The puzzle called Universe.

Our romantic relationship with the Cosmos  will continue.   The more it reveals  the less we recognise.  Primitive man looked at the lustrous objects in the sky with awe. The Unknown  elicited fear and suspicion. He feared and  suspected it affected him, his health, his family his crops...... Bewilderment launched  imagination to the utmost bounds. He built an unattainable heaven in the skies and spun tales of myriad hues  to appease his troubled heart.   But his  yearning to know all, continued.

Time went by.  Man made rapid progress in path of knowledge.   In 400 BC Aristotle  came up with the geocentric model of the Cosmos in his book De Caelo( On the Heavens). Though in 300 BC Aristarchus murmured the cosmos is heliocentric, no one took him seriously. Aristotle's model continued o hold good without  being questioned for almost   thousand years.  Then came Copernicus, who in his books substantiated the concept of heliocentric universe. So did Giordino Bruno and later Galileo. But alas, Copernicus had to keep his writing hidden from Church, Bruno was burnt at stakes and Galileo was made to apologise. For it was unbiblical to negate geocentric universe.  Nevertheless, even as he apologised,  Galileo muttered eppur si muove ( still it moves)

A year after Galileo died, Newton was born. Alexander Pope, the English poet puts it emphatically: 

Nature and Naure's laws lay hid in night; 

God Said let Newton be! and all was light 

Newton brought about a paradigm shift in many areas of science. Most important being in recognising  Gravity as the  fundamental natural force.  He described a static, steady state infinite Universe. But this model was rather unstable because the gravitational  pull would have caused the universe to collapse into itself. Notwithstanding this, our repertory  was  getting crammed  with information on stars, planets, comets, nebulae, galaxies.......

Introducing  Λ  the Cosmological constant ,an equivalent repulsive force to balance the  gravitational pull, Einstein steadied Newton's model. Before we could  get settle down with that model,   Edwin Hubble's  observations and calculations showed that  galaxies are receding and that meant  the universe is expanding.  But that didn't  in anyway hinder our space projects, we sent Man to the Moon, probed Venus and Mars for possible life, built space stations.......Figured out the necessity of black holes and wormholes  to explain the unexplainable. 

Artist's concept of the Cosmic explorer to be launched in 2020

Scientists  built more and more sophisticated instruments to peer into the darkness.  And based on what they saw  were forced to revise their stand:  No,  the universe was not just expanding at a slow monotonous rate, but rather   expanding at an accelerated rate. They needed   Dark Matter  and Dark Energy to  explain the unexplainable.  


We practically know nothing about Dark Matter and Dark Energy except that  the material Universe that   we know including all the far and near galaxies, black holes and other cosmic matter  account for  only roughly 5% of the normal matter, the rest is divided between dark matter  (~27%) and dark energy (~68%). 

Euclid is getting ready to probe the Darkness  around us. The launch is scheduled for 2020. 

REFERENCES:
1. De Caelo by Aristotle
2. Aristarchus of Samos- The Ancient Copernicus by Thomas Heath Oxford @ Clarendon Press 1913
3. On the Shoulders of Giants: Stephen Hawking. Viva Books Private Ltd. New Delhi ISBN 8176494518
4. Dark Energy, Dark Matter
5. Euclid