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Gravity and Electromagnetism

  1. Oct 7, 2009 #1

    Apologies an advance for any general ignorance (not a physics student - just happen to have an interest and no background!)

    Is there generally a strong electromagnetic field associated with any mass demonstrating a strong gravitational field? Are there exceptions?

    I've heard that radio receivers for example can bend the received signals due to their receiving field being wide enough to catch enough of the transmitted wavelength. Does this mean a wide enough field could do the same with light, and effects aren't observed on a smaller scale? (or is the bending due to a non polarised atomic pull, amplified by the large mass?)

    What exactly is gravity, and how is it's strength increased? Is this the same force we witness on a much smaller scale from the atom, along with it's electromagnetic properties?

    If we take several small pieces of magnet and join them together, does the field length become wider? If we witness this same effect from gravity in larger masses (ie having a wider field), can it be said that gravity is also a net field effect?

    Is there potentially another form of field that acts in the same manner ie gravity, lacking the polar charge?

    If all of these forces are fields / waves is the nature of matter entirely curve / wave and field based.

    How do we differentiate between electromagnetic fields and gravity, bearing in mind that at the atomic level, electromagnetic fields are also present? (When placing a magnet near a flow of water, the - charge for example may be attracted to a pole. The +ve would be expelled. The -ve, being closer, exerts more force?)

    One more.. Does gravity really bend light? If matter can propogate waves etc, are we really seeing a bend at all?
    Last edited: Oct 7, 2009
  2. jcsd
  3. Oct 7, 2009 #2
    Sorry - lots of questions for one post. I've heard lots of reference to the need for "dark matter" to explain forces at work.

    Is anyone able to summarise why the need for "dark matter" arose / what the problem was under current theory?
  4. Oct 7, 2009 #3


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    No, there isn't. electromagnetic field has nothing to do with mass.

    I have no idea what you are talking about. I have never heard of radio receivers "bending" signals. In any case, radio waves and light waves are both forms of electromagnetic energy. Anything that affects one will affect the other. Certainly a large mass, such as a star does "bend" the path of light. That was measured in, I think, 1928.

    If I could say "what exactly is gravity", I would reach out for my Nobel prize! I don't know what force you are talking about witnessing "on a much smaller scale from the atom". Certainly an atom exerts a gravitational force on other objects but it is extremely weak. There are four known forces: gravity, electro-magnatism, the "weak atomic force", and the "strong atomic force". The last two have a very very short "scale" and are only witnessed in nuclei.

  5. Oct 7, 2009 #4
    Some bad wording there... (sure sign of a newbie)

    You state an electromagnetic field has nothing to do with mass, yet you state that an atom has mass and an electromagnetic field can have effect on an atom? Please explain.

    In terms of "bending signals" from radio waves, this was poor wording on my behalf. I was trying to ask if a receiver has a strong field, will it's "effective" size, be increased? Do you need a larger "effective" size on receivers for long radio waves? (Does the term "long" make sense in this context?).

    You have compared light waves with radio waves in your reply and state both can be affected by the same forces. Obviously, the two are not the same. Does light have a significantly longer wavelength?
  6. Oct 8, 2009 #5
    Simon, there is absolutely no relation between electromagnetic fields and gravitational fields. An EM field field can have an effect on atom. But this is not due to the mass of an atom but due to charge particles like electrons inside the atom.
  7. Oct 8, 2009 #6
    Many thanks. Makes more sense.

    In terms of gravity, black holes are named appropriately. Is the lack of light due to the strength of the gravitational field? Is so, do the effects of gravity appear as a reverse wave?

    What effects do weaker gravities, if any, have on other waves ie Radio / UV / Infra red / sound / electromagnetic / light? As gravity increases, are similar effects encountered with other types of wave, aside from light, or does the critical point hit by a black hole suddenly have a blanket effect on all wave types at the same time?
  8. Oct 8, 2009 #7
    the lack of light is due to the fact that time stops at the event horizon
  9. Oct 8, 2009 #8


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    You may be referring to visible light. Radio waves are in fact light, much longer wavelength and lower frequency than the visible spectrum. Same force, same basic rules.


    Light in a black hole is trapped by the strength of the gravitational field. The field at that point is so distorted that escape is not possible, but it is not due to "reverse" waves. There is a large black hole at the center of the Milky Way.
  10. Oct 8, 2009 #9
    the field at the event horizon is not necessarily unusually strong.
  11. Oct 9, 2009 #10
    No but inside the event horizon all photon trajectories remain inside the event horizon.
  12. Oct 9, 2009 #11
    let me ask you this. if time stops at the event horizon then what does it do inside the event horizon?
  13. Oct 9, 2009 #12
    Many thanks.

    Was wondering the same thing. On a side note, if gravity has such an effect on radio / light waves, does the reverse apply?

    Does gravity affect all wave types / is there a list of those it does / those it doesn't etc?

  14. Oct 9, 2009 #13
    On a related subject, if light fails to escape a black hole, in lesser gravity, are light / radio waves slowed down or reduced in some manner?

    ... and is this in someway related to the density / movement of mass, or to over-simplify it, escape velocities, or the "scrambling" effect occurring in the singularity?
  15. Oct 9, 2009 #14


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    Yes, that is correct. Time is "slower" in the presence of mass. This effect is measurable, even here on Earth. The orbiting GPS satellites take that into account, as they are farther from Earth and therefore time passes "more quickly" for them. Since it is essential that time be synchronized for the signals to be analyzed to determine the location accurately, general relativity is a factor.
  16. Oct 9, 2009 #15
    Time stops only for a distant or accelerating observer outside the event horizon; for a free falling observer, time passes "normally" as the event horizon passes uneventfully..and in fact is not even observable.

    Inside a black hole time proceeds in the direction of the singularity...away from the event horizon...so the future is inward toward the black hole singularity.

    See this thread for a little background explanation...
  17. Oct 9, 2009 #16
    Does this apply to radio waves / light waves etc in exactly the same ratio?

    Is it accurate to say then, that while the compenents of the atom may cause waves through what we perceive as space-time, it is the mass itself that dictates the shape of space-time? In a simple term, the equivalent of magentised marbles on a sheet, but the less weighed down areas representing those with a faster flow?

    If that's the case, presumably the old theories about the increasing speed in growth of the distance between galaxies etc are out the window too? ie because our perception of the flow of time may potentially become increasingly warped with the bends in space-time and the non-constancy of space-time in any given region?

    What model would support this type of mechanic? The equivalent of a liquid light being sucked down a funnel?
    Last edited: Oct 9, 2009
  18. Oct 9, 2009 #17

    I believe I know what the poster is trying to express, but this is just NOT a good way to think about gravity and electromagnetic fields (EMF).

    Here are a few "relations" just off the top of my head: gravity curves EMF; both have virtually infinite reach/influence; Both are massless particles; both fields are continuous in classical theories; both fields carry energy; both curve spacetime..and on and on and on.

    And at singularities no one knows the relationship between these forces nor any other forces...that's where relativity and quantum mechanics break down.

    It is far better to understand that in typical atoms, for example, EMF reflects significant forces (due to charge) while gravity can usually be ignored because its so relatively weak....in other words, charge causes a lot stronger EMF than it does gravitational forces. For example, when studying electrical conductivity and current flow, gravity is insignificant, charge is almost everything.
    For relative strengths, try http://en.wikipedia.org/wiki/Electromagnetic_field#Electromagnetic_and_gravitational_fields
    Last edited: Oct 9, 2009
  19. Oct 9, 2009 #18
    Sorry for the flood of questions - the more information I get the more I want.

    We are commonly taught at schools that the + charge attracts the -ve charge, and that the -ve charge bears significantly less mass.
    What attracts the +ve charge to the neutral?
    (Does this occur?) Is this in some way reducing it's effects?
  20. Oct 12, 2009 #19
    There has been much debate over what is gravity and how it effects matter. We know that a bowling ball and a base ball fall at the same rate why ? Gravity is equal in all directions and effects all mass equally The vastness of space can not be comprehended by the human mind however there are surely other cultures in the universe who just might.Steven Hawkins has tried to establish a reason for all of this and so far has failed.
    Steven is not at fault , however he has had to re think all of his findings.

    I say you need to understand our atmosphere .

    When re-entering our atmosphere we need ceramic tile on the space shuttle because of friction of entering gravity. .
    I think of earth as a ball surrounded by atmosphere .
    Since space is a vacuum there can be no gravity. however when we re enter our atmosphere we are bound by Gravity.

    There has also been great debate about "Black holes"
    To understand that paradox, we must first understand that space is endless, and the human mind can not comprehend such forever space !

    I can not go any deeper at this time,however
    there is much more to my findings.
    Please feel free to contact. I am currently working on my own model

  21. Oct 13, 2009 #20
    As far as the commonly accepted forces are concerned, our gravity is fairly simple. We are aware of the attractive and repulsive forces within the atom, and around it, and on the larger scale, the planets own fields. We record the effects of gravity, on the smaller scale and the larger. Friction, we put down to the former - the huge energy expenditure needed to face the forces from the atom.

    in both cases, we witness the larger scale effects demonstrated by the smaller scale. Some, at least in my experience, seem to be skipped over in the typical education (ie + attracts -, but what attracts + to o? The nature of bonds between atoms - what keeps molecules together. Do the fields behave differently?)

    The prospect that space is endless isn't one I have difficulty with, nor I expect would most people.

    Features such as black holes I've picked on to better understand the nature of light and other waves. To some extent though, I'm surprised the nature of those waves has never changed.
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