# Possible alternatives to quantum theory that explain the double slit experiment?

A lot of quantum theory has evolved to explain the double slit experiment with electrons and photons. While fascinated by the quantum concept, I'm just a little skeptical as well. Has anyone encountered a competing theory that also explains the double slit experiment without resorting to particles that act as waves? For example, couldn't the same observations be expected if the particle was traveling through a field, and the observed path was a result of an interference pattern in the field instead of the particle interacting with itself through the slits?

• The QM double-slit thought experiment was first used by Feynman in his Lectures to illustrate what QM is about; Young's actual double-slit experiment just showed that light has a wave nature. QM did not evolve from this experiment, it evolved from the study of black body radiation. See en.wikipedia.org/wiki/History_of_quantum_mechanics. Oct 18 '16 at 8:52
• Comments are not for extended discussion; this conversation has been moved to chat. Please only use comments to improve the question. Oct 18 '16 at 10:48
• In that spirit, are you looking for a different theory or for a different interpretation? Oct 18 '16 at 10:53

There is indeed a different interpretation of quantum mechanics, or if you want, a different approach to interpret the same equations. It's called De-Brogolie-Bohm-Theory or bohmian mechanics or Pilot-Wave-Theory which is an equivalent formulation of standard QM. The essence is that this theory introduces another force-field the so called pilot-wave which is coupled to the particle itself. This force-field is responsible for the wave-like behaviour one encounters in some experiments because it "guides" the particle along its path.

Recently, there have been experiments with oil-droplets that are guided by a similar wave-like interaction, which show that the general results of the double-slit experiment and particles trapped inside a potential-barrier are compatible with their quantum-mechanical counterparts. However, this experiments are clearly on a macroscopic-scale, which previously was believed to be impossible.

Also there are two videos I can recommend watching, to see the experiments in action: click1 and click2

This interpretation doesn't work with quantum-field-theory because QFT is not designed to describe particle movment but rather the dynamics of fields. Only later one introduces particle states that can be made to correspond to what we call a particle. However, if one allows a statistical interpretation of the process of quantization there is the possibility to introduce a similar pictorial view: Particles are statistical excitations of fields. The field's behaviour is wave-like. The exitations/particles are then "guided" by the field-dynamics.

• "QFT is not designed to describe particle movment but rather the dynamics of fields. Particles are statistical excitations of fields." - most elegant explanation, and call to understant QFT I've ever read! I wish there were more of you. Nov 19 '19 at 2:56

While fascinated by the quantum concept, I'm just a little skeptical as well. Has anyone encountered a competing theory that also explains the double slit experiment without resorting to particles that act as waves?

Particles don't act like waves in quantum theory. Particles are emergent properties of the wave function:

https://physics.stackexchange.com/a/237872/28512

For example, couldn't the same observations be expected if the particle was traveling through a field, and the observed path was a result of an interference pattern in the field instead of the particle interacting with itself through the slits?

That theory already exists. It is commonly called the pilot wave interpretation of quantum mechanics. It is described as an interpretation of quantum mechanics, but it really an alternate theory that in principle may make different predictions.

The pilot wave theory has severe problems. First, it puts particles on top of the wave function so it is more complex than quantum theory. It also does not explain anything that is not already explained by quantum theory:

Second, it has problems with relativity, like all 'realistic' theories that try to match quantum mechanics (i.e. - theories in which all measurable quantities are represented by a stochastic variable):

• Actually, pilot-wave theory has the same set of equations as standard QM. Both theories predict exactly the same, since both rely on the same equations. As long as you don't consider field theories but particle theories (that is standard QM), there is no difficulty regarding relativity. In fact, Klein-Gordon's equation and the Dirac-equation can be interpreted in much the same way as Schrödinger's equation. See for example: journals.aps.org/prl/abstract/10.1103/PhysRevLett.52.2009 Oct 18 '16 at 13:41
• The particles do not have the same equation of motion as the wave function or there would be no point in adding them. The fact that they have a different equation of m0tion is illustrated by the fact that they can have probability distributions different from the born rule arxiv.org/abs/1103.1589. Oct 18 '16 at 15:24
• QM $\Leftrightarrow$ $(-\frac{\hbar^2}{2m}\Delta+V(\vec{r}))\Psi(\vec{r},t) = i \hbar \partial_t \Psi(\vec{r},t)$ with Ansatz: $\Psi(\vec{r,t}) = R(\vec{r},t)\exp\left(\frac{S(\vec{r},t)}{\hbar}\right) \Leftrightarrow$ $(1) \dot{\vec{p}} = \vec{F} - \vec{\nabla} Q \textrm{ and } (2) \frac{\partial R^2}{\partial t} + \vec{\nabla} \cdot \left(\frac{\vec{p}}{m} \cdot R^2\right) = 0$ with $Q = -\frac{\hbar^2}{2m} \frac{\Delta R}{R}$ $\Leftrightarrow$ Bohmian mechanics. The equivalance holds in any direction. Oct 18 '16 at 16:08
• The equations you cite assume that the particles are in equilibrium with the wave function. If you don't assume that you can get different predictions until the particles come into equilibrium as explained in the paper I linked. And that's basically the only existing hope for the pilot wave theory to be interesting cuz otherwise it's just quantum mechanics with unnecessary sprinkles. Oct 18 '16 at 21:28
• Well, if you impose some additional assumptions on the pilot-wave to make it "interesting" and then get difficulties, probably those assumptions should be dropped. Also, if bohmian mechanis would never be more than standard-QM there is still an advantage that is underestimated quite often. It gives a pictorial view of QM-effects and as such is more accessible to intuition. Oct 18 '16 at 22:15

As @innisfree says in his comment

I don't think we need to be quite so defensive when people ask questions about established theories in physics. If the question isn't interesting to you, don't upvote it. If it's really bad question, downvote it. But don't feel obligated to offer hyperbolic defenses of QM just because alternatives to QM are mentioned.

To your question, yes there is alternative view (of mine) and it is similar (better in German kongruent) to your thoughts. There has to be an interaction between edges and photons and that should be described by their electric common field. This field has to be quantized and by this the deflection of the photons is not equally distributed. The manifestation of this is the intensity distribution, called fringes.

My similar question "Can the intensity distribution behind edges and slits be explaint by the interaction with the surface electrons of the edges?" see here.

• Please also see my following comment, chat.stackexchange.com/transcript/message/32985201#32985201 Oct 18 '16 at 11:19
• 'OK, I didn't mean to open the floodgates and turn this (or any part of PSE) into a forum for discussing fringe ideas about QM. Maybe the first reactions (defending QM) were the best ones and I made a mistake.' Oct 18 '16 at 11:20
• My son is an aspiring Physicist (currently in high school), and we have very interesting chats about things like this. I'm trying to teach him about Scientific Skepticism, but I'm finding my ancient Engineering training to be deficient in these matters. So, thank you folks! This is a great pointer to more information. And I enjoy reading 'contentious' comments, so feel free to keep discussing! Oct 19 '16 at 16:55
• There are good reasons that progress, whether scientific or not, often only happens a generation at a time - as prior generations resist having their thinking challenged, or are unable to defend it with logic and so resorts to ridicule, withdrawal of funding, etc. Nov 19 '19 at 3:06