# The Nature of Light - Particle, Wave - both? **URL:** \ **Category:** Factual Questions\ **Created:** [January 2, 2003, 4:15pm UTC](https://boards.straightdope.com/t/the-nature-of-light-particle-wave-both/146216 "2003-01-02T16:15:28Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![WordMan](https://avatars.discourse-cdn.com/v4/letter/w/e8c25b/32.png) [@WordMan](https://boards.straightdope.com/u/WordMan)\ **Post date:** [January 2, 2003, 4:15pm UTC](https://boards.straightdope.com/t/the-nature-of-light-particle-wave-both/146216/1 "2003-01-02T16:15:28Z")
I swear I tried a few different searches on the SDMB about this and couldn’t find a thread that speaks to the nature of my question - if there are a bunch, do feel free to point me in that direction with a little sarcasm. Okay - so Maxwell established that light was a wave and Einstein and Planck established that light was a particle. I have been reading a few books about relativity (e=MC^2, by David Bodanis, Great Equations (?) by Guillen and It Must be Beautiful, edited by Farmelo), and want to see if I understand how this paradox works out: - So light manifests as a transition between electric and magnetic states of energy - it propogates at the speed of light (duh); Bodanis (IIRC) likens a light pulse to a slippery fish being grabbed by an alternating set of magnetic and electric hands with the fish moving ever forward as it transitions between states. - The reason that ether - i.e., a medium through which the wave can propagate - is not needed is because the wave is propogated through our reality - it is winking between states of existence and that serves as the means through which the wave travels. - As stated above, Einstein and Planck demonstrated that light is comprised of quanta - little packets of energy - so how does that work? Is it because the wave of light is in fact bundles of energy moving in wave-like fashion, propogated by the never-ending transition between energy states? Am I getting any of this? ---
**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:** [January 2, 2003, 4:22pm UTC](https://boards.straightdope.com/t/the-nature-of-light-particle-wave-both/146216/2 "2003-01-02T16:22:44Z")
It gets weirder than that; if you set up the famous double slit experiment to demonstrate the wave-like properties of light and show that light from slit A interferes with light from slit B, then reduce the soource intensity so that individual photons are emitted, the pattern of detection on the other side of the slits still works out the same - a single photon passing through the apparatus behaves as if there were other photons there with which to interfere. ---
**Author:** ![WordMan](https://avatars.discourse-cdn.com/v4/letter/w/e8c25b/32.png) [@WordMan](https://boards.straightdope.com/u/WordMan)\ **Post date:** [January 2, 2003, 4:28pm UTC](https://boards.straightdope.com/t/the-nature-of-light-particle-wave-both/146216/3 "2003-01-02T16:28:49Z")
> [@](#): > > \*Originally posted by Mangetout \* > **It gets weirder than that…** Does that mean I am getting it up to that point? Your photon experiment seems to work within the context of what I described… ---
**Author:** ![g8rguy](https://avatars.discourse-cdn.com/v4/letter/g/7cd45c/32.png) [@g8rguy](https://boards.straightdope.com/u/g8rguy)\ **Post date:** [January 2, 2003, 7:00pm UTC](https://boards.straightdope.com/t/the-nature-of-light-particle-wave-both/146216/4 "2003-01-02T19:00:01Z")
Light really just manifests as a transition between states of energy; I think it’s misleading to think of it as a transition between electric and magnetic. However, associated with light are electric and magnetic fields; the strength of these fields changes so that whenever one is getting stronger, the other is getting weaker. The reason that there’s no need for an ether is roughly that changing the strength of one field changes the strength of the other automatically, so you’ve roughly understood that correctly. The problem with resolving the wave/particle paradox is, as always, that quantum mechanics is very confusing. It’s traditional to invoke the “wave-particule duality,” which I think is misguided. In my view, it’s more proper to say that photons and electrons and the like are particles. It’s just that they’re particles which happen to satisfy a wave equation and hence can exhibit wave-like behavior. This may be somewhat unorthodox, however. ---
**Author:** ![Wearia](https://avatars.discourse-cdn.com/v4/letter/w/13edae/32.png) [@Wearia](https://boards.straightdope.com/u/Wearia)\ **Post date:** [January 2, 2003, 7:02pm UTC](https://boards.straightdope.com/t/the-nature-of-light-particle-wave-both/146216/5 "2003-01-02T19:02:01Z")
Just to add my 2 cents, the way that light behaves like waves and particles is called Wave Particle Duality. ---
**Author:** ![Wearia](https://avatars.discourse-cdn.com/v4/letter/w/13edae/32.png) [@Wearia](https://boards.straightdope.com/u/Wearia)\ **Post date:** [January 2, 2003, 7:03pm UTC](https://boards.straightdope.com/t/the-nature-of-light-particle-wave-both/146216/6 "2003-01-02T19:03:56Z")
Oh sure beat me to it **g8rguy** … ---
**Author:** ![Yossarian](https://avatars.discourse-cdn.com/v4/letter/y/9de0a6/32.png) [@Yossarian](https://boards.straightdope.com/u/Yossarian)\ **Post date:** [January 2, 2003, 8:49pm UTC](https://boards.straightdope.com/t/the-nature-of-light-particle-wave-both/146216/7 "2003-01-02T20:49:30Z")
I think that it is better to say that light can be _modeled_ as either a wave or as a particle, not that it necessarily _is_ one of those things. ---
**Author:** ![hobbes730](https://avatars.discourse-cdn.com/v4/letter/h/97f17d/32.png) [@hobbes730](https://boards.straightdope.com/u/hobbes730)\ **Post date:** [January 2, 2003, 9:29pm UTC](https://boards.straightdope.com/t/the-nature-of-light-particle-wave-both/146216/8 "2003-01-02T21:29:52Z")
Actually it’s not just light. Any sufficiently small piece of matter, ranging up to a few hundred atoms in size, will behave exactly the same as light in a double-slit experiment. Weird, huh? ---
**Author:** ![scotth](https://avatars.discourse-cdn.com/v4/letter/s/b9e5f3/32.png) [@scotth](https://boards.straightdope.com/u/scotth)\ **Post date:** [January 2, 2003, 9:55pm UTC](https://boards.straightdope.com/t/the-nature-of-light-particle-wave-both/146216/9 "2003-01-02T21:55:09Z")
I hate to do this, but… Light behaves as a particle. That’s it. When you get to modern QED, there is no duality any more. Every single aspect of Electromagnatism is now explainable using only particle ideas. ---
**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:** [January 2, 2003, 9:58pm UTC](https://boards.straightdope.com/t/the-nature-of-light-particle-wave-both/146216/10 "2003-01-02T21:58:08Z")
Matter and energy are just the same thing anyway, sort of. Every time I ponder the whole issue I start wondering if maybe nothing is real. ---
**Author:** ![artemis](https://avatars.discourse-cdn.com/v4/letter/a/91b2a8/32.png) [@artemis](https://boards.straightdope.com/u/artemis)\ **Post date:** [January 2, 2003, 11:07pm UTC](https://boards.straightdope.com/t/the-nature-of-light-particle-wave-both/146216/11 "2003-01-02T23:07:07Z")
Asking “is light a wave or a particle?” is like asking “is a coin heads or tails?”. A coin is neither, of course; it may SHOW heads or tails, depending on how it lands when it’s flipped, but it doesn’t posess some mysterious property of “headness” or “tailness”. Light is light; under some observational conditions it may show the appearance of a particle, and under others it may show the appearance of a wave, but its essential nature can no more be described as particular or wavelike than a coin’s essential nature can be described as heads or tails. ---
**Author:** ![Scott\_Dickerson](https://avatars.discourse-cdn.com/v4/letter/s/f04885/32.png) [@Scott\_Dickerson](https://boards.straightdope.com/u/Scott_Dickerson)\ **Post date:** [January 2, 2003, 11:12pm UTC](https://boards.straightdope.com/t/the-nature-of-light-particle-wave-both/146216/12 "2003-01-02T23:12:35Z")
WordMan, Part of the problem is assuming that your semi-namesakes, Words, are tame and well-behaved little things. What sort of thing do you “have in mind” when you think of what a particle is? What a wave is? Sure, you know what grains of sand are like, what waves on the ocean are like. But are these things general forms that can be appled anywhere, to any kind of “substance”? Does it make sense to talk about a grain of sound? How about a wave of hours? The kind of thing that light and other such radiations “is” can not be expected to fit neatly into our ordinary human-sized categories. It may have properties that are paradoxical (which only means: disturbing to common opinion). If you think of radiant light not as something like a fine spray spritzing outward from a nozzle, but rather as a more-or-less endless region of space with a certain set of properties–it may be less difficult to think that sometimes it acts in ways that remind us of particles, other times in ways that remind us of waves. But mostly it’s just its inimitable self. ---
**Author:** ![scotth](https://avatars.discourse-cdn.com/v4/letter/s/b9e5f3/32.png) [@scotth](https://boards.straightdope.com/u/scotth)\ **Post date:** [January 2, 2003, 11:14pm UTC](https://boards.straightdope.com/t/the-nature-of-light-particle-wave-both/146216/13 "2003-01-02T23:14:36Z")
> [@](#): > > \*Originally posted by artemis \* > \*\*Asking “is light a wave or a particle?” is like asking “is a coin heads or tails?”. A coin is neither, of course; it may SHOW heads or tails, depending on how it lands when it’s flipped, but it doesn’t posess some mysterious property of “headness” or “tailness”. Light is light; under some observational conditions it may show the appearance of a particle, and under others it may show the appearance of a wave, but its essential nature can no more be described as particular or wavelike than a coin’s essential nature can be described as heads or tails. \*\* Light is a particle. ---
**Author:** ![bonzer](https://avatars.discourse-cdn.com/v4/letter/b/45deac/32.png) [@bonzer](https://boards.straightdope.com/u/bonzer)\ **Post date:** [January 3, 2003, 12:26am UTC](https://boards.straightdope.com/t/the-nature-of-light-particle-wave-both/146216/14 "2003-01-03T00:26:03Z")
> [@](#): > > \*Originally posted by scotth \* > When you get to modern QED, there is no duality any more. Every single aspect of Electromagnatism is now explainable using only particle ideas. And it’d be equally useful to say that because a Feynman sum-over-histories is essentially wave interference writ large, QED is explainable using only wave ideas. It’s undoubtedly tempting to believe (the hope has ocurred to most of us) that all the philosophical arguments about quantum mechanics might be resolvable merely by focussing on field theory instead, but this ain’t a common position in the literature. I think I have seen it at least suggested as a possibility in print, but I don’t think I’ve ever seen it seriously argued. Not least, there’s the difficulty of agreeing what QFT is: try the experiment of getting a bunch of theorists in a bar and asking them what their definition is. In my experience, you all just wind up jovially disagreeing - and the more distinguished the theorist, the more esoteric and unpopular their definition is likely to be. This might disturb the philosophers, but it doesn’t bother working physicists too much. Then again, neither does wave-particle duality. ---
**Author:** ![MC\_Master\_of\_Ceremonies](https://avatars.discourse-cdn.com/v4/letter/m/bb73d2/32.png) [@MC\_Master\_of\_Ceremonies](https://boards.straightdope.com/u/MC_Master_of_Ceremonies)\ **Post date:** [January 3, 2003, 12:53am UTC](https://boards.straightdope.com/t/the-nature-of-light-particle-wave-both/146216/15 "2003-01-03T00:53:28Z")
Anyway, way is this disscussion only about light? All “particles” are subject to wave-particle duality. There is no paradox, just because we cannot observe this duality in macroscopic objects (though in theory they are subject to it too) is no reason to think that wave-particle duality is not the fundamental behaviour of all objects. ---
**Author:** ![scotth](https://avatars.discourse-cdn.com/v4/letter/s/b9e5f3/32.png) [@scotth](https://boards.straightdope.com/u/scotth)\ **Post date:** [January 3, 2003, 1:35am UTC](https://boards.straightdope.com/t/the-nature-of-light-particle-wave-both/146216/16 "2003-01-03T01:35:06Z")
> [@](#): > > \*Originally posted by bonzer \* > \*\*And it’d be equally useful to say that because a Feynman sum-over-histories is essentially wave interference writ large, QED is explainable using only wave ideas. > \*\* Incorrect. There are a number of phenomena that cannot be handled as waves. The big one the jumps right out is any single photon behaviour. Also, you clearly don’t grasp what sum over histories are. It is a way of calculating the probability that a particle will arrive at a spot, but the whole point is that it is NOT interference. ---
**Author:** ![bonzer](https://avatars.discourse-cdn.com/v4/letter/b/45deac/32.png) [@bonzer](https://boards.straightdope.com/u/bonzer)\ **Post date:** [January 3, 2003, 2:06am UTC](https://boards.straightdope.com/t/the-nature-of-light-particle-wave-both/146216/17 "2003-01-03T02:06:46Z")
> [@](#): > > \*Originally posted by scotth \* > Also, you clearly don’t grasp what sum over histories are. It is a way of calculating the probability that a particle will arrive at a spot, but the whole point is that it is NOT interference. Naturally, I disagree. And so would Feynman. To quote from _The Character of Physical Law_ (BBC, 1965, p138): > [@](#): > > I will sumarize, then, by saying that electrons arrive in lumps, like particles, but the probability of arrival of these lumps is determined as the intensity of waves would be. It is in this sense that the electron behaves sometimes like an electron and sometimes like a wave. It behaves in two different ways at the same time (fig. 31). > That is all there is to say. ---
**Author:** ![bonzer](https://avatars.discourse-cdn.com/v4/letter/b/45deac/32.png) [@bonzer](https://boards.straightdope.com/u/bonzer)\ **Post date:** [January 3, 2003, 2:14am UTC](https://boards.straightdope.com/t/the-nature-of-light-particle-wave-both/146216/18 "2003-01-03T02:14:29Z")
Slight, but important, correction: “It is in this sense that the electron behaves sometimes like **a particle** and sometimes like a wave.” ---
**Author:** ![scotth](https://avatars.discourse-cdn.com/v4/letter/s/b9e5f3/32.png) [@scotth](https://boards.straightdope.com/u/scotth)\ **Post date:** [January 3, 2003, 2:57am UTC](https://boards.straightdope.com/t/the-nature-of-light-particle-wave-both/146216/19 "2003-01-03T02:57:08Z")
bonzer, The problem is, that was discussing things in the simpler quantum mechanics framework, not the more complete QED framework. This is Feynman in 1985 (20 years later). This is just a couple paragraphs before he begins explaining sum over histories. > [@](#): > > I want to emphasize that light come in this form–particles. It is very important to know that light behaves like particles, especially for those of you who have gone to school, where you were probably told something about light behaving like waves. I’m telling you the way it _does_ behave–like particles. > > You might say that it’s just the photomultiplier that detects like as particles, but no, every instrument that has been designed to be sensitive enough to detect weak light has always ended up discovering the same thing: light is made of particles. btw, the italics were Feynman’s as well. ---
**Author:** ![Ring](https://avatars.discourse-cdn.com/v4/letter/r/6a8cbe/32.png) [@Ring](https://boards.straightdope.com/u/Ring)\ **Post date:** [January 3, 2003, 4:35am UTC](https://boards.straightdope.com/t/the-nature-of-light-particle-wave-both/146216/20 "2003-01-03T04:35:46Z")
> [@](#): > > \*Originally posted by scotth \* > \*\*bonzer, > The problem is, that was discussing things in the simpler quantum mechanics framework, not the more complete QED framework. > > This is Feynman in 1985 (20 years later). This is just a couple paragraphs before he begins explaining sum over histories. > \*\* **scotth** I don’t know if you’re aware that **Bonzer** is a Ph.D. physicist and one sharp cookie, but unless you have equivalent qualifications I would listen to him if I were you. I know I do. Anytime a photon is detected it presents itself as a particle, but in between observations, if it’s anything at all, it’s a wave. In fact the probability of finding a photon in a small volume centered on a given point in an electromagnetic wave is proportional to the square of the electric field vector at that point. IOW it is usually postulated that light propagates not as a stream of photons but instead as a probability wave or, more commonly, as an electromagnetic wave. [Next page](https://boards.straightdope.com/t/the-nature-of-light-particle-wave-both/146216.md?page=2)