RE: Why is there gravity?
March 28, 2015 at 10:35 am
(This post was last modified: March 28, 2015 at 10:51 am by Alex K.)
Yeah, with why questions, there's always the question what kind of answer would even be possible. Often, "why" questions in every day life work like this - something happens, and you try to find the part of the causal relationship that is most relevant, thus tracing what happened back to other events. Or there's an established rule which allows us to trace back reasons to conditions in that rule. Like, why did I get a speeding ticket? Because I was going 100 in an 80 zone.
With things as fundamental as gravity, and existence questions, that's not so easy. What one can do, and the others have already done that nicely here, is to give an explanation inspired by our currently best theories. Of course, this answer to the why question will change somewhat when new theories are developed.
Explanations from theory don't answer the why question in a temporal fashion (as in: how did it come to pass that our universe has gravity) but rather attempt to trace the phenomenon back to more fundamental principles and descriptions of what is going on. However, nothing keeps you from again asking - why is that? like a 4 year old, and there wouldn't be an answer.
With gravity, it's currently this explanation from general relativity: All Energy, including mass, leads to the curvature of spacetime. Objects moving in curved spacetime get diverted and accelerated. Hence, gravitational attraction occurs.
(Why is that so? It just is...)
100 years ago, the explanation would have been less of an explanation: massive objects attract each other with a force which goes like 1/distance squared.
Maybe in a 100 years time, when we better understand the quantum nature of spacetime, the explanation will again read somewhat differently. Already today, one can attempt a quantum version of general relativity (which breaks down at the Planck scale). In this interpretation of the theory, gravitational force arises in analogy to electromagnetic force, because Gravitons are exchanged between objects.
With things as fundamental as gravity, and existence questions, that's not so easy. What one can do, and the others have already done that nicely here, is to give an explanation inspired by our currently best theories. Of course, this answer to the why question will change somewhat when new theories are developed.
Explanations from theory don't answer the why question in a temporal fashion (as in: how did it come to pass that our universe has gravity) but rather attempt to trace the phenomenon back to more fundamental principles and descriptions of what is going on. However, nothing keeps you from again asking - why is that? like a 4 year old, and there wouldn't be an answer.
With gravity, it's currently this explanation from general relativity: All Energy, including mass, leads to the curvature of spacetime. Objects moving in curved spacetime get diverted and accelerated. Hence, gravitational attraction occurs.
(Why is that so? It just is...)
100 years ago, the explanation would have been less of an explanation: massive objects attract each other with a force which goes like 1/distance squared.
Maybe in a 100 years time, when we better understand the quantum nature of spacetime, the explanation will again read somewhat differently. Already today, one can attempt a quantum version of general relativity (which breaks down at the Planck scale). In this interpretation of the theory, gravitational force arises in analogy to electromagnetic force, because Gravitons are exchanged between objects.
The fool hath said in his heart, There is a God. They are corrupt, they have done abominable works, there is none that doeth good.
Psalm 14, KJV revised edition
