Phage

How then do you reconcile a conversion of matter to energy in a closed system without violating thermodynamics? Where did the mass go?

Slavakion

It turned into energy. I might be wrong, but I think this might be quantum mechanics, which doesn't exactly follow every rule.

Phage

Did you look at my links earlier in the thread?
Can you give some justification for saying that the Law of Conservation of Mass does not apply, or why such a reaction would not follow the rules of Thermodynamics and instead would be described by a system without definite rules?

Your last post seems to be in essence "I don't like the rule that you cited, so instead I think I will apply a different system in which I don't have to follow rules."

Yakk

Well, there is a bit of confusion.

First of all, both Phage and I are not talking about "rest mass". Photons do not have rest mass.

Good old Baryonic Matter has rest mass. Photons do have mass, but no "rest mass".

If you heat up Baryonic Matter, it's "rest mass" doesn't increase. But, it's mass does.

If you add energy to a system, the system will generate more gravitational force (gravitational mass), and will have a higher inertial mass (it will be 'harder' to change it's velocity).

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Last edited by JHVH : 10-29-4004 BC at 09:00 PM. Reason: Time for a rest.

fckm

Energy is not a thing. Energy is not a particle, it's not a force. Energy is a property of matter, kinda like color. Energy, being a property of matter, cannot have mass. It's like saying the color blue has mass. It makes no sense. Energy is a term that we use to describe a specific property of matter, and obeys certain conservation laws.

Conservation of Mass is not a universal law. The correct themodynamic law is conservation of Energy (1st law). Mass conservation only applies when you are dealing with classical physics, like balls colliding or chemistry. Mass conservation fails when you start dealing with relativity and nuclear reactions.

It is possible to change mass into energy. The atomic bomb, for instance, does just that. It takes some mass from the plutonium/uranium and converts that mass into energy which we then feel as 1) light 2) heat 3) shock waves. (Remember, we don't feel the energy directly, energy is a property of matter)

It is possible to convert energy into mass. A photon, which has no rest mass, of a high enough energy (say a gamma ray) can spontaneously convert itself into an electron/positron pair. This process is called pair production. Where you had zero rest mass before hand, you now have a mass of 2 Me (electron mass). Hence, we say that Mass Conservation is not a Universal Law, it's scope is limited to classical physics.
(well, I suppose you could use E=MC^2 to calculate the mass equivilance of all energy and say that mass is constant, instead of energy, but that would be silly and none in physics would do that.)

The statement E=MC^2 is an equivilance statement. X amount of energy is equal to Y amount of mass. It doesn't mean that energy has mass, or mass has energy (it's like saying Red has Shiny. It makes no sense). Mass and energy are both properties of matter. It simply means that these two properties are equivilant under certain contexts.

Edit: Positron, not proton. oops

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fckm

The laws of thermodynamics are as follows:
0th law: Transitive Law. If A is in thermodynamic equlibrium with B (A=B), and B is in thermodynamic equlibrium with C (B=C), then A is also in thermodynamic equilibrium with C (A=C). Basically, this means, if A and B have the same temperature, and B and C have the same temperature, A and C have the same temperature.

1st Law: Energy Conservation. In a closed system, Energy is conerved. or U=Q + W. The energy of the system is equal to the heat of the system plus the work done on/by the system. (U= total internal energy, Q = heat, W = work)

2nd Law: Entropy always increases or stays the same. For any spontaneous process, the associated Entropy change is always positive. For a quasistatic process (if I move things infinitesimally slowly), the entropy change may be zero.

3rd Law: Temperature approaches absolute zero assumptotically. You can never reach absolute zero, and you can never have a true quasistatic process. Thus, entropy always increases, and at some point, heat will be so evenly distributed across the universe, that there will be no spatial gradient to the heat, thus no more usable energy (heat death of the universe).

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Yakk

If I meant to say that Energy has "rest mass", I would have said "rest mass".

Instead, I said:
Photons have mass. They have no rest mass. All energy, no matter what form, has mass.

If you take two atoms that each weigh X, and bind them together so that Y energy is absorbed by the breaking of the bond, the resulting molecule will have (2X-Y/c^2) mass.

If you take a proton and a neutron that weigh P and N, and you bind them together such that Z energy is absorbed by breaking their bond, the resulting atom will have (P+N-Z/c^2) mass.

You heat something up, the same amount of matter will now have an extremely small increase in the amount it bends space and how hard it is to change it's velocity. Otherwise known as it's mass.

As an aside, fckm, you forgot 'in a closed system' requirements in your 2nd law.

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Last edited by JHVH : 10-29-4004 BC at 09:00 PM. Reason: Time for a rest.

fckm

The moclecule has mass.

The atom has mass.

That something, has mass.

See the pattern here? The property, _Mass_, is a characteristic of the material you are talking about. The property, _Energy_, is also a characteristic of the material you are talking about. The property, _Mass_, is not a characteristic of the property, _Energy_. Again, Atom, Molecules, Photons, My beer gut, all have mass. They also all have energy.

Energy doesn't have mass. Energy is not a thing. Energy cannot have mass, because Energy itself is a characteristic of some material. It cannot, it does not, exist independantly of matter.

My beer belly can have Energy. The more Energy my beer belly gets, the more inertial Mass it obtains. It's not the Energy that "has mass", it's my beer belly. It's not the energy that has mass, it's the molecule. It's not the energy of a nulcear bond, it's the atom that has mass.
Only things can have mass. Energy isn't a thing, it's not a particle, it's not some object, it's a property of matter. It doesn't make any sense to say "Blue has Shiny", so it doesn't make any sense to say "Energy has Mass".

Ah yes. Thanks for pointing that out. Oops.

The reason I'm being so pedantic here, is because of the thread in Philosophy, titled E=MC^2, discussing beings made of energy. I just want to make it clear that energy isn't a thing, it's a property.

Edit: more clarity?
Edit2:

I'm quoting myself for emphasis here.

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Slavakion

Well, if you had read my earlier posts, you would see that I did read your links. What I failed to convey was that the laws of conservation of mass/energy only work in classical physics. fckm has done a much better job.

Yakk

Is a Photon Matter? Or, are you asserting a Photon cannot exist without Matter? That's getting pretty obtuse. Gravaton?

Because, Photon's aren't very "Matter"-like, and they contain Energy (and hence have Mass).

(ok ok, Non-Baryonic matter. Meh, not very Matter-esque!)

How about Negative Energy Fields? I think it is believed they have negative mass. (you can apparenly build them by placing two metal plates very close together in a vacuum -- between the plates, you end up with something that is more empty than a vacuum.)

Are Negative Energy Fields matter? (I suppose you can renormalize the universe, so hard vacuum isn't at zero, and thus make 'Negative Energy Fields' just 'a place with less stuff than a hard vacuum')

Being further pedantic, I think I can build a non-bounded universe model in which heat-death never occurs. So, your conclusion you rolled into the 3rd law isn't derivable from the 0th, 1st 2nd and 3rd laws of thermodynamics. In order to do this, I think I need negative enthropy systems (which isn't ruled out by the 0th, 1st, 2nd or 3rd law).

Build a universe model where the total enthropy is unboundedly negative, but for all compact subsets of the universe it is bounded. You end up with a universe that looks like ours does locally, but possibly never reaches heat death (there is always some point that is hotter than others by as any margin you want).

I don't know what "negative enthropy" systems would look like.

Measuring energy as mass has some nice properties. It does away with two extra units: distance and time are no longer "dimensions" to your energy unit.

The photon has 2*10^-16 kg of Energy.
We provided 2*10^-20 kg of heat to the water.
The bomb blast was 2.5 * 10^-1 kg of Energy! (5 megatonnes, if I did my math right)

It is sort of like measuring distance as time, or time as distance. Once you have a nice conversion factor (c), keeping track of both units seems silly.

I think this is a philosophical position, or a convention, not a scientific statement.

If you interprited Energy as the thing (maybe the only thing!) that has Mass, and note that all Matter has Rest Energy, you should be able to do the exact same physics. Just with slightly different translations into English.

Hell, you could say that Energy is the only thing, and that it "must" have Matter (instead of Matter "must" have Energy).

Slavakion, from what I can tell, Fckm was mostly disagreeing with terminology.

I don't believe Fckm disagrees with the statement "the gravitational and inertial mass of a closed system is constant". Which means melting an icecube results in water that weighs more than the ice cube did, by an increadibly small amount.

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Last edited by JHVH : 10-29-4004 BC at 09:00 PM. Reason: Time for a rest.

fckm

I like to think of matter as anything that's defined as being a particle in the current Standard Model.

I'm an engineer, not a theorist, so this is currently beyond me. But here's a good article about the Casimir effect:
http://physicsweb.org/articles/world/15/9/6
Notice that all fields being refered to are still EM fields, which , I believe, still have to be quantized as photons.

I'm not sure about this. I don't think it would be very useful, since most physics work is done in energy. In fact, it's far more common to use energy units to measure mass, than to use mass units to measure energy.

Except that in a historical context (and a teaching context), classical physics came first. Also, I'm not sure how the Higgs boson fits into all this. (I'm an engineer, not a theorist).

yup
I agree, although the amount is so small, it's not measureable.

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Slavakion

After thinking about it, I guess it makes sense that if a little bit of mass contains a huge amount of energy, a huge amount of energy contains a little bit of mass. That's still thinking about it in terms of e=mc^2, though. *shrug*

mo42

This has been a fascinating read. I think that gases *would* gain a small amount of mass over solids. I'll have to debate this one with my physics friends and see what they think.

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