An electron's wave properties?

[jse7]

As an electron travels through space, is it spacially spread apart to travel in as a wave? Over how many wavelengths is an electron spread as it travels along the wave path through space?

Same question for a photon.
Thanks for any help.

 

[jse7]

sorry it is supposed to be "is it spacially spread apart to travel as a wave?"

 

[Crosson]

To clarify any confusion, electrons are point-like particles and they are never "spread out".

In quantum mechanics every electron is associated with a wavelength, but every electron that has ever been detected was a particle .

 

[jse7]

point particle?

I don't understand, how can a point particle travel as a wave, wouldn't it be more like a string? How does a point particle overcome a potential energy barrier? Also, if the electron is a point particle traveling in a wave path, why can't its position be known absolutely?

 

[dextercioby]

I don't understand, how can a point particle travel as a wave, wouldn't it be more like a string?

Actually, it always travels as a particle, it's just that in certain conditions it stops behaving like a classical particle anymore and more like a "quantum particle", i.e. it has wavelike behavior.

How does a point particle overcome a potential energy barrier? Also, if the electron is a point particle traveling in a wave path, why can't its position be known absolutely?

In principle, the electron's position can be known with arbitrary accuracy.

 

[jse7]

What wave-like behaviors does a quantum particle have? Does it have a definitive location/coordiante, dimensions? Why, why not?

 

[Moridin]

Here is a brief description of the underlying reason as to why electrons can sometimes be though of having wave properties.

In classical physics, an electron is a point-like particle as said above and have all the properties we classically associate with an electron. When we look at a subatomic scale, there is a problem. If an electron was a point-like particle orbiting the nucleus due to centripetal force, why didn't it simply emit energy due to acceleration and crash into the nucleus? If it did, that would mean that the world as we know it wouldn't exist. As a result of actual existence of the world as we know it must mean that we cannot treat the electron as a point-like particle in this situation. Also, the classical description didn't describe why there can only be discrete energy levels of an electron in a nucleus.

Quantum mechanics explains both. The reason that there is only discrete energy levels is because that is the only time that the orbit of the electron is equal to its quantum mechanical wavelength times a constant 1,2,3... forming a standing wave. If electrons have wave-like properties at this level, the entire issue goes away.

However, this description is perhaps too simplified. There is a post in the General Physics forums sticky called Physics FAQ that covers it more exhaustively.

 

[jse7]

An electron doesn't crash into a nucleus because a complete wave path can only exist within certain radii, right?

But whatever an electron is doing around an atom, it doesn't explain my original question. It seems that an electron can't exist as a point because it wouldn't be bound by certain wave paths (when it transitions from one quantum level to the next), and thus would crash into the nucleus of an atom.

Which brings me back to my original question, essentially is an electron spatially spread out? After all mass is energy, right? If it is, over what distance (one wavelength, two)?

 

[jtbell]

What wave-like behaviors does a quantum particle have?

You can produce diffraction and interference patterns with beams of particles, just like you can with light and other waves. Furthermore, you can build up these patterns one particle at a time. See this article for an example:

http://physicsweb.org/articles/world/15/9/1

Note especially the pictures near the bottom of the page.

 

[Schrodinger's Dog]

What wave-like behaviors does a quantum particle have? Does it have a definitive location/coordiante, dimensions? Why, why not?

It's best not to consider a photon a wave or a particle but as a warticle, ie something that has the attributes of both. As jtbell says if you look at slit experiments - especially Feynman's two slit - you'll see what he means. It'll make it clearer, if not easier to grasp.

That article and this website is where I first got to grips with the idea, both are excellent.

http://www.upscale.utoronto.ca/GeneralInterest/Harrison/DoubleSlit/DoubleSlit.html"