In the past two decades, astronomers have made a truly revolutionary discovery: that
the cosmos is not only expanding, but is doing so at an ever-faster rate.
The discovery of the accelerated expansion of the Universe was awarded the 2011 Nobel
Prize in Physics.
The Universe we live in was created in the Big Bang some 13.7 billion years ago.
Ever since then, the Universe has been expanding.
And for decades, astronomers have wanted to learn more about the nature of this expansion.
For a long time, there were two main ideas:
Either the expansion would gradually slow down and would ultimately come to a halt Ñ
after which the Universe would start to contract towards a ÒBig Crunch.Ó Or that the Cosmos
would continue to expand forever.
But how could astronomers find out which of these models of the Universe is the correct
one?
Well, one of the simplest ways of doing this is to accurately measure distances to very
faraway galaxies, and then to compare these measurements with the predictions from these
models for these particular galaxies.
The comparison between the measurements and the predictions tells us which of the models
is the right one.
But how does this work?
How can astronomers precisely determine these huge distances across the Cosmos?
Well, stellar explosions, or supernovae, play a key role here.
Supernovae are rare cosmic events: They are exploding stars.
There is a certain type of explosion, known as a Type Ia Supernova, which is ideal for
measuring distances in the cosmos.
These supernovae are very bright, which means they can be seen even in distant galaxies.
And whatÕs more their intrinsic brightnessÕs are always the same, meaning that their distances
can be inferred from how bright they appear to us from Earth.
By the 1990s two separate research teams had begun to carefully observe these exploding
stars.
For their studies, astronomers partly used telescopes at ESOÕs La Silla Observatory
in Chile.
The discovery of the accelerating expansion of the Universe was one of the most unexpected
and important of the last decades.
It was so unexpected because up until that point, everyone believed that the expansion
of the Universe should be slowed down by the attractive force of gravity exerted by all
of the matter in the Universe.
But, as it turns out, the Universe is in fact much more interesting than that.
But why is this acceleration so important?
Well, as far as we know, there are two possible explanations for the acceleration:
The number one explanation is that nearly 3Ú4 of the Universe consist of some form
of this mysterious dark energy.
Dark energy is so mysterious because it exerts negative pressure.
ThatÕs pretty exotic stuff.
The number two explanation is that there is something wrong with our understanding of
gravity.
In other words, that EinsteinÕs theory of general relativity is not quite correct.
In either of these cases, we are confronted with completely new physics, and thatÕs why
this is so important and why this discovery was awarded the 2011 Nobel Prize in Physics.
This is Dr J signing off for the ESOcast.
Join me again next time for another cosmic adventure.