The Center of the Earth and Black holes and Gravity

[Bandersnatch]

The question doesn't arise if they distribute the force of gravity or calculate it, it is why. I know this is how it is, but if all atoms generate their gravitation potential towards their center of mass, why would it change their gravitational energy from the center of an atom to the center of a larger gravitational body. Even if each atom still possesses their gravitational pull (I'm guessing they still do) and it's still exerted on the atoms, why would gravitational energy be stronger at the center of larger masses? An atom itself would have limited gravitational energy but compared to larger objects their gravitational pull is stronger. What would cause it to change?

Of course every massive particle still keeps on attracting every other bit of mass. The attraction towards the centre of mass is the net effect of adding all the forces. It's a mathematical "trick", for the lack of a better word, in the same category as adding two equal and opposite forces nets you a 0 even though the two forces never dissapear.

It's not that hard to understand intuitively - if you stand on a sphere of massive particles (a planet, say), the particles right under your feet are exerting a large (relatively speaking) force on you because they're close and gravity falls with distance, and for the same reason the particles farther away are exerting smaller and smaller attraction.

But at the same time the farther you look under your feet, the more massive particles there are to pull you in. If you add the effects from all the particles in the sphere, you find out that the total attraction is exactly the same as if you were attracted by a single particle containing all the mass residing in the centre of the sphere.

Mathematically, this is shown here:
http://en.wikipedia.org/wiki/Shell_theorem
You might need to brush up on some calculus to understand what's going on. The net is full of other explanations, as the theorem is as old as Newton.

 

[Firedog89]

At the center of the Earth, a particle cannot contain the same amount of mass as say the total masses of the sphere. At the center, all the masses will be above you. Therefore, you should be attracted to the masses that are above you so in effect (you should be branded away from directly at the center of Earth). If you are attracted directly to the center of gravity if the center of gravity relies at the direct center of the Earth, there must be force pulling you toward the center... if the force of gravity is 0... then there should be a cancelling out of gravity to net you 0 in the first place. All the opposite forces should equal a net of 0 as you say. What will bridge the connotation to equal 0? Mathematically everything makes sense but the problem is; if there is an equal and opposite force to almost everything and gravity's force is only attractive, then you should be still attracted completely to the source. If the force of gravity isn't completely attractive, then you can have equal and opposite gravitational forces to lead to a net of 0. Simply, -1G's+1G's=0G's. Therefore, simple math is applied to get total net 0 gravitational pull at the center of gravity. The key term center of gravity implies that there should be a singular point directly at the center of gravity (center of the Earth). Something must diverge the possibility that nets gravity to 0.

Even if the masses above you can generate enough gravity for your mass to be pulled off center from the Earth, then there is still a singular point of gravity that pulls you toward any mass. If there is concentration of atoms that implicitly pulls you toward the groupings of the atoms center of gravity, then there still procure a singular point of gravity even if it was a concentration of atoms.

This may be a bit confusing to explain and I'm also implying that none of this is true just speculation.

 

[Drakkith]

This may be a bit confusing to explain and I'm also implying that none of this is true just speculation.

You're right, it is confusing. I suggest simplifying the discussion to the basics of gravity and starting over from there.

 

[PeterDonis]

At the center, all the masses will be above you. Therefore, you should be attracted to the masses that are above you so in effect (you should be branded away from directly at the center of Earth).

If you were at the center of the Earth, all the masses above you would be attracting you; but they would be doing so equally in all directions (we are idealizing the Earth to be perfectly spherically symmetrical so all the masses above you are symmetrically distributed), so all the forces would cancel out, and you would feel zero net force.

If you are attracted directly to the center of gravity if the center of gravity relies at the direct center of the Earth, there must be force pulling you toward the center... if the force of gravity is 0... then there should be a cancelling out of gravity to net you 0 in the first place.

At the center of the Earth, there is. See above.

If the force of gravity isn't completely attractive, then you can have equal and opposite gravitational forces to lead to a net of 0.

You can, because "attractive" is not the same as "always in the same direction". Gravitational force is a vector, not a number; the force of attraction caused by a particular piece of matter points toward that piece of matter. Different pieces of matter in different directions from you will cause forces that point in different directions, and they add as vectors, so they can cancel each other out; if the forces point symmetrically in all directions, then they all cancel out.

 

[Firedog89]

If you were at the center of the Earth, all the masses above you would be attracting you; but they would be doing so equally in all directions (we are idealizing the Earth to be perfectly spherically symmetrical so all the masses above you are symmetrically distributed), so all the forces would cancel out, and you would feel zero net force.

ohhh ...I see it now. gravity will keep you interacted in all directions. So, therefore, you will feel the effect of net 0 force... Let's say you look at just one atom in a theoretical universe with just you imagined smaller than the atom and this particular atom. You will feel the effect of gravity very minimally of course. Where would the effect of gravity be located? Let's say it is at the center. What are the interactions? Would the effect of gravity be relevant to open spaces added up equally or is there a particle or object responsible for it?

 

[PeterDonis]

Where would the effect of gravity be located?

An atom is not a single object--it has a nucleus and electrons. The nucleus and each electron all, in principle, are sources of gravity. Note that we are imagining the atom as like a miniature solar system here--in other words, we are ignoring quantum effects, which for a real atom are much, much larger than gravity. A better example might be the actual solar system: where is the gravity of the solar system located? There isn't a single source of gravity; the Sun is the biggest, but not the only one.

Would the effect of gravity be relevant to open spaces added up equally

I'm not sure what this means.

is there a particle or object responsible for it?

Anything that has mass or energy is a source of gravity. Of course, it takes a lot of mass or energy for the source to be significant.

 

[Firedog89]

Anything that has mass or energy is a source of gravity. Of course, it takes a lot of mass or energy for the source to be significant.

An atom has mass. I don't know about if energy is required to have gravity. Gravity is a source of potential energy. It is already energy. One of the 4 states of energy. While looking at the solar system you can recognize gravity. That doesn't mean that gravity cannot be looked in on smaller scales. For reasons unknown there should be a reason why gravity exist. Just like atoms have particles like gluons, guons, sluons (just naming random names), maybe one of these particles is responsible for the attraction of gravity. If I dig deeper, maybe it's not the particles themselves that exhibit gravity, maybe it's the open places between these particles that exhibit gravity.

While the nucleus can be responsible for gravity, I don't see how electrons can be. The attraction of the proton and electron is a source of electromagnetic energy. If an electron has mas that ma qualify it to contain gravity as well. Gravity is attractive so where would any mass be attracted to the electron? If we dig deeper into the electron, proton, or nucleus, where would the exhibition of gravity be located? Or is it just a force that is, completely gratified from the spaces in the particle. Which particle would be said to have no mass at all? Or even sub-particles tend to have mass as well?

 

[PeterDonis]

I don't know about if energy is required to have gravity.

I do; it is. General relativity is quite clear on this point, and its predictions in this regard have been verified by experiments.

Gravity is a source of potential energy. It is already energy.

No, it isn't. First, the concept of "gravitational potential energy" is problematic in GR, for reasons which are probably too involved to get into here. Second, again, GR is quite clear about drawing a distinction between "gravity"--more precisely, spacetime curvature--and its source, which includes, as I said, anything with mass or energy, but also includes momentum, pressure, and other stresses--the full source is expressed mathematically by an object called the "stress-energy tensor", and there is nothing representing gravity in the stress-energy tensor; everything about gravity (spacetime curvature) is contained in a different object called the Riemann curvature tensor.

One of the 4 states of energy.

I don't know what you mean by this.

While looking at the solar system you can recognize gravity. That doesn't mean that gravity cannot be looked in on smaller scales.

Of course not. But on smaller scales, with smaller objects acting as a source, gravity is a lot weaker, so it's harder to measure. We can measure the gravity of ordinary objects like lead weights by using sensitive devices. But we can't measure the gravity of individual atoms; they're too small and their gravity is too weak.

maybe one of these particles is responsible for the attraction of gravity.

Our best current belief is that there is such a particle; it's called the graviton, and it mediates the gravitational interaction in the same way as the photon mediates the electromagnetic interaction, gluons mediate the strong interaction, and the W and Z bosons mediate the weak interaction. However, all of this about particles mediating interactions comes from quantum field theory, and while we have directly measured the quantum nature of the other three interactions, we haven't done that with gravity. As far as we can tell, that is because gravity is so much weaker than the other interactions that we can't do experiments sensitive enough to reveal its quantum aspects.

If I dig deeper, maybe it's not the particles themselves that exhibit gravity, maybe it's the open places between these particles that exhibit gravity.

I'm not sure what you mean by this either, but it looks to me like pure speculation. I think you would be better off not engaging in such speculation until you know a lot more about what we already know about gravity and the other interactions.

While the nucleus can be responsible for gravity, I don't see how electrons can be.

I don't see why you don't see this. Electrons have mass just like the nucleus does; their mass has been measured very accurately. So, like anything else with mass, they produce gravity. Of course, as I said above, the gravity of an individual electron, just like the gravity of an individual nucleus, is far too weak for us to measure. But the electrons contained in the atoms in the Earth, for example, make up a small part of the mass of the Earth, so they contribute to the Earth's gravity.

If we dig deeper into the electron, proton, or nucleus, where would the exhibition of gravity be located?

I'm not sure what you mean by this either. Suppose we could do experiments that probed an electron or nucleus down to as small a distance scale as you like. What sort of experimental results would you be looking for to show you where "the exhibition of gravity" is located?

 

[Firedog89]

I don't know what you mean by this.

The 4 forces nature.

I'm not sure what you mean by this either. Suppose we could do experiments that probed an electron or nucleus down to as small a distance scale as you like. What sort of experimental results would you be looking for to show you where "the exhibition of gravity" is located?

Have we been able to single out the graviton? Or is the graviton just a theory?

I understand that the electron can produce gravity because it has mass. You are right, It is pure speculation. I know it would be weak on the molecular basis. Gravity just seems to come out of nowhere. It doesn't seem to form based on any interactions only increase and decrease by mass. It just seems to be a force that just is.

 

[PeterDonis]

The 4 forces nature.

Ok. "States of energy" does not seem like a good term for this; "fundamental interactions" would be a better one.

Have we been able to single out the graviton? Or is the graviton just a theory?

As I said, we are not able to do any experiments that probe the quantum aspects of gravity; we have no way of producing or accessing strong enough gravitational fields to do that.

However, I don't think that means the graviton is "just a theory" either; there are many good reasons to expect gravity to be fundamentally a quantum phenomenon, just like everything else. That's not to say it would be impossible to construct a theory in which gravity was purely classical (no quantum aspect, hence no graviton) and everything else was quantum; but I don't think anyone is seriously pursuing such a theory.

Gravity just seems to come out of nowhere.

If you just mean that we can't observe the graviton, so we can't experimentally verify that gravity arises from particle exchange, you should be aware that we can't observe gluons (the particles that mediate the strong interaction) directly either. In fact, we can't even observe quarks (the particles that make up mesons and nucleons) directly. We can only observe these particles indirectly, by experimenting on the properties of strongly interacting objects that we can directly observe, like mesons and nucleons. So "being able to directly observe the particle mediating the interaction" is not a good criterion to use.

If you mean that gravity only depends on mass, not on any other property of the object, I'm not sure why that's a problem, because every interaction only depends on one property of the object. For electromagnetism, it's electric charge; for the weak interaction, it's weak isospin; for the strong interaction, it's strong "color" charge. Mass (or more precisely stress-energy) is just the "charge" associated with gravity.

If you mean that, unlike the other interactions, there's no way to have an object that does not have the "charge" for gravity (mass-energy), that is indeed a feature unique to gravity. This feature actually helps us to determine what properties the graviton must have, if it exists, since only a particular kind of quantum particle can mediate an interaction with this property.