What are the chances that life exists on other planets?
It is highly likely that there is life of some form on other planets.
This is a difficult question because the distances between stars and galaxies are so big that travelling to them is almost impossible given our current technology.
We do know that there are very large number of stars in the known universe.
We also know that life can exist in a range of conditions based on life discovered in extreme places on Earth.
Now that we have space telescopes, we have already discovered over 3,000 planets around other stars. Based on these findings planets are common and many stars will have them.
All that is required for life is that the planet is the right distance from the Sun and has the right chemicals. Some of the Moons in the outer solar system such as Europa and Titan have conditions where some form of life could exist.
Given the vast numbers of stars and planets are common, the chances of a planet having just the right conditions for life are high. This is the general opinion amongst the scientific community.
Of course when we say life it may be primitive, like bacteria. We do know that the building blocks of life exist in space. There are theories that the building blocks of life on Earth originated from comets.
Given the vast age of the universe it is entirely possible that advanced life forms have evolved. It they did evolve, they may have died out.
It is highly unlikely that there are other living things in the the universe.
Life as we know it requires complex information in a form that can be copied and passed on.
The creation of the dual coding information system that provides both the information and the code for translating and copying the information that exists on earth is most likely unique in the universe.
W.Y. Chung of the Center for Comparative Genomics at Penn State says that " existence of "dual coding" and overlapping protein coding reading frames, just one of the many cellular innovations for concentrating genomic information is " virtually impossible by chance. (Chung a First Look at the ARFome)
The odds of getting even one functional amino acid sequence by chance are
Then the dual coding must also occur where DNA, RNA or some similar information carrying molecule can replicate the protein, increasing the odds against a living thing occurring by chance.
If biological information occurred by a virtually impossible chance on earth, it is unlikely that such an impossible accident happened twice.
There's an equation describing this. But it doesn't help us much...
There is an equation that describes the number of alien civilisations in existence that we might make radio contact with. It is called the "Drake Equation", and there's info on it e.g. here: http://www.astrodigital.org/astronomy/drake_equation.html
The equation is
The exact numbers of each of these values are all highly uncertain, and so people have used the Drake equation over the years to assert that the existence of advanced alien life is anything from highly improbable to highly probable. It's fun to play with the values - you can download a spreadsheet from the link above that will let you do so.