Alien life ... on Earth

I have always been dubious about our form of life being the only kind there is and can be. While as the only type of life we actually know about, scientists have little choice but to base their search of extraterrestrial life on what we know of carbon-based life, it is rather premature to exclude other possibilities. So the possibility that life as we do not know it might exist right alongside us on Earth is rather intriguing.

It is almost certainly not the case that that there are multicellular life forms, or at least what would correspond to life forms, that are not based on familiar DNA, RNA, or even proteins. However, we have not microscopically examined even a significant portion of the entire Earth, and we may not even recognize totally different life forms even if they are staring us in the face, since almost all of our knowledge of microbiology is rightly focused on life as we know it. While it may be a quixotic quest, considering that any such alien life forms would likely be quickly gobbled up by more familiar life, it's a slim possibility. I would still consider a search for alien life on our own planet to be worthwhile: if discovered, it would really expand how we think about life, and it would also be evidence for life arising multiple times on Earth.

It could be interesting to hear what Paul Davies said about the topic in his lecture on February 15.

Replenishing methane on Mars

Methane in an atmosphere is something that astronomers look for as a possible sign of life. So its discovery in the atmosphere of Mars four years ago would understandably cause a bit of excitement. But there are other possibilities of what might be producing methane on Mars, so concluding the existence of life would be premature.

Nili Fossae, a methane hotspot
Nili Fossae, a methane hotspot

Things became even more interesting when it was recently discovered that methane is produced around a few hotspots around Mars, and that these pockets of methane would dissipate within just a few years without replenishment. This means that there's something around these hotspots creating a lot of methane, either biological or chemical. Surprisingly, only one hypothesis for a chemical process is being put forward, methane clathrates, which is frozen water with a high concentration of trapped methane. Even if it turns out the methane is created from such a "mundane" chemical source, it would still be exciting since methane hotspots would also be water hotspots.

The only other possibility put forward so far is that the methane is generated by microbiological life, similar to the methanogens found on our own Earth. Or the hotspots could even be small surviving colonies of methane-exhaling Martians who evolved from methanogens, in contrast to oxygen-breathing animals such as ourselves that evolved from aerobes. The latter is way too far-fetched, but it's a fun thought to contemplate ...

Is fine-tuning really fine-tuning?

A paper speculating about the probability of stars forming in alternative universes mentioned at Cosmic Variance got me thinking again about whether our universe is fine-tuned for the emergence of intelligent life. I have always found fine-tuning arguments to be a sort of argument from ignorance, in that they tend to ignore the possibility of other forms of intelligence. While they might be correct in claiming that if the physical constants were significantly different then our form of carbon-based organic life could not arise, they don't really succeed in excluding other possibilities.

Sometimes I imagine that there could be universes with intelligent life that imagine that it's their own universe that's fine-tuned, and them unable to imagine life emerging in a universe that is almost entirely empty like our own. (Greg Egan's Schild's Ladder deals with similar concepts.) Or perhaps galaxy-wide life forms that somehow emerge from the interactions of entire stars acting similarly to cells might be unable to conceive of intelligence at an incredibly microscopic and fast scale like us. Thoughts like these sometimes makes me wonder whether we could even recognize some forms sentience even when it's in plain sight.

Stephen Baxter has a good grasp on how fragile the fine-tuning argument is, and he draws a vivid picture of what alternative forms of life could have arisen throughout the development of the universe in his Xeelee Sequence of stories, from those that form from defects in space-time itself to carbon-based life forms like ourselves. And really, given only the fundamental laws of physics we know today, could anyone have predicted the rise of carbon-based intelligent life like humans? Just because we don't know how intelligence could arise from different laws of physics doesn't mean it's impossible.