time to the Big Bang
Ellen Look, the Andromeda
galaxy is our nearest neighbor - 'only' 1.5 million light years away.
Tim Its light set off when the first human-like creature
walked on two legs!
Ellen So when we look into the remote corners of our Universe,
we see what happened a very long time ago.
Tim Now I see why you called it a time machine. Although we're
not really traveling back in time, we're seeing things which happened
a long time ago.
Ellen Looking at pictures from the Hubble Space Telescope, astronomers
have discovered a galaxy so far away that its light started to travel
more than 8 billion years ago - that was even before our Earth had formed!
So do you grasp why I called the telescope a 'time machine'?
Tim Yes, but I don't understand how you can tell that this
little red dot there is a galaxy 8 billion light years away?
Ellen We owe that to Mr. Hubble: he observed that all galaxies
move away from each other - the further away from us, the faster! And
when a source of light moves away, its waves get 'stretched', and its
color is shifted towards red.
Tim So we are sitting in the middle of the Universe and
all the galaxies are moving away from us?
Ellen No - although people in the olden days would have liked the
idea! Imagine a huge black balloon which is being blown up. Place a few
white spots on its surface, and see how they all move away from each other.
The further they are apart, the faster they separate.
Tim I get it. The balloon is our Universe. Its diameter
increases, and so does the distance between everything inside - stretching
Ellen This is one of the strongest arguments in favor of a violent
start of the Universe - the Big Bang. It is of course possible to calculate
at what time all these galaxies occupied the same position - and the answer
is somewhere between 10 and 15 billion years.
Tim Wow, I wonder what the Universe was like thenů