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What is the difference between wave and particle?

  1. Dec 13, 2008 #1

    I am new to this forum. I suffer from asperger's syndrome, so I am not very good at grasping stuff. I am very slow, so please be gentle.

    I've heard that particle is something that's localized in space and time. Does that mean a table, for instance, can be considered a particle? But what's a wave, what does it mean when they say it's spread out in space? I am finding it hard to understand that, perhaps, some examples might help. Is a wave something that exists in two different points in space at the same time?:confused:

    Some simple examples may help me understand this.

    Thanks in advance.
  2. jcsd
  3. Dec 13, 2008 #2


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    The analogy is not very good, but you could imagine something like this: suppose I have a rope. If I have a bead, I can slide it up and down the rope. At any moment, you can say where the bead is on the rope, so it's like a particle. A wave is what you get when you give the end of the rope a swing. You will get some hill-like pattern in the rope, which moves from one side to the next (and, if you tie the rope to a wall or something on the other end, it will come back to you). It's not possible to say "where" the wave is though. If the hill-like pattern doesn't change its form, you could look at the position where it is highest, but in general the wave does not really have a "position" on the piece of string.

    I hope that helps.
  4. Dec 13, 2008 #3
    Lot's of people have had trouble understanding that.....
    as "particles" were first thought to be something specific, and concrete and quite identifiable. So a simple model, the Bohr model, had electrons circling a central nucleus like the earth circles the sun...lots of problems developed from that view...and it was found via quantum theory particles are a bit like a cloud...somewhate indefinite.... and we have trouble locating them exactly.
    A "particle" became more of a concentration of energy or momentum, kind of a peak value of a wave...All this is called "wave particle duality" because sometimes particles seem indentifiable and other times they seem "cloudy" and spread out....so in some sense nobody understands it all, but quantum theory has done pretty well explaining a lot...

    And don't worry here, nobody understands everything!!!

    "we know much, we understand little"
  5. Jul 15, 2011 #4
    First of all---it seems that everything is a wave. The word "particle" seems to be used only for linguistic convenience in order to facilitate visualization. Of course---in dealing with quantum physics the word "visualization" is quite misleading because what the "particle" is relly can not be visualized.

    Originally particles were thought of as what is shot out of a BB gun. Some think that the dead-for-100 years-particle came back to life in the photoelectric effect. But there was no reason to think of the quantized emissions from the photoelectric filaments were anything like BBs. Just because they were quantized in energy did not make them BBs. No---rather they were like short radar pulses having quantized--allowed and dis-allowed--energy levels.

    Radar pulses are not particles--they are packets of energy--and so should the photoelectric emissions be considered---quantized energy bursts.

    DeBroglie and others have shown and continue to show that what some people like to call "particles" are really waves.

    If we MUST visualize---then try to visualize the emission of a water-pistol rather than the emission of a BB gun. The water pistol emision spreads out---which is what quantum emissions do. Quantum emission do not shoot out like a BB--which is not very spread out.

    When some say that a photon "particle" can, at the same time, go through both slits of the 2 slit experiment---isn't that really stretching the point? If the emission is going through both slits at the same time the emission is a wave---not a particle.

    It seems that no matter how hard some try to claim an emission is a "particle"---the claim seems to beg the qustion---for the description winds up describing what a wave does .
  6. Jul 15, 2011 #5


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    The general term 'wave' simply means some phenomena that satisfies some form of wave equation. So a wave description can be applied to many different physical phenomena.
    Often, a wave equation expresses some 'amplitude' as a function of position. For example: electric field as a function of position. Or displacement of a string as a function of position.
    A particle, in its most direct expression is something that exists at a point in space. (Which means it has no size, and isn't made up of anything smaller). But it does have its own properties, like electric charge (for example an electron).
    So can a table be said to be like a particle? Well, if we want to calculate the gravitational potential energy of a table, then we can approximate the table as existing at a single point in space, so we can calculate its gravitational potential. Of course, we can't always apply this approximation for other phenomena. The reason it works in this case is because the gravitational field doesn't change significantly over the length of the table.

    Now on to a whole other issue: a couple of posters have talked specifically about the terms 'wave' and 'particle' used to describe matter at its most fundamental level. To explain it as simply as I can: The theory of quantum mechanics has opened our eyes in showing us that matter can neither be described as a wave or a particle. The fundamental reality of our universe is actually more complex than just 'wave or particle'.

    EDIT: Although there theoretically could be pure position eigenstates, matter is generally not in a position eigenstate.
  7. Jul 15, 2011 #6


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    To explain your questions more directly:
    Yes, a particle is something that is localised in space and time. And strictly speaking, this means its position can be narrowed down to greater and greater precision, but a table only exists on a length scale of a metre or so. Therefore a table isn't strictly a particle. But it can sometimes be approximated to be so in certain theories.
    A wave is just a function of position, which obeys a certain equation. (So in a sense, yes it exists everywhere). What the function actually represents could be whatever you're trying to model: for example temperature, electric field, height against horizontal position of a string, an actual wave on the sea.
  8. Jul 15, 2011 #7
    A wave has varying levels of intensity at different points in space and time.

    Traditionally, a particle is something that exists at only one point in space.

    In quantum mechanics, subatomic "particles" move like waves, and interact like particles.

    They move like waves because they have different levels of intensity at different points in space and time.

    They interact like particles because they consist of only one unit of energy, which can only be absorbed in one place.
  9. Jul 15, 2011 #8
    You are actually talking about matter wave described by shrodinger, which well describes electrons in atomic orbitals. They are able to appear at two different positions in the orbital where the matter waves or possibility waves lie. But it might be different from other waves probably.
  10. May 2, 2013 #9
    To Naty 1 - wave/particle

    You have given a superb explanation of the above. Now please help me (try) to understand:
    (a) what are waves/particles made of?
    (b) does dark energy travel through dark matter?
    (c) If there are voids in dark matter how does spacetime behave there.
    (d) If there are no truly void places what's the best guess about what is there?
    (e) Is/are there a void/voids within atoms?
    (f) Can the ("spooky") electrons that may somehow be connected across the entire universe and their bizarre behavior be explained by the idea that they may actually constitute parts of the same, very large atom?

    Okay, enough Looney Tunes for a while.
    Thank you, richard sneed
    Last edited: May 2, 2013
  11. Dec 17, 2013 #10
    Okay so I was just wondering when a group of particles defined by a wave equation then they can be said to be waves ? As in DC current we have electrons moving in certain directions so can we consider an electron as a particle or in AC current the motion of electrons as a wave ????
    I am sorry if my questions sound pretty stupid but being educated in India when you are in school you only study for marks and teachers only teach for marks so my basics are not that strong
  12. Dec 18, 2013 #11


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    I have seen some YouTube videos of such things. Ghastly! And not at all fun or interesting. You have my sympathy.

    Rather than suggest that they could be "said to be waves", it would be more fruitful to suggest that, at times, treating the phenomenon as a wave phenomenon would produce a more useful result. That's a slippery answer, I know, but it avoids the deadly question "What is it really?". It may not be very satisfying but Science is only, ever, models and those models work to a greater of lesser extent in different circumstances. You just can't rely on them telling you the whole story. The statement that a particle is a wave is an oxymoron. That can be very upsetting if you like your world to be too literal.
    Keep reading and reading. :biggrin:
  13. Dec 18, 2013 #12
    I understand what you are saying but I actually have trouble to distinguish between an ac and a dc current I am an electronics engineering student and I get that all the difference between the doc voltage and ac voltage and all that but I guess if we are suppose to cut open a wire which is carrying both ac and dc currents then what will be able to see I mean what will be the flow of electrons .
    And the next question which troubles me is in ac current where will the electrons flow I mean considering either conventional or the flow of electrons I mean in dc the electrons flow from the negative terminal to the positive terminal i mean consider a conductor with loose electrons and due to battery the electron gets into motion or I would say there speed increases and they hit one another and transfer energy but in ac what happens is my problem
    I would be super happy even if anyone can suggest any book for my problem I have tried to find books here which explains this but it only talks about the voltage goes from positive to negative and the frequency and all that but not the movement of electrons
  14. Dec 18, 2013 #13


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    That's because the movement of electrons is of totally secondary importance.They move incredible slowly (1mm/s, typical) and carry no significant Kinetic energy. Treat current and charge as entities in themselves when dealing with 'electricity' and you will soon become familiar enough with it to reach an understanding of it. The electron flow model has been regarded as essential in recent versions of Science education. It is not. In the 60s, it was hardly even touched on and it never interfered with my grasp of electricity. I would go as far as to say that the fact that electrons flow in a metal wire is virtually irrelevant to the way a circuit functions.
  15. Dec 18, 2013 #14
    If I am suppose to treat current and charge as an entity then would an ac current mean that a cloud of charges are moving in a wire back and forth at very high frequency ? And i suppose if we replace the word charge and loose electron then it would be correct right ??
    I mean the sinusoidal wave of voltage versus time graph is just the representation of the charges that we get at the output right ? And in dc we get continuous clouds of charges at the output ??? Is this correct the way I am describing coz it makes sense to me now when I think of charges and there motion
    The other thing is actually we don't have waves inside the wires it's just the motion of charges and when we consider output we get a wave
    I really want to thank you coz I was really disturbed for many days or rather many years but I guess now I am starting to get I hope
  16. Dec 19, 2013 #15


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    I can understand your reaction but let me ask you this: when you approach a mechanics problem, using a free body model of a mass, connected by a number of springs on an inclined plane, would you feel a great need to include a description of the interatomic forces or the details of gravitational theory? Because you are familiar enough with the concepts of mass, rigid bodies, Forces etc. you use that, appropriate level for analysing the problem. You encountered words like Force and Gravity before the ideas of interatomic force so you find your 'understanding' in very familiar terms.

    I could ask you whether you 'really' have an understanding about what you mean when you talk of a cloud of electrons. Are you aware of the fermi statistics at work with electrons? If the answer is not "yes" then why look for help in that direction for your understanding? The simple level electron model is a delusion, in fact, and it nearly always leads to confusion. Using the phrase "cloud of electrons", rather than the word 'Charge' is hardly helping you. Are you referring to all electrons in the metal or just the valence electrons. Are you sure you're dealing with the same electrons all the time? How do you know?. Are these electrons the equivalent to water going through a pipe or are they significantly different? Do they carry kinetic energy? How does that energy get so fast along a wire, when the electrons are only moving at 1mm/s?
    I could go on. :smile:
    Using the word Charge includes all of that (and also includes the conduction of a current by positive ions) You just need to concern yourself with how much charge passes a point in the conductor in a second, to say what the current is. As soon as the rate of change gets high enough (sharp voltage spikes and high frequency AC) the energy does not even pass through the metal at all, but through the empty space around it as a guided wave. There is a so-called Displacement Current involved whenever the E and H fields change in space. No electrons there, at all. If your inbuilt mental model involves electrons then how could you deal with that?

    You are welcome to use any private model that you like but you will find it increasingly difficult to converse about these things if you do not get familiar with the standard approach. Remember that it has stood the test of time and that your simple 'school' model was never invented by mainstream Science. Your model asks more questions than it answers.
  17. Dec 19, 2013 #16
    Yes you may be right I mean I am just considering a metal as a conductor
    Yes and I guess when I wrote the reply I didn't consider electricity due to holes I mean that has always been a big issue for me to consider electricity due to an "absence of charge " and it plays very important role . When I say cloud of electrons I actually must have considered only metal as a conductor and that too I have overlooked other current flowing through that same conductor .
    Mostly I have been simplifying circuits and analyzing them in terms of electrons but this year we were introduced to electromagnetic waves and it has been a big mountain to climb as my basics of waves have been terrible , but now I guess I was thinking or looking at it in different way I guess I was actually imagining a wave passing through but actually it is like if we take output or connect Cro probes in air ( just assuming for simplicity and explanation) and we take the output ( considering it is the path of electromagnetic wave ) then we will get a waveform because it plots the graph of voltage with respect to time . Here I guess I underestimated the "time" because of its use in our life . I was considering as the motion of a wave in air ( or for that matter any other medium ) to be like that of a wave in water ? But I fact it is simple a graph or analysis when respect to time
    Again thanks for the replies guys I will even go through the book mentioned
    Again I don't want to get into scientist and what one did and what one didn't donor anything like that because I am more interested in science than them and science is great because what we think is true now can change the next second if someone is able to prove that false
  18. Dec 19, 2013 #17


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    You a seem to have a good attitude to this. If you are in the early stages of Physics (what am I saying - I mean at ANY stage) you will find things just don't make sense. That goes with the territory. I (lucky for me) learned Electricity without referring to electrons, at an elementary level and all the way up. Occasionally, electrons come into descriptions of particular components (valves, CRTs and transistors) - but they are exceptions and still can be described in terms of their basic electrical behaviour, ignoring the electron aspects.
    If you get obsessed with Electricity as a concrete entity, you will have troubles. As soon as you can start to treat it mathematically you will find another rock to cling on to. That rock will not let you down like some of the simple models in early Science education.
    Waves: The wonderful thing in studies of Waves is that, whatever form the wave takes, the Maths tends to be common to them all. Get the Maths and you have the waves tied up. You can see water waves but you can't see many other forms of wave. But they all behave in the same way. EM wave are a total abstraction but the Equations describe what you can expect from them.

    Stick to the 'academic' stuff and try to avoid 'arm waving' descriptions. Treat all posts (even on PF) with reservations.
    Read read read.
  19. Dec 20, 2013 #18
    A particle is one particle. To make a wave requires at least 2 particles.
  20. Dec 20, 2013 #19
    Sorry... after re-reading your question, the answer is YES, I think you are correct.

    As an aside.... you could talk about time in two different structures. Does a wave form when the time-structures are different, but the point in space is the same?
  21. Dec 20, 2013 #20


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    Were you hinting at the need for a nucleus or some obstacle to reveal the wave nature of electrons (bound or diffracted)?
    But it's a good point. A particle could be said only to be a particle when it interacts with something - at each end of the journey. In between, the energy is / could be spread all over space as a wave. So, introducing your pebble in the pond and causing more intellectual ripples, the particle is always a particle, even when it's a wave.
    Oh the dangers of trying to classify things. The only 'really' in Physics is that PF is really good fun.
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