Gravity and the narrow confines of life

Life on Earth has evolved within a very fine set of parameters.  We are going to find it a challenge to survive outside the sheltering cocoon of this planet, not the least because our atmosphere protects us from several types of radiation, not the least from our friendly sun.

Now there's another limitation.

Our body's physiological processes are to a great extent governed through the triggering of gene expression, which generates proteins that affect metabolic pathways of chemical reactions.  Translated, this means chemical signals trigger the unwrapping and copying of genes (sections of our DNA blueprint) that in turn generate proteins that... make our body work.

For that to happen, amongst other things we need... gravity.

On the one hand, one might intuit that gravity shouldn't be an essential part of our processes.  But we are generally pulled in a single direction: towards Earth, the largest mass at hand.  From an evolutionary perspective, that amount of gravity is an intrinsic part of the environment in which so many successive iterations (generations) successfully mutated and survived.  Our environment tempered the direction of successful mutation.

So it makes sense that our metabolic processes could be so finely tuned that significant change (ie, to zero gravity) could disrupt some of these processes.

And that's what's been found, as reported in New Scientist this week (4 February 2012).  Specifically: "weightless conditions... could disrupt the activity of 200 genes linked with immunity, metabolism and heat tolerance."

There is a slight caveat on that: the study used flies, and simulated weightlessness through magnetic fields.  Still, the researchers are confident of their results, it sounds plausible, and doubtless the result will be tested by others in other experimental contexts.

Still, just as science can bring the science fiction of space travel crashing to Earth, surely technological solutions will be developed.  After all, science fiction has already imagined simulated gravity.  It just hasn't filled in the details.

Life on Earth is indeed a rare contingency

New Scientist reports that cosmic radiation would be too dangerous for NASA to send people to Mars.

NASA's current rules on risk aim to keep each astronaut's lifetime risk of radiation cancer to below 3%.  That limit would be reached in under 200 days, but a round trip to Mars would take 750 days.

Read the report here.


It would be relatively easy to shield a spacecraft from the sun's radiation.  But galactic cosmic radiation, comprising "protons and heavier atomic nuclei" has higher energy than the sun's, and can cut through DNA in living cells, which damage can lead to cancer.  On Earth, we are protected from such bombardment by both atmosphere and the Earth's magnetic field.

It does seem that the particular set of circumstances that fostered evolution and maintains life on Earth is a rare contingency, requiring the right combination of atmosphere, magnetic field, distance from the sun, type of sun and type of planet - even plate techtonics contributes to the ongoing habitability of the planet.

The piling up of such factors could help explain the lack of success in the Search for Extra Terrestrial Intelligence project.  It remains inconceivable that those factors could not arise repeatedly elesewhere, but the very delicacy of balance of all these factors is a plausible explanation for why we have fould no near neighbours.

Postscript 20-Oct-09: I have come across two memes that claim to speak to this.  First, the Drake Equation, which purports to estimate the number of civilizations in our galaxy (the Milky Way) with which we could establish contact.  Seven factors are included, including the rate of star formation and  the proportion of life-potential planets that go on to develop life.  A current estimate of the solution to that equation is 2.31; however, the equation (and estimates of factors) must be seen as so conjectural that to my mind it's little more than a philosophical exercise (or something akin to economists being asked to estimate something they know very well they don't have enough information for).

There is also a claim that there are "20 factors" necessary for the emergence of life with the complexity that we know.  However, I have not found the origin for this meme, and it's debated more in circles religious (both Christian and Muslim) than logic, scientific, or mathematical - invariably to "prove" the small contingency of life.  Still, there are necessary factors, and they're worth considering - albeit some of them surely overlap in terms of contingency.  For the purposes of debate, some of those mentioned include:
 - a liquid iron planetary core (to provide a magnetic field that shields us from some cosmic radiation);
 - a moon to pull tides (and circulate oceans) - (how necessary?);
 - the sun's composition;
 - the planet's distance from the sun;
 - distance from the centre of the galaxy... etc.
A scientific enumeration (and discussion) of such a list would be interesting to read (factors in Drake's equation are rather more broad - and conjectural - than these).

Yet I'd have to point out that at least some of these factors only pertain to our version of life.  It is hard for us conceive of life emerging in radically different form (and I'm not talking SF bugs or tentacled aliens: more, different formations of cells, etc), but that doesn't mean it can't happen.

The big bang was a bounce?

A recent article in New Scientist posited the idea that the big bang was really a bounce.

It details a computer simulation, based on Loop Quantum Theory, that runs time backwards to the big bang, which demonstrates a bounce back to a previous(ly collapsing) universe. This is apparently one up on general relativity, which breaks down at the big bang.

Having only completed undergraduate physics and maths, the article will take some time for me to absorb properly. But there is a certain neatness to the concept of a universe continuously expanding and collapsing. I would imagine that in that case, there would be no state memory retained from the previous incarnation, so all prior information/knowledge (both about and within the prior universe) would be lost. There is sufficient unevenness to the expansion after a big bang that successive universes would not develop identically.

I have previously drawn a depiction of how time could work going backwards to the big bang. It's a conceptualisation, rather than based on hard physics. The above theoretical paradigm would be closer to hard physics, but still just theory at this point.

In the process of conceiving a universe running backwards to the big bang, most people might imaging a large box, with the matter filling a decreasing amount of space in the middle of the box. Fewer would imagine space as being a contracting 'box', with nothing 'outside' it, because it's hard to think of a space without automatically extending one's thoughts beyond the limits. Likewise with time. Is 'what happened before the start of time' a valid construct?

There is no certainty yet, but I think the ultimate solution would have a satisfying neatness and symmetry.