Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: thebrain13 on 13/12/2006 04:20:41
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I seem to hear this alot. Gravity does not accelerate an object, gravity bends space-time so the objects merely follow curved paths. Then they give an analogy, usually a bowling ball on a mattress.
I dont understand the above. How can an object that is not moving follow a curved path? An object cant be driven by geometry alone. I might point out that, a bowling ball, on a mattress away from gravity, wont move at all.
What does he literally mean?
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It means this:
in newtonian mechanics, a free body in an inertial ref. frame (free = no forces on it) moves with constant velocity. Let's imagine, e.g., a coin forced to move, without friction, on a flat table. It will keep moving forever, undisturbed. In this sense we can say that it follows the geometry of space, that is, in this case, the plane of the table.
Now imagine that the table is not flat anylonger, but is a spherical surface covering our planet earth. Observing locally the body's behaviour, you will see that it still moves with constant velocity, if you don't apply forces on it.
You could say: "one moment!" "the velocity is not constant anylonger now, because the velocity changes in direction, along the spherical surface"
But, to say that, you have to move away from the surface, and see things from the 3rd dimension.
If we were beings living in only the 2 dimensional spherical surface, we couldn't say that.
Now, what happens is that we live in a 3 dimensional space, but this is not flat, is warped! To see it, we should be able to see things from the 4th dimension, but, unfortunately, we can't!
The fact is that according to Einstein's GR, gravity (produced by: mass, energy, momentum) warps the 4-dimensional space-time so that we are forced to follow that " 4-D analogus of a 2-D warped surface". So, from that 4-D point of view, we are not experiencing any acceleration, in absence of other forces (for example, electrical), but we simply "keep moving freely" on that warped space.
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Not trying to be rude, but to me this is the same as every other analogy.
Question, how can an apple that is not moving, follow a curved path?
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You are inside an orbiting laboratory. You place your apple in a specific point of space inside the laboratory (e.g.: half a metre over the "." key on your computer's keyboard), without making it touch anything else, and it remains in that position forever, even if it's following the curved path of the orbit.
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If gravity is acting on an object it must be moving because gravity will accelerate the object. It can't accelerate if it isn't moving, unless it accelerates from rest. Then, of course, there is inertia. That is a body's resistance to acceleration -I think [???]
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I seem to hear this alot. Gravity does not accelerate an object, gravity bends space-time so the objects merely follow curved paths. Then they give an analogy, usually a bowling ball on a mattress.
I dont understand the above. How can an object that is not moving follow a curved path? An object cant be driven by geometry alone. I might point out that, a bowling ball, on a mattress away from gravity, wont move at all.
What does he literally mean?
The bib "E" was tryng to bring in gravity and within the confines of theorem came up with the plausibility, yet he was still unhappy as it did not take into account energy.
Bottom line is it is an incorrect model.
IN fact most do not realize that the only force used in the cosmic models of the universe is gravity and why they had to create Dark Matter and Dark Energy to answer questions data shared.
The key is yes, mass exchanges energy and this energy causes acceleration of mass until the threshhold of mass is reached then gravity becomes apparent. The key is the volume in relation to causal effects to be measured.
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I like that scenario much better lightarrow. Its so simple yet, I think only a genius can understand that. eesh beesh, let me mull this over a little.