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The Expanding Universe


THE EXPANDING UNIVERSE


Since ages man have wondered, what are the dimensions of the universe and where does it end? If the universe is finite then if one stuck at their hand at one edge where would it go? In 1929, Edwin Powell Hubble at Caltech discovered that the universe is expanding. If the universe has been static, then in accordance with Newton's law of motion of gravity the attractive forces of all the objects within the universe should have caused the complete collapse of the universe on itself. But in reality, it doesn't take place at all, eventually keeping people with some paradox.

When Einstein discovered the speculation of gravity by the Theory of relativity, his equations couldn't identify whether the universe was expanding or collapsing. His original equation contained a term called the cosmological constant which neglected the effect of gravity and the universe was thought to be a static one. After Hubble's discovery, he realized that the constant is actually wrong.

The theory of the expansion of the universe was developed by observing the redshifts of celestial bodies which implied that the space between galaxies is expanding, so they seem to recede from us at velocities that increase with their distance. (Redshift means a rise within the wavelength of electromagnetic radiations)

But what exactly means by the fact that the universe is expanding?
It means every heavenly body i.e. galaxies are moving aloof from one another. However, the galaxies don't seem to be moving through space, they are moving in space because space is additionally moving. In other words, the universe has no centre, everything is moving away from everything else.

Recently, Astronomers have seen that the Hubble constant (a value to detect how fast the cosmos is expanding with time) is 74 kilometres (46 miles) per second per megaparsec. It means a galaxy which is 3.3 million light-years aloof from us appears to be moving at a rate of 74 km faster because of expansion of the universe which is 9% faster than the predicted 67 Km (41.6 miles) per second per megaparsec. It comes from Planck's observations of the first universe, as well as our present understanding of the universe.

Several hypotheses are given to clarify this discrepancy. Some said it will be the matter comprising 70% of the universe which will be accountable for accelerated expansion. Another explanation is that the Universe contains a new fundamental particle that travels close to the speed of light (also called dark radiation) can be taken into account.

But actual explanation remains a mystery. Adam Reiss, laureate and lead researcher at Space Telescope Science Institute (STScI) and Johns Hopkins University, Baltimore, Maryland said that "The Hubble tension between the early and late universe may be the most exciting development in cosmology in decades." 
Written by
Debasmita Sharma Chaudhuri
BIOTECHNOLOGY 2ND



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