Understanding the Mechanics of Gravity: How and Why It Works

[Ryan Lucas]

In school we are taught that gravity is a force of attraction between two bodies. This is very vague, and it bothers me that a broader knowledge of gravity is not "common knowledge". Could someone please explain in deatail the mechanics of gravity, how and why it works?

"If an apple falls, does the moon also fall"
Isaac Newton

 

[Ryan Lucas]

Let me add to this. Why do possitive and negative attract? I know they do, but exactly why, and how eludes me. This relates to sub atomic particles and also much larger models. I am very curious to know, so please write back.

 

[HallsofIvy]

I'm afraid you aren't going to get a lot here. While there are some fairly deep theories (General relativity) that suggest mechanisms for gravity, I doubt that anyone can give an elementary explanation.

(Newton himself, in his theory of gravity, talking about HOW gravity works, wrote "hypothesi non fengo" (I frame no hypotheses).

 

[Ryan Lucas]

M, this is very interesting, HallsofIvy. is the same true for positive and negative charges? Is the mechanism for this known?

 

[Danger]

M, this is very interesting, HallsofIvy. is the same true for positive and negative charges? Is the mechanism for this known?

I'm not meaning to intrude upon HallsofIvy's turf, because he is far more knowledgeabe than I, but I notice that he hasn't yet resonded. Positive and negative charges attract each other simply due to the fact that neither one is in its natural state, and the oppostie will serve to return it to that state. A positively charged particle is missing one or more electrons, whereas a negatively charged one has too many. They take the path of least resistance toward alleviating that situation, which means that they choose to share. If you were referring to magnetic rather than electrical charges, the same basic principle applies, although it seems to manifest itself differently.

 

[whozum]

Its pretty much at "This is the way things are, we know how they work, but we can't tell why."

 

[Danger]

Its pretty much at "This is the way things are, we know how they work, but we can't tell why."

It's a lot more complex than that. I'm not qualified to extrapolate, but the science advisors and mentors and gurus will be able to inundate you with facts at such a rate that it could very well leave your optic nerves in a knot.

 

[whozum]

It's a lot more complex than that. I'm not qualified to extrapolate, but the science advisors and mentors and gurus will be able to inundate you with facts at such a rate that it could very well leave your optic nerves in a knot.

I have a basic idea of what its at, but at the OPs level the explanation is suitable IMO.

 

[Danger]

I have a basic idea of what its at, but at the OPs level the explanation is suitable IMO.

This would appear to be a situation where we should agree to disagree. Admittedly, I never looked at Ryan's bio until your last post, so I had no idea of what age he is or at what level of education. My tendency is to treat everyone as an equal (even those with demonic ancestors). Most are far more knowledgeable than I (I never finished high-school), but some are a bit behind. Regardless of the current knowledge or even intellectual capacity of the questioner, I believe that an attempt at an explanation (as much as I'm capable of) is deserved. Saying that "we don't know" is proper when applied to things that we don't know, but when we do know, it's very equatable to saying 'because' when a child asks why the sky is blue. I always fervently hope that a mentor or at least a Science Advisor will answer, and usually one will. In the meantime, it bothers me to see a question unheeded that I can at least steer toward a proper answer. If nothing else, at least it keeps the thread near the top of the stack so it's more likely to be noticed by someone who can properly help.

 

[Dr.Brain]

Gravity, in short, can be called "distortion in space-time curve caused by a massive object on , as a result of which some other object moves in this curve"

Taking the case of earth, Due to the mass of earth, as per einstein, any type of matter distorts the space-time fabric such that under the influence of distorted
coordinates another object moves in it, and this field or "field of distortion" only depends on the mass which causes the distortion.

SImilarily taking the case of earth, as i sAID IN THE LAST LINE, DUE TO ITS OWN MASS EARTH DISTORTS THE SPACE AROUND IT and as a reults objects on Earth are bound to it.

It is like:

"Matter tells the fabric how to curve, and curved fabric tells matter how to move"

 

[whozum]

Regardless of the current knowledge or even intellectual capacity of the questioner, I believe that an attempt at an explanation (as much as I'm capable of) is deserved. Saying that "we don't know" is proper when applied to things that we don't know, but when we do know, it's very equatable to saying 'because' when a child asks why the sky is blue. I always fervently hope that a mentor or at least a Science Advisor will answer, and usually one will.

People who tell a child 'because' are either too lazy or don't know themselves! Ofcourse I'm not in any position (and no one is) to decide what information is enough for a student, as there is never enough, but to a certain extent, bringing in spacetime and quantum gravity to a sophomore's doorstep would blow his mind. I also want to add that spacetime and quantum gravity do not explain WHY gravity occurs, but are also under the 'how' section of questions. Or maybe the problem is I'm asking the wrong kind of why.

edit: In all honesty, when I first read the thread, I only noticed the OP asking 'why it works', which was the topic of my reply. I now see he is also asking how, for which a proper explanation is justified.

 

[Danger]

People who tell a child 'because' are either too lazy or don't know themselves! I now see he is also asking how, for which a proper explanation is justified.

Also, if you check back, you'll see that I was responding only to the question of charges. Gravity definitely has to be left to experts. The 'charge' thing comes down to a matter of answering as well as I can and hoping that someone smarter comes along soon. If I were to give him bad information about gravity, he might fall off of the Earth before anybody else realizes that he missed by a decimal point.

 

[Anomalous]

...
"Matter tells the fabric how to curve, and curved fabric tells matter how to move"

Now how does that explain the similar pulls of electrics and magnetics ?

 

[Ryan Lucas]

Hey, um, I am not a kid. My uncle is a physics lecturer, my father is a doctor, and I am the biggest science nerd I know, your scientific jargon and terminology is not wasted on my "youthful naivity and incompetence"!
Thanks danger, for the respect, right back at to mate! Your description of ionic particles was very helpful, thanks. However, what about the charge of say, electrons vs. protons? Why do they repel? What are the mechanics behind this.

Thanks Dr. Brain for your help, I suppose gravity can be best described by the analogy of a bowling ball on a trampoline? With the fabric being the fabric of the space-time contiuum?

 

[whozum]

Nobody said you are incompetant nor naive.

 

[dreamfly]

i remember that I've read stephen hawking's <<a brief history of time>>.in the book it mentioned that Gravity works through photon.but i don't know too much about that.

 

[SpaceTiger]

I don't know if this is what you're looking for, but gravity is also an inverse square law (for your purposes). This means that its strength gets weaker by the square of the distance from the pulling object. We don't notice this on Earth because the distance to its center is very large. As far as we can tell in everyday experience, the Earth's gravitational pull is a constant. Also, it turns out that if you combine Newton's Laws of motion with this law of gravitation, you can derive the possible orbits for planets around the sun (ellipses).

 

[Dr.Brain]

Now how does that explain the similar pulls of electrics and magnetics ?

Similarily to Gravitation , the electric charges also distrort the space-time fabric in a way , the only difference is that this distortion is different from that of Gravitational distrortion.Gravitational attraction is caused by matter, similarily the Electrostatic distortion in fabric is caused by charges.

While on the other hand, Magnetic Field , is due to "moving charges", a moving charge has both an electric field and a magnetic field , merged as "Electromagnetic field"

 

[Danger]

what about the charge of say, electrons vs. protons? Why do they repel?

Simply put, they don't. An electron with a particular energy has to remain a certain distance from the nucleus (its 'orbital'). A gain of enough energy (say from collision with a photon), kicks it up one quantum state which is limited to another specific distance farther away. When that energy is released (once again, by spitting out a photon), it will drop a discrete distance. No 'in-between' values are allowed by Planck distance. This is how lasers work, for instance. If an electron is forced into the nucleus, it will merge with a proton and form a neutron. If it encounters a positron instead, they will annihilate each other in a little gamma flash.

I am somewhat curious about something, though. This is an awesome place to find information (I learn something every time I log on), but wouldn't a straight Q&A conversation with your uncle be an easier way to accomplish it?

 

[krab]

Why do they repel? What are the mechanics behind this.

It would be easier to answer you if we knew how you define "mechanics" in this context. Are you looking for some mechanical analog? (Like the bowling ball on the trampoline.) Or do you want a detailed microscopic level answer. If the latter, none will be forthcoming. The thing is, you have some mechanical intuition about bars and pulleys and strings, but at the detailed level, you are no better off than you are with gravity. Worse in fact, since (e.g.) a bar is held together by the very same electrical forces you are enquiring about (but attractive instead of repulsive).

At the fundamental level, we have the facts that charges have electrical forces between them and these force fields obey elegant and simple laws. The same is true of gravity and masses. That's what we know. It's not like a machine where we say Oh! this shaft is turning because it is geared to another shaft, and that one is powered by a chemical explosion, and so on. The electromagnetic and gravitational forces are the end of the line as far as this line of questioning is concerned. At least for now. There are 4 such fundamental forces. See more info here.

 

[icvotria]

In school we are taught that gravity is a force of attraction between two bodies. This is very vague, and it bothers me that a broader knowledge of gravity is not "common knowledge". Could someone please explain in deatail the mechanics of gravity, how and why it works?

"If an apple falls, does the moon also fall"
Isaac Newton

Let me add to this. Why do possitive and negative attract? I know they do, but exactly why, and how eludes me. This relates to sub atomic particles and also much larger models. I am very curious to know, so please write back.

I posted some questions similar to the ones you're asking a couple of weeks ago. I can't work out how to post links to other threads (sorry!) but if you go to "Gravity?" (or something like that, I can't exactly remember) in the Philosophy of Maths and Physics, and "Charge?" (again, I'm not really sure if that's exactly what it's called...) which is in Nuclei and Particles you'll find some more info on the topics.

 

[Anomalous]

...the electric charges also distrort the space-time fabric in a way ...

You mean space is made of something ?

Then how come we can't feel it like air or the resistance. Moon should have fell down due to such resistance ?

 

[Danger]

You mean space is made of something ?

Then how come we can't feel it like air or the resistance. Moon should have fell down due to such resistance ?

No, space isn't made of something. That's aether theory as was believed ages back. The older generations of people, including scientists, couldn't really conceive of matter or energy propogating through 'nothing'. No one yet knows just what space is, hence all of the various 'string', 'superstring', 'membrane' etc. theories currently being pursued. It might be simplest to think of it as an array of stress factors in a constant state of quantum flux. (Some of those terms might mean to a scientist something specific as opposed to my general use of them, so be cautious about taking that literally.)

 

[Icebreaker]

Wouldn't it be interesting if matter weren't in spacetime, but rather, is spacetime?

 

[Dr.Brain]

Anomalous ,

You can imagine the spacetime fabric as something "imaginary" .Its like a stretch of threads shaped as squares and anything when presses it , particularly matter it "distorts", now the true meaning of a straight line changes.

What was the shortest distance becomes the longest in the bent space fabric.The dimensions change and thus the shape of fabric.Take it as imaginary , its easy that way.

 

[Crosson]

However, what about the charge of say, electrons vs. protons? Why do they repel?

You are barking up the wrong tree by asking this. There is no better way to make this clear then by using a quote from Leonard Euler:

"Although to penetrate into the intimate mysteries of nature
and thence to learn the true causes of phenomena is not allowed
to us, nevertheless it can happen that a certain fictive
hypothesis may suffice for explaining many phenomena."

In the case of electrons and protons I can give you two fictive hypothesis:

1) They repel each other because of an electromagnetic field that fills all space (and has its owns peaks and valleys). Charges create fields, and fields move charges.

2) An electron is constantly pouring out massless particles called virtual photons (virtual because they cannot be observed). These virtual photons smack into protons and move them around (photons carry momentum).

These two fictive hypothesis are sufficient to explain all the phenomena we observe. In the case of gravity, I would speak of gravitons and gravitational fields.

 

[Pi_314B]

Wouldn't it be interesting if matter weren't in spacetime, but rather, is spacetime?

BINGO!

That is to say that space is the extension of matter.

 

[Danger]

There is no better way to make this clear then by using a quote from Leonard Euler:...
...These two fictive hypothesis are sufficient to explain all the phenomena we observe. In the case of gravity, I would speak of gravitons and gravitational fields.

Say what?!

 

[Anomalous]

Nope, I don't agree.

Anomalous ,...Take it as imaginary , its easy that way.

My question was related to the ray of light bending towards BH. and hence I conclude that something is bending indeed. Or why and who did first made such a graph ? It seems that the actual cordinate system of space bends because space is made of nothing ( no ether) ?

 

[Anomalous]

...

In the case of electrons and protons I can give you two fictive hypothesis:

1) They repel each other because of an electromagnetic field that fills all space (and has its owns peaks and valleys). Charges create fields, and fields move charges.

2) An electron is constantly pouring out massless particles called virtual photons (virtual because they cannot be observed). These virtual photons smack into protons and move them around (photons carry momentum)...

3) It may be that the space is bending and reaching out the electros to its destination ?

 

[Dr.Brain]

My question was related to the ray of light bending towards BH. and hence I conclude that something is bending indeed. Or why and who did first made such a graph ? It seems that the actual cordinate system of space bends because space is made of nothing ( no ether) ?

A ray of light can be thought of something which carries energy.As per Einstein's Law Of Gravitation, anything carrying energy has mass , in a way, that the light is deflected under gravitational fields. That is, if a light ray passes near a massive object (like Sun), the light ray finds that the 'imaginary' spacetime fabric is distorted and now it cannot travel in straight line as it should have.

Remember that the spacetime fabric is just to make us understand "what fields do to other objects" ...Spacetime fabric concept is made by man..although nature does its own phenomena without ever knowing what the phenomena is called...Like a frog would never know it is called a frog ...got it?

 

[antigravitation]

I think our understanding of gravity is completely wrong !There is no doubt that we must search for another theory which involves at least quantum-mechanics !
We must know all interactions of all forces to each other to be able to explain and understand gravitation completely!A theory which would explain it really is the Heim-Theory !I will set a link to a site where you can read everything about it!Certainly a 80 site script you can find there too.Maybe i will open a new thread for this theory!
So i am new here i don't know exactly where i should post this theory !
But now here is the link :
http://www.heim-theory.com/Contents/contents.html

Have anybody ever heard here from the mass formula of heim ?

Greetings
Antigravitation

 

[Danger]

It seems that the actual cordinate system of space bends because space is made of nothing ( no ether) ?

I've come up with my own 'thought model' because the rubber sheet thing is pretty much 2 dimensional. If you think of a globe of the Earth, the shortest distance from one side to the other is a 'straight' line along the surface. If you consider it to be made of something like soft rubber, then a weight of some type would make a dent in the surface, which would deflect the course of another object that passes it on the way to the other side. The real shortest distance would be if you poke a stick through the thing.
Space-time is somewhat similar, although far more complex. What to us is a straight line is not the shortest distance between 2 points. The 'stick' through the fabric of space-time, which Einstein referred to as a 'geodesic', is the actual shortest path. That's one reason that some of us hold out hope for possibe 'faster-than-light' travel or communications, if we can somehow access the geodisics rather than be forever restricted to normal space. (This is a very scant hope, because it would appear that the energy requirements would be prohibitive.)
Something to keep in mind as well is that Newton's theory was not so much wrong as it was incomplete, just as Einstein's is in light of quantum mechanics. It still quite adequately expresses anything that you're likely to encounter in normal life, such as how long it will take a dropped bowling ball to land on your foot, or how much it will hurt when it gets there.

 

[antigravitation]

I've come up with my own 'thought model' because the rubber sheet thing is pretty much 2 dimensional. If you think of a globe of the Earth, the shortest distance from one side to the other is a 'straight' line along the surface. If you consider it to be made of something like soft rubber, then a weight of some type would make a dent in the surface, which would deflect the course of another object that passes it on the way to the other side. The real shortest distance would be if you poke a stick through the thing.
Space-time is somewhat similar, although far more complex. What to us is a straight line is not the shortest distance between 2 points. The 'stick' through the fabric of space-time, which Einstein referred to as a 'geodesic', is the actual shortest path. That's one reason that some of us hold out hope for possibe 'faster-than-light' travel or communications, if we can somehow access the geodisics rather than be forever restricted to normal space. (This is a very scant hope, because it would appear that the energy requirements would be prohibitive.)
Something to keep in mind as well is that Newton's theory was not so much wrong as it was incomplete, just as Einstein's is in light of quantum mechanics. It still quite adequately expresses anything that you're likely to encounter in normal life, such as how long it will take a dropped bowling ball to land on your foot, or how much it will hurt when it gets there.

You said that it is a very scant hope to manage to travell faster than light besause of the need of enormous energy !That is wrong because if we would find a way to interact with another force in the space-time and in a gravitational field it would be possible to do it with not so much energy !
But please read my previous post of the heim mass-theory !
greetings
antigravitation

 

[Anomalous]

... 1) As per Einstein's Law Of Gravitation, anything carrying energy has mass , in a way, ...

2) if a light ray passes near a massive object (like Sun), the light ray finds that the 'imaginary' spacetime fabric is distorted and now it cannot travel in straight line as it should have.

3) Remember that the spacetime fabric is just to make us understand "what fields do to other objects" ...Spacetime fabric concept is made by man..although nature does its own phenomena without ever knowing what the phenomena is called...Like a frog would never know it is called a frog ...got it?

1) If that is true then how come every body lied to me uptill now that light has no mass. Or r U taking me for a ride ?

2) So U don't agree that the ray light should regain its original green path of direction. BTW for that not to happen the space will have to be in kinda worm holes state but predictable stable ones.

3) So U don't agree that the natural cordinate system of space is changing ?
i.e. U don't agree that a 10 centimeter object can be actually longer in distorted space when compared to normal space ?

I am not a Frog. Frogs don't ask such questions.