Time Travel
Speed of Light
Another way of looking at the scale of the Universe is to think about the speed of light, which is about 300,000 km/s. To get an idea of what this means, notice that with this speed you can go around the Earth at the equator seven and a half times in one second.
To reach the nearest star besides our Sun, you need to travel 4.5 years with this speed.
Back in Time
When we look into space, whether with the naked eye or with a telescope, we are actually looking back in time. There is no other way, because the speed with which the light that we see now has travelled, is finite compared to the huge distances of travel.
So how far back in history do we look? |
|
| The light we see from the centre of the Milky Way galaxy, left its source about 25,000 years ago, that was when in the Upper Paleolithic the Venus of Dolní Věstonice figurine was created, one of the earliest known depictions of the human body. |
|
|
The light we see from the Andromeda galaxy today, left 2.5 million years ago. That was when the Pleistocene began in the geological time scale, when on Earth the genus “Homo” appeared, from which the modern humans have evolved much later. This skull is 1.9 million years old, discovered in Kenya in 1973. Homo habilis is arguably the first species of the Homo genus to appear. |
|
|
The faintest and reddest objects in the Hubble Ultra Deep Field image are likely the oldest galaxies ever identified, having formed between only 600–900 million years after the Big Bang. More here. These objects are at a distance of about 13 billion light years. |
 Photo credit: NASA/ESA/S. Beckwith(STScI) and The HUDF Team. |
A sense of scale of the Universe, is that reality or just a dream?