We from the Milky Way. The Doppler shift is

We all know that the universe is huge. But did you know that it’s
actually expanding? In fact, its expanding at a rate faster than ever before!
This profound discovery of the universe’s accelerating expansion was uncovered in
1988 by the Nobel labeurate, Brian Schmidt.

Now Dr. Schmidt and his team not only revolutionised cosmology’s
perspective on the universe’s dynamics, but also propelled research on dark energy,
provided scientists with new insights about the history of the universe and has
increased public understanding about space using TEDx talks, lectures and even
free astronomy courses.  
So how exactly was this discovery made?

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Well there are several key concepts and
discoveries which we need to first understand that form the foundations to Dr.
Schmidt’s uncovered the accelerating expansion of the universe.  

Slipher & the Doppler Shift

Now, one of the very first discoveries in modern
cosmology was made by a scientist called Vesto Slipher. In 1916 he used the
Doppler shift to observe that almost all nearby galaxies were moving away from
the Milky Way.

The Doppler shift is the increase (or decrease)
in the frequency of a wave, as the source of the wave moves towards (or away
from) the observer.  Although most people
have

this concept of the Doppler effect with sound can
also be applied to light waves in space.  

If an object in space is moving towards earth,
the light waves reflecting from it would be compressed and perceived as high
frequency 8. Higher frequency visible light waves are interpreted as a blue
colour; hence why objects in space moving towards Earth are blue shifted 7
& 8.
On the other hand, if a star was moving away from them, the light waves
produced behind the star would be stretched out. This results in the perception
of low frequency light waves which are interpreted as a red colour in visible
light 7 & 8. Hence why objects travelling away from Earth are 4red
shifted. 

So, when Slipher made the observation that light
from most nearby galaxies were redshifted, he was able to come to the
conclusion that they were moving away from us. However, as almost all
discoveries do, this led to even more questions. Why was almost everything
moving away from us? Are we in a special part of the universe that everything else
was trying to get away from? 

Hubble
and the Expansion of the Universe

Around a decade later, these questions were solved
by the famous American astronomer, Edwin Hubble. Using the Hooker telescope on
Mount Wilson, Hubble constructed the velocity-distant table below where
distance of a particular galaxy from Earth in parsecs is the x-axis and speed
moving away from Earth in km/s is the y-axis. (A parsec 3.26 is light-years. A light-year is how much distance light travels
in one year approximately equal to 9,460,730,472,580.8 km).

 

As you can see, the galaxies that are further to
the right on the x-axis also tend to be much higher up on the y-axis. This
means that the velocity of recession is proportional to the distance of the
galaxy from us. In other words, on average, the further away a galaxy is, the
faster it is moving away from us.

This means that most galaxies weren’t just moving
away from us. Almost every galaxy is moving away from each other! Hubble
uncovered that the entire universe was expanding!

Alright, so many of you might be sceptical and
might be wondering, “How does