken the energy. At the same time, the rays are also blocked by the intervening stars and that also reduces their energy. The rays then possess the energy far lower than that at the time of their emission from the source star.

5. Also flux density of light is inversely proportional to the square of the distance between source and destination, larger distance will reduce the flux density to larger extent. As stated earlier the distances of stars from the sun in some cases, is thousands of light years, therefore, flux density gets appreciably weak.

6. It is also submitted that some stars emit light for some duration and then these do not. Therefore, light rays are available to the extent t/t’ where t’ is time from Big Bang and t is time during which it emitted light.That also reduces the flux density.

7. Without going into details of the Big Bang, I submit that expansion took place after after Big Bang and energy converted to mass. But relic of Big Bang is still present in the universe in the form of cosmic microwave background or CMB. Hot photons cooled down and reached that temperature which was in thermal equilibrium with matter. 

    Cosmic Microwave Background

The result is 2.7 K microwaves. These CMB is still present in the universe equally at day and night. But these are not strong enough to illuminate the sky. This is also called Olbers’ Paradox.

8. Summing up, it is submitted that despite huge number of stars, obstructions by intervening stars to rays, absorption of rays by galactic gases and dust, exponential reduction of flux density due to large distances between source and the sun, intervention to the rays by massive stars, reduce the energy and the rays are highly red shifted to the extent of infra red band.  CMB, a relic of Big Bang, is too weak to illuminate the sky. Thus though 10000000000000000000000 stars twinkle yet these can not illuminate the sky. This is a situation similar to, ‘Water water everywhere but not a single drop to drink.’