# Deriving Einstein's Equation: Calculating ##R_{00}##

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• JonnyG
In summary, Carroll is deriving Einstein's equation from the Newtonian limit by calculating the ##00## component of the Ricci tensor, denoted as ##R_{00}##. To do this, he uses the perturbation ##h## and sets ##g_{\mu \nu} = \eta_{\mu \nu} + h_{\mu \nu}##. He then simplifies the equation to ##-\frac{1}{2}\delta^{ij} \partial_i \partial_j g_{00}##, which can be rewritten as ##-\frac{1}{2} \partial_i g^{i \lambda} \partial_\lambda g_{00}##. This simplification is possible because of the
JonnyG
Going through Carroll's book, he is deriving Einstein's equation by looking at what it should reduce to in the Newtonian limit. Part of this process is in calculating ##R_{00}## (the ##00## component of the Ricci tensor). So he let's ##g_{\mu \nu} = \eta_{\mu \nu} + h_{\mu \nu}## where ##h## is some small perturbation. So ##\begin{align*} R_{00} &= R^i_{0i0} \\ &= \partial_i[\frac{1}{2}g^{i \lambda}(\partial_0 g_{\lambda 0} + \partial_0 g_{0 \lambda} - \partial_\lambda g_{00})] \\ &= \partial_i(-\frac{1}{2} g^{i \lambda} \partial_\lambda g_{0 0}) \\ &= -\frac{1}{2} \partial_i g^{i \lambda} \partial_\lambda g_{00} \\ &= -\frac{1}{2}\delta^{ij} \partial_i \partial_j g_{00} \end{align*} ##

I don't understand how he gets from the second last step to the very last step?

EDIT: Is this correct: ##g^{i \lambda} \partial_\lambda = \partial_i## and hence ##\frac{-1}{2} \partial_i g^{i \lambda} \partial_\lambda g_{00} = \frac{-1}{2} \partial_i \partial_i g_{00} = \frac{-1}{2} \delta^{ij} \partial_i \partial_j g_{00}## where ##\delta^{ij}## is the Kronecker delta?

Last edited:
Keep only terms which are linear in h and use the fact that ##\eta## is constant.

JonnyG
Thank you. The calculation worked out.

## 1. What is Einstein's equation and why is it important?

Einstein's equation, also known as the Einstein field equations, is a set of 10 equations that describe the relationship between the curvature of spacetime and the distribution of matter and energy in the universe. It is important because it is a cornerstone of Einstein's theory of general relativity, which has revolutionized our understanding of gravity and the universe.

## 2. How do you calculate ##R_{00}## in Einstein's equation?

To calculate ##R_{00}##, also known as the Ricci curvature tensor component, you first need to solve for the metric tensor, which describes the curvature of spacetime. This involves solving a set of partial differential equations known as the Einstein field equations. Once you have the metric tensor, you can then use it to calculate ##R_{00}## using a specific formula based on the components of the metric tensor.

## 3. What does ##R_{00}## represent in Einstein's equation?

##R_{00}## represents the curvature of spacetime in the time direction, also known as the time-time component of the Ricci curvature tensor. This component is important because it describes how the presence of matter and energy affects the fabric of spacetime, leading to the effects of gravity.

## 4. What is the significance of calculating ##R_{00}## in Einstein's equation?

Calculating ##R_{00}## allows us to understand how the distribution of matter and energy in the universe affects the curvature of spacetime. This is crucial for understanding the behavior of gravity and the evolution of the universe. It also allows us to make predictions and test the predictions of Einstein's theory of general relativity.

## 5. Are there any practical applications of calculating ##R_{00}## in Einstein's equation?

Yes, there are several practical applications of calculating ##R_{00}##. For example, it is used in the study of black holes, which are regions of spacetime with extremely strong gravitational fields. It is also used in cosmology to study the evolution of the universe. Additionally, it has practical applications in technologies such as GPS, which relies on precise measurements of time and space, which are affected by the curvature of spacetime.

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