Dev.SN

Life On Earth Might Not Be So Special After All

posted by janrinok on Sunday March 02 2014, @09:30PM   
from the its-life-Jim-but-not-as-we-know-it dept.

AnonTechie writes:

"What If We Have Completely Misunderstood Our Place in the Universe ? A Harvard astronomer has a provocative hunch about what happened after the Big Bang. Our universe is about 13 billion years old, and for roughly 3.5 billion of those years, life has been wriggling all over our planet. But what was going on in the universe before that time ? It's possible that there was a period shortly after the Big Bang when the entire universe was teeming with life. Harvard astronomer Avi Loeb calls this period the 'habitable epoch,' and he believes that its existence changes how humans should understand our place in the cosmos. The full article is here"

• Lack of gradient makes Life unlikely... Lack of gradient makes Life unlikely... (Score: 5, Interesting) by Anonymous Coward on Sunday March 02 2014, @11:12PM

  by Anonymous Coward on Sunday March 02 2014, @11:12PM (#9884)

  My problem with this concept is that it discusses the 'habitable zone' in terms of temperature, but doesn't mention temperature gradient. TFA says:

  10 to 20 million years after the Big Bang, the universe was still bathed in that warm gas we saw in the CMB, but it had cooled down to a temperature that would keep water liquid no matter where it was relative to its star. The ambient temperature of the universe would provide enough heat to turn an ice giant like Neptune into a water giant. That's why Loeb has dubbed this era the "habitable epoch."

  So the idea is that the entire universe is, say, at ~5C. So there will be a wide band around a given star where the temperature will be suitable for liquid water. So far so good. However, one of the reasons that life exists on Earth is not just the average temperature, but also the temperature gradient. Life is sometimes called 'counter entropic': life represents the formation of order, which seems to contradict thermodynamics, which says entropy must increase. Of course, what's really going on is that the Earth is not a closed system: the sun is pumping energy into the Earth. So even though the entropy of the Earth is decreasing, the entropy of the solar system is still massively increasing as the Sun radiates.
  
  Another way to think about this is that life is exploiting the local gradient in temperature/energy to actually exist. All of the energy-harvesting organisms on Earth (algae, plants, etc.) are in some way capitalizing on the energy gradient established by the Sun.
  
  In the limit of having a zero temperature gradient, a system is at equilibrium. You can't extract energy from a system at equilibrium (that would violate thermodynamics, allow for perpetual motion machines, etc.). In this 'habitable epoch' concept, since the background temperature of the universe is so high, the local temperature gradient on any world with liquid water is going to be very small. In other words, such worlds will seem to be in a nearly equilibrium state, which is not favorable for the emergence of complexity.
  
  In principle, such worlds could have various local temperature gradients (radioactive cooling of the core, day/night cycle of heating, etc.). And perhaps overall this ends up being more favorable for life (because you have so much liquid water, so your probability of life emerging is greater). But I'm still skeptical; I would love to see a more detailed analysis that addresses this issue.

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• Re:Lack of gradient makes Life unlikely... Re:Lack of gradient makes Life unlikely... (Score: 1, Insightful) by Anonymous Coward on Sunday March 02 2014, @11:24PM

  by Anonymous Coward on Sunday March 02 2014, @11:24PM (#9887)

  since the background temperature of the universe is so high, the local temperature gradient on any world with liquid water is going to be very small.

  That is only true if the world is floating around in the uniform, high background temperature, but you're never anywhere close to an equilibrium state as you mentioned two paragraphs above. You have a nice, hot star pumping energy into the system.

  Parent

  • Re:Lack of gradient makes Life unlikely... (Score: 2, Insightful) by Anonymous Coward on Monday March 03 2014, @12:09AM

    by Anonymous Coward on Monday March 03 2014, @12:09AM (#9898)

    Yes, but with a high background temperature the available gradients will be smaller ("close to equilibrium"...). That's not favorable for the formation of life...

    Parent