Is Gravity Caused by Mass or Other Factors?

[quantumdude]

okay sorry about the "homegrown crackpottery"

I wasn't talking to you, Ki Man. I deleted your post by mistake, and have now un-deleted it. We don't mind answering questions here.

anyways for gravity to be instantaneous it would have to pull something far away faster than it would take for light to reach that object (the light coming fromt he pulling object) and that would mean gravity would have to break the light speed barrier.

How would that be possible for it to be instantaneous?

It's precisely for this reason that gravity is believed to propagate at a finite speed.

 

[quantumdude]

i think that gravity might be a pull caused by a cluster of mass. just my theory. don't take my word for it though I'm only in 8th grade.

Our best understanding of gravitation is embodied in General Relativity, which states that not just mass, but also energy and momentum contribute to gravitation.

what if... you have some mass. all mass is equal to energy right because E=MC^2? and all matter is made up of quarks, which are... charges of energy i believe. correct me if I'm wrong, but if quarks attract then wouldn't a large object floating in an area with very very few atoms, like space, have a somewhat of a pull on objects around it?

Yes, it would.

 

[Ki Man]

so that would be a possible theory on what causes gravity? or just a crazy idea of mine.

i know it would be possible but would it be strong enough to cause gravity the way we know it. that's the only thing i can think of to disprove my own theory

 

[quantumdude]

so that would be a possible theory on what causes gravity? or just a crazy idea of mine.

As I said, it is not only mass but also momentum and energy that cause gravity.

Just a note: Personal theories and/or speculations are not appropriate for the Physics section of PF. We host discussions of non-peer reviewed work only in the Independent Research Forum, and it must be done according to our https://www.physicsforums.com/showthread.php?t=82301. This is to ensure that the scientific and academic integrity of PF is maintained.

i know it would be possible but would it be strong enough to cause gravity the way we know it. that's the only thing i can think of to disprove my own theory

Truthfully: You don't have a theory. Physical theories are not just qualitative, but also quantitative. If a 'theory' of gravity does not even permit one to calculate the strength of the gravitational influence of one body on another, then it is no theory at all.

Let's stick to Newton and Einstein for now, OK?

 

[Pi_314B]

Claiming that the gravitational influence of the 'zapped' body disappears instantaneously is equivalent to claiming that gravitational effects propagate instantaneously. You did just that in Post #18 of this thread.

I did no such thing. I should know ...I typed it, and now that you have (zapped!) some post - you can quote me out of context. What I was trying to get across was that a mass that is zapped would also require the zapping of the gravitational field, because the mass and the gravitational field are one and the same. I am in complete agreement that gravity propagates at C.

 

[quantumdude]

I did no such thing. I should know ...I typed it,

You did, in fact, claim that the gravitational influence would drop to zero instantaneously if an attracting body is 'zapped'. I should know...I read it.

and now that you have (zapped!) some post - you can quote me out of context.

Give me a break. Post #18 is still there, and I did not quote you out of context.

What I was trying to get across was that a mass that is zapped would also require the zapping of the gravitational field, because the mass and the gravitational field are one and the same. I am in complete agreement that gravity propagates at C.

And the point I am trying to get across is that the instantaneous vanishing of gravitational effects requires that the gravitational interaction propagate infinitely fast. I know you don't think that your statements imply this, and I am informing you that they do.

I am not interested in your ideas on gravity. If you've got questions, then that's fine. If you're here to tell us "how it is" then that's not fine.

 

[aaroman]

The gravitational effect would disappear instantaneously

Instantaneously for which observer? :)

 

[Doc Al]

In a not to terribly roundabout way it states that the gravitational field is the moon itself. I don't know how you could take this any other way. So if the moon is zapped surely the field is gone as well in an instantaneous fashion.

Again you think that the moon and its gravitational field are instantaneously linked. Not so. Let's forget about making the moon disappear (as pervect points out, that is an unphysical premise). Instead, say that the moon is quickly moved a mile further away. (Again, this may prove to have some unphysical elements, but let's assume it's OK for this discussion.) The moon's gravitational pull on us will change as a result, but that change takes time to reach us since a disturbance in the gravitational field travels at the speed of light, not instantaneously.

How could I know or anyone else for that matter (the post is deleted).

I deleted that post because all it contained was idle speculation. (Please reread our policy regarding overly speculative posts.)

 

[quantumdude]

Instantaneously for which observer? :)

aaroman,

The best way to deal with people such as Pi_314B is to simply correct him, rather than ask him to explain. He simply doesn't know what he is talking about.

That said, if a body were to suddenly disappear there is no reason to think that its gravitational influence on another body would drop to zero instantaneously. That is because it would necessarily imply that gravitation propagates with infinite speed, and we have good reason to think that that is not true.

If someone says on the one hand that gravitation propagates at 'c', and on the other hand that gravitational influences can be instantaneously changed at points which are some distance from a source, then one is simply contradicting oneself.

 

[HallsofIvy]

Can gravity be drawn on a piece of paper so as to be understood by the masses?

"masses" understand gravity very well- it's us people that don't!

 

[quantumdude]

I tried my damndest not to make a joke just like that when I read this last night!

 

[Lisa!]

"masses" understand gravity very well- it's us people that don't!

As far as I remeber people are masses too, so they should be able to understand gravity like other masses!

 

[rbj]

if Whitedragon and Pi_314B say that gravity is instantaneous, then i guess it must be true.

You have that wrong. I didn't say that gravity was instantaneous.

this is the post that i was referring to.

I'm going to guess that zapped means removed from existence. If so - The gravitational effect would disappear instantaneously, because the gravitational field of the moon is every bit as much the moon as the rock itself, while the photon coming your way is no longer a part of the moon and must travel at C.

it's on the record.

 

[Kazza_765]

i think that gravity might be a pull caused by a cluster of mass. just my theory. don't take my word for it though I'm only in 8th grade.

what if... you have some mass. all mass is equal to energy right because E=MC^2? and all matter is made up of quarks, which are... charges of energy i believe. correct me if I'm wrong, but if quarks attract then wouldn't a large object floating in an area with very very few atoms, like space, have a somewhat of a pull on objects around it?

Damn, nice grasp of physics for someone in 8th grade. Keep up the good work and curiosity Ki Man, you'll go far.

 

[Whitedragon]

Okay everybody I was wrong... I forgot that Einstein wrote a paper that said light was exactly the same speed as gravity, no more, no less. What I was reffering to was Newtonians gravitatonial thingy that stated that gravity was indeed faster thant the speed of light. But what I had forgot about was that Einstein didn't think that was true and worked a theory out that nothing, according to our known theories and laws that absolutly nothing is faster than the speed of light. My original question is what gravity is and I guess nobody has an answer to that. Sorry.

 

[Agnostic]

I love reading threads like this. Some people who take an introductory class in physics and without every studying any mathematics higher than algebra, they are able to correct people with PH.D's in mathematics, physics, etc...

 

[Whitedragon]

I love reading threads like this. Some people who take an introductory class in physics and without every studying any mathematics higher than algebra, they are able to correct people with PH.D's in mathematics, physics, etc...

Are you talking about me or someone else?

 

[Ki Man]

Damn, nice grasp of physics for someone in 8th grade. Keep up the good work and curiosity Ki Man, you'll go far.

thank you. haven't learned physics formally in school yet though they've made me wait until this year and its just "physical science".



i think whitedragon is right. gravity probably is not slower than light, and there's no way it can be faster. a pull can't be faster than the universal speed limit. it very very likely goes at the same speed at light.

lets say this smiley is 3 lightminutes away from the other smiley

and the smiley with glasses is rotating around the spinning smiley and is controling the currents on planet spinning smiley. if the people on planet spin have their "moon" blown up, the water and currents would ripple and lose their usual cycle at the same time that they no longer see their moon, not 3 minutes before they see it blow up.

so you have this

instead of the one you saw before, but at the moment the moon blows up and goes from this: to this the people on the planet spin won't notice any changes at all until the light hits their planet, because the gravity was going the same speed as the light.

I have a limited amount of documents. can someone give me links to Newton and einsteins theories on gravity?

BTW i don't see why everyone is arguing with each other about who said what. its over. forget what they said. that was post 18. we're on page 3.

 

[Ki Man]

Are you talking about me or someone else?

*cough cough*me*cough cough*

True: speed of gravity's pull = speed of light
False: speed of gravity's pull > speed of light

nothing can pass the speed of light. no energy wave. no sound wave. no solid object. why would a pull effect something faster than light would hit it? if a large planet was in space and suddenly disappeared its moons would not float away until it saw its planet blow up. a person on a lunar colony would not feel a sudden jerk at the exact moment the planet blows up while the planet is still visable in the sky. like the lag of light there is lag of gravity. by lag i mean delay don't yell at me for using bad terms

 

[Mk]

(what Whitedragon said)
Of course not, you are one of the confused people asking questions, whereas Pi_143B is misguided, and is saying strange things.

 

[Kazza_765]

Okay everybody I was wrong... I forgot that Einstein wrote a paper that said light was exactly the same speed as gravity, no more, no less. What I was reffering to was Newtonians gravitatonial thingy that stated that gravity was indeed faster thant the speed of light. But what I had forgot about was that Einstein didn't think that was true and worked a theory out that nothing, according to our known theories and laws that absolutly nothing is faster than the speed of light. My original question is what gravity is and I guess nobody has an answer to that. Sorry.

Yep, according to Newtonian gravity, gravity acts instantaneously, but Newton knew there was problems with this. As for what gravity actually is, I don't think anyone has an answer to that. We can describe it, and predict how it will behave. But you can keep asking why? forever and eventually physics can not answer it. Why is gravity attractive and not repulsive? Why does it exist at all? Eventually we have to say that that's just the way the universe is.

 

[Ki Man]

and on the specific subject of what causes gravity, this is a very unique subject. the closest we can get to explaining it is have someone come up with a theory and have basically every 4 out of 5 scientist approve it. even then if we are totally set on what causes it, we have asboslutely no way of proving that the theory is true, so all we will ever have is a theory

its not like we can create a new planet with absolutely no gravitational pull and then do things to the planet to see if it will cause gravity.

 

[Danger]

Only because I sometimes interpret things a little differently than others, I'd interject one clarification here regarding pi_314b's comment. I know that it can't be done, but if the moon could be zapped, the gravitational field would vanish at the same time in that space. The waves that had already been dispatched would continue on their way at c.

 

[rbj]

*cough cough*me*cough cough*

True: speed of gravity's pull = speed of light
False: speed of gravity's pull > speed of light

nothing can pass the speed of light. no energy wave. no sound wave. no solid object. why would a pull effect something faster than light would hit it?

Ki Man, nothing you're saying is wrong, but i want to point out that it is some kind of misconception that somehow the physics of light control the physics of gravity. $c$ is not just the "speed of light", it is the "speed of all things previously thought to be 'instantaneous'." in which light (electromagnetic interaction) and gravity are two examples of it.

just like if God₁ was holding a planet and his/her friend, God₂, was holding another planet, and God₁ shakes his, causing a disturbance to affect the planet that God₂ is holding and that disturbance moves at the speed of $c$, the same would be true if God₁ and God₂ were both holding a very large glob of electric charge and God₁ sent a disturbance to the charge that God₂ was holding (via the Coulomb force law, which is ostensibly instantaneous, just like Newton's universal law of gravity). both disturbances travel at the speed of $c$ and we happened to notice that the electromagnetic wave traveled at $c$ first.

$c$ is $c$. it doesn't have to be light's $c$ or gravity's $c$. it is the speed of any "instantaneous" action.

 

[Ki Man]

i never said the physics of light controls the physics of gravity, i just said that gravity must be equal to "c" and no more faster. like you just said both disturbances would be felt at the same time. one disturbance can't be felt before the other oen. they will appear at the same time because both are going at c

but c can't be completely instantaneous right. like how light is "instantaneous" but still takes 8 minutes to reach us from the sun even though its "instantaneous"

 

[Ki Man]

maybe i didn't word my examples well but to me we are talking about the same thing.

If i were a God and I were to make the sun to disappear right now, the Earth wouldn't be affected while the changes are still rushing toward Earth at the speed of c it would take 8 minutes of me waiting until i see the people on Earth running around in fear right?

 

[Whitedragon]

Yes we are just in different examples.

 

[rbj]

i never said the physics of light controls the physics of gravity,

i tried not to imply it that way.

but c can't be completely instantaneous right.

no, but we (humans) used to think it was.

If i were a God and I were to make the sun to disappear right now, the Earth wouldn't be affected while the changes are still rushing toward Earth at the speed of c it would take 8 minutes of me waiting until i see the people on Earth running around in fear right?

from the POV of any observer far away somewhere around the axis of the Earth's orbit around the Sun. and you wouldn't even have to be a God (maybe, if you were the one turning off the light). i am not exactly sure how, as physical manner a God would observe things, but i make use of the same rhetorical tool (obviously).

 

[the blob inc]

why is gravity a pull not a push?

 

[the blob inc]

in fact whut would be the difference?

 

[Sir_Deenicus]

If anyone knows exactly what gravity is, can you please tell me as well (in a private manner so others do not steal the idea)? We can share the Nobel Prize money and I'll take you to McDonalds with a portion of my share.

 

[Sir_Deenicus]

maybe i didn't word my examples well but to me we are talking about the same thing.

If i were a God and I were to make the sun to disappear right now, the Earth wouldn't be affected while the changes are still rushing toward Earth at the speed of c it would take 8 minutes of me waiting until i see the people on Earth running around in fear right?

More or less, Yes.

 

[Pi_314B]

why is gravity a pull not a push?

I don't think this has been determined.

 

[Pi_314B]

in fact whut would be the difference?

It could make a difference if it is determined.

 

[Sir_Deenicus]

why is gravity a pull not a push?

(a) Because the concepts of push and pull do not encapsulate the idea of force very well. Abysmally so in fact, is how well they do at it.

(b) Gravity is not due to a force (or an instataneous one for that matter, as Newton pointed out as early as the 18th century).

(c) There are no gravitational sources(i.e. "antigravity") so the idea of pulls and pushes does not apply. A body is not attracted so much as is its motion is altered so it will move more towards the body due to the relationship between matter and space. Or classically, the existence of potentials which affects acelerations, which change depending on position.