View Full Version : Question for all of the Physics geniuses

10-19-2002, 09:56 PM
Everyone knows that gravity exists and that it pulls things. However, I was thinking (a rarity :D), why does gravity exist? I couldn't come up with a logical solution.

10-19-2002, 10:35 PM
What do you mean why does it exists?

It couldn't be any other way. It has to exist because we exist. If it didn't exist, we wouldn't be here to think about it.

It's liek the Queen waking up one morning and finding herself surprised to realise she is the King's daughter! Given that she is the Queen, it should be no surprise.

Look up the 'Anthropic Principle' in google.

10-20-2002, 12:12 AM
I think he meant what makes gravity exist....

10-20-2002, 12:52 AM
Mass of course!

10-20-2002, 02:16 AM
My theory is that mass displaces emptyness, which in turn creates a gravitational (attractive) force. Emptiness, on the other hand, encourages dispersal and dissipation. However, because mass is simply energy encapsulated in bundles, then perhaps the solution has something to do with the internal velocity of the energy flux within. That's a really mysterious question, you know?

10-20-2002, 06:11 AM
I agree with Sebastiani.
Gravity is a force that exists between any abjects that have masses.
But we can feel the gravity caused by earth because of the HUGE difference between the humans mass and the earth mass.

10-20-2002, 08:16 AM
From a technical point of view not even the best scientists can explain why gravity exists. There is no quantum theory of gravity and that is probably the biggest hurdle to a quantum theory of everything.

The Dog
10-20-2002, 08:55 AM
Do you think that magnetism (an unexplained phenomenon), can somehow be related to gravity?

10-20-2002, 09:13 AM
>an unexplained phenomenon

not true

>can somehow be related to gravity?

Yes. See Grand Unification Theory.

10-20-2002, 10:05 AM
i think it has to do with earths rotation. As it spins its my belief it pulls everything twords its center, if it sat still, maybe we'd float.

Maybe i'm just an idiot, but its a thought.

10-20-2002, 10:12 AM
What happens when you sit on a rotating round about? You don't get attracted you get forced outwards, same with the earth. Only difference is is that gravity counteracts on earth.

10-20-2002, 10:46 AM
The short answer to what/why gravity is that we don't really have a good answer yet. As mentioned, there are some interesting ideas (ie grand unified theory) but nothing really solid.

Magnetism is one of the better understood phenomina in physics. It is an aspect of the electric field, arising from the finite propagation velocity of changes in the electric field. The field experienced by a charged particle depends on where other charged particles were at various times in the past. Hence moving particles affect each other differently than would the same arrangement of stationary particles. That basically is magnetism. The mathmatics is "somewhat" challenging so often this is glossed over is lower level education, leaving an impression that magnetism is unexplained. Of course, ultimately we don't really know what the electric field is, but at some point you have to admit that you are dealing with an original postulate. What's interesting is to reduce the number of these to the minimum needed, and derive everthing else from these. Thus the interest in Grand Unified Theories.

Ride. Sorry, it's not spin. If it were then gravity would depend on angular momentum and not interial mass. In other words, celestial mechanics would be messed up big time.

10-20-2002, 12:23 PM
When i first considered gravity, I was stunned to here that it was a constant accelaration - not velocity. I then imagined it to be a force that was in a sense, "sucking" us into a vortex - I was perplexed. When I asked my father about this, (a physicist, by the way), he made an interesting point: Take a bucket of water that is tied to a string and spin it around. The force exerted is constant (like velocity). The angular momentum imparted to the bucket causes it to experience a constant acceleration (in the direction of the bottom of the bucket), and the water undergoes a gravitational pull. Thus, he said, gravity is really a constant force applied through an angle that moves in a circle tangent to the body of mass. The warping of space was proved several times, by the way, by the fact that a star "behind" another seems to slow down, when in fact it is an illusion caused by the light bending around the star in the foreground.

10-20-2002, 01:04 PM
"There is no pull, it's only the spacetime's curvature"

10-20-2002, 01:21 PM
"...some say the world is flat. Others say it is spherical. In reality, both are true...it is merely due to the limitations of mental conception that the two views contradict."

- buddha ~550 b.c.

10-20-2002, 01:43 PM
Yes, but some models of the world are more useful than others.

*The model of a round earth is more useful than a flat earth, because it makes travelling and satellite calculation possible.

*Einsteins special theory of relativity is more useful than the "classic time theory" because it makes high-precision systems like the GPS system possible.

No physical model is "wrong", it's all a matter of usefulness.