Manipulating the Quantum Vacuum

As always when I read quantum optics papers, I'm struck by the distance between experimental reports and textbook elementary theory. I suppose the quantized electromagnetic field is being used, with a PoincarГ© invariant vector |0вЊЄ, and squeezed states are something of a variation of coherent states that are theoretically described by the action of an exponentiated quadratic creation and annihilation operators, which one can see here. [For such a theory fluctuations of the EM field are clearly expected in the vacuum state, but they do not represent "energy" (which is not a measurable local variable; the vacuum vector is the unique eigenvector corresponding to the minimum eigenvalue of the Hamiltonian -- a squeezed state has higher energy than the vacuum state), nor do fluctuations represent photons coming in and out of existence (photons, at least by the Wigner definition, are also not local objects).]

For the experimentalist, however, the squeezed states are produced in this case by a crystal: "12-fs near-infrared (NIR) pump pulse (red/yellow envelope) and mid-infrared (MIR) vacuum fluctuations (green band; with amplitude О"Evac) co-propagate into a generation crystal (GX) with second-order nonlinearity". It's only by having something like a specific type of crystal available that a squeezed state can be prepared.

Measurement of the state is as esoteric (in the sense that it is distant from an operator-acting-on-Hilbert-space description), for which "A 6-fs probe pulse (blue envelope) is superimposed to sample the electric field amplitude as a function of delay time tD in an electro-optic detector crystal (DX)", after which the electric field that is generated by the whole process is measured over a period of about 100 femtoseconds (from the Science article, using a "radio-frequency lock-in amplifier").

Essentially no manipulation of the electromagnetic field is possible without the use of matter to introduce a significant degree of nonlinearity, so an alternative description would seem to be that the various light sources are used to measure the nonlinear properties of the various macroscopic crystals rather than that the light and various macroscopic crystals are used to measure the vacuum.

This slightly cantankerous critique of the language and mathematics of the paper linked to does not extend to criticism of the experimental merit. I look forward to other comments. I can't legally attach the Nature paper, but I guess it's OK to attach Figures 1 and 2.Attachment #1: Capture.JPG

"Essentially no manipulation of the electromagnetic field is possible without the use of matter to introduce a significant degree of nonlinearity, so an alternative description would seem to be that the various light sources are used to measure the nonlinear properties of the various macroscopic crystals rather than that the light and various macroscopic crystals are used to measure the vacuum."

Good point!

James A Putnam

An e-mail sent to me by Springer Nature today tells me that because I am at an institution that subscribes to Springer Nature I can post a link to the Nature article that anyone can read, http://rdcu.be/tBxT. To use that link (as I understand it, having just downloaded ReadCube), I'm pretty sure you will have to download ReadCube, an App from Springer Nature, and I'm also pretty sure that through that link you will only be able to read the paper in the App, you won't be able to download the paper as a PDF. If you use the App, they're pretty open that they'll track how you use any papers that you read, so there's that.

Anyway, please let me know if this works successfully or not for you and if you in fact have to download ReadCube. If we can't get it to work, we can let others know not to download ReadCube, but if it does work it slightly lowers the barrier for research outside universities, subject to whatever strictures they enforce against systematic sharing (they can enforce whatever adaptive set of rules suits their business model because of ReadCube usage tracking. There's a marketing description at http://www.springernature.com/gp/researchers/sharedit.)

If it works, this seems something of a gamechanger for FQXi's ability to discuss published papers from Springer Nature.

"According to quantum mechanics, a vacuum isn't empty at all. It's actually filled with quantum energy and particles that blink in and out of existence for a fleeting moment - strange signals that are known as quantum fluctuations."

I've heard the term "quantum foam" and believe it describes the quantum vacuum. Foams seem to comprise lots of tiny bubbles, so can someone please tell me what are the "bubbles" (if any!) that comprise the quantum foam?

3D spherical volumes :)

I suggest you don't get too committed to any one model proposed for very small scales. Even if someone can show that their model gives pretty good predictions for a few experimental contexts, they most likely can't show that there's no other model that's as good, or, to throw a spanner in the works, that's better for some experiments but worse for others. Experiments that can distinguish what's happening at scales as small as or much smaller than the Planck scale with the kind of certainty we get from looking through a microscope at bacteria don't seem likely for a few or more generations.

Words like "foam" or "strings" call to mind classical analogies that may be the closest someone can think of for a particular mathematical model, and ideas such as bubbles or knots may have inspired the creation of the mathematical model, but the word "quantum" signals disanalogies that are likely more significant than the analogies.

Even at somewhere like CERN, but certainly in the paper discussed in this thread, the parts of the apparatus, such as photomultipliers, are typically on the order of microns or larger in size. Everything about much smaller scales, down to millionths of millionths of a micron, say, 10-18 meters, is reconstructed from information that we obtain at the micron scale. Intervals of time as well as of length are also very small, but our measurements cannot be more precisely timed directly than to within the time it takes light to travel one micron (we can use attosecond "strobe" lighting, as this Nature article describes, to get to about a thousand times better than that). Experiments at CERN, reconstructing events at smaller than femtometer scales from more than a few centimeters away, are not wholly unlike examining bacteria from the orbit of the moon, but with the added encumbrance that we are only allowed to see results averaged over the course of years to do it; now let's talk about exact details at scales millions of times smaller than the bacteria and the lifetimes of the bacteria, from the orbit of the moon.

Thanks for this answer,It is well said. I consider in my model, the theory of spherisation with quantum and cosm 3D spheres inside an evolutive 3D universal sphere that the scales are in the same universal logic. You are right about the scales, we know so few still and even our standard model is not complete. We are so youngs still,our knowledges are so youngs about this quantum gravitation even.

Best Regards

Peter,

Bravo!

happy to see you, but where were you Tom ? :)

Hi, Peter and Steve

Re "Experiments that can distinguish what's happening at scales as small as or much smaller than the Planck scale ...", Peter: Can any thing/quantum be smaller than its Planck size? I thought the Planck scale described irreducible minimum sizes for things/quanta?

Re "I consider in my model, the theory of spherisation with quantum and cosm 3D spheres inside an evolutive 3D universal sphere ...", Steve: To achieve a 100% packing ratio for your quantum foam model, would not these spheres have to be dodecahedra? That way there would be no unexplained interstices between the 'bubbles' comprising the 'foam'.

Hello Colin,

I have an other explaination, the space disappears when we consider a fractal with a decreasing in volumes and increasing in number from the central singularity, the biggest volume in logic.That is why this space soes not existy, only matter and energy exist.I see the main primordial quantum of energy like that, gravitational, and 3D sphericalvolumes coded encoding. The relevance is these volumes and their motions, the 3 orbital, spinal and linear. The angles, the velocities.....make the complexification and evolution. Our main codes seem gravitational.

Best

Hi Steve - May I think of your 'central singularity' (CS) as the one from which the Big Bang (BB) started? If so, your BB seems more like a Big Budding, in which the CS keeps on budding off increasing numbers of tiny spheres, each containing:/being? 'one quantum' of 'gravitational energy'. These 3-D spheres start off at a certain size, but get smaller ... over 'time', thus creating a spherical 4-D universe containing?/being? your tiny spheres of energy.

Fed by energy from the CS 'mother', layers of 'daughter' spheres would be clustered around the CS, layers that are analysable into 'generations'. However, I don't see why the spheres of the outermost/later generations need necessarily be smaller in volume than those of the innermost/earlier generations.

I can envisage the initial production being quite rapid, compared with later production ... the famous initial Inflation epoch of Big Bang theory. I also can imagine the tiny energy spheres coalescing into sub-atomic particles then sinking back into your model quantum vacuum. Somewhere, sometime, these random processes will have kicked into existence, in one place, the right ingredients to glom together into a single hydrogen atom. At last: matter from energy.

Then it'd be on for young and old. The large 'Ur-Atom' would be surrounded by your tiny energy spheres and this might explain why you talk of a 'decreasing in volumes'. I guess shock waves would spread through the baby Universe, raising the chances of more random assemblies of H2 atoms occurring.

No doubt I've either missed your point, or cantilevered it out too far, or both. Looking forward to getting the real story, from you and anyone else who can shed light on this fascinating topic.

The Planck scale might or might not be the "smallest" scale. Wikipedia gives the Planck scale as:[math]\ell_P=\sqrt{\frac{\hbar G}{c^3}}\approx 1.6\times 10^{-35}\ \mathrm{meters,}[/math]but this is just what you get when you look for the simplest way to construct something that has units of length using some of the dimensioned constants in QM+gravity, it's not in itself part of any theory. An actual theory might reference the Planck length multiplied by any dimensionless constant whatsoever (for example, e-137.035999=.306ﾃ--10-59 would be nicely small, where 137.035999 is the inverse fine structure constant, which is dimensionless, but of course any such number depends on details of how a theory works).

If a specific theory, even something much more accurate and much more beautiful than the Standard model smashed with general relativity, says there is nothing smaller than the Planck length, that is a theoretical statement that might be supported by experiments for a few centuries or a few millions of years, but we can never be certain that some future experiments won't demonstrate that in fact there is a much smaller scale. Even if in fact there is no smaller scale, we can't be certain there is no smaller scale. One can have theories, this is not a counsel of despair, but nonetheless one has to be cautious of hubris, IMO, albeit that also includes that one shouldn't be too attached to lengths in a 3- or 4-dimensional geometry as necessarily absolutely important, perhaps something else altogether yet to be imagined is the measure of what it's really at.

In philosophy of science this argument, more-or-less, is called "the pessimistic (meta)induction" (at the link, reasons are given that hope to limit the consequences of the argument for scientific realism, but see also Structural Realism for a different response, or one can be an optimistic anti-realist[The theory might not be real, or it might be, but so what, we can still do stuff, we can even spray stuff even if it's only theoretically real]).

Hi Colinn

It is a beautiful explaination. But it is more complex. When I speak about the volumes ,I speak about a kind of gravitational primordial fractal. In logic this serie is finite and correlated with primes. This serie is also probably the same for the two series, the finte quantum serie and the cosm serie finite also. Now take my two equation E=m(b)c²+m(nb)l² and mlsoV=cosntant this second has a problem of equivalence with the 3 motions of quantum and cosm 3D spheres. So what I say is simple when you consider a decreasing of volumes from this cenytral singularity,the central cosm BH the biggest volume the number 1. Now about this BB,I must say that I prefer a gravitational spherical expansion? That impkies that I consider a gravitational aether with l tending to infinity due to this central volume See that this aether ,these particles of gravitation are not relativistic nor baryonic, the dark matter probably. Now you can see easily why I see a fractal of volumes. You can see easily alos that our standard model is encircled by this gravitation, cold.The zero absolute is fascinating.We have so a serie of quantum BHs with these volumes farer than nuclear forces and we have also particles encoded weaker than electromagnetic forces and photons;You can see that the gravity encircles this standard model at all scales, quant and cosm. Now see that all quantum central BHs these quantum singulaties, these biggest spherical volumes turn around this central cosm singularity.They turn so they are these spheres. I work actually about the creation of spherical geometrical spherical algebras. I search to encircle this gravitation and this infinite entropical potential and its codes and informations.

Hope that helps :)

Hi Peter,

Nice to see you around again:). You have always been so kind to comment on my idea, so please could you do it one more time, it should take you 5-10 minutes. In the latest FQXI contest I presented a very brief paper that shows the results of my simulations that predict the electron mass and proton size actually already exists in standard physics! Moreover, my simulation( which already produce many QM results) produce Newtons gravity law( at large distance) with a very simple constraint.

essay

Thanks

Adel Sadeq

I'm sorry, Adel, that I do not have anything at all constructive to say about your essay. As little as I often think the mathematics I use makes too little contact with what physicists are accustomed to using, I fear you have the same problem even more severely. I do not see that you make any contact with quantum field theory at all, for example, which I think you have to if you care what physicists think, at least to persuade them why you don't have to make any contact with, say, the Standard Model of Particle Physics and the experiments that are understood to support it.

Hi Peter,

Thanks for your most informative post and for the references, which I've looked up. They and you have opened my eyes in that I no longer regard the set of Planck units as always fixing the "smallest possible" measure of anything, e.g. "Most Planck units are fantastically small and thus are unrelated to "macroscopic" phenomena (or fantastically large, as in the case of Planck temperature). Energy of 1 EP, on the other hand, is definitely macroscopic, approximately equaling the energy stored in an automobile gas tank (57.2 L of gasoline at 34.2 MJ/L of chemical energy)." Learning about Entity Realism was fun ... I got a lovely mental picture of all those electrons and positrons speeding towards that superconducting metal sphere at Stanford!

Thank you, Colin, the Stanford Encyclopedia of Philosophy is a worthwhile place to learn about how philosophers of physics think -- not always sensibly, because philosophers, but it's almost always at least not obvious why an idea is nonsense. The SEP often doesn't obscure ideas by using technical words quite as badly as does the philosophy literature proper.

Indeed, the whole concept of a smallest scale is tendentious. One has the Javelin argument that the universe is infinite in extent and the turtles-all-the-way-down argument, which one can turn to anything that rests or relies on anotherthing. So, I suppose, one could have a microscopes-all-the-way-down argument, or one could just talk of fractals, which in broad summary is apparently Steve Dufourny's approach, though there is an infinite diversity of possible fractal structure). Such arguments are not definitive: the Wikipedia page is very keen to deflate the javelin argument by mentioning that the universe might be a closed space, like a sphere, but the javelin argument also fails if the javelin we use keeps breaking (because temperature or whatever) so we have to keep replacing each javelin with successive different kinds of javelin, if we can, or if we cease being able to detect the javelin from where we are, so that perhaps the javelin does or does not exist (and, mutatis mutandis, microscopes for javelins); so perhaps the world is fractal, but perhaps it is not. I think the question, however, is how much of life rests on whether it's all the way out or inwards or not? For me the answer is that it is not at all, even though knowledge and skills still seem precious things.

Ian Hacking's idea that spraying electrons makes them really real (or something like that) has had a profound effect on how people think about electrons, but we do not know whether there will be such a thing in some future theory. There will be an account, more-or-less, of how what an electron used to be thought to be is related to the structure of the future theory (just as quantization is an account, more-or-less, of how classical is related to quantum), but electrons may eventually be thought to be no more helpful as an idea than was phlogiston, even though we will very likely continue to use quantum mechanics as a practical mathematics just as we still use Newtonian mechanics. That's the pessimistic metainduction applied to the specific case of the electron, so it could be wrong, and anyway it's OK to use at least the idea of an electron field until we have something else to use (again, this is not a counsel of despair, it's a counsel against hubris). Against thinking in terms of electrons too much, try my YouTube video, Quantum Mechanics: Event Thinking, because, after all, too much Particle Thinking is a bugbear of mine.

Colin, I forgot to discuss the Planck energy scale that you mention, EP. I suggest that we should take EP to be no more significant than the other Planck scales unless it is put in the context of a specific theory, wherein it will have specific measurable consequences for some experiments, almost none for others. In a specific theory, the Planck energy scale times some arbitrarily small or large dimensionless constant may be the energy scale at which measurable effects occur.