In quantum field theory, all particles are "excitations" of their corresponding fields. Is it possible to somehow "measure" the "value" of such quantum fields at any point in the space (like what is possible for an electrical field), or the only thing we can observe is the excitations of the fields (which are particles)?

  • 4
    $\begingroup$ Does the electromagnetic field count? $\endgroup$ – probably_someone Dec 11 '18 at 0:17
  • 1
    $\begingroup$ Notice that technically you can't even measure classical fields (what you measure are the forces and the equation of motion). $\endgroup$ – gented Mar 17 at 3:30

You're asking about a central question in QFT, the "measurement problem."

The wave function calculates the quantum field at any point. But the calculation does not tell us the strength of the field. It tells us the probability of detecting (measuring) a particle.

For example, let's say that we're talking about the electromagnetic field and the calculation is for predicting the likelihood of detecting a photon in a particular position. Here's an image of the relationship of the quantum field to the particle: Red grid represents quantum field; Green film represents particles in spacetime.

The red grid graphs the wave function's calculation of the probabilities that a particle will be detected. The green film shows where a photon has actually been measured in spacetime. In this sequence, its path has been measured in 4 positions.

This image is a still from an excellent 5-minute film by Fermilab on QFT 3. It addresses your question. Also, see this article on measurement in quantum mechanics in an encyclopedia for laypeople which addresses this issue in straightforward terms.

  • 1
    $\begingroup$ Unfortunately, this answer appears to try address a different question than the one that is being asked. $\endgroup$ – Peter Kravchuk Mar 17 at 4:13

Your Answer

By clicking "Post Your Answer", you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.