Expert: Jayendra Upadhye - 7/13/2007

Question
Hello,
 I have some sort of strange questions that I would very much like to know the answers to: first, how many planets are there estimated to be in the universe?  I read in Bill Bryson's  "A Brief History of Nearly Everything"  that Carl Sagan estimated it to be about 10 billion trillion and I was wondering if that was still an accurate estimate?  My other questions are, what percentage of space does the earth take up in the universe?  And what percentage of the space in the universe does the human race take up?  I know that these are slightly odd questions that there are no exact answers to, but if you could just give me the best estimate that you know of I would really appreciate it. Thank you!!!

P.S. I am not a student, so these questions have absolutely nothing to do with homework or anything like that.

Thanks,

Skylar

Answer
Hi Skylar,
By definition the universe is "all inclusive"..meaning includes "everything there is!".

Everything that we know and do not know, but which exists physically, is part of the universe.

Due to this all inclusive definition, The universe is VERY LARGE. (But not infinite).

All this "prefacing" for my answer is necessary to put my answer to your question in perspective.

1 - You see Sagan's estimate or my estimate or your estimate are all "guesstimates" in the end when faced with the above definition of the universe.

The notion of exactness does not apply. One only gets the "sense" of the answer.
{Like one can say more sweet / less sweet but can never quantify sweetness which is at best a subjective idea.

Guesses about number of planets are like that.

2 - The earth takes up or occupies  "next to nothing" space in this universe. It is worse than like comparing the size of an atom with that of the earth.

3 - What earth is to universe, humanity is to earth!

After all we "came here" only in the last second if you equate all time since the bang to 24 hours!

Nature does not need humanity but it is vice versa.
Sagan knew that! Actually in the Drake equation, this has been factored in, as the time for which "intelligence endures" on any planet.
factors contributing to that are :-
1 - self destructive behaviour with its environment. (like the classic easter island case).
2 - Self destruction due to atomic wars for supremacy.
3 - Destruction due to Calamity. (Meteor impact / accelerating Green house / Ozone depletion...etc.

So in clear cut terms answers are:-
1 - Insufficent data for a clear answer.
2 - practically 0
3 - practically 0

regards

Pls do rate the answer.
Jayen