Einstein and Riemann curvature tensor
$begingroup$
Riemann curvature tensor is dirrectly related to a path dependence of parallel transport. I read that Einstein first thought of this tensor to be the one that goes into his field equation but it didn't fit. Now, I know why this was problematic. There is a clear explanation of that. What I am asking is, is there a formulation of theory of gravity where equations give us directly $R$ and not $G$? $G$ is Einsteins tensor and $R$ Riemanns. Because, non-relativistic equation was used and directly translated, with energy-momentum tensor. Is there some other tensor related to the physics which would give $R$ instead of $G$? $G$ itself is not curvature...but from $G$ I guess we could calculate $R$ so there should be some equation that gives $R$ directly?
general-relativity curvature stress-energy-momentum-tensor
$endgroup$
add a comment |
$begingroup$
Riemann curvature tensor is dirrectly related to a path dependence of parallel transport. I read that Einstein first thought of this tensor to be the one that goes into his field equation but it didn't fit. Now, I know why this was problematic. There is a clear explanation of that. What I am asking is, is there a formulation of theory of gravity where equations give us directly $R$ and not $G$? $G$ is Einsteins tensor and $R$ Riemanns. Because, non-relativistic equation was used and directly translated, with energy-momentum tensor. Is there some other tensor related to the physics which would give $R$ instead of $G$? $G$ itself is not curvature...but from $G$ I guess we could calculate $R$ so there should be some equation that gives $R$ directly?
general-relativity curvature stress-energy-momentum-tensor
$endgroup$
add a comment |
$begingroup$
Riemann curvature tensor is dirrectly related to a path dependence of parallel transport. I read that Einstein first thought of this tensor to be the one that goes into his field equation but it didn't fit. Now, I know why this was problematic. There is a clear explanation of that. What I am asking is, is there a formulation of theory of gravity where equations give us directly $R$ and not $G$? $G$ is Einsteins tensor and $R$ Riemanns. Because, non-relativistic equation was used and directly translated, with energy-momentum tensor. Is there some other tensor related to the physics which would give $R$ instead of $G$? $G$ itself is not curvature...but from $G$ I guess we could calculate $R$ so there should be some equation that gives $R$ directly?
general-relativity curvature stress-energy-momentum-tensor
$endgroup$
Riemann curvature tensor is dirrectly related to a path dependence of parallel transport. I read that Einstein first thought of this tensor to be the one that goes into his field equation but it didn't fit. Now, I know why this was problematic. There is a clear explanation of that. What I am asking is, is there a formulation of theory of gravity where equations give us directly $R$ and not $G$? $G$ is Einsteins tensor and $R$ Riemanns. Because, non-relativistic equation was used and directly translated, with energy-momentum tensor. Is there some other tensor related to the physics which would give $R$ instead of $G$? $G$ itself is not curvature...but from $G$ I guess we could calculate $R$ so there should be some equation that gives $R$ directly?
general-relativity curvature stress-energy-momentum-tensor
general-relativity curvature stress-energy-momentum-tensor
edited Jan 27 at 21:57
Qmechanic♦
104k121871191
104k121871191
asked Jan 27 at 20:46
Žarko TomičićŽarko Tomičić
903511
903511
add a comment |
add a comment |
2 Answers
2
active
oldest
votes
$begingroup$
The formulation you are looking for exists. Starting off from Einstein's field equations: ($R_{ik}$ Ricci tensor, $R$ curvature scalar and $T_{ik}$ the stress tensor and $g_{ik}$ the metric tensor, $kappa=frac{8pi G}{c^4}$ with $G$ gravitational constant)
$$R_{ik} -frac{1}{2}g_{ik} R = kappa T_{ik}$$
One can alternatively move one index up in all tensors:
$$R_i^k -frac{1}{2}delta_i^k R = kappa T_i^k$$
and then taking the trace (we put the indices $i$ and $k$ equal and sum over it according to Einstein's summation convention):
$$ R = - kappa T$$
with $T = T_i^iequivsum^3_{i=0} T_i^i$. We substitute this expression for $R$ in Einstein's original field equations and bring the term with $T$ on the right side:
$$ R_{ik} = kappaleft(T_{ik} -frac{1}{2} g_{ik} Tright)$$
and if you like with the Riemann curvature tensor according to the definition of the Ricci tensor $R_{ik}:=g^{lm} R_{limk}$
$$ g^{lm} R_{limk} = kappaleft(T_{ik} -frac{1}{2} g_{ik} Tright)$$
$endgroup$
$begingroup$
Great! Isnt this then better? From geometrical point of view?
$endgroup$
– Žarko Tomičić
Jan 27 at 21:45
$begingroup$
When one searches for a vacuum solution of the EFEs, one can immediately start off with $R_{ik}=0$ which is easier than $R_{ik}-0.5g_{ik}R=0$
$endgroup$
– Frederic Thomas
Jan 27 at 22:12
add a comment |
$begingroup$
Here is one difference: If you believe that the EFEs should follow from a stationary action principle (as Hilbert did), then the Einstein tensor $G_{munu}$ is preferred over the Ricci curvature tensor $R_{munu}$, as only the former has the form of a functional derivative $frac{1}{sqrt{|g|}}frac{delta S}{delta g^{munu}}$ of some action functional $S$. (For the Einstein tensor $G_{munu}$ this is the Einstein-Hilbert action.)
$endgroup$
$begingroup$
Yes, I know, but the key word is "believe" . Why would anyone choose that action?
$endgroup$
– Žarko Tomičić
Jan 28 at 12:59
$begingroup$
The point is whether an action exists or not. Its specific form is irrelevant for the argument presented here. Actions play an important role in modern physics.
$endgroup$
– Qmechanic♦
Jan 28 at 13:13
$begingroup$
Yes yes...I see. I was just, you know, sayin..
$endgroup$
– Žarko Tomičić
Jan 28 at 13:15
$begingroup$
That is a great way to think of it.
$endgroup$
– R. Rankin
Jan 28 at 19:15
add a comment |
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2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
$begingroup$
The formulation you are looking for exists. Starting off from Einstein's field equations: ($R_{ik}$ Ricci tensor, $R$ curvature scalar and $T_{ik}$ the stress tensor and $g_{ik}$ the metric tensor, $kappa=frac{8pi G}{c^4}$ with $G$ gravitational constant)
$$R_{ik} -frac{1}{2}g_{ik} R = kappa T_{ik}$$
One can alternatively move one index up in all tensors:
$$R_i^k -frac{1}{2}delta_i^k R = kappa T_i^k$$
and then taking the trace (we put the indices $i$ and $k$ equal and sum over it according to Einstein's summation convention):
$$ R = - kappa T$$
with $T = T_i^iequivsum^3_{i=0} T_i^i$. We substitute this expression for $R$ in Einstein's original field equations and bring the term with $T$ on the right side:
$$ R_{ik} = kappaleft(T_{ik} -frac{1}{2} g_{ik} Tright)$$
and if you like with the Riemann curvature tensor according to the definition of the Ricci tensor $R_{ik}:=g^{lm} R_{limk}$
$$ g^{lm} R_{limk} = kappaleft(T_{ik} -frac{1}{2} g_{ik} Tright)$$
$endgroup$
$begingroup$
Great! Isnt this then better? From geometrical point of view?
$endgroup$
– Žarko Tomičić
Jan 27 at 21:45
$begingroup$
When one searches for a vacuum solution of the EFEs, one can immediately start off with $R_{ik}=0$ which is easier than $R_{ik}-0.5g_{ik}R=0$
$endgroup$
– Frederic Thomas
Jan 27 at 22:12
add a comment |
$begingroup$
The formulation you are looking for exists. Starting off from Einstein's field equations: ($R_{ik}$ Ricci tensor, $R$ curvature scalar and $T_{ik}$ the stress tensor and $g_{ik}$ the metric tensor, $kappa=frac{8pi G}{c^4}$ with $G$ gravitational constant)
$$R_{ik} -frac{1}{2}g_{ik} R = kappa T_{ik}$$
One can alternatively move one index up in all tensors:
$$R_i^k -frac{1}{2}delta_i^k R = kappa T_i^k$$
and then taking the trace (we put the indices $i$ and $k$ equal and sum over it according to Einstein's summation convention):
$$ R = - kappa T$$
with $T = T_i^iequivsum^3_{i=0} T_i^i$. We substitute this expression for $R$ in Einstein's original field equations and bring the term with $T$ on the right side:
$$ R_{ik} = kappaleft(T_{ik} -frac{1}{2} g_{ik} Tright)$$
and if you like with the Riemann curvature tensor according to the definition of the Ricci tensor $R_{ik}:=g^{lm} R_{limk}$
$$ g^{lm} R_{limk} = kappaleft(T_{ik} -frac{1}{2} g_{ik} Tright)$$
$endgroup$
$begingroup$
Great! Isnt this then better? From geometrical point of view?
$endgroup$
– Žarko Tomičić
Jan 27 at 21:45
$begingroup$
When one searches for a vacuum solution of the EFEs, one can immediately start off with $R_{ik}=0$ which is easier than $R_{ik}-0.5g_{ik}R=0$
$endgroup$
– Frederic Thomas
Jan 27 at 22:12
add a comment |
$begingroup$
The formulation you are looking for exists. Starting off from Einstein's field equations: ($R_{ik}$ Ricci tensor, $R$ curvature scalar and $T_{ik}$ the stress tensor and $g_{ik}$ the metric tensor, $kappa=frac{8pi G}{c^4}$ with $G$ gravitational constant)
$$R_{ik} -frac{1}{2}g_{ik} R = kappa T_{ik}$$
One can alternatively move one index up in all tensors:
$$R_i^k -frac{1}{2}delta_i^k R = kappa T_i^k$$
and then taking the trace (we put the indices $i$ and $k$ equal and sum over it according to Einstein's summation convention):
$$ R = - kappa T$$
with $T = T_i^iequivsum^3_{i=0} T_i^i$. We substitute this expression for $R$ in Einstein's original field equations and bring the term with $T$ on the right side:
$$ R_{ik} = kappaleft(T_{ik} -frac{1}{2} g_{ik} Tright)$$
and if you like with the Riemann curvature tensor according to the definition of the Ricci tensor $R_{ik}:=g^{lm} R_{limk}$
$$ g^{lm} R_{limk} = kappaleft(T_{ik} -frac{1}{2} g_{ik} Tright)$$
$endgroup$
The formulation you are looking for exists. Starting off from Einstein's field equations: ($R_{ik}$ Ricci tensor, $R$ curvature scalar and $T_{ik}$ the stress tensor and $g_{ik}$ the metric tensor, $kappa=frac{8pi G}{c^4}$ with $G$ gravitational constant)
$$R_{ik} -frac{1}{2}g_{ik} R = kappa T_{ik}$$
One can alternatively move one index up in all tensors:
$$R_i^k -frac{1}{2}delta_i^k R = kappa T_i^k$$
and then taking the trace (we put the indices $i$ and $k$ equal and sum over it according to Einstein's summation convention):
$$ R = - kappa T$$
with $T = T_i^iequivsum^3_{i=0} T_i^i$. We substitute this expression for $R$ in Einstein's original field equations and bring the term with $T$ on the right side:
$$ R_{ik} = kappaleft(T_{ik} -frac{1}{2} g_{ik} Tright)$$
and if you like with the Riemann curvature tensor according to the definition of the Ricci tensor $R_{ik}:=g^{lm} R_{limk}$
$$ g^{lm} R_{limk} = kappaleft(T_{ik} -frac{1}{2} g_{ik} Tright)$$
edited Jan 27 at 23:02
answered Jan 27 at 21:13
Frederic ThomasFrederic Thomas
1,5861115
1,5861115
$begingroup$
Great! Isnt this then better? From geometrical point of view?
$endgroup$
– Žarko Tomičić
Jan 27 at 21:45
$begingroup$
When one searches for a vacuum solution of the EFEs, one can immediately start off with $R_{ik}=0$ which is easier than $R_{ik}-0.5g_{ik}R=0$
$endgroup$
– Frederic Thomas
Jan 27 at 22:12
add a comment |
$begingroup$
Great! Isnt this then better? From geometrical point of view?
$endgroup$
– Žarko Tomičić
Jan 27 at 21:45
$begingroup$
When one searches for a vacuum solution of the EFEs, one can immediately start off with $R_{ik}=0$ which is easier than $R_{ik}-0.5g_{ik}R=0$
$endgroup$
– Frederic Thomas
Jan 27 at 22:12
$begingroup$
Great! Isnt this then better? From geometrical point of view?
$endgroup$
– Žarko Tomičić
Jan 27 at 21:45
$begingroup$
Great! Isnt this then better? From geometrical point of view?
$endgroup$
– Žarko Tomičić
Jan 27 at 21:45
$begingroup$
When one searches for a vacuum solution of the EFEs, one can immediately start off with $R_{ik}=0$ which is easier than $R_{ik}-0.5g_{ik}R=0$
$endgroup$
– Frederic Thomas
Jan 27 at 22:12
$begingroup$
When one searches for a vacuum solution of the EFEs, one can immediately start off with $R_{ik}=0$ which is easier than $R_{ik}-0.5g_{ik}R=0$
$endgroup$
– Frederic Thomas
Jan 27 at 22:12
add a comment |
$begingroup$
Here is one difference: If you believe that the EFEs should follow from a stationary action principle (as Hilbert did), then the Einstein tensor $G_{munu}$ is preferred over the Ricci curvature tensor $R_{munu}$, as only the former has the form of a functional derivative $frac{1}{sqrt{|g|}}frac{delta S}{delta g^{munu}}$ of some action functional $S$. (For the Einstein tensor $G_{munu}$ this is the Einstein-Hilbert action.)
$endgroup$
$begingroup$
Yes, I know, but the key word is "believe" . Why would anyone choose that action?
$endgroup$
– Žarko Tomičić
Jan 28 at 12:59
$begingroup$
The point is whether an action exists or not. Its specific form is irrelevant for the argument presented here. Actions play an important role in modern physics.
$endgroup$
– Qmechanic♦
Jan 28 at 13:13
$begingroup$
Yes yes...I see. I was just, you know, sayin..
$endgroup$
– Žarko Tomičić
Jan 28 at 13:15
$begingroup$
That is a great way to think of it.
$endgroup$
– R. Rankin
Jan 28 at 19:15
add a comment |
$begingroup$
Here is one difference: If you believe that the EFEs should follow from a stationary action principle (as Hilbert did), then the Einstein tensor $G_{munu}$ is preferred over the Ricci curvature tensor $R_{munu}$, as only the former has the form of a functional derivative $frac{1}{sqrt{|g|}}frac{delta S}{delta g^{munu}}$ of some action functional $S$. (For the Einstein tensor $G_{munu}$ this is the Einstein-Hilbert action.)
$endgroup$
$begingroup$
Yes, I know, but the key word is "believe" . Why would anyone choose that action?
$endgroup$
– Žarko Tomičić
Jan 28 at 12:59
$begingroup$
The point is whether an action exists or not. Its specific form is irrelevant for the argument presented here. Actions play an important role in modern physics.
$endgroup$
– Qmechanic♦
Jan 28 at 13:13
$begingroup$
Yes yes...I see. I was just, you know, sayin..
$endgroup$
– Žarko Tomičić
Jan 28 at 13:15
$begingroup$
That is a great way to think of it.
$endgroup$
– R. Rankin
Jan 28 at 19:15
add a comment |
$begingroup$
Here is one difference: If you believe that the EFEs should follow from a stationary action principle (as Hilbert did), then the Einstein tensor $G_{munu}$ is preferred over the Ricci curvature tensor $R_{munu}$, as only the former has the form of a functional derivative $frac{1}{sqrt{|g|}}frac{delta S}{delta g^{munu}}$ of some action functional $S$. (For the Einstein tensor $G_{munu}$ this is the Einstein-Hilbert action.)
$endgroup$
Here is one difference: If you believe that the EFEs should follow from a stationary action principle (as Hilbert did), then the Einstein tensor $G_{munu}$ is preferred over the Ricci curvature tensor $R_{munu}$, as only the former has the form of a functional derivative $frac{1}{sqrt{|g|}}frac{delta S}{delta g^{munu}}$ of some action functional $S$. (For the Einstein tensor $G_{munu}$ this is the Einstein-Hilbert action.)
answered Jan 27 at 22:28
Qmechanic♦Qmechanic
104k121871191
104k121871191
$begingroup$
Yes, I know, but the key word is "believe" . Why would anyone choose that action?
$endgroup$
– Žarko Tomičić
Jan 28 at 12:59
$begingroup$
The point is whether an action exists or not. Its specific form is irrelevant for the argument presented here. Actions play an important role in modern physics.
$endgroup$
– Qmechanic♦
Jan 28 at 13:13
$begingroup$
Yes yes...I see. I was just, you know, sayin..
$endgroup$
– Žarko Tomičić
Jan 28 at 13:15
$begingroup$
That is a great way to think of it.
$endgroup$
– R. Rankin
Jan 28 at 19:15
add a comment |
$begingroup$
Yes, I know, but the key word is "believe" . Why would anyone choose that action?
$endgroup$
– Žarko Tomičić
Jan 28 at 12:59
$begingroup$
The point is whether an action exists or not. Its specific form is irrelevant for the argument presented here. Actions play an important role in modern physics.
$endgroup$
– Qmechanic♦
Jan 28 at 13:13
$begingroup$
Yes yes...I see. I was just, you know, sayin..
$endgroup$
– Žarko Tomičić
Jan 28 at 13:15
$begingroup$
That is a great way to think of it.
$endgroup$
– R. Rankin
Jan 28 at 19:15
$begingroup$
Yes, I know, but the key word is "believe" . Why would anyone choose that action?
$endgroup$
– Žarko Tomičić
Jan 28 at 12:59
$begingroup$
Yes, I know, but the key word is "believe" . Why would anyone choose that action?
$endgroup$
– Žarko Tomičić
Jan 28 at 12:59
$begingroup$
The point is whether an action exists or not. Its specific form is irrelevant for the argument presented here. Actions play an important role in modern physics.
$endgroup$
– Qmechanic♦
Jan 28 at 13:13
$begingroup$
The point is whether an action exists or not. Its specific form is irrelevant for the argument presented here. Actions play an important role in modern physics.
$endgroup$
– Qmechanic♦
Jan 28 at 13:13
$begingroup$
Yes yes...I see. I was just, you know, sayin..
$endgroup$
– Žarko Tomičić
Jan 28 at 13:15
$begingroup$
Yes yes...I see. I was just, you know, sayin..
$endgroup$
– Žarko Tomičić
Jan 28 at 13:15
$begingroup$
That is a great way to think of it.
$endgroup$
– R. Rankin
Jan 28 at 19:15
$begingroup$
That is a great way to think of it.
$endgroup$
– R. Rankin
Jan 28 at 19:15
add a comment |
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