Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

How would this universe be if there's NO UNCERTAINITY PRINCIPLE

  1. May 26, 2012 #1
    how would this world appear like if energy,time &&& momentum,distance can commuate...and anyone please describe relation between energy and time
     
  2. jcsd
  3. May 27, 2012 #2

    Ger

    User Avatar

    Universe would be completely static and invisible. The same as nothing. There is a relation between energy confined to a space (the confined energy named mass as in m= E/c2). That same energy is creating the space and the time associated with it. Start of time is with every event wich takes place in that mass system and time it takes to distribute mass/energy into that same space.
     
  4. May 27, 2012 #3
    The uncertainty principle must exist for a dynamic universe.
    If a universe doesnt obey the uncertainty principle, then there shall be no quantum fluctuations. The spacetime would be a static one
     
  5. May 27, 2012 #4

    tiny-tim

    User Avatar
    Science Advisor
    Homework Helper

    a more realistic question would be …

    how would the universe be if planck's constant were very much smaller? :smile:
     
  6. May 27, 2012 #5

    bhobba

    User Avatar
    Science Advisor
    Gold Member

    I don't think atoms as we know it would exist - the electron would spiral into the nucleus.

    Thanks
    Bill
     
  7. May 27, 2012 #6

    Ger

    User Avatar

    More realistic yes. But than it would make no difference at all. Typical QM effects would be much smaller. The maths do not change. Convinient is to substitued h=c=1 in the maths to get rid of those many constants in formulas.
     
  8. May 27, 2012 #7

    bhobba

    User Avatar
    Science Advisor
    Gold Member

    Yes - but if say objects like atoms etc remained the same size then they would behave differently - if planks constant was much smaller quantum effects would not hold for the distances between electrons and the nucleus and they would spiral inwards and decay.

    Thanks
    Bill
     
  9. May 27, 2012 #8

    Ger

    User Avatar

    All other things scale with the values proposed for h and c. Set the light speed at a 300 km/hr and special relativity will become a part of daily life
     
  10. May 27, 2012 #9

    bhobba

    User Avatar
    Science Advisor
    Gold Member

    And you don't think that would be change in how the universe behaves?

    Thanks
    Bill
     
  11. May 27, 2012 #10

    Ger

    User Avatar

    Does the setting of h=c=1 change something in the maths employed? I dont think so. Only a value of h=0 (removes the uncertainty at all) would defintly change the physics, as does it do for the maths as well.
    The behaviour of the universe is one of changes which we try to measure and can observe. That is described by excatly the same maths as before. So why should behaviour change?
     
  12. May 27, 2012 #11

    bhobba

    User Avatar
    Science Advisor
    Gold Member

    No it doesn't - but in changing the units (which is what you are suggesting) the value of the size of things like you, me and atoms is now different - you are implicitly assuming they remain the same - they don't. The value of planks constant sets the size limit where quantum effects start to occur - change that and the world will be a different place - the same with the speed of light - change its value relative to the speeds of everyday experience and the world will be entirely different.

    Thanks
    Bill
     
  13. May 27, 2012 #12

    Ken G

    User Avatar
    Gold Member

    We can set some of the constants to 1 if we choose, but we cannot set them all to 1 without changing the universe. This is because the constants can be joined into unitless numbers, like the fine structure constant "alpha", and if a number has no units, then we are not free to choose its value. So you can set h=c=1, but the fine structure constant also depends on the charge of the electron, so you would then have to take that charge to be the square root of 1/137, you have no choice. So the problem is, what do we mean by h being "small"? Small compared to what?

    Thus, there are actually several ways to answer the OP, depending on how we take its meaning. We could take the meaning:

    Interpretation #1: Keep all the physics we know the same, but make h much smaller, in the same unit system we use now. In particular, this requires that alpha be made much much larger, and so atoms become completely different, possibly even impossible as bhobba said.

    Interpretation #2: Replace our physics by some other version that does not include an uncertainty principle. This is harder to answer, because if we are going to change the physics, we can do anything we want, especially if we allow the observations to be different! We would thus have to say that the observations stay the same, so the universe is the same, but it is explained without an uncertainty principle, and this is not what the OP asked. We could nevertheless change physics back to what we thought it was prior to the discovery of the uncertainty principle, i.e., change it back to Newtonian physics, and ask how we might have proceeded without an uncertainty relation. However, Newtonian physics was not a complete description-- it had paradoxes it could not resolve, like why don't atoms spiral into themselves. So without an uncertainty principle, we'd need some other principle to prevent this, and we're off to inventing new physics of the type that many were speculating about pre-1900. I don't know if anyone came up with something that could have worked but didn't agree with observations, but we know that no one came up with something that did agree with the observations, so we'd be kind of stuck at this point!
     
  14. May 27, 2012 #13

    Vanadium 50

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    Ger has it in post #10: set h = 0 to see. And yes, that would have enormous effects, such as the Rydberg becoming infinite.
     
  15. May 27, 2012 #14
    Something tells me that this is beyond human capability to know.
     
  16. May 27, 2012 #15

    Vanadium 50

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    No, one can calculate this. Now, one also has to be a bit careful, because one needs to carefully specify what is being held constant and what is not. But given that, it is calculable.
     
  17. May 27, 2012 #16

    Ken G

    User Avatar
    Gold Member

    The problem is, you'll quickly run into the "anthropic principle." If you change h by too much (typically only a few percent can present a problem!), then we no longer find it possible to have anything that we would recognize as human intelligence. Immediately we run into the difficulty of how much of quantum mechanics depends on the kinds of questions that human intelligence is interested in answering, as opposed to some other kind of intelligence (or worse, no intelligence at all, if h is changed to a point where intelligence itself is impossible). When we encounter that problem, no self-consistent calculation is possible any longer, because it would have to use quantum mechanics, and quantum mechanics would not be applicable if the kinds of questions it answers are not questions that can be posed in that universe.
     
  18. May 27, 2012 #17
    See this paper here, from the American Journal of Physics, for an attempt to prove that the operators like position and momentum cannot possibly commute, and thus quantum mechanics is in some sense necessary. (Actually, he doesn't show that the operators don't commute, rather he tries to show the equivalent statement that such operators cannot have simultaneous eigenstates.)
     
  19. May 28, 2012 #18
    Sure, you can calculate this. But no one knows what the universe would look like.
     
  20. May 28, 2012 #19

    Vanadium 50

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    What is the difference between being able to calculate something and knowing what it looks like?
     
  21. May 28, 2012 #20

    Ken G

    User Avatar
    Gold Member

    I would still say that if you calculate something using certain postulates, and obtain a result that does not make it possible for you to exist, then your calculation has no meaning because you know the postulates do not approximate anything useful or physically meaningful. What does it serve you to do a calculation that you know results in a useless conclusion? It would be incorrect to say "in my calculation, the universe would be like X" if X does not include a person who can do that calculation-- the conclusion that the universe would be like that, based on application of that physics, is then internally inconsistent and meaningless. Instead, you could calculate the range in h for which quantum mechanics could be the correct physics of any universe, and say that outside that range, you know quantum mechanical calculations cannot mean anything. Typically, such ranges are astonishingly narrow! The same argument can be leveled as a criticism as a concept of a "multiverse" being used to "explain" why we find ourselves in such narrow ranges.
     
    Last edited: May 28, 2012
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: How would this universe be if there's NO UNCERTAINITY PRINCIPLE
  1. Uncertainity Principle (Replies: 23)

  2. Uncertainly principle (Replies: 7)

Loading...