# is mass equal to energy?

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E=mc^2

Mass can neither be created nor destroyed. Energy can neither be created nor destroyed. And we know from observation of an object exploding that there is less mass after a release of energy. From this can we assume mass is stored energy? Or is mass transformed from this abstract substance into another abstract substance? Are they equal in value or two forces interacting? Before you respond let me ask you a few off topic questions. what do the curvature of a circle, the parallels of a right triangle, and many other observations of existence have in common? How do they differ from Euler's identity?

E=mc^2 expanded or the theory of movement.

relativity.doc

They are similar in their interactions. I don't know why. But I can show you how. Maybe how is all we can know.

-b^2

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Mass contributes to energy, but it is not equal to it. There are other forms of energy that are not mass. Your equation is even invalid for a moving object. You would need to augment it to $E^2=p^2c^2+m^2c^4$ where $p$ is momentum.

Also, your first and third sentences are contradictory; mass can be created and destroyed.

Edited by Severian
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E=mc^2

Mass can neither be created nor destroyed.

You have to be cautious in forums suchs this. Different people mean different things when they use the term mass. For example, in A first course in general relativity by Bernrd F. Schutz the author writes on page 94 ..energy and 'inertial mass' are frame dependant ... and on page 104 he writes ...energy and mass are the same.... Other people refer to mass as being synonymous with proper mass. Severian is talking about proper mass (aka rest mass). I think that with this in mind you'll better understand the subject matter.

Energy can neither be created nor destroyed. And we know from observation of an object exploding that there is less mass after a release of energy.

The way Taylor and Wheeler describe mass then in such explosions the mass remains unchanged. In their text the term "mass" refers to what is known as invariant mass. This means that we sum up all the energies of all the particles and cal it E and sum up all the momenta of the particles and call it p. The mass according to them is the m in $E^2 - (pc)^2 - m^2c^4$ and this remains constant during a nuclear explosion. This is because energy is conserved and in the zero momentum frame E = mc2

From this can we assume mass is stored energy?

In a sense, sure. The energy is bound up in what is called binding energy which is essentially potential energy, which is negative.

Or is mass transformed from this abstract substance into another abstract substance?

While its true that both energy or mass are conserved, its also true that matter changes form. When an electon and a positron annihilate what is left is photons. So the form of the matter changed.

Before you respond let me ask you a few off topic questions. what do the curvature of a circle, the parallels of a right triangle, and many other observations of existence have in common? How do they differ from Euler's identity?

Ya got me.

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As Severian correctly notices a more correct expression is $E^2=p^2c^2+m^2c^4$ although this is not still the more general relativistic expression. $m$ in that expression denotes mass. For particles at rest $p=0$ and $E_0=mc^2$.

Check

http://ajp.aapt.org/...isAuthorized=no

Unfortunately, sometimes and especially in his popular writings Einstein was careless about the subscript 0 and spoke about the equivalence of mass and energy and omitted the attribute "rest" for the energy. As a result Einstein's equation E0 = mc2 became known in its famous but misleading form E = mc2.

Note: The above article criticizes the old concept of "relativistic mass". This "relativistic mass" is what pmb above renames to "inertial mass".

Edited by juanrga

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