Abstract. The recent experimental proposals by Bose et al. and Marletto et al. (BMV) outline a way to test for the quantum nature of gravity by measuring gravitationally induced differential phase accumulation over the superposed paths of two ∼ 10−14kg masses. These authors outline the expected outcome of these experiments for semi-classical, quantum gravity and collapse models. It is found that both semi-classical and collapse models predict a lack of entanglement in the experimental results. This work predicts the outcome of the BMV experiment in Bohmian trajectory gravity – where classical gravity is assumed to couple to the particle configuration in each Bohmian path, as opposed to semi-classical gravity where gravity couples to the expectation value of the wave function, or of quantized gravity, where the gravitational field is itself in a quantum superposition. In the case of the BMV experiment, Bohmian trajectory gravity predicts that there will be quantum entanglement. This is surprising as the gravitational field is treated classically. A discussion of how Bohmian trajectory gravity can induce quantum entanglement for a non superposed gravitational field is put forward.
This paper is a result of a talk I gave at DICE2018. The trip and the talk allowed me to sharpen the math and the arguments in this paper. I’m convinced that the results of a BMV like experiment would show these results – namely that gravity violates QM! Most physicists are of course on the opposite side of this and would assume that QM would win in a BMV experiment.
For those of the main camp, this paper is still important, as it describes another way to approximate quantum gravity – one that works better than the very often used Rosenfeld style semi-classical gravity. Sitting through talks where researchers use the semi-classical approximation in order to do sophisticated quantum gravity phenomenology has convinced me that often the results would change significantly if they had of used a Bohmian trajectory approach instead. The chemists figured this out a while ago – a Bohmian approximation is much more accurate than semi-classical approximations.
]]>In some sense semi-classical gravity seems more complicated than Bohmian trajectory gravity, as in semi-classical gravity the gravitational field has to somehow integrate the entire position space of the wave function (a non local entity) in real time (via the Schr ̈odinger – Newton equation), in order to continuously use the expectation value as a source for the gravitational field. In Bohmian mechanics, the gravitational field connects directly to an existing ’hidden’ particle position, which is conceptually simpler.
I am attending GR22 in Valencia Spain, to present a poster and also take part in the talks. I will be presenting a poster based on this paper (soon to be published) from a talk I gave at DICE2018.
What the paper and poster argue is that in the BMV experiment, observing entanglement is not enough to show that gravity is quantum. I do this by showing that a classical gravitational field coupled to the Bohmian trajectories of the individual particles will show entanglement.
The conference looks like its going to be interesting to attend.
The image at the top shows 4 runs of the BMV experiment, with all 4 Bohmian particle trajectory combinations shown. There is entanglement generated 1/4 of the time, when the experiment happens to look like the 2nd diagram from the left.
The poster is 90 x 200cm, available in real 3D, if you visit Valencia From July 7-12 2019 :-)
The BMV experiment sets out to show that gravity is quantized. If gravity is quantized, we expect to be able to form a gravitational field into a superposition, so that fundamentally the gravitational field is not certain at one spacetime point. Trying to come up with a theory of gravity that can be in a quantum superposition, while still working for all present tests of Einstein’s General Relativity has proved impossible so far, despite thousands of very smart people working over 50 years on the problem.
Perhaps gravity cannot be quantized. With Bohmian trajectory gravity, gravity is not quantized and has a well-defined connection to the sub-atomic particles.
If gravity is not quantized, all sorts of assumptions about quantum mechanics suddenly fail, as an unquantized gravity allows one to cheat behind the back of quantum mechanics. This is a large part of the reason why many people think gravity must be quantized. I’m not in the gravity must be quantized group, mostly because I think it just won’t work.
]]>Consider the following facts.
Given the above facts, the simplest spacetime I can come up with looks roughly like this:
So this spacetime, which is not new, ( Wheeler had similar ideas), seems to cover our knowledge about the logical structure of quantum mechanics and general relativity. Until someone comes up with something better, this is what I use.
This is how our universe operates: we feel everything locally causal. But experiment shows some non-local (in the global sense) connections.
Therefore, the phase shift of this interferometer is not determined by the local acceleration along a single populated trajectory, demonstrating that the atomic wavefunction is a nonlocal probe of the spacetime manifold [34].
Thus they have experimentally shown that wave functions feel gravity pretty much where they ‘are’ in real space ( try not to think of configuration space at this point! ). No one really doubted this would happen. Still, it leads one to wonder what about the other side – the backreaction – to this. Do the atoms in the Asenbaum experiment source gravity in the same way they detect it? It would seem obvious that they should, but no one has done an experiment to verify this (see later in this article).
A proposal in the opposite spirit to the above results is given by Kafri, Taylor, and Milburn (KTM) in A classical channel model for gravitational decoherence. KTM posits a way for the gravity to be sourced as follows:
That is, the gravitational centre of mass coordinate,x_{i}, of each particle is continuously measured and a classical stochastic measurement record, J_{k}(t), carrying this information acts reciprocally as a classical control force on the other mass.
In other words in the KTM model, the source and detection channels for a particle are both as in semi-classical gravity. The expectation value of the particle’s is the mass location for both source and detection.
You can sense that the Asenbaum experiment shows KTM does not work – the experiment shows that atom, which is in a dual humped wave function with a separation of centimeters cannot be seeing only the average field – the wave function senses the curvature. The paper by Altamirano, Corona-Ugalde, Mann, and Zych Gravity is not a Pairwise Local Classical Channel , confirm these feelings about KTM – like theories. They don’t work.
Here we show that single-atom interference experiments achieving large spatial superpositions can rule out a framework where the Newtonian gravitational inter-action is fundamentally classical in the information-theoretic sense: it cannot convey entanglement. Specifically, in this framework gravity acts pairwise between massive particles as classical channels, which effectively induce approximately Newtonian forces between the masses.
So gravity is not truly semi-classical. No surprise to me, or to the quantum gravity workers (LQG, String Theory, etc). What many/most quantum gravity people like to think, however, is that KTM or similar (Diosi – Penrose), Rosenfeld like semi-classical gravity basically exhaust the spectrum of classical gravity theories.
The papers describing the BMV experiments by Bose et al., Marletto and Vedral, and Christodoulou and Rovelli.
These proposed experiments are in some ways similar to the Asenbaum experiment described above, but instead of atoms, small particles like micro diamonds are prepared in position-dependent superpositions, and instead of a huge mass of lead, two diamonds are dropped near each other, so they can feel the gravitational effect of the other also in a position superposition diamond. The promise of these experiments is tremendous – if successful they might show that gravity is quantized: Christodoulou and Rovell state
...detecting the [BMV] effect counts as evidence that the gravitational field can be in a superposition of two macroscopically distinct classical fields and since the gravitational field is the geometry of spacetime (measured by rods and clocks), the BMV effect counts as evidence that quantum superposition of different spacetime geometries is possible, can be achieved..
A problem I see in these BMV papers is that they all use the predictions of semi-classical theories (not KTM but semiclassical as a source only) as a classical test case, without much thought to the predictions of other ‘classical’ theories of gravity. The possibilities are many and the experimental consequences are not simple.
There have been some papers over the years touting the usefulness of the Bohmian trajectory viewpoint as a better approximation to classical field – quantum system interaction. Usually, the case for using Bohmian trajectories is one of computational or conceptual efficiency, but as Ward Struve in Semi-classical approximations based on Bohmian mechanics puts it:
Finally, although we regard the Bohmian semi-classical approximation for quantum gravity as an approximation to some deeper quantum theory for gravity, one could also entertain the possibility that it is a fundamental theory on its own. At least, there is presumably as yet no experimental evidence against it.
The interpretation of the BMV experiment if one assumes Bohmian trajectories are ‘real’ results in the following conclusions:
The last point is the most surprising. We look at why an experimenter will see entanglement with Bohmian trajectories.
At the heart of the argument is the fact that while these Bohmian trajectories look very classical, they are actually quantum – more clearly subquantum aspects of (Bohm/de Broglie) quantum theory. So we have a situation where we can get behaviour very similar – ( i.e. showing entanglement ) to quantum gravity for the BMV experiment by using classical gravity coupled to Bohmian trajectories, where there is a superposition of gravitational fields – but only in the boring classical histories of the experiment viewpoint. Since the experimenter has only histories to look at, showing that the gravitational field was in a superposition requires more than merely observing some level of entanglement in the BMV experiment.
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Abstract:
Some physicists surmise that gravity lies outside of quantum mechanics. Thus theories like the standard semiclassical theory of quantum to gravity coupling (that of Rosenfeld and Møller) are possible real models of interaction, rather than a mere approximation of a theory of quantum gravity. Unfortunately, semiclassical gravity creates inconsistencies such as superluminal communication. Alternatives by authors such as Diósi, Martin, Penrose, and Wang often use the term ’stochastic’ to set themselves apart from the standard semiclassical theory. These theories couple to fluctuations caused by for instance continuous spontaneous localization, hence the term ’stochastic’. This paper looks at stochastic gravity in the framework of a class of emergent or ontological quantum theories, such as those by Bohm, Cetto, and de Broglie. It is found that much or all of the trouble in connecting gravity with a microscopic system falls away, as Einstein’s general relativity is free to react directly with the microscopic beables. The resulting continuous gravitational wave radiation by atomic and nuclear systems does not, in contrast to Einstein’s speculation, cause catastrophic problems. The small amount of energy exchanged by gravitational waves may have measurable experimental consequences. A very recent experiment by Vinante et al. performed on a small cantilever at mK temperatures shows a surprising non-thermal noise component, the magnitude of which is consistent with the stochastic gravity coupling explored here.
If we take values of a strain of 15 orders of magnitude lower than LIGOs sensitivity, and a frequency of the Compton frequency, we get levels of energy flux and density that are very surprising. No one talks about this, though, since HFGWs are ‘known’ not to exist. I posit that we should not assume anything about gravitational waves at this point. Its an obvious place for experimentalists to work in. Are there any experiments that can detect gravitational radiation at millions of watts per square meter and nuclear frequencies? This is something that experiments should decide.
Just think about it – there is no way we can tell – there may be billions of watts of gravitational wave energy passing through your body right now. They may be there, waiting for us to find them.
The comments on dark energy and dark matter in the calculator are to be interpreted as follows:
Dark Matter is measured as an excess of mass/energy – as it’s presence is determined by gravitational effects on regular matter. In fact- experimentally, dark matter is too tied to matter – one can predict the amount of dark matter in a galaxy or galaxy cluster, etc by simply writing down the total mass distribution of baryons! What we know of dark matter is that it’s weakly coupled to matter and that it’s much denser than the level of dark energy that is spread throughout the universe.
Dark Matter is gravitational waves associated with matter. Call it DarkGW. It looks like the presence of matter controls the amount of dark matter present and DarkGW interacts very weakly with matter (perhaps not in a linear fashion?), perhaps even violatiing the rules of quantum mechanics – after all there is no quantum theory of gravity yet.
In this scenario, dark energy is the ‘leaking’ of this DarkGW into intergalactic space. Thus there is a source for DE and it does not have to have a transcendental source. Its ‘just’ regular radiation – radiation that does not redshift as the Universe ages, as the redshifted bits are replaced on a continual basis by the DarkGW.
This tells us why the amount of DarkGW is related to the amount of Dark Energy (why are they within a factor of two of each other?). As the DarkGW has leaked out, the Universe has expanded. Once the galaxies start to get cold and far apart (say in 200billion years) – the dark energy would start to redshift, and the Universe would approach a ‘balance point’ universe instead of a runaway expansion as in modern LCDM.
Riess says that it could be caused by hypothetical “sterile neutrinos”, interactions with dark matter, or a strengthening over time of dark energy (which accelerates the universe’s expansion).
Sterile Neutrinos are a last ditch effort to keep dark energy as a parameter (Lambda) in Einstein’s equations. Its clear to me that the best answer is that dark energy is getting stronger over time. Dark Energy is on the right side of the Einstein equations, not the left. Lambda was a mistake. Its zero.
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What about a field associated with every nucleon that saturates at some level, called S here. (its saturated near dense matter like here on Earth or in the Milky Way plane, while when protons/neutrons get below a certain density, the field then eventually drops as the density of matter drops.
This solves the cuspy galaxy core problem, it also makes the BTFR (Baryonic Tully Fisher Relation) work, it also seems it would work on the bullet cluster, galactic clusters, etc.
The Baryonic Tully Fisher Relation is one of the most accurate relations in cosmology. It’s a huge thorn in the side of LCDM cosmology, since dark matter and regular matter are not supposed to be in lockstep with one another. See Stacy McGaugh
THE SMALL SCATTER OF THE BARYONIC TULLY–FISHER RELATION
With the S field presented here, there is a saturable field associated with every nucleon. When nucleons are about a mm apart or less on average, the S field is at some standard strength, then as the density lowers more, the S field maintains its density (or slowly loses density) until at some limiting low matter density this saturable field S starts to drop. By the point this happens there is ~100x more energy in the saturable field S than the baryonic density.
This effect can explain the BTFR as dark matter is present in quantities as a function of baryonic mass in some fashion.
The bullet cluster poses a problem for MOND like theories – there seems to be excess dark matter causing lensing. So dark matter really exists, it seems. The S field solves this nicely. No one thinks that the lensing areas of the Bullet cluster are completely free of matter, it’s just that the dark matter is not located where the bulk of the matter is.
Clusters of galaxies would not hold together without about 5 times the mass of the individual galaxies available between the galaxies to hold the galaxies together. See Galaxy clusters prove dark matter’s existence as an intro by Ethan Siegel .
The mechanism is clear – the intergalactic dust and gas provide the framework to energize a large S field which keeps the cluster gravitationally bound.
The S field is associated with matter and has a limiting high density. At low densities (ie halo galactic densities) the field has a mass of up to about 10 (or 100?) times the mass of a nucleon, per nucleon.
Where does the energy come from? It’s dark energy – just clumped. So S is dark energy. There is always a flow of it running around, and its pulled from dark energy as needed to saturate around matter.
What is the form of the field?
What is the minimum energy density in say GeV/m^{3} ? Dark Energy has an energy density of about 0.5 GeV/m^{3} .
The max is determined by the maximum density measured for dark matter which is about 0.5 GeV/cm^{3} (note the centimeter scale used by astronomers when dealing with matter clouds) see my earlier related post Is Dark Matter merely Inactive Matter? so about 100^{3} or a million times the density of dark energy.
Thus the S field saturates at a density of ~ 5e5 GeV/m^{3} and is present all around us.
The S field density is then some function of the matter density. It turns out that it’s a cumulative effect from all matter enclosed inside ‘R’.
Stacy S. McGaugh and Federico Lelli
Consequently, the dark matter contribution is fully specified by that of the baryons. The observed scatter is small and largely dominated by observational uncertainties. This radial acceleration relation is tantamount to a natural law for rotating galaxy.
From http://stacks.iop.org/0004-637X/836/i=2/a=152?key=crossref.21cde6b778a1e42d6160598a6ba24e03
Start at Equation 22:
Then use and simplify to
Thus the quantity of DM inside a certain radius is wholly dependent on the amount of baryonic matter inside that radius. The S field is a cumulative effect of density of regular baryons.
When I use this on density I get
This equation states that the density of dark matter depends only on the enclosed average density of baryonic matter.
Calculating the acceleration at R , given a 35kPc distance R, and a density of baryons of 1GeV per cm^{3 }gives = 1.2×10-10 m/s2 – ie which is the Milgrom acceleration. So that’s the cut where dark matter starts to be apparent, as the denominator starts to take off.
Of course, this density equation has limits on both ends. The dark matter S field has a maximum density of about a GeV per cm^{3} and once the density goes down to about dark energy levels one no longer calls it dark matter. Don’t forget my density version of the equation requires the average density inside R for the galaxy/gas cloud/cluster.
In my mind this S field is HFGW, but it’s not important what is the nature of the field, vs the mass of the field.
It seems to me that battling it out as MOND vs LCDM is perhaps not the best way to approach the problem as there are obviously more models around that might work. One just has to throw out some part of standard model physics!
Looking at the above more, I’m not convinced that sticking exactly to the MOND formula for mass and density is the way to go with this S field idea. I’m hoping there is a function where the density of DM is only given by the local density of matter, but perhaps that will not work. Perhaps there is something happening where DM depends on the total SUM of all all the matter interior to the radius R.
]]>MOND (MOdified Newtonian Dynamics) is one explanation for the Tully-Fisher relation. It posits that the force towards the centre of a galaxy at large distances is not simply that of Newton, but is modified with the a_{0} of 1.2×10^{-10}m/s^{2} in all galaxies in addition to the usual force predicted by standard Newton or General Relativity’s gravity. LCDM Dark matter is a clumsy explanation for the BTFR, as it needs fine tuning for every galaxy (or every galaxy type) in order to make that straight line be so, well, straight.
There is another way to generate an inward acceleration.
We need a force on each nucleon that changes with how much matter is inside the radius where the particle is. It somehow ‘knows’ the gravitational potential at R, and has a force that depends on that!
What I have so far on this is something to do with dark energy being more concentrated in galaxy cores, so the particle feels this dark energy slope and responds to it.
NOTE: This needs to include a dependence on the enclosed M (ie enclosed Dark Energy inside R). I call this emission based acceleration ‘Anomalous radial nucleonic radiation’ (ARNR). MOND tells us that particles in the galactic halo can ‘weigh’ the galaxy. They have that information. So there must/might be something like dark energy concentrated in the galaxy and the particles react to this, pushing radiation outward and reacting inward. Note in the galactic core the divergence of the DE is 0 – so no extra force on the particle in the middle of the galaxy.
It might seem strange to have this concerted outward radiation pattern though! Here are some possible explanations for an outward constant radiation by the halo constituents.
People don’t generally like the MOND theories because general relativity (GR) in its usual form is so well tested and accurate. LCDM is disliked by many because of the fine-tuning required in order to get everything to match observations. ‘Anomalous radial nucleonic radiation’ (ARNR) allows GR to exist as is.
If nuclei really do radiate continuously, (perhaps in violation of quantum – mechanics) then there will be experimental consequences. These consequences may be largely hidden from earth-based experiments, as the emission would be isotropic and take place in some field (such as gravitational waves) that is hard to detect with current instruments.
There may be other places where cosmological or galactic cluster observations might note this energy output.
In other posts, I have wondered if dark matter is ‘sleeping regular matter‘ and I still think that it may be a viable option, but it seems like any explanation in terms of dark matter may need to be fine-tuned to match observations.
Also, see:
http://backreaction.blogspot.ca/2016/10/what-if-dark-matter-is-not-particle.html
https://tritonstation.wordpress.com/2016/09/26/the-third-law-of-galactic-rotation/
https://tritonstation.wordpress.com/category/dark-matter/
at http://iopscience.iop.org/article/10.1088/0004-637X/802/1/18/pdf
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I attended in 2015. The event has the byline – the 4th International Symposium about Quantum Mechanics based on a »Deeper Level Theory«. Its mission this year is
Towards Ontology of Quantum Mechanics and the Conscious Agent David Bohm Centennial Symposium
When I first really understood what quantum mechanics really was – in second-year undergrad at the University of Toronto, I immediately read all sorts of books and papers by and about Bohm’s theories. He made quite a change in my outlook of physics in general. I became convinced in 1985 that quantum mechanics was incomplete and that something along the lines of Bohm’s theory was the way to go. That makes the conference more special for me, and I’m sure many other attendees share the same view.
I am presenting a poster which I’m still polishing that up right now (the abstract at least was well received!). Its based on a paper called ‘Fully Classical Quantum Gravity (see link)‘. I have renamed the poster to Stochastic Gravity and Ontological Quantum Mechanics and rewritten most of it.
The poster describes the results of a paper by Vinante et al. :
Improved noninterferometric test of collapse models using ultracold cantilevers . If the results hold up, they are quite breathtaking as they state:
The finite intercept, clearly visible in the inset of Fig. 3 implies that the data are not compatible with a pure thermal noise behavior, and a nonthermal ex-cess noise is present.
The paper details the careful procedures followed to chase down possible experimental problems. The analysis is carefully thought out. The paper claims the results show a possible signature of Adler’s Continuous Spontaneous Localization (CSL), but to me it seems like if the results hold up that its simply a great puzzle to solve! My take (in line with the ‘Fully Classical Quantum Gravity‘ paper) is that this noise is caused by the continuous emission and/or absorption of gravitational waves at nuclear frequencies.
Gravitational waves are notoriously hard to see, and these high-frequency ones (HFGWs) even more so. Indeed, since gravitational wave power goes with the square of frequency, truly tiny values of the gravitational wave strain ‘h’ (h == 0 in flat space and h < 1) make for large energy fluxes. The LIGO observations saw gravitational waves with . The formula for the flux of a gravitational wave is:
So LIGO can see gravitational waves with a flux of about , while at nuclear frequencies like , the same formula yields an incredible – another way to look at that flux is that it represents 400+ kg! of mass per square meter per second! I propose that results like this suggest that matter itself can be made of nothing but elaborate patterns of gravitational structures. Clearly, high-frequency gravitational structures can hold an incredible amount of energy.
Another way of thinking about this result is that anytime a better telescope is built, or one is built that looks at a new wavelength, field or pattern of signals, those signals are not only discovered, they produce deep new insights about our universe. The fact that HFGWs are hard to detect does not mean that they are not there! Indeed, instead of calculating what the flux of HFGWs might be around us, we should instead admit our ignorance and calculate what we don’t know. Huge amounts of gravitational wave energy could be whipping by everything right now and we would not know a thing about it.
It’s going to be a quick few days in London!
–Tom
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Which of course is what I have been saying all along. Of course Susskind’s paper is actually ‘of course’ not about QM emerging from GR, which is what I believe, and have good reason to follow up on.
Instead Susskind says:
Dear Qubitzers, GR=QM? Well why not? Some of us already accept ER=EPR [1], so why not follow it to its logical conclusion? It is said that general relativity and quantum mechanics are separate subjects that don’t fit together comfortably. There is a tension, even a contradiction between them—or so one often hears. I take exception to this view. I think that exactly the opposite is true. It may be too strong to say that gravity and quantum mechanics are exactly the same thing, but those of us who are paying attention, may already sense that the two are inseparable, and that neither makes sense without the other.
The ‘paper’ (perhaps letter is a better name), has made the rounds/ Not Even Wrong,
Instead of that happening, it seems that the field is moving ever forward in a post-modern direction I can’t follow. Tonight the arXiv has something new from Susskind about this, where he argues that one should go beyond “ER=EPR”, to “GR=QM”. While the 2013 paper had very few equations, this one has none at all, and is actually written in the form not of a scientific paper, but of a letter to fellow “Qubitzers”. On some sort of spectrum of precision of statements, with Bourbaki near one end, this paper is way at the other end.
While Woit’s nemesis Lubos Motl,
Susskind also says lots of his usual wrong statements resulting from a deep misunderstanding of quantum mechanics – e.g. that "quantum mechanics is the same as a classical simulation of it". A classical system, a simulation or otherwise, can never be equivalent to a quantum mechanical theory. The former really doesn't obey the uncertainty principle, allows objective facts; the latter requires an observer and is a framework to calculate probabilities of statements that are only meaningful relatively to a chosen observer's observations.
Sabine Hossenfelder put it visually on Twitter:
My take is about the same as these popular bloggers. Don’t really think much of it.
Except the title. QM can, I believe, emerge from Einstein’s General Relativity, in much the same way that Bush and Couder’s bouncing drops can display quantum behaviour.
My research gate page has more.
Its ridiculous that 11 dimensions and sparticles have hundreds of times more study than fundamental emergent phenomena. Emergence is the way to go forward. You don’t need a new force/particle/dimension/brane to make fundamentally new physics from what we already have in electromagnetism and general relativity.
See the search links on the side of this blog for some recent papers in these areas.
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