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Do we know why + and - attract?

  1. Aug 28, 2005 #1
    Why is it that electrons, and protons attract? What is this invisible electric force field anyways? Why is it there? Electrons have energy right? Their energy determines their orbital right? Do protons, and neutrons have energy? Like the actual particles, or is the energy between the gaps of neutrons and protons?

    Oh, and can someone please briefly explain to me how magnets work? Is it the same idea as electrons, and protons attracting? Why do they get attracted to a lot of metals?

    Whats the deal with gravity? I have no clue what gravity is the more I think of it. I just think that the more mass something has the more gravity it has. Then I think about blackholes and how they have so much gravity. Do blackholes have mass or are they not even made of matter?

    ....yeah I'm an idiot. Hahahhaa oh well. I'll be back I'll never stop asking questions here.
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  3. Aug 28, 2005 #2


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    These aren't the type of questions that we can answer. Even if you knew why + and - attracted, whatever force is there, you can question why that force is there. And whatever may explain that, you can ask why that is there. There is nothing necessary about physical reality. Maybe space and time, but there's nothing there that gives a reason as to why physical things behave the way they do.
  4. Aug 28, 2005 #3
    If we look to deep into the first few questions then yes I suppose the sad truth is we as humans have a hard time understanding what we observe...for now atleast. There is always hope though.

    Anyways I had a lot of questions that I would really appreciate answers to in my first post. Thanks in advance.
  5. Aug 28, 2005 #4
    I agree with AKG's post, but I'd like to point out that surprisingly we do find out sometimes that some basic ideas we haven't always thought required an explanation have emerged from even simpler ideas. The example that comes to mind is Euclid's parallel postulate, which isn't regarded as a fundamental postulate today, but something that emerges from flat Riemannian geometry. And right now, some theorists are working on finding the basic postulates from which our concept of apparently continuous space can emerge, so there are times when the answers to seemingly metaphysical questions such as these are explained, but as AKG pointed out, solving one of these questions just leads to another, so my guess is that the closest we'll ever have to a satisfying theory of "why" will require the anthropic principle, assuming we ever get close enough to fundamental reality.

    I wouldn't be surprised if this gets moved to philosophy, but here's some answers to some of your physical questions (the answers we know right now atleast :biggrin:):

    Well, of course with Einstein's [itex]E=mc^2[/itex] we know that matter is a condensed form of energy (this is why both concepts are sometimes refered to as "energymatter"). Also, protons and neutrons have kinetic energy (if they didn't they would be at absolute zero, which I have read violates the Heisenberg uncertainty principle). And I'd be surprised if they don't also have potential energy too.

    Magnets attract metals because the molecules in metals don't hold onto their electrons very tightly. Electrons can move freely in metals, so when you hold up a magnet, the electrons can either run to the other side of the metal to escape a negative magnetic pole, or they can move toward a positive magnetic pole, so then the metal is no longer magnetically neutral and is attracted by the magnet.

    Yes, black holes have mass, and yes they're made of matter. Black holes are formed when a very large star collapses. All the atoms in the star get squeezed into an unimaginably small point. Black holes are extremely compressed versions of stars.

    I'm the same way. :wink:
    Last edited: Aug 28, 2005
  6. Aug 28, 2005 #5
    I'm not sure if physics deals in questions such as 'why unlike charges attract' . We can 'explain' a phenomenon only in terms of a few basic experimental results which are formulated mathematicallly. One can't have an absolute answer to a 'Why' without assuming the truth of something else. The questions you asked about the
    'essence' of gravity & electricity put me at a nonplus - I think these are fundamentals.
    I am, with great respect,
  7. Aug 28, 2005 #6


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    Magnetism is not like electricity; there are no magnetons. Maxwell's equations are sometimes said to cry for a symmetry that would be possible if there were magnetons, but nothing like the electric field of an electron (a particle) occurs as a magnetic field. Magnetism occurs when there's a change in current with respect to a region of space. This way, not only does changing current affect magnetism, but a rotating circuit would generate a magnetic field as well.

    And as far as I know, mass and gravity are related, and black holes have lots of mass. It was originally thought that masses, by their very nature, exert a force on one another. A more modern theory suggests that masses affect the geometry of space, and the geometry of space accounts for the "force" by simply creating a gravitational field. Of course, mathematically, it doesn't make a difference if you refer to gravity primarily as a field (as is the modern convention) or as a force (the classical convention) because they are equivalent.

    Electrons have energy, energy determines the orbital (or the probability I guess). Everything (I think) has energy, protons and neutrons included. I don't know what this question means: Like the actual particles, or is the energy between the gaps of neutrons and protons?

    Everything I've said is possibly false.
  8. Aug 28, 2005 #7
    Thanks a lot guys! Thank you Ellipse for answering every question. Hahaha I feel like even more of a fool now for asking,

    " Do protons, and neutrons have energy? Like the actual particles, or is the energy between the gaps of neutrons and protons?"

    I should have thought about this for a little longer, and I would have remembered how many times I heard, and read atoms vibrate, and that EK=(1/2)mv^2, and that E=mc^2.

    As for the magnet, and blackhole responses....wow. The super dense matter from a star is just so cool. I don't fully understand though about the poles. What makes one positive, and the other negative?

    Edit: Posted before I saw your post AKG. Thank you aswell.
  9. Aug 28, 2005 #8
    Do we know why + and - attract? Could we imagine the opposite?

    Could we imagine electromagnetism worked the other way around?

    A first answer is that the world could be divided in to part: the + and the - parts.
    Each part would behave as if governed by a kind of gravity. The two parts might prefer to produce two separated worlds. These would reppel each other. There would be no atoms. Things would be quite different. But this is all fiction.

    It is much more probable that this +- attraction result from much more fundamental reasons. Indeed, it is an amazing fact of physics that all fundamental laws can be derived from the so-called "principle of least action". This principle says, for example, that particle trajectories follow "the least action path". But it also says that the electromagnetic field minimizes the field-part of the action in its response to particles behaviour.

    I just had a look at §27 "Field theory" by Landau & Lifchitz. There, it is explained that the field action must be given a certain sign. If the sign was the opposite, there would be never a minimum for the action of the field. Conversely, if the sign is the actual one, then there is always a minimum, and this is exactly what leads to the +- attraction and ++ repulsion and the known law of electromagnetism. After reading the paragraph27 a few more time, I think it tells us that a ++ attraction and +- repulsion would lead to an explosive field. But I would need more time to think about it, and maybe other on the forum could answer directly.
  10. Aug 28, 2005 #9


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    To expand on this, a black hole is an object with a concentration of mass great enough that gravity prevents almost anything from escaping after crossing the event horizon. The gravitational field is so strong that the escape velocity near it exceeds the speed of light, this implies that nothing, not even light, can escape its gravity, hence the word "black."

    Observationally, black holes are formed from stellar collapses that are large enough to completely suck in the whole star by its own gravity. Black hole sizes are measured by their Schwartzchild radius, the radius of their event horizon. Its event horizon is the imaginary spherical boundary which divides the region surrounding the black hole, where the escape velocity is ?c, and the rest of space. In the simplest case, where there are no hidden dimensions or ones smaller than the black hole, its size is directly proportional to its mass.

    If you compressed the Sun to its Schwartzchild radius, it would form a black hole and would be three kilometers wide - about 4 millionths, of its present radius. For Earth to meet the same fate, it would have to be squished into a sphere 18 millimeters across - about a billionth of its present diameter. Thus the smaller the hole, the higher the degree of compression that is required to create it. So far, theoretically, black holes can have any size: from near-Planck length sizes, to near the size of the observable universe. The density to which matter must be squeezed scales as the inverse square of its mass. For a hole with the mass of the Sun, the density is about 1019 kilograms per cubic meter.

    The actual particles as you now know do, and there is energy between them, the residual strong force. The residual strong force holds an atom's nucleus together.

    Before the 1970s, when protons and neutrons were thought to be fundamental particles, the phrase "strong force" was what is today known as the strong nuclear force, or the residual strong force. What were being observed were the "residual" effects of the strong force, which act on hadrons, both baryons and mesons. This force was postulated to overcome the electric repulsion between protons in the nucleus, and for its great strength, it was dubbed the "strong force". After the discovery of quarks, scientists realized that the force was actually acting upon the quarks and gluons making up the protons, not the protons themselves. For some time after this realization, the older notion was referred to as the residual strong force, and the "new" strong interaction was called colour force.
  11. Aug 28, 2005 #10
    There is another option in theory, that neither the quarks nor the nucleons are the fundamental particles, but that the fundamental particles are a quantum entanglement of first quarks at the microscopic level, then nucleons at the macroscopic level of existence. Consider the fact of QM that "free quarks do not (can not) exist", they always are observed as either biquarks (mesons) or triquarks (baryons)--likewise, the nucleon cluster model of Brightsen concludes that "free (unbound) nucleons do not exist in stable isotopes", they always occur as either 2-nucleon bosons or 3-nucleon fermion clusters. Is it possible that fundamental nucleon clusters may represent the "strings" of "string theory" ? Since there is already a thread on "what are the fundamental particles", perhaps this response is best moved to that thread, I will leave that to others to decide.
  12. Aug 28, 2005 #11
    There isn't really a need for Maxwell's equations to have a certain symmetry if we look at the magnetic field as a byproduct of the Lorentz invariance of charge, and therefore we end up with a four-vector with three components the magnetic potential and the fourth the electric field or what have you.
  13. Sep 5, 2005 #12
    They attract each other because there's nothing like a good turkey sandwich! duh!!!

    thats it, we can close the book on that one... All those years wasted, thinking about this question, it wasn't until I made a nice turkey sandwich with lettuce, swiss cheese, a sprinkle of dill, and a dab of mayo and bam! the answer just hit me. They do what they do because I like turkey! :tongue2:

    As Edison said (I'm paraphrasing) "If you're working on a problem that you can't figure out and you're thinking of scrapping the idea, just relax, take your mind off the problem, and the answer will present itself" (something like that but you get the idea)
    Last edited: Sep 5, 2005
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