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Thread: are there equal amounts of positive and negative charges in the universe?

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    are there equal amounts of positive and negative charges in the universe?

    see title.

    thx.
    "It's only a model....?" :-)
    https://www.youtube.com/watch?v=m3dZl3yfGpc

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    Depends on the net charge of the Universe. I think this is generally assumed to be zero, but people have thought about alternatives.
    The paper discusses the possibility of a universe that is not electrically neutral but has a net positive charge. It is claimed that such a universe contains a homogeneous distribution of protons that are not bound to galaxies and fill up the intergalactic space. This proton 'gas' charges macroscopic objects like stars and planets, but it does not generate electrostatic or magnetic fields that affect the motion of these bodies significantly. However, the proton gas may contribute significantly to the total dark matter of the universe and its electrostatic potential may contribute to the dark energy and to the expansion of the universe.
    Grant Hutchison

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    Another idea (https://www.space.com/40768-does-dar...ic-charge.html) is that dark matter is not baryonic, but does have a tiny charge. The problem with calling it protons and electrons (with a slight proton excess) is that the whole reason dark matter is regarded as non-baryonic is that we can't understand early nucleosynthesis if there are an order of magnitude more protons than we thought, as would be needed to get the early gravity right (not to mention how electrostatic repulsion would make that problem even worse, not better). Also, using electrostatic repulsion to replace dark energy would not seem to work at all-- we need an effective repulsion that increases with expansion, not decreases with it.

    The alternative idea of having dark matter be non-baryonic, but have a tiny net charge, isn't used to replace dark energy, it is used to try to explain the early behavior of the temperature of the universe by playing with dark matter's ability to cool. But count me a skeptic-- fixing the temperature problem by letting dark matter participate in cooling takes away the reason that stars form out of baryonic matter but not out of dark matter, it just seems like they are fixing one problem with one kludge, creating other problems in the process. I'm sure they've thought about this a lot more, but it seems a little desperate to me-- unless it also fixes other problems.

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    Are there any theories (barring the usual 'anthropic 'arguments') why positive/negative charges should be equal or not... or is this just reflecting a 'symmetry'/ beauty argument?
    Is the idea something like the early universe being like particle/anti-particle creation from high energy photons... so you'd get net equal charges?

    I guess I'm also wondering if 'symmetry' in equations (forgive me if I use that word incorrectly) is something one COULD argue from a scientific point of view.. e.g. other theories that relied on symmetry have proven useful in the past(although the problem of induction rears it's head)... e.g. postulated other particles which were later discovered etc.
    Or is the idea of symmetry/ mathematical simplicity a totally non-scientific view? Truth is Beauty but is Beauty Truth?
    We seem to accept some asymmetries.. e.g ratio of matter/anti-matter but not others?
    "It's only a model....?" :-)
    https://www.youtube.com/watch?v=m3dZl3yfGpc

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    The gauge invariance of QED implies charge conservation, via Noether's theorem (a particularly beautiful piece of theory that shows that for each symmetry there is a conserved quantity) - see https://en.wikipedia.org/wiki/Charge...uge_invariance. This gauge invariance is well tested as it would have a number of easy to spot effects if it were not valid. So by the processes we know of charge is conserved. The waters muddy slightly when you look at electroweak unification in the early universe. Because the EM side of things is handled by a duplication of the original U(1) symmetry I'm not sure if we know enough to say how well conserved what ended up as charge was during this symmetry breaking.

    So if there is an imbalance in charge in the wider universe it could be that:
    - New physics we have not observed and have no theories for
    - There was an existing imbalance that led to a charge asymmetry
    - Something in the electroweak symmetry breaking led to an asymmetry

    There are bound to be other options that didn't immediately leap to mind. But hopefully that kind of shows why assuming that the charge balance is zero is more than just an argument from simplicity.

    Your second question - I've kind of touched on it in the above. Symmetries are absolutely integral to modern physics. They are core to conservation laws, they are key to electroweak theory and QFT in general. In fact I believe Weyl (who is one of the great physicists often overlooked by pop culture) said something like "As far as I can see, all a priori statements in physics have their origin in symmetry"

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    Quote Originally Posted by Shaula View Post
    ....So by the processes we know of charge is conserved....
    But there remains The Mystery of the Missing Antimatter [2007] -- Helen Quinn & Yossi Nir.
    Everyone is entitled to his own opinion, but not his own facts.

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    Quote Originally Posted by Cougar View Post
    But there remains The Mystery of the Missing Antimatter [2007] -- Helen Quinn & Yossi Nir.
    Indeed but as the kaon decay work shows you can have matter-antimatter asymmetry and charge conservation through both direct and indirect CP violation in the weak sector. This not enough, with the current magnitude of CP violation observed, to fix that problem but it is possible to conserve charge and end up with a matter-antimatter imbalance.

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    Quote Originally Posted by Shaula View Post
    In fact I believe Weyl (who is one of the great physicists often overlooked by pop culture) said something like "As far as I can see, all a priori statements in physics have their origin in symmetry"
    One wonders what he means by an "a priori" statement in physics-- I would have said that all a priori statements in physics are not physics! Or put differently-- symmetries were made to be broken. But we can certainly agree that symmetries are crucial, and the fact that they are so close to unbroken has got to be trying to tell us something.

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    I think that's what Weyl was saying - that physics initiates itself from the idea of symmetries. If we burrow back far enough asking "but why" questions, we run into the basic assumption that there are fundamental symmetries, and that they mean something.

    Grant Hutchison

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    Quote Originally Posted by grant hutchison View Post
    I think that's what Weyl was saying - that physics initiates itself from the idea of symmetries. If we burrow back far enough asking "but why" questions, we run into the basic assumption that there are fundamental symmetries, and that they mean something.
    I guess it depends on what "a priori" is intended to mean, it is commonly intended for "knowledge which proceeds from theoretical deduction rather than from observation or experience." That sounds quite unphysical. But I can certainly agree that when a chain of "but why" questions reaches a point that looks like "because there's a symmetry there", there won't be much point in the continuation "but why is there that symmetry." Noticing symmetries is our hint that any of this will be possible, that our limited brains will have the slightest hope of understanding. It might even be argued that symmetries are the way we cull our perceptions in our process of making sense of them (and to what extent the symmetry is "really there" at all depends on how we adjudge the error we incur.) So I take your point that one may regard the issue as resolved to the best it's going to be when one identifies the symmetry that anchors any given phenomenon.

    My issue was with the concept of an "a priori" statement in physics, as if we could ever tell ahead of time that the symmetry would be present. A classic example is how we think of symmetries in space and time on the global scale of the universe. Almost all mythological stories of the universe exhibit neither a symmetry in space or time-- where we live is fundamentally different from everywhere else, and it has only been around for a fairly short time, in almost all mythologies. Early attempts at cosmology by physicists, once there was a such an animal, generally involved adopting a symmetry over both time and space (as Newton and Einstein both tried to do), or only over time (like the more Aristotelian approach of putting the stars in a kind of finite shell with who knows what beyond) because they had no way to account for a beginning to time. But these are not "a prior" symmetries, it was only the observations that led us to our modern approach of abandoning time symmetry in favor of spatial translational symmetry. So we'd need a deeper analysis of what Weyl meant-- I agree that a good physical understanding should fundamentally be rooted in symmetry, but I don't see anything "a priori" about where those roots find fertile soil.

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    I think we certainly have found our way to the symmetries of physics by a posteriori reasoning, but have now adopted the concept of symmetry as an a priori foundation for reasoning about physics (both because we guess that the Universe "likes to do" symmetries, for some reason, and, as you say, because symmetries are useful mental tools).
    An analogy stolen from my old philosophy class would be that we observe good outcomes from people being in a state of happiness, which may then lead us to adopt the stance that maximizing human happiness is a good thing in itself.

    Grant Hutchison

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    In the context of present best models the net charge of the universe must be zero.

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    Quote Originally Posted by grant hutchison View Post
    I think we certainly have found our way to the symmetries of physics by a posteriori reasoning, but have now adopted the concept of symmetry as an a priori foundation for reasoning about physics (both because we guess that the Universe "likes to do" symmetries, for some reason, and, as you say, because symmetries are useful mental tools).
    An analogy stolen from my old philosophy class would be that we observe good outcomes from people being in a state of happiness, which may then lead us to adopt the stance that maximizing human happiness is a good thing in itself.
    There's a certain irony in backtracking an a posteriori discovery until you can call it an a priori foundation, given that a priori means "before experience". That's a bit like stepping into a time machine, going back into your own history, and reverse engineering the workings of the time machine so you can build it in the first place (a la Terminator)! But perhaps the crucial issue in all this is not what we want to call an a priori foundation, but just a foundation period. I agree that widespread symmetry is a nice foundation for physics, and widespread happiness is a nice foundation for philosophy, and that's probably all he meant.

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    so... for the layman...

    is the conclusion that the universe likes symmetries, or just that we are good at looking for them because they make scientific theories simpler? / make scientists happy? / make the math more elegant?
    "It's only a model....?" :-)
    https://www.youtube.com/watch?v=m3dZl3yfGpc

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    Quote Originally Posted by plant View Post
    is the conclusion that the universe likes symmetries, or just that we are good at looking for them because they make scientific theories simpler? / make scientists happy? / make the math more elegant?
    That's the $64,000 question. About all I could add is that the purpose of asking a question like that is not so much that it has an answer that we are trying to find, but rather, the process of trying to answer it gives a kind of tour of our understanding of our universe. To avail ourselves of that full tour, we should instead ask, "what insights can we gain by imagining that the universe favors symmetries, and what insights can we gain by studying the ways we hold up simplified templates to what we perceive?" We should not be surprised to encounter various different insights on both sides of that question. If the universe loves symmetries to pieces, why don't they go unbroken, whereas if all symmetries come from our tendency to focus attention on the situations where symmetries are exhibited (the proverbial "spherical cows" if you will), why does it work so well? One possible answer is anthropic-- a universe of complete symmetry lacks the richness required for intelligent life, and a universe completely devoid of symmetry finds no use for intelligence so does not develop it. But then there's the question of whether anthropic thinking is really any kind of "answer" at all.

    Keeping this connected to event horizons and coordinate systems, we can say that all coordinate systems that get used are inspired by some kind of symmetry. In physics, we tend to restrict coordinate systems to ones in which the quantities locally correspond to measurements with rulers and clocks, but the creation of a global coordinate system requires cobbling these local measurements together, essentially by imagining a hypothetical continuous series of observers who would get those outcomes on their own hypothetical rulers and clocks. The symmetry is then in the relation between those observers, and the simplicity of the coordinates (and their convenient usage) stems from putting in a high level of symmetry into that connection between hypothetical observers. In this example, it is very clear that the symmetry is indeed a template that we are holding up-- there is little that is "in the universe itself" about Cartesian or polar coordinate systems. But nevertheless, we do find that the laws of physics exhibit symmetries that are coordinate-free, so not all the symmetry we encounter when solving for the motion of a cannonball is coming from the coordinate templates that we employ. It behooves us to notice the coordinate symmetries, and the coordinate-independent symmetries, encountered when doing a cannonball problem, because they are both telling us about our process of understanding, how we do it, and why it's possible at all.
    Last edited by Ken G; 2020-Jan-03 at 03:05 PM.

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    Quote Originally Posted by grant hutchison View Post
    as you say, because symmetries are useful mental tools).
    A fundamental goal of a physical lheory is to be general. So it ends up saying that for a collection of different situations that are identical in a certain aspects, the same outcomes happen with respect to some other aspects. The assumption that different situations are interchangeable (i.e. invariant, in some sense, under certain transformations) seems essential for physics and for science in general.

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    Quote Originally Posted by tashirosgt View Post
    The assumption that different situations are interchangeable (i.e. invariant, in some sense, under certain transformations) seems essential for physics and for science in general.
    That's true, but we probably should not call that an "assumption." Instead, it is something that we have found to work well with much experience, but we have also had to take pains to distinguish situations where it does not work well. By that I mean, we have had to do a lot of work in figuring out what "similarities" we can expect to exhibit symmetries (such as interchangeability), and what ones don't. For example, we don't assume that all electrons are indistinguishable, we find that if they were distinguishable, we could not understand why white dwarf stars lose heat so slowly, or why atoms have the electronic levels they do. Nevertheless, in many situations we still choose language that makes electrons sound like they are distinguishable, so we actually find it easier to imagine that extreme symmetry is spectacularly broken!

    Also, the indistinguishability we sometimes need is not so simple that you can just interchange them and nothing happens-- remarkably, when you imagine interchanging them, you have to also equip their total wavefunction with a minus sign, or again we cannot understand why white dwarfs lose heat so slowly, or why atoms have the structure they do. So looking for symmetries is a crucial part of science, and little of physics would work without finding symmetries, but it is not "assumed" that there will be various types of interchangeability-- it's all part of the hard work of figuring out what symmetries actually, in some sense, "blessed" by observations. Getting back to my objection to the concept of "a priori" symmetries, there are no "a priori" assumptions in science, it's all about what has been found to work, and when it doesn't.

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