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Which Is It?





Dennise
Two questions:

1.Does Newton's gravity explain Einstein's warped space, or does Einstein's warped space explain Newton's gravity?

2. If space is really warped - and there is really no Newtonian gravity - why DOES space curve around objects with mass?
Bikerman
1) The latter
2) We don't know if the question has any meaning. Why do electrons and protons have opposite charge?
It could be that this is simply the inevitable result of the BB, or there could be some deeper theory that explains the fundamental constants...we don't know.
kelseymh
Dennise wrote:
Two questions:

1.Does Newton's gravity explain Einstein's warped space, or does Einstein's warped space explain Newton's gravity?


As Bikerman said, the latter. Newtonian gravity is valid in the limit of low masses or large distances (i.e., small-ish M/R), and in the limit of low velocities. General Relativity, as near as we can determine, is valid for <i>all</i> M/R where R is large enough to be semi-classical (i.e., >~ 10<sup>-15</sup> m), and it is valid for all velocities. GR reduces to Newton's equations in the small M/R limit, and hence "explains" it.

Quote:
2. If space is really warped - and there is really no Newtonian gravity - why DOES space curve around objects with mass?


Because the field equations require it. The equations Einstein discovered say that there is a proportionality between the stress-energy tensor (basically, the distribution of density and pressure in a region) and the metric (the local curvature of that region).
_AVG_
In science we do not Assume that nature works in the way we model it. We just keep searching for the next best most accurate model of nature. In one time, Newton explained everything necessary, then Einstein explained even more ... Now, there are some things which even he didn't explain.

The curving of space is a very accurate model in that it explains the phenomenon of gravitation much better (for it involves geodesics, a straight line on a higher dimensional surface becomes curved). We assume that space-time is warped by mass in order to understand the workings of nature better.
Dennise
AVG,

Great explanation! Makes perfect sense to me.
Adiiforu
both theories hold good ground. If we think abt which explains which than i would say nothing explains. What i mean is when newton discovered gravity einstiens theory did nt even exist, and einstien tried to find out abt space wrapping because he was unhappy abt gravity. Also curving of space is controversial.
kelseymh
Adiiforu wrote:
both theories hold good ground. If we think abt which explains which than i would say nothing explains. What i mean is when newton discovered gravity einstiens theory did nt even exist, and einstien tried to find out abt space wrapping because he was unhappy abt gravity. Also curving of space is controversial.


Can you provide any references for either of your claims?

According to the published papers, Einstein was not "unhappy about gravity" as such. Rather, he formulated general relativity in order that gravity should be (a) consistent with special relativity, and (b) have a logical, justifiable basis (unlike Newton's theory, which is essentially phenomenological).

Curvature of spacetime is only "controversial" among non-physicists who don't have the wherewithal to study or understand the mathematics.
saberlivre
Adiiforu wrote:
(...) curving of space is controversial.


Not talking
hspb
What was first - chicken or egg?
ocalhoun
hspb wrote:
What was first - chicken or egg?

The egg.

The very first thing you could identify as a 'chicken' would have been a mutant that hatched from the egg of a different (but probably extremely similar) species.
Or, put another way, fishes and dinosaurs were laying eggs a long time before chickens ever came around.

Next question?
Arrogant
Ofcourse the later one is true and Newtonians law is right for some cases only
it couldn't explain the orbit of mercury
Bikerman
Well, the results obtained were different to the observed precession of the orbit. Indeed this was one of the first empirical tests of Relativity - the first being Arthur Eddington's expedition to observe starlight deflection during an eclipse:

Eddington is said to have 'proved' Einstein correct, but his results were actually pretty noisy and I'm not sure how conclusive he could have reasonably been..

The mercury precession test came later.



It was recently (1993) redone by Roy North, to give the following degree of correspondence between observation and theory:
  • 5599 total advance with respect to to geocenter (our reference frame.)
  • 5025 contribution of precession of Earth's equinoxes.
  • 531 Classical or Newtonian contribution of the other planets.
  • 43 General relativity correction (modern theory: 42.98 )
(Figures here are arcsec per Julian century. You'll notice the GR correction is actually an order of magnitude smaller than the Classical correction needed for the other planets, so Newton wasn't that far out )

I actually wrote an introductory tutorial on SR a while back...hold on...yep, it is on my website if anyone wants to check it out..

http://www.bikerman.co.uk/science/multimedia/special-relativity-tutorial
spinout
1. Einsteins errorly warped space explains the Newton...
2. because of resonance I suppose.
asnani04
For the first question, I think the latter is the correct option. I don't know for sure about the second one.
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