Neutron interferometer

Lubos Motl:

You have completely misunderstood the neutron gravitational interference experiment. They showed that the force acting on the neutron is simply not negligible. Quite on the contrary, these interference experiments could measure and did measure the gravitational acceleration – and even the tidal forces – on the phase shift of the neutron’s wave function. It’s the very point of these experiments.

So whatever theory predicts that such forces are “negligible” is instantly falsified.


From Wikipedia

In physics, a neutron interferometer is an interferometer capable of diffracting neutrons, allowing the wave-like nature of neutrons, and other related phenomena, to be explored.
Interferometry inherently depends on the wave nature of the object. As pointed out by de Broglie in his PhD-thesis, particles, including neutrons, can behave like waves (the so called wave-particle duality, now explained in the general framework of quantum mechanics). The wave functions of the individual interferometer paths are created and recombined coherently which needs the application of dynamical theory of diffraction. Neutron interferometers are the counterpart of X-ray interferometers and are used to study quantities or benefits related to thermal neutron radiation.

Neutron interferometers are used to determine minute quantum-mechanical effects to the neutron wave, such as studies of the

  • Aharonov-Bohm effect
  • gravity acting on an elementary particle, the neutron
  • rotation of the earth acting on a quantum system

they can be applied for

Like X-ray interferometers, neutron interferometers are typically carved from a single large crystal of silicon, often 10 to 30 or more centimeters in diameter and 20 to 60 or more in length. Modern semiconductor technology allows large single-crystal silicon boules to be easily grown. Since the boule is a single crystal, the atoms in the boule are precisely aligned, to within small fractions of a nanometer or an angstrom, over the entire boule. The interferometer is created by carving away all but three slices of silicon, held in perfect alignment by a base. (image) Neutrons impinge on the first slice, where, by diffraction from the crystalline lattice, they separate into two beams. At the second slice, they are diffracted again, with two beams continuing on to the third slice. At the third slice, the beams recombine, interfering constructively or destructively, completing the interferometer. Without the precise, angstrom-level alignment of the three slices, the interference results would not be meaningful.

Only recently, a neutron interferometer for cold and ultracold neutrons was designed and successfully run. As neutron optical components in this case three artificial holographically produced, i.e., by means of a light optic two wave interference setup illuminating a photo-neutronrefractive polymer, gratings are employed.


V. F. Sears, Neutron Optics, Oxford University Press (1998).
H. Rauch and S. A. Werner, Neutron Interferometry, Clarendon Press, Oxford (2000).


On the Origin of Gravity and the Laws of Newton

Starting from first principles and general assumptions Newton’s law of gravitation is shown to arise naturally and unavoidably in a theory in which space is emergent through a holographic scenario. Gravity is explained as an entropic force caused by changes in the information associated with the positions of material bodies. A relativistic generalization of the presented arguments directly leads to the Einstein equations. When space is emergent even Newton’s law of inertia needs to be explained. The equivalence principle leads us to conclude that it is actually this law of inertia whose origin is entropic.


The Neutron Interferometry and Optics Facility (NIOF) located in the NIST Center for Neutron Research Guide Hall is one of the world’s premier user facilities for neutron interferometry and related neutron optical measurements. A neutron interferometer (NI) splits, then recombines neutron waves. This gives the NI its unique ability to experimentally access the phase of neutron waves. Phase measurements are used to study the magnetic, nuclear, and structural properties of materials, as well fundamental questions in quantum physics. Related, innovative neutron optical techniques for use in condensed matter and materials science research are being developed.


Neutron Interferometer. A three blade neutron interferometer, machined from a single crystal silicon ingot is shown in two views. A monoenergetic neutron beam is split by the first blade and recombined in the third blade. If a sample is introduced in one of the paths, a phase difference in the wave function is produced, and interference between the recombined beams causes count rate shifts of opposite sign in the two detectors.
The Neutron Interferometer Facility in the Cold Neutron Guide Hall became operational in April 1994. It became available as a National User Facility in September 1996. Phase contrast of up to 88 percent and phase stability of better than five milliradians per day were observed. These performance indications are primarily the result of the advanced vibration isolation and environmental control systems. The interferometer operates inside a double walled enclosure, with the inner room built on a 40,000 kg slab which floats on pneumatic pads above an isolated foundation.

See AlsoGravity is Entropy is Gravity is…

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7 Responses to Neutron interferometer

  1. Javier says:

    Sorry, but you have searched or the wrong experiments. The experiments Lubos is talking are relatively recent (around 2003, but I am not sure bout it). The idea behind them is quite simple. The gravitatory potential in the nearby of earth surface is V=mgh. Well, do ordinary Q.M for that potential and you get that the energy is quantized in a precise way (The problem even is analitically solvable). The great thin is that you can measure that energy levels separation in a experiment using neutrons (because they are neutral, that is). That is what I know (I read the articles): I don´t know what he says about phases, but I bet that he knows what he is talking about ;):

  2. Plato says:

    Javier,Can you link the specific articles?Thank you for responding . Best

  3. PlatoHagel says:

    Javier,Can you link the specific articles?Thank you for responding . Best

  4. Click here, i believe that's it, yes Javier?It took me while to find that, it's much older than I thought it was. So much has been happening lately!

  5. Javier says:

    That neutron experiments were not made to disprove that gravity as an entropy force (although they can put , a posteriori, be used to put some bounds on that kind of idea, or maybe rule hem if I understand right the point of Lubos). Simply they were earlier that this entropic forces fashion (b.t.w. as lubos says smoot idea and verlinde idea are quite different). A quick search has taken me to an entry in backeaction. I think that sabbine will link the original articles.

  6. Plato says:

    This is an interesting comment to me, yet, I would have to say that I can not put my finger on it.The fundamental issue is that for the last 25 years, physicists have been working at the 100,000 ft level and not at the 100 or 10 ft level. Verlinde's paper is a symptom, not a disease.Entropic Everything

  7. PlatoHagel says:

    This is an interesting comment to me, yet, I would have to say that I can not put my finger on it.The fundamental issue is that for the last 25 years, physicists have been working at the 100,000 ft level and not at the 100 or 10 ft level. Verlinde's paper is a symptom, not a disease.Entropic Everything

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