Talk:Mass–energy equivalence/Archive 1

message: I was wondering if someone could explain the units used in this equation. I have never seen an explanation which includes the units. It would seem that the equation would not hold if the units changed. User:jimaginator
This relation will be true if the units are consistent. For example using all SI units (E in Joules, m Kilograms and c in metres/second). But other units would be valid, for example natural units (E and m in MeV, c=1). 137.138.46.155 07:37, 23 August 2006 (UTC)
thread_title:  Units of E=mc² 

message: :If we measure E and m in units of mass (kilograms, grams, etc...), the formula becomes E = m, which is much more simpler than the usual one and much more easier to understand. The c² is just a factor of conversion to adjust the mass measure in grams to the E measure in joules: grams can not simply be equal to joules. 24.202.163.194 17:31, 30 December 2005 (UTC)
replies: text:  That is 100% true and, simltaneously, completely non-enlightening to non-expert users. -- SCZenz 00:35, 14 January 2006 (UTC)
thread_title: E = m

message: I have written a new article on Celeritas which I feel should be linked to from this article but can't really figure out how. Any input would be welcomed. Majts 00:03, 12 October 2005 (UTC)
replies: text: thanks, that works, although I took the liberty of making a change to the wording Majts 01:12, 12 October 2005 (UTC)
thread_title:  Celeritas 

message: OK, I can't even read the mess above without hurting my head, so here area couple of facts to help you:
# Physicists rarely use the "relativistic mass"—usually m just denotes the rest mass.
# E=mc2 is incomplete.  The full version, as it is usually written out, is
#:E^2=p^2c^2+m^2c^4.
#E = mc2 is thus valid only in the reference frame where the object is stationary.
Yes, you can do this other ways, but they are much less common in modern physics. -- SCZenz 00:53, 23 November 2005 (UTC)
replies: text: That being said, if the article is presenting Einstein's original treatment, and is clear about it, that's not a problem.  But it definitely is different than how the material would be presented today. -- SCZenz 00:56, 23 November 2005 (UTC)
replies: text: I agree 100% with SCZenz, including the head-hurting part, and I'm glad someone else said all this so I don't have to. (go Bears!) Melchoir 01:04, 23 November 2005 (UTC)

text: I agree that this is what's taught, and what some will expect to see.  I therefore think it has to be visible in this article too.  However, certain users seem to be having a giant POV war over equivalent formulations of these equations, which is absolutely absurd.  I think this needs to be rewritten by someone who understands this and doesn't have an axe to grind. I'll put it on my own list unless someone else wants to do it. -- SCZenz 04:58, 23 November 2005 (UTC)

text: I didn't help, but I'm glad to hear that it's cleared up! Melchoir 00:23, 27 November 2005 (UTC)

text: That sounds more or less what the article says now, I think. -- SCZenz 07:06, 24 December 2005 (UTC)
thread_title:  A physicist's view 

message: It seems to me that there is 3 systems of concepts related to mass: </br>
1- Newtonian system where the mass stay always the same; </br>
2- Relativistic mass system where the mass is changing with is content in energy, wich one give raise to the concept of rest mass;</br>
3- The energy-momentum 4-vector system where the mass is an invariant as seen from various reference frames of inertia, but not necessary invariant in a collision, and in wich the mass is also called rest energy. But even in this last one, physicists still use the term rest mass, increasing the confusion.
I think that when we use the word mass, we have to know, or specifie if it is not clear, in wich system we are, and adjust all our wording to that system. It would be less confusing, the theory of relativity being enough confusing in itself without the neeed of adding to it.
What do you think of this view?</br>
24.202.163.194 17:33, 27 December 2005 (UTC)
replies: text: I think too much specificity could make some articles confusing.  I also don't think that 1 and 3 are really very different; in fact, 1 is just a special case of 3. -- SCZenz 18:22, 27 December 2005 (UTC)

text: Yes, but there can be too much specificity in an encyclopedia.  We want to avoid confusing people with details that aren't relevant, and we want to use common terms in the majority of sources when possible.  Unfortunately, in this case, undergrad-level/popular sources (which we should be taking as a cue for our terminology) don't all agree. -- SCZenz 19:45, 27 December 2005 (UTC)
thread_title:  3 systems of concepts 

message: Contrary to the first sentence in the article, Einstein was not the originator of E=mc². Instead it was Henri Poincaré, 1900 (5 years before Einstein) in Arch. Neerland. 5, 252. "a pulse of light with energy E has mass m = E/c²", Lev Okun in Phyiscs Today, June 1989, p.33. Lev Okun makes a reasoned suggestion that we use a single (velocity-invariant) mass definition and substitute E0=mc² as the standard formula for today's use. The article could use a revision that clarified the source of confusion seen elsewhere in this discussion, including exactly how Einstein's relativity theories helped clarify issues concerning mass and energy.
: Does the Okun article also point out that the equation only takes on its present importance in the broader context of special relativity, not just a special case of light pulses? Since special relativity had yet to be proposed in 1900, Poincaré could not have been saying what Einstein said in 1905. --KSmrqT 05:26, 29 December 2005 (UTC)
thread_title:  Origin of E=mc² 

message: If you don't like this new structure, we can always go back to the precedent one or try another new one. What do you decide?
--24.202.163.194 22:52, 31 December 2005 (UTC)
thread_title: New structure: first try

message: This article seems to imply that this equation led to the atomic bomb being developed. I don't think this is true at all -- the developments in nuclear fission were not as a result of pursuing this equation at all. It is true that the equation is often associated with the bomb (in a misleading way, usually), but that doesn't actually mean it was important in the bomb's physical development. --Fastfission 03:39, 8 January 2006 (UTC)
thread_title: Bomb again

message: I edited this, thinking I was signed in.  I changed the first sentence of "Background and consequences" to give our possesive pronoun an antecedent, at approximately 1951EST.--Josh Rocchio 00:53, 11 January 2006 (UTC)
replies: text: No prob, it was the grammar that irked me more than the translation.  Can't well have an its without a something.----Josh Rocchio 04:42, 11 January 2006 (UTC)
replies: text: Ack...both 69.yadda.yaddas were me.--Josh Rocchio 04:42, 11 January 2006 (UTC)
thread_title:  Apology for the word «body» in the Einstein statement 

message: A body at rest in a reference frame, according to Newtonian mechanics, usually has some form of Potential Energy. You cannot say it has no energy at all. --atou 01:01, 13 January 2006 (UTC)
replies: text: You are completely free to define the 0 of potential energy so can chose any body to have no energy. 137.138.46.155 07:54, 23 August 2006 (UTC)
thread_title:  The first sentence in the first section is physically wrong 

message: Going through this article I found pretty many errors in physics. Such as confusion in energy, rest mass, relativistic mass, and some convoluted sentences. I think this article need not to be a special relativity thesis, but at least this should be clear and correct. --atou 01:40, 13 January 2006 (UTC)
replies: text: Yes, I've stopped paying attention since I rewrote it last.  The rate at which people make helpful contributions that screw things up is mind-boggling; I just noticed a section which used to be correct, with words added to the equations so that it was now wrong.  I'll rewrite the whole thing again soon. -- SCZenz 15:17, 13 January 2006 (UTC)
thread_title:  Can somebody rewrite this article? 

message: In his book How the World Was One: Beyond the Global Village, Arthur C. Clarke mentions that the equation was known to the famous physicist Heaviside; that's older than the other alternate origin.
Most standard works agree with this article in attributing it to Einstein.  But they don't deal with claims that it was older.  We do need clarification.
--GwydionM 15:31, 15 January 2006 (UTC)
replies: text: For this one, I suggest looking into the Wikipedia article for Olinto de Pretto. As usual, popular science simplifies and romantisizes the process of scientific inquiry, and attributes a discovery purely to one guy as if he just came up with it out of the blue like some magic Buddha. --129.10.116.232 16:44, 22 May 2006 (UTC)
thread_title:  Equation not original to Einstein? 

message: what I am missing in the article, is the difference in apparant inertia perpendicular to and parallel to the motion of a particle? I don't feel very confident to write about that without looking into the stuff again first... — Xiutwel (talk) 20:19, 15 January 2006 (UTC)
thread_title:  inertia perpendicular to motion 

message: How did he get the equation? Could there be some explaination on that? I mean did he know the ratio of energy to mass was going to be the speed of light squared to begin with or was it E=mx; x being the unknown. Is it an coincidence that the mass to energy ratio is the speed of light squared or is there some speical reason? If c² is only a conversion factor from kilograms to joules, and a kilogram was originally defined as "the mass of one litre of pure water at a temperature of 3.98 degrees Celsius and standard atmospheric pressure" and then later defined as "precisely the mass of a particular standard mass created to approximate the original definition." and a joule is "the absolute minimum amount of energy required (on the surface of Earth) to lift a one kilogram object up by a height of 10 centimetres." then how did he get the equation? Since the measurement of both above are defined by humans before they had any knowledge of mass to energy relationship. Unless there is some scientific reason for joules and kg that I am not getting. Or...does the speed of light squared/the speed of light have something to do with the amount of energy used to move an given mass? If so, someone should explain it. Pseudoanonymous 02:22, 14 February 2006 (UTC)
replies: text: The equation arose as a consequence of taking existing laws of physics and modifying them to work in a spacetime setting. In particular, all equations should be invariant under Lorentz transformations, which are the permissible changes between inertial frames. This familiar form of the equation is a limited version of the general rule. Maxwell's equations for electromagnetism, discovered years earlier, were already invariant and a helpful guide. In fact, Maxwell needed to add an electromagnetism term to his equations, just as Einstein later added and combined terms for the rest of classical physics. Gravity was still a problem in special relativity, one which was to force Einstein to curve spacetime for general relativity theory. Not only does energy act as inertial mass, it also acts as gravitational mass, as embodied in Einstein's stress-energy tensor. The upshot of all this is that Einstein could not choose some arbitrary formula and expect it to satisfy the conditions required to make a consistent theory, no more than an elementary school student could look at 3+x=5 and choose anything other than x=2. --KSmrqT 04:16, 14 February 2006 (UTC)

text: Wouldn't derivation be a better title? You don't really prove physics equations. Zarniwoot 22:54, 13 June 2006 (UTC)

text: It should be noted that the derivation is of my own work, and I really have no idea how Einstein figured it out.  I remember seeing in some physics video that he figured it out with his little thought experiments, but as I can't remember the source on that, don't take my word for it.  Again, the derivation may not be the same one Einstein used; I have no idea what he did, and the purpose of the derivation is so that somebody wondering why it is true can see why.  Also, the derivation shows that (total energy) = (relativistic mass)c^2, and while that is true, a lot of people on this page say that Einstein meant his equation to be in terms of the change in internal energy and rest mass, not total energy and relativistic mass.  Sorry for any confusion. --AmaanMitha 03:32, 14 June 2006 (UTC)
thread_title:  How did he get the equation? 

message: The article says:
:It is not a coincidence that mass bends spacetime, while the charges of the other three fundamental forces do not.
I keep on staring at this and not understanding it. If there exist two electric charges at a certain distance, the electric field contains energy. And by E=mc², the system containing the electric field will therefore have mass proportional to the energy in the electric field (in addition to the non-electric-related mass of the particles involved). And because all mass is the same, that mass will bend spacetime. So the sentence above is not correct - an electric field will bend spacetime - and so, presumably, will the other forces. Just slightly.
What did I miss? --Alvestrand 20:04, 27 March 2006 (UTC)
replies: text: You're not wrong.  Charge creates field, and field contains mass/energy, and that bends spacetime.  But you're supposed to think of the mass/energy as the source of curvature, and the fact that the mass/energy has some charge as its own source is incidental.  Maybe this could be worded a little better. -lethe talk [ +] 20:24, 27 March 2006 (UTC)
thread_title:  Non-gravitational forces and spacetime 

message: This equauation is undeniably associated with relativity, although whether it's derived  depends on your pedagogical approach to the subject.  In any case, relativity should certainly be mentioned in the introduction somehow; what should we say? -- SCZenz 17:42, 9 April 2006 (UTC)
replies: text: That is a good point (alough I think the sentence was factual correct). Maybe something like: The formula was first published in a slightly different formulation by Albert Einstein in 1905 in one of his famous articles. He derived it as a consequence of the special theory of relativity which he had proposed the same year.? Zarniwoot 21:41, 22 April 2006 (UTC)
thread_title:  Association with relativity 

message: Could someone please add an explanation of how the equation works, especially the bit about C^2? I understand the result of the equation, but I do not understand the exact math involved. For instance, why is the speed of light squared used to relate mass and energy, and what are the resulting units? It seems to me that if I multiply 1 pound by the speed of light in miles per second, squared, I get 34701131432.066 (lbs.)(mi.^2)/sec^2, which is not like any unit of energy I've ever seen.
--scienceman 21:31, 10 July 2006 (UTC)
replies: text: Assuming that you are using a "pound" as mass rather than weight (force), it may not be a common or useful unit of energy, but it is a valid unit of energy (mass × length² / time², much like the joule=kg×m²/s²).  A very similar discussion occurred near the top of this talk page. -- Coneslayer 22:02, 10 July 2006 (UTC)
replies: text: Yep. I personally vote for dram-furlongs^2/fortnight^2 as our basic energy unit. The drams to come from a dram shop not too many furlongs and fortnights away. SBHarris 22:28, 10 July 2006 (UTC)
thread_title:  Explanation 

message: Whole article needs rewriting to emphasize right from the start, instead of mentioning it halfway through, that the m is the relativistic mass, not a rest mass.  A crank is going apeshit crazy over this at various photon articles. --Michael C. Price talk 18:24, 9 August 2006 (UTC)
replies: text: It can be a rest mass. Then it gives you the rest energy. Which isn't very interesting for a particle, but IS interesting for a system at rest, since it includes all kinds of system internal energies (rest mass = relativistic mass for systems in the system "rest" frame = COM frame). SBHarris 07:52, 23 August 2006 (UTC)
thread_title: Relativistic mass

message: Okay, how comes that this formula is using kilos, not any other scale of weight?
You measure the earth from pole to pole, then divide that with a large number. then you devide this number by 10 and get a decimeter. You then make a cube of decimeter sticks and fill it with water that is under normal preassure and is 4 degress C. This weight is now a kilo. And somehow this e=mc2 , wich seem kinda simple, is using this strange scale.
Am I just confuzing myself? —Preceding unsigned comment added by 217.209.215.117 (talk • contribs) 
: The formula is not tied to any particular units.  The units you use for two of the quantities will determine the units of the third.  See my longer explanation near the top of this page.  -- Coneslayer 16:40, 17 August 2006 (UTC)
thread_title:  why is it kilos? 

message: E=MC2 should be E=MC3 because if it is 2 then that means everything is in 2D, although space is in 3 dimentions. -David Knott
:why does the squared make it mean that everything is in 2D? - 9/19/06
::It doesn't.  The statement was nonsense. -- SCZenz 02:22, 20 September 2006 (UTC)
thread_title:  E=MC3!!! 

message: User:Thljcl has made several edits to this article. Based on his questionable edits in kinetic energy, and his failure to discuss the matter when asked to, he appears to be a problem user. I do not, however, have the knowledge to comment on his edits here. Any thoughts? -- Meni Rosenfeld (talk) 09:56, 21 September 2006 (UTC)
thread_title:  [[User:Thljcl]]'s edits 

message: I'm not going to claim to know much on the subject; I'm merely able to spot discrepancies. This article says 'It is a little known piece of trivia that Einstein originally wrote the equation in the form Δm = L/c² (with an "L", instead of an "E", representing energy, the E being utilised elsewhere in the demonstration to represent energy too).'
The article Celeritas says 'In the nineteenth century, an upper-case V was commonly used to describe the speed of light. This was the notation used by Einstein in his 1905 papers, thus his most famous equation was originally written as m=L/V² (E having being used elsewhere for a different energy)'
Which of these is correct?--Jcvamp 23:32, 5 October 2006 (UTC)
thread_title:  Which One?