
#1
Jan413, 12:57 PM

P: 2

i have encountered a problem with gravity, acording to logic gravity should not be able to work as it does in our universe or any other that has spatial dimensions that work in an identical way (even if said universe has less dimensions than our own). you are probobaly aware of a paradigm that allows us to visualise exactly how gravity works. the precise nature of this concept varies but it goes along the lines of this. if four people held up a sheet, and a fith then places a basketball (representing a planet or star) in the center of the sheet, it will create a dip in the sheet. if the fith person places a marble (representing say, an asteroid) on the sheet, it will roll toward the ball. this is all very well, the only problem is that in reality objects are not sitting on a flat sheet or film of spacetime that can be warped and manipulated, rather they exitst in space with three dimensions (excluding the additional dimensions the existence of wich is implyed by string theory). objects are pushing outward on spacetime in all directions so objects should repulse not attract




#2
Jan413, 01:22 PM

P: 197

I don't think you can say that objects are pushing outward on spacetime. Where did you get that?




#3
Jan413, 01:45 PM

Sci Advisor
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#4
Jan413, 01:45 PM

P: 3,551

three dimensional gravity paradox 



#5
Jan413, 04:13 PM

Sci Advisor
PF Gold
P: 11,378

The rubber sheet thing is only a loose analogy and not a serious model. The Maths describe what is going on pretty well  so stick to that for any meaningful conclusions.




#6
Jan413, 05:38 PM

P: 74

As Sophiecentar has said, the rubber sheet analogy is just that, a very basic way to explain how gravity acts on different masses in 2 dimensions! You must realize that the universe we are in doesn't exist in 2 dimensions. And if you are not looking at the situation from directly above, the analogy becomes irrelevant. It is a 2d representation (loosely) of 3d gravity.
Your argument would be like me saying that I have discovered a flaw with maps, the fact that they don't represent what is actually on the ground when you are standing on the top of a mountain (or any other place). A map is a 2d representation of a 3d surface. Everything with mass in the universe sits inside the space/time of the universe, and that space/time IS bent and distorted by the mass. I don't understand your take on mass pushing against space/time? Also, you can't use a bed sheet for your explanation, as gravity doesn't increase or decrease at a linear amount from any mass, the square of the distance is used, which means even the 2d gravity analogy needs a 'rubber sheet' to mimic this. Damo 



#7
Jan513, 08:38 AM

P: 3,551

http://www.relativitet.se/spacetime1.html 



#8
Jan513, 10:55 PM

P: 74

Damo 



#9
Jan713, 10:17 AM

P: 2

i understand that the sheet model is only a two dimensional representation, i am stating that when we add the third dimension, the dip created in the sheet, would exist in all directions.




#10
Jan713, 10:34 AM

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#11
Jan713, 11:27 AM

Sci Advisor
PF Gold
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#12
Jan713, 11:43 AM

PF Gold
P: 244

An important thing to notice with the rubber sheet, is that the deflection is increasing closer to the "sun", representing the increased gravity that does not increase linear, but exponential to the distance. A useful experiment to understant the basics, even if it will for most people confuse more than educate if not explained "with a tweezer". Vidar 



#13
Jan713, 12:03 PM

Mentor
P: 28,836

You only saw the shadow of the animal. You haven't seen the animal itself. Zz. 



#14
Jan713, 12:05 PM

P: 750




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