Whenever there is discussion about speed, everybody knows that the speed of light is the ultimate limit, nothing can move faster than that. Then how come according to a report, galaxies are moving away from us at a speed greater than the speed of light? It is simple, if you are standing and something is moving away from you then it is moving at its own speed…. but when you are moving and the thing is moving in a direction opposite to you then the thing moves with a speed which is a sum of yours and its own. The same applies to galaxies. But can two space bodies move away from each other at such speeds that their relative speed becomes even greater than speed of light?
Here comes the concept of ‘Hubble Constant’. According to this, for every megaparsec of distance between us and a distant galaxy, the speed separating them increases by about 71 kilometres per second. Galaxies separated by 2 parsecs will increase their speed by 142 kilometres every second.
If you run the marathon, once you get out to 4,200 megaparsecs away, two galaxies will see each other travelling away faster than the speed of light. But do we have that much space in the universe? Sure we do dear readers! The first light ever, the cosmic microwave background radiation, is 46 billion light-years away from us in all directions and if calculated, 4,200 megaparsecs is a little over 13.7 billion light-years. So to say, there’s humongous room for objects to be more than 4,200 megaparsecs away from each other.
Now the next question that arises because of this finding is that if most of the universe is already moving away at a speed greater than the speed of light. Then how can we see the lights from galaxies moving faster than the light itself? Actually, the galaxies may be moving away from us but the light emitted by the galaxies is moving towards us. That is the reason why photons emitted by all the stars in these galaxies can still reach us.
These wavelengths of light get stretched out, and shift further into the red end of the spectrum, off to infrared, microwave, and even radio waves. So with the passage of time there will come a time when the photons will be stretched so far that all galaxies and radiations that we see today will become totally undetectable. The universe never ceases to surprise and confuse us at the same time.
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Author:Technology and Beyond
