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Troubled Times for Alternatives to Einstein’s Theory of Gravity
- daxfohl 8y agoI still think the answer will have to confront the problem of local realism. It was the issue that drove Newton nuts (that gravitation was, in Einstein's language "spooky action at a distance"), and Einstein resolved that through Relativity, which redefined how we think about "distance". Now the lack of local realism in QM is driving Einstein's ghost nuts. I think the resolution of all this will again redefine "distance" to take resolutions involving quantum entanglement into account. Vaguely I picture some quantum relativity theory where from the perspective of an entangled particle it's still d=0 from its entangled partner and everything else is splitting apart. So like relativity, it's all about which perspective you take. Then perhaps with these relative distances, and however the math falls out with some kind of quantum Lorentz transforms maybe we see that in galaxies with lots of entangled particles this can slow down rotation. That said, dark matter is entirely possible too. There's no particular reason to think that all particles need to have an EM effect as well. In fact it's somewhat crazy to think they should. Why wouldn't there be particles that only show themselves gravitationally? Or through other perhaps insanely strong forces that for whatever evolutionary reason Earth Life is just not evolved to care about or see even indirectly. That said, I have no training in physics and this is entirely crackpot concept. (Of http://www.goodtheorist.science/ http://www.goodtheorist.science/ I've only read ~6.)
- cobbzilla 8y agoYour idea reminds me of Wheeler's "single electron universe" [1]. I think you're on to something but I also think the next big step will involve a formal (re)definition of time as well as distance. [1] https://en.wikipedia.org/wiki/One-electron_universe https://en.wikipedia.org/wiki/One-electron_universe
- deleted 8y ago[deleted]
- dbasedweeb 8y agoWhen you think about particles as excitations of a field, the indistinguishable nature of said particles stops being such a puzzle.
- daxfohl 8y agoBut the concept of a field itself was troubling to 18-19th century physicists. "So you put this (mass/charge/entanglement/whatever) here and automagically there's this whole force that extends across the universe in zero time? How? Why?" Philosophically I don't know if this question has ever been answered satisfactorily. But over the last 100 years fields have become so mathematically convenient that they're too hard not to use.
- dbasedweeb 8y agoWell those 18th-19th century anything didn’t have a concept of entanglement or FTL, they were struggling with the notion that light, gravity, and other forces could propagate without a medium. They saw that waves could be transmitted through water, sound through air, and the idea that light or gravity could be transmitted through vacuum was baffling. Their resolution to the issue was to propose the existence of a substance which was invisible, intangible, but which permeated everything: the luminiferous ether. Light, in their understanding, wasn’t really moving through a vacuum, but this ever-present “stuff” instead. That started to fall out of favor long after the 18th century, and was finally conclusively shot down by Michelson and Morley with their interferometry. The problem Einstein and others grappled with was different, and concerned the fact that according to relativity nothing should exceed c. Entangled particles seemed to violate that principle, because the collapse to a given pair of states was instantaneous. The modern resolution to that is more practical than philosophical, and points out that information isn’t transmitted faster than light in entangled particles. Information propagates at or below c, even though at some scale entangled particles are statistically correlated. Relativity is only violated, and causality threatened if information is transmitted FTL, but entanglement doesn’t allow for that. You need a classical channel make entanglement work for communication, and that classical channel is going to be no faster than light. Without a classical channel, entanglement just gives you random noise.
- daxfohl 8y agoWell if someone ever bothers to go through all the math this thing would entail, I think this would eventually come to some physically testable experiment. Whereas Wheeler's thing seems more pie in the sky.
- bdamm 8y agoIndeed, we seem to treat time like a passive component, a constantly ticking clock, where I wonder if time is distance, and it's time that's expanding our apparent distance. We measure distance in terms of time, or in terms of energy required to cross a given distance in a given time, and I can't shake the idea that energy required is exactly time, and distance itself is the meaningless measurement. It's energy required in 3D that's expanding. That doesn't mean space is expanding, only that energy required in 3D is expanding. And, obviously, I'm not a physicist. If I ever get a second chance at school, maybe physics.
- coldtea 8y ago>It was the issue that drove Newton nuts (that gravitation was, in Einstein's language "spooky action at a distance") Was Newton ever much concerned about this? He was into alchemy and magic, even spookier actions at a distance. Plus, by all they knew at the time, why would "action at a distance" feel strange?
- daxfohl 8y agoSee Newton's quote here https://en.m.wikipedia.org/wiki/Principle_of_locality https://en.m.wikipedia.org/wiki/Principle_of_locality
- DmenshunlAnlsis 8y agoThis has very little to do with the modern issue of action at a distance vis a vis entanglement, and everything to do with the prevailing belief in an aether during Newton’s time. Einstein meanwhile, was actually commenting on entanglement physics.
- daxfohl 8y agoYeah I'm not trying to imply they're the same physical cause, just the same philosophical perception of ickiness. How to phrase better? Newton had issues with aether messing philosophically with local realism. Einstein fixed that through SR and then GR. But then QM introduced new problems with local realism, and maybe the next physics revolution is reconciling that problem. So, not the same thing, but perhaps two different sides of the same million-sided armchair-philosophical dice.
- antonvs 8y agoBut Einstein's objection was almost identical to Newton's. Newton wrote, "It is inconceivable that inanimate Matter should, without the Mediation of something else, which is not material, operate upon, and affect other matter without mutual Contact." Einstein wrote, "I cannot seriously believe in it because the theory cannot be reconciled with the idea that physics should represent a reality in time and space, free from spooky actions at a distance." Newton was talking about gravity, Einstein about entanglement. But the objection is essentially the same one. That's the reason that Newton's quote above is included in an article on the principle of locality.
- kowdermeister 8y ago> that gravitation was, in Einstein's language "spooky action at a distance" You are mistaking gravitation for quantum entanglement which Einstein used to describe as spooky action at a distance.
- daxfohl 8y agoNo, that was intentional. They were both concerned with the lack of local realism delineated in the physics of their time, each of which occurred for different reasons (and the latter of which we still live with). Einstein just had a more memorable phrase for it. I can see how that was misleading though.
- jessriedel 8y agoThe way you've written it is very misleading. > that gravitation was, in Einstein's language "spooky action at a distance" This definitely suggests you're claiming that Einstein was talking about gravity, regardless of the literal interpretation.
- daxfohl 8y ago:%s/"in Einstein's language"/"as Einstein may have phrased it"/g
- DmenshunlAnlsis 8y agoThe problem is that locality, realism and “spukhafte fernwirking” are all issues of quantum mechanics and not relativistic physics. You weren’t misleading, you were mistaken.
- daxfohl 8y agoBut in the 1800s they were issues of Newton's theory of gravitation.
- renox 8y agoWith a true 'd = 0' for entangled particuls you could have faster than light communication no? But entanglement as far as we know now doesn't allow FTL communications.
- daxfohl 8y agoKinda the opposite. If you redefine what "distance" means, that's explicitly how you's avoid FTL communication and eliminate the EPR paradox. Again though, I really am not an expert, or even more than armchair knowledgeable, on the subject.
- jcoffland 8y agoOn their own, entangled particles do not allow information to be communicated.
- nol13 8y agoEntangled particles just share the same ref, distance is a function of lookup complexity. This makes sense right? right?!?
- gus_massa 8y ago> I think the resolution of all this will again redefine "distance" to take resolutions involving quantum entanglement into account. Vaguely I picture some quantum relativity theory where from the perspective of an entangled particle it's still d=0 from its entangled partner and everything else is splitting apart. The problem with this idea is that entanglement is everywhere. The electrons inside a molecule can't be described individually, you must use the superposition of anisometric combinations of them, because only one combination is not enough. It's usually not called entanglement, but mathematically is the same phenomena. Every time two particles collide they get entangled. If they somehow collide or they split and the new particles collide you can see the entanglement as interference. If they go far away, it's difficult to measure the correlation, but it still there. Again, it's usually not called entanglement, but mathematically is the same phenomena. You have probably only read about cases where it's easy to characterize and isolate the superposition state of two particles that are far away. It's an interesting case because you can make some measurements and see that the classic description is wrong and prove that you must use the quantum description of the particles. But if you make any two particles, they will be entangled, just in a non easy to guess form, so they are not nice for experiments. Or if some of them collide with a third particle now you must consider the join state of the tree particles that is more difficult (there are some nice theoretical entanglement results with three particles, but I think nobody had measure them yet). If you see only two of the three entangled particles now the lack of some part of the information makes the result less clear, because you always must repeat the experiment many times and now you must take a weighted average of the possible states of the third particle you are not seeing. So if you are lucky you will see a smaller quantum effect, but if the state of the third particle is important enough you will see an average that is essentially equal to the classic result. And if they collide with more particles they all get in a superposition state that is equivalent of an entangled state, but it's very difficult od impossible to control it in an experiment. So when you see some part of them they look like a usual classical system. So after a few collisions all the particles are somewhat entangled, it's uncontrollable but mathematically there is no sharp criteria to distinguish the controllable states that are nice for entanglement experiments and the uncontrollable states where the decoherence make they look as classic system and everything in between. So if you say that two entangled particles have a distance d=0 then all the particles in the universe have d=0.
- dmfdmf 8y agoI agree. I think people miss your point that within their respective contexts Newton and Einstein were rejecting a form of an acausal theory. However, there is a significant philosophic difference in Newton's era vs Einstein's. Newton was honest in his writing essentially admitting defeat in solving how gravity could work instantaneously across space but nevertheless the math works. In contrast, today the physicists (and philosophers) claim not only does the math work but it proves that reality is fundamentally acausal, or probabilistic, etc. which are various forms of denying identity. In my view, the crude circularity at the root of physics (which leads to multiple conundrums) is the assumption that the "speed" of light can be measured when measurement presupposes light (or its E/M equivalents).[1] Light is special in this regards. [1] https://fqxi.org/community/forum/topic/3104 https://fqxi.org/community/forum/topic/3104
- goatlover 8y ago> not only does the math work but it proves that reality is fundamentally acausal, or probabilistic, etc. which are various forms of denying identity. Proves, as in all deterministic interpretations of QM are impossible? What about MWI? Also, the wavefunction itself is deterministic. Maybe reality isn't fundamentally particle-like, but field-like.
- dmfdmf 8y ago> Maybe reality isn't fundamentally particle-like, but field-like. But then we get into metaphysical and epistemological questions which are obviously unavoidable once you start making claims about what is or is not "fundamental". This is because "fundamental" has to include both the nature of reality and our means of perceiving it. It is common today to project how we perceive onto what we perceive but they must be distinct in any valid theory. Claiming that reality itself is probabilistic is one example of this projection, though it may very well be a fundamental limit of our means of perception it is not a property of what we perceive.
- cameldrv 8y agoI have heard some physicist friends of mine speculate that perhaps space and time themselves are just statistical ensembles of entanglement. At the macro scale, we can measure distances and read clocks, but at the micro scale it’s like trying to measure the temperature of a single electron. Perhaps the definition of “close by” is just two states that are highly entangled. Since entanglement is contagious, this leads to clustering. It’s not clear why this would lead to 4 dimensional space time, and I’m not a physicist, but I thought it was an interesting idea.
- chr1 8y agothis is indeed a very interesting idea. http://blog.stephenwolfram.com/2015/12/what-is-spacetime-really/ http://blog.stephenwolfram.com/2015/12/what-is-spacetime-rea... was describing something similar several years ago.
- ksaxena 8y agoThis article discusses LIGO's detection of gravitational waves as a problem for alternate theories of gravity. But the claim of that discovery seems to have been withdrawn by the LIGO team. Here: https://www.nature.com/news/gravitational-waves-discovery-now-officially-dead-1.16830 https://www.nature.com/news/gravitational-waves-discovery-no... I'm an amateur but something feels amiss to me here. Can anyone shed more light on this contradiction?
- bmuon 8y agoI thought they had confirmed LIGO's detection of gravitational waves coming from a certain pulsar that Fermi saw independently. The article you link to seems to be about gravitational waves from the background. I'm also curious now.
- civilitty 8y agoThat article is about a redaction from the research team at BICEP2, a telescope in the South Pole. It has nothing to do with the Super LIGO detector, which has detected gravitational waves from black hole collisions several times now.
- pdkl95 8y agoLIGO's comments[1] about the 6 gravitational wave detections they are currently confirming (and related publications): [1] https://www.ligo.org/detections.php https://www.ligo.org/detections.php After following the major science experiments over the last ~15 years, I've gotten the impression that the LIGO team is being very careful to not announce anything prematurely. In an interview[2] with Prof. Rana Adhikari about the first detection, he describes how incredibly lucky it was to detect a very strong wave in the middle of the detector's sensitivity range, only ~30 minutes after each site independently enabled data collection. That's the type of situation that raises serious questions about the validity of the data and might even suggest sabotage (someone could be faking data). Fortunately, it sounds like they were careful to investigate the alternative explanations, including searching the labs for anything that looked like a possible sabotage device. It's always good to see scientists paying extra attention to rigor. [2] https://www.youtube.com/watch?v=ViMnGgn87dg https://www.youtube.com/watch?v=ViMnGgn87dg
- Zamicol 8y agoMy money is still on additions/modifications to relativity in the next 100 years. (Sorry for the sources, just using Google to pull up something.) - Hubble's constant has not been calculated, and when it is, there are problems. https://www.space.com/38496-hunt-for-hubble-constant-standard-model.html https://www.space.com/38496-hunt-for-hubble-constant-standar... - Like the fallacious search for Vulcan, there are modern problems with the orbits of some of the outer planets. https://solarsystem.nasa.gov/planets/hypothetical-planet-x/in-depth/ https://solarsystem.nasa.gov/planets/hypothetical-planet-x/i... - A galaxy with 99 percent dark matter and one almost without any. https://www.quantamagazine.org/a-victory-for-dark-matter-in-a-galaxy-without-any-20180328/ https://www.quantamagazine.org/a-victory-for-dark-matter-in-... https://www.theverge.com/2016/8/25/12647540/dragonfly-galaxy-discovered-99-9-percent-dark-matter-stars https://www.theverge.com/2016/8/25/12647540/dragonfly-galaxy... - The bullet cluster, the speed of rotation in galactic arms, etc. - The apparent changing rate of expansion in the universe. - We have no idea of the physics behind red shift "caused by the metric expansion of space". - We still don't know what gravity actually is. The 1998 discovery of the accelerating expansion of the universe was beautifully simple and clean. It proved a huge swath of experts dead wrong. https://en.wikipedia.org/wiki/2011_Nobel_Prize_in_Physics https://en.wikipedia.org/wiki/2011_Nobel_Prize_in_Physics Dark matter/energy could be apart of the mix, but in light of the problems I would not bet it's the end of the story.
- sxcurry 8y agoYour second point - I don't think the potential Planet Nine has anything to do with "problem with the orbits of some of the outer planets". It has been proposed as a solution to the orbits of some distant smaller Kuiper Belt objects. This in return doesn't really have anything to do with relativity, just basic orbital mechanics.
- Zamicol 8y agoI could have sworn there were problems with Pluto's orbit where it was faster/slower than it should have been, but it looks like I'm wrong. >Specifically, this paper shows that, contrary to recent assertions in the literature, the current ephemeris for Pluto does not preclude the existence of the Pioneer effect. We show that the orbit of Pluto is currently not well enough characterized to make such an assertion. https://arxiv.org/pdf/0905.0030.pdf https://arxiv.org/pdf/0905.0030.pdf
- Xeoncross 8y agoThe article shows two demonstrations: 1) a spiral galaxy and 2) a triple system (a neutron star and a white dwarf orbit each other, with another white dwarf orbiting the pair at a distance). I think the spiral galaxy is showing that the problem is that it still has the arms attached. After this amount of time they should not be there so either the amount of time assumed is wrong or something is modifying the speed (like dark energy, modified Newtonian dynamics, etc). However, I don't understand what the "fall" in the triple system is about. What are they measuring that agrees with Newtonian Physics?
- cryptonector 8y agoAre we reading the same FA? The one I read was about a neutron star collision/merger, and a triple star system with a pulsar, and also a double-pulsar system. The word 'spiral' does not appear.
- d_burfoot 8y agoI've been thinking recently that physics should import an idea from software engineering: the test harness. For physics, the test harness would include a large database of X/Y pairs where X represents an experimental configuration and Y represents the outcome. Theories of physics would be instantiated as software libraries. The most modern physics library would pass the vast majority of the tests, by correctly predicting the outcome Y for every configuration X. But since physics is not yet complete, there would presumably be some tests that the best current theories cannot pass, or can only pass by jumping through some really ugly hoops - such as postulating the existence of dark matter and energy. To be taken seriously when proposing a new theory, a researcher must submit an update to the current library, and show that the new theory passes all the tests. The research can also identify new X/Y combinations, not covered in the current test suite, where the new theory diverges from the old one. Experimentalists could then decide the question by running the corresponding experiments and adding the results to the main suite.
- dbasedweeb 8y agoThis is already essentially how it works. A new theory has to be complementary to old ones. This is often said in terms of “matching the predictions of...” another theory. There are more standards of course, but that’s the baseline. A lot of pet theories people have for things like QM fall apart because they don’t match the tested predictions of QM. For example, Special and General Relativity make new and more accurate predictions which complement, but do not contradict Newtonian theory. An issue with a theory replacing QM for example, other than the high degree of precision needed, is Bell’s Theorem, which tends to rule out LHV theories. https://en.m.wikipedia.org/wiki/Bell%27s_theorem https://en.m.wikipedia.org/wiki/Bell%27s_theorem
- deleted 8y ago[deleted]
- aleksei 8y agoTo anyone reading the comments, don't bother.
- mirimir 8y ago> Theorists have dozens of alternative gravity theories that could potentially explain dark matter and dark energy, Freire said. Some of these theories can’t make testable predictions, Archibald said, and many “have a parameter, a ‘knob’ you can turn to make them pass any test you like,” she said. But at some point, said Nicolas Yunes, a physicist at Montana State University, “this gets silly and Occam’s razor wins.” That's very kind. Some would say that theories that can't make testable predictions, or are highly tunable, just aren't science.
- cryptonector 8y agoRight now that includes Dark Matter...