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A question please ?

  1. Jan 17, 2009 #1
    Hi all

    I have a question please.

    Now, for every action, there is a reaction ... For matter, there is anti-matter ..

    These actions, reactions, matter, and anti-matter,, cancel each other .. so the sum of it is equal to zero ..

    ok .. so my question is:
    if we looked at the whole universe from outside which forms the sum of all actions and reactions that cancel each other, i guess we will see nothing .. because they have already cancelled each other ... right ??! or wrong ??!

    please answer yes or no with explanation..

    thank you ..

  2. jcsd
  3. Jan 17, 2009 #2


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    How do you intend to look at the universe 'from outside'?
  4. Jan 17, 2009 #3
    I know that it's impossible to look from outside, because there is no outside ..

    But i mean, isn't the sum of all actions, reactions, matter, anti-matter, and everything in the universe ,, equal to ZERO ??!
  5. Jan 17, 2009 #4


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    Ok, to avoid the whole bit about looking at the universe from the outside, just consider an isolated system of two bodies. Might as well be a universe in itself if it is truly isolated. Now, if the bodies collide, say, it is true that the force body A exerts on body B is equal and opposite in direction to the force body B exerts on body A. But would we, the outside observer, see nothing?
    Surely not.
  6. Jan 17, 2009 #5
    Maybe the perspective from the outside of the universe is similar to that of a black hole - sensing Hawking radiation. It might be possible for an observer to occupy "superspace," as John Archibald Wheeler once called extra dimensions. Nowadays, branes are the more popular structure for explaining phenomena beyond spacetime limitations. The universe has various symmetries, but as it is finite it is also in part asymmetric.
    Last edited: Jan 18, 2009
  7. Jan 18, 2009 #6
    More explicitly: For every action there is an equal and opposite reaction.

    I think the word "opposite" might be confusing you. It does not mean we subtract one force from the other and end up with 0 forces left. "Opposite" simply means the reactive force acts in a direction opposite to the active force. In the end we end up with the same amount of force: Action = (re)action. Nothing has been lost or annihilated here. When you hit a baseball with a bat, the baseball and bat both still exist, and so does the energy you gave the baseball.

    So, by that logic: Everything in the universe = everything in the universe, and NOT: everything in the universe - everything in the universe = 0
  8. Jan 18, 2009 #7


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    I'm going to modify your question a bit because I think it will make a bit more sense AND, in fact, is being studied.

    What you're asking is that why is there anything at all since there should be matter and antimatter of equal amount (that action=reaction thing is really 'trivial' because it just means that the whole universe has no net momentum, which isn't really a problem, is it?). Yet, our universe that we've seen is populated with matter. So that is a problem with the concept.

    It turns out that there is a possible reason for such imbalance. The leading candidate for this is the observed CP-violation in rare events. In these events, the CP symmetry is violated, leading to one possible explanation that matter-antimatter may not decay and behave in "mirror image" of each other all the time. Not all of their decay products are identical all the time, and thus, these will not "cancel" each other out. You can read more about it here:


    So in that sense, we may have an explanation for why our universe is made up of more matter than antimatter.

    Last edited by a moderator: Apr 24, 2017
  9. Jan 18, 2009 #8
    "For every action there is a reaction" - What this ultimately means is that the centre of mass of the universe will not accelerate. And the angular momentum of the entire universe will not change. But it will obviously still be there.

    "For all matter, there is anti-matter" - This means that if you add up all the properties of all the particles in the universe (like charge, lepton number, spin etc.) The final value for each property will be zero. (i.e. the universe will have no overall charge).

    BUT: What you are missing is that there is no such thing as "anti-energy". So the universe does have a final value for that. And so I guess the answer would unfortunately be no, the universe is still here and we still need to explain how all that energy came about.

    We could say that there is another universe that is made from anti energy I suppose. But this is just philosophy, and has no real-world implications.
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