Is Gravity Caused by Mass or Other Factors?

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Discussion Overview

The discussion revolves around the nature of gravity, specifically whether it is caused solely by mass or if other factors play a role. Participants explore various theories, including Newton's law of universal gravitation and Einstein's General Relativity, while also questioning the speed of gravity in relation to light. The conversation includes speculative scenarios and challenges to established theories.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants inquire about the fundamental nature of gravity and how it operates, expressing confusion over its mechanisms.
  • Several contributions discuss whether gravity propagates faster than light, with some asserting that it does while others argue it does not, citing General Relativity.
  • A hypothetical scenario is presented where the moon is suddenly removed, prompting debate about the timing of gravitational effects versus light reaching observers.
  • Some participants speculate on the instantaneous nature of gravitational effects, while others challenge this view, insisting that gravity's effects travel at the speed of light.
  • There are claims that current understanding of gravity is speculative, with references to established theories like Newton's and Einstein's, which some participants defend as valid frameworks.
  • Discussions include the limitations of current measurements of gravity's speed and the implications of theoretical physics on understanding gravity.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the nature of gravity, with multiple competing views regarding its speed and the validity of established theories. The discussion remains unresolved with ongoing debate about the implications of gravity's properties.

Contextual Notes

Some claims rely on assumptions that have not been universally accepted, such as the instantaneous nature of gravitational effects. The discussion also highlights the lack of empirical measurements regarding the speed of gravity, which remains a theoretical topic.

  • #61
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?
 
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  • #62
Yes we are just in different examples.
 
  • #63
Ki Man said:
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).
 
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  • #64
why is gravity a pull not a push?
 
  • #65
in fact whut would be the difference?
 
  • #66
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.
 
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  • #67
Ki Man said:
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.
 
  • #68
the blob inc said:
why is gravity a pull not a push?

I don't think this has been determined.
 
  • #69
the blob inc said:
in fact whut would be the difference?
It could make a difference if it is determined.
 
  • #70
the blob inc said:
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.
 
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  • #71
Pi_314B said:
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.
 
  • #72
the blob inc said:
in fact whut would be the difference?

the difference would be that everything would float as far as it can from everything else
 
  • #73
Ki Man said:
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.. :smile:
 
  • #74
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.
 
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  • #75
Ki Man said:
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.
 
  • #76
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
 
  • #77
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.
 
  • #78
Dook said:
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.
 
  • #79
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?
 
  • #80
Dook said:
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.
 

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