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Definite Path of the Universe

  1. Dec 14, 2011 #1
    Assuming we could understand all the laws of physics and understand all forces that exist in our universe, does the universe have a definite path? Could we theoretically calculate the result of all the properties of the universe to determine exactly how everything in the universe would behave? The first variable that would arise that can't be explained by any physics would be life. The universe and all matter and energy had a definite and determinable path until life became. Actions taken by life are completely unpredictable by any physics. The universe and all matter had a definite path until life came about. Is this true? What other unexplainable variables in the behavior of matter and energy could possibly exist?
  2. jcsd
  3. Dec 15, 2011 #2
    You are not the first person to have brought up such an idea: the French mathematician Laplace imagined an intellectual being with the knowledge of "all forces that set nature in motion, and all positions of all items of which nature is composed" and with the processing power to analyse these data. This being, often referred to today as "Laplace's Demon", would then, according to Laplace, be able to know both the past and future of the universe.

    There are various reasons today as to why Laplace's Demon cannot exist, for instance from a computing viewpoint (computational power) or a thermodynamical viewpoint (entropy, irreversibility). The strongest objection to Laplace's Demon, of course, comes from quantum mechanics. Laplace's arguments are based on a deterministic universe, but from quantum theory, we now know that the universe is intrinsically non-deterministic: chance plays a role in its development. Furthermore, due to the fundamental uncertainty between position and momentum (Heisenberg's Uncertainty Principle), we cannot determine both the position and momentum of a particle precisely at the same time.

    (of course, there are still "hidden-variable" theories lurking around that attempt to postulate a deterministic universe, but these are unorthodox and controversial)
  4. Dec 15, 2011 #3
    I have been wondering about how exactly "but from quantum theory, we now know that the universe is intrinsically non-deterministic: chance plays a role in its development." is true.

    I don't very well understand QM but what I get from it is that we cannot determine with absoluteness the path the universe is taking. Does this mean it doesn't take a definite path? I wouldn't say so. All we can do is compare the results we get, with the ones we think we should get, when they are different I would simply say that means we were wrong, not that the universe is working on chance.

    And why is life any different than any other complicated process? I believe all phenomena have natural causes, by natural causes I mean that every phenomena is caused only by the physics surrounding the event. Your brain is composed of matter, the state of that matter determines the signals going through your nerves and thus what you do as a "living" being. The state of the matter is determined by the state it is in and the signals coming in from nerves. What in this combination of matter and energy makes it any different than any other combinations of matter and energy?

    As for the uncertainty principle, does it also state that since we cannot accurately know both momentum and position an object doesn't have a definite(relative) momentum and position at any given time.
  5. Dec 15, 2011 #4


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    No, if I understand it correctly, the inability to determine position and momentum simultaneously at the quantum level is NOT due to any inability on our part to make the measurement, but rather on the inherent characteristics of quantum particles. The universe IS working on chance at the quantum level.
  6. Dec 15, 2011 #5
    Hmm...I know how much everyone love wikipedia as a source but oh well:

    In his Nobel Laureate speech, Max Born said:
    “ ...To measure space coordinates and instants of time, rigid measuring rods and clocks are required. On the other hand, to measure momenta and energies, devices are necessary with movable parts to absorb the impact of the test object and to indicate the size of its momentum. Paying regard to the fact that quantum mechanics is competent for dealing with the interaction of object and apparatus, it is seen that no arrangement is possible that will fulfill both requirements simultaneously...[1] ”

    Directly stating that it is due to the fact that our devices must interact to measure, and that this interaction changes the results. And I agree with that, however, if we never measured it, I believe it would have continued it's definite path, we would just know nothing about it.

    It does go on to say: The uncertainty principle states a fundamental property of quantum systems, and is not a statement about the observational success of current technology.[2]

    However, I take that to mean that no matter how much better technology becomes it will still be the case. If this is a poor viewpoint from that sentence let me know
  7. Dec 15, 2011 #6

    Of course, all this comes from our current understanding of how everything works. Who is to say that another Max Planck won't come by and turn things around all over again? :)
  8. Dec 15, 2011 #7


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    Ah ... now I see where we differ in our understanding of QM. My understanding is that there IS NO SUCH THING as a definite path. I believe that QM states that position is a statistical wave function and you believe that it is deterministic.
  9. Dec 15, 2011 #8
    It is more likely that we differ in that you have an understanding of QM....

    So you say: I believe that QM states that position is a statistical wave function

    What does that mean exactly, and how does that relate to it's actual position versus or knowledge of it's position?
  10. Dec 15, 2011 #9
    What does that mean for the large scale like a baseball flying through the air, it does take a predictable path, so even if on the quantum level the particles of the ball are taking "random, chance determined" paths their overall path is still determinable, which implies to me that the quantum-level movements, while appearing random, must have had some sense of direction to give rise, overall, to the predictable path.
  11. Dec 15, 2011 #10


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    I'm no guru on QM and I do agree w/ you that macro objects don't SEEM to have any QM properties, but from what I read, that's not exactly true.

    As for the statistical wave function, that means that the position of a QM particle is NOT in any particular place unless it is measured, and if it is measured then the degree of precision with which the position is measured implies a corresponding IMprecision in the ability to measure the momentum.

    On of the most bizarre ways I've seen of describing this is in talking about an electron that goes through a slit and then hits a phosphor screen. You can see where it hit the screen BUT at an arbitrarily small amount of time prior to its hitting the screen you have NO IDEA where it was. It was NOT (necessarily) right next to the place where it ended up hitting the screen.

    EDIT: getting back to the macro objects, QM folks say that the probability that you will suddenly dematerialize where you are and re-materialize elsewhere is infinitesimal. The key here is that "infinitesimal" is NOT zero.
    Last edited: Dec 15, 2011
  12. Dec 15, 2011 #11
    It has not been proven that appearance of life and its behaviour are not fully described by the laws of physics. This has not even been proven for old-fashioned Newtonian physics and electromagnetism.

    It is unknown until someone determines if it is possible or not.
  13. Dec 15, 2011 #12


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    I think that the very first clause in this thread is where it starts to go off the rails. We can't assume anything like that for a real Universe - only for the axiomatic model that you propose.
  14. Dec 15, 2011 #13
    life can be completely explained by concepts from classical mechanics, organic chemistry, statistical thermodynamics and solid state physics.
  15. Dec 16, 2011 #14
    How can any of those things explain the emergence of life, or the fact that you and I are both conscious and self-aware?
  16. Dec 16, 2011 #15


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    Perhaps he doesn't have high expectations of validity.
  17. Dec 16, 2011 #16


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    I can explain life using a thermodynamics equation if I want to, yet it explains very little. And it by no means can be explained COMPLETELY by what you have mentioned. All one has to do is to simply ask a few more questions and dig a little deeper and more unknowns appear.
  18. Dec 16, 2011 #17


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    Here we have the perennial problem.
    Some people actually believe that there is 'an answer' to everything and some do not; I do not. The two views are totally incompatible so threads like this one will never end up anywhere useful.
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