What is Gravity

[tonyj18]

What do we know about gravity; we know that on earth gravity acts on every object known to us here on earth, nothing escapes the gravitational attraction from Earth's inner core. And if we consider that everything on Earth share the same building blocks (atoms),then the attraction must relate to a part of the atom ;
either the proton, electron or neutron.
Protons carry a positive electrical charge, electrons carry a negative electrical charge and neutrons carry no electrical charge at all. The protons and neutrons cluster together in the central part of the atom, called the nucleus, and the electrons 'orbit' the nucleus. A particular atom will have the same number of protons and electrons and most atoms have at least as many neutrons as protons.

Protons and neutrons are both composed of other particles called quarks and gluons. Protons contain two 'up' quarks and one 'down' quark while neutrons contain one 'up' quark and two 'down' quarks. The gluons are responsible for binding the quarks to one another.

It is possible that every atom on earth also produces Gravity and is attracted to other atoms is the same way ,such as us, are we producing gravity but only on a small scale, not enough to be affected by the greater gravitational force produced at the earths inner core.

So what could this inner core consist of ,to produce a superior gravitational force, I would suggest that it could consist of anything, but the only overriding requirement is that it is immensely dense, i.e. well compacted almost like a small 'black hole" but visible.
So you would in effect have a huge amount of Atoms compressed into a small space, but producing a superior gravitation force that is attracting every other atom on the earth surface.
This would explain why other objects in space produce gravity, but they don't necessarily have to share the same material make up, in essence they could be made of any type of material ,but it needs to be very dense.

And this may be directly related to the spherical shape of the planets, stars etc , their inner cores are immensely dense and radiating out a combine gravitational force that would supersede any object of a lesser density on the surface.

I would be interested to know your thoughts mainly on the nature of gravity ,specifically on what you think it actually is.

[Greg H.]

Actually things escape the earth's gravity all the time - we call them rockets. Acouple of them have even escaped the sun's gravity and are currently burrowing into interstellar space.

[tonyj18]

Yes I agreed, I was not commenting on the specific gravitational force that earth creates, it is easily overcome, as you say ,and earth gravity has a limited range, this is more about what specifically is gravity or what causes gravity

[swansont]

What do we know about gravity; we know that on earth gravity acts on every object known to us here on earth, nothing escapes the gravitational attraction from Earth's inner core. And if we consider that everything on Earth share the same building blocks (atoms),then the attraction must relate to a part of the atom ;

either the proton, electron or neutron.

 

 

Light is affected by gravity, and is not part of an atom.

Yes I agreed, I was not commenting on the specific gravitational force that earth creates, it is easily overcome, as you say ,and earth gravity has a limited range, this is more about what specifically is gravity or what causes gravity

 

Theory tells us that gravity has an infinite range, and there is a lot of confirmation for the theory.

[Endy0816]

I'd advise a good bit of reading rather than further speculation.

 

If you really want an answer then "curvature of space-time" is the best one we have at present.

[tonyj18]

I think we are getting slightly off topic, light is affected by gravity but in a slightly different way

" Albert Einstein. In 1915 he proposed the theory of general relativity. General relativity explained, in a consistent way, how gravity affects light. We now knew that while photons have no mass, they do possess momentum . We also knew that photons are affected by gravitational fields not because photons have mass, but because gravitational fields (in particular, strong gravitational fields) change the shape of space-time. The photons are responding to the curvature in space-time, not directly to the gravitational field. Space-time is the four-dimensional "space" we live in -- there are 3 spatial dimensions (think of X,Y, and Z) and one time dimension.

 

I was more interested at the nature of gravity.

[swansont]

I think we are getting slightly off topic, light is affected by gravity but in a slightly different way

" Albert Einstein. In 1915 he proposed the theory of general relativity. General relativity explained, in a consistent way, how gravity affects light. We now knew that while photons have no mass, they do possess momentum . We also knew that photons are affected by gravitational fields not because photons have mass, but because gravitational fields (in particular, strong gravitational fields) change the shape of space-time. The photons are responding to the curvature in space-time, not directly to the gravitational field. Space-time is the four-dimensional "space" we live in -- there are 3 spatial dimensions (think of X,Y, and Z) and one time dimension.

 

I was more interested at the nature of gravity.

 

You have to acknowledge how it behaves. That it affects more than just the components of an atom tells us something about it.

[tonyj18]

I accept Albert's explanation that gravity its not directly affecting light, but that light is following the curvature in space time, so light be the one exception to the rule.

[swansont]

I accept Albert's explanation that gravity its not directly affecting light, but that light is following the curvature in space time, so light be the one exception to the rule.

 

I think you misunderstand. According to relativity, curvature of spacetime is gravity.

[imatfaal]

tony's quote is from Nasa http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/961102.html but in my limited knowledge I do not really like their take on GR

Enter Albert Einstein. In 1915 he proposed the theory of general relativity. General relativity explained, in a consistent way, how gravity affects light. We now knew that while photons have no mass, they do possess momentum (so your statement about light not affecting matter is incorrect). We also knew that photons are affected by gravitational fields not because photons have mass, but because gravitational fields (in particular, strong gravitational fields) change the shape of space-time. The photons are responding to the curvature in space-time, not directly to the gravitational field. Space-time is the four-dimensional "space" we live in -- there are 3 spatial dimensions (think of X,Y, and Z) and one time dimension.

 

This seems to give the impression - that I believe tony has taken notice of - that GR does talks of gravitational fields separate from spacetime curvature ; this I think is incorrect. The phrases "in particular, strong gravitational fields" and "responding to the curvature in space-time, not directly to the gravitational field" strike me as being contrary to the idea of GR that gravity is merely, completely, only (etc) the curvature of spacetime (as I have just noticed swansont just wrote above). There is no mechanism for gravity other than the curvature of 4 d spacetime.

[tonyj18]

point taken, but I am not sure this explains what gravity is, but would I be correct is saying, it explains one theory as to how gravity could work .

[pzkpfw]

tonyj18, to take a couple of steps back, to your OP:

It's already thought that every atom has a Gravitational effect. Every atom in your body is "attracting" every atom in the Earth. If you step off a ledge and fall down to Earth, it's also falling up to you. (Just, you know, it moves much less).

Your talk of "inner core" seems to imply you think Earths gravity all "comes from" the centre. That's not quite true, it's "coming from" all of Earths atoms; it's just convienient in most cases to assume it all originates from the centre of mass. Example: as you go deep under ground, you'll experience less acceleration from Gravity, as more of Earth is above you and less below. Example: the "attraction" of a nearby mountain can and has been measured.

 

After that, I don't really understand your leap to an "explanation" of gravity.

[ajb]

point taken, but I am not sure this explains what gravity is, but would I be correct is saying, it explains one theory as to how gravity could work.

Welcome to the world of theoretical physics.

 

The aim is to mathematically model the phenomena of nature, thinking about what something is lies more in the realm of philosophy than science.

This seems to give the impression - that I believe tony has taken notice of - that GR does talks of gravitational fields separate from spacetime curvature ; this I think is incorrect. The phrases "in particular, strong gravitational fields" and "responding to the curvature in space-time, not directly to the gravitational field" strike me as being contrary to the idea of GR that gravity is merely, completely, only (etc) the curvature of spacetime (as I have just noticed swansont just wrote above). There is no mechanism for gravity other than the curvature of 4 d spacetime.

You can have theories that phenomenologically identical to GR but we have just torsion and not curvature or a bit of both. But this is probably off topic here.

 

You are right that we see gravity as space-time curvature, but when we speak of the gravitational field one maybe talking about the connection or metric or something equivalent to that like vierbein and spin connections etc. These are the things that are fields in the field equations.

[tonyj18]

Thanks Mike, nice to finally see someone who has been developing their own theory ,most of the other postings are just quotes from historical theories from Newton and Einstein and the more recent non-relativistic gravitational calculations ,which still doesn't explain the nature of gravity specifically here on earth and what is actually is and where it emulates from.

I was hoping this forum you encourage people like your self to put forward you theories, and we seem to be getting somewhere and maybe collectively we can discover or deduce how it occurs.

 

I would like to know your thoughts of what I can understand so far.

Gravity appears to be strong enough to attract all objects downwards towards the centre of the planet ,regardless of my position above or below sea level the overwhelming attraction is downwards.

It also appears as though gravity does not depend on mass ,if I was to place a small object on the ground beside Mt Everest, I would not observe the object been drawn sideways to the mountain, it would continue to be drawn down towards the centre of the earth.

There may be a infinitely small attraction sideways but for this discussion lets ignore this.

Someone also suggested how can you be certain its the centre of the earth, but it you were to examine core samples taken from the earth ,you can see the upper most layers are less compacted than the deepest layers because gravity is pulling continually pulling downwards compacting the deepest layers as the weight of the upper layers pushes down on them.

So I am suggesting if Gravity does not really depend on the mass or size of the object then it must be dependant on the density of the object, the density of the inner core must be incredibly superior to anything we have seen to date.

Their must be some many atoms compacted into a tiny space, that is producing a superior gravitation attraction that all objects above it ,are drawn down to it regardless of their mass.

 

I don't believe that this gravitational matter needs to be of the same composition for every planet ,moon ,star ,because it would be silly to think every other planet etc. share the same composition as the earth, but it is probable that they formed in a similar manner and have at their centre a hugely dense mass producing a similar gravitational attraction and this would be proportional to the size of the object, so Isaac's mathematically equations still apply.

[pwagen]

Someone also suggested how can you be certain its the centre of the earth, but it you were to examine core samples taken from the earth ,you can see the upper most layers are less compacted than the deepest layers because gravity is pulling continually pulling downwards compacting the deepest layers as the weight of the upper layers pushes down on them.

The other option would be that gravity "pulls" towards somewhere that is not the center of Earth (or rather, Earth's center of gravity). Are you suggesting that?

 

So I am suggesting if Gravity does not really depend on the mass or size of the object then it must be dependant on the density of the object, the density of the inner core must be incredibly superior to anything we have seen to date.

Do you have any reason to believe the pull of gravity is not dependent on mass? If so, what would show that to be the case? Also, if gravity depends on the density of the core, how did the core get there in the first place?

 

I don't believe that this gravitational matter needs to be of the same composition for every planet ,moon ,star

Atoms, yes.

 

,because it would be silly to think every other planet etc. share the same composition as the earth, but it is probable that they formed in a similar manner

and have at their centre a hugely dense mass producing a similar gravitational attraction and this would be proportional to the size of the object, so Isaac's mathematically equations still apply.

Again, is the more compact core a result of gravity, or the cause of it?

[tonyj18]

The inner core I suspect is extremely compact due to the weight of everything above it, so I imagine this would have evolved slowly over time, initially the gravitation pull would have be less towards the centre, but as the earth formed and the layers of earth grew and developed it would have become more and more compact and gravitation would have increased, perhaps...........

I am quite convinced the mass is not as important and the density ,I guess one extreme example is a black hole, not really a good example.

[hypervalent_iodine]

!

Moderator Note

Mike Smith Cosmos,

 

Please do not hijack threads with your own hypotheses. If you wish to discuss your own ideas, you are welcome to start your own thread (if you do not already have one). I have split your post and the reply into the trash.

[pzkpfw]

The inner core I suspect is extremely compact due to the weight of everything above it, so I imagine this would have evolved slowly over time, initially the gravitation pull would have be less towards the centre, but as the earth formed and the layers of earth grew and developed it would have become more and more compact and gravitation would have increased, perhaps...........

I am quite convinced the mass is not as important and the density ,I guess one extreme example is a black hole, not really a good example.

 

Density is important in a way, but gravity is well understood as an effect of mass.

 

If Dr Evil shot the Sun with a shrinking ray, so all its mass were compressed until it became a black hole - Earth would still orbit it the same way (same distance) it does now. The density has no effect on how "much" Gravity Earth feels from the Sun. (Especially at this distance, where we can calculate gravitational effects as being from the centre of mass).

 

The difference would be as you get closer: if the Sun were compressed enough it could become black hole, where it would be possible to get so close you couldn't escape. That even applies to Earth. Right now we can stand - and even jump a little ... because we are far enough away from it's centre of mass. But if the mass of Earth were compressed enough (essentially, by magic, same mass but smaller radius), then standing on the "surface" we'd be squashed by the gravity - even to the point where (again, this would take magic) Earth became a black hole.

 

This is quite different to digging down into Earth in its current un-compressed state. As we dig down, some of the mass is above us instead of below, so we'd actually feel less and less gravity.

[swansont]

 

It also appears as though gravity does not depend on mass ,if I was to place a small object on the ground beside Mt Everest, I would not observe the object been drawn sideways to the mountain, it would continue to be drawn down towards the centre of the earth.

There may be a infinitely small attraction sideways but for this discussion lets ignore this.

 

 

You can't do this. Small is not the same as nonexistent. The effect is predicted to be small because the masses are small, but you can't then dismiss or ignore it for being small.

 

We have fairly precise maps of gravity of the earth and it's not uniform — it depends on the mass distribution. You can try to recast this as density, but density is also mass dependent; claiming that gravity doesn't depend on mass implies that you are saying that it's independent of mass, and that's clearly false. An equation that uses density isn't going to be as elegant — mass works better.

[Sensei]

It also appears as though gravity does not depend on mass ,if I was to place a small object on the ground beside Mt Everest, I would not observe the object been drawn sideways to the mountain, it would continue to be drawn down towards the centre of the earth.

 

If you would place Mt Everest in cosmic space (or find equivalent mass asteroid) where influence of other objects and planets would be negligible, you would see that it's attracting our spacecrafts. It already happened.

http://www.nytimes.com/2000/02/15/us/spacecraft-is-orbiting-asteroid-a-first-for-a-man-made-satellite.html

Edited March 7, 2014 by Sensei

[tonyj18]

Yes point taken swansont , what if we were to look at the mass of two objects and give then a volume of 100 kilograms and 100 m3 each ,and for argument sake say that this would equate to 980newton's .

And if we were to take one of the objects and compress it into an area of 10 m3 ,their gravity would be the same, but if I was to add another 90 m3 of similar compressed particles to achieve the same 100 m3 of space, then this object should produce a superior gravitational force to the first object .

What if at the centre of the earth or near to it we have matter that has been compressed by 1,000,000 into a much more compressed/denser object that is able to emit an overriding gravitation force that predominates over other objects, this doesn't exclude other objects on earth each having their own gravitation attraction to each other, but the overriding influence is pulling objects down the this central object.

This object doesn't need to be a perfect ball, it could resemble the gravitational maps we see showing a distorted earth surface and variations in gravity depending on where you are standing on the earth's surface

[pwagen]

Saturn has a lower density than water. Earth has the highest density of all the planets. According to what you propose, Saturn wouldn't have even close to the same gravity as Earth. However, both planets' gravity is consistent with gravity being dependent on mass, not density. How does that fit with your hypothesis?

[swansont]

Yes point taken swansont , what if we were to look at the mass of two objects and give then a volume of 100 kilograms and 100 m3 each ,and for argument sake say that this would equate to 980newton's .

And if we were to take one of the objects and compress it into an area of 10 m3 ,their gravity would be the same, but if I was to add another 90 m3 of similar compressed particles to achieve the same 100 m3 of space, then this object should produce a superior gravitational force to the first object .

What if at the centre of the earth or near to it we have matter that has been compressed by 1,000,000 into a much more compressed/denser object that is able to emit an overriding gravitation force that predominates over other objects, this doesn't exclude other objects on earth each having their own gravitation attraction to each other, but the overriding influence is pulling objects down the this central object.

This object doesn't need to be a perfect ball, it could resemble the gravitational maps we see showing a distorted earth surface and variations in gravity depending on where you are standing on the earth's surface

 

Gravity doesn't get divided up as your description here suggests. If I have mass A and mass B sitting on or above the earth, whether A attracts B has no effect on the earth attracting either of them, and by how much. All I care about are the two masses that show up in Newton's gravitation equation. It tells us the force that one object exerts on one other object.

 

The overriding influence is the earth because the mass of the earth is really big. That's all there is to it. "Overriding" means big. Small does not mean nonexistent.

[tonyj18]

I believe Saturn's radius is approx 58,232 km and it's gravity 10.44 m/s2

earths radius is approx 6,371 km and its gravity 9.78 m/s2 ,do you see the problem with gravity being dependant on mass alone?

[pwagen]

Density of Earth: 5.51 g per cubic centimeter

Density of Saturn: 0.687 g per cubic centimeter

 

Earth has a density 8 times as high as Saturn. So why isn't Earth's gravitational pull 8 times higher?

 

Edit: Just did some quick math, which anyone can check for me. But since I recall the 10.44 m/s2 figure would be when measured on the surface of Saturn, which is much further away from the planet's center of gravity, I think it would only be fair to see what the gravitational pull would be on Earth, at the same distance.

 

Saturn's radius is something like 60268000 m, and Earth's mass is about 5.97219 * 10^24.

 

So F = Gm1m2/r^2 gives 6.67*10^-11 * 5.97219 * 10^24 / 60268000^2 = 0.11.

 

So, at equal distance from the gravitational center, more mass = more pull.

Edited March 7, 2014 by pwagen