# Three photon questions **URL:** \ **Category:** Factual Questions\ **Created:** [April 15, 2002, 10:13pm UTC](https://boards.straightdope.com/t/three-photon-questions/103830 "2002-04-15T22:13:58Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![Fern\_Forest](https://avatars.discourse-cdn.com/v4/letter/f/71c47a/32.png) [@Fern\_Forest](https://boards.straightdope.com/u/Fern_Forest)\ **Post date:** [April 16, 2002, 12:43pm UTC](https://boards.straightdope.com/t/three-photon-questions/103830/21 "2002-04-16T12:43:49Z")
> [@](#): > > \*Originally posted by Mangetout \* > **Shadows can travel faster than light, but the problem is that they don’t really exist; they are just the lack of photons, but not the lack of _the same_ photons at any two moments.** Are you sure about that? I can’t see it. Rather I would say that a shadow can apparantly move up to the speed of light but not faster. Let’s say my hand is making a shadow on top of sheer 100 meter cliff with the sun directly ahead. Then I quickly move my hand out over edge. My hand will only block the the photons that come after so photons will continue to hit the ground where my shadow will be after my hand has moved out there. The shadow you can think of as an negative space under my hands moving downards at the speed of light. So a shadow can move slower then its originating object. But if it’s faster it has a natural upper limit (the speed of light) beyond which it cannot move. Hmmm, Clicking of Libertarian’s link I see that they concur. Ok I used that word to sound smart. They agree. ---
**Author:** ![scm1001](https://avatars.discourse-cdn.com/v4/letter/s/c4cdca/32.png) [@scm1001](https://boards.straightdope.com/u/scm1001)\ **Post date:** [April 16, 2002, 12:48pm UTC](https://boards.straightdope.com/t/three-photon-questions/103830/22 "2002-04-16T12:48:56Z")
> [@](#): > > \*Originally posted by Whack-a-Mole \* > \*\*Oops…I forgot to address the FTL communication issue (been a long day). > > Anything moving faster than light violates causality. Time stops for anything moving AT the speed of light. From my perspective the photon in my laser sent to Alpha Centauri took 4+ years to arrive. If I rode along with the photon (forgetting for a moment that is not possible) the trip to Alpha Centauri would take zero time. I’d arrive the moment I left. > > However, if I went faster than the speed of light then I’d actually be travelling backwards in time (myself or the photon). From my persepctive, going faster than light, I’d arrive at Alpha Centauri _before_ I left. If I could do such a thing I’d make a fortune in tonight’s $300 million lottery. My future self could send the winning numbers back in time to me…but wait, if I won now my future self would already have won and may forget to transmit the winning numbers in his glee! Hmmm – that’s what you call a paradox and one of the good reasons FTL communication isn’t possible. \*\* Bit confused here. OK you send your twin into a faster than light ship, send him up to adromeda and back. He arrives younger, but to himself he has sort of gone forwards in time (relative to where he started). You have just plodded on as normal. No lottery winnings here? You would have to send whole the earth on a faster than light trip and you stay still if you wanted to win the lottery. This seems somehow connected to the twins paradox of near to light speed travel. Could one way round the time paradox be that time stops (but does not go backwards) for anything travelling at or faster than light speed, Would that violate another physical law? ---
**Author:** ![bryanmcc](https://avatars.discourse-cdn.com/v4/letter/b/eada6e/32.png) [@bryanmcc](https://boards.straightdope.com/u/bryanmcc)\ **Post date:** [April 16, 2002, 1:15pm UTC](https://boards.straightdope.com/t/three-photon-questions/103830/23 "2002-04-16T13:15:11Z")
**Osiris** , I _think_ what you’re describing as a shadow is the column of darkness between a partition and, say, the earth, correct? So that when you move the partition, the column gets shorter at the speed of light? If I’ve understood you correctly, this is true, but not what people mean when they say shadows can travel faster than the speed of light. What they are speaking of is the two dimentional shadow cast on the surface. I think it is easier to explain with a laser, but you can substitute shadow and it’s the same thing. The speed the dot of a laser moves on a surface is proportional to the distance between that surface and the emitter. If I aim a laser at the wall, I can move the spot faster than my wrist is flicking. If I aim it at the moon, I can make the spot move faster still. My wrist might have to move in inch to make the spot move across the entire surface of the moon in an arbitrarilly short amount of time. You can see there would be no limit to the speed I’d be capable of producing, provided I could shine the laser far enough away. The reason this doesn’t violate Relativity is that the laser spot is not an object, it is a concept. It is different photons every instant, and our brains just interperet it as a spot. In effect, you are just aiming photons in a fast series of directions, which gives the impression of a spot when the intersect something. Same thing works with shadows, but with the absence of photons. **scm1001**. these paradoxes are precisely why nothing with mass can go faster than light. It is rather pointless to speculate what would happen if they could, because they can’t. It’s a bit like arguing about the properties of a square circle, or what happens when an irresistable force meets an imovable object. And yes, time stopping instead of running backwards at faster than light speed would directly violate the equations in question. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [April 16, 2002, 1:16pm UTC](https://boards.straightdope.com/t/three-photon-questions/103830/24 "2002-04-16T13:16:02Z")
> [@](#): > > \*Originally posted by Osiris \* > \*\* > > Are you sure about that? I can’t see it. Rather I would say that a shadow can apparantly move up to the speed of light but not faster. Let’s say my hand is making a shadow on top of sheer 100 meter cliff with the sun directly ahead. Then I quickly move my hand out over edge. My hand will only block the the photons that come after so photons will continue to hit the ground where my shadow will be after my hand has moved out there. The shadow you can think of as an negative space under my hands moving downards at the speed of light. So a shadow can move slower then its originating object. But if it’s faster it has a natural upper limit (the speed of light) beyond which it cannot move. > > Hmmm, Clicking of Libertarian’s link I see that they concur. Ok I used that word to sound smart. They agree. \*\* Sure a shadow can _apparently_ move at the speed of light; just like **Whack-a-Mole** ’s spot of light. Imagine: You are facing an infinitely large plane surface at a distance of one light-year; you shine your laser at a spot 45 degrees to your right, then move it rapidly to a spot 45 degrees to your left; the spot (when it reaches the surface in a year’s time) will _appear_ to move about 2 light-years distance in a matter of seconds. But it doesn’t because it the spot isn’t an object; no individual photons are moving across the surface, they are just streaming from your laser to the surface in a straight line, but the _image_ projected appears to move. There’s no reason why a shadow can’t do the same; a shadow is just an image (or the lack thereof). ---
**Author:** ![scm1001](https://avatars.discourse-cdn.com/v4/letter/s/c4cdca/32.png) [@scm1001](https://boards.straightdope.com/u/scm1001)\ **Post date:** [April 16, 2002, 1:36pm UTC](https://boards.straightdope.com/t/three-photon-questions/103830/25 "2002-04-16T13:36:30Z")
> [@](#): > > \*Originally posted by bryanmcc \* > \*\ ***Osiris** , > > **scm1001**. these paradoxes are precisely why nothing with mass can go faster than light. It is rather pointless to speculate what would happen if they could, because they can’t. It’s a bit like arguing about the properties of a square circle, or what happens when an irresistable force meets an imovable object. \*\* Au contraire, your two examples are simple paradoxes of definition. Faster than light travel is easily defined, and mathematically described. It may of course not be possible, but by speculating about it, one can learn all sorts of things about the world, or your understanding of the world. Faster than light objects have been speculated about by many respectable physicists. They may not be able to interact with our world, or slow down across the light barrier or even exist, but lets speculate away. ---
**Author:** ![Stinky](https://avatars.discourse-cdn.com/v4/letter/s/43a26b/32.png) [@Stinky](https://boards.straightdope.com/u/Stinky)\ **Post date:** [April 16, 2002, 1:43pm UTC](https://boards.straightdope.com/t/three-photon-questions/103830/26 "2002-04-16T13:43:49Z")
> [@](#): > > The energy of a photon equals Planck’s constant times the frequency. So the energy is continuously variable. Sorry to disagree but this means that photons come in discreet units of Plancks constant called quanta,thus the term quantum. I would like to suggest the book,“The Elegant Universe” by Brian Green. He explains Relitiveity,Special Relitiveity and Quantum Theory and how they contradict each other as well as String Theory and how it addresses thease contradictions. He uses laymans terms and thought experiments and very little math. You can find this book here: [http://www.amazon.com/exec/obidos/search-handle-form/002-9800585-9372807](http://www.amazon.com/exec/obidos/search-handle-form/002-9800585-9372807) ---
**Author:** ![bryanmcc](https://avatars.discourse-cdn.com/v4/letter/b/eada6e/32.png) [@bryanmcc](https://boards.straightdope.com/u/bryanmcc)\ **Post date:** [April 16, 2002, 1:47pm UTC](https://boards.straightdope.com/t/three-photon-questions/103830/27 "2002-04-16T13:47:32Z")
> [@](#): > > \*Originally posted by scm1001 \* > \*\* > > Au contraire, your two examples are simple paradoxes of definition. Faster than light travel is easily defined, and mathematically described. It may of course not be possible, but by speculating about it, one can learn all sorts of things about the world, or your understanding of the world. > > Faster than light objects have been speculated about by many respectable physicists. They may not be able to interact with our world, or slow down across the light barrier or even exist, but lets speculate away. \*\* I disagree. The objects you are speaking of, I believe, are tachyons. These proposed particles would have imaginary mass, would traveling backwards through time, would be required to _always_ move faster than light, and have other wacky properties like that. I was not intending to imply that speculation along those lines was less than fruitful, or uninteresting. What I was referring to was speculating the properties of things known to be impossible – i.e., what would happen to regular mass if it were accelerated beyond _c_. It cannot be done, so who could say what the results would look like? Might as well speculate that everything turns plaid for all the validity it would have. ---
**Author:** ![David\_Simmons](https://avatars.discourse-cdn.com/v4/letter/d/9de053/32.png) [@David\_Simmons](https://boards.straightdope.com/u/David_Simmons)\ **Post date:** [April 16, 2002, 1:49pm UTC](https://boards.straightdope.com/t/three-photon-questions/103830/28 "2002-04-16T13:49:39Z")
> [@](#): > > \*Originally posted by Libertarian \* > \*\*_1. What information do photons carry?_ > > I’ve always heard that it is information that cannot travel faster than light, and I’ve taken this (maybe incorrectly) to mean that photons carry information. But what information? Something about the last subatomic properties of the particle that it bounced off of?\*\* **Everything** that we know about extra terrestrial objects is brought to us by photons. What the objects are made of, their temperature, their radial velocity relative to us, and on and on. In plain language, the factual input data to our knowledge about cosmology comes from the analysis of the light from extraterrestial entities. > [@](#): > > **2. How do photons originate? Are they caused by particle collisions or something? Do they come out of nothing? If so, by what mechanism?** The electrons surrounding the nucleus of an atom reside in various energy bands. When an electron at a particular energy level, or band, moves to a lower energy level a photon is emitted with the energy of the difference in the two levels. > [@](#): > > **3. How is a photon destroyed?** Already well answered. The energy of the photon that is absorbed by your desk top remains and heats the desk. > [@](#): > > **Is there an anti-photon by which the two will annihilate?** Well, if the photons of light are considered in their wave aspect, then reinforcement and cancellation takes place. That’s where the interference fringes come from when light passes through a pair of thin slits. So if someone insists that light is always photons it seems to me that they would have to postulate an antiphoton to account for interference patters. However, the use of the both particle (photon) and wave (electromagnetic) model for light answers that question and so many others in such an elegant manner that it is used. > [@](#): > > **Will an electron beat a photon, like rock on scissors?** Sorry, but the import of this question is over my head. > [@](#): > > \*\* Do black holes destroy them? \*\* I don’t think anyone knows anything about the physics of the inside of a black hole. ---
**Author:** ![bryanmcc](https://avatars.discourse-cdn.com/v4/letter/b/eada6e/32.png) [@bryanmcc](https://boards.straightdope.com/u/bryanmcc)\ **Post date:** [April 16, 2002, 1:54pm UTC](https://boards.straightdope.com/t/three-photon-questions/103830/29 "2002-04-16T13:54:15Z")
> [@](#): > > \*Originally posted by Stinky \* > **Sorry to disagree but this means that photons come in discreet units of Plancks constant called quanta,thus the term quantum.** That would only be true if frequency were quantized too, which, as far as I’m aware, it is not. For example, say Plank’s constant is 6 (which it is not). Then photons could have energy of 6\*(1 Hz), or 6\*(1.01 Hz), or 6\*(1.0001 Hz), or any other energy. ---
**Author:** ![scm1001](https://avatars.discourse-cdn.com/v4/letter/s/c4cdca/32.png) [@scm1001](https://boards.straightdope.com/u/scm1001)\ **Post date:** [April 16, 2002, 1:59pm UTC](https://boards.straightdope.com/t/three-photon-questions/103830/30 "2002-04-16T13:59:00Z")
> [@](#): > > \*Originally posted by bryanmcc \* > \*\* > > What I was referring to was speculating the properties of things known to be impossible – i.e., what would happen to regular mass if it were accelerated beyond _c_. It cannot be done, \*\* I agree that I feel that it can’t be done normally. However, that is under the present laws of nature. These laws may not hold everywhere (e.g in singularities) or may be changing slowly (e.g. there has been a recent debate on whether the speed of light is truely constant). Never say never. ---
**Author:** ![scotth](https://avatars.discourse-cdn.com/v4/letter/s/b9e5f3/32.png) [@scotth](https://boards.straightdope.com/u/scotth)\ **Post date:** [April 16, 2002, 2:03pm UTC](https://boards.straightdope.com/t/three-photon-questions/103830/31 "2002-04-16T14:03:46Z")
Libertarian: The questions are getting into the hearts of two fields that are legion for confusing poeople. People are answering pretty well, but they really need to be writing 10’s of pages to really give you the feel for it I think you are looking for. I have picked up alot of books on quantum mechanics and relativity. I can tell you they vary greatly in quality. The best single book I have found is called “The Strange Story of the Quantum”. It was written in the late 40’s I think. A new edition of it is available from Barnes and Noble currently. The book really covers the 20 years of problems leading up to quantum theory and maybe its first 20 years of development. It does this nice and slowly and is wonderfully clear. You could not ask for a better base understanding of the subject. While much work has gone on in the field beyond what it covers, it is all extensions of the original concepts. This book make those concepts CLEAR. For the lay person, this is probably all the understanding you would ever need. If you want to learn more, what you learn in this will make any further learning much easier. “Einstein’s Theory of Relativity” by Max Born is another great one. I can’t tell you how good this book is. It nearly defies description. This book walks you right through “modern” physics from the beginning. This book makes sure you are completely clear on every physical principal that is needed to clearly follow relativity before it begins discussing relativity. In fact, it gives you a pretty good history of physics for several hundred years leading up to relativity. Most books start with relativity, and do one of two things. 1. Strip too much of the math and original reasoning out and leave you with a “fuzzy” understanding at best. 2. Start in with with stuff you don’t understand and lose you, and you never finish the book. This book provides maybe 300 pages of background material that make it completely clear and understandable. Of the 20 or so books on the subject I own or have read, this is BY FAR the best. Anyway, I bring these up for a reason. The follow up questions point to a real desire to understand. Mostly, what can be answered here are the bald consequences, not the reasons for. That provides you with “revealed truth” that is most similar to religion, not a science understanding. ---
**Author:** ![CalMeacham](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/calmeacham/32/35_2.png) [@CalMeacham](https://boards.straightdope.com/u/CalMeacham)\ **Post date:** [April 16, 2002, 2:24pm UTC](https://boards.straightdope.com/t/three-photon-questions/103830/32 "2002-04-16T14:24:23Z")
> [@](#): > > ## quote: > > ## Originally posted by Stinky Sorry to disagree but this means that photons come in discreet units of Plancks constant called quanta,thus the term quantum. > > That would only be true if frequency were quantized too, which, as far as I’m aware, it is not. For example, say Plank’s constant is 6 (which it is not). Then photons could have energy of 6\*(1 Hz), or 6\*(1.01 Hz), or 6\*(1.0001 Hz), or any other energy. Guys, guys. Photons are a candy _and_ a breath mint. And a dessert topping _and_ a floor wax. (Let’s see how many people get _those_ references.) The energy of a given photon _is_ quantized. It only contains a given amount of energy. If your photon has insufficient energy you can’t liberate electrons from a metal surface, but with just a skosh more every photon _will_ liberate electrons. This is the Photoelectric Effect, and Einstein got himself a Prize for this when he wrote a paper about it back in 1903. On the other hand, photons _can_ be generated with any energy you wish. Photons associated with a given system are quantized by the allowable energy levels in that system (hydrogen atom, square-well potential, or what have you), but there are plenty of systems in which the energy levels are tunable (Zeemann effect, for instance), and in that case the energy is continuously tunable. This is how (and why) we have the Free Electron Laser, for which the ouput is continuously tunable. So you’re both right – photons are discrete packets of energy, and the packet size is often determined by the generating system, but the energies of the photons are continuously tunable. ---
**Author:** ![bryanmcc](https://avatars.discourse-cdn.com/v4/letter/b/eada6e/32.png) [@bryanmcc](https://boards.straightdope.com/u/bryanmcc)\ **Post date:** [April 16, 2002, 2:26pm UTC](https://boards.straightdope.com/t/three-photon-questions/103830/33 "2002-04-16T14:26:03Z")
> [@](#): > > \*Originally posted by scm1001 \* > \*\* > > I agree that I feel that it can’t be done normally. However, that is under the present laws of nature. These laws may not hold everywhere (e.g in singularities) or may be changing slowly (e.g. there has been a recent debate on whether the speed of light is truely constant). Never say never. \*\* True. And when I say “cannot be done,” I of course mean “cannot be done according to our current understanding of physics.” It is entirely possible that we will find out that we are wrong about the limiting factor of the speed of light, just as it’s entirely possible for a brick to jump three feet off a table. It’s just not very likely. And I still hold that any speculating done about things that are absolutely impossible according to all we know about physics is meaningless. On what basis would you judge the speculation? The speculation that everything turns into tapioca pudding when accelerated faster than light is just as valid as any other. ---
**Author:** ![bryanmcc](https://avatars.discourse-cdn.com/v4/letter/b/eada6e/32.png) [@bryanmcc](https://boards.straightdope.com/u/bryanmcc)\ **Post date:** [April 16, 2002, 2:34pm UTC](https://boards.straightdope.com/t/three-photon-questions/103830/34 "2002-04-16T14:34:15Z")
> [@](#): > > \*Originally posted by CalMeacham \* > \*\* > > The energy of a given photon _is_ quantized. It only contains a given amount of energy. \*\* Of course. I was only trying to point out that it could contain _any_ amount of energy (as you stated in the next paragraph). Sorry if I was unclear. -b ---
**Author:** ![Ring](https://avatars.discourse-cdn.com/v4/letter/r/6a8cbe/32.png) [@Ring](https://boards.straightdope.com/u/Ring)\ **Post date:** [April 16, 2002, 3:00pm UTC](https://boards.straightdope.com/t/three-photon-questions/103830/35 "2002-04-16T15:00:45Z")
> [@](#): > > \*Originally posted by CalMeacham \*\*\* > > The energy of a given photon _is_ quantized. It only contains a given amount of energy. > > On the other hand, photons _can_ be generated with any energy you wish. > > So you’re both right – photons are discrete packets of energy, and the packet size is often determined by the generating system, but the energies of the photons are continuously tunable. \*\* I’m sorry but that’s not correct. Within the constraints of the uncertainty principle the energy of a specific photon is set, but this is different from what quantized means. Charge is quantized ….it only comes in discreet units of e and nothing else. The energy of a photon can be anything, so it most definitely is not quantized. When energy interacts with matter it must do so in discrete quantized amounts. I think this may be where your confusion originates. ---
**Author:** ![scm1001](https://avatars.discourse-cdn.com/v4/letter/s/c4cdca/32.png) [@scm1001](https://boards.straightdope.com/u/scm1001)\ **Post date:** [April 16, 2002, 3:20pm UTC](https://boards.straightdope.com/t/three-photon-questions/103830/36 "2002-04-16T15:20:17Z")
> [@](#): > > \*Originally posted by bryanmcc \* > \*\* > The speculation that everything turns into tapioca pudding when accelerated faster than light is just as valid as any other. \*\* “mmmm, tapioca pudding - wheres a warp drive when you need one?” ---
**Author:** ![Urban\_Ranger](https://avatars.discourse-cdn.com/v4/letter/u/e9c0ed/32.png) [@Urban\_Ranger](https://boards.straightdope.com/u/Urban_Ranger)\ **Post date:** [April 17, 2002, 4:41pm UTC](https://boards.straightdope.com/t/three-photon-questions/103830/37 "2002-04-17T16:41:24Z")
> [@](#): > > \*Originally posted by Ring \* > Charge is quantized ….it only comes in discreet units of e and nothing else. The energy of a photon can be anything, so it most definitely is not quantized. Photon energies are definitely quantized, because of the way that photons are generated. ---
**Author:** ![David\_Simmons](https://avatars.discourse-cdn.com/v4/letter/d/9de053/32.png) [@David\_Simmons](https://boards.straightdope.com/u/David_Simmons)\ **Post date:** [April 17, 2002, 5:51pm UTC](https://boards.straightdope.com/t/three-photon-questions/103830/38 "2002-04-17T17:51:22Z")
> [@](#): > > \*Originally posted by Urban Ranger \* > \*\* > > Photon energies are definitely quantized, because of the way that photons are generated. \*\* Ah, but the photons of different materials can have different enegy levels. An incandescent solid material radiates photons in a continuous spectrum of energy levels. Sort of like a black body. The energy of a photon is computed by the formula e = h\*f. Since f can take on any value, a photon can have any value. However, if a _particular_ material is considered, the electrons in that material can only occupy certain energy states so the photons that the _atoms_ of that material will absorb can only have certain values corresponding to the energy states of its electrons. Won’t the material itself absorb photons of any energy and turn that energy into a temperature rise? Even if a photon isn’t absorbed by changing the energy level of an electron (which won’t cause a rise in temperature) it can transfer energy to the atoms or molecules of the material and thus increase their kinetic energy. ---
**Author:** ![Quercus](https://avatars.discourse-cdn.com/v4/letter/q/7ab992/32.png) [@Quercus](https://boards.straightdope.com/u/Quercus)\ **Post date:** [April 17, 2002, 6:00pm UTC](https://boards.straightdope.com/t/three-photon-questions/103830/39 "2002-04-17T18:00:51Z")
Again, just to be clear on quantization of photons, it comes down (as usual) to what you mean by quantized – photon energy comes in lumps, but there can be different sized lumps. Most things that emit photons (for instance, neon lights) emit them only at specific frequencies. That red laser pointer only puts out that exact frequency that our eyes see as red -no other colors at all. Some things can be tuned to different frequencies (some lasers), and some things put out a whole mess of frequencies (really hot things, for instance). All photons of a given frequency (color) have the same energy-- namely Plank’s constant times the frequency. So your red laser can only put out specific amounts of energy – if it doesn’t have enough energy to quite make two photons of red, it can only put out one photon and has to save the rest of the energy, rather than putting out one and a half photon’s worth of energy. In that sense, yes indeedy photons are quantized. On the other hand, with a continuosly tunable laser, or tunable radio transmitter (both putting out photons, you know)you could put out photons of whatever energy you wanted, by tuning to the right frequency. So in another sense, photons are not quantized. This is in contrast to electric charge – everything in the universe has a charge that’s a multiple of one electron charge, and every electron has exactly the same charge. You can’t make something with one and a half electron charges. So in this sense, electric charge is quantized, but photons aren’t. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [April 17, 2002, 7:38pm UTC](https://boards.straightdope.com/t/three-photon-questions/103830/40 "2002-04-17T19:38:51Z")
One other note on photons and information, by the way: Just receiving the photon in the first place can count as information. For instance, suppose Bob and Sue are expecting a baby, but are living far away from their friends Frank and Jane. Well, when the blessed event arives, Bob sends a message to them to say so. Even if the message consists of only a single photon, Frank and Jane will probably get the gist of it. “Oh, gee, Bob just sent us a photon. I wonder why? Might it have anything to do with their new baby?” Of course, they’ll probably want more details, but those could be handled with a few more photons: One photon means it’s a boy, two means it’s a girl, etc. [Previous page](https://boards.straightdope.com/t/three-photon-questions/103830.md?page=1) [Next page](https://boards.straightdope.com/t/three-photon-questions/103830.md?page=3)