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# pmb

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## Posts posted by pmb

### Why does light travel at the speed of light?

he Physis FAQ it says that light has inertial mass. I read this years ago and forgot the details but I like it forhe most part. The new FAQ is here<br /><a href='http://math.ucr.edu/home/baez/physics/ParticleAndNuclear/photon_mass.html' class='bbc_url' title='External link' rel='nofollow external'>http://math.ucr.edu/...hoton_mass.html</a><br /><br />He left me out for credit which upset me a bit but no more. The author uses the symbol $p = m_{rel}v$. The $m_{rel}$ here is a particles relativistic mass. The value is found by deviding the momentume buy its mass. It can also be found otherways. Seems that most GR texts noways define the photons inertial mass using its wavelength/frequency/energy.<br /><br /

My appologies for the messyness of my posts. For some reason there are these darn HTML break line symbols floating all over the place and its ruining my posts. I keep asking the moderators why this happens but nobody is telling me. Perhaps the PM messages they might be sending me are not getting to them just as mine may not be getting to them.

Very confusing.

Note: I made a terrible error above. $\frac{\partial E}{\partial p} = \frac Ep = 1/c$ is so incorrect I just slapped myself. LOL!!

<br />I agree, (I've always struggled with massless particles having momentum) but are these equasions not back engineered? They certianly explain the relationships but not the reason, that is, they do not explain why the photons leaving your display are so repulsed by the atoms in the LED and so attracted to the atoms in your retina.<br /><br />Go easy on me!<br />
<br /><br /><br />

There are famous physicists who teach that light has mass. E.g. Richard Feynman and Alan Guth come to mind. Guth I know personally and he told me that he sometimes finds it useful to think of light has having mass. Others are the exact opposite.

I was wondering something. Some of the physics I learned came from well-known physicists. When I say something like says something that Guth I know personally ... I fell like I'm unnecessarily name-dropping, which I hate. Is this an unwise way to argue opinion in physics?

### Can nothing not exist?

It seems to me that when the day comes that everyone participating in this thread agrees on what it means for something to exist the answer to this question will come quickly.

<br />But could it be meaningless precisely because before time does not exist, in a sense, that time infact has no beginning, no t=0?<br /><br /><br /><br />yes, thats why i say it is a flase question (i might be horribly wrong) and go on and develop a possible answer.<br />
<br /><br /><br />I disagree. IT might verywell be that the universe is jus one big quantum state. Before "time" it might very well be that the universe was described by a static quantum state. The big bang might just have been that state going from a static state to a time dependant state. So in the big picture the universes quantum state was always time depenant. The big bang might therefore have been the universes quantum state going through a change of state. I.e.

$|Psi(r, t)>$

where

t < 0 ===> $|Psi(r, t)>$ = $|Psi®>$

and

t > 0 ===> $|Psi(r, t)>$ = $|Psi(r, t)>$

### Why does light travel at the speed of light?

<br />Sure is. The dispersion relation (the relation between energy  E and momentum p) for the free electromagnetic field is $E = pc$, which is a simplification of the more general dispersion relation for free fields ($E^2 = m^2 c^4 + p^2 c^2$)  resulting from a mass-like term that is zero (m=0). From that, you directly get a group and phase velocities $\frac{\partial E}{\partial p} = \frac Ep = c$ for wave packets of the free electromagnetic field.<br />
<br /><br /><br />That makes no sense to me. Especially The relation you gave is<br /><br />$\frac{\partial E}{\partial p} = \frac Ep = 1/c$ <br /><br />Dispersion relations apply only to waves and a particle moving with velocity <b>v</b> is not a wave. A photon is not a wave. This is a classical photon, not a quantum one. You can't even think of a classical photon as you could quantum one. Here, in classical mechanics, which relatiivity is of, photons move on classical trajectories.<br /><br />
<br />Since no one has shown the derivation,...<br />
<br />That's not true. I just posted a link to the derivation you posted a while back in another thread. Just clicking on the link I gave would have taken the reader to your derivation. That post was praisworthy for doing the workl. Since I posted a link to your post aqbove there really is no need to redo what I've aleady done. Soyou went from praiseworthy to redundant. But I suppose you had a need. I might have done the same thing in your position - and I'm be redundant too. lol! Also imatfal posted the following in post #7<br />
<br />Maxwell's equations will also pop out a speed for Electromagnetic Radiation through vacuum<br />Relation between electricity, magnetism, and the speed of light<br />
<br /><br /><br /><br /><br />Nobody asked him for clarity so its assumed that nobody wanted any or were to embarassed to ask. Hence the reason to link to your post elsewhere. But repeating it here is work you didn't need to do. And its not because we're lazy that it hasn't been provided. I've seen this question many times and decided yesterday to create a new web page to do the work out once and for all. And that will still be gone because in days to come the derivation on my website will be easy to find. This one, not so much.]<br /><br /><br />

### Why does light travel at the speed of light?

<br />One of the pseudoscientific instances is the confusion of correlation with causality. Physics seems to be biased in the dirrection of confusing causality with correlation. Its an ideology as much as a science. Thats the problem also.<br />
<br /><br /><br />This thread i so fagmented along the train of thoughts that I can't follow it. Splitting a thread can make it very disturbing for me to read. My mind is messed up. Perhaps from the pain meds I'm on. Bad juju!

In any case, if you want to see why the speed of light travels at the speed of light then let's start off with what we're really looking for. I want to determine what the speed of an EM Wave is where light is an EM wave. The speed is derived here http://www.scienceforums.net/topic/66476-supernovae-and-time/ in the first post.

Best wishes,

Pete

### Recommendation

<br />&lt;br /&gt;&lt;br /&gt;&lt;br /&gt;<br /><br />Thermodynamics and Electrodyanmics were not intended by me to be put into one forum. When I created this thread I only had those two in mind. A little bit later I realized that Philosophy of physics should be a sub forum of Physics as well. We have a forum for Philosophy now but people only interesed in physics probably steer away from  it and avoid placing scientific topics in that foum for fear of nobody caring enough to read it. And it should be more popular because it's one of the most important thing a physicist should know. I.e. I'll base my argument on authority where I'll use Fritz Rohrlich as the authority. He's one of the most well known and most brightest person in physics today. <br /><br />Consider the first chapter of his text <b>Classical Charged Particles</b> by Fritz Rohrlich, 2006. The first chapter is entitled <i>Philosophy and  Logic of Physical Theory</i>. The author writes on page 1<br /><br />This is a supurb book for learning relativistic electrodynamics since it is a great arena to apply it.<br />Before judging that chapter I highly recommend reading it first. I also took a course in the Philosophy of Physics as an undergraduate. I'm very glad I did.<br /><br />I had this in mind because it's one of the most important parts of physics and I've enjoyed reading those topics along that line in the American Journal of Physics. The following example comes to mind<br /><br />I recommend reading this. I can send it to you if you want.<br /><br />Personally - It would be a go forum to discuss the subject. It's of my favorite subjects and it'd be much more interesting to share it and discuss it with others. Althought I'm not sure how my blood pressure would hold up. LOL!  There is a text I got which is one of the most well known on the subject written by the most well known philosophers of science. It's called <b>The Logic of Scientific Discovery</b>. It was Karl Popper who made the concept of <i>falsifiability</i> popular. I.e. <br /><br /><a href='http://en.wikipedia.org/wiki/Falsifiability' class='bbc_url' title='External link' rel='nofollow external'>http://en.wikipedia..../Falsifiability</a><br /><br /><br />Some physicists might not even know when their learning of using the philosophy of science. It'll increase awareness of this. Making it sub forum of Physics would draw the otherwise diinterested to take a look and perhaps raise interest in them and perhaps increase their logcial use of science in as much as they'll know what is and what isn't science and why.<br /><br />I could go on but I think I got my point across by now.<br />

There is such a form where I am a helper. It's at http://physicshelpforum.com/forumdisplay.php?f=44

### Help me, help me, help me, HELP ME!!!!!!

Something weird is going on. I can't initiate a PM by clicking on "pmb" at the top right of the web page like I used to. And when I post a thread it gets butso with these "break" symbols <br/> which drive me out of my mind! And then if I exit or modify it incorrectly the whole post has those symbols and it has HTML symbols for all the equations. And there are no Emiticons to the right of this page and when I try "show all" button, nothing happens.

Help. Get me out of this forum hell! (sob!)

### Why does light travel at the speed of light?

&amp;lt;br /&amp;gt;Well, typically $p_\mu p^\mu \equiv m^2$. Since $p^\mu =(E,p^i)$ where  $p^i$ is the three-momentum, it's easy to see for a particle with m=0 that $E^2=p_i p^i$. So massless particles have momentum by virtue of their energy.&amp;lt;br /&amp;gt;
<br /><br />Those equivalences which Klaynos employed originated with electrodynamics. E = pc is derived from an EM calculation. Those calulations are the ones from which the 4-momentum are constructed and the invariance estabished. The expression E^2 - (pc)^2 = (mc^2)^2 is then used with E = pc to deduce the expression m = 0. I believe what you did here was to take that and work backwards to make your point. <br /><br />It's been a while since I've worked these equations. This will be pleasing to derive from the basics again. Please give me time though. I'm studying other material for the moment and will start on this tonight. Ill make these into web pages which will go in my website. Any help in PM would be appreciated. I choose PM so I won't have to get into side debates along the way.<br /><br />Let me start by deriving E = pc. Let b = beta = v/c, g = gamma = 1/sqrt( 1 - b<sup>2</sup> ), m = proper mass of particle.<br /><br />By definition of P, P = M(v)v. I show here <a href='http://home.comcast.net/~peter.m.brown/sr/inertial_mass.htm' class='bbc_url' title='External link' rel='nofollow external'>http://home.comcast....ertial_mass.htm</a><br /><br />that M(v) = gm. Therefore P = gmv. It seem that I never created a web page where I derive E = gE<sub>0</sub> so let's take on assumption. (it may be in <a href='http://home.comcast.net/~peter.m.brown/sr/work_energy.htm' class='bbc_url' title='External link' rel='nofollow external'>http://home.comcast....work_energy.htm</a>)<br /><br />Derivation of E = pc for a photon<br /><br />P = gmv, E = gE<sub>0</sub> ===> E/E<sub>0</sub> = g<br /><br />P = mv(E/E<sub>0</sub>) = mv(E/mc<sup>2</sup>) = v(E/c<sup>2</sup>) <br /><br />P = Ev/c<sup>2</sup> ===> Pc/E = v/c<br /><br />If the particle is a luxon, which is a particle for which v = c, e.g. a photon, the v = c.<br /><br />Pc/E = v/c = 1 ===> E = pc<br /><br />Energy-momentum relatinship for a photon:  E = pc<br /><br />------------------------------------------<br />Next derivation: Derive E<sup>2</sup> - (pc)<sup>2</sup> = (mc<sup>2</sup>)<sup>2</sup><br /><br />P = E/c<sup>2</sup> ===> Pc = Eb ===> E<sup>2</sup>b<sup>2</sup> = (pc)<sup>2</sup><br /><br />E<sup>2</sup> - E<sup>2</sup>b<sup>2</sup> = E<sup>2</sup> - (pc)<sup>2</sup><br /><br />E<sup>2</sup>(1 - b<sup>2</sup>) = E<sup>2</sup> - (pc)<sup>2</sup><br /><br />E/gE<sup>2</sup> = E<sup>2</sup> - (pc) <sup>2</sup> = (mc<sup>2</sup>)<sup>2</sup><br /><br />Therefore E<sup>2</sup> - (pc) <sup>2</sup> = (mc<sup>2</sup>)<sup>2</sup><br /><br />At this point I can now define a 4-vector, the 4-momentum <b>P</b> as <br /><br /><b>P</b> = (E/c, <b>p</b>)<br /><br />This could not be done unless we hadn't derived the equations which allows us to derive the 4-momentum 4-vector as well as its properties. This is too long. All the equations are making mush out of my mind. LOL! I'll argue why one can't logically argue the other way around.

### Gravity

<br />I learned something today, thanks.<br /><br /><br />But<br />Where else in physics or geometry do we encounter Pi squared?<br />
<br /><br /><br />There are so many places that I've lost track. Many many places in math that's for sure.

### What Physics fact or theory fascinated you the most?

<br />Sorry to hear about your condition PMB, its not often we get to interact with forum members on a personal level.<br /><br />What about J A Wheeler, did you have the opportunity to get to know him ?  He is, to me anyway, one of physics' icons of the last century.<br />
<br /><br /><br />Unfortunately, no. I never got to meet him. Edwin lives a mere 30 minutes away from me and MIT is just a 45 minute drive. But Wheeler live in NEw Jersey and had and have no access to that mind of travel. Now that he's passed away I'll never have that chance.

### mechanics

<br />hello every one ,<br />i'm in my engg pre-final year and i'm intrested to do my mini project related to aerospace . <br />my project is on how to carry light weight or delicate objects into space ? main problem here is the heavy vibrations of the launch vehicle which destoys the objects inside it . can anyone suggest me wt mechanism to be used in order to reduce the affect of vibrations on the delicate object inside it .....<br />

You didn't provide any specs which has to be satisfied. Under certain cases such as small payloads, try submersing it in a fluid such as water.

### AJP Resource Letters

Every once in a while The American Journal of Physics has an article which is a list of resourses such as a list of important experiments done to verify relativity. A list of those articles is found here http://ajp.dickinson.edu/Readers/resLetters.html

Is this the right forum to post such a list?

### Science is all about religion?

<br />Everybody behaves religiously, .
Do you actually believe that by merely writing something down it becomes the truth? Your lack of providing an arguement to support your claims tells me that you can't provide one. And any scientist here knows that when you respond to this post without actually providing the evidence everyone keeps asking you for will have more evidence that you have zero evidence. So let me thank you in advance for demonstrating my point.

### Falsifiability

I created this thread in order to demonstrate the usefulness of a sub forum on the philosophy of physics.<br /><br />The philosophy of physics obviously falls under general philosophy. The subject of falsifiability falls under the philosophy of physics. However it someone wishes to create a thread which falls under the philosophy of physics, then, as of now, it should e oosted in the general philosophy forum. Most physicists I know would never poke their nose into a forum labeled <i>General Philosophy</i>. And that includes the famous ones I know. However they just might poke their nose into a forum labeled <i>Philosophy of Physics</i>, if for nothing else for curiosity when the other physics forums have no interest to him/her at that time. <br /><br />Here's a good example to illustrate what I mean. Suppose someone wants to toss the subject of falsifiability around to see what they can learn from the discussion. So, as I did the other day, posted the query of how postulates which are not falsifiable have become part of mainstream cosmology.<br /><br />So to toss the idea of falsifiability around I'll start with the postulate <i>White swans do exist.</i> This is not falsifiable since no counter-example is logically possible. Someone who heard the postulate "White swans do exist" might think it's a scientific postulate but since it's not falsifiable it isn't. Therefore such logic exists in science since I've just stated one. So for a postulate to be true it need not be falsifiable. That notion can certainly confuse any physicist ... including me before I was aware of this example. <br /><br />This discussion belongs in a philosophy forum. However if it finds itself in the general forum a physicist might never become aware of its existance due to the lack of interest of philosophy by physicists.<br /><br />Things like this is why I suggest a sub forum called the <b>Philosophy of Physics</b>. There is a huge amount of very interesting things to discuss in such a forum. For example. In the text I had in my Philosophy of Science course there was an article which, in part, tried to understand how "science" is defined in practice. E.g. one part is the thinking and making mistakes part of physics. We all make mistakes and over come them. That's part of doing the work of a scientist. Another part is how ideas originate and what the scientist is thinking, but not writing part of science. Each of these never get into a scientific paper. That is the kind of thing I enjoy discussing and thinking about and which properly fall under the field of study of the philosophy of science.

### Recommendation

<br />I see three recommendation, not two. I assume you mean 1) Thermodynamics and Electrodynamics, and 2) Philosophy of physics? I am certainly against creating (2) for several reasons (unless someone finally implements the feature to put sub-forums on the ignore list, in which case I am much in favor of it). But what what interests me: Why thermo&amp;Edyn as a common forum (assuming I understood the proposal correctly)?<br />
<br /><br /><br /><br /><br />Thermodynamics and Electrodyanmics were not intended by me to be put into one forum. When I created this thread I only had those two in mind. A little bit later I realized that Philosophy of physics should be a sub forum of Physics as well. We have a forum for Philosophy now but people only interesed in physics probably steer away from  it and avoid placing scientific topics in that foum for fear of nobody caring enough to read it. And it should be more popular because it's one of the most important thing a physicist should know. I.e. I'll base my argument on authority where I'll use Fritz Rohrlich as the authority. He's one of the most well known and most brightest person in physics today. <br /><br />Consider the first chapter of his text <b>Classical Charged Particles</b> by Fritz Rohrlich, 2006. The first chapter is entitled <i>Philosophy and  Logic of Physical Theory</i>. The author writes on page 1<br />
<br />...ignoring philosophy in physics means not understanding physics. <br />
<br />This is a supurb book for learning relativistic electrodynamics since it is a great arena to apply it.<br />Before judging that chapter I highly recommend reading it first. I also took a course in the Philosophy of Physics as an undergraduate. I'm very glad I did.<br /><br />I had this in mind because it's one of the most important parts of physics and I've enjoyed reading those topics along that line in the American Journal of Physics. The following example comes to mind<br />
<br /><i>Realism and/or physics</i>, Carl G. Adler, <i>Am. J. Phys.</i> 57(10), October 1989<br /><br /><b>Abstract</b> - A recent editorial [John S. Rigden, "...to see it as it is ... to know it as it isn't..., Am. J. Phys. 54 397 (1986)] has suggested that as it is physics as it is commonly practiced may be basically an antirealist science. At the same time, it can be observed that the practitioners of biology and chemistry are usually strongly realist in their orientation. A case study in support of the general position of the editorial is presented. In addition, ,a possible reason for the difference in the philosophical perspective of physics and biology/chemistry is also examined. <br />
<br />I recommend reading this. I can send it to you if you want.<br /><br />Personally - It would be a go forum to discuss the subject. It's of my favorite subjects and it'd be much more interesting to share it and discuss it with others. Althought I'm not sure how my blood pressure would hold up. LOL!  There is a text I got which is one of the most well known on the subject written by the most well known philosophers of science. It's called <b>The Logic of Scientific Discovery</b>. It was Karl Popper who made the concept of <i>falsifiability</i> popular. I.e. <br /><br /><a href='http://en.wikipedia.org/wiki/Falsifiability' class='bbc_url' title='External link' rel='nofollow external'>http://en.wikipedia..../Falsifiability</a><br />
<br />The concept was made popular by Karl Popper, who, in his philosophical criticism of the popular positivist view of the scientific method, concluded that a hypothesis, proposition, or theory talks about the observable only if it is falsifiable.<br />
<br /><br />Some physicists might not even know when their learning of using the philosophy of science. It'll increase awareness of this. Making it sub forum of Physics would draw the otherwise diinterested to take a look and perhaps raise interest in them and perhaps increase their logcial use of science in as much as they'll know what is and what isn't science and why.<br /><br />I could go on but I think I got my point across by now.

### Science is all about religion?

<br />Do you classify skepticism as a religion?<br /><br /><br />Forum rule: assertions require support. Please provide some proof of this.<br />
<br /><br /><br />

It is true that assertions require support. Therefore the proper request would be Please provide some support.

### What is energy, exactly?

<br />Pmb, I was replying to gravity guy not you. I'd be very surprised if I had to tell you about peer review or the speculations forum.<br />
<br /><br /><br />

humbly appologize. I got mixed up. What a sad state I'm in tonight.

### What is energy, exactly?

&lt;br /&gt;I'm not sure what you mean by safe?<br />
<br />I wish I knew why I asked that but I can't recall.<br /><br />
<br />You could pursue publication in a peer reviewed journal, ...<br />
<br />I go the speculation forum merely for entertainment. Nothing more.<br /><br />
<br />...but if you have no experience of that then you will find it difficult, ...<br />
<br />I'm quite aware of the peer review process. It's a painstaking process which can take many tries in a particular journal perhaps until you realize that you tried the wrong journal. Then you have to start the whole process all over again.<br /><br />
<br />..not because outsiders are shunned but because the requirements are quite significant.<br />
<br /><br /><br />I have the feeling that some people here don't consider me a physicist, or if they do then perhaps a really bad one. Is this true? I suppose I'll never really know.<br /><br />Why do I ask? Because I find that some people in this forum, and I don't keep track of who says what, I'm not that petty. Certain things keep get repeated even those points an undergrad student in physics/math should know.<br /><br />Let me state for you by background so we can put this to an end just in case people are making assumptions that they don't know that they're making.<br /><br />Carrer; <br /><br />Out of High School ----> Air Force<br />Out of Airforce  ----> Electronics Technician<br />Out of tech field  ----> College - Merrimack College ://www.merrimack.edu/<br />                               Note: Major: Physics, Mathematic (two majors)<br />After college  ----> Industry<br />                          (1) Computational Physicist for Air Force<br />                          (2) Digital Signal Processing for Air Force<br />                          (3) Systems Analyst for FAA<br />                          (4) Software Quality Assurance Engineer for FAA<br />                          (5) Lab Tech at MIT for calibrating CCDs for Chandra X-ray Observatory<br />                          (6) Software Quality Assurance Engineer for Polaroid<br />                ----> Graduate School - Northeastern University, Boston<br />                ----> Layed off and took GR at MIT. At this time I met Edwin F. Taylor <br />                         who was writing a text called Exploring Relativity. I got a chance to proof read the text and come uip with ideas for the book. Ater that I got Leukemia in <br />                         2000 and had to stop working - On disability. I spent from that time until<br />                         now studying certain things in relativity and relativistic electodynamics <br />                         I found interesting. Since I became disabled in 2000 I've been forced to<br />                         work on my own. I decide to work in relativity since I had mastered a lot<br />                         of the material. I've mastered the material to the level of someone who<br />                         did his Masters Thesis in relativity, focusing in things like the concept of mass.<br /><br />I dug into the subject since all my time was spent doing this so I came up with a truck load of ideas and learned material. So I'm no slouch in physics by any stretch of the imagination.<br /><br />Okay. Enough about me. I'l place all this in my "About Me" page and then not mention it again.

### What is energy, exactly?

<br />I'm not sure what you mean by safe?

I wish I knew why I asked that but I can't recall.

You could pursue publication in a peer reviewed journal, ...

I go the speculation forum merely for entertainment. Nothing more.

...but if you have no experience of that then you will find it difficult, ...

I'm quite aware of the peer review process. It's a painstaking process which can take many tries in a particular journal perhaps until you realize that you tried the wrong journal. Then you have to start the whole process all over again.

..not because outsiders are shunned but because the requirements are quite significant.

I have the feeling that you don't consider me a physicist, or if so then perhaps a really bad one. IS th true? I find that people in this forum repeating things that even an undergrad in physics should know.

Let me state for you by background so we can put this to an end just in case people are making assumptions that they don't know that they're making.

Carrer;

Out of High School -> Air Force

Out of Airforce -> Electronics Technician

Out of tech field -> College - Merrimack College http://www.merrimack.edu/

### What is energy, exactly?

As we've talked about before, we tend to make the assumption here that m is rest mass.

Yep. I'm overly aware of that.

I have to ask you, what was the purpose of you post to m? Everything in my post was created so that anybody whow knows anything about SR should be able to grasp it no matter what. That was the purpose of me stating my response for both the m = inertial mass people and the p = proper mass people.

Note: It's my considered opinion that the term rest energy fo a particle be tossed out the window and replaced by proper mass.

In any case, that's why I addressed the proper mass definition first and as such the eqution E = mc^2 is wrong. Given that it was Gravity Guy that you were responding to it seemed likely that there was no reason to assume that he wasn adhering to that rule of thumb you speak of. Hence my inclusion of the second portion. After all it is the esxception of the "tendancy" which I had in mind give my experience with Gravity Guy.

In our experience this is the most common use in the literature and the easiest for people new to the subject to understand. I agree I was a bit lax and should have defined my terms more clearly to ensure we were all on the same page.

That's up to you, of course. However it's very unwise to make that assumption that you just give regarding the literature. If one is working in particle physics then what you'll see in probably all instances is the mass = proper mass notion. If one is working in cosmology then one is usually working in other concepts such as active gravitational mass, proper gravitational mass and inertial mass aka relativistic mass.

However that may be what the author puts in writing. That doesn't mean that's what one uses in private thoughts.

For example: In Alan Guths journal writings I'd wager that he uses the mss = proper mass concept. However I know as fact that this is not how he thinks. Alan is an aquantance of mine. He gave me a copy of his lectue notes on his early universe course he teaches. In it he refers to light having mass and that te mass density of radiation is equal to its energy densty/c^2. I of course use it. I don't plan on having people coerce me into using otherwise. Especially when people want me to teach other than the way Guth does.

Here is a list of the texts I have which utilizes inertial mass (aka relativbistic mass).

Gravitation, Misner, Thorne and Wheeler, W.H. Freeman & Co., (1973).

Cosmological Principles, Peacock, Cambridge Univ. Press, (1999).

A First Course in General Relativity, Schutz, Cambridge Univ. Press, (1990).

A Short Course in General Relativity, Foster & Nightingale, Springer Verlag, (1994).

These texts use m as inertial mass

Relativity: Special, General and Cosmological, Rindler, Oxford Univ., Press, (2001).

From Introducing Einstein's Relativity, Ray D'Inverno, Oxford Univ. Press, (1992).

Here is a list from journals

Apparatus to measure relativistic mass increase, John W. Luetzelschwab, Am. J. Phys. 71(9), 878, Sept. (2003).

Relativistic mass increase at slow speeds, Gerald Gabrielse, Am. J. Phys. 63(6), 568 (1995).

In defense of relativistic mass, T. R. Sandin, Am. J. Phys. 59(11) 1032 (1991).

A simple relativistic paradox about electrostatic energy, Wolfgang Rindler and Jack Denur, Am. J. Phys. 56(9), Sept. (1988).

An elementary development of mass-energy equivalence, Daniel J. Steck, Frank Rioux, Am. J. Phys. 51(5), May (1983).

See list of online journals at

http://home.comcast....vistic_mass.htm

I haven't updated this in a very long time.

My point is this. People may use m = proper mass in print but it doesn't mean that's how they use it in there thoughts or how they teach others.

...we tend to make the assumption

We? I'm we too.

I consider myself to be part of the we so I believe that what I use counts. I should also use m as I see fit. Not as the majority rules. If so you'd be stiffeling thoughts. Using te symbol m as you do almost universall is taken to mean that inertial mass isn't "real" in some way.

I was posting here for four years my first time around and in my second round I think will be staying.. so long as I don't get banned. So I hope I don't get into this dicussion every time I speak of mass or use the symbol m to mean proper mass. It's not as if I don't know what I'm talking about.

We all want to prepare the reader to understand what he reads in journals, especially those who are directed towards teaching physics, like the American Journal of Physics. E.g.check your Private Messages. I sent you a link to an article I wish you to peruse and see if and how m is used as well as E and E_0.

The OP did not ask for a definition of energy. It asked what energy is, and that sort of answer is the best you are going to do. The problem here is that ultimately it's an ontological question that science doesn't address.

Hi Tom. Recall what I was responding to

Energy is, exactly, the conserved current related to time invariance of the Lagrangian. Google "Noether's theorem".

DrRocket stated Energy is, exactly .... and was thus making an assertion about what energy is and was thus making an attempt at a definition of energy. And as you know, whathe was talking about is not a definition of energy but an equality.

Notice the statement that followed me, i.e.

Energy, like several quantities in physics, is one of those things that goes without a definition. I did some research on energy and wrote up the result of what I thought best suited as a good response to the question What is Energy? As Richard Feynman wrote in The Feynman Lectures (see http://home.comcast.net/~peter.m.brown/mech/what_is_energy.htm)

Now I'd like to quote you.

No, it's not a physical thing. It's a useful abstraction because it is a conserved quantity owing to the time-translation symmetry of physics. It helps us keep a good set of books for problems we solve.

You're thinking of something that is derived, i.e. the properties of energy and symmetry of a time-invariant Lagrangian. By the way, to everyone - that pertains only to Lagrangians which don't have "t" in it. Some do have t. Those describe systems in which energy is not conserved.

Now look at the link above. There are 9 instances of the word book (or bookeeping). I was agreeing with you before I even knew you.

Take a look at Fig. 3. Right before the figure 3

As a general example of this type of bookkeeping is given in Fig. 2.

Figure2 outlines an EM system which should give some sort of device in which the energy moves back and forth between two types of energy. Figure 3 shows what a bookeeping tale would look like if such a thing were to be created.

Had you read my previous response on energy which was 6 lines below the comment you were criticizing then you'd have known all of this.

If I sound pissed off then yes. Saddly I am. I take a lot of time to create responses and create web pages after doing a shit load of work and people dismiss them out of hand. Why do you people think I made those things? Let me tell you. It was to help you learn. And I had plenty of help writing those pages. I have some friends at places like MIT who teach physics and wrote texts on these subjects. Maybe I just won't bother with helping any body here. Maybe I'll just sit here and get you people to help me and don't attempt to help anyone else. I know it's be easier for me that way.

### Gravity

If I would say that I'm working on Origin of Gravity, probably I will be penalised.

If so I myself would stick up for you since this seems to be about a searc of knowledge, not a new theory about gravity.

I would like to say that Origin of Gravity,..

There is now known mechanism of gravity. Same with EM either. There is deeper and more precise knowledge of EM too but no known mechanics of it.

Energy and Mass are the most important part of our understanding of physics and our universe.

Not to my knowledge. Please provide your reasoning which led to your conclusion here.

I agree with p-cunfused...

Please define tem p-cunfused.

But look, how one could be so sure what he/she is talking about.

Experience with the theory and the relevant experiments. Anynbody who believes that they know everything 100% is ignorant!

If you (who claim that you are the most educated here) ...

I find that comment offensive. Therefore this is where I end my part in this thread.

### Mass must have spatial extent

Yes indeed your quote is excellent.

It hints at further deductions that may be made about the common misconception of "time travel" in general.

An object has an extent (duration) along the time axis, just as along the space axis.

So why all the talk of time travel as moving one point of that extent when the same proponents would never dream of moving an isolated section in space.

When people talk of time travel they are either speaking of the distant future or the past. The first one requires waiting, the second requires faster than light travel. This is because such travel requires moving on a closed timelike curve which requires faster than light travel.

### What is energy, exactly?

Correct, it's a simplification of E2=(mc2)2+p2c2

If Gravity Guy is using E as total energy and m as proper mass then the equation E = mc2 says that total inertial energy = proper mass * c2 which is wrong. If he's using m as inertial mass and E as total inertial enregy then you're wrong and Gravity Guy is right, at least regarding equation.

Hi

All what is done in schools is calculating tranfering one type of enery to another. Nobody knows origin of energy.

E=mc2 is slightly wrong according to my theory. Beside, formula is correct only 1% and proven with atomic bombs. Only 1% of mass is changed to energy. Even that is not correct 100%.

Please post your theory in the speculation forum. I'm curious as to what it is. More likely than not I'll find an error in it.

### Exploring Black Holes

There is a new version of Exploring Black Holes comming out in the future. It's located at http://www.eftaylor.com/. See http://www.eftaylor.com/comments/ and http://exploringblackholes.com/.

Once again I'll be proof reading for the authors. It'll be a great deal of fun. You can do the same thing if you wish. In any case it will be fun to talk about. Download the book and bind it and read it and let's chat!

### Religion and Morality

Ultimately though, I quit because I value what I stand for, life/family/friends, and made a vow to myself, which I've honored for 20 years now. Not because a god will punish me if I don't, but because I value what my vows stand for.

Congradulations Phi for All! Way to go! I quiet 22 years ago. I think it was because I started exercising and the contradiction between doing areobicxs and having a smoke after that was too much for the logic portion of my mind to handle.

I dislike the idea of being ethical just because I fear the reprisals of a deity if I'm not. I much prefer the rational reasoning that being ethical benefits those around me who will hopefully realize the same thing, extending their ethical behavior to me as well. People lose their faith all the time, and then where is the strength of their morality? Reasoned ethics seem stronger to me, much stronger than those enforced by a threatening deity.

In my experience it never really seemed to work. All the time I was going to church in the last seven years it was like I was surounging myself mostley by hypocrits. I was suffering a lot in life due to loneliness and illness. I thought that surrounding myself by Christians that part of my life would disappeared. Instead if only got worse. There just seemed to be more people who were available to abandon me. I'm still a Christian by one that doesn't surround myself with hypocrits.

### Doomsday

I'm uncertain which fundamentalist groups you could be referring to. The Christian fundamentalists I am familiar with believe Jesus is on his way back, his return is imminent, and all Christians need do to prepare for His return is believe in the Salvation that awaits them. They don't have to kill any infidels, let alone engage in acts of terrorism and mayhem.

I'm a Christian myself and one thing I'm certain of is that nobody knows when the end of days will come. Even Jesus didn't know when I was here. Claiming to know when Jesus was here could be interpreted as blasphemy. There's a reason God doesn't want us to know when the end of days would be here, and only God knows that reason.

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