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-   -   Newtonian vs Einsteinian gravity in everday life? (http://www.physicsforums.com/showthread.php?t=655682)

Fredster1765 Nov29-12 02:13 PM

Newtonian vs Einsteinian gravity in everday life?
 
Let me begin by saying I'm not a student of any kind of physics, I just have a general curiosity about the forces at work in the universe, so for most of the people reading this, my question will probably seem either stupid or strangely obvious!

Anyway, my question is this:
My understanding is Einstein's theory of general relativity basically proved Newton wrong with regard to his universal law of gravitation, but does that mean gravity in the Newtonian sense doesn't exist at all, and that all gravitational attraction between objects is due to curvature in space-time caused by those objects? Even when considering something basic (an apple) falling from some altitude (the branch of a tree) onto the earth?

Or is Einstein's formulation more appropriate when dealing with massive objects like stars and planets, while Newton's idea holds true on smaller scales like people and apples?

mathman Nov29-12 03:09 PM

Re: Newtonian vs Einsteinian gravity in everday life?
 
Newton's theory is a very good approximate description of gravity. Einstein's theory (General Relativity) is more accurate and does provide a theoretical underpinning.

For most calculations Newton's theory works fine - the Apollo mission as well as most space exploration uses it.

A practical example where G.R. is needed is GPS navigation.

K^2 Nov29-12 04:34 PM

Re: Newtonian vs Einsteinian gravity in everday life?
 
We don't know how the gravity really works. We don't know how anything really works. All we have are models that make predictions that we can test. As mathman pointed out, Newtonian Gravity gives you satisfactory approximations in most practical situations. Being far easier to compute, Newtonian Gravity is usually used. But General Relativity is perfectly adequate for describing all the same things. Yes, you can easily describe apple's fall from the tree with Einstein's equations as motion caused by curvature of space-time. It's not even all that hard. But still, way more involved than same computation done according to Newton.

The reason we use Einstein's formulation to compute effects of gravity is because either Newtonian formalism doesn't provide sufficient precision (e.g. GPS navigation) or because it fails completely (e.g black holes). In other cases, we usually use Newtonian formalism because it's easier. But not because GR cannot be used. It always can be.

Fredster1765 Nov30-12 05:40 AM

Re: Newtonian vs Einsteinian gravity in everday life?
 
Ah I see! Thank you both, I believe that answers my questions, for the time being at least.
I can tell these forums will be of great use to me in future!


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