InformedIgnorance
Do you 'know' or believe?
The form of life we are most familiar with is the carbon based organic chemistry - this is by no means the only possible basis of life, but any other basis would require a capacity similar to carbon's suitability for the creation of complex chemical structures. The elements necessary for organic chemistry carbon, hydrogen, oxygen, nitrogen etc are the most abundant in the universe (sans helium, which is quite irrelevant for most discussions of chemical reactions by virtue of being inert). So, of the single basis of life that we are aware of, we know the fundamental components required for its construction are ubiquitous (functionally for the purposes of this discussion).
However, the construction of entities that could be called 'life' (not entirely easy to define btw) requires more than simply the presence of these elements; it also requires the presence of a suitable set of conditions so as to facilitate chemical reactions of the nature required for the construction and replication of these complex chemical structures. How many planets might have conditions suitable for the creation of 'life', much of the work on this has been on attempting to locate planets within a certain distance of a star so as to have liquid water (as needed for organic chemistry). Exactly how common are these conditions is unclear, it is however perhaps more common than we once believed: http://www.religiousforums.com/foru.../156092-earth-uniquely-situated-life-not.html However this is using the perspective that we have formed as a result of the nature of life on earth - there are potentially other forms, sulfur or boron based life for example; given the prevalence of the elements used in organic chemistry, it does however seem to be the more suitable avenue with which to direct our attentions in the search for environments suitable for life.
As for the search for evidence of life (as opposed to the conditions that could give rise to life), I believe that this is a far more problematic endevour as a result of the vast distances (and thus time delays) between stars. Let us assume for a moment that there is another star on the other side of the center of the milky way the same distance from the center as we are (that would make it about 52,000–56,000 ly away from us since we are relatively close to mid way from the center); let assume that right this very instant they developed radio technologies and were thus able to create electromagnetic disturbances that when it reached earth we might possibly be able to detect - we will have to wait 52 to 56 thousand years to detect this (and that is if we were listening for signals from the right direction of the universe).
Given our current technological competencies, searching for suitable conditions for life is a far more fruitful endevour (though were the other to pay off the return would be immensely greater), this may change in the future as our capacity to detect and analyse signals from a wider range of origins, through a wider range of mechanisms and able to achieve reliable results utilising smaller periods of observation perhaps this will change. We have little evidence to suggest there is life outside of earth; but far less to suggest there can not be. Indeed everything seems to suggest it is likely there is but that we merely have not (and perhaps will not) detected them.
However, the construction of entities that could be called 'life' (not entirely easy to define btw) requires more than simply the presence of these elements; it also requires the presence of a suitable set of conditions so as to facilitate chemical reactions of the nature required for the construction and replication of these complex chemical structures. How many planets might have conditions suitable for the creation of 'life', much of the work on this has been on attempting to locate planets within a certain distance of a star so as to have liquid water (as needed for organic chemistry). Exactly how common are these conditions is unclear, it is however perhaps more common than we once believed: http://www.religiousforums.com/foru.../156092-earth-uniquely-situated-life-not.html However this is using the perspective that we have formed as a result of the nature of life on earth - there are potentially other forms, sulfur or boron based life for example; given the prevalence of the elements used in organic chemistry, it does however seem to be the more suitable avenue with which to direct our attentions in the search for environments suitable for life.
As for the search for evidence of life (as opposed to the conditions that could give rise to life), I believe that this is a far more problematic endevour as a result of the vast distances (and thus time delays) between stars. Let us assume for a moment that there is another star on the other side of the center of the milky way the same distance from the center as we are (that would make it about 52,000–56,000 ly away from us since we are relatively close to mid way from the center); let assume that right this very instant they developed radio technologies and were thus able to create electromagnetic disturbances that when it reached earth we might possibly be able to detect - we will have to wait 52 to 56 thousand years to detect this (and that is if we were listening for signals from the right direction of the universe).
Given our current technological competencies, searching for suitable conditions for life is a far more fruitful endevour (though were the other to pay off the return would be immensely greater), this may change in the future as our capacity to detect and analyse signals from a wider range of origins, through a wider range of mechanisms and able to achieve reliable results utilising smaller periods of observation perhaps this will change. We have little evidence to suggest there is life outside of earth; but far less to suggest there can not be. Indeed everything seems to suggest it is likely there is but that we merely have not (and perhaps will not) detected them.
