# I New experiments supporting Bohmian mechanics?

1. Apr 30, 2017

### Sophrosyne

I recently read this article about recent experiments which seems to be resurrecting the idea of a Bohm-deBroglie interpretation of quantum mechanics over the Copenhagen one. Is this legit, or pseudo-science hype?

https://www.wired.com/2014/06/the-new-quantum-reality/

2. Apr 30, 2017

### stevendaryl

Staff Emeritus
I would say that the significance of these experiments for interpretations of quantum mechanics are not understood yet. What they're talking about is a classical analog of Bohmian mechanics. This doesn't prove anything about quantum mechanics, although possibly it could inspire quantum researchers to develop an alternative interpretation.

There is a big technical difference between Bohmian mechanics and this classical analog: In Bohmian mechanics, the "pilot wave" is a wave in configuration space, rather than physical space. The difference doesn't matter if you're talking about a single particle, but for two or more particles, it is a big difference. The two-particle wavefunction $\psi(\vec{r}_1, \vec{r}_2)$ depends on both the position $\vec{r}_1$ of the first particle and the position $\vec{r}_2$ of the second particle. So it is a function on 6-dimensional configuration space--$x_1, y_1, z_1, x_2, y_2, z_2$ rather than 3-dimensional physical space--$x,y,z$. The experiment described in that article explains an analog of Bohmian mechanics in which droplets are moving according to a kind of pilot wave in physical space. So it's not exactly analogous to QM.

3. Apr 30, 2017

### atyy

Hype.

The experiments do nothing for the status of Bohmian Mechanics (which was fine as a conceptual possibility before the experiments).

4. Apr 30, 2017

### vanhees71

I've not even understood why an experiment with macroscopic water waves has created a hype about quantum theory at all. It's a nice classical-wave phenomenon, which is great for the class room (I guess given some effort one can build it up to demonstrate it in the experimental lecture on continuum mechanics ;-)), but has nothing at all to do with quantum theory (except that it's an effective classical description of the fluid which is, of course, finally a quantum system).

5. Apr 30, 2017

### LeandroMdO

This experiment has nothing to do with BM. It's just an analog system with "particles" that happen to follow some kind of wave-like behavior. This is not unusual, nor strange. For example, nobody thinks that quantum mechanics works like this:

6. May 5, 2017

### Flatland

It's just a good visualization of QM and nothing else.

7. May 6, 2017

### oquen

Steve, what is the Bohmian version of the electromagnetic wave.. does it mean photons have positions at all times or the wave function of the electromagnetic wave are real?

8. May 6, 2017

### durant35

Both.

But I believe Steven will give a better and more detailed insight.

9. May 7, 2017

### vanhees71

Photon's don't have a position in the usual sense. They are the quanta which are the least like a classical particle, because they are massless quanta of spin 1. To my knowledge Bohmian mechanics works even less for relativistic QFT than it does for non-relativistic QT.

10. May 7, 2017

### stevendaryl

Staff Emeritus
I have not seen a Bohmian theory of photons. Maybe our resident expert on Bohmian mechanics, @Demystifier, can answer.

11. May 7, 2017

### Demystifier

Have you seen a Bohmian theory of QFT? That includes photons.

12. May 7, 2017

### atyy

But relativistic QED can be simulated by non-relativistic quantum mechanics.

https://arxiv.org/abs/1011.4021
Optical Lattice Hamiltonians for Relativistic Quantum Electrodynamics
Eliot Kapit, Erich J. Mueller

13. May 7, 2017

### vanhees71

So what? How does this substantiate the physics (!!!) content of Bohmian mechanics. I don't see any merit in introducing academic trajectories which cannot be observed to begin with. At least it is a mathematically consistent theory in the case of non-relativistic quantum theory, although adding nothing to standard QM. In the relativistic case, even this seems not to be the case, i.e., it's not even possible to formulate it as a consistent mathematical model.

14. May 7, 2017

### atyy

QED as we know it is an effective theory. Hence if one is interested in QED alone, one can use a high energy theory that is non-relativistic quantum mechanics. Bohmian Mechanics can reproduce non-relativistic quantum mechanics, and thus reproduce QED.

The importance is thus that Bohmian Mechanics is a potential solution of the measurement problem for some relativistic QFTs such as QED.

Whether it is the solution Nature has chosen depends on experiments showing that the predictions of Bohmian Mechanics remain correct even if quantum mechanics is violated.

15. May 7, 2017

### oquen

We need more experiments then. If photons are Bohmians or electromagnetism has substantial existence. Then it has extra prediction not available in the orthodox interpretation where everything is devoid of any substance and they just shout "Shut Up and Calculate!". The extra prediction being that if EM is substantial then it may possible to cause some coherence in it where you should be able to create devices that can extract energy from free vacuum. Something you can't do in orthodox interpretation because there is nothing to extract energy from because you are forced to assume there is no existence of any of it and they just belong to the tools of the shut up and calculate department. Is this a correct observation or I'd appreciate if someone correct me if it may not be right at all.

16. May 7, 2017

### atyy

If you are interested, look up the work of Antony Valentini.

Bohmian Mechanics still has problems though. Although BM can probably reproduce all observations explained by QED, it seems it cannot yet do it for the full standard model.

17. May 7, 2017

### oquen

What is weird about Bohmian Mechanics is that in describing electrons around the nucleus.. it doesn't have trajectories because if it had, the electron can fall to the nucleus after losing the energy by accelerating (via the Bohmian trajectory). So the Bohmian electron only exists when observed and doesn't have trajectories when not observed? How does it differ to the orthodox then?

18. May 7, 2017

### Staff: Mentor

Why do you think the electron's Bohmian trajectory would do this? Remember that the Bohmian trajectory is affected by the quantum potential, which depends on the wave function.

19. May 7, 2017

### oquen

In other words. The electron doesn't lose energy by accelerating and falling down the nucleus because the quantum potential is holding it?

20. May 7, 2017

### Staff: Mentor

Since the electron is in a stationary state with constant energy, that would seem to be what Bohmian mechanics would have to predict, since mathematically it is the same as standard QM.

21. May 7, 2017

### oquen

I looked up Antony Valentini and came across something interesting and puzzling:
http://metanexus.net/essay/when-reality-real-interview-antony-valentini

"Q: You've told me in previous conversations that you feel Bohm's original work on this theory has been misinterpreted. Can you mention that here?

A: Bohm had an interesting trajectory. There are really three Bohms. There's the very early Bohm who was interested in Niels Bohr's ideas about complementarity. Then there's the Bohm of the 1950s who worked on the pilot wave theory of hidden variables. Then in the 1960s he changed again. He met Krishnamurti and got very interested in Indian philosophy and started trying to tag some mystical ideas onto the pilot-wave theory. If you look at the yoga sutras of Patanjali you can see this idea that material objects are somehow illusions and projections from something deeper, that things emerge from this deeper level and disappear into this deeper level again. So Bohm tried to adopt an interpretation of the wave as a manifestation of a deeper level, perhaps associated with consciousness. He called the wave an implicate order and the particle an explicate order."

Dear Bohmian experts or the none so experts. For Bohm 3rd concept about the implicate order.. is it closer to Bohmian Mechanics or Orthodox Copenhagen? I know Bohm implicate order is kinda unallowed here because of its complexity.. but I'm just asking for completion and not implying anything.

22. May 7, 2017

### atyy

I think we should probably ban the 3rd Bohm from PF, on the grounds that those ideas are not physics :)

23. May 7, 2017

### oquen

Is the 3rd Bohm a combination of Bohmian Mechanics and Maldacenia AdS/CFT conjecture.. just wanna have idea why it's not physics. If you combine the BM and AdS/CFT.. isn't it you get the implicate order thing?

24. May 8, 2017

### vanhees71

Non-relativistic theories cannot be high-energy theories, because then the expansion in powers of $1/c$ is not valid anymore. How can BM be a solution of any supposed problem of QT, if there are no other testable predictions than from QT? In the non-relativsitic case BM adds some metaphysical unobservable entities to the theory to solve an apparent metaphysical problem. Fine with me, but it's irrelevant for physics. That there is no problems with measurements is obivous, because the predictions of QT are so far verified by all experiments with very high significance. So the mathematical formalism of QT is very successfully "interpreted" (with the minimal interpretation) to describe what's observed in nature. So there is no problem from a physics point of view.

25. May 8, 2017

### vanhees71

The electron in an energy eigenstate is not accelerated. That's the point of QT vs. the old Bohr-Sommerfeld model! It's a consistent theory and not an ad-hoc assumption on "non-radiating" orbits.