What is Gravity?

Question

Einstein's theory of relativities state that gravity is the wrapt and curves in the fabric of space and time.

Watch this video
http://video.google.com/videoplay?docid=-3387096753325354202&q=nova+is%3Afree+duration%3Along&hl=en

How are these space warpt and curve of space and time possible if the sun moves up and down as it orbit around the galaxy?
How come the orbits of the planets have a part of the year where they are close to the sun and another part of the year where it is the furthest away from the sun in their elipstical orbits around the sun?

Answer 1

Gravity

The gravitational attraction at the surface of a planet or other celestial body. The quantity g is often referred to simply as “gravity” or “the force of gravity” of Earth, both of which are incorrect. The force of gravity means the force with which a celestial body attracts an object, that is, the weight of the object. The letter g represents the acceleration caused by the gravitational force and, of course, has the dimensions of acceleration.

Answer 2

The PBS show was pretty awesome. The question you asked, however, doesn't get into string theory--it goes back to what Einstein was saying around 1922. Another answerer is correct--the idea of the gravity warp being seen as a sort of depression or gutter for planets to roll around in is an analogy--a way to see a 4th dimension "projected" into 3-dimensional space. Elliptical orbits are still possible in this analog. If you go to your bathtub with a small ball (rubber ducky optional) and roll it softly toward the end of the tub, it will turn quickly and roll back. If you roll it hard, it will move up the side quite a ways before turning. Velocity matters. In an elliptical orbit the gravitational force varies throughout, because the distances keep changing. I think some of the models are not well drawn. They should be drawn in the shape of an lily, or horn, with a deep hole at the center, curving up and out until nearly flat further out. Start rolling your ball around that opening and if it gets too close to the center, *plop*, it crashes into the "sun" (deep gravitational "hole") at the center.

Answer 3

I don't understand the problem that you're trying to articulate as to how space is warped just because the sun "moves up and down (?)" in its orbit around our galactic center... But here's what I do know:

Gravity is a manifestation of the warping of both space and time--meaning, because of an object's mass, ANY object's mass mind you, the space about which it occupies becomes "bent," "warped" such that other objects are attracted to that imperfection in space. This attraction is gravity.

If you still don't understand what I mean by "warped," think in two dimensions rather than three (like in our normal world). Suppose you had a taut rubber sheet (which represents our three dimensional world--spacetime, even though it is two dimensions) and upon it you placed a bowling ball (representative of our sun). Notice how the sheet would become "warped" or distorted (that spacetime would become warped because of the mass of the sun) simply due to the fact that the bowling ball is heavy or "massive." Then should you place a marble on the sheet,(representative of our Earth), it would become "attracted" towards this "warping," thus, representative of gravity. This is what Einstein is tryin to state in his General Theory of Relativity.

Now, as for the planet's orbits around the sun--you seem to have misunderstood the meaning of "elliptical." Elliptical means to have the shape of al ellipse--meaning--like that of an oval. Picture a very large oval shaped ring (representive of say, the orbit of Pluto) around a round object (representative of the Sun in this case). Along the sides of the oval (and not the narrow curves) Pluto would be closest to the sun; that's just the way the shape of an ellipse works. Around the narrow, sharp curves of the oval, Pluto would be furthest away.

Thanks for the link to the video by the way...

Answer 4

Gravity is created by distortions in the fabric of space and time. Distortions are created by a mass. the more dense the mass the more acute the gravity would be. You could have an object with much more mass but if it takes up much more area the gravity will be more broad but less intense.

Mass creates a dimple in the fabric of space. If you were in space light years from any matter you would create your own gravity. It would be less than microgravity but you, your body, would generate a gravatational field. We can't measure it around here because of the sun, earth, moon, ect is so much stronger that is cancels out all the small stuff.

Answer 5

I didn't think the sun moves. I thought the planets orbit the sun on an axis.

the planes go close to the sun and far from the sun at different times of the year because they all orbit the sun on an axis and they orbit in a circular motion that is not necessarily equal on all sides.

Answer 6

Gravity
The gravitational attraction at the surface of a planet or other celestial body. The quantity g is often referred to simply as “gravity” or “the force of gravity” of Earth, both of which are incorrect. The force of gravity means the force with which a celestial body attracts an object, that is, the weight of the object. The letter g represents the acceleration caused by the gravitational force and, of course, has the dimensions of acceleration. See also Gravitation

Answer 7

Gravity is a force which pulls anything from a distance.It is directly propotional to mass.

Every thing has a speed(velocity).There is a time when gravity becomes stronger than the speed and mass of the orbitting object and when it becomes weaker than the speed and mass of the orbitting object So sattelites have eliptical orbits.

Answer 8

in mechanics, the universal force of attraction acting between all matter. It is by far the weakest known force in nature and thus plays no role in determining the internal properties of everyday matter. Due to its long reach and universality, however, gravity shapes the structure and evolution of stars, galaxies, and the entire universe. The trajectories of bodies in the solar system are determined by the laws of gravity, while on Earth all bodies have a weight, or downward force of gravity, proportional to their mass, which the Earth's mass exerts on them. Gravity is measured by the acceleration that it gives to freely falling objects. At the Earth's surface, the acceleration of gravity is about 9.8 metres (32 feet) per second per second. Thus, for every second an object is in free fall, its speed increases by about 9.8 metres per second.

Answer 9

That picture is just an analogy. Space is three dimensional and that "up and down" motion they show would have to be in the 4th dimension. It would not really be up and down.

The three directions you can go in three dimensional space are:
1) right - left
2) forward - backward
3) up - down
If you go straight up, you go up over the exact same spot on the ground and are not going forward or backward or right or left at all. If you go straight ahead, you are not going left or right or up or down at all. If you go directly right, you are not going forward or backward or up or down at all. The three directions are all perpendicular. In math they are called orthogonal. You can write math for 4 orthogonal motions (or any number, even a million), and Einstein did that for a 4 dimensional situation. He imagined (mathematically) a direction that you could go where you did not got forward or backward or right or left or up or down at all, but were moving in another dimension; the 4th dimension which we can't see. Since we can't see it, the picture pretends that there is no up and down in our universe; it pretends that we live in a 2 dimensional universe that has no up or down. Then it shows how gravity could be explained by motion in a 3rd dimension by allowing that extra up - down direction. It is an attempt to make something that can be described mathematically but not seen, visible.

I know it is odd, but if you can get your mind around it, it makes perfect sense. Try reading the book, "Flatland: a romance of many dimensions" to gain an understanding of other dimensions.

Answer 10

bends in space time can be defined as gravity, gravity is believed to be put to effect by gravitons,