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Author Topic: So.. what precisely is Gravity?? Does anyone know?  (Read 9239 times)

lean bean

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Re: So.. what precisely is Gravity?? Does anyone know?
« Reply #25 on: 19/01/2013 16:36:35 »
Thanks for the book recommendations.
I think I can understand the non-vanishing of tidal gradients leading to relativists  calling it Ďcurvedí space.
I understand a person in a rocket accelerating at one g could also believe he was standing on earthís surface.
I donít understand on a practical level why a uniform gravitational field can be made to vanish by changing to another co-ordinate frame.  For instanceÖ Only in regions throughout the universe do you find areas of tidal gradients and in other areas uniform gravitational fields.
 So, this means at some point or location you have to enter or exit a uniform gravitational field. A rock would undergo an acceleration or deceleration at that point of entering/exiting such a uniform field. You canít make that particular point vanish, it comes with the territory so to speak. Is that cross over point a tidal point?
 

Offline yor_on

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Re: So.. what precisely is Gravity?? Does anyone know?
« Reply #26 on: 19/01/2013 21:44:35 »
It's about experimentally proving that a gravitational field exist. If you are free falling in a black box without tidal influences on it you have no way of defining if there is a gravity or not. And what the experiments tell you is actually your reality inside that box. That someone else (on some planet maybe) seeing that box fall will define it as it is falling inside a gravitational field, following a geodesic is true for that observer, but as far as you is concerned the gravity he finds doesn't exist. I think you can call that different coordinate systems being used, yours and his.
 

lean bean

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Re: So.. what precisely is Gravity?? Does anyone know?
« Reply #27 on: 20/01/2013 15:19:22 »
yor_on
Yes, I can understand and agree with your description, I think I was being trivial and perhaps over pernickety asking about entering and leaving points of a uniform field. 

I can see why you answered, my ''I donít understand on a practical level why a uniform gravitational field can be made to vanish by changing to another co-ordinate frame.'' Now I'm embarrassed, where's the smelling salts...
 

Offline yor_on

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Re: So.. what precisely is Gravity?? Does anyone know?
« Reply #28 on: 22/01/2013 16:50:12 »
No worries, know you're a smart guy. And furthermore I hope we all are allowed to question life, the universe and all, no matter where it takes us? Sometimes when I get into a certain set of mind I also ask questions that I already know the answer too, realizing it a day later :)

But sometimes it helps me to see the answer better too.
 

Offline yor_on

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Re: So.. what precisely is Gravity?? Does anyone know?
« Reply #29 on: 22/01/2013 16:55:04 »
And it's a question about what defines reality I think,  and so in no way trivial. We have a universe in where we use repeatable experiments to decide that, and the results they present gives me no little headache.
 

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Re: So.. what precisely is Gravity?? Does anyone know?
« Reply #29 on: 22/01/2013 16:55:04 »

 

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