How long could human race survive without the sun?

  1. Hello,
    Here is my question:

    Just imagine the sun would stop shining, without exploding. It would just totally disappear without causing harm. How long would human race survive without the benefits of the sun? 10 minutes? 10 hours? 10 days? Could it stand the cold longer? How long would it take for the atmosphere to get below zero degrees?

    And here is the answer I got from yahoo answers:
    Now I hope to find a specialist who could tell if the human race would live for more than 24 hours or not.

    Thanks :)
     
  2. jcsd
  3. malawi_glenn

    malawi_glenn 4,726
    Science Advisor
    Homework Helper

    A day on the moon last more than 24h, it lasts a month. The guys who wera at the moon in the 60's was there on the day, but in the "morning", moon surface has not reached that very high temperature yet.

    Do a first order approximation with ordinary black body radiation and that the atmosophere refelcts 30% of the outgoing radiation back to earth again. You know the the area of the earth and the mean temperature it has now.
     
  4. russ_watters

    Staff: Mentor

    We had a thread about this a little while back and I think our mentor chroot figured out via black body radiation that the earth would be uninhabitable in a matter of a few days. More than a day, less than a week.
     
  5. Thank you for your answers.

    I found the post you're talking about Russ. Sorry for making a new one, the search I had made wasn't precise enough.

    https://www.physicsforums.com/showthread.php?t=181218

    Taking the "black body radiation" formula doesn't seem right to me malawi (forgive me if I'm wrong, I have nothing to do with Physics), because from what I understood that formula would tell about the temperature of the mass, not of the surface of that mass.

    So the answer would be that the human race would live for a few days before being exterminated. That's what "the mentor" chroot says. ;) Would it be possible to have a closer approximation? If, as he said, it would be comparable to moon, does anyone know how long it takes for a point on the moon to get from, let's say 30 Celsius down to 0? And then could we take into account the atmosphere, providing some kind of protection?

    If anyone has an idea, thank you.
     
  6. I dont know, a few days sounds right...we're not thinking about the variables either. We would probably freeze to death(high probability), or perhaps the Earth would just spin away since there is no sun anymore, since the threadstarter said, "without exploding." A dead star, no gravitational pull...yikes.

    Wow, can you imagine if the Earth stopped spinning? I, myself right now would be flying into air with my computer, turntables and clashing with other people flying out of their homes lol!
     
  7. tony873004

    tony873004 1,584
    Science Advisor
    Gold Member

    I would tend to guess that parts of Earth would be habitable much longer than a few days. People survive at the research station at the south pole, even as the sun vanishes for 6 months.

    Small tropical islands tend to have air temperatures very similar to the temperature of the water that surrounds them. And water has a huge heat capacity. Ice won't form on the surface until the water has been cooled to ~32 degrees F. I imagine this would take weeks or months. Then once frozen, its free to plunge colder than 32 degrees, with air temperature quickly following.

    Additionally, deep mines are often warm from heat from Earth's interior. If you were well stocked in food and water, and you had good air circulation, you could live indefinately, or at least until the atmosphere above you froze out and your air pressure dropped to unacceptable levels.
     
  8. Introducing an atmosphere into the model would be difficult over large temperature changes, since the peak radiations would change and hence the dominant absorbers would change. But over a smallish temperature change you could use water and the Lambert-Beer law to account for reradiation. The temperature would stay warmer for longer because of the atmosphere.
    However, I think this correction would be insignificant compared to the error from the modeling of the earth. Chroot assumed the Earth was a solid ball of iron in thermal equilibrium. From what little geology I know this is a terrible approximation, since the Earth has a molten core with a temperature much greater than the Earth's surface.

    I personally think atmospheric effects would be dominant in determining the period of mass extinction. I can't say exactly what would happen though. The air pressure would drop making it harder to breathe (ideal gas law), the upper atmosphere would get colder, freezing the moisture in the air. In fact the atmosphere would probably change markedly in composition with height.

    The temperature is different at different places on the Earth, so so will the time it takes to cool down.

    I wouldn't know where to start with a calculation because the Earth is so complicated, the oceans and ground would exchange heat with the atmosphere. A blackbody model probably isn't bad.
     
  9. I prefer to answer this question the same way we would treat it had the Earth
    been destroyed by nuclear War. A nuclear winter would envelope the earth not
    allowing any sun to filter thru.

    That being the case humans in your scenario could most likely survive for quite some time as the temperature begins to drop world wide. Our biggest problem would be the effects of no sun and no production of oxygen thru photosynthesis. As the plant life begins to die our oxygen levels would begin to drop.

    We may very well seek shelter in caves for warmth but . . . Without oxygen how long could you survive anywhere?

    I would give us about 6 months. So your good to go with your 24 hours concerns. Most likely if you could survive the freezing cold temps you would suffer death of suffocation as the oxygen levels reduce to levels below our needs.
     
  10. We'd have to go outside in space suits and dig out frozen oxygen from the ground. As the atmosphere's temperature lowers, it will condense and fall down as a thick layer of snow. First water, then carbon dioxide, then nitrogen and - lucky for us - oxygen at last.

    Regarding the need for a stable heat source, remember that the Earth is a huge ball of molten iron ,nickel and various silicates. The crust we walk on relative to the size of the Earth is thinner than the skin of an apple. Below that thin crust is a source of energy almost as long-living as the sun itself!

    So, given the proper time to prepare ourselves I'd bet we could live indefinitely without sunlight.

    Cheers,
    Michael
     
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