# Q & A: Gravity vs. Magnetism

Q:
where does gravitational/magnetic force originate from and why does all matter get pulled by gravity(which is magnetic i believe) yet only certain metals only appear(ferrous)to get attracted to magnets and other forms of matter like wood or plastic,etc don’t seem to get pulled by magnets? chris (age 10) Halifax, Canada ...AND... I wanted to ask what the difference is between a magnetic force and a gravitational force. If there’s no difference, I’d like to know how come the Earth’s gravitational pull is able to attract non - magnetic materials e.g human beings, yet no matter how much powerfull a magnet is it can never attract non - magnetic(non- ferrous) material.
- curious starvos (age 12)
Kenya
A:

Chris & Starvos -

Since your questions are roughly the same, I'll answer them both at once. Gravity and magnetism are not the same thing. In fact, they are completely separate forces. Gravity is a force that acts between any two objects with mass. No matter what they are made of, both objects get pulled towards each other just because they have mass. The reason it seems like gravity only pulls you towards the earth is because the earth is so big that the pull from you on it isn't enough to do much to its motion.

Unlike gravity, which occurs between any objects, magnetism depends on specific properties of objects. Magnetism can either pull the two objects together or push them apart, depending on which way the magnets point. Most importantly, it depends on what is going on with the electrons in the material, since each electron is like a tiny magnet itself. Most materials feel very little magnetic force because their electrons act like magnets that are pointing every which way, more or less equal numbers pulling or pushing.

In some materials, the electrons can lower their energy by lining up magnetically into magnetic domains. In each domain, most of the electrons pull and push together, so you can get big forces. In some materials (permanent magnets) the domains can all be lined up so you get really big magnetic forces. If you measure very carefully, however, you find that there are small magnetic forces between magnets and 'non-magnetic' materials like pieces of copper or pieces of wood or people. Some of those 'non-magnetic' things are attracted to magnets and others are repelled.

By the way, only some ferrous materials are magnets, and only a few magnetic materials are ferrous.

Both magnetism and gravity can affect objects at a distance. Both get weaker as the objects get farther apart. This is why you are affected by the pull of gravity from the earth, but not from distance planets. It's also why two magnets may move together if you set them near each other, but if you set them far apart nothing will happen. However, as two objects get far apart, the gravity between them goes down by a factor of four when you double the distance, but the magnetic force goes down by (at least) a factor of sixteen. On the scale of the solar system, with planets far apart, gravity is much more important than magnetism.

-Tamara (and mike)

(published on 10/22/2007)

## Follow-Up #1: magnetism and gravity

Q:
Why is magnetism only one direction, should there not be a third direction or more. why only north to south. Does it have another dimension. Why are we trying to explain gravity through means of mathematics, has maths evolved enough.
- brett kendall (age 46)
johannesburg, south africa
A:
Brett- Magnetic fields can align along any direction. We call the two poles of a magnet "north" and "south" as a way of keeping track of which would be attracted which way in the presence of the Earth's magnetic field. When the Earth's field reverses, those names will be awkward.

Math has certainly evolved enough to do a very good job of describing gravity. For most purposes Newton's calculus and force laws, more than 300 years old, work well. For greater accuracy, one needs General Relativity, but even that uses math that had already been developed before 1917.

It may be that for extremely small distances and extreme situations, a new theory (perhaps a string theory) will be needed, and some new math will have to be developed.

Mike W.

(published on 05/16/2013)

## Follow-Up #2: Repulsion of gravity?

Q:
I know it sounds like sci-fi but if you have opposite poles to magnetism and they either repel or attract each other would it be possible that the same is true for gravity or am I talking apples and oranges here? Maybe we just haven't discovered it yet, or maybe it's a theory that we just haven't figured out how to achieve physically yet?
- Derrick (age 30)
Lake Charles, LA USA
A:
This a very interesting question.  We know that two like-sign electrons, or positrons repel each other whereas an electron is attracted to a positron.  This is the nature of the Coulomb force of electricity: like-sign charges repel, unlike sign charges attract. The extension to the forces between magnets is straightforward.  We also know that two chunks of ordinary matter attract each other.  You might ask the question, 'does a chunk of ordinary matter attract or repel a chunk of anti-matter' ?  Curiously, the answer is they still attract each other.  Now the reason for this is pretty obscure and has to be explained by quantum field theory.
The electromagnetic force is transmitted by exchange of spin 1 quanta called photons.  The gravitation force is transmitted by exchange of spin 2 quanta called gravitons.  The difference between spin 1 and spin 2 makes all the difference.
See:     for information on the graviton

If you don't follow all of this, don't worry.  I had to go and ask our local quantum field theorist guru for an explanation a few years back when a similar question came up.

LeeH

(published on 01/27/2010)

## Follow-Up #3: graviton and magnetism

Q:
Within the last few years, physicists proved the existence of a particle that governs gravity, called a graviton. My question is this; are or could gravitons be affected by magnetism, and would supermassive magnets (like planets or stars) affecting clouds of gravitons by way of magnetic attraction be how gravity exists as we know it? And if this is all theoretically possible, what would the ramifications be for science (such as giving a possibly viable unified field theory?)
- Sean Brown (age 24)
Salt Lake City, UT, United States of America
A:

The existence of the graviton is almost certain on theoretical grounds, but there is no experimental evidence for its existence. Nothing much has happened recently to change that. [The BICEP2 collaboration claimed to have seen what looks like the leftover effects of the quantum zero-point spread of gravitational waves, left as tiny "B-mode" ripples in the polarization of the cosmic microwave background radiation. It now looks like they really saw something more local and less interesting. If one of the more sensitive versions of this experiments works, then it will be fair to say that a real quantum gravity effect will have been seen. /Mike W.]

Meanwhile, the energy in magnetic fields, like the energy in any other sort of field, is a source of gravity. (Remember that energy and mass are just two words for the same thing.) However, there is no special connection between magnetism and gravity.

Since absolutely nothing in physics itself suggests a special connection between magnetism and gravity, it's interesting to speculate about why so many people have the impression that there must be such a connection. I guess it's because these are the two forces which we often notice acting between objects that aren't in contact. Static electricity does as well, as you can see by charging up balloons on strings etc, but I guess that isn't as familiar.

Mike W.

(published on 04/03/2010)

## Follow-Up #4: gravity and magnetism again

Q:
With virtual particles that are spin one bosons causing warping of extremely small chunks of spacetime with their mass or effective mass, it would seem like their is a connection between the energy density of a magnetic field and gravity. Is part of the issue that there is a symmetry breaking that keeps these two long range forces from being synonymous? I know we have an electroweak model, but why not an Electrogravitational model as einstein proposed? Due to the orders of magnitude difference in their strength (not referring to Higgs and range). Why are they so different in energy?
- Nick
Jersey
A:
This is very much the same question that has also come in in more classical form.
The forces are both long-range because their carriers (photons and gravitons) have no rest-mass.

The next stage of force unification will presumably unify the electroweak and strong forces as remnants of a more symmetrical fundamental law, just as electromagnetism and the weak force were unified.

Including gravity in the unification is trickier because the quantum mechanics of spin-two massless particles leads to all sorts of infinities in a standard treatment. String theory is an attempt to construct a consistent quantum theory that includes gravity, but it requires an extra six spatial dimensions.

The question about the enormous range of strengths of the different forces is profound. It's an active area of research, part of the whole unification issue, but over my head.

Mike W.

(published on 04/04/2010)

## Follow-Up #5: magnetism and gravity redux

Q:
Magnetism has both an attractive and repulsive force. This obeys newtons law stating that every action has an equal and an opposite reaction. Gravity is an attractive force. Is it not worth contemplating that perhaps gravity also has a repulsive force? Could it not be possible that gravity and magnetism are a consequence of each other or that they are individual parts of a greater force not yet understood or fathomed?
- Joel
Brisbane
A:
There's no connection between the ability of magnetism to either attract or repel and Newton's 3d law. That law says that for any force between two objects, the magnitudes of the force of one on the other and vice-versa are the same, and the directions are opposite. A repulsive force of A on B is accompanied by a repulsive force of B on A. So purely attractive forces can also obey Newton's 3d law. (More generally, it just states that momentum is conserved, even in multi-body interactions, and that still doesn't require any repulsive component.)

As it happens, plain old gravity, as in General Relativity, does have a sort of repulsion associated with it. When the energy density of space, rather than its energy content, is fixed, the gravitational law gives an accelerating expansion. That's actually happening now, and may well have happened very intensely at an earlier stage.

Are gravity and magnetism aspects of some more unified force? We know that magnetism is just an aspect of electricity. It was sort of unified by Maxwell in ~1860, with the unification completed by Special Relativity in 1905. More recently electromagnetism has been unified with one nuclear force to give the electroweak force. It's generally assumed that the remaining chromodynamic force will also be integrated into this framework, giving a Grand Unified Theory (GUT). Working gravity into the same unified structure is tough. That's what the string theorists are trying to do. Maybe they will succeed. If they do, however, there will be no special connection between the magnetic piece of the electrical sector of the electroweak subset of the GUT  portion of the overall theory and the gravitational side of the same theory.

We're still a little puzzled by the persistent sense that these two phenomena have some special connection. See above for speculation.

Mike W.

(published on 05/10/2010)

## Follow-Up #6: force mechanisms

Q:
What is the mechanism that causes one massive object to move toward another? Just saying that two massive objects attract each other does not explain the movement. There has to be some sort of mechanics or propulsion by both toward each other. Perhaps the god particle or the particle that gives all matter it's mass also emits a particle in the opposite direction of other mass particles and thus causes the two masses to be propelled toward the each other? Perhaps magnets are individually propelled toward each other rather than pulled toward each other. That would explain the fact that no substance can be placed between them to nullify their actions
- Jim Wells (age 64)
Valparaiso,IN 46383
A:
I'm not sure I follow all of your question closely enough to give a direct answer (and also I'm probably not knowledgeable enough to give a complete answer) but some parts can be addressed easily.

The force between magnets can be eliminated by placing a sheet of conventional superconducting material between them. So that would seem to argue against your idea about the origin of the magnetic force.

With regard to gravity, the standard theory (General Relativity) describes a space-time geometry whose curvature is sensitive to the local density of mass and momentum. In some sense this curvy space can be considered a "mechanism" for the interaction. However, the quantum mechanical versions of the same idea (not yet developed to a complete consistent form for gravity) do involve exchange of gravitons, which does sound related to the idea you are thinking about.

Mike W.

(published on 07/24/2010)

## Follow-Up #7: Atomic magnetism and peyote

Q:
I always believed they were different forces and magnetism did not work on anything but iron etc. While reflecting on Einstiens' trying to tie it all together I said "Wait a cotton pickin' minute here, on the Atomic level Magnetism IS at work in everything and holding all Atoms together Magnetically via Electrons, Protons and Neutrons ~ Perhaps there is no magical force called "Gravity" after all! Hey Al I think you were on to something! ~
- Peyote Sky (age 66)
Youngstown, FL, Bay Co.
A:
Dear Mr. Sky- go easy on that peyote.

Magnetism plays only a small role in atoms. They're held together by simple electrostatic attraction.

Nuclei are held together primarily by the strong (chromodynamic) nuclear force. The electrical force tends to push them apart. Magnetism is again relatively minor.

All these forces are kind of magical when you think about them enough, even without peyote.

Mike W.

(published on 02/21/2011)

## Follow-Up #8: magnetism and gravity are unlike

Q:
i want to know that the magnetic force and the gravitational force are like or unlike forces. if they are unlike give me the clear cut explanation.
- gowtham (age 18)
india
A:
Here's a few ways magnetism and gravity are unlike:

1. Gravity acts between any two objects, magnetism only between some.

2. Gravity is always attractive, magnetism is sometimes repulsive.

3. At large distances the gravitational force falls off inversely with the distance squared. The magnetic force falls off at large distances at least as fast as inversely with the distance to the fourth power.

4. A uniform gravitational field is undetectable by any local measurement, but a uniform magnetic field is detectable.

Convinced?

Mike W.

(published on 03/02/2011)

## Follow-Up #9: Magnetism and other forces

Q:
Sorry but it seems to me that they are the same force. that the diferences you describe are just levels of order. A single atom has week magnetic forces keeping electrons in orbit around positive nucleus. Lump lots of atoms together and you have lots of attractions in a large number of directions. I suspect that the outer electrons are shared throughout this mass and do not stay with their parent Nucleus. Lump more atoms together increase the mass and overall increase in attraction to other masses but yet it is still unordered so overall weak in any one direction. Magnets these are materials in which the atoms have been ordered such that the majority of the outer shell electrons are to one end of the material giving a directional increased pull at that end.
- Dave (age 44)
Manchester
A:
As we've often mentioned here, there's something abut magnetism that seems to evoke a high level of confusion. Your note is very useful because it represents many of the ideas we hear. Let me go over these ideas one at a time.

"A single atom has week magnetic forces keeping electrons in orbit around positive nucleus." You're mixing up the electric force and its magnetic aspect. To take the simplest example, the hydrogen atom ground state, the only magnetic force is the spin-spin interaction between the proton and electron. It's very weak (around 10-17 ergs, compared to a binding energy of over 10-11 ergs) and can either be attractive or repulsive depending on the relative sign of the spins.

"I suspect that the outer electrons are shared throughout this mass and do not stay with their parent Nucleus." There's no need to speculate on this. A major part of condensed matter physics includes the study of which materials have how many electrons running around freely vs. localized on atoms. Metals, for example, have many shared electrons.

"Lump more atoms together increase the mass and overall increase in attraction to other masses but yet it is still unordered so overall weak in any one direction." That may need a follow-up, since I'm not sure I follow it. It's also well understood which materials are ordered and which are disordered. You can tell via x-ray scattering, for example.

"Magnets these are materials in which the atoms have been ordered such that the majority of the outer shell electrons are to one end of the material giving a directional increased pull at that end." No, you've again confused electricity and magnetism. Piling up charge on one side makes an electric field, not a magnetic field. Magnetism is made by aligning spins. What you've described here is a ferroelectric, not a ferromagnet.

Mike W.

(published on 03/21/2011)

## Follow-Up #10: magnetic effects in rocks

Q:
Sorry to follow on. At my university I remember looking at ageing lake sediments based on the effects of the earths magnetic field being locked into the sediments as they settled. There was some discussion to the effects of fireing of clays giving a magnetic effect such that an application of energy can force magnetic effects. Electro magnatism and ferrite Magnatism. Ferrite mags i understand to weaken over time but can be zapped using electro magnets to restrengthen them. pulling electrons towards one end or other much easier in materials of the same element with excess electrons in outer orbits. In materials of mixed elements there is cross linking reducing the number of free electrons. By order I am thinking that a mass of elements where the overall balance of electrons is in one direction forced by some application of energy. In unordered I asume a more ballanced distribution of outershell electrons so no overall directional force. The bottom line is that a theory that requires there be a separate force for everything does not "feel" right.
- Dave (age 44)
Manchester
A:
What was happening with those old rocks was not that the magnetism had any major effect on the formation of the minerals. It simply aligned the magnetic domains somewhat in those materials which were going to form magnetic domains anyway.

Those electromagnets don't pull electrons toward one end. They align the spins of the electrons, like the earth's field does only much more powerfully.

The sense that all the forces are connected is shared by most physicists. The efforts to find a correct GUT (grand unified theory) and beyond that to a unification of gravity with the other forces (string theory?) are ongoing.

Mike W.

(published on 04/05/2011)

## Follow-Up #11: psychology of gravity/magnetism

Q:
I don't know if I have a question per say, rather an offer of opinion as to why people, like myself, wonder if gravity and magnetism are related. Lately I have been wondering a lot about gravity and that led me to think about magnetism mainly due to them both being an invisible but measurable force. I find I don't have a firm grasp on the what/why behind gravity, and magnetism still seems mystical despite the fact I know the mechanics of it. It's the invisible part. We can measure and describe the forces through mathematics, but it doesn't really explain them. I suppose a lot of people struggle with this same question since there are only theories out there as to why forces like gravity occur. Am I wrong in the thinking that we can describe these forces, but are not yet able to explain them?
- Nate (age 32)
Alexandria, VA
A:
Thanks for the thoughtful comments, which help go some way toward understanding this psychological puzzle.

It's interesting that static electricity also acts at a distance, and isn't hard to observe, but  it doesn't seem to get swept into the same mental category as gravity and magnetism. Maybe that's somehow because we usually have to do something active to generate the charge separation, and it usually doesn't persist very long.

When you get a little deeper all of physics becomes mathematical expressions. The distinction between "describe" and "explain" fades away. Maybe because gravity and magnetism take rather simple mathematical forms on the scale that we can see, they offer the first glimpse of this beautiful but disconcerting property of the universe.

Mike W.

(published on 04/15/2011)

## Follow-Up #12: bogged down in math: 'Why' versus 'How'

Q:
I have to admit that once explanations are provided in math equations, I get lost. It always feels like the math explains the what happens, but not the how. I'm always left not understanding the how. Like how does gravity pull, what exactly is it pulling? What is magnetism actually pushing and pulling? What are these tiny invisible strings of the universe that push and pull against everything. And force! what is force anyways... Things are often described as a force, but that seems like such a hollow term that doesn't really tell you what it is. All you know is it pushes and pulls, but doesn't tell you how, or atleast I'm not understanding how. I want to imagine magnetism like a hose spraying water out of one end, and sucking it in the other. If you get caught in the flow water it will push or pull you depending on what end you're on. For a magnet, I don't know what the "water" is. Is it electrons, some other particle that is moving and running into things? I want to understand what exactly these forces are, not just what they do.
- Nate (age 32)
Alexandria, VA
A:

Dear Nate,

You're puzzling about some of the very things that physicists are puzzling about. Understanding the exact mechanisms by which gravity, electromagnetism and other physical phenomena manifest themselves is exactly what physicists try to do. As humans we start from a high level concept or observation (for instance, seeing an apple fall) and slowly work our way to more fundamental understanding by studying the physical phenomena we're interested in (in this case, gravity). Newton took more than a few steps in that direction when he described the physical law of gravitational force. However, for centuries, people like you and me wondered "why? Why this law of gravitation? Where does this come from?". Einstein took a couple of more steps with his enlightening discovery of general relativity. The "why" of Newton's gravity was answered with this new understanding that mass curves spacetime, objects travel on geodesics and the speed of light is the same in to any observer (among other things). But now there are plenty of "why's" associated with Einstein's theory!

As Mike said, "how" and "why" ("describe" vs. "explain") are used interchangeably by physicists. In fact, I would challenge you to find a difference between the two when talking about physical phenomena! Asking "how" a physical phenomenon manifests itself will inevitably lead to a more fundamental understanding of it.

The most rigorous, specific, and efficient way to explain the "how" is through mathematics (pure symbolic logic). The alternative, describing things with words, fails sooner or later. While in many cases describing physical concepts with words can be extremely helpful (since for most people it provides for a better intuitive understanding about the topic at hand), it will always be subject to the ambiguity of the language and many times will produce only partially accurate analogies. In short, there is no perfect way to describe things with words. Mathematics, on the other hand, allows us to be precise.

In fact, you can think of mathematics as being analogous to a language like English. The reason we usually prefer things to be explained with words is because our language is, to us, the most familiar way to communicate ideas. While Mathematics might seem like an unfamiliar foreign language at times, it is by definition the most precise way to communicate ideas.

"What is magnetism actually pushing and pulling?" A magnetic field exerts a force on moving electric charges. If you think of a loop of wire with a current running through it, the magnetic field exerts a force on the moving charges in the loop in a direction perpendicular to the path of the current. You also brought up a "hose" analogy for the magnetic field. Your understandable question can really be translated to this: "what exactly is a magnetic field made of?" The answer to that question was given a few years ago on this site. You can see the explanation here: What are magnetic fields made of?

And last but not least, you asked the question "what is force?"

Force is a more general term which describes something that changes an object's momentum. The physical quantity is measured by that change in momentum divided by the time it took to occur. So, kind of like how speed measures the change in distance over time, force measures the change in momentum over time.

I hope that satisfies at least some of your curiosities. Feel free to prod us with more questions!

John H.

I'll take a crack at this too, in parallel with John's answer, since these philosophy issues aren't cut-and-dried. We seem to accept certain types of interactions (strings pulling, hands pushing,...) without much trouble. These are interactions where the visible objects involved touch, i.e. they are too close for us to see any gap. This feeling is captured in your language: "tiny invisible strings....running into things..." Probably we have some evolved sense of expecting interactions of that sort.

When you think enough about it, though, such interactions are no more or less mysterious or explained than other interactions, such as between the earth and moon or between two magnets. On a small enough scale, all of our descriptions turn into patterns of mathematical fields filling space- even those strings, and hands, etc. So our role here is in one way like what you're looking for- to eliminate the dualism between the familiar contact forces and the more abstract field-based forces. Unfortunately it's by converting the former into the latter, not vice-versa.

Mike W.

(published on 04/15/2011)

## Follow-Up #13: gravity and magnetism again

Q:
If gravity and magnetism are not the same then why do they correlate to each other. If one acts on the other and vise verse then they must be connected. Gravity is a force acting on an object with mass, magnetism is a force exerted by virtue of charged particles. Both are based on ferrous material, one is created by mas the other by the movement of the mass. I suspect gravity is a direct result of a magnetic field. If there is no atmosphere like on mars then the gravitational effect is weakened. Also the larger an object is regardless of the presence of a solid core the shear mass can distort the area around the object and induce a magnetic field, this in turn creates the effect of gravity.
- James (age 38)
south cairo, ny
A:
James- Your question is close to many others, so I've marked it as a follow-up. In addition to the original question, you may be particularly interested in follow-ups 3, 8, and 11.

Just to recap some points:

Gravity acts on everything, so it's not exactly surprising that it acts a little bit on magnetic fields. It also acts on things with absolutely no magnetism.

Gravity acts on everything, (did I say that?) so of course it acts on ferrous metals, as it does on non-ferrous metals, non-metals, etc.

There is no basis whatsoever for your other speculations about gravity and atmospheres and so forth. However, you have many co-thinkers. We're mystified.

Mike W.

(published on 06/30/2011)

## Follow-Up #14: More philosophical questions about magnetism

Q:
Sorry to frustrate you with yet another repetition of earlier sentiments on this thread, but you still have not convinced me that magnetism is unrelated to gravity, undoubtedly due to my lack of scope in scientific knowledge. However, why can't it be possible that 'magnetic' objects exhibit a greater amount of gravitational force than other objects. There are varying degrees of magnetism in magnetic bodies, and there are varying degrees of attraction in any bodies due to mass. Where do we make the distinction between a magnetic force, and a gravitational force. Gravity is present whatever the conditions, but what if magnetism isn't so much a force, but rather like a lens focusing or manipulating gravitational force? (sorry for the vague analogy, I hope you get my meaning). The differing rates at which the supposedly distinct forces become weaker over distance could be explained by this 'lens' effect. For a continuation of my (poor) analogy, imagine focusing sunlight on an object with a magnifying glass. Sunlight is hitting the object regardless, but with a magnifying glass, you can focus the sunlight into a beam. As you pull the lens away from the object, the beam gets weaker/more diffused. In this analogy, the regular sunlight is gravity, and the lens is magnetism. I oppologise if you find my ignorance of science irritating, but the common man thinks about these things too : )
- Mike (age 31)
Australia
A:
"However, why can't it be possible that 'magnetic' objects exhibit a greater amount of gravitational force than other objects."
That's something you can measure, and they just don't.

"what if magnetism isn't so much a force, but rather like a lens focusing or manipulating gravitational force?"
I sort of can guess what you mean, but if that were the case, then magnets would work differently when they were in regions with weak gravitational fields (say on distant space probes) but they don't.

I'm not irritated at all. I'm glad that you're representing a very widespread view. I'm still puzzled about the motivation. We have nice complete theories of electromagnetism and gravity. (OK, the quantum version of gravity isn't complete, but for our purposes here plain old Newtonian gravity and Maxwell's EandM suffice.) I'd love to hear  more explanation about why you're seeking a closer connection between these two particular forces, and not say electricity and gravity, or some other pair.

Mike W.

(published on 08/23/2011)

## Follow-Up #15: Gravity is NOT magnetism

Q:
Magnet and gravity r the same? Does a magnet just have gravity captured inside it? I have not read all of this yet but there is something here. Is gravity created by spinning something and the faster the spin the more gravity there is or resistance on an object, like a motor?
- John hudson (age 48)
Jackson tn USA
A:
If you read the earlier posts, you'll see we say the opposite: gravity and magnetism are very different things. The effect of spinning on gravity is very small. In fact, it was just in the last few months that the Gravity Probe B experiment was able to measure the tiny effects of the Earth's spin on its gravity.

Mike W.

(published on 09/26/2011)

## Follow-Up #16: Hollow earth theory?

Q:
I heard a crazy and strange theory that i have not been able to exactly prove wrong. Its called the Hollow Earth Theory, Theory that there are large holes at each pole and a small star inside our planet with the inside reflecting the planet outside. First off any proof against this i found are just photos of Earth so i looked up a photo of Earth on nasa.gov and it looked doctored. Could just be my eyes but the ice looks offish and slightly off color at the north pole where a giant hole would be. But secondly i was sure gravity had to do with magnetism but it turns out that all studies conducted into gravity can find little to do with magnetism. Instead i heard that it was very similar to the suns gravitational pull. So i guess my question would be than If the Earth was Hollow and a Small Star was truly inside it would the pull of that star be equal or close to the gravity we experience and if so could this change modern theories?
- Marc (age 24)
Lebanon IL
A:
In principle if you had a very dense object at the center of a hollow earth with just the right size and mass you could mimic the earth's gravitational field both at the surface and far away. However, using this model, there is no decent explanation about the internal structure of the earth that could explain all of the geophysical data that exists. For example, the density profile of the interior is well-measured by seismological effects and it would be completely inconsistent with this model.  See for example.

LeeH

(published on 10/30/2011)

## Follow-Up #17: Matter antimatter: attraction or repulsion?

Q:
You said antimatter is attracted to matter, but s it the same deal with antimatter to antimatter? Also, how is the gravity of matter to antimatter tested if when antielectrons and electrons or whatever particle collide, they release a massive amount of energy, equivalent to the energy that can be determined by E=MC^2 mass of the particle?
- Jack Gifford (age 12)
Hanover, Marlyand, America
A:
Hello Jack,
Your question touches on some fundamental aspects of forces in physics.  The four forces we know of: strong, electromagnetic, weak, and gravitational, all have different strengths and characteristics.    The strong force is the one which hold a nucleus together.  It is, by and large, independent of the signs of the electrical charges between them as well as matter-antimatter distinction.  The electromagnetic force on the other hand is different.   An electron will be repelled by another electron but will be attracted by a positron.  Let me skip the weak force for a moment, you can ask later.
Now as to the gravitational force, it is matter-antimatter blind.  All it cares about is the mass or effective mass of the two objects.  It is always attractive.  In any situation you have to add up the separate contributions to find the total force.  So you have to design a careful experiment in order to make sure that one of the other forces is not masking the effect you are trying to measure.
A good question is "why the differences in attraction/repulsion among the forces?"   I once posed this question to our local guru on these matters.  He pursed his lips, thought for quite a while and then said "It's complicated".  It turns out that there are some subtle points in quantum field theory that have to do with the transmitters of the force such as the photon, the gluon or the graviton.  If the transmitter has even spin, like the gluon or graviton, then the force is always attractive.   If the force has odd spin, like the photon, then the sign of the force changes sign,  like electron-electron repulsion and electron-positron attraction.   As he said:  "it's complicated".

LeeH

(published on 12/15/2011)

## Follow-Up #18: Dark energy and dark matter

Q:
Our universe is expanding at an ever increasing rate. This would imply that there is a force, perhaps dark matter, that is "pushing" everything. What if this dark matter is a polar opposite of the gravity force? Is it possible that gravity has poles but the only one experience in our everyday lives is the attractive form of it?
- John W (age 45)
A:
Hello John,

Dark matter actually acts like normal matter and exerts an attractive gravitational force on other forms of matter. It's just that it cannot be seen with our telescopes because it is not giving off light nor is it reflecting light.

The term you're looking for is actually "dark energy". Dark energy is thought to be in all space and accelerates the expansion of the universe. The concept of dark energy came about when the theory of general relativity was used to explain the accelerating expansion of the universe. However, the origin of dark energy is still not known.

As for the question about whether gravity actually has two poles, one attractive and one repulsive, that would require a new theory of gravity, other than Einstein's general theory of relativity. However, no new theories have been established as of yet.

For more information, NASA has done a great job of explaining some of the possible theories behind dark energy on the following webpage:

Maurice

(published on 01/12/2012)

## Follow-Up #19: What are electromagnetic facts?

Q:
Actually I know these facts... The Earth is one big magnet. Electricity is the movement of magnetism. Magnets have a north and south pole because the force of magnetism is flowing from north to the south. The Earth has a north and south pole named so because of the magnetic force flowing through it. As you go toward the north or south pole, you begin to enter greater magnetic forces. The reason we stick to the ground is the same reason why lint sticks to your pant legs in the winter when you get static charge built up. The static charge is a form of magnetism and lint (a totally neutral object) sticks to the pants. Also, the pants stick to your legs, even though a human is also a neutral object. This is the same reason we stick to the Earth. The earth has a great static charge to it (what we call gravity) and we are so small that we just are pulled toward it. When you see lightning in the sky, this is visible evidence that the static is discharging itself (you can do the same thing under your covers at night... just rub around on the blanket and you will get shocks of electricity going). Anyways, I guess my question is... If we spray a bunch of static guard all over our selves, will we fall off the Earth?
- melissa (age 34)
washington, DC, USA
A:
"Actually I know these facts... "

OK, let's look at them.

"The Earth is one big magnet. "  True, the earth is a magnet.

"Electricity is the movement of magnetism. " Huh? Is this a reference to one term in Maxwell's equations? It's sure not anything that represents a standard physics description.

"Magnets have a north and south pole because the force of magnetism is flowing from north to the south." No, there is no such flow. It's not even clear what force you're talking about.

"The Earth has a north and south pole named so because of the magnetic force flowing through it." See above.

"As you go toward the north or south pole, you begin to enter greater magnetic forces." It's true that the field gets stronger near the magnetic poles.

"The reason we stick to the ground is the same reason why lint sticks to your pant legs in the winter when you get static charge built up. " Absolutely false. Gravity affects all objects regardless of their electrical properties.

"The static charge is a form of magnetism..." Totally false.

" and lint (a totally neutral object) sticks to the pants. Also, the pants stick to your legs, even though a human is also a neutral object. " This can happen due to redistribution of charge on the person, but we generally are not "totally neutral". Think of sparks from your finger when you touch a knob on a dry day.

"This is the same reason we stick to the Earth." Nope

"The earth has a great static charge to it (what we call gravity) and we are so small that we just are pulled toward it." If that were true it would repel like-charged things. That doesn't happen. It's complete nonsense.

"When you see lightning in the sky, this is visible evidence that the static is discharging itself (you can do the same thing under your covers at night... just rub around on the blanket and you will get shocks of electricity going). " True! (but not relevant to gravity)

"Anyways, I guess my question is... If we spray a bunch of static guard all over our selves, will we fall off the Earth?"
Seriously? I'd say to try it but some of those static guards may have some toxic chemicals. No need to huff anything more.

Mike W.

(published on 07/30/2012)

## Follow-Up #20: Gravity:magnetism as squid:brick

Q:
How could gravity and magnetism not be closely related if the Earth itself has both? What if "magnetism" is just an overly-simplistic form of gravity? Ed Leedskalnin of "Coral Castle" claimed all objects have a "polarity" opposite the Earth's and that he had managed a way to reverse the polarities, rendering the coral used in the construction weightless and easier for a 5' man to move by himself (legend as it may be). Not all science is fact. The laws of physics prove themselves wrong, especially with the discovery that electrons can be in two places at the same time. Is a relationship between gravity and magnetism possible from a theoretical viewpoint? Is there room for speculation?
- Anthony DeVincent (age 23)
Florida
A:
I've marked your question as a follow-up to many similar ones.

From the little I've read of Leedskalnin he just rambled incoherently.

You ask "How could gravity and magnetism not be closely related if the Earth itself has both?" How could squids and brick not be closely related if the restaurant I'm going to has a brick wall and serves squid?

"the discovery that electrons can be in two places at the same time" is just a confirmation of the physics that has been in use since about 1925. It would be shocking if it weren't true.

And yes, there's always room for speculation, even about that squid-brick relation.`

Mike W.

(published on 04/10/2013)

## Follow-Up #21: Are gravity and magnetism connected?

Q:
Q1) If Gravity and Magnetism are different forces then why does a magnet come to rest aligned with the North and South pole of the earth. Q2) Has there been any study on magnetic forces between to magnets under various gravitational environments (Moon, Space and on Earth).
- Sam D (age 38)
Bangalore, India
A:

1. Take any magnet near a compass magnet and you can see the compass align with the field of the other magnet. The earth is a magnet, so so the same thing happens with the earth when no stronger magnets are near the compass. Yes, the earth also has gravity, as do all other things, but that doesn't logically mean that the magnetism and gravity are the same. The earth's gravitational field has about constant magnitude over the whole surface and always points toward the middle. The magnetic field has different strengths in different places and only points directly up-down at the two magnetic poles.

2. Mars Rovers etc. all have some electric motors on them. These employ magnetic forces to convert electrical energy to mechanical energy. They work just the same in the lower-gravity environments of Mars, the moon, etc.

Mike W.

(published on 07/18/2013)

## Follow-Up #22: magnetism and charge

Q:
This might seem as far fetched science, but is it possible to super charge a magnet by its polarity? Say you were able to beam electrons to the negative side of the magnet and shoot protons to the positive side of the magnet? Would that charge it?
- Jay (age 23)
Los Angeles, CA, USA
A:

Those are electrical charges that you're shooting at the magnet. They will make it (briefly) into an electric dipole, with a plus and a minus end.

There are no known magnetic charges. The magnetic strength won't change.

Mike W.

(published on 07/29/2013)

## Follow-Up #23: philosophy of magnets and gravity

Q:
I know tis may be quite a bit incorrect, but in my defense, my teachers only tell me so much. First off why can gravity not be a giant scaled magnetism, most say it pulls at all directions where as magnetism only pulls the north and south poles. But what if our knowledge of magnetism were wrong and there was much more going on at a subatomic level that correlates to gravity at only a very small level? How do we know that as the smaller things get it becomes even more vast than our universe, and that the world we know it may just be an atom or something of this sort under a microscope? Why do we base all of our knowledge over something that may not be true?
- Caleb (age 14)
Ohio
A:

Q: "Why do we base all of our knowledge over something that may not be true?"

A: What other choice do we have? Those are the rules of the game.

Q:"First off why can gravity not be a giant scaled magnetism, most say it pulls at all directions where as magnetism only pulls the north and south poles. But what if our knowledge of magnetism were wrong and there was much more going on at a subatomic level that correlates to gravity at only a very small level? "

A: Well if magnetism were to mean something completely different from the magnetism we study on scales from the size of the solar system to the size of an atomic nucleus, then sure, it might be anything you want it to be. But since we have a huge set of observations of what we call magnetism that all fit with an extremely tightly defined mathematical theory, why would you take that name and use it for something entirely different?

I couldn't quite follow the other question.

Mike W.

(published on 09/24/2013)

## Follow-Up #24: GUTs and TOEs

Q:
If the existence of the graviton is almost certain, why are there such intense discussions of a Grand Unified Theory (GUT) rather than just solely a Theory of Everything (TOE)? As I understand it, GUTs and TOEs differ primarily in that GUTs don't include gravity and TOEs do. Why then isn't there a "usual" way for incorporating gravity into the standard model? LQG and String theory make so many other proposals, I often can't tell what to think about the graviton or understand how it might relate to the other interactions.
- Ben (age 24)
USA
A:

The possible GUTs, incorporating both the electroweak interaction and the chromodynamic interaction, are in the same general family as the electroweak theory. It's generally assumed (but not guaranteed) that the correct GUT will be a quantum field theory on the standard 4-D spacetime of special relativity. Thus it may well be possible to complete the GUT program without worrying about quantum gravity.

Although gravitons should be present in any quantum theory of gravity, they represent a low-energy limiting behavior in a nearly flat patch of spacetime. The heart of a quantum theory of gravity would have to include the regime of the Planck energy scale, not just the low-energy regime. Trying to cope with that involves the theories that you mention (Strings or Loop Quantum Gravity), well beyond the sort of modifications of the Standard Model considered in typical GUTs.(also well beyond my understanding)  Approaches to quantum gravity via more familiar methods lead to all sorts of infinities.

Mike W.

(published on 09/28/2013)

## Follow-Up #25: has Earth's gravity changed?

Q:
with grafity are we able to prove it has been a constant for as long as the earth has been here, or has the earth sped up creating more gravity. as a common thinker it makes me wonder if this has happened within the last 100 million years. as dinosaurs we very heavy, could there have been less gravity or more over the life of the planet and has gravity been increasing or decreasing causing other changes
- ken (age 55)
A:

We are quite sure that the Earth's gravity has been nearly constant. There are numerous lines of evidence to support that. The overall strength of the gravitational attraction in the universe can't have changed much, because galactic clustering, the details of the cosmic microwave background, etc. fit a model in which the strength of gravity is precisely constant. So the only way the Earth's gravity would have changed is via changing mass of the Earth.  We know of no process that could have changed the Earth's mass much since whatever event happened that formed the Moon. Any event like that would have left enormous geological traces. Furthermore the Moon's orbital period, strongly sensitive to the Earth's gravity, has only gradually changed, in the way expected for tidal effects from constant gravity.

This raises the issue of why some dinosaurs could have been larger than any present-day land animals. Maybe one of our biologist colleagues can add something here.

Mike W.

(published on 09/28/2013)

## Follow-Up #26: mass of magnetic fields

Q:
Does strong magnetic fields have measurable mass. ie does a very strong electro magnet weight more when it's turned on than when it's not? Are Photons effected by strong Magnetic fields ie refracted or bend in the same manner that Einstein proved that the Gravity of the sun bent the light from from distant stars?
- Anthony Giraud (age 40)
Kimball
A:

I've combined your two questions and put them in a thread with related questions.

The extra mass of the magnetic field of a lab magnet is very small. For a powerful and fairly large superconducting magnet it would be in the neighborhood of 10-8 gm, very small compared to the ordinary mass of the magnet. I don't think anyone has been able to measure it.

As we've said before, the field energy plays the same role as any other mass as a source of gravity.

Mike W.

(published on 11/26/2013)

## Follow-Up #27: magnetizing steel

Q:
Using ferrite ring magnets,when like poles are placed together,with a piece of mild steel plate of the same inside and outside diameters as the magnets,is placed between them,and the plate thickness is of the right thickness as to cause the two magnets to nearly totally lose their attractive powers,why is the magnetic field/ mass in the m/steel plate so very strong?
- Bert Holland (age 59)
Cairns, Australia
A:

Pure iron has strongly magnetized domains. Some steels (not stainless) are fairly close to being as magnetic. The reason that you don't see permanent magnets made out of such iron is not the lack of magnetism but the lack of permanence. (I believe that the domains in iron have bigger fields than those in the ferrite.) It's easy for the iron's magnetism to change directions. Left to themselves, neighboring domains in normal-shaped iron samples will line up to cancel the average large-scale magnetism, because that lowers the magnetic energy. In the presence of an external field, these domains can line up to make a very strong magnet.

Mike W.

(published on 01/28/2015)

## Follow-Up #28: Is gravity due to spinning?

Q:
We are all attracted towards the centre of the Earth as it's centre of mass lies there. However, are we attracted to the centre because of a centripetal force caused by Earth's rotation? Is gravity the centripetal force? Please do explain also how artificial gravity is produced ?
- Asher (age 19)
India
A:

No, but there is a connection. The gravity depends on 3 different components. The most important one is the force between two objects just because they have mass. This is proportional to the mass of both of the objects, and was formulated as early as 18th century by Newton. Rotation of the Earth is irrelevant for this. So the oak trees in the local park also attract you, but this is force is very small for typical size objects that most of the time they are unnoticable - i.e. if you feel a temptation to go outside, it is definitely the weather not the gravity. This pulls you towards the center, the reason why we take the center for this gravity purposes you can read .

Now, there is the inertial property of mass, which says they tend to preserve their state of motion forever. But the fact that Earth rotates confuses the observations made by us, who rotate by the Earth. The objects seem to deviate from their trajectories due to some extra forces, but in reality they do not "feel" any force. There are two such fictitious forces, one is the centrifugal force that you mentioned which pulls the objects radially outwards from the rotation axis. The other one is the Coriolis force, which causes objects to deviate from their linear trajectories and trace curves (as in the oceanic currents). Both its magnitude and direction depends on the velocity of the object of interest, and is 0 for stationary objects. So the force on the object that you measure is the vector sum of all those three, the former being by far the dominant term.

An easy answer for your third question should now be obvious: you could accelerate (decelerate) the system linearly to exploit the inertia, in which case you will feel a force backwards (forwards). But a more practical way is to rotate around a point, in which case the "gravity" will be radially outwards. There is a more exciting was of doing this by magnetism, but is mostly good for small objects because it requires extremely high field magnitudes.

Tunc

(published on 03/10/2015)

## Follow-Up #29: black hole gravity and magnetism

Q:
This is not a question but more a statement and answer to some of the curiosities being asked. Actually, in a since, there is a specific relationship between gravity and magnetism. Gravity is due to a warp in the fabric of space time. This is a documented fact of Einstein's theory or relativity. This warp is what pulls things in. The greater the mass, the greater the warp and greater the gravity. And in turn, the greater the mass, the greater the magnetism. They are not the same but they work together. I might also add that you do not need a giant size mass to have a giant size warp in the fabric of space time and a giant magnetic field. You can have a great amount of mass in a small space that will generate both. This is the black hole. Matter is pulled in at great amounts into a small space. The warp in the space time fabric becomes greater and so does the magnetism. You do not need to see this effect, it can be felt. There will be a very strong gravity and a very strong magnetic field in the presence of a black hole. So, in a since, there is a specific relationship between gravity and magnetism.
- Gary (age 58)
Aberdeen, MD USA
A:

The sort of black holes we "see" are typically almost electrically neutral (https://en.wikipedia.org/wiki/Charged_black_hole) and not spinning all that much and thus they are not very magnetic. The very strong magnetic effects found near some black holes (http://blogs.scientificamerican.com/dark-star-diaries/confirmed-black-holes-are-magnetism-powered-eating-machines/) come from the things that are getting sucked in and pulled apart. So there are cases where gravity and magnetism are both strong, but there are also cases where there's gravity and no magnetism or magnetism and very little gravity. So there are circumstances where they're related, as for more or less any two effects in nature, but no special relation.

Mike W.

(published on 02/04/2016)

## Follow-Up #30: gravitomagnetism

Q:
I have been following this thread about Gravity vs Magnetism for years and would like to thank you for your efforts in trying to explain a complex subject. There have been numerous question where people instinctively see a relationship between these two forces, but it has been repeatedly explained they are fundamentally different forces with different characteristics. If Gravity and Magnetism (specifically Electromagnetism) are not the same force what purpose of Gravity Probe B's experiments, Gravitoelectromagnetism (GEM) and attempts to unify them mathematically. https://en.wikipedia.org/wiki/Gravitoelectromagnetismhttp://www.jmess.org/wp-content/uploads/2016/07/JMESSP13420148.pdfhttp://adsabs.harvard.edu/full/1995Ap%26SS.227..133BThank you in advance!
- Gary (age 47)
Los Angeles, CA
A:

Gravitomagnetism is like magnetism in one way and unlike it in another. It's like magnetism in that it's a necessary consequence of incorporating gravity into a relativistic framework, where distances and time intervals are dependent on fthe observer's motion. The math in getting gravitomagnetism from gravity is essentially the same as that involved in deriving magnetism from electrostatics +Special Relativity.

So the analagy is

gravitomagnetism is to gravity
as
magnetism is to static electricity.

The difference between gravitomagnetism (barely detectable here by delicate measurements) and magnetism (easily detctable by anybody) flows from the very big differences between gravity and electricity.

Mike W.

(published on 08/09/2017)