To an observer in space, does our planet even exist?

If intelligent life is out there, way out there, would Earth even be visible? The strange answer is "no," but not because we are small or hard to see; but rather because to an observer far away our planet may not exist - yet.
Yes, indeed, another mind-challenging concept from the world of science.

An astrophysicist held an interesting discussion on Canadian radio earlier this year. The topic was the expanding universe, the speed of light and relative distances.

The scientist reminded listeners that when we see light from the stars, we're actually looking back in time. When we look at our nearest star, our sun, we're not seeing how the sun looks now, but how it looked a full eight minutes ago. That's how long it takes light to travel the distance from the sun to the earth.

The really interesting concept relates to other solar systems and galaxies. If we turn the thought around and place ourselves in the role of an observer from far away looking at the earth, then that observer would also be seeing OUR past.

They say the Milky Way, our home galaxy, is about 100,000 light years across. If someone's out there watching us from the other end of our own galaxy, they may be seeing Earth not as it is now, but only as it was when our species, Homo Sapiens, was just distinguishing itself from our "cousins," the Neandertals. No cities, no technology.

And that's just our own galaxy. The universe has millions of galaxies. Any observer watching from any of the other galaxies in our universe would see Earth much earlier in it's history.

So all the observations in space are true only as measurements of the past. Since the size of space is so enormous, even at the relatively fast speed of light, at 300,000 kilometers per second (186,000 miles per second), it takes a relatively long time for light to travel across these vast distances.

Finally, then, if intelligent life were searching for us from 5 billion light years away, they would not see us at all ! To them, we still don't exist. That's because Earth is calculated to be about 4.5 billion years old.

5 billion years ago, our solar system probably was just a loose collection of gases.


For more thoughts on our universe, see posts in August (Are parallel universes real?)


  1. Ok so somebody at the other side of our "humble" Galaxy sees "earth 100.000 years ago".

    So what!

    But in 100.000 years this person will see earth as we have it today!

    The problem is, that you will only life for some 80 to 104 years and therefore 100.000 years are for you a super long time scale.

    But those 100.000 years are only a fraction in relation to those years of our universe.

    Imagine we discover sooner or later how to stop aging (due to some genetic correction) and we live for 500.000 - 1.000.000 years.

    Would then anybody think/say "To an observer ...."

    No because 100.000 years are then like today 25-Years!

  2. Okay...NOW I get it...
    AZ ! You scoundrel!

    You'll have to forgive me... I'm still as gullible as ever.

    You'll be happy to know I won't be dabbling in any more space math for a while. Definitely out of my league. You've spun my head around.

    Nice to hear from you. Dziękuję!