What is the difference between wave and particle?

asperger

Hi,

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?

Some simple examples may help me understand this.

Thanks in advance.

CompuChip

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.

Naty1

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"

Bob Donatelle

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 .

BruceW

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.

BruceW

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.

CJames

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.

ZealScience

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.

Richard Sneed

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