# Einsteins thoughts behind c2 in E=mc2

• Incyder
In summary: E=mc2 is an equation that summarizes a lot of physical relationships in terms of a single quantity. The fact that it has the form of an equation is a coincidence, not something that was deliberately chosen.

#### Incyder

I've seen a previous threads where it was a mathematical consistency based on four-dimensions, and a host of other reasons. I'm currently trying to reconcile my belief that it has to do with time dilation and the observer effect.

The square (^2) comes from the definition of Energy. (momentum is proportional to velocity => Force = dp/dt => Energy = Integral of force w.r.t distance=> Energy is proportion to velocity squared). This also can trace back to the definition given by Leibniz and Chatelet. But this does not lead to the c term.
The c comes from the conservation of momentum and the postulates of special relativity proposed by einstein (which leads a different addition of velocities compared to that in Newtonian mechanics).

jedishrfu said:

http://www.emc2-explained.info/Emc2/Deriving.htm#.VMRN2oFOKrU
I've read that. I am completely a layman in this rodeo. That math seems to be the only refuge for some. I was hoping that knowledgeable people here could possibly tell me if the observer effect had any bearing on two observable quantities, both being the speed of light.

The maths simply shows you that E=mc2 is implied by the statements "The laws of physics are the same in all frames of reference" and "The speed of light in the same in all inertial frames of reference". That's pretty much all there is in the way of thinking underlying it.

Nuclear reactors and nuclear weapons are a fairly powerful demonstration that the thinking is justified.

The observer effect doesn't really come into it. E=mc2 is just the end of a chain of reasoning from the principles I stated.

By the way, the tone I read into your posts suggests to me that you might want to take another glance at the personal theories parts of the guidelines for posting before continuing the conversation. Apologies if I am castlng aspersions.

The title of the thread suggests that you're just asking about the factor of c2. Is that correct? It has to be there because of units. In the relativistic system of units normally used in relativity, c=1, so the equation is simply E=m. To convert it back to SI units, you put in the c2.

If you want to know more generally about how Einstein arrived at E=mc2, you could just read his original paper: http://www.fourmilab.ch/etexts/einstein/E_mc2/www/

I agree with bcrowell, it is just a unit conversion factor. It comes about because the SI system uses incompatible units for energy, momentum, and mass, just like the traditional nautical system uses incompatible units for distance (nautical miles) and depth (fathoms).

## 1. What does "c2" stand for in E=mc2?

The "c2" in E=mc2 stands for the speed of light squared. This is a constant value that represents the speed at which light travels in a vacuum, which is approximately 299,792,458 meters per second.

## 2. Why did Einstein use the speed of light in his famous equation?

Einstein used the speed of light in his equation because he discovered that it is the fastest speed in the universe and is constant regardless of an observer's frame of reference. This led him to believe that it is a fundamental property of the universe and must be incorporated into his theory of relativity.

## 3. How did Einstein come up with the idea of using the speed of light in his equation?

Einstein's idea of using the speed of light in his equation was based on his theory of special relativity. This theory states that the laws of physics are the same for all observers, regardless of their relative motion. Through his thought experiments and mathematical equations, Einstein showed that the speed of light is a fundamental constant that is intertwined with space and time.

## 4. What is the significance of c2 in E=mc2?

The significance of c2 in E=mc2 is that it represents the relationship between mass and energy. By multiplying the speed of light squared by the mass of an object, it shows how much energy is equivalent to that mass. This equation has revolutionized our understanding of the universe and has been used in many scientific discoveries and technological advancements.

## 5. Can the c2 value in E=mc2 change?

No, the c2 value in E=mc2 is a constant that does not change. The speed of light is considered to be one of the fundamental constants of the universe and has been measured to be the same for all observers. Therefore, the c2 value will always remain the same in Einstein's famous equation.