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ajv
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When we observe an electron it is always a localized excitation in the electron field. But when it's not being observed, does the excitation begin to spread through space and become a delocalized excitation?
So sum up what you are saying, the excitation is extended (delocalized) prior to measurement rather than being localized during measurement, right?vanhees71 said:Why should it always be localized? If you don't measure its position by, e.g., puting a detector in its way, it is in general not well localized. For such a measurement there is, given the state of the electron, a probability distribution for its position, not more not less. An electron is the better localized the narrower the position probability distribution is. That's it. According to quantum theory you can't tell more about the electron's position, and it can never be exactly localized at one point, because the position operator has a continuous spectrum.
ajv said:When we observe an electron it is always a localized excitation in the electron field. But when it's not being observed, does the excitation begin to spread through space and become a delocalized excitation?
Ok so if an electron is not being measured in any way shape or form, is it an extended object/ excitation?zhanhai said:I don't quite understand "When we observe an electron it is always a localized excitation in the electron field".
First, it would depend on what is measured. If you are measuring the position of the electron then the statement could be right. If on the other hand you are measuring the energy/momentum of an electron in a crystal, that electron should possibly still be non-localized after the measurement.
Second, it may basically depend on the interpretation of the wave function; is it a characterization of matter distribution of electron? In some mainstream interpretation, it seems that the electron is localized even before it is measured, and what is non-localized is its probability of distribution of measured position; so the statement "When we observe an electron it is always a localized excitation in the electron field" would be wrong by itself.
ajv said:Ok so if an electron is not being measured in any way shape or form, is it an extended object/ excitation?
Electrons (whether measured or not) are almost always extended objects. For the notion of a localized electron is a semiclassical concept that, strictly speaking, makes sense only at sizes bigger than its Compton wavelength. At smaller distances, the intuitive imagination associated with the particle concept breaks down completely, and the only right description is in terms of quantum field theory.ajv said:Ok so if an electron is not being measured in any way shape or form, is it an extended object/ excitation?
A delocalized excitation refers to a phenomenon in which an electron is not confined to a specific location or energy state, but instead exists as a spread-out wave or probability distribution. This is a fundamental concept in quantum mechanics, where particles such as electrons can exhibit both wave-like and particle-like behaviors.
An electron is typically measured using a device called an electron microscope, which uses a beam of electrons to create an image of an object. In this process, the electrons are scattered and their paths can be detected and recorded, providing information about the object's structure and properties.
Before measurement, an electron is in a state of superposition, meaning it exists in multiple possible locations or states simultaneously. This is known as delocalization, as opposed to being localized in a specific position or energy level. Only when the electron is measured does it "collapse" into a definite position or state.
The concept of delocalization is important in quantum mechanics because it helps to explain the behavior of subatomic particles, which do not behave in the same way as larger, classical objects. Delocalized particles can exhibit strange and counterintuitive behaviors, such as being in two places at once or appearing to be in multiple energy states simultaneously.
Delocalized excitations are not limited to electrons; they can also occur in other particles, such as photons (particles of light) and phonons (particles of sound). Other examples include delocalized vibrations in molecules and delocalized charge carriers in solids, such as in metals or semiconductors. The concept of delocalization is also relevant in fields such as chemistry, where it helps to describe the behavior of molecules and chemical bonds.