2006-11-20 07:21:56 · 6 answers · asked by connie 1 in Science & Mathematics ➔ Astronomy & Space
Its depends on what you mean by the earth. If you are talking about just our planet then yes we are the only one, but if your talking about a planet that is similar to earth that can harbour intelligent life (and i use that term loosely) then personally i believe that the earth is unique and that we are the only ones.
However in 1961 a man by the name of Frank Drake came up- with an equation to calculate and determine how many intelligent, communicating civilizations there are in the galaxy.
The Drake Equation is:
N = N* fp ne fl fi fc fL
The equation can really be looked at as a number of questions:
N* represents the number of stars in the Milky Way Galaxy
Question: How many stars are in the Milky Way Galaxy?
Answer: Current estimates are 100 billion.
fp is the fraction of stars that have planets around them
Question: What percentage of stars have planetary systems?
Answer: Current estimates range from 20% to 50%.
ne is the number of planets per star that are capable of sustaining life
Question: For each star that does have a planetary system, how many planets are capable of sustaining life?
Answer: Current estimates range from 1 to 5.
fl is the fraction of planets in ne where life evolves
Question: On what percentage of the planets that are capable of sustaining life does life actually evolve?
Answer: Current estimates range from 100% (where life can evolve it will) down to close to 0%.
fi is the fraction of fl where intelligent life evolves
Question: On the planets where life does evolve, what percentage evolves intelligent life?
Answer: Estimates range from 100% (intelligence is such a survival advantage that it will certainly evolve) down to near 0%.
fc is the fraction of fi that communicate
Question: What percentage of intelligent races have the means and the desire to communicate?
Answer: 10% to 20%
fL is fraction of the planet's life during which the communicating civilizations live
Question: For each civilization that does communicate, for what fraction of the planet's life does the civilization survive?
Answer: This is the toughest of the questions. If we take Earth as an example, the expected lifetime of our Sun and the Earth is roughly 10 billion years. So far we've been communicating with radio waves for less than 100 years. How long will our civilization survive? Will we destroy ourselves in a few years like some predict or will we overcome our problems and survive for millennia?
When all of these variables are multiplied together we can dtermine how many communicating cilvilisations are out there.
N, the number of communicating civilisations in the galaxy.
N* = the number of stars in the Milky Way galaxy:
fp = fraction of stars with planets around them: .
fl = fraction of those planets where life actually evolves: .
fi = the fraction of fl that evolves intelligent life: .
fc = the fraction of fi that communicates: .
fL = the fraction of the planet's life during which the communicating civilisations survives:
I personally dont believe in the drake equation, but its interesting to ponder about.
2006-11-20 08:34:31 · answer #1 · answered by Pete 2 · 0⤊ 0⤋
There are so many planets very similar to Earth it would be hard to count, but there is only 1 planet Earth
2006-11-20 07:35:06 · answer #2 · answered by SteveA8 6 · 0⤊ 0⤋
the earth should have a moon, magnetic field, Air with Oxygen and nitrigen, and a sun with this energy, that we can live in it
there is no planet like the earth in the universe that we have seen
but Mars may be alittle like earth in the future
2006-11-20 07:53:33 · answer #3 · answered by yuri Romanov 2 · 0⤊ 0⤋
There is only one Earth
Earth is the third planet in the solar system in terms of distance from the Sun, and the fifth largest. It is also the largest of its planetary system's terrestrial planets, making it the largest solid body in the solar system, and it is the only place in the universe known to humans to support life.
2006-11-20 07:24:42 · answer #4 · answered by DanE 7 · 0⤊ 0⤋
there is only one Earth, thank God, the Universe couldn't stand being infected with too many humans.
2006-11-20 07:47:54 · answer #5 · answered by Anonymous · 0⤊ 0⤋
Atleat 2 according to the theory of Relativity : One exists above space-time fabric and the other underneath it.
There could be so many of them, its very uncertain.
2006-11-21 04:06:39 · answer #6 · answered by Anonymous · 0⤊ 0⤋