GR explanation of Newtonian Phenomena

aachenmann
Messages
11
Reaction score
0
1. How would a general relativist explain why an object falls towards the earth?

2. Is it correct to say that it is not the apple that falls towards the Earth but it is the Earth that accelerates towards the apple? Why is this ok to say?
 
Physics news on Phys.org
The apple follows a geodesic path through space-time. One way o describing the mathematical characteristics of this path is to say that it satisfies the principle of extremal aging.

see for instance http://www.bun.kyoto-u.ac.jp/~suchii/extrem.aging.html
http://www.eftaylor.com/pub/chapter2.pdf

and look for past PF posts with this keyword.

2) The question is really irrelevant in GR - it doesn't matter which viewpoint you use.
 
Last edited by a moderator:
aachenmann said:
1. How would a general relativist explain why an object falls towards the earth?
Science does not explain, it describes. To say that it explains leads one into a logical circle.
2. Is it correct to say that it is not the apple that falls towards the Earth but it is the Earth that accelerates towards the apple? Why is this ok to say?
What accelerates is actually doing the acceleration is a coordinate dependant statement. Once you choose a coordinate system you can state whose coordinates in that system represents an accelerating object. Here I speak of 3-acceleration since the 4-acceleration of each object, i.e. Earth and apple, is zero.

Pete
 
Since the OP is no longer with us, there seems no point in keeping this thread open.
 

Thread 'I don't see how a black hole's event horizon can be crossed'

OK, so this has bugged me for a while about the equivalence principle and the black hole information paradox. If black holes "evaporate" via Hawking radiation, then they cannot exist forever. So, from my external perspective, watching the person fall in, they slow down, freeze, and redshift to "nothing," but never cross the event horizon. Does the equivalence principle say my perspective is valid? If it does, is it possible that that person really never crossed the event horizon? The...
View full post »

Thread 'Synchronizing clocks in an inertial frame if light is anisotropic'

ASSUMPTIONS 1. Two identical clocks A and B in the same inertial frame are stationary relative to each other a fixed distance L apart. Time passes at the same rate for both. 2. Both clocks are able to send/receive light signals and to write/read the send/receive times into signals. 3. The speed of light is anisotropic. METHOD 1. At time t[A1] and time t[B1], clock A sends a light signal to clock B. The clock B time is unknown to A. 2. Clock B receives the signal from A at time t[B2] and...
View full post »

Thread 'Is the variation of the metric ##\delta g_{\mu\nu}## a tensor?'

From $$0 = \delta(g^{\alpha\mu}g_{\mu\nu}) = g^{\alpha\mu} \delta g_{\mu\nu} + g_{\mu\nu} \delta g^{\alpha\mu}$$ we have $$g^{\alpha\mu} \delta g_{\mu\nu} = -g_{\mu\nu} \delta g^{\alpha\mu} \,\, . $$ Multiply both sides by ##g_{\alpha\beta}## to get $$\delta g_{\beta\nu} = -g_{\alpha\beta} g_{\mu\nu} \delta g^{\alpha\mu} \qquad(*)$$ (This is Dirac's eq. (26.9) in "GTR".) On the other hand, the variation ##\delta g^{\alpha\mu} = \bar{g}^{\alpha\mu} - g^{\alpha\mu}## should be a tensor...
View full post »

Similar threads

B Eddington Exp vs Newton: Comparing Starlight Deflection
Replies
6
Views
2K
I Source of Gravity of heavy mass as per GTR
Replies
14
Views
2K
I Proper vs. coordinate acceleration
Replies
37
Views
6K
I Is Absolute Position Necessary to Understand Relativity?
Replies
5
Views
1K
I Why does an object initially at rest begin to fall?
Replies
24
Views
4K
I Beginner's Guide to GR: Questions & Answers
Replies
13
Views
2K
I Richard Feynman: Deriving Lorentz Mass Transformation
Replies
9
Views
2K
I Reconciling smooth spacetime with variable, rotating, earth gravity
Replies
4
Views
1K
B Why Does Matter Fall to Center of a Mass? Explained
Replies
4
Views
1K
I Understanding Gravity with GR: Beginner's Guide by Aerodyn
Replies
10
Views
2K

Hot Threads

Recent Insights

Back
Top