What are the accepted theories for the source of gravity?

[Drakkith]

I'm going to spend some time thinking about how I would feel if gravity were to pull on me from every direction at the same time and same force.

I believe you would feel like you were weightless and in freefall.

 

[sophiecentaur]

I don't think this is correct at all. The amount of mass near the Earth's surface (Depending on what "near" means), is far exceeded by the amount of mass in the outer and inner core of the Earth (where 25-35% of the Earth's mass is located).

The reason why gravity drops off is because you start having more and more mass AROUND you instead of UNDER you, so the pull in every direction starts to equal out. At the Earth's surface the curvature of spacetime due to mass should be at its greatest.

Are you sure you're sure you're sure about this? How about the curvatures all cancelling out in the middle?

 

[Drakkith]

Are you sure you're sure you're sure about this? How about the curvatures all cancelling out in the middle?

Wait... my post says greatest at the surface. I think I meant at the core.
Which one did you mean?

Also, we might want to avoid talking GR in this thread, it's getting really messy.

 

[mijalasthapit]

In September 1905, Albert Einstein published his theory of special relativity, which reconciles Newton's laws of motion with electrodynamics (the interaction between objects with electric charge). Special relativity introduced a new framework for all of physics by proposing new concepts of space and time. Some then-accepted physical theories were inconsistent with that framework; a key example was Newton's theory of gravity, which describes the mutual attraction experienced by bodies due to their mass

 

[mijalasthapit]

Most effects of gravity vanish in free fall, but effects that seem the same as those of gravity can be produced by an accelerated frame of reference. An observer in a closed room cannot tell which of the following is true:

*Objects are falling to the floor because the room is resting on the surface of the Earth and the objects are being pulled down by gravity.
* Objects are falling to the floor because the room is aboard a rocket in space, which is accelerating at 9.81 m/s2 and is far from any source of gravity. The objects are being pulled towards the floor by the same "inertial force" that presses the driver of an accelerating car into the back of his seat.

 

[mijalasthapit]

We can use Newton's Law of Universal Gravitation to calculate how strong the gravitational pull is between the Earth and the object you dropped, which would let us calculate its acceleration as it falls, how long it will take to hit the ground, how fast it would be going at impact, how much energy it will take to pick it up again, etc.

 

[mijalasthapit]

A theory starts as one or more hypotheses, untested ideas about why something happens. For example, I might propose a hypothesis that the object that you released fell because it was pulled by the Earth's magnetic field. Once we started testing, it would not take long to find out that my hypothesis was not supported by the evidence. Non-magnetic objects fall at the same rate as magnetic objects. Because it was not supported by the evidence, my hypothesis does not gain the status of being a theory. To become a scientific theory, an idea must be thoroughly tested, and must be an accurate and predictive description of the natural world.

 

[sophiecentaur]

Wait... my post says greatest at the surface. I think I meant at the core.
Which one did you mean?

Also, we might want to avoid talking GR in this thread, it's getting really messy.

Haha. I assumed you meant Centre. But mine was an actual question. I am not sure about any of this except to say "expect to be confused and misled". It will not be intuitive.
Any ideas we offer must be consistent with classical experience.

 

[ZionsRodeVos]

All the information is very useful too me as I want to understand all the theories related to gravity and how those theories relate to one another.

If I have understood correctly string theory is the theory that has a graviton in it and thus far there is little or no evidence to support string theory. Does that mean that even though it is called string theory it is really only a hypothesis at this point?

If graviton's were found would that change people's understanding of general relativity and/or Newton's theory of gravity?

 

[DrewD]

If I have understood correctly string theory is the theory that has a graviton in it and thus far there is little or no evidence to support string theory. Does that mean that even though it is called string theory it is really only a hypothesis at this point?

I'm pretty sure that Feynman and others worked out a gravitational field theory in the 60's that predicted a graviton. The theory did not work under certain circumstances (maybe all?) when combined with GR and was scrapped. I think gravitons show up in a number of theories, but none that are fully consistent with GR or that have been experimentally confirmed.

If graviton's were found would that change people's understanding of general relativity and/or Newton's theory of gravity?

I don't think that confirmation of a graviton alone would change theories much, but there might be certain values related to it that could rule out certain theories. For example, a graviton with mass would cause trouble in a number of theories. I don't think anyone is seriously looking for them though. They are (would be) very difficult to observe.



mijalasthapit, it would be better if you posted everything in one post.

 

[darkxponent]

I'll tell you why things have mass.
They just do.

Awesome lines!