Fred56 Posted October 19, 2007 Author Posted October 19, 2007 Ah, the unpredictability of human response... "This one is tough for most people, like accepting that time doesn't exist." Most physicist know that information is convayed by energy' date=' not mass. How are the two related? And why do you say that time does not exist?[/quote'] Klaynos, do you think any of these questions you posted have been answered in any way yet? If not, I (and maybe others) can have a go at it. What conclusion, or kind of conclusion, do you feel is needed here? Well, this seems (to me) to be the crux of it (the current objections). I don't follow the sequence of reasoning, and what does "our model" refer to? Sequence of “reasoning” goes something like: Classical information is believed to be something we can gather, or extract, for free. Information is weightless (like thoughts are). QM illustrates that this is completely wrong -photons have energy/mass, therefore information must also. The EPR paradox illustrates a problem with the QM model, this is yet to be resolved. But we know that (quantum) information is certainly not weightless, or costless. Sorry if this is obvious to anyone, or they think I am just rehashing. What I would like is some “deeper” questions, but of course everyone is busy, and distracted with their own ideas and plans.
ydoaPs Posted October 19, 2007 Posted October 19, 2007 What are you talking about!? There is nothing about the existence of massless particles that implies that the applicability of the mass-energy equivalence is somehow not universal. Actually, it does. The version he quoted assumes a reference frame in which the massless particle is at rest. Massless particles travel at c. So you feel the concept of information having mass/energy doesn't pose a problem for the determinist/empiricist view? Mass and energy aren't exactly the same thing. As I said above, E=mc2 is assuming a reference frame in which the particle at rest. E2=m2c4+p2c2 is the equation where the particle in question is not at rest relative to you. And guess what! Photons have momentum!
Fred56 Posted October 19, 2007 Author Posted October 19, 2007 A reference frame, however, is something that is projected from a human mind. Is there a point somewhere (in the universe) that is at rest? This can only be relative (to the observer, the one projecting a "static" frame of reference). Anyone want to (try to) shoot the following down?: Heat/disorder is equivalent (there is a symmetry) to information/uncertainty. This is apparent in Boyles's and Shannon's equations. There is debate over this apparent symmetry, but information clearly does have energy/uncertainty, and our model of the quantum world also tell us this. Therefore information also has (an equivalent) mass, and presumably also has gravity (rather than gravitas). There is a vast (spatial and conceptual) gap between the classical (Boyle/Shannon), and the quantum (Einstein/Heisenberg). But “obviously” there is a connection...
ydoaPs Posted October 20, 2007 Posted October 20, 2007 Is there a point somewhere (in the universe) that is at rest? Motion is meaningless without a reference frame. You must define motion relative to something else. This is a BIG part of Special Relativity. "Without defining a reference, it's like asking, 'What the difference between a duck?'"--Swansont Heat/disorder is equivalent (there is a symmetry) to information/uncertainty.Heat is not the same as disorder. What makes you think they are the same as information and/or uncertainty? Therefore information also has (an equivalent) mass, and presumably also has gravity (rather than gravitas).As I said above, energy is not the same as mass, but they are related. Which has more mass: one kilogram at rest with respect to you or one kilogram moving at 4x105m/s with respect to you? There is a vast (spatial and conceptual) gap between the classical (Boyle/Shannon), and the quantum (Einstein/Heisenberg). But “obviously” there is a connection...Obvious, eh?
Fred56 Posted October 20, 2007 Author Posted October 20, 2007 Motion is meaningless without a reference frame. What does "meaningless" mean? Who or what is "motion" meaningless to (without a reference)? Heat is not the same as disorder. What makes you think they are the same as information and/or uncertainty? A couple of guys called Boyle and Shannon. Also just about any textbook about entropy -and I don't say they are "same" things. As I said above, energy is not the same as mass, but they are related. Correct, energy isn't the same as mass. But it is the equivalent (there's a symmetry). Which has more mass: one kilogram at rest with respect to you or one kilogram moving at 4x105m/s with respect to you? This would depend on the frame of reference. A kilogram is only "meaningful" in a gravitational field. But mass/energy is (fundamentally) conserved, isn't it?
ydoaPs Posted October 20, 2007 Posted October 20, 2007 What does "meaningless" mean? Who or what is "motion" meaningless to (without a reference)?An observer is not necessary. There is a red ball and a blue ball. They pass each other. Which one was moving? How do you know? The universe consists of a green ball. Is it moving? How do you know? A couple of guys called Boyle and Shannon.This guy Ken told me that the Universe was made roughly 6000 years ago. Also just about any textbook about entropy -and I don't say they are "same" things.Define the terms "heat" and "disorder". Heat and entropy are related, but not the same. The way you worded the post implied that they are the same. This would depend on the frame of reference. A kilogram is only "meaningful" in a gravitational field.A kilogram is a kilogram is a kilogram. Mass is independent of a gravitational field, weight is not. But mass/energy is (fundamentally) conserved, isn't it? Mass/energy is conserved IN A REFERENCE FRAME. Let's expand my previous example. There are three balls(one red, one blue, and one yellow). The red and blue balls are at rest with respect to each other, but moving with respect to the yellow ball. From a reference frame in which the yellow ball is at rest, the red ball has the energy from mass, but since the red ball is moving, it also has kinetic energy. Now, let's move our reference frame to one in which the blue ball is at rest. The red ball still has the same energy due to mass, but, since it is at rest relative to the blue ball, has no kinetic energy. The red ball has more energy in the reference frame of the yellow ball than it does in the reference frame of the blue ball. Thus energy is dependent on the reference frame and is not conserved from frame to frame. Mass, however is the same in every frame of reference.
foodchain Posted October 20, 2007 Posted October 20, 2007 Mass/energy is conserved IN A REFERENCE FRAME I thought that was invariant mass?
Fred56 Posted October 20, 2007 Author Posted October 20, 2007 An observer is not necessary. There is a red ball and a blue ball. With no observer, how can there be a "red ball" or a "blue ball"? Define the terms "heat" and "disorder" Maybe you should have a go at this. I'll post one if you do. A kilogram is a kilogram is a kilogram A duck is a duck is a duck. Ducks don't walk around in single file... Mass/energy is conserved IN A REFERENCE FRAME. Mass, however is the same in every frame of reference. Yes, surely a reference frame isn't a necessary condition for conservation of mass?
ydoaPs Posted October 20, 2007 Posted October 20, 2007 With no observer, how can there be a "red ball" or a "blue ball"?You're right. With no observer, the balls cease to exist. I labeled them with colours simply as a way to distinguish them in the example. Explain the difference in energy without reference frames. Maybe you should have a go at this. I'll post one if you do. Heat: Energy in transit from one system to another due solely to a temperature difference. Entropy:A property of a system describing amount of energy unavailable to do work(meh, not a very good definition, but it's the best I can do off the top of my head at this time of night after working all day) On a completely unrelated and irrelevant note, your posting style reminds me of revprez
Fred56 Posted October 20, 2007 Author Posted October 20, 2007 Your definition of heat is a definition of enthalpy, no? Sorry about your head, but Boltzmann's law (of entropy) tells us that ordered states (tend to) degenerate into disordered ones (in a closed system). Unavailable energy? your posting style reminds me of revprez Mate, sounds like you do need some more sleep... Here's mine: Heat energy is the result of, or is caused by, "kinetic" -(translational, rotational, vibrational) motion, and the emission and absorption of infrared radiation. Heat disperses, or diffuses, in a kinetic way (but the “transfer” is not governed solely by motion or vibration, as EMR is involved). What emerges from heat is motion (of molecules). This motion is coupled to all other bodies (molecules) so that it eventually diffuses throughout the “space” the gas (system) occupies: a thermodynamic process. This diffusion is otherwise called entropy. Edit: I revise my opinion of your definition of heat: energy transfer due to temperature gradient actually does describe it too (thermodynamically).
Martin Posted October 20, 2007 Posted October 20, 2007 Well this thread has gotten somewhat heated and out of control so I would like to ask you all to stop the thread for a 24 hour cooling off period. I am reluctant to ask this----because it is an interesting thread. It brings up among other things a degree of SEMANTIC conflict. Physics has some terms that are defined differently by different people, depending on context. Like time. Even energy. even mass can have different definitions although there may be one that is more prevalent. So this thread brings up a lot of interesting concepts and challenges people to get straight on them. But just as a matter of courtesy, to restore calm, I'm asking everybody to lay off for a kind of voluntary cease-fire until same time tomorrow.
ydoaPs Posted October 20, 2007 Posted October 20, 2007 Your definition of heat is a definition of enthalpy, no? No Sorry about your head, but Boltzmann's law (of entropy) tells us that ordered states (tend to) degenerate into disordered ones (in a closed system). Yes, entropy TENDS to increase. "Tends" is a big word here. Unavailable energy?Energy that's not available for work. Like waste heat from friction in a bearing. Mate, sounds like you do need some more sleep...Here's mine: Heat energy is the result of, or is caused by, "kinetic" -(translational,rotational, vibrational) motion, and the emission and absorption of infrared radiation. Do you know what the average molecular kinetic energy of a substance is? I'll give you a hint. It starts with a "T" and ends with "emperature" Heat disperses, or diffuses, in a kinetic way (but the “transfer” is not governed solely by motion or vibration, as EMR is involved) what emerges from heat is motion (of molecules).What do you think causes the IR radiation? edit: Well this thread has gotten somewhat heated and out of controlso I would like to ask you all to stop the thread for a 24 hour cooling off period. This post wasn't visible when I made this post. Will do.
Martin Posted October 20, 2007 Posted October 20, 2007 Fine. I am double-posting this to make sure it is visible as a temporary end-marker Well this thread has gotten somewhat heated and out of controlso I would like to ask you all to stop the thread for a 24 hour cooling off period. I am reluctant to ask this----because it is an interesting thread. It brings up among other things a degree of SEMANTIC conflict. Physics has some terms that are defined differently by different people, depending on context. Like time. Even energy. even mass can have different definitions although there may be one that is more prevalent. So this thread brings up a lot of interesting concepts and challenges people to get straight on them. But just as a matter of courtesy, to restore calm, I'm asking everybody to lay off for a kind of voluntary cease-fire until same time tomorrow.
Fred56 Posted October 20, 2007 Author Posted October 20, 2007 Comment: I have posted something relevant to this discussion in pseudoscience:"it's all connected" q.v. I think part of the difficulty is I need to look through the same goggles yourdad is wearing. I've used a thermometer, I know temperature is "out there"...!? Heat and entropy are related, but not the same. The way you worded the post implied that they are the same. I don't think that's what I did at all... surely a reference frame isn't a necessary condition for conservation of mass? I certainly hope it isn't... What do you think causes the IR radiation? Well, I know that a molecule can vibrate hard enough to cause one of its electrons to emit a photon of infrared; electrons can absorb a photon and the molecule will vibrate more...but which one is the quantum chicken? Which the egg? Is the egg across the road and the chicken has to get to it? Stay tuned folks...
Martin Posted October 20, 2007 Posted October 20, 2007 Thanks to everybody for cooperating---with courtesy and self-restraint. The thread will wake up in just about 12 hours from now. I have a bit of trouble with timezones sometimes so I'll be explicit. I asked for a 24 hour cooling off period at around 8PM pacific daylight (PDT) which is GMT-7. So that must be 3AM GMT. That would correspond to 11 PM on the east coast of US. For Fred, who initiated the thread, it is 4PM in the afternoon (Kiwi daylight time). Please correct me if I've made a mistake in the damned arithmetic. This is a good thread IMHO with a bunch of interesting concepts, which however don't always have a single right definition. To get it sorted out maybe people can give links to sites like Wikipedia and Answers.com and quote from definite linked sources to make clear what definition they propose to follow. (If that turns out to be an issue.) If anybody thinks a cooling off period was not a good idea at this point---or that it should have been 12 hours instead of 24---or anything like that, please send me a PM about it. Looking forward to discussion resuming. Well this thread has gotten somewhat heated and out of controlso I would like to ask you all to stop the thread for a 24 hour cooling off period. I am reluctant to ask this----because it is an interesting thread. It brings up among other things a degree of SEMANTIC conflict. Physics has some terms that are defined differently by different people, depending on context. Like time. Even energy. even mass can have different definitions although there may be one that is more prevalent. So this thread brings up a lot of interesting concepts and challenges people to get straight on them. But just as a matter of courtesy, to restore calm, I'm asking everybody to lay off for a kind of voluntary cease-fire until same time tomorrow.
vincent Posted October 20, 2007 Posted October 20, 2007 Hi Martin, You didn't respond to my earlier post: A lot of people do not seem to know that E = mc2 is not a general truth. It does not hold for photons, for example. Because they are not at rest. For the equation to hold the observer frame would have to be one where the photon was at rest, which doesnt happen. What I pointed out there was that contrary to your above remark, there is nothing about the existence of massless particles that implies that the applicability of the mass-energy equivalence is somehow not universal. In fact, it is in terms of the mass-energy equivalence that we understand why there are processes in quantum electrodynamics in which photon energy is converted into electron and positron mass and vice versa! I'm just curious why you would believe that the mass-energy equivalence, which is perhaps the world's most famous equation, doesn't apply to massless particles?
YT2095 Posted October 20, 2007 Posted October 20, 2007 I dunno, I could be wrong but I`m fairly sure it`s stated somewhere (perhaps even by Martin himself) that although the particle itself is massless, it`s Momentum velocity or whatever it`s called is Not without "Mass" per se. and that`s why E=MC^2 works both ways. and when you think about it if a photon Had mass, the equation wouldn`t be what it is would it it would be M=M^regardless
swansont Posted October 20, 2007 Posted October 20, 2007 Hi Martin, You didn't respond to my earlier post: What I pointed out there was that contrary to your above remark, there is nothing about the existence of massless particles that implies that the applicability of the mass-energy equivalence is somehow not universal. In fact, it is in terms of the mass-energy equivalence that we understand why there are processes in quantum electrodynamics in which photon energy is converted into electron and positron mass and vice versa! I'm just curious why you would believe that the mass-energy equivalence, which is perhaps the world's most famous equation, doesn't apply to massless particles? I think the problem here, as happens quite often, is that the mass term has not been defined. Relativistic mass and rest mass cannot be interchanged freely. Also, I think that a similar problem exists with regards to the OP. Nobody has defined information (or if they did I missed it) so any argument about it is going to be muddled. However, here's a thought experiment. We know we can transmit digital information with photons. I send a signal: 10011111. You reply: 11000001. Did my data contain more information? It used more energy, since I needed more photons. How much mass or energy did the nonexistent photons (i.e. the zeroes) have?
ydoaPs Posted October 20, 2007 Posted October 20, 2007 Hi Martin, You didn't respond to my earlier post: What I pointed out there was that contrary to your above remark, there is nothing about the existence of massless particles that implies that the applicability of the mass-energy equivalence is somehow not universal. In fact, it is in terms of the mass-energy equivalence that we understand why there are processes in quantum electrodynamics in which photon energy is converted into electron and positron mass and vice versa! I'm just curious why you would believe that the mass-energy equivalence, which is perhaps the world's most famous equation, doesn't apply to massless particles? I think he did say why it didn't apply. A lot of people do not seem to know that E = mc2 is not a general truth. It does not hold for photons, for example. Because they are not at rest. For the equation to hold the observer frame would have to be one where the photon was at rest, which doesnt happen. The emphasis is obviously mine. I had explained further. Actually, it does. The version he quoted assumes a reference frame in which the massless particle is at rest. Massless particles travel at c. Mass and energy aren't exactly the same thing. As I said above, E=mc2 is assuming a reference frame in which the particle at rest. E2=m2c4+p2c2 is the equation where the particle in question is not at rest relative to you. And guess what! Photons have momentum! What I'm assuming Martin did was quote E=mc2 because it is the popularized version and because it seems that this is the equation that would imply that photons had mass. Let's use the full equation, plug in the the momentum value, and not assume m=0. [math]\rho=\frac{h}{\lambda}[/math] [math]E=h\nu[/math] [math]c={\nu}{\lambda}[/math] [math]E^2=(mc^2)^2+({\rho}c)^2[/math] [math]E^2=(mc^2)^2+({\frac{h}{\lambda}}c)^2[/math] [math]E^2=(mc^2)^2+({\frac{h}{\lambda}}\nu\lambda)^2[/math] [math]E^2=(mc^2)^2+(h\nu)^2[/math] [math]E^2=(mc^2)^2+E^2[/math] [math](mc^2)^2=0[/math] m=0 Since photons always travel at c, m will always be zero. This means E=mc2=0 which isn't true, as we've seen above the energy of a photon is given by [math]E=h\nu[/math]. Thus, E=mc2 clearly does, in fact, NOT apply to photons.
Martin Posted October 20, 2007 Posted October 20, 2007 Next time I'll ask for a ceasefire of only TWELVE hours instead of 24 Thanks to everybody for restarting the discussion on a good issues-oriented plane. Looking good.
vincent Posted October 20, 2007 Posted October 20, 2007 What I'm assuming Martin did was quote E=mc2 because it is the popularized version and because it seems that this is the equation that would imply that photons had mass. Let's use the full equation, plug in the the momentum value, and not assume m=0.[math]\rho=\frac{h}{\lambda}[/math] [math]E=h\nu[/math] [math]c={\nu}{\lambda}[/math] [math]E^2=(mc^2)^2+({\rho}c)^2[/math] [math]E^2=(mc^2)^2+({\frac{h}{\lambda}}c)^2[/math] [math]E^2=(mc^2)^2+({\frac{h}{\lambda}}\nu\lambda)^2[/math] [math]E^2=(mc^2)^2+(h\nu)^2[/math] [math]E^2=(mc^2)^2+E^2[/math] [math](mc^2)^2=0[/math] m=0 Since photons always travel at c, m will always be zero. This means E=mc2=0 which isn't true, as we've seen above the energy of a photon is given by [math]E=h\nu[/math]. Thus, E=mc2 clearly does, in fact, NOT apply to photons. The above is really a result of a basic misunderstanding of the mass-energy equivalence you and martin seem to share. The mass-energy equivalence is not meant to apply in this way to individual elementary particles. Rather, it is a statement about the general interconvertability between mass and energy. The kind of statement the mass-energy equivalence does make about photons, again in the context of quantum electrodynamics, is that it’s energy can be converted to invariant-mass of electrically charged particles like the electron and vice versa. For further clarification, if you need any, you can consult any introductory text on the subject of special relativity. Whichever text you might choose, I am quite confident that you will find nowhere in it any statements along the lines of what you and martin are saying. Respectfully, Vince.
swansont Posted October 20, 2007 Posted October 20, 2007 The above is really a result of a basic misunderstanding of the mass-energy equivalence you and martin seem to share. The mass-energy equivalence is not meant to apply in this way to individual elementary particles. Rather, it is a statement about the general interconvertability between mass and energy. The kind of statement the mass-energy equivalence does make about photons, again in the context of quantum electrodynamics, is that it’s energy can be converted to invariant-mass of electrically charged particles like the electron and vice versa. For further clarification, if you need any, you can consult any introductory text on the subject of special relativity. Whichever text you might choose, I am quite confident that you will find nowhere in it any statements along the lines of what you and martin are saying. Respectfully, Vince. Again I'll point out the problem of not defining which mass to which one is referring, and the separate questions of whether photons have mass or can be converted into particles that have mass (referring, of course, to rest mass). Both Martin and yourdad seem to have responded to a statement in which E=mc2 was misused. You seem to be missing that context (as well as the context of their >3000 posts, each, which if you had read them, you might discover that they do understand this)
Martin Posted October 20, 2007 Posted October 20, 2007 Both Martin and yourdad seem to have responded to a statement in which E=mc2 was misused. Implicitly misapplied. Exactly. Swansont thanks for making that point. Fred seemed to me to be arguing that a photon, carrying a bit of information, would have energy and therefore would have mass. This goes back to post #1 and #2 It's probably something we don't think about, but photons have energy. Information, ultimately, is also energy, or uses it to "carry" a message.. My post was just meant to remind folks that just because a photon carries energy it does not necessarily have mass. The familiar equivalence relation does not apply to that case. I think this dispute has been blown out of proportion---I just wanted to remind Fred not to simply apply E=mc2 to a photon and conclude that the photon had mass. I would suggest that any hostile posts concerning this rather trivial point be moved to wherever quibbles go, and that we let Fred's thread proceed unobstructed. ================ EDIT I set up a Quibbles thread in General Physics, to serve the whole physics department as a catch basket for quibbles when they get obstructive. http://www.scienceforums.net/forum/showthread.php?t=29120
Fred56 Posted October 20, 2007 Author Posted October 20, 2007 just because a photon carries energy it does not necessarily have mass. The familiar equivalence relation does not apply to that case. Where does it get momentum from then? Apart from energy a photon also carries momentum and has a polarization. It follows the laws of quantum mechanics, which means that often these properties do not have a well-defined value for a given photon. Rather, they are defined as a probability to measure a certain polarization, position, or momentum. For example, although a photon can excite a single molecule, it is often impossible to predict beforehand which molecule will be excited. -Wikipedia
Martin Posted October 20, 2007 Posted October 20, 2007 Where does it get momentum from then? Excellent question! Glad you rejoined the thread. It is a doozy. We've been having a good time. Look at the Wikipedia article on momentum. Section 4 MODERN definitions of momentum http://en.wikipedia.org/wiki/Momentum Section 4.1 has what momentum is in the case of massless particles like photons. It's good not to think of momentum as necessarily a measure of inertia x velocity. You can think of it as a fundamental conserved quantity. For light the definition is E/c. There is a nice calculation where you calcuate the pressure on a mirror or a solar sail. The amount of momentum hitting the sail and being reflected back is proportional to the POWER or wattage of the light DIVIDED BY C. So you can calculate the force on a square meter mirror just knowing the "solar constant"---the wattage of sunlight. Momentum as energy divided by c is just something to get used to by working a few problems. The Wikipedia definition is just what is needed to make the conservation law work.
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