The expansion of Universe is the most weirdest phenomena Physics world have ever seen. May be,Expansion of Universe have made it more interesting than the Universe itself. It was Edwin Hubble who found the proof for an Expanding Universe for first time.
What Hubble found was,Red shift. Red shift is the observational effect we have,whenever we observe a light source,which is going away from us. Hubble,observed the light source from many stars and other distant sources. He found this Red shift – which in turn told us,YOUR UNIVERSE IS UNDER EXPANSION!
Next thought arised was to find the properties and reasons for this expansion. The questions arised was this : How and Why?
The How resulted in finding the nature behind expansion,while Why resulted in the later assumption of presence of Dark energy and Dark Matter.
Lets keep the Dark energy and Dark matter for another time,and concentrate on the nature of this expansion.
When we talk about Expansion, we will always consider the genera view,not the local view. we generally avoid the expansion between earth and moon,but consider the expansion between Milky way and Andromeda Galaxies. Its not because,they are important,but negligible to be found either observationally or Experimentally.
The rate of our expansion is what we can find easily. It is found to be 72 – 76 km per second per megaparsec. Well,you will be thinking what does this mean,sometimes you would have already heard this figure.
A Parsec is 3.26 Light years. So,a megaparsec is – adding 6 zeros at the end. A megaparsec is one million Parsec. Like the light year,parsec and Mega parsec is also a unit of distance. So 72 km/second is varying per 1 megaparsec of distance.
Roughly,i can say,the expansion rate is increasing at the rate of 72 km/s,for each megaparsec from us. To understand it,we can consider it analogous to Acceleration. an amount of acceleration means,the velocity is getting increased by the accelerated amount.
If you are look at a galaxy,which is 1 megaparsec away from my you, it will be appearing to be receding away from you at 72 km/s. instead If you are looking at a galaxy,which is 2 megaparsec away, it will be receding at a rate of 144 km/s. then what about a galaxy,3 megaparsec away? yes, 216 km/s. And on and on: for every megaparsec, you can add 72 km/s to the velocity of the distant object of observation.
So, at some distant point,we would be getting a galaxy with a speed with a speed of Light’s velocity,and beyond that there will be galaxies with more than it. OMG! I have violated Special Relativity!
Sorry to say,its not me,but its the universe who have violated it. The Key to this is lack of knowing the reality behind special relativity. Special relativity is a local rule,for local areas. But the General rule for the farthest galaxies and such vast domains are General Relativity.
What does General Relativity says?
General relativity doesn’t care about it. General relativity was built from the limitations of special relativity. Later understood,the Special relativity was only a Special case of the General view.
So,’nothing can move faster than light’ is the local rule for local areas,not for the larger or universal domains.
Special Relativity doesn’t care for anything like Speed,of a farthest distant galaxy!