Talk:Conservation of energy/Archive 1

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Photons is not matter?

"The new feature of relativistic physics is that "matter" particles (such as those constituting atoms) could be converted to non-matter forms of energy, such as light; or kinetic and potential energy And poop (example: heat)" -is writen in this ARTICLE :) Sorry, but since when photons ceased to become a form of matter? Matter could convert only in matter,not in pure energy.Energy is just form of interaction between matter.There is energy coservation law but in the same time there is matter conservation law.Somebody correct this article. —Preceding unsigned comment added by 174.0.228.58 (talk) 22:18, 7 December 2009 (UTC)

This doesn't make any sense!

The classical form of the energy conservation law (and in fact the notion of energy in the first place) is directly related (through the corresponding equation of motion) to the force- concept describing the interaction of particles. The latter can be shown to be necessarily instantaneous (i.e. Newtonian) as otherwise one would not be able to define a force objectively, i.e. independent of the state of motion of the observer. One can therefore say that the law of energy conservation does, by definition, only strictly hold for this case of a static interaction of particles, but is not more than an arbitrary ad hoc concept if applied to other situations, in particular those involving light: two light waves can be made to extinguish each other completely if superposed with the correct phase, which proves that a form of energy conservation does not apply here.

--- Roadrunner

This is not true. First of all, light cannot "extinguish". What you're talking about is destructive interference which doesn't destroy the light. For example, if you have one beam of light traveling right, and one traveling left, and they destrvtively interfere at a point, then an observer at that point won't see any light. However, the light will continue on after they "hit" eachother, in their original path - ie no energy is gained or lost, there is only a place in time and space where the light won't be observed.

The thing about conservation of energy is that it doesn't *need* to figure in any forces. The force can last decades, but after the force stops, the total energy will remain the same as it was before. I hope that helped. Fresheneesz 09:54, 20 April 2006 (UTC)

It is somewhat paradoxical when you are saying that destructive interference doesn't destroy light. Surely, for the particular example you mentioned it doesn't destroy it everywhere, but it violates already energy conservation when intermittently the energy disappears and then reappears. In principle, you can in fact arrange the situation such that the emission from two light sources vanishes completely (e.g. by putting two sources that are 180 deg out of phase sufficiently close together; you could in principle even make emissions of different frequencies disappear if you have a continuous emission spectrum and the emissions are somehow phase-locked; the radiation would then disappear with a time dependence as given by the Fourier-transform of the frequency spectrum). -Thomas-

I think you're going to have to simplify this problem and provide some math. So far as I can see, you're just wrong. Are you proposing that two sources of coherrent light 180 degrees out of phase will combine into darkness??

Well, the maths is actually the easiest part of it:

sin(k*x-ω*t) + sin(k*x-ω*t +π) =0. -Thomas-

What is this equation meant to represent? I know that the sine waves presented are used in basic physics to represent the amplitude of the B or E field of an unphysical wave of perfectly defined frequency and infinite length (no source, no termination). This is meaningless in this discussion. A physical wave cannot have a perfectly defined frequency, but assuming that these two waves did, then they never existed anywhere at any time. Also, if you want to talk about "destroying" light, then you must speak in terms of photons, i.e. particle physics. In this case, there are already known rules in place that conserve energy. In the wave theory of electromagnetism, waves do not affect each other as they "interfere".

More importantly and generally however, the concept of 'energy' in the first place requires that the principles of classical mechanics (and in particular that of a 'potential energy' ) can be applied. Noether's theorem purports to prove a general law of energy conservation, but it actually implicitly assumes that the physical system is a classical one as it uses the Lagrange function L which in turn is defined as the difference between the kinetic energy T and potential energy V (L=T-V). Now if a force field can be derived as the gradient of a potential energy function, it must be necessarily a conservative force. In other words, the use of Lagrangians (or Hamiltonians) *implies* already energy conservation, so it is no surprise if this is the result of Noether's theorem. However, it is obvious that this can not be applied to light as you can't define a conservative force field and hence a potential energy for it (in order for a force to be conservative, the curl of the force field must be zero; however, according to Maxwell's equations curl(E)=-dB/dt (Faraday's law)).(see my page http://www.physicsmyths.org.uk/conservation.htm for more). -Thomas-

There is nothing in the Lagrange function which demands a conservative force field per se. If the field isn't consevative, like a time varying B field, then the particle simply picks up kinetic energy continuously at the expense of energy being tapped from the field. That's how dB/dt (nonconservative) makes electrons circulate in the windings of a generator, or particles go faster and faster in a cyclotron. And light, which has a non-zero vector potential, does the same things to charged particles--- consider Compton scattering. But the photon which leaves in a Compton process does not have the same energy as the photon which goes in-- the difference is imparted to the electron, and that's the end of it. None of it violates conservation of energy. When you write down the Lagrangian of an EM interaction in field terms, you must do it for the WHOLE system, which means the kinetic energy is the energy of the accelerated particle, and the potential energy is the complete potential of the particle in the field, which is its charge multiplied by both scalar potential and vector potential terms. If the particle gains in kinetic energy, it produces a field which causes the vector potential to suffer. In a generator, those electrons getting their energy from dB/dt turn into a current which generates its own opposing B field and "back-emf" in the coils that supply it. The energy transferred comes out of the changing B field and the vector potential associated with it. Anyway, buy yourself a copy of Jackson, for Heavensake. Steve 18:41, 23 June 2006 (UTC)

First of all, the fact that in certain cases one observes experimentally some kind of 'energy conservation' in connection with light (or electromagnetic fields in general) is not the point of discussion here, but the assertion that a general principle in this sense follows theoretically from certain fundamental assumptions in physics.

It is in fact quite obvious that you are already implying energy conservation when you are using a Lagrangian, as the latter contains, as already mentioned, the potential energy. Using the notion of a 'potential energy' (in fact that of an 'energy' in the first place) would make no sense whatsoever unless you imply energy conservation i.e. assume that the system can be described like a conservative mechanical system. If one is not actually dealing with mechanical systems (e.g. in the case of light), one may be lucky in certain cases that this works out in reality, but there is no guarantee for it. -Thomas-

I have worked myself on the analysis of airglow observations where the intensity of the airglow exceeds that expected from energy conservation (i.e. assuming E=h*nu ) by more than one order of magnitude (see http://www.plasmaphysics.org.uk/papers/airglow2.htm#34 ; Chpt.3.4). The point is simply that the energy differences in the atom correspond to set frequencies of the radiative emissions but in general not to set intensities (i.e. amplitudes of the emitted electromagnetic wave). Furthermore, on detection, the apparent intensity also depends for instance on the coherency of the radiation. Completely incoherent radiation will simply not be detected anymore, i.e. for all practical purposes it is non-existent (see http://www.plasmaphysics.org.uk/photoionization.htm ).

By the way, the paragraph you commented on was literally taken from my website, but not by me. -Thomas-

Thats not true either, light doesnt cause "destructive interference" it washes out and combines with other light. when you add light, light increases, its not destroyed. If a light washes out another light its not destroyed, the other light is simply brighter than the weaker light, the weaker light is still thier because when the brighter light is removed the weak light is still thier. The only way you would not see light is if your eyes are closed, what the H are you on and talking about thomas, light doesnt cause light to become dark unless its colored light. A bright light overtakes a lesser light but the overall effect is the produced light becomes brighter (two lightbulbs are brighter than one, you can feel free to test that). why do physicists and scientists all act like they have major sticks up thier butt and act like pompous ass knowit-alls. Newtons opinion isnt any better than yours or mine I hate to break it to you, other than luck and popularization. We all put our pants on one leg at a time. Thier are two kinds of thinkers, those that quote from others and those that think for themselves. You guys are stuck on 200 year old ideas and book thumping nonsense. I guess thiers truth to the saying if you cant dazzle them with brilliance..baffle them with.. well we all get the picture. Science and physics need to focus on making the complex simple, not the simple more and more complex.

Secondly thomas I hate to break it to you, but thier is no such thing as a closed contained system. space isnt a true vacumme because light travels through space in the form of starlight. Closed systems are popycock and nonsense. all objects age and decay even metal. the other thing is you might say a vaccume in a glass tube is contained,if thats the case how does light get in and heat will still be able to affect the inside in the form of light showing a closed system is impossible simply because temperatures can change and enter any system.

Heres a simple expiriment, take any vaccume tubed area and put something in it that is susceptible to temperature changes. expose it to either

An ideal expirement mr. genius is to take some water and place it in a vaccumed airless tube. put the vacummed tube in either a freezer or out in the sun. you will find that temperatures still change the water in the vaccume tube, showing thiers no such thing as a closed invironment. the water will either freeze just like normaly showing its not in a closed contained system or heat up and evaporate over time left in the hot sun showing that light and temperature enter a vaccume and a vaccume is not a closed invironment, thiers no such thing. objects decay and become gaseous, liquids and solids both become gasseous when cooled or heated. Also time is still present in a vaccumed area and the effects of time.

Anotherwords, if the area was truly sealed and contained, neither light nor heat/cold would be able to enter a vacummed glass area...

you can also put a small mirror in a vaccumed glass container and shine a laser on it, the laser light should pass through the glass and bounce off the mirror showing the area is not contained because the laser can travel through the glass and light and hot/cold can enter a vaccumed/contained area easily.

A third expiriment is to place something in a vacummed area and using time lapse photography see if it ages naturaly as it should showing the affects of time are still present in a "contained area".

and a fourth would be to try and burn something with a laser and see if light passes through the glass and burns it showing light and heat easily enter a contained area, im assuming that by contained area your talking about a "vaccumed" airless area as thats the only really contained that truly is suppose to exist.

also objects in a vaccumed area should be suseptable to forms of radiation showing a contained area isnt contained at all.

The other would be the reverse to see if various items can emit outside a contained area in anyway, even vibrations are able to enter/leave contained areas. Microscopic evidence shows solid surfaces are not as solid as they look with speckly cracked looking surfaces (with no models of atomic structure waving at us or carbon molecule models etc.) also showing light and radiation are passing through them wich is how heat can heat passing through metal and reach an object. If metal were a contained solid heat wouldnt pass through it. Man why are we using 500+ year old ideas and patting ourselves on our backs. U must unlearn what you have learned *giggles*.

—Preceding unsigned comment added by Funnydude71 (talk • contribs) 03:07, 15 December 2009 (UTC)

energy equivalence / conservation of energy?

I'm not a physicist or an engineer, but is conservation of energy really considered a special form of mass/energy equivalence? I would have expected it to be the other way around -- conservation of energy seems to apply in far more situations than mass/energy equivalence. Could somebody clarify this for me? --Fastfission 05:11, 6 Apr 2005 (UTC)

I see your confusion. That section was worded ambiguously. Check the way it is written now, and let me know if the matter is still unclear. — Cortonin | Talk 14:34, 6 Apr 2005 (UTC)

nguyenvantien

Separating Conservation of energy from First law

I have it in my mind to split this into two articles:

• Conservation of energy - centrality to science/ implications for humanity/ "The Universe"/ history/ types of energy and transformations between them - examples/ Modern physics and relativity/ link into classical mechanics & principle of least action
• First law of thermodynamics - content currently as Conservation of energy#Mathematical formulations/ importance in thermodynamics

Any comments? Cutler 18:48, July 14, 2005 (UTC)

Presumably the article did get split as we now have the article: First law of thermodynamics. But this article on conservation of energy now seems to consist of two unrelated sections, as there is no explanation of the link between the First law of thermodynamics and conservation of energy. I think they are equivalent, and the principle of conservation of energy is an alternative statement of the First law of thermodynamics. But is that too strong, i.e. should we say the principle of conservation of energy and the First law of thermodynamics can each be derived from the other? Aarghdvaark (talk) 03:59, 20 May 2011 (UTC)

Explicit Examples?

I feel like it would be a helpful illustration of this principle to include some equations that show energy conservation for closed systems: ΔE_mass + ΔK = 0, ΔE_int + Q = ΔW, etc. Does this deserve its own section? Loonybin0 23:44, 6 May 2010 (UTC) —Preceding unsigned comment added by Loonybin0 (talk • contribs)

Removed paragraph

I removed the following paragraph:

I Loris Erik Kent Hemlof dissgree with the law of conservation of energy; that energy may never be created or destroyed only transformed. The repulsive force which keeps the universe expanding seems to be created in a vacume from nothing. Gravity seems to create from nothing the heat and pressure inside the sun to convert through fusion single atoms into higher atomic density elements. The strong and week atomic forces also seem to create energy from nothing. Perminant magnets attract and repel without any consumption of mass. All that is required to transform these forces into electricity or directed motive force is a method of turning off and on these forces. All energy is either free energy or an end product of free energy. For example fission is a product of uranium which is formed in a sun from gravity. Fusion is not a net producer but a consumer of energy. The effort to create energy from fusion should be directed into other new energy technologies. Coal is created from plants energy, from photosynthess, from sunlight, from gravity. The part which seems to be correct is that energy is not destroyed but transformed into elements or dissipated throughout the universe.

I encourage the author to find sources for this claim and cite them, without such citations it constitutes original research and cannot be included in wikipedia. Thanks for your interest. --best, kevin [kzollman][talk] 00:54, 12 December 2005 (UTC)

Antimatter

How does E = mc^2 relate to the energy created by the annhilation of matter and antimatter? 62.249.242.232 09:49, 21 December 2005 (UTC)

its the maximum amount of energy that can be emitted by such an annihilation (assuming the particles and antiparticles have no velocity - cause that would add more energy). In particle physics, matter and energy are the same thing, so in an annihilation like that you'd probably get a whole lot of light, but perhaps some other weird stuff like quarks or neutrinos or who knows what. Fresheneesz 10:00, 20 April 2006 (UTC)

Twin Towers claim

The events of September 11, 2001 appear to cast serious doubt on the scientific validity of conservation of energy. Calculations have shown the falling twin-towers expended far more energy than was originally available in the form of an elevated mass (gravitational potential energy). According to more modern theory, "conservation of energy" is subsumed and invalidated by "progressive collapse".

No, the events of September 11, 2001 do not appear to cast serious doubt on the scientific validity of conservation of energy. Which calculations are you talking about? According to WHICH more modern theory, "conservation of energy" is subsumed and invalidated by "progressive collapse"? Please, this is an encyclopedia, there is no room for speculations based on "I heard...", "somebody told me..", "they say..." —Preceding unsigned comment added by 76.26.73.179 (talk) 22:39, 4 September 2007 (UTC)

Such an extravagent claim demands some citation or authority.Cutler 09:49, 3 January 2006 (UTC)

I removed the paragraph. Jobh 11:37, 3 January 2006 (UTC)

I put the extravagent paragraph back, this time with the appropriate references. It is true ladies and gentlemen, the scientific community is almost unanimous in agreement that the twin towers crushed themselves, an obvious revocation of conservation of energy. There are "conspiracy theorists" who claim that energy was added to the twin towers via explosives (thus preserving conservation of energy), but such wild speculation has no place in a scientific article.

Thanks for providing the citations. A much better engineer than I once said something to the effect that engineering is the art of forming materials that we cannot accurately characterise into geometries that we cannot exactly specify while trying to convince the public that they will perform adequately in environments that we cannot truly assess. I think that the principle of conservation of energy survives these interesting calculations (published in some very "grey" non-peer-reviewed website). What is illustrated is just how difficult it is to establish an exact energy balance other than under experimental conditions. I have reframed the contribution. Please sign posts on talk pages by typing four tildes ~~~~. The date/ time and your username will then appear automatically. Cutler 23:34, 3 January 2006 (UTC)

Yes, Cutler, you've convinced me of my error. You are correct, conservation of energy DOES survive the Hoffman and Trumpman papers! Therefore, the 3 WTC "collapses" were controlled demolitions after all, and it is the official theory of 9-11 which must go. Clearly it has to be one or the other, no?

69.238.209.182 03:00, 4 January 2006 (UTC)

Discussion of 9-11 theories is interesting but doesn't belong here. May I suggest 9/11 conspiracy theories#World Trade Center towers where it's already covered? I don't mind a section on the practicality of large scale engineering energy budgeting, but it should be at the bottom, and preferrably use a less controversial example to avoid, well, controversy. Jobh 11:53, 4 January 2006 (UTC)

Wikipedia has strict guidelines about remaining NPOV. Avoidance of the most important scientific event in Amercian history would violate this, sorry. The discussion belongs here because the Wikipedia account of 9-11 hinges crucially on a violation of conservation of energy, and cannot be true. Or can it? Maybe Bazant and Zhou, Scientific American, FEMA, NIST, Poplular Mechanics are correct after all, and conservation of energy is doomed. We can't have a Wikipedia that is self-contradictory, we must resolve this. Does the official version of events violate conservation of energy, or doesn't it?

I've flip-flopped again. I think you guys are wrong, and the vast majority of mainstream scientists are correct. Each falling twin tower had about 100,000 kW/h of GPE, and manufactured >1,000,000 kW/h out of thin air. Conservation of energy is dead. I'm citing Bazant and Zhou.

69.238.209.182 16:14, 4 January 2006 (UTC)

WTC7.net is a nonscientific site which publishes minority theories about the 9/11 attacks. It is not a valid scientific reference and it has no business in this article. Neither Jim Hoffman nor Wayne Trumpman is a peer-reviewed scientist. Rhobite 18:45, 5 January 2006 (UTC)

Well, how about Steven Jones then ?

http://www.wtc7.net/articles/stevenjones_b7.html

Jones is a respected and published physics professor at BYU. In his paper, he points out that none of the official theories account for loss of momentum or angular momentum.

As to Hoffman, et al being "minority", this is an unsupported claim. As far as I can tell, a MAJORITY of the scientific papers which analyze the 911 collapses conclude that something is amiss with the gravity-driven theory. Please note that the FEMA, NIST and 911 commission reports do NOT analyze the collapses, merely the events leading up TO the collapses.

Please, if I have missed scientific literature on any of the 3 structural collapses that occured on 911, post links here.

208.57.142.128 19:22, 8 January 2006 (UTC)

I have removed an added sentence referencing the twin towers. [1] It was inappropriately added to a section describing the law, which as formalized never discusses skyscrapers. With respect to this later paper, it is not questioning conservation of energy, but rather concluding that there must have been explosives in the building. This is therefore, not an argument about conservation of energy, but rather one about the 9-11 attacks and should go to the appropriate pages. I hope that .128 can understand, while we strive to have a neutral point of view, this does not mean that every mildly relevant thing should be in every article. It is my opionion that this theory about the 9-11 attacks deserves mention, but not in an article about the conservation of engery. --best, kevin [kzollman][talk] 20:32, 8 January 2006 (UTC)

It is my opinion that it does deserve mention in an article on conservation of energy. The "law as formalized" is refuted. You have hundreds of photographs and dozens of videos of clear refutations of the conservation of energy, and they all involve skyscrapers. Scientific history is full of examples of discarded theories which failed to stand up to experiment and data. According to the rules, we must not allow speculation and conspiracy theories to clog up a scientific article. Since speculation and conspiracy theories are the only alternative to modifying conservation of energy, we must modify conservation of energy. You simply cannot have it both ways, it is unscientific to do so.

I appreciate your persistence. I suggest that your read wikipedia's guidlines on original research and verifiability. Unless there is a peer reviewed scientific publication supporting your claim that conservation of energy is refuted by the events of 9-11, it does not warrent inclusion in this article. The article you suplied above by Steven Jones does not assert that conservation of energy is refuted, but instead concludes that there were explosives in the towers. I understand that you wish to use the same argument to refute conservation of energy, but that is not the same as that argument appearing in a journal. --best, kevin [kzollman][talk] 00:05, 9 January 2006 (UTC)

I get all that, Kzolllman. Aware of all that, and aware that the article on "collpase of the WTC" has been singled out as being a "good article" and is considered for "article of the day", and noticing that that article is completely and utterly at odds with this one (as anyone with intellectual honesty will agree), I set out to resolve matters. Matters have not been resolved, but I will admit here in writing that the problem is with the other article. Conservation of energy is safe and sound, it is the theory of 9-11 that is unscientific hogwash. One cannot accept the "official" theory of 9-11 AND maintain a belief in conservation of energy. It is my sincere hope that you and others will help correct the scientific fallacies rampant in that article, as it is at odds with this one, which is great.

69.238.209.182 01:54, 9 January 2006 (UTC)

An event in which thousands of innocent people were burned, crushed, or died from falling from a great height should not be cavalierly or offhandedly used to discuss a crank theory in a Wikipedia article.Lestrade 03:35, 10 February 2006 (UTC)Lestrade

Shut up, using a tragedy as a front for trying to dismiss a valid claim is already done enough by our own government and has no place in Wikipedia. Thanks. --vex5 17:45, 14 March 2006 (UTC)

Unquestionably, this article is not the place for such speculation. -- SCZenz 23:45, 14 March 2006 (UTC)

Why do you so? Is it because this is is the first time in over a century that the laws of physics are seriously questioned? Or maybe it's because the pure fundamental structure of the conservation of energy has been rejected by many respectable minds after the 9/11 attacks? --vex5 05:51, 15 March 2006 (UTC)

The laws of physics are not seriously questioned by the event of 9/11 and they are far from that. Do you wonder why the real respectable minds in physics have not made a statement about it? Because it is a waste of time. I am a physicist with several years of training in this field and although I am not one of those respectable minds, even I find this 9/11 violation of the conservation of energy ridiculous. I urge you to rather research, but not only reading half-science articles, but instead try to understand the mathematical background of this phenomenon and you will find out how ridiculous this is. By the way, algebra and 1 year of calculus will not help at all, real physics takes more, much more than that, so please take some time to do your research because this is not a space to educate you or correct your indeficiencies in science, real and serious science. —Preceding unsigned comment added by 76.26.73.179 (talk) 22:54, 4 September 2007 (UTC)

Take it to the 9/11 pages. Noone is seriously questioning the laws of physics, its just a sarcastic attack on the US government. 137.138.46.155 12:45, 23 August 2006 (UTC)

theory?

I always thought that the Conservation of Energy was billed a theory, and not a 'fundamental law' in physics? Is this correct, since this 'law' cannot be proven with Newtonian physics? --vex5 20:00, 9 March 2006 (UTC)

Actually it follows from Neweton's laws. I just checked this on paper, and it works nicely. -- SCZenz 23:44, 14 March 2006 (UTC)

Please ellaborate. --vex5 05:50, 15 March 2006 (UTC)

In newtonian physics it does indeed follow from newton's laws. Equal and opposite reactions to forces embodies the conservation of energy, and object in motion stays in motion embodies conservation of momentum. If an object hits another, one forces the other, and vice versa - this is a transfer of energy - an equal transfer of energy. Since energy has no sign, the "opposite" part doesn't apply to it really, but it does apply to momentum. The conservation laws are all bundled up in newton's 3 laws.

These are considered fundemental laws nowadays. Of course, we've gone much farter than newtonian physics - and i'm pretty sure that there has not been a verifiable case of violation of this law. Sometimes you hear of physicists "creating" particles from "nowhere". I think that what the "media" means is that physicists transfer large kinetic energy of particles such as an electron, into larger particles with less kinetic energy. Mass goes up, kinetic energy must go down, or potential energy - either one. Fresheneesz 10:10, 20 April 2006 (UTC)

the conservation of energy-momentum???

This article says that its sometimes called the "conservation of energy-momentum". Is this right? Where does momentum fit in? I'm pretty sure this is a mistake. Fresheneesz 10:16, 20 April 2006 (UTC)

It's not a mistake. Translation invariance in Minkowski space entails both conservation of energy and conservation of momentum. The conservation law resulting from this symmetry is sometimes called "conservation of energy-momentum" (though I don't like that name). The larger law (energy-momentum) is more general than the particular law (energy), so it isn't quite right to say "the conservation of energy is sometimes called the conservation of energy-momentum". On the other hand, I don't think the article says that, so we might be OK. -lethe ^{talk +} 10:06, 27 April 2006 (UTC)

another nonsensical statement

This article (in the intro) has

"Law of conservation of energy is a mathematical consequence of continuous translational symmetry of time (no moment of time is different from any other)."

What does that mean? How does it help the article? Its very obscure. I'll actually remove it now, and we can discuss on how to change it so it makes sense. Fresheneesz 10:17, 20 April 2006 (UTC)

What it is trying to say is There are many physical phenomena that can best be understood in terms of a universal principle of conservation of energy. Further, the aesthetically appealing and empirically supported principle that the laws of physics are invariant under time translation (see Symmetry in physics#Spacetime symmetries can be shown mathematically to entail the conservation of energy. - but this is a subsection, not in the intro. Cutler 11:34, 20 April 2006 (UTC)

Maybe we should include a link to Noether's theorem if this is mentioned? As that should explain the derivation of conservation laws from invariance principles.137.138.46.155 12:47, 23 August 2006 (UTC)

Yes, such a link is a good idea. --Michael C. Price ^talk 12:54, 23 August 2006 (UTC)

Conditions on conservation?

I was wondering if conservation of momentum only holds in inertial reference frames. For example, given a stationary ball 1 a stationary star, and a moving ball 2 - if ball 2 hits ball one, then ball one jumps frames and now sees the star moving as well as ball 2. Since the star is now also moving, energy has been "created". 68.6.112.70 08:55, 27 April 2006 (UTC)

That's right, momentum (and energy) are not generally conserved in non-inertial frames. The general condition is this: momentum is conserved in systems that are translation invariant, and energy is conserved in systems that are invariant under shifts in time. An accelerating system is not invariant under translations in the direction of acceleration, so momentum is not conserved in that direction. It is invariant under translations in transverse directions, so momentum is conserved in those directions. -lethe ^{talk +} 09:57, 27 April 2006 (UTC)

Shall we add something to that effect about the conditions under which conservation holds? Becuase, I posed that ball one, ball two question to my physics teacher (teaching relativity and quantum mechanics) and he said that conservation always holds and that "theres something wrong in your assumptions but I can't see it". He is obviously wrong (which I find disturbing), but it shows that the assumptions people have of when conservation is relevant is not always the same. Fresheneesz 18:43, 27 April 2006 (UTC)

Currently the article states "Conversely, theories which do not have time translation symmetry result in lack of conservation of energy." Does that not meet your needs? (I sympathize with you for having a physics teacher who doesn't know physics. Probably you shouldn't take any more physics classes from that prof.) -lethe ^{talk +} 20:02, 27 April 2006 (UTC)

Well, ideally that sentence could be written in a more understandable way - translational symmetry is a term that I would think most people don't understand. Thanks for the sympathy. Fresheneesz 10:31, 28 April 2006 (UTC)

Hmmm... well, which bit is confusing you: translation, invariant, or theory? Or something else? Translation in space is the change of coordinates like x → x + a. Translation in time is a shift of the time parameter like t → t + t₀. The term "invariant" refers to stuff that stays the same when you change the coordinates. Kinetic energy stays the same if you translate in space or time, but distance from the origin doesn't. The part of the theory which is supposed to be invariant varies, depending on the technical description you want to use, but one version is kinetic energy plus potential energy. Free particles have no potential energy, so there's just kinetic energy. That's invariant under both translation in space and in time, so free particles have constant energy and constant momentum. The Kepler problem has a potential energy like 1/r², which doesn't change under shifts in time, so energy stays the same for a Kepler particle. It is not invariant under translations in space, so its momentum is not conserved. The general form of this idea is given by Noether's theorem, which says roughly that to every symmetry, there is a conserved quantity, and every conserved quantity (for some definition of quantity) gives rise to a symmetry. That's essentially what the statement says. I'm not sure of an easier way to convey the idea of "time translation invariance", but I agree that it is phrased awkwardly. I've reworded the sentence. How do you like it now? -lethe ^{talk +} 11:28, 28 April 2006 (UTC)

Its better, but I was under the impression that all theories or physical laws are invarient over time. Also, I don't see how that connects to ones frame of reference. Fresheneesz 20:37, 28 April 2006 (UTC)

Let me give you some situations which are not invariant over time: the equation of state of a star (stars are constantly losing energy), the temperature inside an over while it's preheating, the potential energy of an electron in an atom when the atom is in an external magnetic field which is oscillating, the motion of the planets around the sun (when you take into account friction), the entire universe (it's expanding). In summary, lots of systems are time dependent and your impression that all systems are time independent shows a disconnect of common sense with physical intuition: certainly you know that all kinds of things change. Now consider a physical model in the vicinity of any changing system, and you've got a time independent system. You can often get a time independent system from a time dependent one by incorporating the time dependent external bit into your system and using a more complex model. This never reaches an exactly time independent model, since the entire universe is expanding. There are no closed systems which are exactly time independent. Energy is never conserved exactly.

As far as what "reference frames" means. Well, my reference frame refers to those coordinates with which I make measurements. One of them is time. If I measure time since the birth of christ, that's one reference frame. If I measure time since the founding of the city, that's another reference frame. If density of Helium is the same whether I measure it in 2006 AD or 2006 AUC, then I say that's constant. If the name of Pope is different depending on which calendar I use, then I say that is not constant. Some stuff is constant, other stuff is not. -lethe ^{talk +} 21:41, 28 April 2006 (UTC)

Of course I understand that things change. However, laws of physics (as far as i know) only apply to closed systems. All the systems you described represent open systems (usually with implied boundries on the things outside the sysem which can act on the system of interest). In real life, there is only one closed system, the entire universe. Once you try to analyze an open system, you lose the ability to predict what will happen. This is why in all experiments, experimenters try to produce a situation that is approximately closed.

I also know what a reference frame is. My point was that - even considering a closed system - conservation of energy doesn't hold if the reference frame isn't inertial (if it changes speeds). 68.6.112.70 00:24, 29 April 2006 (UTC)

OK, I think I see better what your concern is now. There are two ways to look at this. Imagine a free particle which is not accelerating in an inertial frame. Its energy is 1/2mv². The basic principles of physics say that its laws of motion are the same in any inertial frame. Therefore you expect the energy to be conserved under any change of coordinates to another inertial frame, where the energy will be 1/2mv² again. In this view, you can either agree not to try to do physics in non-inertial frames (or just say that the laws don't hold in that frame). You can also recognize that even noninertial frames are just another choice of coordinates, and the equivalence principle says that any frame is valid, except that the transformation rules will be more complicated. If you're willing to put up with that, then you can still say that energy is conserved. So like if you boost to reference frame accelerating at a, the energy gets changed to 1/2m(v–at)², and this quantity is still conserved. This is the point of view you have to use in relativity theory, where any reference frame (inertial or not) is allowed, and energy is conserved in all frames (if it is conserved in any of them).

If you don't want to deal with the machinery of transformations into noninertial frames, then you have another option. You can view the noninertial frame as your new inertial frame. This introduces pseudoforces (like the centrifugal force in a rotating frame). In this frame, the pseudoforces are some how external, and they destroy the symmetries of the old inertial frame. In this frame, energy need not be conserved. This is the process by which gravity in relativity theory (which is simply the motion of free particles along geodesics) is turned into a force in Newtonian gravity. Thus, if you move to the accelerating frame, the particle is accelerating with rate a, so its energy is constantly increasing due to the pseudoforce.

To sum up: conservation of energy is a mathematical property of the theory, it doesn't depend on what coordinates you use (even noninertial). This is done in relativity. Nevertheless, we often like to view noninertial systems as inertial systems attached to noninertial frames. This is done in transitioning from relativity to Newton. In that view, pseudoforces are introduced, symmetry is gone, conservation fails. -lethe ^{talk +} 09:25, 29 April 2006 (UTC)

Ahh, that is very interesting. ${\frac {1}{2}}m(v-{\bar {a}}t)^{2}$ seems to fix everything. But I think that implies one special initial-rest frame from which all others are judged. I'll have to think about that. Fresheneesz 01:19, 30 April 2006 (UTC)

You should think of it this way: there is a physical number, called energy, which is conserved. You can do anything you want to the coordinates, and all that does is make the formula for the coordinates change. The value that the formula takes is still the same. You're absolutely correct that the formula I gave you ties me to a particular reference frame. Energy is not invariant, it depends on your reference frame. Change frame, change formula. Energy is covariant, not invariant. Whether or not energy is conserved is a consequence of the symmetry of the theory, not of the symmetry of the coordinates you chose to describe the theory. Still, there is a point of view in which you like to pick a privileged inertial frame and form for the theory, and if you violate that choice, you can violate the form (and conservation can fail). Depends on where you stand on the issue of active versus passive transformations, which is something of a philosophical question. -lethe ^{talk +} 03:36, 30 April 2006 (UTC)

Intermediate Gauge Bosons

If energy cannot be created or destroyed then where do the carries for the four fundamental forces come from ? The gluons that exert the strong force upon quarks and hold nuclei together can't jsut appear if this law holds true. Naming them virtual particles and then creating an uncertainty principle seems to me to show that the law is wrong and an attempt is being made to hide this fact. Should it jsut not be ammended that energy can be created and destroyed but only by gauge bosons? I don't have a very good physics background but my teacher can't really help with my queries so any feedback would be appreciated

The conservation laws are true statistically, and only within the uncertainty principle. So a given particle of energy E can appear out of vacuum for a period of approximately t = E/h, so long as it all goes back before the time is over. It's sort of like a rule that an employee can embezzle all they want from petty cash, so long as it's back in the box to be counted the next morning. This rule holds not just for guage bosons, but any kind of bosons, and for fermions also. Electrons and positrons pop in and out of the vacuum and disappear again, for short times. This has real physical effects-- it slightly changes the spectra of elements, and it actually causes some of the "spontaneous" emission effects. By the way, remember that massless guage particles can last a longer time because they have less energy. This is one of the things that makes electrical fields so long-range compared with nuclear fields. "Virtual" particles can have real and big and lasting amounts of energy-- there's energy in static charges like the charge on a big capacitor, and also a lot of energy in the magnetic field of your MRI machine, and both both cases all that energy is "made" of virtual photons. The missing energy in atomic nuclei is basically virtual pions in hydrogen that have been destroyed in fusion. Virtual photons transfer all the energy between the windings of a transformer, too. In that sense, these things are as real as "real" particles, and have all the same energy, in many circumstances. It's just that a virtual particle is sort of like a check rather than a coin, and if the energy it contains is used (check is cashed), then there's a time limit on how long it takes to show up as a draft on nature's books. But energy conservation and Planck's constant set that time-- it's not arbitrary. 22:26, 18 May 2006 (UTC)

I don't believe the law!

If the law is true that energy cannot be created or destroyed - I have a theory that proves the theory wrong. This theory takes place in an airless room. If a book is dropped in an airless room, the kinetic energy won't be transferred into any type of energy than a minute amount of heat energy due to some friction. If you say that heat will be transferred into the air...well that's not possible is it?-since it is an airless room. At the moment, the book which had potential energy before it was dropped now has no potential because it is on the ground. The book has also lost kinetic energy.

My question is where has the energy gone...has it been transferred as some unknown type of energy?

--Dhanish007 09:16, 29 June 2006 (UTC)

As I understand it, the gravitational potential energy was converted to work when it was dropped. After all, couldn't you attach the book to a pulley system and have it do work? Splintercellguy 10:51, 29 June 2006 (UTC)

All of the energy of the book has been converted to heat. When the book hits the ground, its kinetic energy is converted to sound waves which propagate inside the book and the ground, since there is no air. These sound waves are then absorbed by the book and the ground and converted to heat. PAR 13:57, 29 June 2006 (UTC)

Err, have you guys forgotten about the object the book hits? It will absorb all the book's energy and start moving Bipedia 01:19, 26 October 2006 (UTC)

Well, not exactly, but it is a fact that the motion of the earth has not been taken into account. There is the book and the earth separated by some distance. Neither are moving, so their total momentum is zero. Then the book is "let go" and the book goes most of the distance until it hits the earth. The earth moves an extremely small amount upwards to meet the book. When they collide, both stop moving relative to each other, and all of what was once potential energy of the book-earth system now becomes sound waves inside the book and the earth, which dissipate to become heat energy. But in their final position, neither are moving. (conservation of momentum) (forget orbital and rotational motions). PAR 03:03, 26 October 2006 (UTC)

Creating energy

I think that the fact that energy can be created by destroying matter was included in his law, but he put that "energy cannot be created or destroyed". They both seem to contradict! It just doesn't make sense to me at all!

Well, it can be if you consider mass to be a sort of frozen energy. It's mass+energy which is conserved. This is total energy (if you count any mass as energy also) OR it's also total mass (if you don't let any energy or mass out of the system, the mass doesn't change, even if some energy is liberated inside).

This is confusing, yes. See the main article mass in special relativity.Steve 02:33, 7 July 2006 (UTC)

The thing is that matter is energy. So when you speak of energy being able to be created by destroying matter, that's only because you didn't consider the matter as being energy. But in reality it is, and you're just looking at energy in different forms. The statement "energy can't be created/destroyed" refers to energy in the strictest sense, i.e. including matter. So that's why things don't contradict. -- Northgrove 13:37, 19 August 2006 (UTC)

"The new feature of relativistic physics is that "matter" particles (such as those constituting atoms) could be converted to non-matter forms of energy, such as light; or kinetic and potential energy (example: heat). However, this conversion does not affect the total mass of systems, since the latter forms of non-matter energy still retain their mass through any such conversion." - this paragraph is either phrased in a very woolly way that's confused me or it is just demonstrably wrong - nuclear fusion produces massless photons, and therefore changes the total mass of the system. Energy + mass, as stated above, is the quantity that is conserved. —Preceding unsigned comment added by 163.1.174.79 (talk) 17:03, 4 December 2009 (UTC)

Conservation of kinetic energy

This article doesn't give the formula of the change of kinetic energy in relation to the potential energy. -Iopq 08:50, 9 October 2006 (UTC)

Mentioned now in the intro sentence.--Michael C. Price ^talk 10:04, 9 October 2006 (UTC)

Conservation

The conservation of energy neither means energy could not be created nor destroyed. This is a misleading statement by science for a long time. Better is 'Energy is transformable.'

I'll give you one (pair of principles) of the proofs:

1. What is conserved was once created 2. What has been lost is considered destroyed

ZS 05:21, 4 January 2010 (UTC)

What? SBHarris 06:32, 4 January 2010 (UTC)

Section ordering

Would anyone object to the current order of the sections Modern physics (which appears first) and Thermodynamics be reversed to follow chronological order? --Michael C. Price ^talk 10:04, 9 October 2006 (UTC)

Wait a sec...

If energy cannot be created or destroyed, then why does anything exist in the first place? JONJONAUG 13:47, 15 November 2006 (UTC)

Because the universe has zero total energy -- probably. See cosmic inflation and note that gravitational energy is usually negative.--Michael C. Price ^talk 16:23, 15 November 2006 (UTC)

Quantum fluctuation universe as the ultimate free lunch. A joke that never palls. Beats hell out of universe as God's screensaver program, waiting for him to get back from lunch and hit the space bar. SBHarris 16:58, 9 December 2006 (UTC)

How does this apply in real life?

You have all done outstanding work with the level of detail and intricacy in this article, however, after reading the piece in its entirety, I am still very curious as to how the law of conservation of energy appears out in the world. That is, if I were to go about my normal routine, where would I see this law in practice? Thank you all. 66.10.167.1 20:47, 10 December 2006 (UTC)

You see it everytime you apply a force through a distance. That either stores up energy (like lifting a bucket of water) which can be released later, or it puts something into motion (like a auto which must then be stopped). Stored energy and energy of motion are interconvertable into each other. But either can also be turned into heat (as in your brakepads). When this happens, the heat has an equivalent in terms of mass and motion, or force and distance. And some of the heat can be turned back into these, but not all. In any case, all this stuff is the same thing in different forms. It connects to mass itself, so it's apparently some kind of "stuff" like mass is. Ultimately, it's hard to say what. SBHarris 22:04, 10 December 2006 (UTC)

Thank you. Another quick one: how would you see this law applied in something like, say, a roller coaster? Would the energy be converted into "stuff" like the noise that the coaster makes? 66.10.167.1 22:45, 10 December 2006 (UTC)

Some would. Both the kinetic energy (velocity-related) and the potential energy (height related) of the roller coaster are available to make any other kind of stuff that has energy. This includes heat and noise. The more heat and noise made, the faster the thing loses height or comes to a stop to sap this energy to do the job.SBHarris 22:49, 10 December 2006 (UTC)

inertial reference frame

This is my first wikipedia edit. Yay! Anyway, the main reason for my edit was that the statement that "Each of the four components... of [the energy-momentum 4-vector] is separately conserved" jumped out at me because, by itself, it makes it sound like there is something special/invariant about the components. However, the components vary depending on the observer's inertial reference frame. The vector itself is conserved, but it's components vary with your coordinate system. So I thought it required that qualification. I was also wondering whether it needs an explicit mention that energy depends on your reference frame.

The sentence after, I tweaked a little because I felt that it wasn't immediately clear what "The latter" refered to. Also I changed "associated with rest mass" to "is the rest mass" because the 4-momentum is equal to the rest mass times the 4-velocity, which has unit length.

Finally, the sentence, "The relativistic energy of a single massive particle contains a term related to its rest mass in addition to its kinetic energy of motion," is a little hand-wavy. It seems like it would be better to just give the formula. The formula is found half-way down the page on mass in special relativity. Is it possible to link to that spot on that page? —The preceding unsigned comment was added by Jgompert (talk • contribs) 07:13, 12 December 2006 (UTC).

Overlap between this article and the vis viva article

It seems that some of the text in this article overlaps text in the vis viva article. Are there any guidlines regarding duplication of material/internal plagiarism within Wikipedia? Robert K S 16:00, 11 April 2007 (UTC)

Perpetual motion

Perpetual motion is not impossible, whoever wrote that on this page is lacking logic. The universe can only lose energy/mass to itself therefore never actually losing energy/mass. It is therefore a system of perpetual motion.

"A consequence of the law of energy conservation is that perpetual motion machines can only work perpetually if they deliver no energy to their surroundings..."

It was never claimed that the universe delivers energy to its surroundings. Thus, it is a type of "perpetual motion machine" which is possible. The conservation law states only that machines that do work on their surroundings (thus delivering energy and mass from themselves) without eventually disappearing, are impossible. SBHarris 06:44, 22 January 2010 (UTC)

Empirical

The phrase "empirical law" appears. This implies that non-empirical laws exist. I am not sure how the two are identified. —Preceding unsigned comment added by 217.42.19.13 (talk) 11:07, 15 January 2010 (UTC)

I guess that empirical laws rule in physics (or in science in general), whereas non-empirical laws rule in mathematics and logic. DVdm (talk) 11:40, 15 January 2010 (UTC)

Exactly. One set of laws is deductive, analytic, syllogistic, and secure. The other is inductive, synthetic, ampliative, and insecure because ever-vulnerable to further observation, and the vagaries of the future. 03:39, 4 March 2010 (UTC)

Limitations to energy conservation law

Energy conservation law is not absolute law and holds only under certain conditions. It does not hold for reactive propulsion. For reactive propulsion power consumption P in engine does not depend on vehicle speed v, but only on the thrust F: P = f(F). But, according to laws of mechanics, mechanical power produced by engine is P = F∙v. For constant thrust power consumed in engine is constant, but mechanical power produced by the same engine is so grater so grater is the speed of vehicle. This implies that theoretically there exists speed v = const/F, after achieving which engine begins to produce more mechanical power than uses.
There is also a plenty of other examples, where energy conservation law does not hold.—Preceding unsigned comment added by 95.135.179.169 (talk • contribs)

You did not take into account the energy of the exhaust gases. If P is the power produced by the engine (a constant) and Po is the rate at which energy is added to the engine (Po=F.v  plus any heat energy), and Px is the rate at which energy is added to the exhaust, then the conservation of energy says P=Po+Px. You did not take into account the Px term in your analysis. The "other examples" that you mention will also have errors in their derivation. PAR (talk) 14:30, 8 April 2010 (UTC)

For real jet engine - General Electric CF6 turbofan - overall fuel consumption per 1 kN of thrust is 8.696 g per second. If heat of combustion of fuel is about 45 MG/kg, then engine uses roughly 400 W of power per 1 N of thrust. If vehicle is loaded with force 1 N - generator load - and has velocity 400 m/s, then mechanical power produced by engine is also 400 W. But if we accelerate vehicle to higher speed, to say 800 m/s, then, if thrust is the same – 1 N, power, consumed by engine in form of fuel is the same – 400 W, and mechanical power, produced by engine, namely generator, is P = F∙v = 800 W. So the overall consumed power is 400 w and overall produced power is 800 W. So grater is the speed so grater is the ratio produced/consumed power. If specific fuel consumption (SFC) is grater, then minimal speed, necessary for achieving positive energy balance, will also be grater – v_min = SFC. 95.134.115.203 (talk) 07:34, 9 April 2010 (UTC)

What makes you think the thrust is going to be the same (per rate fuel consumption; this is the reciprocal of thrust specific fuel consumption) if you run air through the engine at twice the velocity? It won't be. It takes 4 times the energy to get air from 0 m/sec to 800 m/sec as it does to get it from 0 to 400 m/sec, and thus when you go from 400 to 800 m/sec your power consumption will quaduple and so will our fuel consumption. You're basically saying the engine will NOT have to burn fuel at 4 times the rate to go twice as fast. But of course, it will. P = F∙v because E = F∙d. SBHarris 07:58, 9 April 2010 (UTC)

I took as reference General Electric CF6 turbofan engine only because it has the lowest SFC and, therefore, practically achievable v_min. But, if the question is about principle, we can take into consideration rocket engine. It has no air intake and, therefore no dependence on air flow. Since motion is relative there is not absolute speed. In different reference systems rocket will have different speeds. If thrust would be dependent on speed, it would be different in different reference systems and rocket would accelerate differently depending on from which reference system we regard it. But acceleration is the same in all reference systems.

This implies that thrust also is the same in all reference systems and is not dependent on speed, but only on fuel consumption. Since SFC is defined relative only to thrust, not to speed, the same shall be true also for air breathable engines. But this is only technical question. 95.134.178.229 (talk) 10:51, 9 April 2010 (UTC)

Lets just assume a rocket in empty space, no complications with air intake etc. The mistake we are all making is blindly assuming that the increase in the kinetic energy of the engine is equal to the thrust force (F) times the velocity. In fact, during an infinitesimal time dt, the engine gains energy F.dx and also loses energy because some of its mass has been "reclassified" as exhaust. If the rocket loses mass to the exhaust at a constant rate $\mu \,$ then the amount of energy loss to the engine, due to mass loss, in time dt, is $(\mu dt)v^{2}/2$. This mass is then accelerated, and exhausted. If $dE_{0}/dt\,$ is the rate at which the kinetic energy of the engine is increased, then the correct statement is

$dE_{0}/dt=Fv-{\frac {1}{2}}\mu v^{2}$

Note that the thrust force F is the rate of change of engine momentum at zero velocity, not the rate of change of engine momentum at higher velocity. For a high enough velocity, the engine can actually be losing energy and momentum while it accelerates. For example, if the engine is moving at +800 m/sec (in "our" frame of reference) and its exhaust velocity (in the engine frame of reference) is -300 m/sec, then the exhaust gases at exit will have a forward velocity of 800-300=500 m/sec, and thus the exhust gases as a whole will have a positive rate of momentum increase in our frame. By conservation of momentum, the engine must be losing momentum (in our frame) at this same rate. PAR (talk) 15:12, 9 April 2010 (UTC)

Energy is not conserved in GR

There seems to be a consensus among cosmologists that energy is NOT conserved in general relativity however this is not mentioned in this article, from reading it you would think that energy is always conserved, so this should be added.—Preceding unsigned comment added by 82.211.209.53 (talk • contribs)

Please sign your talk page messages with four tildes (~~~~)? Thanks.

Perhaps we can find something in one of these to be added to the text. It's always better to have standard text books as a source that some chat blog. DVdm (talk) 19:10, 10 June 2010 (UTC)

• There is some validity in your point. Energy in general relativity is a subtle concept, as can be glimpsed if you follow the link to the stress-energy-momentum pseudotensor in the one sentence explicitly referring to GR in the article. Maybe the text needs to be expanded. As the essay you linked mentions, whether energy is conserved depends on the definitions accepted. The problem as I see it, is that without the concept of conservation, the whole idea of energy is essentially meaningless. It's quite a stretch to say that energy is without meaning in general relativity. The vast majority of experiments are not sensitive to the expansion of the universe in any case.

  I had to chuckle at the commenter on the blog who stated "the short answer: Wikipedia is wrong." While undoubtedly a correct statement in some sense, one wonders whether the commenter would be as quick to say "the short answer: Feynman is wrong"[2]. In any event, that commenter is welcome to help fix up the article, should he choose. Tim Shuba (talk) 19:26, 10 June 2010 (UTC)

I would encourage all to carefully read this little blog entry cited above.energy is NOT conserved in general relativity The guy knows what he's talking about, I think. MTW in the book Gravitation make the same point about the problem that gravitational energy not being localizable, which really screws up "local conservation" of energy that we take for granted in all but GR. It's not as though if some disappears HERE, it must go THERE. In GR sometimes it disappears HERE (or appears here) and goes into the general fabric of spacetime in a very diffuse way, where you can't see or measure it, and have to take in on faith. That's not very appealing. But if a bunch of photons are trapped in expanding space-time and they all redshift, energy is lost. If you insist that energy must be conserved in this process, the missing energy must be said to go diffusely into the structure of space-time, in some non-localized way, where it just hangs out. Happy, now? SBHarris 19:59, 10 June 2010 (UTC)

The blog author is Sean M. Carroll, who quite clearly knows what he is talking about. Tim Shuba (talk) 20:15, 10 June 2010 (UTC)

Sure, if you can reword some of this into properly sourced (i.e. not blogged, and not almost-but-not-quite-published-yet) Encyclopenglish, it could be mentioned in the article. DVdm (talk) 20:18, 10 June 2010 (UTC)

Actually Sean does not say energy is not conserved and that's the end of it, he says it depends on your definitions. Since the link to stress-energy-momentum pseudotensor has been provided I shall leave it at that. --Michael C. Price ^talk 20:50, 10 June 2010 (UTC)

Gentlemen, I notice the claim has made it into the article without any source provided. A blog source in reliable. I suggest we find a better source or remove the claim.RonCram (talk) 23:11, 6 November 2011 (UTC)

the bigger picture

As was partially discussed above this article should clearly contain some more words on General Relativity. The intro probably works well on the school level but still gives the wrong impression.

What this article does is listing lots of theories which can be motivated within statistical mechanics (Newtonian mechanics, thermodynamics,...), i.e. theories which are a limit of classical statistical mecanics, which in turn is practically defined via Hamiltonian energy hypersurfaces and thus satisfies conservation of energy. In doing so the article makes it seem like "conservation of energy" is a general statement, some kind of meta law or natural cornerstore - which is not the case.

The term energy can have multiple meanings in GR and on a cosmological level conservation of energy is not a "given fact" as one might think reading the sections here. If you go even further and consider algebraic QFTs on curved spacetimes, then not even the hamiltonian is well defined for most metrics. Briefly speaking GR doesn't tell you that there has to be a timelike killing vector. Cheers 212.186.99.222 (talk) 01:39, 11 August 2010 (UTC)

Actually it is a "given fact", cf the Landau-Lifshitz pseudotensor. --Michael C. Price ^talk 09:15, 15 October 2010 (UTC)

Sprotect this article

This very general topic article suffers daily vandalism from school IP editors. Could some admin just sprotect it? Please? SBHarris 01:12, 15 October 2010 (UTC)

Sound in the video

I don't know if its only on my browser, but the video of Prof. Walter Lewin demonstrating the conservation of mechanical energy has no sound. —Preceding unsigned comment added by 77.253.6.114 (talk) 19:07, 9 May 2011 (UTC)

Poor wording

"$\sum _{i}m_{i}v_{i}^{2}$ was conserved so long as the masses did not interact" If this accurately described Leibniz's concept, there'd be nothing extraordinary about its conservation. Most quantities are conserved in the absence of interactions. What were the actual conditions for conservation? JKeck (talk) 20:06, 8 August 2011 (UTC)

Mass is not converted to energy

"Matter" can be converted to non-matter (electrons and positros to (say) to photons). And energy (kinetic energy) to matter (as in a collision of particles in modern accelerators). But mass (a property of matter and energy) is never "converted" to energy (another property). The mass of an isolated system remains constant, no matter what happens inside it. Mass is conserved, period. (Of course the system must be closed for the conservation, but that's true of any conserved property, including energy and momentum). So mass is conserved by the usual definition of "conserved"-- closed isolated system, single observer. This is true for any definition of mass you like.

Would you all stop screwing around with the lede of this article and read mass-energy equivalence and mass in special relativity. A relevant text is Taylor and Wheeler's text on SR called Space Time Physics. Referenced here.

If you want to argue this, give me a thought experiment where mass is "converted" to energy, and mass is lost and energy is gained. While the system stays closedisolated and nothing escapes. Thanks. SBHarris 03:04, 27 October 2011 (UTC)

No disagreement here. A concern with the present version is that it is not quite clear what you mean by a "closed system". Do you mean an isolated system? The present sentence "In closed systems conservation of mass holds as a separate law, and also the conservation of energy. Both mass and energy may be defined in different ways in special relativity, but for each of the ways, conservation laws hold." is not clear to me as to what you intend to mean.

You have removed from the lead mention of processes in which the mass of ponderable matter does not change; these are ordinary chemical reactions and perhaps may be worth distinguishing from nuclear reactions in which the mass of ponderable matter does change. This is a question of taste, and is not too important for me. But many people think mostly of ordinary chemical reactions in which questions of mass-energy equivalence are irrelevant and even mystifying complications; perhaps such people should be considered in the lead.Chjoaygame (talk) 12:11, 27 October 2011 (UTC)

Sorry, I do mean "isolated" = closed to everything. My point is that every time mass is lost from a system via energy loss, it's not that mass has been "converted" to energy, but rather because the lost mass HAS energy. So there's nothing remarkable about the fact that a system has mass, and you removed mass, and now it has less mass. Everybody was used to that before Einstein. The remarkable thing is that the mass could be lost via radiation or heat loss. But the radiation and heat retain the lost mass-- they retain their invariant mass while considered as part of the original system, and they deposit that mass in any system that absorbs them. So the mass is conserved. Attempts to look at the radiation in isolation while it is "in flight" from one open system to another, are not looking at mass<->energy conversion, they are doing bad physics. You aren't allowed to change your observer that way, or else arbitrarily redraw system boundaries that way, DURING a conservation experiment, especially if you isolate a photon on the process. If you were allowed to do this, energy wouldn't be conserved, either.

If you let a gas molecule out of a bottle of hot gas, energy is not conserved unless you continue to stay in the frame of the hot gas. As soon as you go to the frame of the escaped molecule, its kinetic energy disappears and now energy is not conserved and mass-plus-energy is not conserved, either, due to the frame-change (invariant energy is conserved, but it's not a simple sum of mass+energy, but the norm of energy and momentum, and it corrects for frame changes). If you let a single photon out, invariant mass continues to be conserved for the system so long as you look at both bottle and photon. If you isolate the bottle or the photon, of course mass is not conserved, but that only shows you can't re-draw boundaries and add up contents of systems to get conservation in relativity. Some odd proposed low of "conservation of mass-energy" doesn't help you either, because the energy of the isolated photon energy is anything you like, depending on what frame you want to view it in. Photons, by themselves, have zero invariant mass (no rest mass), just as particles, by themselves, have zero invarient kinetic energy (their invariant mass is their kinetic energy).

Perhaps the real problem is that energy conservation is a system thing. Two massive particle flying apart have some of their energy only as a system property. If you look from the frame of one particle, all the kinetic energy is at the other, and if you choose the other, all the kinetic energy is with the first. From a frame between them, it is distributed. But where is it? No particular place. That's why these artibrary re-drawing of system boundaries during a conservation experiment is so pernicious. If it's allowed, nothing works. It's not really a mass<-->energy conversion issue. SBHarris 15:34, 27 October 2011 (UTC)

superluminal acceleration

The edit was not reliably sourced, not even sourced at all, and was revertible for that reason alone.

More importantly, the experimental finding is very interesting, but is acknowledged to be still subject to empirical review and need for empirical reproduction. It is so exceptionally important that a Wikipedia reference to it must be exceptionally well supported by exceptionally reliable sourcing. The criterion here is reliability of sourcing by Wikipedia standards.Chjoaygame (talk) 03:45, 15 November 2011 (UTC)

Speedy neutrinos

Are not speedy at all, since the scientists forgot to take into account the effects of relativity in the GPS measurements. Once that was done, the mystery was perfectly resolved. [3] Stop messing with this article! SBHarris 01:44, 16 November 2011 (UTC)

Bad link in the opening paragraph

In the opening paragraph it states that "the total amount of energy in an isolated system remains constant over time", and if you click on the word "energy" you are taken to a page which defines energy as "the ability a physical system has to do work on other physical systems".

However, the word "energy" in that article is different to the definition used in this article, namely "a quantity in an isolated system that remains constant over time". Historically this was called "vis viva", but from 1807 started to be known as "energy".

While vis viva energy is conserved (by definition), the "energy" described in the linked article and defined as "the ability a physical system has to do work on other physical systems", is not what is referred to in the first law of thermodynamics, and is not conserved within the universe. (e.g. when energy dissipates due to entropy it no longer has the ability to do work on physical systems.

Gcsnelgar (talk) 23:17, 22 December 2011 (UTC)

Isolated system

Someone has become confused over this topic. I was visiting this page to refresh my memory but find myself having to leave a comment instead to correct the page.

What is not made clear is what is meant by an isolated system the linked page has no references. A closed system is created by drawing a control loop around an area. It is possible for energy to cross any closed system. i.e. EM radiation. The only possible isolated system would be the universe itself and this is only if there is nothing oustide of the universe.

e.g. potential energy is mgh but g is a factor of r. So if a body outside of the system is moved g changes and so too does potential energy.

• conservation of energy only applies if there is a system where there is no energy lost to noise or heat. It is not equiavalent to conservation of momentum.

It is a rule not a law. It doesn't always apply and is a common beginners mistake for systems such as a collapsing chain to use conversation of energy.

• Energy cannot be created or destroyed is a law which then relates to Einstein etc E^2 = m^2*c^4 to be more accurate.

The isolated system idea can only exist as a cyclical idea. — Preceding unsigned comment added by 149.170.169.1 (talk) 18:24, 27 April 2012 (UTC)

logic of the present form of the article

The logic of the present form of the article is that mass and energy are separately conserved when relativistic effects are not involved; this is a nineteenth century perspective. When relativistic effects are involved, mass and energy are defined differently for nineteeth and for twentieth century physics. The article is presently structured starting from the nineteenth century perspective, and the relativistic effects are considered as being developed from that starting point. It would perhaps be reasonable at some future time to re-structure the article so as to start from the twentieth century perspective. Then the lead would not need to give explicit advance notice that it was starting from the nineteenth century perspective.Chjoaygame (talk) 22:53, 27 May 2012 (UTC)

You should probably read conservation of mass, mass in special relativity and mass-energy equivalence before complaining here. The short form is that there's not much need to restructure this thing, since mass by both definitions is conserved (meaning conserved over time) in special relativity, for any given observer, if you have an isolated system (nothing-- no energy/mass -- in or out). This includes relativistic mass (conserved but not invariant, since it is total-E/c^2) and it includes invariant mass (which is both conserved AND invariant). In SR, the only new thing is that (unlike in the 19th century) matter is not conserved, so you have a sort of conservation of (matter+energy) which is (very unfortunately) sometimes referred to as conservation of (mass+energy) by those speaking loosely who don't differentiate matter and mass, and who don't know that mass is a scientfic word, well defined in SR, but matter is NOT (either scientific OR well-defined). This confuses hell out of students of SR, along with the two different type of mass in SR-- and well it should.

Another source of endless confusion to students is the loose consideration of closed systems that are NOT isolated, so that energy is free to leak out (like heat or light) but matter is not. So you have teachers "explaining" to students that the split nucleus is lighter because mass has been converted to energy, which is totally wrong. It is lighter because energy was allowed to escape when the fragments were stopped/cooled, and the system wasn't isolated as that happened, so what do you expect? It lost mass as kinetic energy that was removed, and now is less massive (duh). But the lost mass (the binding energy or the atom bomb energy) just went elsewhere and shows up as mass THERE (where it went-- into the cooling water of the reactor). Mass continues to be conserved if you don't lose track of it.

An atom bomb is lighter (less massive) only when the products have been collected AND cooled (as Feynman notes), but then you're no longer weighing the heat and radiation, which do have a mass that escaped, and which they deposit on whatever cools the fission products and absorbs the gamma radiation and heat. And so on.

The last confounder is that single photons are massless (they lack rest mass) but they confer mass (both relativistic mass AND rest mass!) upon all systems of which they are a part. This is another confounder to students, who have a hard time believing that a pair of annihilation photons, as system, has a mass (yea verily, even a rest mass) even though each individual photon does not have a rest mass. But even the kinetic energy of any two particles moving away from each other has a system rest mass (and contributes to the system invariant mass) even though you can't locate it at either particle. It moves around according to the observer, but refuses to go entirely away, showing up as an irreducable minimum in the COM frame, which is where it makes its contribution to the system invariant mass (which the same as the system relativistic mass, in the COM frame). SBHarris 21:42, 28 May 2012 (UTC)

Don't worry, I am very far from thinking of making such a re-structure myself. And I did say "would perhaps be reasonable at some future time". Not at a particular future time that I have in mind.Chjoaygame (talk) 23:35, 28 May 2012 (UTC)

I don't want to wait to some far off "future time". I want to do it now. If you don't want to help, get out of my way. SBHarris 01:58, 29 May 2012 (UTC)

as it was formulated

I think it would have been polite of you to put your case here in the talk page, rather than just as a peremptory dismissive posting note.

You read into the previous version that “"nineteenth century law" makes it sound like it's been done away with, which it hasn't.″ There's quite some room for discussion about your reading. I don't agree with it, but I don't say that it is an entirely unreasonable reading. The twentieth century version of the laws use definitions different from the nineteenth century ones. Whether that means doing away with the nineteenth century versions is a matter of interpretation. I have above drawn attention to the structure of the article. So I am proposing a compromise.Chjoaygame (talk) 00:58, 29 May 2012 (UTC)

Indeed I should have come here first; had I been aware of your previous post on the topic, I would have done so. Apologies.

The main problem with calling it a "nineteenth century law" is that the use of "nineteenth century" is chronologically limiting. To pick a random example, Stephen A. Douglas could be described as a "nineteenth century politician" since he was only active as a politician (not to mention above ground) during the nineteenth century. Placing "nineteenth century" before "law of physics" grammatically implies that the law is either discredited, or is no longer in active use. You point out, quite rightly, that the exact way the law functions in a relativistic system is a matter of debate. In fact, this is an issue for many laws, theories, etc. formulated prior to Einstein's theories of relativity, but I'm not aware of any that are described, least of all in the lead section of their articles, in such a chronologically specific way.

Keep in mind that I'm not an expert in physics, so maybe my reading is founded on some fundamental misunderstanding of the way Newtonian physics is discussed, post-relativity. I'm going to give the present version of the article some thought, and will be back with you later. Evanh2008 ^{(talk|contribs)} 02:00, 29 May 2012 (UTC)

I don't fully agree that “Placing "nineteenth century" before "law of physics" grammatically implies that the law is either discredited, or is no longer in active use.” The word "grammatically" is the weakest element of that statement. I agree that it might be interpreted in those ways, but such is not a necessary interpretation. In any case, I have compromised by acceptng your proposal to put it after instead of before.

I agree with your plan that some thought is needed. That is why I am not seeking myself to initiate a new round of editing. I think it quite a difficult problem to work out a good way to edit this article. I think a good deal of careful work is needed for it.Chjoaygame (talk) 03:52, 29 May 2012 (UTC)

Making the break by century works fine, here, as the ideas that were to transform the Lavoisier concepts of conservation of chemical matter and elements (no more alchemy) and separate element weight, more or less got wiped out in a fin de siècle avalanche by the discovery of radioactivity (1896), the gigantic energies involved (1903), radioactive trasmutation of one element to another (1903), Einstein's SR and mass-energy equivalence (1905) and Planck's suggestion that radium salt energy loss was so high that it might be used to test the mass of energy-loss empirically (1906). The game all changed, right about then. Energy was conserved, mass was still conserved, but matter, as it had been known to 1903, took a beating. SBHarris 04:35, 29 May 2012 (UTC)

premature edit of lead without adequate attention to body of article

The edits that I just undid were edits of the lead, without attention to the body of the article. Moreover they were perhaps editorial comment and an extension of the length of the lead with material that if it appears should be in the body of the article.

The lead is a summary of the article, not a diktat of the mastermind.

The edits that I just undid might well be part of a proper edit of the body of the article. I do not intend, if I can avoid it, trying to re-structure or rewrite the body of the article. If someone is worried about the lead, he should first attend to the body of the article.Chjoaygame (talk) 01:52, 29 May 2012 (UTC)

On the contrary, get the lede correct (as an outline) and the rest follows. The lede now says that the separate laws of mass-conservation and energy-conservation have been "updated" into mass-energy conservation, which is not explained. This is wrong. Mass and energy conservation both continue to exist, it's just that now we realize they are the same law with different units. What has changed is "ponderable matter conservation" which we now know is false. If you want to revert, per WP:BRD, then let's see you do better. Don't sit and be reactionary. SBHarris 01:56, 29 May 2012 (UTC)

As I read you here, you seem to propose that the mastermind will dictate the lead and the elves will follow with fixes to the body of the article. Your previous comment "get out of my way" says a lot about your attitude.

I am not defending the article, just asking that it be edited properly. I am not being reactionary, just asking that the editing be done properly.

I am not wanting to delay others from fixing the article now. I am just saying that any attempt to initiate such a process by me would be in the future.

You don't like the wording of the lead, and you peremptorily spin it as "wrong". I will agree that it is vague and imprecise and open to improvement, but I read your statement that it is wrong as spin to justify your massive dictation of a commentary in the lead.

Fixing the lead doesn't fix the problem that the article is not written from a consistent twentieth century viewpoint. That needs to be fixed if the article is to come into the twentieth century and it won't be fixed by elves. It needs careful work to re-structure the article. If you want to do that work, well and good. So far you have not given any hint that you are prepared to do it. Rather you seem to be hinting or saying that you won't. If you want to dictate the lead in the way you did initially, and let the elves fix the remaining problems, I don't approve.Chjoaygame (talk) 03:44, 29 May 2012 (UTC)

I never said I was unwilling to work on the body of the article, or did not intend to. I've been at it now, after all, for six years. But whether I do or not is none of your concern. There is not some WP: approved way of writing any article, like working everything out in the references or body first, and only then being permitted to work on the lede, like a kid with dessert. That might be YOUR idea, but it is not my idea, and it is not some prescribed idea of MoS. I can do as I please, unless I'm outvoted as an editor here.

As for the idea of waiting for "elves" to work on this article, how dare you? I've been working on this thing since 2006 and am presently the lede contributor, while you're down at #5 or so. [4], having started last year. If there's anybody waiting for elves to do the work, it would not appear to be me.

Having said that, I've now decided you're being so outrageous as to revert you up to 2R, and then let you sit on it. If you can get some other editors to vote it out your way, bring them on. I think you're simply being obstructionist, and I've had enough of it. SBHarris 04:18, 29 May 2012 (UTC)

Dear SBHarris, feel free to call me names, and to out R me. I am used to violent and impatient and mastermind and self-righteously indignant editors by now. I don't try to out R them, or "bring ... on" opposition to them. I just let the Wikipedia get worse as a result of their violence and impatience.

It is my concern if the lead is being edited in a way that I think is wrong. But not to the extent of edit warring. I can see you have not structured the article well in the past, and perhaps won't do so in future.Chjoaygame (talk) 04:55, 29 May 2012 (UTC)