The reality of the wavefunction

If you haven’t read any of my previous posts on the geometry of the wavefunction (this link goes to the most recent one of them), then don’t attempt to read this one. It brings too much stuff together to be comprehensible. In fact, I am not even sure if I am going to understand what I write myself. đ [OK. Poor joke. Acknowledged.]

Just to recap the essentials, I part ways with mainstream physicists in regard to theÂ interpretationÂ of the wavefunction. For mainstream physicists, the wavefunction is just some mathematical construct. NothingÂ real. Of course, I acknowledge mainstream physicists have very good reasons for that, but… Well… I believe that, if there is interference, or diffraction, thenÂ somethingÂ must be interfering, or something must be diffracting. I won’t dwell on this because… Well… I have done that too many times already. MyÂ hypothesisÂ is that the wavefunction is, in effect, aÂ rotatingÂ field vector, so itâs just like the electric field vector of a (circularly polarized) electromagnetic wave (illustrated below).

Of course, it must be different, and it is. First, theÂ (physical) dimension of the field vector of the matter-wave must be different. So what is it? Well… I am tempted to associate the real and imaginary component of the wavefunction with a forceÂ per unit massÂ (as opposed to the force per unit charge dimension of the electric field vector). Of course, the newton/kg dimension reduces to the dimension of acceleration (m/s2), so thatâs the dimension of a gravitational field.

Second, I also am tempted to think that this gravitational disturbance causes an electron (or any matter-particle) to move about some center, and I believe it does so at the speed of light. In contrast, electromagnetic waves doÂ notÂ involve any mass: theyâre just an oscillatingÂ field. Nothing more. Nothing less. Why would I believe there must still be some pointlike particle involved? Well…Â As Feynman puts it: âWhen you do find the electron some place, the entire charge is there.â (FeynmanâsÂ Lectures, III-21-4) So… Well… That’s why.

The third difference is one that I thought of only recently: theÂ planeÂ of the oscillation cannotÂ be perpendicular to the direction of motion of our electron, because then we canât explain the direction of its magnetic moment, which is either up or down when traveling through a Stern-Gerlach apparatus. I am more explicit on that in the mentioned post, so you may want to check there. đ

I wish I mastered the software to make animations such as the one above (for which I have to credit Wikipedia), but so I don’t. You’ll just have toÂ imagineÂ it. That’s great mental exercise, so… Well… Just try it. đ

Let’s now think about rotating reference frames and transformations. If theÂ z-direction is the direction along which we measure the angular momentum (or the magnetic moment), then theÂ up-direction will be theÂ positiveÂ z-direction. We’ll also assume theÂ y-direction is the direction of travel of our elementary particleâand let’s just consider an electron here so we’re moreÂ real. đ So we’re in the reference frame that Feynman used to derive the transformation matrices for spin-1/2 particles (or for two-state systems in general). His ‘improved’ Stern-Gerlach apparatusâwhich I’ll refer to as a beam splitterâillustrates this geometry.

So I think the magnetic momentâor the angular momentum, reallyâcomes from an oscillatory motion in the x– and y-directions. One is theÂ realÂ component (the cosine function) and the other is the imaginary component (the sine function), as illustrated below.Â

So the crucial difference with the animations above (which illustrate left- and a right-handed polarization respectively) is that we, somehow, need to imagine the circular motion isÂ notÂ in theÂ xz-plane, but in theÂ yz-plane. Now what happens if we change the reference frame?

Well… That depends on what you mean by changing the reference frame. Suppose we’re looking in the positive y-directionâso that’s the direction in which our particle is movingâ, then we might imagine how it would look like whenÂ weÂ would make a 180Â°Â turn and look at the situation from the other side, so to speak. Now, I did a post on that earlier this year, which you may want to re-read.Â When we’re looking at the same thing from the other side (from the back side, so to speak), we will want to use our familiar reference frame. So we will want to keep theÂ z-axis as it is (pointing upwards), and we will also want to define theÂ x– andÂ y-axis using the familiar right-hand rule for defining a coordinate frame. So our newÂ x-axis and our newÂ y-axis will the same as the oldÂ x- andÂ y-axes but with the sign reversed. In short, we’ll have the following mini-transformation: (1)Â z‘ =Â z, (2) x’ = âx, and (3) y’ =Â ây.

So… Well… If we’re effectively looking at somethingÂ realÂ that was moving along theÂ y-axis, then it will now still be moving along the y’-axis, butÂ in theÂ negativeÂ direction. Hence, our elementary wavefunctionÂ eiÎ¸Â = cosÎ¸ +Â iÂˇsinÎ¸ willÂ transformÂ intoÂ âcosÎ¸ âÂ iÂˇsinÎ¸ =Â âcosÎ¸ âÂ iÂˇsinÎ¸ =Â cosÎ¸ âÂ iÂˇsinÎ¸.Â It’s the same wavefunction. We just… Well… We just changed our reference frame. We didn’t change reality.

Now you’ll cry wolf, of course, because we just went through all that transformational stuff in our last post. To be specific, we presented the following transformation matrix for a rotation along theÂ z-axis:

Now, ifÂ Ď is equal to 180Â° (so that’s Ď in radians), then theseÂ eiĎ/2Â andÂ eâiĎ/2/â2Â factors areÂ equal toÂ eiĎ/2Â =Â +iÂ andÂ eâiĎ/2Â = âiÂ respectively. Hence, ourÂ eiÎ¸Â = cosÎ¸ +Â iÂˇsinÎ¸ becomes…

Hey ! Wait a minute ! We’re talking about twoÂ veryÂ different things here, right? TheÂ eiÎ¸Â = cosÎ¸ +Â iÂˇsinÎ¸ is anÂ elementaryÂ wavefunction which, we presume, describes some real-life particleâwe talked about an electron with its spin in theÂ up-directionâwhile these transformation matrices are to be applied to amplitudes describing… Well… Either anÂ up– or a down-state, right?

Right. But… Well… Is itÂ so different, really? Suppose ourÂ eiÎ¸Â = cosÎ¸ +Â iÂˇsinÎ¸ wavefunction describes anÂ up-electron, then we still have to apply thatÂ eiĎ/2Â =Â eiĎ/2Â =Â +iÂ factor, right? So we get a new wavefunction that will be equal toÂ eiĎ/2ÂˇeiÎ¸Â =Â eiĎ/2ÂˇeiÎ¸Â =Â +iÂˇeiÎ¸Â =Â iÂˇcosÎ¸ +Â i2ÂˇsinÎ¸ =Â sinÎ¸ âÂ iÂˇcosÎ¸, right? So how can we reconcile that with the cosÎ¸ âÂ iÂˇsinÎ¸ function we thought we’d find?

We can’t. So… Well… Either my theory is wrong or… Well… Feynman can’t be wrong, can he? I mean… It’s not only Feynman here. We’re talking all mainstream physicists here, right?

Right. But think of it. Our electron in that thought experiment does, effectively, make a turn of 180Â°, so it is going in the other direction now !Â That’s more than just… Well… Going around the apparatus and looking at stuff from the other side.

Hmm… Interesting. Let’s think about the difference between theÂ sinÎ¸ âÂ iÂˇcosÎ¸ andÂ cosÎ¸ âÂ iÂˇsinÎ¸ functions. First, note that they will give us the same probabilities: the square of the absolute value of both complex numbers is the same. [It’s equal to 1 because we didn’t bother to put a coefficient in front.] Secondly, we should note that the sine and cosine functions are essentially the same. They just differ by a phase factor: cosÎ¸ =Â sin(Î¸ +Â Ď/2) andÂ âsinÎ¸ =Â cos(Î¸ +Â Ď/2). Let’s see what we can do with that. We can write the following, for example:

sinÎ¸ âÂ iÂˇcosÎ¸ =Â âcos(Î¸ +Â Ď/2) âÂ iÂˇsin(Î¸ +Â Ď/2) =Â â[cos(Î¸ +Â Ď/2) +Â iÂˇsin(Î¸ +Â Ď/2)] =Â âeiÂˇ(Î¸ +Â Ď/2)

Well… I guess that’s something at least ! The eiÂˇÎ¸Â and âeiÂˇ(Î¸ +Â Ď/2)Â functions differ by a phase shiftÂ andÂ a minus sign so… Well… That’s what it takes to reverse the direction of an electron. đ Let us mull over that in the coming days. As I mentioned, these more philosophical topics are not easily exhausted. đ