Where do space, time and gravity come from?
quantamagazine.org
quantamagazine.org
I noticed, as I progressed through my studies of physics, a tendency for people to go from “what if” to “it is” before finally reaching “what if” again, as their knowledge grew and developed - I think many went into it for the same reason as me, seeking explanations for reality, and there’s a tendency to mistake theory for explanation, if it’s explanation you’re looking for.
All of it, from QFT to Cartesian coordinates to mathematics itself is just a construct that we humans have come up with to create a rational framework of information that can describe reality - but as anyone who has ever written software knows, there are many ways to reach the same behaviour with different underlying code.
It’s all essentially reverse engineering from a point where you begin without even language or the concept of logic, and everything, everything that you have to work with is the stuff you’ve created, outside of the black box of the universe - but made only with the stuff of the black box.
I moved diagonally into computer science and philosophy, as I was only ending up with more questions the deeper I went into physics - and the whole information as reality concept has stuck with me, as it’s the only part of all of our frameworks which remains a consistent truth.
I think our next big breakthrough in understanding will likely come not purely from physics, but the intersection of physics and computing, as I think we will come to realise that they are essentially one and the same.
I'm not sure how this relates to quantum gravity, I think that one is going to be harder to figure out.
At some level, even systemd is built on a superloop, or "main" method, which depends on a power supply.
So the computers are depending on physics again, to persuade us that:
• electron + positron = photon
• photon really is a fundamental particle in the Standard Model
• Elementary charges are measured as +1, -1 electron... ok I'm confused now.
• One Electron Universe?
We use terms like “speed of light” when what we actually mean is “speed of information”.
We use terms like “speed” to describe ds/dt, but again, that may be a result of our perception rather than a relevant physical phenomenon.
We look at mass, and describe things as having, well, mass - or energy - but what they actually have is information.
So, for gravity, quantum gravity, I think it’s more about a shift in perception (what is this “force” thing anyway?) than necessarily new science or techniques at this point. I mean, you could look at it as “more information in a given region of spacetime induces a computational overhead due to network effects, which slows time locally respective to an external observer, resulting in an apparent “gravity” force across the time differential”.
What are your thoughts on the regions outside of space time? An empty set? I.e. not reality?
- Fermilab 2013: https://youtu.be/gEKSpZPByD0
- The Royal Institution 2014: https://youtu.be/_8bhtEgB8Mo
- The Royal Institution 2020: https://youtu.be/5hVmeOCJjOU
And I will add: The Big Picture: From the Big Bang to the Meaning of Life - with Sean Carroll
https://www.youtube.com/watch?v=2JsKwyRFiYY
Mysteries of Modern Physics by Sean Carroll
> But in gravity, you’re sort of combining a whole bunch of different possible geometries of space-time. And what that means is, you’re not really sure what time is, for one thing, and you’re not really sure where things are in space, because if you don’t know the geometry of space, it is impossible to identify a point in space uniquely throughout all the possible quantum combinations of the geometry of space-time. So, we really, at a fundamental level, have difficulty knowing what we’re talking about, when it comes to quantum gravity.
Stephen Hawking once summarized this as "Gravity shapes the arena in which it acts" and concluded that, therefore, it'd be unlikely that gravity would be a quantum field like any other. It really annoys me that this is so often forgotten by people in high-energy theory and that quite a few of them pretend that
> We have a pretty good idea of what a theory of quantum gravity must look like
when in reality we have no clue at all. (That quote is from one of Sean Carroll's guests on the former's podcast – for better or for worse I don't remember her name. Notably, as becomes clear from the podcast, Sean Carroll is not among the people subscribing to this view.)
A while ago I was pretty certain that gravity was emergent and was caused by Gluon Colour Confinement. Here was my incredibly naive rationale:
Assumption for the purposes of this idea that gravity is not an absolute, gravity is an emergent phenomenon.
My logic
Gravity around a black hole Photons can't escape Heavier particles and even molecules can't escape
Gravity around a planet sized mass Photons can escape Heavier particles and even molecules can escape
Gravity is not a force that acts at a distance (absolute) Spacetime is being dragged into any object with mass (emergent)
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We are not being 'pulled' into the earth We are being 'kept under' by a shower of space time being consumed
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What causes this 'consumption' of spacetime around objects with mass?
Gluon color confinement
https://gist.github.com/TheMightyLlama/135fd67eb0577c34093ca...
Sadly, there's some of us who would explore these topics, yet the pay and some of the conditions surrounding this profession are less than ideal, so to speak.
Also, you might want to study the math around the strong interaction and gravity before making any speculation like that. What is explained to you in words might not be accurate.
In black holes, this process would break down in a particular way such that it's not possible to create more spacetime. That's why the amount of information a black hole can store grows with the area of the black hole, not the volume. There is no spacetime inside it for information to enter.
I feel like this could explain "dark energy".. spacetime piles up in the empty regions between galaxies, and the curvature isn't strong enough to create significant attraction, so at that scale, things end up moving away from each other. So basically the same idea you had I think, but opposite.
I believe in a stochastic process for wavefunction collapse, and I think entanglement may be related to the process of spacetime creation. Entangled particles are connected by a single filament of spacetime. This filament can only be used once before being destroyed, so it'd participate in the "resolution" necessary for wavefunction collapse, but then disappear. That is: there is no "spooky action at a distance" because from the entangled particles perspective they're still right next to each other in the graph of spacetime.
It was interesting to see that Stephen Wolfram seems to be suggesting something along those lines, but I'm not smart enough to understand if my ideas are similar to what he's proposing. I'm probably completely wrong anyway.
It a great example of the fundamental process at the root of all humans progress/knowledge: a creative conjecture/idea which can (hopefully) be tested against reality and rejected or accepted based on how well it solves the problem and explains something about reality.
> Gluon color confinement
This seems rather unlikely, given that not all particles interact strongly[0] (i.e. have color charge) but still interact with gravity.
I've heard something like "the Feynman path integrals spit out infinities" many times but I'm wondering if there is a deeper explanation I could grasp without reading several books.
Physics theories are not supposed to be mutually incommensurable, like the ideas of two philosophers from different schools who don't understand each other. Physics doesn't work that way, and physicists have never been satisfied with that.
In QM, gravity is a force, and efforts to express gravity in a quantum framework use the graviton, a massless force carrier for gravitation.
We don't necessarily expect this to exist, the graviton is simply a mathematical tool if you don't like the idea. In relativity, it makes no intuitive sense to have a force carrier for gravity, as gravity is not a force in the same way the others are, it's a property of the geometry of spacetime.
In GR, spacetime is continuous, there is no minimum or maximum length. In QM, spacetime is discrete. There is a minimum quantity.
So already, you can see some incompatibility, because both GR and QM make many predictions that have proven both models to be pretty good descriptions of nature. GR has been more or less proven by experiments with time dilation, gravitational lensing, and more recently gravitational waves. QM has been supported by many experiments too, double slit experiment, experiments with quantum entanglement, you name it, QM has predicted it and with extreme accuracy.
So you have two descriptions of reality that work on two different scales, which is sort of acceptable. Use the two at the appropriate scale and you have the Standard Model of physics, and that mostly works. Except when you have to tackle something like a black hole or the big bang where the scale is quantum level, but the mass-energy is relativistic.
So we want a quantum theory of gravity, and the infinities emerge when trying to formulate a quantum theory of gravity. Specifically, gravitation is non-renormalisable, i.e. at high enough energies, our usual methods to deal with divergences toward infinity doesn't work and itself results in problems with infinities.
Physicists have been working for the best part of a century to unify the fundamental forces, well what does this mean? It means that if you put enough energy into a system, like the amount you'd have at the big bang, it is possible to demonstrate that the electromagnetic force and the weak nuclear force are one force, and "grand unified theories" refer to theories in which the strong nuclear force and gravitational force are similarly found to be all part of one force at the unification energy.
Unification is far from complete, but we have at least a decent picture of the electromagnetic, weak and strong forces individually, in quantum mechanics.
The problem with unification is primarily gravitation, which is extremely weak compared to the other fundamental forces, and we don't know how to describe it in quantum mechanics without using a representative particle. And even then, as you can tell, we haven't gotten all that far.
Most efforts have produced purely mathematical extensions to the Standard Model, like String Theory. Problem with string theories is that they do not make predictions that we can check, and thus the theories are not falsifiable. And there could probably be n different string theories that all work and stitch GR and QM together, but no way to determine which string theory us right.
A lot of people dislike the idea that string theories and some other alternative quantum gravity theories propose which is that there are more than 4 dimensions, anywhere from 5 to 26 to n dimensions.
The reason why people don't like that is that we have no idea what these extra dimensions would look like, we wouldn't even see them, they're basically just more co-ordinates but it doesn't seem very satisfactory just to say there's extra dimensions and that gravity leaks out that way.
Even then it's not every theory of quantum gravity, but certainly those with any traction have tended to discretise spacetime (e.g. loop quantum gravity).
And yes I was trying to keep it simple/accessible. Given the parent question, why would I word my response inaccessibly?
Firstly, I'll note that I read your comment about another answer here seeming like pop sci to you. I will also not leave the answer at only my next two words.
> deeper explanation I could grasp without reading several books
Probably not, and I'm not sure undergrad SR helps enough, although I'll assume you encountered quantum electrodynamics, and so guess that maybe we can slyly work out a weak comma-goes-to-semicolon approach[1], replacing partial derivatives in Schrödinger's i\hbar \partial \psi /\partial t=-(\hbar^2/2m)\nabla^2 \psi with covariant derivatives and ignore that we have only Galilean invariance in the time-dependent Schrödinger eq (TDSE), rather than full Lorentz covariance. Not ignoring that turns into a course in differential geometry and curved spacetime. In fact, I will even trim the "explanation" to "we can adapt TDSE to some distributions on some spacetimes, changing its partial derivatives to covariant derivatives, which looks really easy when you just write it (i\hbar \partial \psi /\partial t=-(\hbar^2/2m)\nabla^2 \psi), but making that typographical trick work is where you find the 'deeper explanation'". But the takeaway is that doing weakly-relativistic quantum mechanics in a weakly-curved spacetime (like our solar system, or even the overwhelming majority of the central parsec of our galaxy) is tractable, and we can leave "the problem of time" in a box to be opened at leisure by philosophers.
Now we've taken an initial step towards QM on a more general spacetime than that of the very special one of SR.
Let's step back a bit.
If you can cope with Gauss and Poisson laws for electromagnetism (http://web.mit.edu/6.013_book/www/chapter4/4.3.html and surrounding sections in that chapter), and the usual Schrödinger equation, you can take a step towards a Gauss law for gravity (\Phi_g = -4 \pi Gm_{enc}, where we have substituted the constant 1/ε_0 with -4 \pi G, and the enclosed electric charge q_{enc} becomes the enclosed "gravitational charge" m_{enc}). As Carroll says in the fine article at the top, we can quantize this just fine, given at least the conditions in my first paragraph (and typically several others too).
Purely electromagnetically, one might set out a number of sources, with each source's generating a Poisson potential. Those sum linearly through the principle of superposition, so this is just fine. We can then perform a "second quantization" or "canonical quantization". This goes outside your implicit scope, but essentially we convert a classical electromagnetic system into a quantum field theory by this procedure. From that we can recover our usual TDSE. This is a grad topic, books required.
Gravitationally, we can follow the same approach. We have to be careful with our distributions of sources (mass, rather than electric charges), but if they are far enough apart (the idea being that the Poisson potential for any source asymptotes to zero at infinity) and not moving relativistically (i.e., compared to the speed of light), we can do a "second quantization" of gravitation. This is called Canonical Quantum Gravity, and works well for many applications. I think CQG is beyond an undergrad background without resort to books. Try to see how much of DeWitt you can follow at [2].
We can then combine these two paragraphs following the <https://en.wikipedia.org/wiki/Schr%C3%B6dinger%E2%80%93Newto...> approach, extracting the adapted TDSE decorated with partial derivatives (commas -> semicolons ~ d -> \partial).
Now let's return to "my" elephant in the room: the superposition principle. The matter we describe with either form of TDSE above superposes linearly: we can take a distribution of charged sources and completely determine their interactions, and we can drop in a test particle that feels these interactions, so can probe them by being attracted to our various sources, even as we strongly densify sets of sources. This works for all the charges in the Standard Model, with some effort. Unfortunately, this fails for our notion of the gravitational charge m_{enc}: as we densify m, we can get to a runaway collapse, which we capture in the nonlinearity introduced in Schrödinger-Newton. Worse, even without the runaway, we can't in general linearly superpose the gravitational potential from significant sources (for less significant sources we can pretend that instead of asymptoting to zero at infinity, the potential reaches zero closer to the source; we do this for other long-range potentials too, in practice). So we can't with generality solve the whole Schrödinger-Newton calculation: we need to be careful about the distribution of mass.
We already have this problem in classical General Relativity, where the Raychaudhuri equations lead to caustics, so it's not exactly surprising that a flavour of that appears in a system which arose from quantizing classical General Relativity. Dealing with those takes some mathematical work classically and in QFT approaches like the one I've very briefly sketched above, and there is no approach known to be fully general. Caustics associated with colliding gravitational waves is something we can't deal with satisfactorily, and we have reasons to suspect those may occur in a relevant way in the very early history of our universe. Singularities in the deep interior of black holes are something we can't deal with satisfactorily either. However, even in classical General Relativity practically nobody trusts the interior solution of the Kerr metric (not even Kerr himself! [3]). And of course, classically, black holes do not evaporate. They likely do in most QFT approaches and certainly should in the approach I sketched above. But we also don't know what goes on in the black hole interior in practically any QFT approach that has a universe like ours (i.e., no extra dimensions we fail to notice all the time; an expanding rather than collapsing universe; things like that; and formal descriptions things that are like black holes but also formal descriptions that recover the motions of objects in our solar system). All of that arises from the nonlinearities in the Einstein Field Equations of General Relativity; those nonlinearities have real astrophysical significance (multi-pulsar systems are excellent testbeds for nonlinearities), so we can't just wave them away.
So wherever we add a nonlinear term to a quantum field theory, as done above, or in several alternative approaches, we are doing the right thing to model natural phenomena we observe. But we also encounter mathematical difficulties. These may be technical (there may be non-perturbative renormalization procedures that don't rely on power counting yet to be invented by mathematicians and/or mathematical physicists). These may be solved by nature itself (there may be some UV fixed point, where UV is "extremely short distances" in essence, coming from ultraviolet, which has extremely short wavelengths, and a fixed point is something that saves perturbative renormalization for gravitation, as it did with quantum chromodynamics (2004 Nobel Prize in Physics)). Nonlinearity problems might still be found in the non-gravitational sector (the standard model of particle physics is not completed into the UV), and if so, maybe there's a way to kill two birds with one stone. Just nobody knows for sure if there are zero, one, or two (or more) birds; and if you don't know what the birds are like (or if they even exist), it's hard to plan seriously about what stone is the right tool.
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Quantum field theory actually coughed up an answer.
Degeneracy pressures -- very much quantum mechanical effects -- keep these compact stars from collapsing further, but those pressures can be overwhelmed (electron degeneracy pressure is overwhelmed in a precursor phase of any neutron star) leading to further collapse. Is there some ultimate degeneracy pressure that sets a minimum volume for an arbitrary amount of matter? We just don't know.
Relatedly, we don't have a general solution to have two spatially separated masses not eventually (after infinite time, even) become one enclosed mass: we can only keep them separated in select families of model universes (in ours, dark energy keeps distant clusters galaxies apart, but not the members of any given cluster) or with selected initial conditions. That is manifested in the formal inability to linearly superpose two gravitational potentials (even though we can do so with other potentials). And we can only handle so much non-linearity with modern tools and techniques (although that keeps improving too).
Another problem is that degeneracy pressure itself becomes a large source of gravitation within compact stars, since it is stress-energy which gravitates [4], rather than individual particles of matter, so a sufficiently strong degeneracy pressure (quark degeneracy, maybe? or something stronger?) spells its own gravitational demise!
So, the tl;dr is that the standard model of particle physics is a linear theory, the standard model of gravitation is a non-linear theory. For astrophysical reasons we can't get rid of the nonlinearities entirely. And we run into problems if gravity's nonlinearities "infect" the linear theories of matter. But we don't know how to avoid that infection for black holes and the very early hot dense universe. QFT approaches give answers, GR approaches give other answers, and our study of nature has not let us decide which answers, if any, are close enough.
Finally, the mathematics of General Relativity are complete and self-consistent, but have a big "box" called the stress-energy tensor. The study of the mechanisms that generate stress-energy is the GR-first approach to strong gravity. Quantum effects can arise in the stress-energy tensor, and degeneracy pressures are an example. There are technical and conceptual problems about quantum mechanical effects on a purely classical background, though. Nevertheless, the straightforward way to avoid infinitely-strong gravity is to block it via the action of the stress-energy tensor. A quantum field theory first approach starts on a different footing in terms of mathematical completeness and/or consistency at all energy ranges, but has different escape valves for strong gravity, precisely because it is no longer a classical background. For instance, gravitons (which are not a feature of classical General Relativity, but are a feature in perturbative quantum gravity [5]) might decay at extraordinary energies (an example lifted out of a real approach: with additional symmetries in a beyond-the-standard-model theory, a Kaluza-Klein type graviton might decay into a pair of Z bosons, which then immediately decay into things that could be spotted by something like ATLAS/CMS (muons, jets, diphoton resonances)).
- --
[1] Carroll's introductory grad-student course notes (chosen because they're online and because Carroll is in the linked article) at https://ned.ipac.caltech.edu/level5/March01/Carroll3/Carroll... deals with this briefly; his GR textbook (and others') will supply details if desired, and lead you towards some of the depth, but away from your desire to avoid "reading ... books".
[2] https://blogs.umass.edu/grqft/files/2014/11/DeWitt-Quantum-g... which goes into greater detail than the article linked at the top where Carroll says: "You can have the same classical theory that maps on to two different quantum theories. You can have two different classical theories mapping onto the same quantum theory. So, there’s no direct correspondence and after all, why should there be?
"But again, nevertheless, it has worked for electromagnetism, the nuclear forces and everything else. When you straightforwardly apply that quantization procedure to gravity — we have a classical theory, general relativity, we can quantize it. It just blows up. It just gives us infinite crazy answers."
[3] Kerr lecture on Spinning Black Holes (2016) https://youtu.be/nypav68tq8Q (iirc, around the 51 minute mark, although he raises the point several times in the second half of the lecture, particularly highlighting that the Kerr solution is strictly a vacuum solution).
[4] one can analogize: just as the motion of sub-proton particles within a proton gives it a large fraction its rest mass, exceeding that of the sum of the rest-masses of those internal particles, the motion of particles within a compact star (neutron star, white dwarf) generates a large fraction of the gravitational mass of the compact star, which is more than that which would be generated by its components if they were spread out within a larger enclosing volume. The analogy is deeply interesting, quoting Strassler: "... there is positive motion energy from all those particles running around in there, as well as some amount of positive mass energy, and then there is also a very negative potential energy from the fact that all those particles are tightly bound in there. We do not have a simple description of a proton analogous to a hydrogen atom, where you can work out where all the energy comes from. It’s a big complicated mess, but in the end the sum of the energies for a proton at rest is 0.938 GeV. Yes, highly relativistic bound states are a lot more complicated than nice simple non-relativistic atoms." (a comment in the excellent <https://profmattstrassler.com/articles-and-posts/largehadron...>).
[5] 't Hooft Lecture - Perturbative QUANTUM GRAVITY - Universiteit Utrecht https://webspace.science.uu.nl/~hooft101/lectures/erice02.pd...
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[1] Or any transcendental number, for that matter, or any truly random sequence.
Also note that it is not true that any transcendental number must have every finite sequence of digits in its decimal expansion. A common counter-example would be a Liouville number:
sum k=1->inf (1/10^k!) = 0.11000100000000000000000100000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000001...
You were probably thinking of Normal numbers [1], pi is widely believed to be a normal number.
Do the digits of pi exist independent of doing a computation process to turn pi into a digit-by-digit representation? In which case it gets into messy stuff about infinities, right, e.g. it could take an infinitely long amount of time to find the sequence you're looking for. And is it valid to say "any circle contains an infinite amount of information" just because there's this ratio, given that just from looking at the circle, you couldn't compute the ratio to infinite precision? Whereas if we're talking a theoretical circle, and the equations for finding all the digits of pi, how much do those concepts truly "exist" in a way that they could "store" information?
My conclusion is that there is no difference between a number and an algorithm. Pi is not a "number" in a sense that integers and rationals are - it is not a finite string of symbols that represents a quantity for us. But it does represent some quantity, though in an indirect way - all irrational numbers can only be represented by an algorithm that approaches the infinitely-precise value.
So, integers and rationals only seem "like numbers" to us because we don't consider them "algorithms" - they seem intuitive to us. But looking from the perspective of Peano axioms, even integers are just algorithms for computing numbers - 3 is just s(s(s(1))), which is an algorithm that states that the successor function has to be applied 3 times to the number 1. So we can't really draw any kind of objective line between a number and an algorithm. Every number is an algorithm, it's just that some of them are trivial for us.
Same thing with circle - circle is just an algorithm for drawing a specific shape. All the properties of circles are just algorithms for approximating real-world properties of our drawings of circles.
So basically, pi (the algorithm) does in fact "contain" all sequences of digits when computed - but it does it in the same way that an infinite grassfield contains a grassleaf of any size - the size of the grassfield only makes it harder for us to find the grassleaf.
[1] https://en.m.wikipedia.org/wiki/Eternalism_(philosophy_of_ti...
Treating space and time as emergent may be a potential solution.
GR and QM are fundamentally incompatible and will never be, however one can fork either GR or QM to reconciliate them.
* Single author
* No affiliation
* Not peer-reviewed
* Claims to trivially solve a huge problem on a few pages
* Barely contains any math except for some basic equations that are known to undergrads
If the solution is so simple, why hasn't anyone thought of it and why won't anyone recognize this paper? How do you answer this question without resorting to some conspiracy theory in which a shadowy elite a.k.a "the establishment" suppresses progress for nebulous reasons?
And lastly one question on the actual subject: the paper claims that as a consequence there is no expansion and no big bang. The most obvious question that arises immediately is: how do you explain the CMB? The fact that author has not preemptively answered this crucial question already tells me that this is not worth my time.
Independent researchers have a higher propensity of saying bullshit and also have a much higher propensity of thinking outside of the normative box and disrupt it, see e.g. physics research in the 20th century. As a reminder Einstein refused peer review. I'm not advocating against peer review but it is not absolutely necessary to bring consideration to a paper.
Also, variations of classical gravity has already shown huge potential with MOND. moreover it is so simple because his works build upon the work of giants such as Lorentz and Poincare.
> how do you explain the CMB?
The author has not to explained every subtopics of his theory though. He has an interesting result solving the whormhole information loss paradox though, which is huge.
Scientifically, there is very strong evidence to says that parkinson, alzheimer and cancer are mostly solved problems. Nobody knows this because most of the scientific research is siloed. The concept of meta-researcher, someone that actively research the research is almost inexistant, otherwise I wouldn't be the only person on the internet to cite thoses papers on major issues on forums (I have checked) You have to understand that scientific papers in quantum mechanics have on average 0.93 citations. Now consider then most of the citations a paper get are from a future paper from the author himself, or from the same organization. I don't have numbers on that propensity but it seems credible to me that ~80% of papers have 0 citations outside of the organization/friends. Does that means we have to discard ~80% of scientific knowledge ? No. That means there is much more scientific revolutions to find in the past (even more for the pre internet era) that there is in the future. 1) because of the diminishing returns of the search space and 2) because most of the pearls have been consistently ignored. Some of the pearls are frauds or mistakes, and the rest are sleeping revolutions waiting to be woke by the few meta-researchers like me. Unfortunately, I do not have the media power to give them enough recognition so the best I get are the self fullfilling prophety of "nobody has analyzed it so I won't take my time to analyze it"
While (true) { /* do nothing */ }
More generally, I like to observe the reality that scientific research is "frozen". There is no public issue tracker for methodically tracking progress. Imagine a technical github-like repository (but with collaborative issue editing like on wikipedia) where we could observe in real time, with sub-threads, progress of the search space on major scientific problems. You could have an issue "implement quantum cannonical quantization" as a sub issue of quantum gravity and this link should receive major attention there. Except no, scientific research is not methodological progress driven globally, only miserably internally to some extent, by siloed organizations. Which is the reason mankind progress so slowly. One day I will die and those things will not have changed much.
The pdf version is somehow showing a date in 2021, although this is clearly a 1997 preprint. SemanticStrength's reply to you also implies this was written in the 90s. The PDF has the 1997 date on the clickable link back to the arxiv, so there is some time-travel going on that I do not understand.
The date of the preprint is important context, for reasons I'll return to at the end, wrt your point about the CMB.
> huge red flags
Are there? I'm not sure I agree.
> Single author
Common enough in theoretical physics. Just today : https://arxiv.org/list/gr-qc/new there are at least half a dozen.
> Not peer-reviewed
That's your parent comment's complaint, isn't it? I do not know if it was peer-reviewed. I don't expect the paper to gain much traction with anyone in 2022 since it advocates abandoning local Lorentz covariance (which is exceptionally well tested, directly, in our solar system), so I don't feel any desire to play Reviewer 2 today. I have a handful of comments below, though.
But cf. https://scholar.google.com/scholar?hl=en&as_sdt=0%2C5&q=Ilja... for this author, who has been published in this field.
> No affiliation
Hardly unknown in this field. Also hardly unknown for an instutionally employed author to omit an affiliation for unstated reasons (or even accidentally), which appears to be the case here. See also the later preprint's affiliation of Weisterstrass Institute, Berlin[1]. And, if there is any doubt, <https://archive.wias-berlin.de/receive/wias_mods_00000235>.
> Barely contains any math except for some basic equations
I'd love to meet the people who think §3 is basic stuff.
> known to undergrads
I spent more minutes than I care to admit hunting down p.14's "well known Lagrangian". In another preprint [1] the author gives a reference for it as Rosen, Ann. of Phys. vol. 22, nr. 1, pp. 1-11, 1963. Which, it turns out, corresponds to https://sci-hub.se/https://doi.org/10.1016/0003-4916(63)9029... at eqn (13), which the author has rewritten in modern notation.
Is this well-known? You decide: <https://scholar.google.com/scholar?hl=en&as_sdt=0%2C5&q=flat...>
I would say, at the very least, that it isn't something expected to be known by undergrads.
> Claims to trivially solve a huge problem on a few pages
Also hardly unknown in this field. Sometimes successful, even, although I think it's more common that short papers tend to reveal or create huge problems instead.
In the broadest sense the idea is not entirely insane for 1997. Starting with a continuum theory acting on a fixed background, then quantizing that into a QFT, is a frequently-used approach. Lattice QCD was all the rage, so "de-continuumizing" the resulting QFT doesn't strike me as particularly bad. Claiming results on a lattice hold up as we take the lattice spacing to zero was very 1990s.
Where things go off the rails is in §5: "The conclusion is very non-trivial: we have to choose this non-relativistic theory as the best available theory of quantum gravity. That means, the relativistic paradigm has to be rejected. Instead, we have to use pre-relativistic ether-theoretical metaphysics." That would have been an impossibly hard sell to a 1997 journal editor, just for tone. For reviewers, it is not clear they would agree this point is supported by the preceeding sections. For potential reviewers in 2022, the core approach itself and the other arguments raised in the Discussion section have been overtaken by other developments, notably in numerical relativity and numerical methods for quantum gravity.
However, the idea of a Galileo-invariant ether was not particulary insane (Jacobson & Mattingly 2000 <https://sci-hub.se/https://journals.aps.org/prd/abstract/10....> cf the preprint under discussion at Definition 1's second bullet; more broadly, <https://en.wikipedia.org/wiki/Einstein_aether_theory>). This also answers your
> why hasn't anyone thought of it
They have.
> why won't anyone recognize this paper?
I have no idea whether the author submitted it to a journal or not, or even planned to do so without further work. I don't think SemantincStrength or you knows either. However, it is not "the first valid cannonical quantization of Gravity" (as SemanticStrength wrote), by three decades. (Bergmann, 1966; DeWitt, 1967 -- DeWitt is what you find in textbooks and DeWitt is also what you find in [6] of the preprint SemanticStrength took us to).
> how do you explain the CMB? The fact that the author has not preemptively answered this crucial question already tells me this is not worth my time.
You took time anyway, as did I. I don't buy the novel arguments raised in the preprint, but I have twenty-five years of history accumulated since it was written. Speaking of since it was written, the first data from BOOMERanG was in 1997 with 2000 data being acutely relevant; MAXIMA wasn't until 1998, so even coarse knowledge about the anisotropies arguably postdates this 1997 preprint. I don't think you can lean on COBE's primary findings (or anything earlier) without further developing your objection. \Lambda-CDM was very new when the author was writing this preprint. It was not even the favoured model until the discovery of the accelerated expansion in 1998 (High-Z, SCP).
Finally, I think we have conflated SemanticStrength's comments with the content of the preprint, and perhaps only because the preprint is in numerous places rather forceful in tone.
- --
[1] https://arxiv.org/abs/gr-qc/0104013v1 (2001 but dated 2011) p.5, "There are Lagrangians which are not strong covariant but have covariant Euler-Lagrange equations, like the well known Rosen Lagrangian [20]. This is a consequence of the fact that the Lagrangian is not uniquely defined by its Euler-Lagrange equations. But the Rosen Lagrangian is a well known GR Lagrangian too." Emphasis mine. Also, O RLY.
Preprint version <https://arxiv.org/abs/gr-qc/0205035>; interesting the spread of dates in the submission history.
I don't have time to comment in any detail on this new link (or to peruse it, although I did read Appendix H.3 with some care), other than to say that it is a better read (and more professional) than the 1997 preprint you supplied earlier. I don't know Advances in Applied Clifford Algebras, but I hope that was a good choice for the author.
It does bother me though that the journal reproduces the latest preprint's typo "exteriour bundle" (superfluous u) in the second sentence of the second paragraph of the article. This is hardly a ringing endorsement of Springer quality on a "transformative journal" which is trying to squeeze out of authors 2300 euros in article-processing charges... https://sci-hub.se/https://link.springer.com/article/10.1007... (for the published version)
You're interested in Schmelzer's papers. The author has a colourful website <https://ilja-schmelzer.de/> on which he solicits comment and provides an email link. I think you should feel reasonably welcome to send a brief initial hello and a couple of questions about his work. Additionally, he might have some ideas on your point (1), beyond the reference sections of his various papers. He might also have some thoughts on (2), which could turn out to be related to what I see as a remarkable contrast between his 1997 preprint's Discussion section and the final paragraph before Appendix A in his 2012 publication.
Question 1: Now where is the source of the Coulomb field of the electron?
Question 2: Where is the source of the gravitational field of the mass of that electron?
It's traditional to derive equations and functions from higher principles, not to work back from them.
You can't assume there's a wavefunction, because it's a metaphysical position. You're literally assuming an entire mathematical apparatus just sort of exists for no reason, in some wholly unspecified way, in an unspecified medium, with completely unknown properties.
By starting with an abstract premise and asking "let's work out what would happen?", any useful and surprising results tell us connections that we didn't see until we worked them out. If those results match the real world, we learned about the connection between the real world and a plausible abstract underlying structure.
This is a useful method how to derive equations and functions from other principles and empirical observations. You can think of it as a search strategy, to find simpler explanations and mechanisms that produce the complex consequences we observe in real life.
A lot of quantum theory was figured out this way, which has proved very useful in practice. Much of our modern technology depends on it.
but all we really know about space is that it makes quantum systems touch once in a while
(and that galaxies don't rotate at the right speed)
feels like we're waiting for a 'weird but up close' result in space so we can start doing experimental physics on it. maybe this is nonlocality / entanglement tricks, but my money is on benchtop black holes
I quite like this 1876 pop sci article about 'are the elements elementary' -- shows what a top 1800s chemist thought about the coming subatomic revolution. I wonder what the 2022 equivalent of this essay is
We cannot observe anything outside of space and time.
[1] - https://physicsworld.com/a/new-evidence-for-cyclic-universe-...
What happened before the big-bang? If time is a product of the big-bang, then how can it be used to provide any sort of perspective outside of the very thing that created it? (poor phrasing, sorry)
Imagine asking the question "what was @tempodox2 like before he was born?".
Moreover, our ability to perceive time shapes our way of thinking about it, potentially in ways that lead us to incorrect theories and conclusions. Simplest, although maybe worst example might be that time is actually flowing in the opposite direction that we perceive it. Isn't the direction of time just a subjective observation based on who or what the observer is? We have just happened to evolve with certain sensors that allow us to perceive time in a particular direction as a result of a subset of properties/reactions potentially exclusive to our universe.
Or
It's just something that we haven't figured out yet, and eventually will.
[0] https://www.indiatoday.in/science/story/big-bang-didn-t-star...
For example, do you think it's necessary to ask what created the natural numbers? When did they begin existing?
1. Everything that begins to exist has a cause.
2. The universe began to exist.
3. Therefore, the universe must have a cause of its existence, and that cause is God.
The issue is with the first premise. If you only understand causality from within a temporal framework, then your understanding only works from within a temporal framework. "Everything that begins to exist has a cause" presupposes the cause exists before the effect and that presupposition becomes incoherent at the beginning of time itself. If the big bang is the start of time, then nothing exists "before" the big bang because the very notion of "before" is meaningless without time. Our understanding of every event on the universal timeline is that it is linked inextricably by necessity and sufficiency to some set of prior events, and we call that causation, but attempting to use the same logic and language regarding the existence of the timeline results in paradoxical, meaningless statements.
It is comical to claim that some "physicist" has managed to resolve a deeply _philosophical_ question such as Creatio ex nihilo.
The existence of God is a philosophical question and not a scientific one. One can't reach for a scientific method to resolve everything; if that were the case, then we might as well throw out the entire domain of philosophy all together.
I fully recognize that this is not a very popular comment on a forum like HN, however what I dislike about "Scientisim" today, is that they claim that the entire realm of human knowledge and experience can be reduce to Science alone.
I hold that this line of thinking forces you into a very narrow and reductive line of reasoning.
> "One can regard imaginary and real time as beginning at the South Pole, which is a smooth point of space-time where the normal laws of physics hold. There is nothing south of the South Pole, so there was nothing around before the Big Bang," Hawking said.
My layman's reading of that imagines if you move south, get to the south pole, and then keep going the same direction you had been going, you are still moving but no longer going "south." In this metaphor, you could go back in time, be "at" the Big Bang, keep going the direction you had been going in time, but the direction you're going would no longer be "before."
I have no idea how practical this metaphor is and how far it extends, but it's an appealing one to me. Maybe someone else could clarify.
[1] https://www.cnet.com/science/stephen-hawking-tells-degrasse-...
What if our reality (and universe) is on the same journey as the one you just described? What if the North Pole is our starting point (Big Bang), we walk southward and as soon as we cross the South Pole, everything reverts back into the Big Ben (you would eventually reach the North Pole again) just to start all over again. Like a piston, or a ballon that is being inflated, then deflated and re-inflated again; our reality is just "one stroke" (or "walk", in your metaphor) of a bigger "engine".
Somebody else commented about this: https://physicsworld.com/a/new-evidence-for-cyclic-universe-...
Perhaps this is like asking the question "What value did the system clock have before the computer was turned on?"
The question may be unanswerable from the information available in this universe (or, in the analogy, within the computer), but we know that there had to be something there.
The latter isn't trying to obtain an external perspective, but rather a more fundamental perspective, somewhat like how when you dig deep enough, the weak and electromagnetic force become unified, emerging from more fundamental properties. Similarly, with space-time and gravity being so heavily associated, there may be a more fundamental mechanism at work which is responsible for the properties of both.
The former is asking something potentially similar. In the early universe, there's a popular theory that the weak, strong and electromagnetic force were unified. Similarly, if the mechanisms for the properties of space, time and gravity can be unified, perhaps we may find that the big bang itself wasn't as much of a singularity as we think, instead being the result of some more fundamental properties of the universe being in a certain state. Thinking of it like the idea of a false vacuum decay, perhaps the fundamental properties of the universe were the same before the big bang, and the 'bang' was the vacuum dropping down to a more stable state, in which case "what happened before the big bang" makes some sense.
On the other hand, if the big bang was indeed the start of all physics including time, the big bang very well can have happened because this question would be asked.
As for our ability to perceive time shaping our way of thinking about it, from what I understand, we currently believe that physics holds under simultaneous charge, parity and time reversal. The various promising theories of quantum gravity have cases that might break this rule, which I think would effectively define a physical direction of time.
Roger Penrose applies this thinking to the problem of consciousness and thinks this points to a special characteristic of humans that we can decide if things are true by 'stepping outside' of a problem, and that no mathematical function can do this. Therefore no computer running a mathematical function can be like us in that way.
Well no, not if it's a consistent system, but why does it have to be consistent? We're not consistent systems and we build systems that aren't consistent all the time, including computer systems.
https://en.wikipedia.org/wiki/New_mysterianism
This can be either because one posits a fundamental limitation on self-conceptualization of systems, or a practical one on human biological or social intelligence.
If there was an AI, it would encounter the same problem: it exists in some indescribable form, but it cant touch itself, it cant see itself, it cant understand itself. So it would create a 'reality' - also a fictional thing, but with properties such as inertia, reaction and invariance (the three laws of Newton), and then it would constrain itself with that reality, so it would feel real. After that it would start building fictional sandcastles and understand itself.
And what’s more, this satisfies a longing for the transcendent, because in so far as people think they can see the “limits of human understanding,” they believe of course that they can see beyond these.
— Ludwig Wittgenstein [1]
[1] https://archive.org/details/culturevalue0000witt/page/n44/mo...
Or, there is something wrong with the theory?
Note that we do teach classical mechanics (to a point) in high school, even though it was the cutting edge of physics at some point.
When you manage to write down your thoughts so future generations can build on prior work, and when you manage to formalize problems by abstract notation (math), and when you gain the capability of breaking down complex problems into small solvable chunks, then maybe, and I want to stress maybe, there is no limit to understanding things.
On the other hand, there also may be problems with irreducible complexity, so it really could be either way.
Maybe his discrete, computable mathematics (which is merely alluded to) is the temporary step back we need to move forward again.
Although removing the continuum from QM seems questionable. AFAIK (which isn’t much) continuous change is a feature of QM. It’s one reason quantum computation has an advantage. No 0 or 1, but a continuous range of states somehow.
Heck, that form might not even be consistent between "bubbles".
Part of the reason little progress has been made is that it was considered career-ending in physics to work on those questions, because some of them dive into philosophy (What is knowledge? What is real? What is emergent?) Throughout the latter half of the twentieth century graduate students were counseled away from any work related to the field. Oppenheimer famously organized the shunning of Bohm for daring to publish (at Einstein's encouragement) on the subject. Hugh Everett was driven out of academia altogether.
Hard problems can be solved when people actually work on them. Often the problem is other people preventing the work. Thankfully this attitude seems to be easing thanks in part to the efforts of people like Sean Carroll and Lee Smolin.
One of Sean's papers, in fact, proposes a way to falsify Everettian mechanics through experiment (though the experiment would be exceedingly difficult in practice).
Copenhagen was "just an interpretation" but serious work on the subject is actually advancing work on new theories (with distinct mathematical models), not just hand-waving and dismissal.
It took hundreds of years between Newton and Einstein and relativity was only possible once we were able to produce data about the speed of light.
What's wrong about it? If humans evolved, there's no good reason to think that even the smartest human has the mental capacity to do something like that, or to do it quickly. Science will hit a wall determined by human limits, and it's quite possible that limit has already been hit in some areas.
There are a lot of popular fairy tales that portray humans as universal understanders (with no limits as long as they Science™ hard enough), but they seem kind silly to me.
EDIT: I mean, who does revisit long established facts everybody just agrees upon, without checking, because they are long established?
The thing is there is no shortage of theories, or whole classes of theories, the problem is getting the data we need to verify and refine them.
Of the 4.4 million software developers in the US, most of them produce really bad code and have a lot of wrong ideas about development and don't think twice about what they're doing.
Same with the medical field - rife with dysfunction and malpractice.
Pretty much all fields work like this as far as I can tell. It sometimes takes hundreds of years for new correct ideas to be actually accepted and integrated into the mainstream knowledge/practice in any given field. Most people have giant egos and are resistant to change.
I'm saying "you", not "author", because the paper's author seems to be interested in a very specific, somewhat niche question, which is studying the equation of motion of test particles (at rest) in alternative theories of gravity and in the situation where, in addition, the test particle is charged and interacting with a fixed gauge field. (One needs to be very careful with the term "gauge" here because the author confusingly uses it for both, the matter gauge theory / gauge group and the "gravitational gauge" group, i.e. coordinate invariance.)
This question might be interesting to a few select people but there is certainly no "problem of motion in gauge theories of matter" at large, at least not in the way you portrait it.
I mean, for classic gravity / General Relativity, one expects that, depending on whether the particle is charged or not charged, the equation of motion reduces to:
- the geodesic principle – i.e. the hypothesis that (uncharged) test particles at rest move along geodesics.
- a Lorentz-force-type law for gauge-charged test particles that (only) interact with a (fixed) gauge field and are otherwise at rest.
But both are quite well-established I'd say:
- The geodesic principle can actually be rigorously derived from the Einstein field equations for a large class of matter or situations[0]. Given this body of evidence, it's rather likely it's a mathematical theorem and does not actually need to be assumed as an axiom of General Relativity.
- The Lorentz law can already be derived[1] from the special-relativistic Lagrangian of the matter field and its coupling to the gauge field (where both fields are obviously classic, not quantum).
As for the latter, sure, strictly speaking the special-relativistic derivation (i.e. on a flat background) can only be a "local" one in light of General Relativity. In a fully relativistic derivation one should instead consider a curved background, i.e. the Einstein-Maxwell action (or a generalization thereof for arbitrary gauge fields). But then again – given the evidence for the geodesic principle – we know the Lorentz force must come from the interaction of the particle with the (fixed) gauge field (not gravity) and that interaction is largely "understood" – with the usual fine print that:
- forces are a classical concept but particles are actually quantum and there is backreaction (so the Lorentz force can only be the lowest-order term, anyway),
- obviously we don't really know how quantum fields work on curved backgrounds / in conjunction with General Relativity. Then again, we don't know how to make quantum fields mathematically rigorous on a flat background to begin with. So there is no point in asking for mathematical rigorisity in the context of deriving the Lorentz force from first principles when much larger issues would need to be tackled first.
So again, what "problem of motion" exactly would you like to see solved?
[0]: https://physics.stackexchange.com/questions/24359/why-do-obj...
[1]: https://math.stackexchange.com/questions/554488/derive-the-e...
Also, if you spin someone in a barrel, it produces a force that is indistinguishable from gravity, for the person in the barrel. Simple, but scientists like to make things complicated and confusing. Probably makes them sleep better at night.
See Newtons bucket argument. Spin is relational to the universe. If something spins, it produces gravity gradients. These come from differing frames of reference to time, or more specifically, variance in the pace of causality.
A spinning barrel has all the motion of the atoms "lined up" in a curve. The curve becomes a frame of reference to the remainder of the Universe. Whether or not the individual atoms of the barrel are lined up with each other, or not, is irrelevant to developing a gravitational gradient.
Magnets pull together field lines in the extant magnetic field. These field lines either don't exist or are straight lines, unless they happen to intersect with a gravity gradient or a piece of matter, which is itself a manifestation of vibrations in various fields. These vibrations are assumed to have various alignments, depending. When the Curie temperature is reached in a particular piece of matter, those vibrations become randomized in direction. So, the field lines passing through that matter would then remain "straightish". They aren't bent significantly in one direction or the other.
There is another possibility, which accompanies the idea of divergent magnetic field lines. Crystalline bismuth will causes fields lines to diverge along certain directions of the crystalline lattice. Above the equivalent idea of a Curie temperature for dielectrics, the material ceases to diverge the field lines and they regain their "straight" nature. If a plate of crystallized bismuth is placed in a magnetic field, it will tend to spin to align its lattice to the field lines with the least amount of divergence.
So, take a crystalized plate of bismuth. Create a strongly aligned and coupled magnetic field with two bifilar coils. Rotate the plate through the field, aligned perpendicularly to the field lines. Ensuring the planes of the lattice, as it rotates, impact the lines of force at an angle that maximizes the divergence of those field lines. Increase the rotation to the point that the field lines, in the frame of rotation are diverged significantly to form an effect. This would be assumed to have proportional effects based on the inertial mass of the rotating crystal. This would be visualized as a circle of bent field lines within a larger lattice of straight field lines, which grow larger as the rotational velocity is increased.
The resulting effect should manifest as an inertial field dampener for existing gravitational gradients. In other words, it should nullify the existing curvature of space in a particular area around the device, in a particular plane, maybe in the form of a circle.
If this were possible, it might have significant implications for developing a gravity shield. Or not.
Like curved spacetime inside a gravity well? :P