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Thread: Does momentum have a force carrier?

  1. #1 Does momentum have a force carrier? 
    Forum Professor Daecon's Avatar
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    If you were somehow able to study an object frozen in time, would there be any possible way of determining it's momentum? Or would that violate Heisenberg's Uncertainty Principle?

    Is speed and momentum the same thing in this case?


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    Moderator Moderator Markus Hanke's Avatar
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    If you were somehow able to study an object frozen in time, would there be any possible way of determining it's momentum?
    This is unphysical - you cannot separate time from space. All you can do is study events in space-time. As such, all objects are actually static world lines through space-time, and you can, at each event along that world lines, define an energy-momentum 4-vector associated with that object :

    Four-momentum - Wikipedia, the free encyclopedia

    Is speed and momentum the same thing in this case?
    Speed and momentum is not the same thing.


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    Theatre Whore babe's Avatar
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    How could you define momentum on an frozen item.

    (NON science person here)

    Wouldn't you have ot have SOME type of movement to have a basis for momentum?
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    Administrator KALSTER's Avatar
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    Frozen in time would mean there is no relative movement between anything in the universe (there is no absolute frame of reference), i.e. you'll only be working with the 3 spatial dimensions. By definition you need a time component (measure of relative motion) to work out something that is time dependant. So to me it is a meaningless question.

    Edit: On the other hand, if you knew the rest mass of the object and could measure the relativistic mass, I think you should then be able to deduce it's relative motion...
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    Quote Originally Posted by KALSTER View Post

    Edit: On the other hand, if you knew the rest mass of the object and could measure the relativistic mass, I think you should then be able to deduce it's relative motion...
    Not if the motion is inertial. Because it would contradict the relativity postulate.
    If the motion is accelerated, this is different.
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    Quote Originally Posted by KALSTER View Post
    Frozen in time would mean there is no relative movement between anything in the universe (there is no absolute frame of reference), i.e. you'll only be working with the 3 spatial dimensions. By definition you need a time component (measure of relative motion) to work out something that is time dependant. So to me it is a meaningless question.

    Edit: On the other hand, if you knew the rest mass of the object and could measure the relativistic mass, I think you should then be able to deduce it's relative motion...
    well I think I got about 75% of that *laughing* up to the 3 spatial dimensions........relative motion, I think I understand....

    thanks for explaining to the non science lady
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    Quote Originally Posted by Daecon View Post
    If you were somehow able to study an object frozen in time, would there be any possible way of determining it's momentum? Or would that violate Heisenberg's Uncertainty Principle?

    Is speed and momentum the same thing in this case?
    No, there wouldn't be any way. The simplest case of momentum, involving a mass, means one of two things. It can have a large momentum with having a large mass or it can have a large momentum by having a large velocity, but a frozen picture doesn't help me determine the momentum of a classical system. I'd need to know it's velocity for an accurate determination of the momentum.
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    Forum Professor Daecon's Avatar
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    So would this have any bearing on the theory that time is discrete and not continuous?

    How are momentum and inertia carried over from one Planck time-unit to the next, if time is not continuous?
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    Quote Originally Posted by Daecon View Post
    So would this have any bearing on the theory that time is discrete and not continuous?

    How are momentum and inertia carried over from one Planck time-unit to the next, if time is not continuous?
    All of reality is made of snapshots and if you want to think about time in any kind of way, best not to even think about it. Some very serious scientists right now are exploring solutions to GR which dictate that we live in a timeless universe. Momentum is a property of mass in motion (can be massless radiation) but the simplest is a property of a mass in motion. Inertia appears to be the same property which makes mass.

    So if there is no time, how is anything carried from one place to another? Simply, there is no time - only change. Julian Barbour has been very successful recently in modelling systems through changes rather than a time derivative. Things can either stay constant, dissipate or change form in the universe. The changes in everything in the universe encapsulates that rule. But we don't have evidence for time other than being a handy piece of instrument we can use to calculate things. Time isn't even an observable.
    Last edited by Geometrogenesis; August 26th, 2013 at 11:47 AM.
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    Forum Professor Daecon's Avatar
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    Doesn't that then become an issue of semantics?

    If "time" is merely an idea we use to measure the rate of change in the Universe, how is there any real distinction if we replace the term "Planck time" with the term "smallest possible unit of change at the quantum scale" when they refer to the same thing?

    A rose by any other name, and all that...
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    Quote Originally Posted by Daecon View Post
    Doesn't that then become an issue of semantics?

    If "time" is merely an idea we use to measure the rate of change in the Universe, how is there any real distinction if we replace the term "Planck time" with the term "smallest possible unit of change at the quantum scale" when they refer to the same thing?

    A rose by any other name, and all that...
    Yes... true.
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