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How Can a Living Being Contribute to the Heat Death of the Universe?

written by: Dr. Crystal Cooper•edited by: Lamar Stonecypher•updated: 6/8/2009

Living organisms cause a decrease in entropy. How then does life contribute to the eventual heat death of the universe?

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    What Does This Mean?

    I Cause An Increase In Entropy? In our previous article, we saw how the fact that entropy is always increasing means that the universe will end in an inglorious heat death, along with everything living in it. How does this inexorable march, like that of lemmings approaching the Norwegian coast and hurling themselves off, indicate this?

    When entropy increases, the amount of energy available for work decreases. We say that the quality of the energy involved has been permanently degraded. Orderly mechanical energy transformed to the disorderly form of thermodynamic energy is one form of this degradation.

    An example is when a ball, moving forward with all of its particle going basically in the same direction, hits a wallBouncing ball  in a collision that is not totally elastic. Kinetic energy is released, and the ball and the wall have a slight increase of thermal activity i.e. temperature change. The ball bounces off with less kinetic energy than it originally had, along with some random motion imparted to it by the temperature increase, and with its capability of doing useful work reduced.

    Living things actually cause a decrease in entropy. This is how you can maintain your body heat, grow five fingers and toes, and are able to help create other living beings, for example. But you are not an isolated system. You interact with the universe and in doing so, you increase its entropy.

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    How Living Organisms Increase Entropy

    Drop an egg on the floor, and it will break.Will this egg reassemble?  The chances of the egg reassembling itself are so improbable as to be effectively zero. The useful energy expelled through your inadvertent inelastic collision cannot be retrieved, even if you feed it to your dog or cat or let the microbes have it. You have increased the entropy of the universe.

    Scramble an egg, and eat it for breakfast. Or better yet, feed it to a chicken, who will use it to make another egg. But only part of it will be used in new egg production. Dreaming Hen Most of it will not be used. Furthermore, you and the chicken contribute waste products to the universe, in the form of perspiration or urine. Waste products of sewage and garbage can be used to produce more energy such as for fertilizer or biogas plants, but again, this is inefficient as you will not recover all of the original useful energy put into it to make it. So while living things decrease entropy, living things plus their waste products yield a net increase of entropy.

    If you are further curious about how waste is helpful in the entropy battle, the biogas series mentioned above also has articles on the construction of the plants, how they process the material, and the chemical reactions involved - these are not for the squeamish!

    Life contributes to a net increase in the entropy of the universe, and thereby heat death. But is this still true when a living thing dies? Also, what is the shortest way to summarize the laws of thermodynamics? Both of these questions will be explored in part four.

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    • Conceptual Physics by Paul Hewitt
    • Physics for Scientists and Engineers by Douglas Giancoli
    • Physics For Scientists and Engineers by Raymond Serway
    • University Physics by Richard Wolfson

    Image Credits

    Surprise by Achim Hering

    Broken egg by Jorge Barrios

    Fried egg by David Benbennick

    Running chicken by Lily M.