# Any such equation to relate spacetime to energy/mass

• professor
In summary: Ricci Tensor is a measure of how curved a space is, and the Ricci Scalar is a measure of how much curvature the space has. The larger the Ricci Tensor, the more curved the space. The larger the Ricci Scalar, the more curved the space is.

#### professor

this may be quite a usefull euation indeed by my standards... and think its worth looking into, though i do not suspect one would exist

by this i have no definite meaning, just anything you have that fits the catigory even a little let me know... (this sure would help with quantum gravity if there is even an indirect relation of some sort...atleast i suspect it would)

Einstein's General Relativity is the theory of the interaction between matter and spacetime. There is a system of equations, the Einstein Field Equations, that uniquely determines the 4-dimensional curvature in a region given the distribution of matter and energy.

The EFE are a system of 16 highly nonlinear coupled partial differential equations in 16 unknowns. Unless you have a truly exceptional backround in physics, it is unlikely that you have encountered anything like this. Without the aid of specail notations, it is essentially impossible to express the tens of thousands of individual terms (all quadratic differentials). Here is an example of one of the 16 components of the Reimann curvature tensor (which is highly simplified due to symmetry) which is just one a part of EFE:

#### Attachments

• EFE.jpg
28.3 KB · Views: 476
Crosson said:
Here is an example of one of the 16 components of the Reimann curvature tensor (which is highly simplified due to symmetry) which is just one a part of EFE:
That would make a great wallpaper pattern! The whole set would probably be enough to do my living room.

could you explain a bit more about theis EFE, you are right i have never heard of it... and am fairly surprised to hear it exists...but then again what exactly is it, or its point? i could use a more in depth explination... and while I am not a physics genious just yet, i can handle all the equations you throw at me. so in such a manner direct me to anything that may help (tensor calc more likely then not, i believe i should be able to atleast determine a good amount of the reason for such equations with the equations themselves and defined variables)

in that thumbnail just about all i can make out is some wave functions, and what may be some sigmas... i relate sigma with bonding generaly, what is the use for it here... and what are those reallly blurry smaller symbols :P

Long before Einstein, Reimann found that distance on any curved (or not) space could be expressed by a metric. Here are some examples:

$$ds^2=dx^2+dy^2$$

$$ds^2 = dr^2 +r^2 d\theta ^2$$

Hopefully, these two metrics look familiar to you Professor. They both represent flat space, one is in cartesian coordinates and one is in polar coordinates. It is noteworthy that although the two metrics look different, they both represent the same thing. Here is a metric that expresses distance on the surface of a sphere:

$$ds^2 = R^2d\phi ^2 + R^2 Sin^2(\phi) d\theta ^2$$

This surface now has a curvature (the first two metrics haves zero curvature they are flat). It is certainly not obvious by looking that this metric belongs to a curved surface where as the flat metric in polar coordinates does not. How can we tell the curvature of a space using the metric? Reimann and Gauss found that all you have to do is take a lot of derivatives!

Here is Reimann's general form of the metric:

$$ds^2 = \sum_{\mu,\nu} g_{\mu,\nu} dx^{\mu}dx^{\nu}$$

Hopefully you can see that this is:

$$ds^2 = g_{0,0} (dx^0)^2 + g_{1,0}dx^1 dx^0 +...$$

Notice that the metric coeffecients $g_{i,j}$ (there are 16 of them in 4-d space time because we have four coordinates $x^i where i = 0,1,2,3$) contain all the information, for the reason we put them in 4x4 matrix called the metric tensor. Now like I said, once we have the metric tensor, we are only a few thousand derivatives away from finding the curvature.

From the metric tensor we define the affine connection:

$$\Gamma_{\sigma,\mu,\nu} = \frac{1}{2}\sum_{\mu,\nu} g^{\mu,\nu}(\partial _{\nu} g_{\mu,\sigma}-\partial_{\sigma}g_{\mu,\nu} + \partial_{\mu}g_{\sigma,\nu})$$

As you can see, any particular affine connection (Ex. $\Gamma_{1,1,1}$) contains 48 terms. So we already have 64 affine connections with 48 terms each.

From the affine connection we find the rank 4 reimann curvature tensor:

$$Reimann_{\lambda,\mu,\nu,\kappa} = \frac{1}{2}(\partial _{\kappa,\mu} g_{\lambda,\nu} +\partial_{\kappa,\lambda}g_{\mu,\nu} +\partial_{\nu,\lambda} g_{\kappa,\mu} + \sum _{\sigma,\epsilon} g_{\sigma,\epsilon}(\Gamma_{\epsilon, \nu, \kappa}\Gamma{\sigma,\mu,\kappa}-\Gamma_{\epsilon,\kappa,\lambda}\Gamma_{\sigma,\mu,\nu}$$

For General Relativity we contract this to the Ricci Tensor:

$$R_{\mu,\kappa} = \sum_{\nu,\lambda} g^{\lambda,\nu} Reimann_{\lambda, \nu,\mu,\kappa}$$

And the Ricci Scalar:

$$R = \sum_{\nu,\lambda} g^{\lambda,\nu} R_{\lambda, \nu}$$

In the most general case, computation of the Ricci Scalar involves over 15,000 terms. But at least now we have reached a point where we can express the EFE:

$$R_{\mu,\nu} -\frac{1}{2} g_{\mu,\nu}R = \frac{8 \pi G}{c^2} T_{\mu,\nu}$$

You should be able to interpret the left side of the equation as the curvature of space time. The right side is called the stress energy tensor, and it is basically energy density (and momentum densities in different directions).

The dependent variables in the system of PDEs are the metric coefficients, the independent variables are the four coordinates of spacetime; the components of the stress energy tensor are the inhomogeneous terms. A straightfoward method of approach would be to choose a stress energy tensor and solve the system of PDEs for the metric coefficients; but, in all but the simplest cases, the equations are so ultra-complex that nothing on Earth is capable of this method. A more much more tractable approach is to input a particular metric and stress energy tensor, and solve the EFE for the time evolution of that metric.

Last edited:
i feel I am on the verge of some sort of mental break though...dont worry i doubt i means much though, you have been a great help-thx for the info

It's actually RIEMANN and the comma between sub/superscripts means a differentiation wrt "x"...

Daniel.

## 1. What is the equation that relates spacetime to energy/mass?

The equation that relates spacetime to energy/mass is E=mc², also known as the mass-energy equivalence equation. This equation was proposed by Albert Einstein in his theory of general relativity and it states that energy (E) and mass (m) are equivalent and can be converted into one another.

## 2. How does the equation E=mc² explain the relationship between spacetime and energy/mass?

The equation E=mc² explains the relationship between spacetime and energy/mass by showing that energy and mass are two forms of the same thing. According to Einstein's theory of general relativity, matter (mass) and energy both curve the fabric of spacetime, and this curvature is what we experience as gravity.

## 3. Can you give an example of how E=mc² has been proven to be true?

One example of how E=mc² has been proven to be true is through nuclear reactions, such as nuclear fission and fusion. In these reactions, a small amount of mass is converted into a large amount of energy, following the ratio of E=mc². The atomic bomb and nuclear power plants are both based on this principle.

## 4. Is the equation E=mc² applicable to all forms of energy and mass?

Yes, the equation E=mc² is applicable to all forms of energy and mass. This includes all types of particle energy (such as kinetic and potential energy), electromagnetic energy (such as light and heat), and mass of any kind (such as atoms and subatomic particles).

## 5. How does the equation E=mc² impact our understanding of the universe?

The equation E=mc² has greatly impacted our understanding of the universe by providing a deeper understanding of the relationship between energy, mass, and spacetime. It has also led to advancements in nuclear energy and technology, and has played a crucial role in the development of theories such as the Big Bang and the formation of black holes.