Further contributions of GR study to understanding of the Universe

[Ras72]

What have been the major contributions to our understanding of the Universe made by the study of GR from 10 years after its formulation to this day?

[Klaynos]

A quick web of science search gives more than 16000 results, a bit too much to post here I fear.

[Ras72]

I'll rephrase more clearly. Aside from GR's confirmations, applications, observations.

What are the major new physics and new predictions brought about by the study of GR in the last 90 years?

 

 

 

[timo]

Everything related to a Big Bang scenario would come to my mind, e.g. understanding the cosmic microwave background.

[imatfaal]

[timo]

I wonder why you and Klaynos are so dismissive of the question. I'd rather like to see concrete examples, too.

[Mystery111]

I'll rephrase more clearly. Aside from GR's confirmations, applications, observations.

What are the major new physics and new predictions brought about by the study of GR in the last 90 years?

 

 

 

 

I can think of extensions. Like the Einstein-Cartan theory where curvature is replaced with torsion.

[Klaynos]

Sorry, I didn't mean to seem dismissive, it's an incredibly broad question, where a conclusive list is probably impossible past vague comments like "situations, experiments etc. where very accurate clocks are required" ...

[timo]

Well, I guess "precision timing" would be a nice example, not strictly for "major contribution to our understanding" (whatever that may be exactly) but at least for the related "major contribution to our civilization".

[Ras72]

I can think of extensions. Like the Einstein-Cartan theory where curvature is replaced with torsion.

Thank you. That's more along the lines was thinking of.But has any work on GR led to new predictions? As opposed to making new predictions based on GR(and eventually having them confirmed I am not doubting GR's validity or importance)

 

 

[Mystery111]

Thank you. That's more along the lines was thinking of.But has any work on GR led to new predictions? As opposed to making new predictions based on GR(and eventually having them confirmed I am not doubting GR's validity or importance)

 

 

 

No offense to the other posters, but no doubt I was a little confused by some of the comments... I thought your question was rather basic.

 

As for new predictions, when the era came that relativity brought about the existence of black holes, were an extension itself of this theory. I think it was Russian Scientists who first outspokenly expressed their opinions on these objects calling them ''frozen stars.'' No doubt my history is incorrect there, and I challenge you to reference it, but essentially I knew that Einstein did not believe originally that black holes could exist in nature.

 

As for new theories beyond that, there are a few alternative general theories, such as Scalar Field Theories, expanded by Nordstrom, or maybe even Littlewood, or even Page and Turner who expanded on this theory. There are what are called Bimetric Theories which contain both the normal tensor metric and the Minkowski metric. There are even Scalar-Tensor and Vector-Tensor Theories of General Relativity.

 

It would be safe to say, Genereal Relativity has a lot of forms.

Edited October 28, 2011 by Mystery111

[DrRocket]

I can think of extensions. Like the Einstein-Cartan theory where curvature is replaced with torsion.

 

 

 

EC theory does not "replace curvature with torsion".

 

GR makes the assumption that spacetime is torsion free. That implies that there is a Levi-Civita connection for which the metric is preserved by parallel translation. So you get a nice metric theory, but one that cannot handle intrinsic spin.

 

EC theory makes no such assumption. The result is a more mathematically complex theory. But it is a theory that is indistinguishable from GR with current measurement technology -- the differences in most circumstances are too small to measure. There is still curvature in EC theory, but you don't have it in terms of a metric. The geometry is not Riemannian or pseudo-Riemannian. The singularity theorems of GR do not, in general, hold.

 

I wonder why you and Klaynos are so dismissive of the question. I'd rather like to see concrete examples, too.

 

I'm not sure what counts as "concrete".

 

GR made cosmology into a science, and provided a framework for study of "the universe" -- the spacetime manifold. Without that it is difficult to be precise about what one means by "the universe". With GR that can be made precise, models constructed, and (as shown by Hawking and Penrose) deep insight gained into the origins, evolution and large scale structure of that universe.

 

GR is really a radical new perspective on what is meant by "space" and "time". One gets a hint in special relativity, but also a distortion because of the use of a single global coordinate system in SR. In GR you are forced to recognize that there is no such thing as global space or global time. What clocks measure is "proper time", which (using units where c=1) is just the arc length of the world line of the clock between events, using the spacetime metric. What is perceived as space is dependent on the local observer. Similarly with time -- "time here' vs "time there" can be meaningless. That is a huge philosophical change.

 

Along with GR you get new phenomena -- an effect of gravity on light, black holes. These have no counterpart in Newtonian physics.

 

You also get some puzzles. Conservation of energy becomes problematic. GR does not handle gravitational energy. Most importantly, GR is purely deterministic and incompatible with quantum theories. Theories uniting gravitation with quantum phenomena have stubbornly resisted consistent formulation.

 

The fact remains that Newtonian gravity makes very accurate predictions under most circumstances, even in astrophysics, and the effects of GR are subtle. You don't need GR to handle typical engineering problems. You can launch a satellite, fix a toaster or pour concrete without any knowledge of GR at all.

Edited October 29, 2011 by DrRocket

[Mystery111]

EC theory does not "replace curvature with torsion".

 

GR makes the assumption that spacetime is torsion free. That implies that there is a Levi-Civita connection for which the metric is preserved by parallel translation. So you get a nice metric theory, but one that cannot handle intrinsic spin.

 

EC theory makes no such assumption. The result is a more mathematically complex theory. But it is a theory that is indistinguishable from GR with current measurement technology -- the differences in most circumstances are too small to measure. There is still curvature in EC theory, but you don't have it in terms of a metric. The geometry is not Riemannian or pseudo-Riemannian. The singularity theorems of GR do not, in general, hold.

 

 

 

 

Ok, I checked this, I agree.

 

I know enough of General Relativity, but near to nothing of the EC theory. All I knew is that torsion becomes a prominent feature and just assumed it replaced curvature.