Is Gravity Caused by Mass or Other Factors?

[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.

 

[ZapperZ]

I don't think this has been determined.

May I suggest you refrain from making this type of response UNTIL you can show me HOW you would solve the equation of motion of an object in a gravitational field WITHOUT unambiguously knowing how to handle the potential term in the Lagrangian/Hamiltonian.

Zz.

 

[Ki Man]

in fact whut would be the difference?

the difference would be that everything would float as far as it can from everything else

 

[Sir_Deenicus]

the difference would be that everything would float as far as it can from everything else

Not only would it float, it would fly (i.e accelerate) away..

 

[Ki Man]

yep. and that would apply on a molecular scale too. solid objects would be physically impossible

why is it a pull and not a push though? maybe it has something to do with how opposites attract on a molecular scale.

 

[Mk]

yep. and that would apply on a molecular scale too. solid objects would be physically impossible

Gravity is usually ignored at the scales you are speaking of, it wouldn't matter if it was attracting or repelling.

 

[Ki Man]

good point maybe it wouldn't be on a scale that small, but objects would be limited to a small size.

the universe would be nothing but a bunch of small clusters accelerating away from each other as fast as possible

 

[Dook]

If gravity is a wave emitted by all objects at the speed of EMR (light) wouldn't that explain why so much energy (an increasing amount) is needed for an object to obtain light speed?

Like a supersonic aircraft trying to break the sound barrier, a spacecraft nearing the speed of EMR needs much, much more energy applied to continue to increase speed because gravity builds up in front of it like a wave or wall that cannot get out of the way.

 

[ZapperZ]

If gravity is a wave emitted by all objects at the speed of EMR (light) wouldn't that explain why so much energy (an increasing amount) is needed for an object to obtain light speed?

Like a supersonic aircraft trying to break the sound barrier, a spacecraft nearing the speed of EMR needs much, much more energy applied to continue to increase speed because gravity builds up in front of it like a wave or wall that cannot get out of the way.

That doesn't explain why photons can't go faster than c... unless you are claiming that photons themselves also give out this "gravitational wave".

Zz.

 

[Dook]

If it is found that photons have no mass then it wouldn't seem that they could possibly have their own gravity. But then our current theory of gravity is that it comes from mass. The greater the mass, the greater the gravity field. What if it doesn't necessarily?

What if there are particles, or other, that emit a gravity field but have no mass?

 

[ZapperZ]

If it is found that photons have no mass then it wouldn't seem that they could possibly have their own gravity. But then our current theory of gravity is that it comes from mass. The greater the mass, the greater the gravity field. What if it doesn't necessarily?

What if there are particles, or other, that emit a gravity field but have no mass?

But now look at what you are doing. You have now come up with an explanation for something using a highly speculative scenario. Notice that if we all can just speculate, all bets are off. Why not go to the extreme and use angels on dirt bikes as a possible explanation?

Now don't take this as a criticism, because it is an important exercise in how we need to think of how to formulate an answer in physics. If we propose something, we need to see the consequences of that proposal. If the reason why an object cannot move faster than c is because it is bumping into its own "gravitational waves", then you look at all possible consequences of that idea. You would run into trouble with photons, and that causes you to now make wild speculation on "other particles that emit a gravity field but have no mass". At some point, you are going to go way to far out on a limb that it will just break!

Notice that this is only ONE of the possible questions that I could bring up to counter your idea. I haven't even point to the the fact that an object can certainly move faster than the 'wave' that it is generating. It is why we get sonic boom and Cerenkov radiation.

Zz.