| MadSci Network: Physics |
Does mass cause gravity? Or, does gravity cause mass.
Yes and no, this is a 'which came first, the chicken or egg' type
question. There are two types of masses, and they are the same. There
is an object's gravitational mass, i.e. the object's weight, and
there is the object's inertial mass -- what causes it to resist when you
push it. These masses are equivalent.
You can 'turn off' the gravitational mass, and have the object appear
weightless by putting the object in free fall (also known as orbit).
It still has inertia, and still has gravity acting on it.
You cannot tell the difference (by your senses or experiment) between
floating in a zero gravity field or falling in a strong gravitational field.
What evidence is there for the origin of gravity?
The particle, not yet observed, that we think causes gravity is the graviton. It has no mass, travels at the speed of light, and is a boson. This model of gravity, proposed by John Schwarz and Joel Scherk, was a result of their work in string theory, about 1974. This proposed particle solves some problems in string theory, but is not yet observed.