# Really nerdy question regarding the relationship betwen energy and mass

So I have a question that has been bothering me but really doesn’t matter to anything. When fuel is converted to energy, is mass invariably lost? In other word, given the equation e=MC(2), (I don’t know how to do a squared sign on this board), is the sum of both (1) energy and its equivalent in mass (as per the equation above) a constant?

Or in other words: Is my life a continual process of converting mass into energy (as per Einstein’s equation)? Or is the sum total of mass in the universe not effected by my existence?

So you’re asking if E ≈ mc^2.

. . .

No. No it doesn’t.

No, most normal fuel Consumption processes are thermodynamic, and preserve mass. You are either doing work to store energy in a system, or extracting stored energy. In both cases efficiency is less than 100%, so you generate waste heat. but that waste heat is not from direct conversion of mass to energy, it’s simply a byproduct of enifficient work. Direct conversion has a ridiculous constant of conversion (speed of light squared). Maybe if spontaneous combustion is real that would be an example, but all the processes we normally associate with non-nuclear energy generation/work is strictly potential to kinetic energy shifting. Even things like huge explosions a la the fertilizer plant which recently blew up.

Cool. This is exactly what I was wanting to know. Thanks for helping educate a neophyte. .

What? First, “potential” energy sources necessarily include nuclear sources. Second, converting potential energy (be it kinetic, nuclear, chemical, electrical) to usable energy does not always entail creating kinetic energy. Very often the desired output is thermal energy (light, heat).

As long as we’re dicussing physics questions, I have a physics question for an experiment I’m doing. I want to lift large amounts of dense mass 3x a week but I seem to not be able to overcome inertia. To motivate me, I want to print out some pictures of some old timey guys from grainy black and white / sepia pictures back’in the day. Basically, we are talking handlebar mustache, shaved head, old timey spherical barbells, belongs on a recurring joke from Family Guy type of guys. I want to print put a few. Or buy prints. Where do I find something like that?

Try entering that in Google, physics.

That archetype is known as a “strongman”. Do a black-and-white Google image search on it.

Thermal energy is molecular kinetic energy. Light is not thermal energy: light is a consequence of the dissipation of thermal energy – blackbody radiation, for example.

So, does the production of light therefore consume mass (might be the case with the sun)?

Okay, seriously, what part of “energy = mass” is tripping you up here?

First, be aware that I’m stupid here. I’m trying to learn. The point that may be ‘tripping me up’ is that involving the creation of energy. I understand now (and I didn’t before) that what I thought was ‘creating energy’ in the context of my everyday living was, in fact, a recycling of energy that has been imparted by the sun. That recycling is referred to as thermodynamics, and it does not involve consumption of mass. And that I now understand (or think I understand) thanks to the poster known and venerated as ‘Mouselock’ (thanks again).

But now, I’m told that the creation of light is not a thermodynamic reaction, which means that the thermodynamic law conservation of mass described to my by Mouselock may not in fact apply-- 0r maybe it does, but to be honest I’m just too ignorant to know. Which is why I was asking this question. So if you’re going to respond to me, please at least humor me: my everyday living is not consuming mass because it is powered by a thermodynamic transfer of potential energy to kinetic energy; but if the generation of light is not a thermodynamic process, then does the generation of light consume energy as per Einstein’s equation?

Wikipedia has a good page on mass-energy equivalence. The bottom line is that the sum total of mass in the universe is not affected by your existence.

Although mass cannot be converted to energy, in some reactions matter particles (which contain a form of rest energy) can be destroyed and converted to other types of energy which are more usable and obvious as forms of energy, such as light and energy of motion (heat, etc.). However, the total amount of energy and mass does not change in such a transformation.

Not in general. Thermal radiation comes from kinetic energy as a hot substance radiates and cools off in the process. Of course there are nuclear and antimatter reactions that produce energy directly from the transformation of matter, but that’s not what you see when any Earth-based light is seen, and moreover I believe all light we see from the Sun is likewise thermal, even though it was indirectly caused by fusion.

Chemical reactions produce energy not by converting matter into energy but by breaking bonds between atoms. A simple example is the combustion of methane, where CH[sub]4[/sub] + 2 O[sub]2[/sub] -> CO[sub]2[/sub] + 2 H[sub]2[/sub]O. Because the sum of the energy required to bond the product molecules is less than the energy required to bond the reagent molecules, the reaction is exothermic and emits energy based on the difference. All energy produced locally on Earth originates from exothermic reactions, with the exception of nuclear weapons. I’m pretty sure that even the energy produced in nuclear reactors results from bonds being broken, though the bonds in question are those in the nucleus rather than those involving electrons being shared by atoms.

Of course you’re right about bonds in the nucleus being broken in a reactor, but I believe in many if not all fission reactions there is a mass difference between the starting result and the ending one. Apart from whatever is gained by breaking bonds, the tiny mass difference must also be accounted for in some kind of energy release.

Well that can be considered somewhat of a meaningless distinction; you can say that all light is thermal at the same time as saying that none of it is, it just depends on how you want to define “thermal.” What we’re talking about here is essentially black-body radiation, which is a wonderfully complex topic. The sun is the largest black-body in the solar system, which seems initially counter-intuitive until you realize that the definition of a black-body is that it does not reflect radiation but rather emits it.

The real problem is that people tend to think of visible light as some sort of different type of radiation than other EM forms of radiation, and it’s not. We just have evolved eyes that see a very limited spectrum of EM emissions. I’m somewhat overstating the case here, but I’ll say it for simplicity’s sake: the vast majority of the photon energy emitted in the interior fusion of the sun is responsible for applying a type of light pressure that counteracts the force of gravity. What eventually escapes can almost be thought of as a waste product.

Well, you’re talking about an entirely different interaction, what we call the strong interaction, or SU(3), which is something on the order of 100 times more powerful than the electromagnetic interaction. If you run through the calculations fully you find it’s a little less than that, realistically. The strong interaction is what holds quarks together and is responsible for confinement; the nuclear binding energy is essentially a short-range leakage of that interaction. It’s somewhat similar to the way the Van der Walls force is a leakage of the electromagnetic interaction.

I think many of the replies so far have missed the point. You really should read the Wikipedia article linked earlier. I’ll quote the most useful parts:

I don’t think it’s meaningless at all.

Some (all?) photons emitted during fission and fusion reactions are not thermal; they result from the transformation of matter to energy, making up the balance sheet of split or fused nucleons when the sum of resulting particle masses comes out to a bit less than that of the original nucleons. However when that direct radiation from fusion reactions in the core of the sun is absorbed by molecules in the photosphere and corona, you are then seeing or being warmed by or irradiated by thermal photons emitted by hot gas. I think some X rays and higher waves emitted by the Sun and other stars and detected on Earth are actually emitted by fusion reactions directly and escape interaction with the Sun’s core and atmosphere, but the vast bulk of the Sun’s radiation is thermal.

At some point OP or some other poster asked if thermal photons result from the destruction of matter, and since they don’t that’s where this line of discussion is coming from; but some photons do result directly from matter transformation, not just in fission and fusion, but in matter-antimatter reactions as well.

Wouldn’t the “true” mass of any two objects in a vacuum at rest be described as their mass + the limit of their gravitational potential energy as the distance between them became infinite?

Actually, I did read that entry. I didn’t find it useful because it seemed to be confirmed my initial impression – i.e., that I am generating and shedding energy, and that therefore the mass-energy equivalence means that I am consuming more mass than I am regenerating. My confusion appears to be resulted from an ungrounded (and unrealized) presumption that the energy part of the mass-energy equivalence referred to kinetic energy. I didn’t realize that it included potential energy as well.