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B Question about Gravity and Elecromagnetism and Attraction

  1. Aug 11, 2016 #1
    I am kind of an arm chair layman,
    The following is just my own curious mind working furiously on something I know I don't completely understand, and yet want to.

    It seems to me that just about every piece of matter is made up of mass, and therefor has some level of electromagnetic and gravitic atttraction. So, techncially, when you talk about gravity, shouldn't the calculation amount to the Force of Gravity minus the Force of Electromagnetism? And vice versa when you are looking for the Force of Electromagnetism? And general attraction is the combination of both? I realize Gravity is a much less powerful force than Electromagnetism at the atomic and sub-atomic levels, but it just seems to me that this is part of why their equations are so similar.
  2. jcsd
  3. Aug 11, 2016 #2
    So, you have noticed a key fact in how the gravity and electromagnetism equations are so similar. The difference is that gravity is attraction between masses and electromagnetism is attraction between charges. This brings a few other differences. First, charge can be negative, so the force can be both attraction and repulsion. Mass, however, is strictly positive (yes, there is some speculation about that however for our purpose, and all purposes in classical physics, it is strictly positive) and so the force can only be attraction. Many massive things like planets don't have charge, and thus there is no term about the electromagnetic force in gravity or the overall attraction (there is never a term of electromagnetism in gravity- they are different things). Many charged things like electrons have such little mass that we consider it to be zero (good luck calculating the gravitational field of an electron- it barely exists). Thus, the force electrons put on other electrons/small charged particles is essentially all electromagnetism. But, what do the forces of gravity and electromagnetism have in common? They are both forces (thus having the dimensions of force) and are both vectors. Because of this, they can be added together! The overall/net force of attraction between two objects is the force of gravity between them plus the force of electromagnetism between them. Additionally, the force of gravity would be the net force of attraction minus the force of electromagnetism, and the force of electromagnetism would be the net force of attraction minus the force of gravity. However, not all objects will have a nontrivial gravitational field or an electric field at all, so gravity and electromagnetism may not always apply in the same situations.
  4. Aug 11, 2016 #3


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    You can keep them separate: things can have mass and be neutral -- only gravity.
    For things that have mass and charge the forces are independent and simply add up without influencing one another.
  5. Aug 11, 2016 #4


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    why ? ... you can have a very massive object that has, for practical purposes, a zero EM field

    EM fields (electric or magnetic) can be attractive or repulsive
    gravity is ONLY attractive

  6. Aug 11, 2016 #5


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    damn in the time it took me to write so little there were 2 other replies haha
    That'll teach me for eating breakfast at the same time
  7. Aug 12, 2016 #6
    Well, my I was trying to keep my ideas simple for now, but since you are asking, I feel like dark energy makes no sense. And I feel like there must be more to the forces we already know are present. rather than suddenly have some new force we never noticed before. The way I look at it, one of two things is happening. Either there is a strong gravitic force on the opposite side of certain galaxies that are causing them to speed up, or because of how small the difference in speed is, we simply didn't account for something. And I feel like that something has to be electomagnetism. The thing that I don't completely know how to explain is that I sort of picture all of the atoms in the universe like little neutral balls with electron shells. But I feel like,the fact that the atom tends to be neutral is less relevant than the fact that maybe the real balance of atoms isn't from electron to nucleus, but from electron to the negative portion of the next atoms electron shell. And that bond is like a bungee cord, And the gravity is the motor pulling on that bond. Now, imagine two planets with almost nothing but hydrodgen atoms and molecules between them (roughly 80% of matter in space). The size difference of the planets basically turns the space between the two plantets to a big inductive electromagnetic rope. And gravity pulls on that rope with a mechanical advantage of the size ratio of the mass of the bigger planet to the mass of the smaller planet. Now I fully acknowledge that everything I just said can be total and complete BS. But it still seems like less BS than jumping to Dark Energy. Of course, now you are free to realize just how short my knowledge of science falls, and just how much of a crackpot I am . I get that I really don't have figures to back any of what I am saying. But I do also think it explains why electromagentism is strong at short distances and weak at long distances and why gravity is the reverse. One last thing...all of the matter between the planets, "the rope" has mass..and should probably be figured into any calculation of gravity. between the planets..all of that mass is part of the system of gravity between the two heavenly bodies.

  8. Aug 12, 2016 #7


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    It's important to understand that scientists didn't just come up with dark energy on a whim. It was the result of a long investigative process (that's still ongoing), is well grounded in math, and requires fewer alterations to previous science than anything else. Seriously. All other proposals require serious alterations to known physical laws that cannot be reconciled with experiments at this time, especially electromagnetic laws. Not only that, the existence of a force that just happens to be pushing galaxies directly away from us (IE, with Earth as the focal point all objects are moving away from, as would be required by your idea) runs into philosophical issues that are difficult to just brush aside.

    It does not. Gravity doesn't work that way anyways. It is very strong at short distances if you can compact enough mass into a small area.

    Let's see... given the extremely low density of interplanetary space, that would change things by about 0.0000000000000000001%, give or take a few orders of magnitude or so.

    I'm going to lock this thread now, but if you'd like to learn more about dark energy then feel free to browse the cosmology forum or make a new thread there. I will warn you, though, that we don't allow personal ideas/theories here at PF, so if you want to make a new thread then please avoid throwing out any personal ideas and instead focus on learning the actual science behind dark energy.

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