# How empty is the empty wave?

by San K
Tags: wave
 P: 915 how empty (or filled) is the empty (matter) wave? The de broglie-bohm interpretation posits that: in a single particle double slit experiment, the photon goes through one of the slits/paths and the matter waves go through both the slits. the path without the photon and just the matter wave has, for convenience, been labelled as empty wave. Also it is generally imagined that the empty wave has no energy or momentum. why is that so? however does this not contradict with some of the below observations: - the empty wave (travelling the other path) effects the behaviour/path of the photon. Is not some form of energy required to effect the path of the photon? - the empty wave is blocked by opaque obstacles however it passes through transparent obstacles. if it was just a probability wave, why would it get effected by an opaque object but not a transparent object. the matter wave passes through the same obstacles that a photon would pass through and gets blocked by the same obstacles that a photon would get blocked by. therefore its properties are similar to that of a photon off track question (and I have asked this before but the response was weak): Does the matter wave of a photon interact with the matter wave of an electron? the above, i guess, must be easy to test experimentally.
 P: 4 First, the empty wave has no energy because it isn't mass. It is only the probability that the mass will exist. Second, the energy that determines the path is generated by the observation. This is a mechanical aspect of quantum physics that is not known. I think it is created from the electromagnetic field generated by the neurons in our body.
P: 4,638
 Quote by San K Also it is generally imagined that the empty wave has no energy or momentum. why is that so?
Because the empty wave is not directly observable. If you wished you could ascribe energy and momentum to the empty wave, but these would be unobservable energy and momentum.

 Quote by San K - the empty wave (travelling the other path) effects the behaviour/path of the photon. Is not some form of energy required to effect the path of the photon?
Not necessarily. This would be required in classical mechanics, but Bohmian mechanics is not classical mechanics.

 Quote by San K - the empty wave is blocked by opaque obstacles however it passes through transparent obstacles. if it was just a probability wave, why would it get effected by an opaque object but not a transparent object.
In Bohmian mechanics, the wave is certainly much more than a probability wave. It is a pilot wave.

 Quote by San K Does the matter wave of a photon interact with the matter wave of an electron?
Definitely, yes. This interaction is described by quantum electrodynamics.

PF Gold
P: 698
How empty is the empty wave?

 Quote by San K - the empty wave (travelling the other path) effects the behaviour/path of the photon. Is not some form of energy required to effect the path of the photon? - the empty wave is blocked by opaque obstacles however it passes through transparent obstacles. if it was just a probability wave, why would it get effected by an opaque object but not a transparent object. the matter wave passes through the same obstacles that a photon would pass through and gets blocked by the same obstacles that a photon would get blocked by. therefore its properties are similar to that of a photon
Arguing against Bohm's "active information" hypothesis, Peter J. Riggs (a supporter of Bohmian mechanics) has suggested that there is energy transfer between field and particle that is really one system:
 It would seem suitable at this juncture to consider whether we might be looking at this problem from the wrong perspective. The discussion so far has been treating wave field and particle as separate but interacting entities for the purposes of the Third Law (like a charged particle in an external electric field). They are not, of course, separate entities and this needs to be taken into account. Equations 13 and 15 together indicate that the energy exchanges between particle and wave field are related to changes in the shape of the wave field. One part of a quantum system merely responds to changes in another part of the system without this being of a classically expected kind. It must be remembered that what is occurring in the quantum case are changes in a single entity.
Reflections on the deBroglie–Bohm Quantum Potential
http://www.tcm.phy.cam.ac.uk/~mdt26/...riggs_2008.pdf

A criticism of Rigg's approach can be found here:

The Causal Theory revisited
http://itf.fys.kuleuven.be/~ward/doc...view-riggs.pdf

This an interesting but not very clear quote from Bohm's paper on what happens to the "empty" waves after interaction:
 While it is clear that what is automatically called the measurement process has thus been given an overall causal and objective description, one may nevertheless ask what is the meaning of all the "empty" wave packets (i.e., those not containing particles). Those still satisfy Schrödinger’s equation, but are nevertheless permanently inactive, in the sense that they never manifest themselves in the movements of the particles at all. Such packets seem to be floating, almost like wraiths in a strange multi-dimensional world... What do all these “empty” packets signify in the causal interpretation?...As long as the measuring apparatus interacts reversibly with the classical system, channels that are inactive with regard to the particles are still potentially active. But as soon as the irreversible interaction with the registration device takes place, the channels not containing particles are permanently inactive. In the usual language, we would say that the information has been “lost”, but as with the diffusion of ink particles, it has merely ceased to be capable of acting in the manifest domain.
An Ontological basis for the quantum theory
http://www.tcm.phy.cam.ac.uk/~mdt26/...yerou_1986.pdf
 P: 22 I have a question I am struggling to understand how a photon becomes polarized.In this model what changes when a photon is polarized?
P: 915
 Quote by Demystifier Definitely, yes. This interaction is described by quantum electrodynamics.
thanks Demystifier and Bohm2

separate/aside question:
why/how does the need for non-locality arise in the DBB interpretation?
P: 4,638
 Quote by derek101 I have a question I am struggling to understand how a photon becomes polarized.In this model what changes when a photon is polarized?
The photon wave function has two components corresponding to two orthogonal polarizations. Both components together determine how the photon will move, so the motion of the photon depends on polarization of the wave function.
P: 915
 Quote by Demystifier Not necessarily. This would be required in classical mechanics, but Bohmian mechanics is not classical mechanics.
on a separate note:
why/how does the need for non-locality arise in the DBB interpretation?
P: 4,638
 Quote by San K on a separate note: why/how does the need for non-locality arise in the DBB interpretation?
The velocity of any particle at a given time depends on the positions of all other particles (entangled with the first particle) at the same time.
P: 915
 Quote by Demystifier The velocity of any particle at a given time depends on the positions of all other particles (entangled with the first particle) at the same time.
is DBB assuming that the velocity of the photon/particle is not constant?

classical mechanics would say that speed of light remains constant (in all frames of reference and all mediums)
P: 4,638
 Quote by San K is DBB assuming that the velocity of the photon/particle is not constant? classical mechanics would say that speed of light remains constant (in all frames of reference and all mediums)
True, but Bohmian mechanics is not classical mechanics.
P: 915
 Quote by Demystifier True, but Bohmian mechanics is not classical mechanics.
why does Bohmian Mechanics assume that velocity of photon is varying when all the experimental data at any point in time and space throughout the experiment matches exactly with the fact that speed of light is constant.

what (assumption, explanation, bridging of logic) is Bohemian Mechanics trying to prove/achieve by assuming that speed of photon varies?
P: 4,638
 Quote by San K why does Bohmian Mechanics assume that velocity of photon is varying when all the experimental data at any point in time and space throughout the experiment matches exactly with the fact that speed of light is constant. what (assumption, explanation, bridging of logic) is Bohemian Mechanics trying to prove/achieve by assuming that speed of photon varies?
What is constant is the propagation-velocity of the front of the photon WAVE. But inside the wave packet, the velocity of the photon POINT-PARTICLE may be different. Moreover, it must be different in order to explain interference fringes in terms of particle trajectories. In fact, a recent weak MEASUREMENT of photon particle trajectories confirmed that average photon particle velocities are not constant, but equal to those predicted by Bohmian mechanics:
http://www.physicsforums.com/blog.php?b=3077
P: 915
 Quote by Demystifier What is constant is the propagation-velocity of the front of the photon WAVE. But inside the wave packet, the velocity of the photon POINT-PARTICLE may be different. Moreover, it must be different in order to explain interference fringes in terms of particle trajectories. In fact, a recent weak MEASUREMENT of photon particle trajectories confirmed that average photon particle velocities are not constant, but equal to those predicted by Bohmian mechanics: http://www.physicsforums.com/blog.php?b=3077
Good point Demystifier...thanks for clarifying.

Is there a statistical distribution (for the velocities) per the equations under Bohmian framework?