How big is a photon and what does it look and behave like?

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  • #151
ZapperZ
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Dense said:
Thanks for the clarification.
So it's not even "a photon has no size," but rather "size isn't something that pertains to photons." Is that the distinction?

Yes, because it was never defined with that characteristics, and STILL today doesn't have a clear definition of that characteristics.

Zz.
 
  • #152
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ZapperZ said:
I'll show you why EVEN the use the the term "relavistic mass" isn't kosher!

Sure I know there are different sides to this issue. I read the article mentioned "On the abuse and use of relativistic mass" by Gary Oas http://arxiv.org/abs/physics/0504110. I don't agree with the author. He can barely think of any reasons why relativistic mass is used. I can think of many. He even moans in the article that "those works directed at the general public still, overwhelmingly utilize this concept (relativistic mass). Maybe that's because using terms such as relativistic mass or velocity mass makes sense to people? I side with textbook author T. R. Sandin who is an ardent promoter of the use of relativistic mass in educational texts.

A similar argument is still being fought by engineers about the use of the word energy. The engineers don't want anyone to use words like helmholtz energy and some don't even want people to use commonly accepted words such as chemical energy, kinetic energy, and potential energy. They want to reserve use of the word energy for the concept of total energy only. The English language only has so many words possible, how about changing chemical energy to clqycv? Few people would know the concepts of energy and clqycv were related.
 
  • #153
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Ben Wiens said:
Sure I know there are different sides to this issue. I read the article mentioned "On the abuse and use of relativistic mass" by Gary Oas http://arxiv.org/abs/physics/0504110. I don't agree with the author. He can barely think of any reasons why relativistic mass is used. I can think of many. He even moans in the article that "those works directed at the general public still, overwhelmingly utilize this concept (relativistic mass). Maybe that's because using terms such as relativistic mass or velocity mass makes sense to people? I side with textbook author T. R. Sandin who is an ardent promoter of the use of relativistic mass in educational texts.

But again, you're missing my point. You were CONVINCED that it is alright to proclaim about the so-called relativistic mass for photons. I pointed out that there are many that can argue with you that such things are nothing more than semantics. When it comes right down to it, what matters for photons is that there is no such thing as a rest mass. Period! There has been no useful purpose (can you show me what physics research or area that would use this?) otherwise. The play on semantics belongs in philosophy.

A similar argument is still being fought by engineers about the use of the word energy. The engineers don't want anyone to use words like helmholtz energy and some don't even want people to use commonly accepted words such as chemical energy, kinetic energy, and potential energy. They want to reserve use of the word energy for the concept of total energy only. The English language only has so many words possible, how about changing chemical energy to clqycv? Few people would know the concepts of energy and clqycv were related.

Sorry, but I don't buy this analogy. And I've never met an enginner who would be adament to want such a thing. In thermodynamics, there is a CLEAR difference between Helmholtz energy, Gibbs energy, Enthalpy, and Internal energy. Look at the Maxwell Relations for thermodynamics and which state function is appropriate to what. And confusing and ignoring the difference between KE and PE is fatal when one tries to write down the Hamiltonian. That would be a huge blunder!

Zz.
 
  • #154
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How about the confusion about mass on this forum?

ZapperZ said:
I pointed out that there are many that can argue with you that such things are nothing more than semantics. When it comes right down to it, what matters for photons is that there is no such thing as a rest mass. Period! There has been no useful purpose (can you show me what physics research or area that would use this?) otherwise.

Who cares what it is, semantics, or whatever. It's an issue in physics. Sure, I can show you why there is a use for relativistic mass. How about the confusion among even people on this forum about the matter? The question about the photon's mass comes up again and again and again. That's because it just doesn't make sense to people that the photon would not have mass when it has energy. It doesn't make sense to people that we are told we are attracted to the earth because we have mass, but the photon isn't attracted to the earth's gravity field because of it's mass, it is because it has energy.
 
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  • #155
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ZapperZ said:
And I've never met an engineer who would be adamant to want such a thing. In thermodynamics, there is a CLEAR difference between Helmholtz energy, Gibbs energy, Enthalpy, and Internal energy.

Check out textbooks like Engineering Thermodynamics by Glen E. Myers. No Gibbs energy. It's Gibbs function. No Helmholtz energy. This concept belongs to the term Availability. Note that no energy was harmed in the making of these terms.
 
  • #156
ZapperZ said:
But it doesn't bother you that the book IS required in the class and the students don't have it? I would have asked "Why DON'T you have a book? Wasn't it listed as required to be in this class"?
The problem here is that you'd rather be told in having-waving forms to the answers you want, rather than specific technical details. I've been trying to ween people off this and make people want MORE details. Hand-waving arguments should no longer be tolerated as being the definitive answer, it is too ambiguous. Yet, look at this thread and see how "satisfied" some people are with such things. I can find unbelievable amount of loopholes in those explanations.
I have taught college level courses before. I have to assume that the students entering my class already POSSESS a certain level of knowledge. If not, I will NEVER be able to tackle the subject matter because I always have to backtrack and answer questions that they should have known already! This is what I had to do with you in this thread. It appears that almost at every turn, we are going back into the fundamentals of not only SR, but QM! At some point, such an exercise is no longer productive and gets nowhere fast. If you want to know about QM and SR's fundamentals, ask THOSE! But if you start asking about a higher-level question that makes use of those foundations, then do not be surprised if someone tells you to go look up those foundations yourself!
And talk about missing points. You missed MY question on where I asserted something to be 100% true. Where did I make such a statement? Or can you not back up things that you say?
Zz.

Don't get me wrong I apreciate the time you've spent explaining this stuff alot. And have been happy with many of the answers. I think you assumed I didn't know about fundementals I did as with the slit thing. perhaps I didn't explain what I meant when I said slits, but I did already understand about interference and waves, I was trying to make a point, I failed. If you have a book that I can't reference then a website with the same info would be useful, I don't mind having references but not all your source material is going to be available to everyone imediately so having something else I can get a general idea from would be useful. And I thought I explained that about 100%, I said the way you present things seem to give people an idea that there's no room to maneuover. That's just your style I expect but it can come across as confrontational. It's interesting that Einstein came up with a ball theory as well to try and disprove quantam mechanics. Not that I believe any of that for a second it was as I said total specualtion, but I'm glad I'm thinking along the same lines as other people as I learn.
Thanks for the info.

If nothing else you now have a thread which has answers to all the FAQ about light in one convenient thread. That has reference to several other threads which ask the same questions. Next time at least you only have to cut and paste one link, I'm sure that's gonna be helpful to you:smile:

It should make you happy then when people think of the same loopholes in theories as you no doubt did whilst learning them.
 
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  • #157
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Ben Wiens said:
Who cares what it is, semantics, or whatever. It's an issue in physics. Sure, I can show you why there is a use for relativistic mass. How about the confusion among even people on this forum about the matter? The question about the photon's mass comes up again and again and again. That's because it just doesn't make sense to people that the photon would not have mass when it has energy. It doesn't make sense to people that we are told we are attracted to the earth because we have mass, but the photon isn't attracted to the earth's gravity field because of it's mass, it is because it has energy.

Excuse me, but SINCE WHEN should everything make sense, especially to people who are ignorant on physics? Your "sense" isn't static. A hot kettle doesn't make sense to a 4 year old even when you tell him or her not to touch it. You LEARN why you shouldn't touch it. What you claim to "make sense" is simply based on an ACQUIRED COLLECTION OF KNOWLEDGE! Think about it! There are tons of stuff that didn't make sense to you before, and only make sense to you now AFTER you learn such a thing.

So why would it be any different than the photon? Most people do NOT learn the intricate physics of QM and QED, so OF COURSE it made little sense. But this have NOTHING to do with the idea that the description is faulty JUST becuase it didn't make sense to you!

It is THIS point of argument that you have brought up that doesn't make any sense!

Zz.
 
  • #158
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Ben Wiens said:
Check out textbooks like Engineering Thermodynamics by Glen E. Myers. No Gibbs energy. It's Gibbs function. No Helmholtz energy. This concept belongs to the term Availability. Note that no energy was harmed in the making of these terms.

And check out Reif's Thermodynamics text. There is a REASON why we give them these names, the same reason why we call something a "Hamiltonian", while another the "Lagrangian". This is like you arguing there's no such thing as Lagrangian/Hamiltonian mechanics just because they're not in a typical engineering mechanics text.

Does the world revolves only around what you know and what "makes sense" to you? Because if that is how you judge the validity of everything, this "discussion" is pointless.

Zz.
 
  • #159
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ZapperZ said:
There are tons of stuff that didn't make sense to you before, and only make sense to you now AFTER you learn such a thing.

Anyone who has taught a introductory physics class knows that to most people coming into the class, Newton's Laws of Motion don't "make sense". Practically everybody knows that objects set into motion come to a stop by themselves, and Newton's First Law doesn't make sense to them until they work with gliders on air tracks or air tables, study motion in free fall in outer space, etc.
 
  • #160
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ZapperZ said:
And check out Reif's Thermodynamics text. There is a REASON why we give them these names, the same reason why we call something a "Hamiltonian", while another the "Lagrangian". This is like you arguing there's no such thing as Lagrangian/Hamiltonian mechanics just because they're not in a typical engineering mechanics text. Does the world revolves only around what you know and what "makes sense" to you? Because if that is how you judge the validity of everything, this "discussion" is pointless.
Zz.

I have no idea what you are arguing about. Are you arguing in favor of using plural energy names or in favor of using energy only as a concept of total energy? Please state your arguments in an understandable way.
 
  • #161
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Ben Wiens said:
I have no idea what you are arguing about. Are you arguing in favor of using plural energy names or in favor of using energy only as a concept of total energy? Please state your arguments in an understandable way.

No, I'm in favor of YOU stopping this nonsense. Go look in Reif text and tell me if there is NO PRACTICAL USE of the various "categories" of the thermodynamical state functions.

You have continued to ignore WELL-ESTABLISHED physics. Have it ever crossed your mind that before you attack something, that you should at least understand what it is first? If all we care about is the "total energy" (whatever that is), then tell me why is the Lagrangian/Hamiltonian mechanics such a powerful tool? If "Helmholtz energy" is so useless, then why don't you NOT use it to tell me if you can find the energy state of a magnetic spin system? Do you even know or care what the Maxwell relations are and why it is such an important part in studying thermodynamics?

These are the points you continue to ignore...

Zz.
 
  • #162
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ZapperZ said:
No, I'm in favor of YOU stopping this nonsense. If "Helmholtz energy" is so useless, then why don't you NOT use it to tell me if you can find the energy state of a magnetic spin system?

I can see it's pointless to discuss issues with you Zapper. I'm in favor of using the term Helmholtz energy and you say I'm not in favor of it. Where did you pull this out of? Obviously when I say things in plain English you read it the reverse, and then twist the argument around.
 
  • #163
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Ben Wiens said:
I can see it's pointless to discuss issues with you Zapper. I'm in favor of using the term Helmholtz energy and you say I'm not in favor of it. Where did you pull this out of? Obviously when I say things in plain English you read it the reverse, and then twist the argument around.

Fine, let's do a review again, shall we?

Ben Wiens said:
A similar argument is still being fought by engineers about the use of the word energy. The engineers don't want anyone to use words like helmholtz energy and some don't even want people to use commonly accepted words such as chemical energy, kinetic energy, and potential energy. They want to reserve use of the word energy for the concept of total energy only. The English language only has so many words possible, how about changing chemical energy to clqycv? Few people would know the concepts of energy and clqycv were related.

Now, when I replied:

ZapperZ said:
Sorry, but I don't buy this analogy. And I've never met an enginner who would be adament to want such a thing. In thermodynamics, there is a CLEAR difference between Helmholtz energy, Gibbs energy, Enthalpy, and Internal energy. Look at the Maxwell Relations for thermodynamics and which state function is appropriate to what. And confusing and ignoring the difference between KE and PE is fatal when one tries to write down the Hamiltonian. That would be a huge blunder!

Notice what is going on here. You were using this various forms of energy and using THIS to support your argument that a similar debate about "relativistic mass"! It is WHY I said I did not buy this analogy. There is a CLEAR USE of Enthalpy, Gibbs, Helmholtz and Internal energy based simply on the state functions each of them represents! This is NOT the same as the idea of "relativistic mass", and there certainly is NO SUCH ARGUMENTS as far as the mass of a photon is concerned, which is what brought all of this up!

Now, is that clear enough for you?

But then you carried this even further!

Ben Wiens said:
Check out textbooks like Engineering Thermodynamics by Glen E. Myers. No Gibbs energy. It's Gibbs function. No Helmholtz energy. This concept belongs to the term Availability. Note that no energy was harmed in the making of these terms.

That would be a VERY strange thing to use if you are actually ".... in favor of using the term Helmholtz energy." And you waited until NOW to explicitly say that when it has been clear all along that I consider the original analogy to be wrong? Then why continue to bring it up when I have shown that such an analogy doesn't work? I clearly stated in response to this quote for you to check out an engineering mechanics textbook and see that there is also no mention of Hamiltonian and Lagrangian. Only of you're ignorant of physics would what I said here meant nothing to you. Yet, these two terms are two of the MOST important concepts in physics.

You are repeating the same fallacy. If it doesn't make sense to you, then it can't be right. And if, what, it doesn't appear in an engineering text, then it is of no use? How could you even say something like that with a straight face?

Zz.
 
  • #164
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Physics is all about intimidation?

reilly said:
Your conditionals are way off -- physics is all about challenging theories; that's what professional physicists do. But, do note that sometimes challenges are met with hostile reactions, and the challenge become very contentious. So, at time, physics is a contact sport. And, surprise, many professional physicists are arrogant -- I know more than you do kind of stuff -- so they tend to ignore beginners, with whom they are not kindly disposed to discuss basics. In a sense , it's little different than say, that the chances of the CFO of GM helping a low-level employee to answer an accounting question are slim to none.(Important people, are important, as many of them know.) If you have the misfortune to make a mistake or two in your challenge, then you may be in for a very tough, antagonistic fight, in which personal attacks may well figure. The unwritten rule is: DO YOUR HOMEWORK. Know as much, if not more, about the subject than those challenging your ideas. https://www.physicsforums.com/showpost.php?p=885150

I'll quote from a book I looked through in my recent search for information at the university library, Collective Electrodynamics, by Carver Mead page xvii. "In those days Physics was an openly combative subject-the one who blinked first lost the argument. Bohr had won his debate with Einstein this way, and the entire field had adopted the style. Feyman learned the game well-he never blinked. For this reason he would never tell anyone when he was working on something, but instead would spring it, preferably in front of an audience, after he had it all worked out. If Feyman was stuck about something, he had a wonderful way of throwing up a smokescreen; we used to call it proof by intimidation".

Perhaps physics is about combat. It's all about winning. But I don't think accurate theories necessarily develop this way. It becomes who the more forceful personality is, who has connections, grants, money etc. But in this Physics Forum, combat it's what I would call fair play. It's sort of like an ordinary person having an argument with the government. Of course the government usually wins. The government has more power. On this forum, if us ordinary members introduce things that a mentor doesn't agree with, we can get banned. The mentors also should have more experience in the subject matter than those asking the questions. But that doesn't make them always right, or that there can't be different opinions. I guess what you are saying is that a student should never have a discussion with their teacher till they study on their own and know more than the teacher? So in the case of Physics Forum, to be safe, we should not get involved in discussions till we are top physics professors at some university?
 
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  • #165
ZapperZ
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Ben Wiens said:
Perhaps physics is about combat. It's all about winning. But I don't think accurate theories necessarily develop this way. It becomes who the more forceful personality is, who has connections, grants, money etc. But in this Physics Forum, combat it's what I would call fair play. It's sort of like an ordinary person having an argument with the government. Of course the government usually wins. The government has more power. On this forum, we argue out of line, we get banned. The mentors also should have more experience in the subject matter than those asking the questions. But that doesn't make them always right, or that there can't be different opinions. I guess what you are saying is that a student should never have a discussion with their teacher till they study on their own and know more than the teacher? So in the case of Physics Forum, to be safe, we should not get involved in discussions till we are top physics professors at some university?

Can we get one thing CLEAR here? You are NEVER banned just because you disagree with a Mentor! That NEVER HAPPENS! Let's make sure we get ONE thing straight out of this convoluted thread! If what you said is true, then why are you still here even though you disagreed with me all along?

You will,however, be banned (or at least pushed to the IR forum) if you start spewing some personal theory that falls under crackpottery! You will start to become annoying if you simply refuse to look up references that were given that can clearly contradict what you are saying. And if you look at what I have said, dispite my annoyance with your post, I NEVER just say "oh, you're full of crap" and that's that! I TELL you why what you brought up was wrong, and even try to give you a reference or two for you to check for yourself that I'm not making this up as I go along! I do NOT expect you to buy wholesale everything I said without doing your own background research!! You are WAY more than welcome (in fact, I expect you to) to look up for yourself what are "lagrangians and hamiltonians".

However, YOU yourself need to be aware that some of the people you are talking to actually WORK in this field. So when someone comes in with very little background knowledge and then start professing stuff that would clearly be wrong if one just do a little bit of work, then what do you expect in return? Applause??! Try doing that in ANY part of life, not just in physics, and see the kind of reaction you get. It has nothing to do with physics. It has everything to do with showing a little bit of respect to the subject area that you are trying to comment on or analyze. You cannot do something out of ignorance - it shows utter disrespect for that subject matter and to the people who spent countless years accumulating the knowledge that you have benefited from.

Zz.
 
  • #166
reilly
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Ben Wiens said:
I'll quote from a book I looked through in my recent search for information at the university library, Collective Electrodynamics, by Carver Mead page xvii. "In those days Physics was an openly combative subject-the one who blinked first lost the argument. Bohr had won his debate with Einstein this way, and the entire field had adopted the style. Feyman learned the game well-he never blinked. For this reason he would never tell anyone when he was working on something, but instead would spring it, preferably in front of an audience, after he had it all worked out. If Feyman was stuck about something, he had a wonderful way of throwing up a smokescreen; we used to call it proof by intimidation".
.................................................................



Perhaps physics is about combat. It's all about winning. But I don't think accurate theories necessarily develop this way. It becomes who the more forceful personality is, who has connections, grants, money etc. But in this Physics Forum, combat it's what I would call fair play. It's sort of like an ordinary person having an argument with the government. Of course the government usually wins. The government has more power. On this forum, if us ordinary members introduce things that a mentor doesn't agree with, we can get banned. The mentors also should have more experience in the subject matter than those asking the questions. But that doesn't make them always right, or that there can't be different opinions. I guess what you are saying is that a student should never have a discussion with their teacher till they study on their own and know more than the teacher? So in the case of Physics Forum, to be safe, we should not get involved in discussions till we are top physics professors at some university?

...........................................
Before Feynman became FEYNMAN he paid a lot of dues. He was in charge of computation -- huge numbers of women with adding machine -- for the Manhattan Project-- down and dirty for several years. It took a while for his approach to QED to be accepted. That it was had nothing to do with Feynman's personality or connections; simply put, he was right.


My strong sense is that physics has been a contact sport for several thousand years -- physics is just a version of J.S.Mills Marketplace of Ideas. Unlike in most other fields, personality, power and reputation will always carry the day only when the work is right, well almost always -- Starwars is an exception -- this program stems from Teller's ability to BS Reagan about giant killer lasers, and who know what else. -- Certainly in academic physics, BS will seldom get you very far. And this assertion is a matter of record for at least several hundred years. Over the long haul, physics is tough, but fair.

Yes, it's about winning -- winning means understandanding nature better, developing new mathematical and experimental tools, finding better ways of teaching. You got a better way? (What we've got now has worked for a few hundred years, and nicely at that.)

Regards,
Reilly Atkinson

A long, long time ago, my wife and I were dissatisfied with our kid's grade school. (At the time I was young physics professor, and, thus was, of course, an expert on education.) We talked at length with the Superintendent of Schools. He clearly heard and understood our concerns; even said he agreed with a few.

Then he gave us some of the best advice I've ever heard: " Our Schools aren't perfect. We know that, and you University folks know that as well. If we're going to make any progress together, you'll have to honor our folkways -- don't tell us what to do. Talk to us in our own language, and ask lots of questions." Over the years, we became strong allies.

Sure, it's, "When in Rome... " But a rose by anyother name ....

Physics is not without folkways.
 
  • #167
gvk
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Ben Wiens,
You gave the question about photon size and it seems did not satisfy with an answer you got.
And you did not satisfy with others answers given by mentors.
Let's come back a bit starting with your original. Why do not find the answers youself?
As Descartes said, the complex question should be split to the several simple questions in order to be resolved. Now we call this baby steps.
What do you think about the following, in some sense less difficult, but more constructive, questions:
1. What does mean 'to measure the size' in SR and in QM?
2. Can we measure 'anything' in Nature without direct or indirect implementation of the electromagnetic field?
3. What is the 'size of the electron' and how to calculate it in SR and in QM?
4. How to measure the electron 'size' and what would be the results?
5. Why are we not asking about the geometrical size of plane electromagnetic field in the 'classical' physics (SR)?
6. How is the notion of the 'classical' electromagnetic field transformed to the notion of 'the wave function' of electromagnetic field in quantum theory? In other words, how is the photon appeared in quantum theory?
7. Is that any difference in the interpretation of 'the wave function' of an electron and 'the wave function' of a photon in QED? If so why is it?

If you find the answers yourself digging the books, solving the problems, etc., you will feel more comfortable with the answer you receive from ZapperZ and others to your question 'How big is a photon?'
If you don't, I am sorry to say, but the advice 'go and study QED' should be extended to SR and QM. Nobody can help you with that.
It's difficult, but there is no other way if you want to understand modern physics.
Sincerely
 
  • #168
We like to keep photons as mystical things and describe them like water waves or marbles. Can we not do better than this? Personally I think we have to get rid of this concept of duality. Photons don't behave like large objects and so we should not think of them as this. Is duality not an old worn out concept that should be discarded?

I've said my thing, but what do you think?

One thing that we do know about photons is that they are most definitely particles. Devices used to detect them register less frequent clicks as light grows dimmer instead of softer clicks. So they are definitely particles...sort of. They still have a probability waveform. Considering that matter itself has a wave-like duality, (matter's wave properties can be made cohesive, like light can with a laser) it is pretty much something we learn to live with.


Just look at my other posts first though to see how much less I know than anyone else about light, lol.

The dual slit experiment, for example, can be done with light, electrons or buckyballs (complex carbon molecules, so definitely larger than electrons)...so the particle/wave duality extends far past light, into matter, and even to some molecules.

The trouble with what light looks like is exactly what was said earlier, we use light to see, and everything we see is light. No, really...EVERYTHING. The "smallest" thing we have to look at anything is the photon, and we can't accurately see anything about photons by "bouncing them off each other". So there is no real way to take a picture of a photon, because we have to use something smaller than the photon to probe it, and we don't have anything with greater resolution. (This explanation was in a lay book and was a few decades old, this might have changed, but I don't think it has).

You mentioned the models of atoms etc earlier. One thing that caught me off gaurd was learning that the "Solar system" model of an atom is just that...it's just a model. More like a caricatured cartoon. It certainly does not represent any appearance of the Atom, but it does organize some properties of the atom in a symbolic, visual way...such as how many electrons are available for bonds and other chemical reactions with other atoms and molecules. Our "picture" of the atom is more defined than that of a photon, however the picture we have of atoms is not necessarily what the atom "looks" like. As we get smaller, things get less certain, and apparently the math just stops giving answers. (which I hate)
 
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  • #169


If Feyman was stuck about something, he had a wonderful way of throwing up a smokescreen; we used to call it proof by intimidation".


Yes, it is very intimidating when your theory brings calculated results from first principles in agreement with observed values to a hair's width compared to the distance from New York to Los Angeles.


Sometimes being that right, is reeeeeeellly intimidating. Especially if you can't do the same.
 
  • #170
jtbell
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Look at the dates on the posts that you responded to.
 
  • #171
berkeman
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Look at the dates on the posts that you responded to.

Actually a newbie did the first necropost today, which I deleted because his response had scientific errors in it. So it's not totally JJR's fault for necroposting -- he probably saw a Today date on the last post in the thread when he clicked on it...
 

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