Big Bang Theory
It is a physical theory produced by astronomers to explain how the universe began. This theory claims that universe has began its journey from the single point which burst and expanded to the current size, and thought to be still expanding. Amazing right !
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| Credits: ESA/Hubble & NASA |
Georges Lemaître is considered as father of Big Bang Theory. Universe is about 13.7 billion years old. But how can we measure the age of universe? Age of universe is measured using two methods. A) By tracing back to the age of the oldest star and B) by rate of expansion of the universe. In method A the age of universe is practically known that it must be greater than the oldest star formed. So by finding the oldest star, we can try to get some idea how old is the universe but not the exact number Method B is quite complex but still lets deal it in pretty simpler way. The universe is expanding which means that all the objects are thrown away with some speed from a single point - the big bang theory. So at t=0, all the objects where at same point and there is no relative distance between them. After long time of expansion, we come to know different objects (say Galaxy A and Galaxy B) are separated by some distance D since they have different velocity say v1 and v2, So the time can be calculated like this.
RD = D
RV = | v2-v1 | = v
time = Relative Distance (RD) / Relative velocity (RV)
time = D / v
This time is same as the age of universe !! Yes, at t=0, D =0, At some time t = t , they are separated by some distance D,
According to Hubble's law the velocity of object say u at distance R is proportional to R.
u = Ho R
Where Ho is hubble's constant
So, v1 = Ho (R1) ; R1 is the distance of galaxy A at present from the observer
v2 = Ho (R2) ; R2 is the distance of galaxy B at present from the observer
Subtracting both, we get v / D = Ho
that is t = 1 / Ho.
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