Waves and Particles, help me

[Ashish]

Hi everybody

 

Well I'm ashish from INDIA (Chhattisgarh,RAIPUR). I'm final year Engineering student from Information Technology branch.

When I was in 12th standard, at that time Physics was my favorite subject and till now. But when I studied physics in the foundation course of first year really I used to get confused by quantum meshanics, there used to be so much of problems regarding that what should I think Light as a wave or a particle.

And I have come up to a thought that there is nothing like a wave and its just a way of represention of various physical phenomenon

So from that time I have a very great enthusiasm about Quantum Mechanic and Modern Physics. For that I started referring to various type of books related to modern physics and Quantum Mechanics and even also Internet. And a few days are happening I've joined this http://www.scienceforum.net, and I've posted few threads regarding to which I used to have doubts and I'm thankful to various members for their reply, am I in the right direction or what please help me.

[Klaynos]

I think the problem you're having is one that most people come across alot of the time with QM...

 

And it's mostly a problem that in our every day world, something is either a particle, like a book, or a wave, like sound. So we have from quite an early age a fixed idea in our head of what a particle and what a wave are.

 

Now with quantum mechanics we come across situations where everything falls into both of these groups, but we still like to label them either wave or particle, this is partially a problem that our language is not equiped to describe something that is neither wave nor particle yet at the same time appears to be both a wave and a particle... And partially a problem of conditioning where we're taught until we're quite old that everything is either one or the other... Ask any 15 year old "is an electron a wave or a particle" and they will answer particle...

[Ashish]

But from the day I've learned about QM I think that there is nothing like a wave.

[Klaynos]

But we can do experiments that clearly show wave properties.

 

Young's two slit experiment being the classic example.

 

You cannot get the same effect if you assume everything is particles.

[thedarkshade]

Hey Klaynos, could you recommend a web site, pfd download or a good book where I could get a real detailed sense of QM? I'm thinking of something, and just want to find out!

 

That'd be really appreciated!

 

Thnx

[Klaynos]

I can recommend 3 things:

 

wikipedia, a good basic place to start...

hyperphysics: http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html I'd say this is generally more to the point and easier to follow than wikipedia, but far less wordy. It goes up to about first year undergraduate.

 

As for books, I would recommend Quantum Mechanics by Alastair I M Rae, published by the institute of physics. It's aimed at undergraduate physicists. It's in depth and informative.

[thedarkshade]

Thanks Klaynos, I'll just run to amazon to buy it!

 

Cheers!

[Severian]

Hmm... I don't like Rae's book at all (although it is sitting on my shelf). This is mainly because I think it makes quantum mechanics seem too complicated.

 

In reality, QM is pretty simple if you stop thinking of things as particles and think of everything as a wave instead. Particles are really just very tightly focused wave-packets.

[Mr Skeptic]

Big things can be a particle (like a grain of sand, etc), or a wave (like sound or water waves). Small enough things are all wavicles, which look either like a wave or a particle depending on what attribute you are looking at.

[DrP]

I'll have to say that Klaynos is right about the Youngs double slit experiment. It is excellent for explaining how an electron travells as a wave and hits as a particle. It is the definitive explanation of wave-particle duallity.

[vagrant51]

"wave-particle duality" is a slightly vague term; it makes sense though if you consider that quantum particles are probabilistic.

 

the way to understand it is that an electron only exists in a defined place when it is being observed, and when it isn't, it is defined only by the probability of its being observed in every place in which it can exist. we say "wave" because the probability, or "wavefunction," changes like a wave moves, and we say "particle" because the electron acts like a particle when it is being observed.

 

as feynman put it, an electron is not a physical object like a brick, but a concept like "the inside of a brick."

[stevo247]

In reality, QM is pretty simple if you stop thinking of things as particles and think of everything as a wave instead. Particles are really just very tightly focused wave-packets.

 

When you say that "particles are really just very tightly focused wave-packets", is that due to the nature of the form of the wave? What kind of wave would form a "wave-packet"?

[5614]

It [double slit experi] is excellent for explaining how an electron travells as a wave and hits as a particle.

Yes, but they never behave as a wave and a particle at the same time. Mind, I once read of an experiment which claimed to show something acting as a wave and a particle at the same point. Although I think the commonly accepted view is that a "thing" is either a wave or a particle, it behaves as one or the other, but never both at the same instant.

 

When you say that "particles are really just very tightly focused wave-packets", is that due to the nature of the form of the wave? What kind of wave would form a "wave-packet"?

Travelling waves can be combined in any way, one combination results in wave packets being produced, see:

http://hyperphysics.phy-astr.gsu.edu/hbase/waves/wpack.html

 

I couldn't find a better image online, but here is an example of the above:

two travelling waves combine to form a wave packet. Now imagine if the wave packets were smaller, the distance between them bigger etc. (or if you were looking at the image from a long way away) it would seem like dense areas of wave, with spaces inbetween, i.e. it would look like particles. Does that help you to understand how a particle can be expressed as a wave packet?

 

[edit] See here:

http://dspace.mit.edu/html/1721.1/35749/1-138JFall-2000/OcwWeb/Civil-and-Environmental-Engineering/1-138JWave-PropagationFall2000/Simulations/detail/groupvel.htm

(wait for the image to load)

[thedarkshade]

I couldn't find a better image online, but here is an example of the above

I don't know if this would apply:

and it tells the interference!

[antimatter]

So if someone asks me whether a photon is a wave or particle, I should say both?

And what about electrons?

 

I usually say an electron is a wave, am I wrong?

[Klaynos]

So if someone asks me whether a photon is a wave or particle, I should say both?

And what about electrons?

 

I usually say an electron is a wave, am I wrong?

 

Electrons are also both

 

As are well everything really, the more massive the object the harder it is to show this, but buckminster fullerene have been shown to be waves and they're BIG!

[antimatter]

I'm really sorry, but I'm not entirely sure what a buckminster fullerene is

[stevo247]

two travelling waves combine to form a wave packet.

 

So the wave aspect of light, and the particle aspect of light, is due to the superimposition of two different waves?

[Klaynos]

An object made up of 60 carbon atoms... in a spherical shape...

 

http://en.wikipedia.org/wiki/Fullerene#Buckyballs

 

BIG!

[antimatter]

How does that form?

[iNow]

antimatter,

 

Have you spent any time researching these ideas for yourself? Much of your question is answered in the link Klaynos shared above. If that wasn't enough, maybe try here:

 

http://en.wikipedia.org/wiki/Chemistry

[Klaynos]

antimatter,

 

Have you spent any time researching these ideas for yourself? Much of your question is answered in the link Klaynos shared above. If that wasn't enough, maybe try here:

 

http://en.wikipedia.org/wiki/Chemistry

 

Or even better...

 

http://en.wikipedia.org/wiki/Quantum_physics

[5614]

thedarkshade: I was looking for an image showing two travelling waves combining to form a distinct wave packet. Similar to what I had in my image, but I wanted a more exagerated version, to make the point as clear as possible.

 

So if someone asks me whether a photon is a wave or particle, I should say both?

When asked if something is a wave or a particle many physicists would answer both. But equally correctly you could answer neither. If something is a wave, then by the classical definitions, it cannot also be a particle. Clasically they are distincy and seperate things. Consequently saying something is "both" can be a bit confusing, sometimes. If you say it is neither a wave, nor a particle, but is in fact a third 'thing', which somehow combines both wave and particle properties in one, then you'll be getting at the right thing.

 

And this applies to everything. Generally things on a smaller scale will display both properties. As you know photons and electrons behave like particles when they collide with things, but will both diffract through a slit like a wave. Whereas something like humans always behave like particles, you couldn't observe a human diffracting through a double slit!

 

I'm really sorry, but I'm not entirely sure what a buckminster fullerene is

The reason the whole fullerene thing came up is because fullerene, which is 60 carbon atoms, is big. Yet fullerene has been observed to diffract through a double slit, just like a wave. I believe it's the biggest thing to have been diffracted through a double slit, and have the resulting dark / bright fringes observed.

 

So the wave aspect of light, and the particle aspect of light, is due to the superimposition of two different waves?

No. If you think of a particle's wave property as a probability wave, then a wave packet would be where the particle is most likely to be found. The travelling waves combining to form a wave packet was just an example of how a wave packet could be formed in a mathematical way.

[DrP]

thedarkshade:

When asked if something is a wave or a particle many physicists would answer both. But equally correctly you could answer neither. If something is a wave, then by the classical definitions, it cannot also be a particle. Clasically they are distincy and seperate things. Consequently saying something is "both" can be a bit confusing, sometimes. If you say it is neither a wave, nor a particle, but is in fact a third 'thing', which somehow combines both wave and particle properties in one, then you'll be getting at the right thing.

 

 

I always say it TRAVELS as a wave and HITS as a particle - which it does.

[antimatter]

antimatter,

 

Have you spent any time researching these ideas for yourself? Much of your question is answered in the link Klaynos shared above. If that wasn't enough, maybe try here:

 

http://en.wikipedia.org/wiki/Chemistry

 

I have actually spent some time on this, I just needed some other opinions from people, I know it comes off like I haven't researched it at all though