# How can light be both a wave and a particle? **URL:** \ **Category:** Cecil's Columns/Staff Reports\ **Created:** [June 20, 2004, 7:11am UTC](https://boards.straightdope.com/t/how-can-light-be-both-a-wave-and-a-particle/251287 "2004-06-20T07:11:02Z")\ **Posts on this page:** 20\ **Page:** 5
**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:** [September 12, 2004, 4:44pm UTC](https://boards.straightdope.com/t/how-can-light-be-both-a-wave-and-a-particle/251287/81 "2004-09-12T16:44:48Z")
The many-worlds model is one model for quantum mechanics, but it’s not necessary, and doesn’t really get you any more explanatory power. In fact, in some sense it gives you less: If you observe the photon, then it does not interfere with itself (or its otherworldly analogues), but if you don’t observe it, then it does. But what if you observe it, but your otherworldly analogue doesn’t? Any model with multiple universes with any sort of interaction between them must eventually fall prey to paradoces. ---
**Author:** ![RM\_Mentock](https://avatars.discourse-cdn.com/v4/letter/r/e274bd/32.png) [@RM\_Mentock](https://boards.straightdope.com/u/RM_Mentock)\ **Post date:** [September 12, 2004, 5:06pm UTC](https://boards.straightdope.com/t/how-can-light-be-both-a-wave-and-a-particle/251287/82 "2004-09-12T17:06:49Z")
Paradoces being ones that are apparent, not real? 🙂 ---
**Author:** ![Complex\_Conjugate](https://avatars.discourse-cdn.com/v4/letter/c/3bc359/32.png) [@Complex\_Conjugate](https://boards.straightdope.com/u/Complex_Conjugate)\ **Post date:** [September 12, 2004, 6:11pm UTC](https://boards.straightdope.com/t/how-can-light-be-both-a-wave-and-a-particle/251287/83 "2004-09-12T18:11:58Z")
> [@Chronos](#): > > The many-worlds model is one model for quantum mechanics, but it’s not necessary, and doesn’t really get you any more explanatory power. In fact, in some sense it gives you less: If you observe the photon, then it does not interfere with itself (or its otherworldly analogues), but if you don’t observe it, then it does. But what if you observe it, but your otherworldly analogue doesn’t? Any model with multiple universes with any sort of interaction between them must eventually fall prey to paradoces. That’s not a paradox in MWI as seperate ‘branches’ (each barnch would correspond to a different result of some measuremnt) cannot interfere with each other. ---
**Author:** ![Mathochist](https://avatars.discourse-cdn.com/v4/letter/m/c89c15/32.png) [@Mathochist](https://boards.straightdope.com/u/Mathochist)\ **Post date:** [September 12, 2004, 8:17pm UTC](https://boards.straightdope.com/t/how-can-light-be-both-a-wave-and-a-particle/251287/84 "2004-09-12T20:17:03Z")
> [@Complex Conjugate](#): > > That’s not a paradox in MWI as seperate ‘branches’ (each barnch would correspond to a different result of some measuremnt) cannot interfere with each other. In the original Many-Worlds, yes. However, **Chronos** was responding to > [@the green hornet](#): > > i’d like to ask you folks how does the multiverse fit into this all. and i mean the hugh everett type. you know like that the photon doesn’t interfere with itself but with it’s numerous twins in parallel universes. You _do_ read the thread, don’t you? ---
**Author:** ![Complex\_Conjugate](https://avatars.discourse-cdn.com/v4/letter/c/3bc359/32.png) [@Complex\_Conjugate](https://boards.straightdope.com/u/Complex_Conjugate)\ **Post date:** [September 12, 2004, 8:43pm UTC](https://boards.straightdope.com/t/how-can-light-be-both-a-wave-and-a-particle/251287/85 "2004-09-12T20:43:15Z")
> [@Mathochist](#): > > In the original Many-Worlds, yes. However, **Chronos** was responding to > You _do_ read the thread, don’t you? MWI of the Hugh Everett type is the type in which seperate branches corresponding to different measuremnts do not interfere with each other, therefore the actions of an observer can never be affected by his counterpart in antoher branch. A particle like a photon in a superpostion of states can be interpreted as interfering with itself. ---
**Author:** ![Mathochist](https://avatars.discourse-cdn.com/v4/letter/m/c89c15/32.png) [@Mathochist](https://boards.straightdope.com/u/Mathochist)\ **Post date:** [September 13, 2004, 1:45am UTC](https://boards.straightdope.com/t/how-can-light-be-both-a-wave-and-a-particle/251287/86 "2004-09-13T01:45:03Z")
> [@Complex Conjugate](#): > > MWI of the Hugh Everett type is the type in which seperate branches corresponding to different measuremnts do not interfere with each other, therefore the actions of an observer can never be affected by his counterpart in antoher branch. A particle like a photon in a superpostion of states can be interpreted as interfering with itself. Details. The poster attached the wrong name to the concept. The key concept is an MWI with interaction. Saying that traditional MWIs don’t have interactions doesn’t answer a thing. Saying that traditional MWIs don’t have paradoxes misses the point as well. Saying that MWIs with interactions necessarily lead to paradoxes does. ---
**Author:** ![SnakeSpirit](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/snakespirit/32/7271_2.png) [@SnakeSpirit](https://boards.straightdope.com/u/SnakeSpirit)\ **Post date:** [September 13, 2004, 2:45am UTC](https://boards.straightdope.com/t/how-can-light-be-both-a-wave-and-a-particle/251287/87 "2004-09-13T02:45:16Z")
Great stuff here that’s just _soooo_ far over my measly social-science capable brain, yet I appreciate it. This **IS**. This is the nature of reality, because it is the foundation of everything we can perceive. (Now there may be another foundation below that, but we’re just barely perceiving this foundation, so… later…) Particles? I don’t believe in them. At least not in the sense of what we conceive of as matter (as in particles of matter). Sub-atomic “particles” are energy (IMNSHO), and like a magnetic field, or electrical field, can act upon other fields, which is why we maybe call them “particles.” I think (and have nothing to support it, so it’s just intuitive), that everything is energy, and only when we get to the point of atoms or molecules can we call anything a “particle.” Even then, that “particle” is just an expression of energy. A wave is an expression of energy. Drop a pebble in a pond, and the waves ripple out, bounce off or are diverted around objects and eventually spread out far enough to be imperceptable. The pebble was energy itself, which displaced the energetic expression of a volume of water, etc. We humans are expressions of energy. Our solidity is the illusion that is created when one of our standing, interlocked energy field complexes (a hand) interferes with another. By this description, we are not 90%, but 100% empty space. Electrons, protons and neutrons are simpler charged fields. Other so-called particles are just more complex configurations. Combinations of these fields in various configurations have certain effects upon the visible world: flesh, iron, gas, liquid. I was having some problem with resolving this with the speed of light in a vacuum, however, since if space is a true vacuum, how can light create a wave? Can energy exist without some sort of matter in which to express itself? Or is it just that energy needs matter to produce _observable_ effects? I know, I know, simplistic thinking, but I’m a simple person. I’d just read your (to me) incomprehensible explanations and shut up, but this stuff has to come out or I’ll just go nuts. I have no reason not to believe what you tell me, but I can’t understand it; this I can understand. Well, magnets operate in a vacuum, so why not light? I guess gravity (whatever _that_ is) operates in a vacuum, too. Perhaps a vacuum is just another form of energy that we can’t yet measure. maybe it’s that “dark matter” scientists are trying to account for. And of course I could be totally wrong, too. I can’t test any of this, or create mathmatical models. So, from the point of view of those who have some experience studying this type of phenomenon, does any of this make sense? In simple terms. please… 🙂 ---
**Author:** ![SnakeSpirit](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/snakespirit/32/7271_2.png) [@SnakeSpirit](https://boards.straightdope.com/u/SnakeSpirit)\ **Post date:** [September 13, 2004, 2:55am UTC](https://boards.straightdope.com/t/how-can-light-be-both-a-wave-and-a-particle/251287/88 "2004-09-13T02:55:58Z")
> [@Mathochist](#): > > I still say the easiest ontological interpretation (keeping spacetime as an ontological primitive) of entanglement is that there _are_ no “separate” particles. There’s one photon field. An EPR pair is a disturbance of the field which is nonnegligible in two spacelike-separated compact regions. From this standpoint it’s perfectly natural that observvations are correlated: there’s only one object to observe in the first place. Yeah, something like that. All energy being one, interconnected, and only manifesting differently in relation to different manifestations of itself. That makes sense. ---
**Author:** ![Complex\_Conjugate](https://avatars.discourse-cdn.com/v4/letter/c/3bc359/32.png) [@Complex\_Conjugate](https://boards.straightdope.com/u/Complex_Conjugate)\ **Post date:** [September 13, 2004, 11:09am UTC](https://boards.straightdope.com/t/how-can-light-be-both-a-wave-and-a-particle/251287/89 "2004-09-13T11:09:40Z")
> [@Mathochist](#): > > Details. The poster attached the wrong name to the concept. The key concept is an MWI with interaction. Saying that traditional MWIs don’t have interactions doesn’t answer a thing. Saying that traditional MWIs don’t have paradoxes misses the point as well. Saying that MWIs with interactions necessarily lead to paradoxes does. Whetehr or not an observer makes a measuremnt in two different branches causes no paradox as no interaction is between the two is allowed in any MWIs. Allowing an observer to interfere with a version of himself in one of the other ‘worlds’ in a non-nominal way is not any sort of MWI, whereas allowing a photon to interefre with itself before decoherence has occured can be fitted into MWI. The real flaw with MWIs is what the different branches observe after the same measurement. Just before a measurement if you have an operator of some observable that has for example 11 different discrete eigenvalues, for the sake of arguemnt the probailty of getting a result corresponding to one eigenvalue could be 0.9, the probailty of getting a result corresponding to any of the other eigenvalues could be 0.1. The problem is that each measurement corresponds to a seperate ‘world’ so in most worlds will actually measure a result with a probailty of 0.1 attached, so probauilty only seems to work in one particular world. This is not necessarily a terminal flaw in MWI though. ---
**Author:** ![Mathochist](https://avatars.discourse-cdn.com/v4/letter/m/c89c15/32.png) [@Mathochist](https://boards.straightdope.com/u/Mathochist)\ **Post date:** [September 13, 2004, 12:16pm UTC](https://boards.straightdope.com/t/how-can-light-be-both-a-wave-and-a-particle/251287/90 "2004-09-13T12:16:17Z")
> [@Complex Conjugate](#): > > Whetehr or not an observer makes a measuremnt in two different branches causes no paradox as no interaction is between the two is allowed in any MWIs. ::sigh:: And why not? _Because it leads to paradox_. You’re really coming at this from the back end of epistemology. You’re describing what theories there are, while the question is about what theories there _might be_. ---
**Author:** ![PRBot.Com](https://avatars.discourse-cdn.com/v4/letter/p/ecccb3/32.png) [@PRBot.Com](https://boards.straightdope.com/u/PRBot.Com)\ **Post date:** [September 13, 2004, 12:22pm UTC](https://boards.straightdope.com/t/how-can-light-be-both-a-wave-and-a-particle/251287/91 "2004-09-13T12:22:49Z")
Light is not a wave. Scientists make all sorts of claims which they later recend. I wrote about dark matter a couple years ago and the gang on Physics forum laughed at me. Now they refuse to apologize after I was right all along. Max ---
**Author:** ![Mathochist](https://avatars.discourse-cdn.com/v4/letter/m/c89c15/32.png) [@Mathochist](https://boards.straightdope.com/u/Mathochist)\ **Post date:** [September 13, 2004, 12:29pm UTC](https://boards.straightdope.com/t/how-can-light-be-both-a-wave-and-a-particle/251287/92 "2004-09-13T12:29:51Z")
> [@PRBot.Com](#): > > Light is not a wave. Would you care to back this up? Even explain how you mean it? Or are you just going to make some blanket assertion with no justification and insist we take you at your word? If that’s the case, take it to the forum for religion and stop whinging about other boards on this one. Anyway, no reputable scientist would say that light is a wave except in casual terms. Properly, light has wavelike properties. In particular, it satisfies a differential equation very similar to that governing the propagation of waves in other media. In a vacuum this is the Klein-Gordon equation (IIRC), but in general it has various interaction terms and nonlinearities coupling it to other differential equations governing other particle species. ---
**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:** [September 13, 2004, 12:30pm UTC](https://boards.straightdope.com/t/how-can-light-be-both-a-wave-and-a-particle/251287/93 "2004-09-13T12:30:04Z")
> [@PRBot.Com](#): > > Light is not a wave. _Anyone_ can do the double-slit experiment. What is your explanation for the interference pattern? ---
**Author:** ![Complex\_Conjugate](https://avatars.discourse-cdn.com/v4/letter/c/3bc359/32.png) [@Complex\_Conjugate](https://boards.straightdope.com/u/Complex_Conjugate)\ **Post date:** [September 13, 2004, 4:00pm UTC](https://boards.straightdope.com/t/how-can-light-be-both-a-wave-and-a-particle/251287/94 "2004-09-13T16:00:02Z")
> [@Mathochist](#): > > ::sigh:: > > And why not? _Because it leads to paradox_. You’re really coming at this from the back end of epistemology. You’re describing what theories there are, while the question is about what theories there _might be_. Any theory in this area must be either able to replicate the QM formalism (which MWI pretty much does) or at least be able to explain the experimental results associated with QM (such as theories that use non-linear wave equations). It also must prevent intereference occuring on a macroscopic scale in physically relaistic situations. The orginal question did not ask about any class of theories where different states of an observer in a superposition of states could interfere with each other. ---
**Author:** ![Complex\_Conjugate](https://avatars.discourse-cdn.com/v4/letter/c/3bc359/32.png) [@Complex\_Conjugate](https://boards.straightdope.com/u/Complex_Conjugate)\ **Post date:** [September 13, 2004, 4:25pm UTC](https://boards.straightdope.com/t/how-can-light-be-both-a-wave-and-a-particle/251287/95 "2004-09-13T16:25:56Z")
> [@PRBot.Com](#): > > Light is not a wave. > > Scientists make all sorts of claims which they later recend. > > I wrote about dark matter a couple years ago and the gang on Physics forum laughed at me. > > Now they refuse to apologize after I was right all along. > > Max Which username are you? Physics forums like any interent message board on physics tends to attract crackpots luckily they take a hardline on crackpot theories. ---
**Author:** ![Mathochist](https://avatars.discourse-cdn.com/v4/letter/m/c89c15/32.png) [@Mathochist](https://boards.straightdope.com/u/Mathochist)\ **Post date:** [September 13, 2004, 5:37pm UTC](https://boards.straightdope.com/t/how-can-light-be-both-a-wave-and-a-particle/251287/96 "2004-09-13T17:37:57Z")
> [@Complex Conjugate](#): > > The orginal question did not ask about any class of theories where different states of an observer in a superposition of states could interfere with each other. > [@the green hornet](#): > > i’d like to ask you folks how does the multiverse fit into this all … you know like that the photon doesn’t interfere with itself but with it’s numerous twins in parallel universes. Yes, it did. ---
**Author:** ![Complex\_Conjugate](https://avatars.discourse-cdn.com/v4/letter/c/3bc359/32.png) [@Complex\_Conjugate](https://boards.straightdope.com/u/Complex_Conjugate)\ **Post date:** [September 13, 2004, 6:52pm UTC](https://boards.straightdope.com/t/how-can-light-be-both-a-wave-and-a-particle/251287/97 "2004-09-13T18:52:22Z")
The question was about a photon in a superpostion of states interfering with each other which can be used as an ontology in MWI as it is possible to observe inereference in photons, but any MWI does not allow parallel versions of the observer to interfere with each other and there was no mention of this in the original question. ---
**Author:** ![Mathochist](https://avatars.discourse-cdn.com/v4/letter/m/c89c15/32.png) [@Mathochist](https://boards.straightdope.com/u/Mathochist)\ **Post date:** [September 13, 2004, 7:10pm UTC](https://boards.straightdope.com/t/how-can-light-be-both-a-wave-and-a-particle/251287/98 "2004-09-13T19:10:44Z")
> [@Complex Conjugate](#): > > The question was about a photon in a superpostion of states interfering with each other which can be used as an ontology in MWI as it is possible to observe inereference in photons, but any MWI does not allow parallel versions of the observer to interfere with each other and there was no mention of this in the original question. The original post of the entire thread, but I’m talking about the subthread started by **the green hornet** … You know what? I give up. Either you really are this dense or you’re trolling and specifically ignoring everything I’m saying. In the latter case, you win. In the former, I can only hope you’ll kick yourself in the head trying to tie your shoes. ---
**Author:** ![Complex\_Conjugate](https://avatars.discourse-cdn.com/v4/letter/c/3bc359/32.png) [@Complex\_Conjugate](https://boards.straightdope.com/u/Complex_Conjugate)\ **Post date:** [September 13, 2004, 7:26pm UTC](https://boards.straightdope.com/t/how-can-light-be-both-a-wave-and-a-particle/251287/99 "2004-09-13T19:26:58Z")
> [@Mathochist](#): > > The original post of the entire thread, but I’m talking about the subthread started by **the green hornet** … > > You know what? I give up. Either you really are this dense or you’re trolling and specifically ignoring everything I’m saying. In the latter case, you win. In the former, I can only hope you’ll kick yourself in the head trying to tie your shoes. I am not trolling and I am not ignoring what you say and I am refering specifically to **green hornet’s** post. He does not mention anywhere in the post two observers interfering with their counterparts in parallel univeres (infact MWI doesn’t really deal with ‘parallel universes’ at all, espeically not the type popularized by the media, but that’s irrelevant). The post that orginally seemed to earn your ire was just to point out that the behaviour of an observer in one branch has no effect on the behaviour of the observer in another branch (these days this can be explained in terms of decoherence) and therefore whether an observer does or does not make a measuremnt in one branch does not constitute a paradox in MWI. ---
**Author:** ![SnakeSpirit](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/snakespirit/32/7271_2.png) [@SnakeSpirit](https://boards.straightdope.com/u/SnakeSpirit)\ **Post date:** [September 13, 2004, 11:49pm UTC](https://boards.straightdope.com/t/how-can-light-be-both-a-wave-and-a-particle/251287/100 "2004-09-13T23:49:25Z")
I know you got an exciting discussion going on about parallel universes and all, but I sure would like some comment on [my earlier post](http://boards.straightdope.com/sdmb/showpost.php?p=5258339&postcount=87) where I posed some questions with a low level of understanding of physics. If anyone has a moment to spare, I’d like to know if I’m on track or off the wall. I really want to understand this stuff, but just can’t keep up with the high level of the discussion. [Previous page](https://boards.straightdope.com/t/how-can-light-be-both-a-wave-and-a-particle/251287.md?page=4) [Next page](https://boards.straightdope.com/t/how-can-light-be-both-a-wave-and-a-particle/251287.md?page=6)