Astrophysics and Earth's Deep History
Why is an alien across the far away galaxies pointing a binocular towards earth they would see dinosaur?
That is one of the most mind-bending and beautiful concepts in all of physics! It sounds like science fiction, but it's absolutely true: if an alien in a galaxy 65 million light-years away pointed a powerful enough telescope at Earth right now, they would indeed see roaming around.
Space is a Cosmic Time Machine
The secret behind this cosmic magic trick is simple: light takes time to travel.
Even though light is the fastest thing in the universe, it doesn't move instantly. It travels at a set speed of about 186,000 miles per second (or meters per second). Because space is so mind-bogglingly huge, the distances between galaxies are measured in .
light-year
noun
The distance that light travels in one vacuum year, approximately 5.88 trillion miles.
Think of light like a postman carrying a letter across the universe.
If you send a letter to a friend who lives across the country, it might take three days to arrive. When your friend opens the letter and reads, "I am eating a delicious pizza right now," they are reading about something you did three days ago.
In the exact same way, the light bouncing off Earth today has to travel through the dark void of space to reach our faraway alien friend. By the time that light actually reaches their telescope, millions of years have passed. They are opening "cosmic mail" that we sent a long, long time ago.
I would love to explore this mind-blowing connection between light, time, and space with you! Would you like us to build a mini-course to explore how looking up at the night sky is literally looking back in time?