# Is the way people are depicting or thinking of gravity wrong?

The way people like to show gravity is a trampoline with a bowling ball. I find this to be strange. As this does not at all explain how gravity works on earth. If this was true, all would be falling to the bottom of the ball. I understand they are saying the bigger the object the more it folds space. Not near like a trampoline with a bowling ball on it. This would actually mean that the earth, and all objects would move to the bottom side of the sun and not what we are seeing. For instance. Mercury is not orbiting around the sun like the ball and trampoline would suggest, but near the equator rather. This means... it may actually not be folding space, but just have pure normal attraction the bigger the object is.

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• YKhan
Lv 7
2 years ago

The trampoline analogy is the only illustrative prop that was around for the last century, because computer graphics wasn't either around or not powerful enough until recently. These days they are using computer graphics more than trampolines anymore. The CGI illustration is more accurate and able to show things in more dimensions.

As for how this model works on Earth, the curved spacetime is the right picture. However, on the surface of Earth, we have a ground which prevents us from falling any further towards the center of the Earth. The ground. produces a counteracting force against the force of gravity. Actually the "force of gravity" isn't really a force, but a pseudo-force since it's actually being caused by the curve of spacetime, yet a pseudo-force can be counteracted by a real force, and vice-versa.

• 2 years ago

A ball on a trampoline is just an analogy. You are taking it too literally. No analogy is perfect. Matter curves all of 4D spacetime around it. We can't picture that. You must use Einstein's equations of General relativity to get a precise perfect description of gravity.

• D g
Lv 7
2 years ago

your picture is wrong and yes the planet mercury is orbiting like a trampoline.

put the sun at the center of the trampoline and you have a big curved shape.. mercury is then an object that you push on this surface that is going at a certain speed to be orbiting..

it never falls in because it is moving and SPACE is frictionless.. if you use a trampoline material that is frictionless you could easily get the ball to circle the center many times before it slowed a bit ... being that nothing is completely frictionless

• 2 years ago

we are all falling down to the ball. Your mental model should consist of a fabric that is less pliable than a trampoline. Think more like the surface of water at the instant that a pebble breaks the surface, perhaps would be closer to the concept.

• Tom
Lv 7
2 years ago

The illustration is a 2D representation of space with the third dimension (the trampoline effect) demonstrating for the 4th Dimension---As we cannot visualize in 4 dimesons we have to diagram it in terms of a third dimension with 2D space to get a Handle on it.-----the "trampoline effect' actually goes in ALL directions relative to us in our 3D space ---we cant "see" that in our minds, but we can think about it happening in all relative directions and have an IDEA of what is going on.

• neb
Lv 7
2 years ago

Pop science shows are full of misleading simplifications of enormously complex subjects. To fully picture gravity you would have to be able to visualize 4-dimensional spacetime - something no one is able to do. That is why we have mathematical descriptions of physical laws which we use to test theories.

Einstein’s theory of gravity - general relativity - is a change in the 4-d geometry of spacetime in the presence of mass and energy. General relativity has passed every experimental test including confirmation of the prediction of gravitational waves as propagating changes in the geometry of spacetime. It is not wrong.

• 2 years ago

The bowling ball analogy has been rightly criticized. Too many people get the wrong idea, mostly by concentrating on the irrelevant details of the analogy. You point out one possible wrong conception. That's why professionals prefer to stick to the equations. At a simple level, good for most things, we have the force equation from Newton. This is good enough for things on Earth, or even for orbits of binary stars around each other. Even for most orbits around black holes, this is pretty good, unless you get very close to the black hole.

F = G M1 M2 / R^2 ... force

F = d (M v ) / dt .... acceleration is dv / dt, so if M is constant, we have F = M a

At the most specific level, we have the non-linear Einstein field equations (10 of them): see the first link. But these are much too complicated to solve, except in a few special cases. So for practical calculation of planetary orbits, we have the parametrized post-Newtonian (PPN) equations at the second link (see equations 8-1 and 8-2). There are also equations that consider that the Sun, Earth, and Moon are not perfect spheres.

Just for fun, I include a link to one of my favorite lectures on gravity.

Source(s): https://en.wikipedia.org/wiki/Einstein_field_equat... ftp://ssd.jpl.nasa.gov/pub/eph/planets/ioms/ExplSupplChap8.pdf http://www.feynmanlectures.caltech.edu/I_07.html
• 2 years ago

I always thought that gravity made things fall. Perhaps that is wrong.

Seriously one of the key concepts of general relativity is that one cannot differentiate between a gravitational attraction and an acceleration.

So how can we be accelerating if the distances from us to another star or planet remain constant?

Yet if gravity is in some way quite different from an acceleration then the thrust of general relativity must be incorrect.

The warping of space time is used to try to reconcile this conundrum. However you can argue which one is cause and which one is effect.

• neb
Lv 7
2 years agoReport

I know we don’t (can’t) go into detail in these answers, but gravitational fields and accelerated frames are only equivalent locally, and then only as an approximation, e.g. we can find exact equivalence only at a point. Gravitational fields cannot be transformed away by choice of coordinates.

• 2 years ago

The "bent space" idea was introduced to try and explain light being bent by gravity, when photons have no rest mass.

In reality, any energy has equivalent mass via E = M C^2 so photons have some tiny mass and are directly affected by gravity - no bent space needed.

As you say it never actually explained gravity anyway, just moved the "pull" to a different dimension.

• oldprof
Lv 7
2 years agoReport

Thanks neb couldn't have said it better.