What are the accepted theories for the source of gravity?

  • #26
sophiecentaur
Science Advisor
Gold Member
2020 Award
26,166
5,373
T. . . . . .When I first discovered I needed to learn it I asked my father to teach me because he has a masters degree in mathematics. He didn't know what a tensor was. (In his defense it has been 40 years since he graduated)

You youngsters. Do you really think Tensors are a new invention? :biggrin: I 'did' them in the 60s and was just as confused as modern students, by this bit of Maths. You just need to learn how to handle them - the same as with vectors and matrices - and follow the rules
 
  • #27
I'll need to learn more about quantum teleportation. Thanks for the link. I listen to a lot of documentaries and lectures on you tube because I can do that while working.

Are there any text books online?

It is true that I feel understanding gravity will help me with my book but since the interest came it has moved beyond just learning about gravity for the sake of the book. My mind often dwells on this as I try to understand. Yesterday or today I realized that with the theory of relativity the reason gravity decreases as you move toward the core of the planet would be because the warp in space is getting less because there is less mass at the center of the planet versus on the surface where the warp in space time should be more.

Those are good ideas for how to control gravity in a sci-fi book.

And as for calculus when I get to that I will learn both differential and integration.
 
  • #28
Drakkith
Staff Emeritus
Science Advisor
21,243
5,071
Yesterday or today I realized that with the theory of relativity the reason gravity decreases as you move toward the core of the planet would be because the warp in space is getting less because there is less mass at the center of the planet versus on the surface where the warp in space time should be more.

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 [STRIKE]surface [/STRIKE] core the curvature of spacetime due to mass should be at its greatest.
 
Last edited:
  • #29
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.

I just realized I probably should have put that part about Einstein's general relativity in my other thread. Only two threads and I'm already getting them confused. 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.
 
  • #30
WannabeNewton
Science Advisor
5,815
537
Don't think of things in terms of space-time curvature; it's going to be utterly confusing for a problem that involves the gravitational force within the Earth; don't make things more complicated than they need to be.
 
  • #31
Drakkith
Staff Emeritus
Science Advisor
21,243
5,071
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.
 
  • #32
sophiecentaur
Science Advisor
Gold Member
2020 Award
26,166
5,373
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?
 
  • #33
Drakkith
Staff Emeritus
Science Advisor
21,243
5,071
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.
 
  • #34
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
 
  • #35
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.
 
  • #36
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.
 
  • #37
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.
 
  • #38
sophiecentaur
Science Advisor
Gold Member
2020 Award
26,166
5,373
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 consistant with classical experience.
 
  • #39
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?
 
  • #40
529
28
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.
 
  • #41
387
8
I'll tell you why things have mass.
They just do.

Awesome lines!
 

Related Threads on What are the accepted theories for the source of gravity?

  • Last Post
Replies
9
Views
2K
  • Last Post
Replies
6
Views
2K
  • Last Post
Replies
1
Views
760
  • Last Post
Replies
12
Views
3K
  • Last Post
Replies
9
Views
594
  • Last Post
2
Replies
32
Views
5K
  • Last Post
Replies
22
Views
5K
  • Last Post
Replies
6
Views
2K
  • Last Post
Replies
11
Views
3K
Top