How can astrophysicists study the story of the Universe?
Billions of years ago, when the Big Bang happened, there was no Milky Way galaxy, no Solar System,
no planet Earth, and, especially, no human beings to witness these and all the events that followed.
So how would they know about this stuff?
Well, it turns out that the Universe is, somehow, like a time machine.
When looking at things in the sky, we are looking at that past.
Yeah, it's a bit confusing but try it this way:
When you hear a plane, you probably have a hard time spotting it in the sky.
You look in the direction where the sound came from but the plane is no longer there
That's because its sound took some time to reach you,
and by the time it did, the plane had already moved on.
In a way you were hearing back in time
as the sound you perceived was the one that left the plane seconds before.
With light it's exactly the same.
Even though light is much faster than sound — in fact, it's the fastest thing we know —
it still takes time to get from where it is emitted to where it is seen.
The father the object the longer it takes light to make the journey to the observer.
By looking at galaxies that are very far away, whose light takes billions and billions of years to reach us,
we are seeing them how they looked billions of years ago,
when the universe was much younger and they were just beginning to form.
But as we look at galaxies that are closer and closer to us, studying them throughout time,
it's possible to see how they aged and change,
just like if we were looking at babies, children, teenagers and adults to see how humans develop.
The problem is when things are very far away from you,
it gets to a point where it's impossible for your eyes to distinguish details.
Telescopes, especially the ones that see the same kind of light as we do, also have a limit
and are not able to detect the light emitted by the first galaxies ever formed,
as they are too distant and their light is too faint.
In those galaxies, however, the first stars were born.
And even though there's no telescope powerful enough to see them shine,
ALMA, with its incredible sharpness and ability to see radio light,
can distinguish the dust and gas clouds which formed the first generations of stars in the Universe.
This can help astronomers know a little bit more about these early phases of time and space,
which are fundamental to understand our present.
Transcribed by ESO. Translated by —.