When you see the topic your mind will go crazy as if there is no such thing ,but the thing is that it is actually the truth .Let us go deep about this expanding of our universe.
In 1912 astronomer Vesto Slipner observe a under thing ,that is he observe that the wavelength of galaxy starts reducing with time. from Doppler effect of sound we see that the wavelength of sound we receive reduces as the object moves away from us. So when we apply this logic we come to the conclusion that universe is expanding.he term this effect as cosmological redshift.
You have a doubt that we can say that the galaxy which observe moves away from us not the whole universe ,but actually it is not
Let me explain with cookie
Consider the outer layer as our space time and all the galaxy as the chocolate above it inside it .When we heat the cookie we see that outer layer is expanding and not the chocolate .So it is the universe expanding not the galaxy
1929 Sir Edwin Hubble discovers the rate of expanding of universe
He identify this by plotting a graph between velocity of some particular galaxy moving vs the distance from us.
We can find the velocity of galaxy moving or redshift by the observing the change in wavelength receive with time.
For the distance he use standard candle method . in this he observe scifi stars ,these stars emit varying intensity that is they emit high intensity at day 1 ,low on day 2,high on the next day.
With this varying intensity we can find the distance by using this formula
b=L/4pi(dsquare)
where b is apparent brightness and L is luminous intensity
So on plotting he get a graph like this
From the graph he find that the hubble constant is equal to gradient of the graph.
From this we get hubble constant value as 72km/s/MPC.
Here 1 MPC is equal to 3.26 million light year . this speed is for on 1MPC and this speed we double for next MPC.
Fun fact is that we can find the age of universe from hubble constant
It is equal to the inverse of hubble constant: Age=1/ho
Has laoreet percipitur ad. Vide interesset in mei, no his legimus verterem. Et nostrum imperdiet appellantur usu, mnesarchum referrentur id vim.
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