11 ms·

Einstein's Other Theory of Everything

178 points by dnetesn 2y ago

paulmooreparks 2y ago
https://archive.ph/Ogx0b https://archive.ph/Ogx0b
dr_dshiv 2y ago
An alternative to the “ball on rubber sheet” model of gravity is “twisting a lump out of a sheet of silly putty.” You get the same curvature without relying on gravity to serve as a model of gravity (which always bothered me a bit) For clarity, here’s what I mean: if you flatten out some silly putty (or pizza dough should work) then pinch and twist together some of the sheet into a lump, that pulls along the surrounding putty. So, if you drew lines on the putty then pulled it into lumps, you’d see the distortion to the lines.
- Levitating 2y ago
  That's a pretty clever model. Do you know any videos demonstrating it?
  - passion__desire 2y ago
    A new way to visualize General Relativity https://www.youtube.com/watch?v=wrwgIjBUYVc https://www.youtube.com/watch?v=wrwgIjBUYVc This uses Adobe tools to visualize and take advantage of video format.
- tambourine_man 2y ago
  The recursive model always bothered me too. That’s nice, though harder to explain in words.
  - IgorPartola 2y ago
    You can compromise: take a rubber net. Now bunch up a number of squares together and hold them with your hand. What happens to the bigger squares? Now explain that mass likes to move from smaller squares to larger squares and towards the bunched up areas.
- dullcrisp 2y ago
  > without relying on gravity to serve as a model of gravity (which always bothered me a bit) Why though? Would it help if the sheet were in a centrifuge?
  - carapace 2y ago
    > Why though? It bothers me too, why? because it's circular reasoning: acceleration can't explain acceleration. > Would it help if the sheet were in a centrifuge? No, for the same reason. (You're imagining a tube-shaped membrane?) To make it worse, it's developing a wrong idea that hides the right and deeply strange idea: when an object passes a mass and its path seems to deflect what's really happening is that the object is moving in a straight line the whole time and space itself is curved. (The situation is actually a little stranger than that, but I'm no physicist so I won't try to explain any further.)
    - photonthug 2y ago
      As a sibling points out, it’s not explanatory as much as a visualization. Or if it explains something it’s not gravity itself but a less familiar kind of geometry and a new concept of straightness where sometimes the shortest path is what we’d usually think of as curved. Seems fine. Little chance of understanding gravity until you can grasp the prerequisite concepts you’re going to describe it with. And anyway explaining gravity v2 in terms of v1’s first approximation isn’t that strange when recursive definitions are going to play a part in lots of higher education anyway. When you’re a kid, 5 is just a concept useful to describe every instance of 5 apples, but later, a number N is perhaps best understood as the successor of N-1.
      - carapace 2y ago
        Gravity is one of the fundamental forces, there's no recursion in it's definition, indeed we don't "define" it we describe it. The actual description of gravity isn't hard to understand, it's just really strange. There is no good reason to introduce confusing and intrinsically incorrect models.
- raattgift 2y ago
  The "balls on a rubber sheet" is a pain because nothing is in free-fall: there are dissipative contact forces between the balls and the rubber sheet. Consequently realistic initial [position, velocity] values for the test ball cannot give you a stable circular orbit around the central mass ball. Venus isn't about to fall into the sun. Now try setting up Earth-Moon or the Jovian-Gallilean systems on the rubber sheet. It's fun to try to peel away defects in the "ball on a rubber sheet" in an effort to arrive at Newtonian limit equations of motion for balls in placed around it. (First advanced question: how do we adapt Einstein-Hilbert to reflect trapping onto the sheet? Does dimensional reduction work?) What sort of membrane in constant acceleration could generate scaled 2+1 timelike geodesics for model solar system objects placed on it? Can one scale this to a model of the solar system with all orbits flattened onto the membrane? For instance, what do the IVs look like for a ~ 1050:1 mass ratio between a model sun and a model Jupiter that is shrunk down to classroom size and retains a good match to Jupiter's real orbital parameters (or if you prefer, lengths and angles) across many orbits? Without destroying this scale model orbit, can we add the inner solar system? Can we get sensible orbits of scale model Galilean moons? (And of course all of the above has completely neglected the rotations of these bodies about their axes, which is clearly always very wrong with a typical in-classroom rubber sheet + balls demonstration. We can blame friction for that.) I'm not sure what you're representing on silly putty: are the drawn lines solutions to geodesic equations? What would the twists-pulls of the putty in a scale model ~kg:g Sun and Jupiter system look like? Or are you thinking about a relativistic regime somewhere in the right half of this diagram : <https://en.wikipedia.org/wiki/Post-Newtonian_expansion#/media/File:GR2bodyparameterspace.png https://en.wikipedia.org/wiki/Post-Newtonian_expansion#/medi...> ?
  - cyberax 2y ago
    > The "balls on a rubber sheet" is a pain because nothing is in free-fall The balls on a rubber sheet model is actually really great, but not in the way it's typically presented (rolling a ball down the curvature). Instead, just use a pen to draw lines to show the concept of geodesics. Start like this: 1. Imagine that you can move without friction if you stay at the same vertical level. 2. Draw a line on a flat rubber sheet, that's a line in free space. It's just a straight line that can go on to infinity. 3. Now put a ball onto the rubber sheet, so you get some curvature. Now the lines near the ball that stay on the same level are not straight lines, but circles.
- smusamashah 2y ago
  Balls on sheet is a wrong model imo. It needs gravity to work and therefore doesn't explain gravity. I like to imagine a sponge. If you could somehow make dense lumps inside the sponge (may be apply heat in its center somewhere using microwaves?) everything around that lump will be feel a tension/attraction towards that lump. That's my mental model.
  - the__alchemist 2y ago
    I think the balls on sheet is an OK compromise. The reason for me is, it's tough (but not impossible as you point out) to visualize functions over 3D space. Your sponge does that and I like it! (You could also use color-coding, vector-gradients etc) The ball and sheet uses a spacial dimension as the function value, and that's the dimension the needs gravity to work acts on. So, if you accept that as a compromise, it's OK; we are saying that dimension is a convenience.
    - IgorPartola 2y ago
      I like to explain it all as graph paper where the squares get bigger or smaller depending on what’s near them.
      - xscott 2y ago
        That helps explain curvature of space, but it doesn't explain any of the motion. When you see those stretched rubber sheets, they rarely/never show the grid lines moving. So let's say you place a small *stationary* object at a specific grid point (coordinate), and there's a large object that deforms the grid itself. Nothing about that visual provides any new intuition about why the small object would leave it's current grid position and move towards the larger one. The visual tries to explain gravity by appealing to your existing notion of gravity.
  - jayd16 2y ago
    It just needs force, no? You could use magnetism or even intertia if you accelerated the system, right?
- jacknews 2y ago
  Or ripples in a table-cloth - the ripples gather the surrounding cloth, just like mass deforms spacetime. These models are also an intuitive way to illustrate why the speed of light is a limit. A ball rolling on a rubber sheet, or a boat on a lake, etc, can travel faster than waves in the rubber or water. So why can't matter travel faster than light? With ball-on-sheet type models, you need to resort to abstract relativity arguments about mass going to infinity, time slowing, causality, etc. But if particles are actually just waves or knots or whirlpools or whatever, they clearly can't possibly travel faster than the speed of waves in the medium.
openrisk 2y ago
Physicists didnt abandon this idea, Wheeler's geometrodynamics was all about the concept of geometry being relevant for more than grabity. As it happens with so many cool ideas it did not germinate something useful.
- tomashubelbauer 2y ago
  Grabity is such an apt typo for gravity
  - Towaway69 2y ago
    And your comment is a perfect demonstration of the fragility of the universe: what if the OP edits and corrects their typo? Edit: edited after 57 minutes - pedantic nerd here :)
    - pestatije 2y ago
      not possible after 5 minutes
      - pantulis 2y ago
        We are talking relativity here, beware with time lapses and Lorentz transformations!
- hughesjj 2y ago
  > As it happens with so many cool ideas it did not germinate something useful. Well, at least, not so far.
  - openrisk 2y ago
    With so many trained mathematical / theoretical physicists around even the slightest experimental hint from nature would bring about a scientific revolution and new paradigms - like in real time. The lack of news from the "deep" frontiers of fundamental physics might end tomorrow or might last a millenium. Its impossible to tell. The pace of our increasing understanding of universe is not particularly predictable beyond these periods that benefit from simple scaling rules (ever bigger detectors etc.)
DFHippie 2y ago
If mass/energy were interconvertible with space, if the former were some curled form of the latter, could you explain dark energy as the uncurling of mass/energy into ordinary space?
- jb1991 2y ago
  Indeed that is exactly what it is.
- tsimionescu 2y ago
  It's possibly even simpler than that. The equations of GR involve a constant, called the cosmological constant, which could be given any value without changing the theory. A positive value for that constant would exactly correspond to what we know about dark energy.
breck 2y ago
> Einstein finished his masterwork, the theory of general relativity, in 1915. He was 37 years old Interestingly if you look at the most popular programming languages they were created by someone 37.5 years old, on average [0]. [0] https://pldb.io/blog/ageAtCreation.html https://pldb.io/blog/ageAtCreation.html
- bmitc 2y ago
  That's not a great comparison. Einstein had already turned physics on its head and kickstarted several foundational paradigms in 1905, when he was only 25-26 years old.
  - breck 2y ago
    Fair enough. I think Linus might be a good comparison. Linux in his 20's, which turned world on its had, but it masterpiece Git at age ~36.
    - bmitc 2y ago
      I don't fetishize physicists by any means, but Linux and Git are nerdy pursuits that caught on somehow, mainly as a revolt against paid software. Git is pretty bad at times, terrible UX, tons of edge cases, and treats the world as if its made from text. Einstein set forth some of the most foundational and tested theories ever.
      - breck 2y ago
        Have you thought about the deeper aspects of what git is doing?
yyyk 2y ago
It's too commonly argued Einstein didn't produce anything after GR. This article is a welcome correction. The same collaboration produced the EPR paradox - a real achievement which taught us a great deal about quantum theory.
- pantulis 2y ago
  For all the glory Einstein deserves as one of the greatest minds I find more interesting the history of this supposed "failure" in later life, but it's even more admirable his tenacity at trying to tackle the problem at different angles for decades. And boy it must be a hard problem if Einstein himself could not crack it!
  - sdenton4 2y ago
    There's some argument that Einstein was in the right place at the right time. Mercury was wobbly, and there was about fifty years of non-euclidean geometry research built up, including (eg) Riemann breaking ground on differential geometry. Maybe matter didn't crack because the right tools weren't available.
    - pantulis 2y ago
      > including (eg) Riemann breaking ground on differential geometry. And also Poincaré getting close to it.
    - raattgift 2y ago
      Einstein solved three very different open problems in one year: the photoelectric effect, Brownian motion, and special relativity. Others may have gotten close to one of these solutions, but nobody else came anywhere close on all three. General Relativity as his own research programme was designed to capture the consequences of constraining the speed of propagation of changes of gravitational influence; it was literally about relativizing gravity. GR was not designed to explain Mercury specifically (or even really motivated by Mercury), the theory just happened to explain why its orbit traces out a daisy-like pattern rather than a perfect ellipse. GR also correctly predicted a deflection of background starlight around the limb of the sun (1919 eclipse and eclipses since), stellar gravitational redshift (Sirius-B initially, many many objects since), and gravitational redshifts induced by Earth (all reliable results were posthumous: Pound-Rebka and similar since 1959, and more recently precision lunar and satellite ranging). Indeed, Einstein liked to explain that his mental toy in understanding relativistic gravitation was someone jumping off the roof of a house, or the behaviour of things (e.g. flashlights/torches) riding in office-tower elevators/lifts (which date from the 1870s). That's a far cry from precision measurement of Mercury's perihelion! There were no real astrophysical or terrestrial problems calling out for General Relativity. Even after General Relativity was a published theory, real gravitational problems were solved with low-order correcting terms to Newtonian gravitation and with linearization: an approach which Einstein practically invented, and which he used himself when thinking and writing about early problems in cosmology (the discovery of Cepheid variables opened up a lot of those). There were quickly alternatives to General Relativity which predicted some but not all of these early classical tests of the theory. Eddington's 1922 book was the first shot in a body of literature analysing different theories of gravitation and how they differ in their predictions of dozens of tests of General Relativity. Will's work in particular is useful: https://en.wikipedia.org/wiki/Parameterized_post-Newtonian_formalism https://en.wikipedia.org/wiki/Parameterized_post-Newtonian_f... -- you can see how it's used in practice in this open access paper https://www.nature.com/articles/s41467-017-02558-1 https://www.nature.com/articles/s41467-017-02558-1 That said, there are mathematical tools available now that weren't available to Einstein in the early 20th century, and he might have chosen to arrive at a different (but equivalent) formulation of General Relativity. The standard Hamiltonian and a variety of modern Lagrangian formulations are particularly useful, and it could have been nice to have had <https://en.wikipedia.org/wiki/Initial_value_formulation_(general_relativity) https://en.wikipedia.org/wiki/Initial_value_formulation_(gen...> before the 1960s (even though it arguably only shines brighter when you have 21st century supercomputers). Indeed, one can imagine Einstein starting with Lie theory, such that Special Relativity from the start is just the theory of spacetime with SO(3,1) symmetry at every point. But Cartan, Killing, and Noether came decades later and were motivated by Einstein. And quite a bit of group theory developed as the Standard Model developed after Einstein was already dead (notably Goldstone's theorem, 1960s). So to first formulate General Relativity as a GL(4,R) group theory with spontaneous symmetry breaking to SO(3,1) one would need to rearrange an awful lot of physics history. Any of these alternative-universe mathematical origins would just have been using different tools to arrive at the central result: we inhabit a Lorentzian spacetime in which there is an exact matching of moving matter and a metric tensor (at each point in spacetime) encoding durations, spatial lengths, and angles, or the equivalent set of orthonormal vector/covector fields. And worse, the physical content of the theory -- however formulated -- probably would still have been considered interesting but practically useless until the 1970s.
deleted 2y ago
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phkahler 2y ago
An electron falling (electrostatically) toward a proton will reach the speed of light at some point. This is of course the same distance where inside it would need an escape velocity greater than c. So that's an event horizon due to a different force. Some claim matter falling into a black hole never really does from the point of view of an outside observer. I've seen weird sounding descriptions like it "spreads out over the surface". What if electron orbitals are some kind of equivalent to that? When I ask these (admittedly naive) questions, physicists will usually say something like "oh you have to treat that with quantum mechanics". But why? Isn't trying to resolve it using more conventional means (including concepts from relativity) a good idea? I feel like it's not right to reject one approach simply because nobody has figured out how to make it work while another does. That's different from showing that it can't work. Or have such approaches somehow been categorically proven inviable?
- cyberax 2y ago
  > An electron falling (electrostatically) toward a proton will reach the speed of light at some point. Only in Newton's mechanics. With special relativity, it'll approach the lightspeed. > Some claim matter falling into a black hole never really does from the point of view of an outside observer. I've seen weird sounding descriptions like it "spreads out over the surface". It doesn't. To an outside observer, the object falling towards the black hole just becomes progressively dimmer and more red, until it disappears.
  - oneshtein 2y ago
    Even in Newton's mechanic, electron cannot accelerate further after reaching speed of light propagation in the medium. When electron exceeds speed of light it a medium (because of change in medium, for example), it produces Cherenkov radiation.
- the__alchemist 2y ago
  Another layman observation, based on your last paragraph: In terms of electron orbitals, the definition of what quantum mechanics means varies. For example: Are you using quantum mechanics when describing an electron in hydrogen's orbital? I have heard both answers. It's spread out over space and is not like the classical pre-Bohr models, but it's described by a classical wave equation, and can be viewed at as a differential equation solution; a function over 3D space (For a time snapshot; or 4D spacetime with rotating phase). In this definition, you are not doing quantum mechanics until dealing with things like anti-symmetry, spin statistics, exchange interactions etc.
defamation 2y ago
Sabine is awesome
motohagiography 2y ago
naively, i'd wonder if the time properties of black holes could be used to effect local super-massive gravitational effects on entangled particles here. e.g. they figured out how to entangle the electron and proton of a hydrogen atom with a complementary particle that is being pulled into a black hole, like if there were a way to entangle or entrain a local atom with hawking radiation from a black hole, where as the effect of entanglement, the local atom adopted the dialated time/gravity of its remote counterpart in the black hole. the effect would be that states of matter which only existed on the ephemeral femtosecond scale here would be stabilizied for longer time periods because its "clock" had been slowed down by its adopted clock entanglement via hawking radiation in a kind of black-hole-time. maybe better for a movie script or fiction, but people who think of these things reason them through logically before doing the math as well.
- vlovich123 2y ago
  I don’t believe you can entangle items remotely like that.
  - motohagiography 2y ago
    photons entangle at a distance as there is tech in the market right now in cryptography that uses entangled photons over distances of several miles into orbit. the naive intuition is that lensing hawking radiation might stabilize unstable elements for longer periods.
    - vlovich123 2y ago
      Huh. I thought you had to entangle them locally & then separate them maintaining entanglement. Entangling at a distance is weird. Can you provide a source of entangling particles remotely on Earth & in orbit?
    - tsimionescu 2y ago
      No, you entangle them locally and they maintain their entanglement as they move away from each other.
transfire 2y ago
Well that’s very interesting because one of the latest ideas getting traction on solving the information paradox is exactly this — that black holes are connected to each other and the outside space by wormholes. Check out the current Scientific American special publication.
- bmitc 2y ago
  I have always understood black holes to be "failed" wormholes. How does that fit into these new ideas?
ls-lah_33 2y ago
I'm surprised Sabine doesn't mention the way fermions are treated in Loop Quantum Gravity [1][2]. My understanding is they are treated as "non-local" or open loops of gravitational force, and thus entry and exit points in space-time. This makes them conceptually similar to the "wormhole model" of matter that Einstein and Rosen originally described. [1] https://arxiv.org/pdf/gr-qc/9404010 https://arxiv.org/pdf/gr-qc/9404010 [2] https://arxiv.org/pdf/1012.4719 https://arxiv.org/pdf/1012.4719
- gradschoolfail 2y ago
  My understanding is that this is the way fermions are treated in any modern theory of quantum gravity, and not specific to LQG?
  - ls-lah_33 2y ago
    Not sure what you mean, are you talking about ER = EPR? I think that's mostly a way of accounting for entanglement between particles, but it doesn't create the particles to begin with like in LQG. But my string theory knowledge is probably out of date, so I could be wrong.
    - gradschoolfail 2y ago
      You already related the “(open)loop quantization” in LQG to EPR=ER above, similar concept occurs in string theory too, almost unknown because its so foundational, see https://en.wikipedia.org/wiki/Born–Infeld_model https://en.wikipedia.org/wiki/Born–Infeld_model, near the end, as well as some of the references there that discuss gravity. “Creating” is a vague(r) term, do you mean “quantization”? Afaik the open-loop geometry of fermions is something any quantization scheme has to start with, the details are how one includes gravity, so without more details, one wouldnt be able to tell how LQG is different from string theory :)
trhway 2y ago
so, Higgs gives mass, and the mass curves the space to produce what the see as gravitation. I think there are some questions here to the Higgs at it seems it has some special relation to the spacetime. And that https://en.wikipedia.org/wiki/Black_hole_electron https://en.wikipedia.org/wiki/Black_hole_electron "...the angular momentum and charge of the electron are too large for a black hole of the electron's mass: a Kerr–Newman object with such a large angular momentum and charge would instead be "super-extremal", displaying a naked singularity, meaning a singularity not shielded by an event horizon." And 2 singularities having worm-hole connection is the entanglement.
- tsimionescu 2y ago
  Energy gives mass. The Higgs mechanism only explains the mass of the elementary particles (electrons, quarks, W and Z bosons, etc). The vast majority of the mass of everything else comes from the energy of the strong force or the electromagnetism. For example, the vast majority of the mass of a proton is explained by the immense energy of the three quarks and gluons being bound together by the strong force. The mass of the quarks themselves is only a tiny portion of that (about 1%), while gluons are massless. The mass of the atom is further increased by the energy of the electromagnetic force. A hydrogen atom has one proton (1.6726×10^-24 g) plus an electron (9.1×10^-31 g), but the mass of the hydrogen atom is slightly higher than their sum (1.6735×10^-24 g). The mass of a composite particle is at least partly coming from the famous E = mc². The Higgs mechanism is ultimely just a way for elementary particles to have this type of energy as well, even in a void and without any other forces present. There is nothing special about it and spacetime, it works like any other field.
throwmeaway222 2y ago
Nothing has satisfied me between why gravity and magnetism are not the same thing. A ferrous material where the electron poles can be aligned show high forces. Most things are totally misaligned, which I believe creates gravity. No explanation on stackexchange or anything else convinces me. Most of the arguments feel egotistical to me.
- damiankennedy 2y ago
  What about when an apple falls to the ground, is the apple magnetic?
amai 2y ago
Einsteins later work led only recently to the following exciting conjecture: https://en.wikipedia.org/wiki/ER_%3D_EPR https://en.wikipedia.org/wiki/ER_%3D_EPR Unfortunately the author doesn't seem to know about this idea.
t8sr 2y ago
As a physics student, I feel compelled to point out, to any readers who might now go read Hossenfelders other articles, that many of her views are generally not shared by a majority of physicists today. She is a real physicist and not a kook, but she has been criticized for presenting her views (e.g. superdeterminism) as having much more acceptance than they actually do. She ignores and misrepresents counter-arguments regularly. Her ideas about, e.g. the explanatory power of entanglement wrt processions of moons around (IIRC) Jupiter are certainly well outside what I’d describe as regular astrophysics. The golden standard of science communication was set by Sagan, and he always carefully pointed out when he was expressing a personal opinion, as opposed to one shared by the majority. Sabine Hossenfelder is no Sagan. So proceed with caution. :)
- DiggyJohnson 2y ago
  Is there any scientist science communicators that this criticism wouldn't apply to? As far as criticism goes, I appreciate how professionally you stated this PSA. Most don't make the same points as gracefully. Best of luck with your studies.
  - dinkumthinkum 2y ago
    Neil deGrasse Tyson; if he is working on a s riot prepared by someone else like on a TV Show, he is quite a nice communicator. But, if he does not have such a script, I would say unless he is debunking a flat earther or some actor’s mythical views of mathematics, I would just ignore it. If he talks about biology, which he often does, I would just leave.
    - wileydragonfly 2y ago
      He comments on fields in which he’s unqualified, and his remake of Nova had a ton of unnecessary swearing. And goes on TV and talks about politics. That’s when he lost me.
      - LastTrain 2y ago
frede 2y ago
This recent presentation from Kepler Airospace claims that Einstein was on the right track and a goes even further, stating that gravity can be manipulated through EM. I've graduated in Physics but not quite sure what to make of it. https://www.researchgate.net/publication/383609891_Gravity_Modification_Experiment_Description_and_Results_presented_at_APEC_Propulsion_Conference_83124 https://www.researchgate.net/publication/383609891_Gravity_M...
- doug-moen 2y ago
  I'm cheering them on, but I'm not confident that the technology works, based on the people involved. I don't think the new physics underlying this work are published in a peer-reviewed physics journal. Here's a page about John Brandenburg, one of the authors: <https://rationalwiki.org/wiki/John_Brandenburg https://rationalwiki.org/wiki/John_Brandenburg>
- imglorp 2y ago
  Given how easy it seems to reproduce, someone had better explain this effect if it's not what is claimed there... PS: this looks like anyone could reproduce or refute it in their basement for a few hundred dollars given all the details in the slides. I'm hoping some amateurs step in.
  - Pompidou 2y ago
    "Gem test" 1 and 2 on john brandenburg 's youtube channel : https://www.youtube.com/watch?v=hqbOnqZtz3Y https://www.youtube.com/watch?v=hqbOnqZtz3Y https://www.youtube.com/watch?v=RSRbLA6dhtk https://www.youtube.com/watch?v=RSRbLA6dhtk
    - imglorp 2y ago
      It all seems to suffer from some of the issues the EM Drive saw: the proposed effect is tiny and very, very difficult to tease apart from environmental and system noise. I hope I'm wrong.
- deleted 2y ago
  [deleted]

178 points by dnetesn 2y ago

https://archive.ph/Ogx0b https://archive.ph/Ogx0b

An alternative to the “ball on rubber sheet” model of gravity is “twisting a lump out of a sheet of silly putty.” You get the same curvature without relying on gravity to serve as a model of gravity (which always bothered me a bit) For clarity, here’s what I mean: if you flatten out some silly putty (or pizza dough should work) then pinch and twist together some of the sheet into a lump, that pulls along the surrounding putty. So, if you drew lines on the putty then pulled it into lumps, you’d see the distortion to the lines.

Levitating 2y ago
That's a pretty clever model. Do you know any videos demonstrating it?
- passion__desire 2y ago
  A new way to visualize General Relativity https://www.youtube.com/watch?v=wrwgIjBUYVc https://www.youtube.com/watch?v=wrwgIjBUYVc This uses Adobe tools to visualize and take advantage of video format.
tambourine_man 2y ago
The recursive model always bothered me too. That’s nice, though harder to explain in words.
- IgorPartola 2y ago
  You can compromise: take a rubber net. Now bunch up a number of squares together and hold them with your hand. What happens to the bigger squares? Now explain that mass likes to move from smaller squares to larger squares and towards the bunched up areas.
dullcrisp 2y ago
> without relying on gravity to serve as a model of gravity (which always bothered me a bit) Why though? Would it help if the sheet were in a centrifuge?
- carapace 2y ago
  > Why though? It bothers me too, why? because it's circular reasoning: acceleration can't explain acceleration. > Would it help if the sheet were in a centrifuge? No, for the same reason. (You're imagining a tube-shaped membrane?) To make it worse, it's developing a wrong idea that hides the right and deeply strange idea: when an object passes a mass and its path seems to deflect what's really happening is that the object is moving in a straight line the whole time and space itself is curved. (The situation is actually a little stranger than that, but I'm no physicist so I won't try to explain any further.)
  - photonthug 2y ago
    As a sibling points out, it’s not explanatory as much as a visualization. Or if it explains something it’s not gravity itself but a less familiar kind of geometry and a new concept of straightness where sometimes the shortest path is what we’d usually think of as curved. Seems fine. Little chance of understanding gravity until you can grasp the prerequisite concepts you’re going to describe it with. And anyway explaining gravity v2 in terms of v1’s first approximation isn’t that strange when recursive definitions are going to play a part in lots of higher education anyway. When you’re a kid, 5 is just a concept useful to describe every instance of 5 apples, but later, a number N is perhaps best understood as the successor of N-1.
    - carapace 2y ago
      Gravity is one of the fundamental forces, there's no recursion in it's definition, indeed we don't "define" it we describe it. The actual description of gravity isn't hard to understand, it's just really strange. There is no good reason to introduce confusing and intrinsically incorrect models.
raattgift 2y ago
The "balls on a rubber sheet" is a pain because nothing is in free-fall: there are dissipative contact forces between the balls and the rubber sheet. Consequently realistic initial [position, velocity] values for the test ball cannot give you a stable circular orbit around the central mass ball. Venus isn't about to fall into the sun. Now try setting up Earth-Moon or the Jovian-Gallilean systems on the rubber sheet. It's fun to try to peel away defects in the "ball on a rubber sheet" in an effort to arrive at Newtonian limit equations of motion for balls in placed around it. (First advanced question: how do we adapt Einstein-Hilbert to reflect trapping onto the sheet? Does dimensional reduction work?) What sort of membrane in constant acceleration could generate scaled 2+1 timelike geodesics for model solar system objects placed on it? Can one scale this to a model of the solar system with all orbits flattened onto the membrane? For instance, what do the IVs look like for a ~ 1050:1 mass ratio between a model sun and a model Jupiter that is shrunk down to classroom size and retains a good match to Jupiter's real orbital parameters (or if you prefer, lengths and angles) across many orbits? Without destroying this scale model orbit, can we add the inner solar system? Can we get sensible orbits of scale model Galilean moons? (And of course all of the above has completely neglected the rotations of these bodies about their axes, which is clearly always very wrong with a typical in-classroom rubber sheet + balls demonstration. We can blame friction for that.) I'm not sure what you're representing on silly putty: are the drawn lines solutions to geodesic equations? What would the twists-pulls of the putty in a scale model ~kg:g Sun and Jupiter system look like? Or are you thinking about a relativistic regime somewhere in the right half of this diagram : <https://en.wikipedia.org/wiki/Post-Newtonian_expansion#/media/File:GR2bodyparameterspace.png https://en.wikipedia.org/wiki/Post-Newtonian_expansion#/medi...> ?
- cyberax 2y ago
  > The "balls on a rubber sheet" is a pain because nothing is in free-fall The balls on a rubber sheet model is actually really great, but not in the way it's typically presented (rolling a ball down the curvature). Instead, just use a pen to draw lines to show the concept of geodesics. Start like this: 1. Imagine that you can move without friction if you stay at the same vertical level. 2. Draw a line on a flat rubber sheet, that's a line in free space. It's just a straight line that can go on to infinity. 3. Now put a ball onto the rubber sheet, so you get some curvature. Now the lines near the ball that stay on the same level are not straight lines, but circles.
smusamashah 2y ago
Balls on sheet is a wrong model imo. It needs gravity to work and therefore doesn't explain gravity. I like to imagine a sponge. If you could somehow make dense lumps inside the sponge (may be apply heat in its center somewhere using microwaves?) everything around that lump will be feel a tension/attraction towards that lump. That's my mental model.
- the__alchemist 2y ago
  I think the balls on sheet is an OK compromise. The reason for me is, it's tough (but not impossible as you point out) to visualize functions over 3D space. Your sponge does that and I like it! (You could also use color-coding, vector-gradients etc) The ball and sheet uses a spacial dimension as the function value, and that's the dimension the needs gravity to work acts on. So, if you accept that as a compromise, it's OK; we are saying that dimension is a convenience.
  - IgorPartola 2y ago
    I like to explain it all as graph paper where the squares get bigger or smaller depending on what’s near them.
    - xscott 2y ago
      That helps explain curvature of space, but it doesn't explain any of the motion. When you see those stretched rubber sheets, they rarely/never show the grid lines moving. So let's say you place a small *stationary* object at a specific grid point (coordinate), and there's a large object that deforms the grid itself. Nothing about that visual provides any new intuition about why the small object would leave it's current grid position and move towards the larger one. The visual tries to explain gravity by appealing to your existing notion of gravity.
- jayd16 2y ago
  It just needs force, no? You could use magnetism or even intertia if you accelerated the system, right?
jacknews 2y ago
Or ripples in a table-cloth - the ripples gather the surrounding cloth, just like mass deforms spacetime. These models are also an intuitive way to illustrate why the speed of light is a limit. A ball rolling on a rubber sheet, or a boat on a lake, etc, can travel faster than waves in the rubber or water. So why can't matter travel faster than light? With ball-on-sheet type models, you need to resort to abstract relativity arguments about mass going to infinity, time slowing, causality, etc. But if particles are actually just waves or knots or whirlpools or whatever, they clearly can't possibly travel faster than the speed of waves in the medium.

openrisk 2y ago

Physicists didnt abandon this idea, Wheeler's geometrodynamics was all about the concept of geometry being relevant for more than grabity. As it happens with so many cool ideas it did not germinate something useful.

tomashubelbauer 2y ago
Grabity is such an apt typo for gravity
- Towaway69 2y ago
  And your comment is a perfect demonstration of the fragility of the universe: what if the OP edits and corrects their typo? Edit: edited after 57 minutes - pedantic nerd here :)
  - pestatije 2y ago
    not possible after 5 minutes
    - pantulis 2y ago
      We are talking relativity here, beware with time lapses and Lorentz transformations!
hughesjj 2y ago
> As it happens with so many cool ideas it did not germinate something useful. Well, at least, not so far.
- openrisk 2y ago
  With so many trained mathematical / theoretical physicists around even the slightest experimental hint from nature would bring about a scientific revolution and new paradigms - like in real time. The lack of news from the "deep" frontiers of fundamental physics might end tomorrow or might last a millenium. Its impossible to tell. The pace of our increasing understanding of universe is not particularly predictable beyond these periods that benefit from simple scaling rules (ever bigger detectors etc.)

DFHippie 2y ago

If mass/energy were interconvertible with space, if the former were some curled form of the latter, could you explain dark energy as the uncurling of mass/energy into ordinary space?

jb1991 2y ago
Indeed that is exactly what it is.
tsimionescu 2y ago
It's possibly even simpler than that. The equations of GR involve a constant, called the cosmological constant, which could be given any value without changing the theory. A positive value for that constant would exactly correspond to what we know about dark energy.

breck 2y ago

> Einstein finished his masterwork, the theory of general relativity, in 1915. He was 37 years old Interestingly if you look at the most popular programming languages they were created by someone 37.5 years old, on average [0]. [0] https://pldb.io/blog/ageAtCreation.html https://pldb.io/blog/ageAtCreation.html

bmitc 2y ago
That's not a great comparison. Einstein had already turned physics on its head and kickstarted several foundational paradigms in 1905, when he was only 25-26 years old.
- breck 2y ago
  Fair enough. I think Linus might be a good comparison. Linux in his 20's, which turned world on its had, but it masterpiece Git at age ~36.
  - bmitc 2y ago
    I don't fetishize physicists by any means, but Linux and Git are nerdy pursuits that caught on somehow, mainly as a revolt against paid software. Git is pretty bad at times, terrible UX, tons of edge cases, and treats the world as if its made from text. Einstein set forth some of the most foundational and tested theories ever.
    - breck 2y ago
      Have you thought about the deeper aspects of what git is doing?

yyyk 2y ago

It's too commonly argued Einstein didn't produce anything after GR. This article is a welcome correction. The same collaboration produced the EPR paradox - a real achievement which taught us a great deal about quantum theory.

pantulis 2y ago
For all the glory Einstein deserves as one of the greatest minds I find more interesting the history of this supposed "failure" in later life, but it's even more admirable his tenacity at trying to tackle the problem at different angles for decades. And boy it must be a hard problem if Einstein himself could not crack it!
- sdenton4 2y ago
  There's some argument that Einstein was in the right place at the right time. Mercury was wobbly, and there was about fifty years of non-euclidean geometry research built up, including (eg) Riemann breaking ground on differential geometry. Maybe matter didn't crack because the right tools weren't available.
  - pantulis 2y ago
    > including (eg) Riemann breaking ground on differential geometry. And also Poincaré getting close to it.
  - raattgift 2y ago
    Einstein solved three very different open problems in one year: the photoelectric effect, Brownian motion, and special relativity. Others may have gotten close to one of these solutions, but nobody else came anywhere close on all three. General Relativity as his own research programme was designed to capture the consequences of constraining the speed of propagation of changes of gravitational influence; it was literally about relativizing gravity. GR was not designed to explain Mercury specifically (or even really motivated by Mercury), the theory just happened to explain why its orbit traces out a daisy-like pattern rather than a perfect ellipse. GR also correctly predicted a deflection of background starlight around the limb of the sun (1919 eclipse and eclipses since), stellar gravitational redshift (Sirius-B initially, many many objects since), and gravitational redshifts induced by Earth (all reliable results were posthumous: Pound-Rebka and similar since 1959, and more recently precision lunar and satellite ranging). Indeed, Einstein liked to explain that his mental toy in understanding relativistic gravitation was someone jumping off the roof of a house, or the behaviour of things (e.g. flashlights/torches) riding in office-tower elevators/lifts (which date from the 1870s). That's a far cry from precision measurement of Mercury's perihelion! There were no real astrophysical or terrestrial problems calling out for General Relativity. Even after General Relativity was a published theory, real gravitational problems were solved with low-order correcting terms to Newtonian gravitation and with linearization: an approach which Einstein practically invented, and which he used himself when thinking and writing about early problems in cosmology (the discovery of Cepheid variables opened up a lot of those). There were quickly alternatives to General Relativity which predicted some but not all of these early classical tests of the theory. Eddington's 1922 book was the first shot in a body of literature analysing different theories of gravitation and how they differ in their predictions of dozens of tests of General Relativity. Will's work in particular is useful: https://en.wikipedia.org/wiki/Parameterized_post-Newtonian_formalism https://en.wikipedia.org/wiki/Parameterized_post-Newtonian_f... -- you can see how it's used in practice in this open access paper https://www.nature.com/articles/s41467-017-02558-1 https://www.nature.com/articles/s41467-017-02558-1 That said, there are mathematical tools available now that weren't available to Einstein in the early 20th century, and he might have chosen to arrive at a different (but equivalent) formulation of General Relativity. The standard Hamiltonian and a variety of modern Lagrangian formulations are particularly useful, and it could have been nice to have had <https://en.wikipedia.org/wiki/Initial_value_formulation_(general_relativity) https://en.wikipedia.org/wiki/Initial_value_formulation_(gen...> before the 1960s (even though it arguably only shines brighter when you have 21st century supercomputers). Indeed, one can imagine Einstein starting with Lie theory, such that Special Relativity from the start is just the theory of spacetime with SO(3,1) symmetry at every point. But Cartan, Killing, and Noether came decades later and were motivated by Einstein. And quite a bit of group theory developed as the Standard Model developed after Einstein was already dead (notably Goldstone's theorem, 1960s). So to first formulate General Relativity as a GL(4,R) group theory with spontaneous symmetry breaking to SO(3,1) one would need to rearrange an awful lot of physics history. Any of these alternative-universe mathematical origins would just have been using different tools to arrive at the central result: we inhabit a Lorentzian spacetime in which there is an exact matching of moving matter and a metric tensor (at each point in spacetime) encoding durations, spatial lengths, and angles, or the equivalent set of orthonormal vector/covector fields. And worse, the physical content of the theory -- however formulated -- probably would still have been considered interesting but practically useless until the 1970s.

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phkahler 2y ago

An electron falling (electrostatically) toward a proton will reach the speed of light at some point. This is of course the same distance where inside it would need an escape velocity greater than c. So that's an event horizon due to a different force. Some claim matter falling into a black hole never really does from the point of view of an outside observer. I've seen weird sounding descriptions like it "spreads out over the surface". What if electron orbitals are some kind of equivalent to that? When I ask these (admittedly naive) questions, physicists will usually say something like "oh you have to treat that with quantum mechanics". But why? Isn't trying to resolve it using more conventional means (including concepts from relativity) a good idea? I feel like it's not right to reject one approach simply because nobody has figured out how to make it work while another does. That's different from showing that it can't work. Or have such approaches somehow been categorically proven inviable?

cyberax 2y ago
> An electron falling (electrostatically) toward a proton will reach the speed of light at some point. Only in Newton's mechanics. With special relativity, it'll approach the lightspeed. > Some claim matter falling into a black hole never really does from the point of view of an outside observer. I've seen weird sounding descriptions like it "spreads out over the surface". It doesn't. To an outside observer, the object falling towards the black hole just becomes progressively dimmer and more red, until it disappears.
- oneshtein 2y ago
  Even in Newton's mechanic, electron cannot accelerate further after reaching speed of light propagation in the medium. When electron exceeds speed of light it a medium (because of change in medium, for example), it produces Cherenkov radiation.
the__alchemist 2y ago
Another layman observation, based on your last paragraph: In terms of electron orbitals, the definition of what quantum mechanics means varies. For example: Are you using quantum mechanics when describing an electron in hydrogen's orbital? I have heard both answers. It's spread out over space and is not like the classical pre-Bohr models, but it's described by a classical wave equation, and can be viewed at as a differential equation solution; a function over 3D space (For a time snapshot; or 4D spacetime with rotating phase). In this definition, you are not doing quantum mechanics until dealing with things like anti-symmetry, spin statistics, exchange interactions etc.

defamation 2y ago

Sabine is awesome

motohagiography 2y ago

naively, i'd wonder if the time properties of black holes could be used to effect local super-massive gravitational effects on entangled particles here. e.g. they figured out how to entangle the electron and proton of a hydrogen atom with a complementary particle that is being pulled into a black hole, like if there were a way to entangle or entrain a local atom with hawking radiation from a black hole, where as the effect of entanglement, the local atom adopted the dialated time/gravity of its remote counterpart in the black hole. the effect would be that states of matter which only existed on the ephemeral femtosecond scale here would be stabilizied for longer time periods because its "clock" had been slowed down by its adopted clock entanglement via hawking radiation in a kind of black-hole-time. maybe better for a movie script or fiction, but people who think of these things reason them through logically before doing the math as well.

vlovich123 2y ago
I don’t believe you can entangle items remotely like that.
- motohagiography 2y ago
  photons entangle at a distance as there is tech in the market right now in cryptography that uses entangled photons over distances of several miles into orbit. the naive intuition is that lensing hawking radiation might stabilize unstable elements for longer periods.
  - vlovich123 2y ago
    Huh. I thought you had to entangle them locally & then separate them maintaining entanglement. Entangling at a distance is weird. Can you provide a source of entangling particles remotely on Earth & in orbit?
  - tsimionescu 2y ago
    No, you entangle them locally and they maintain their entanglement as they move away from each other.

transfire 2y ago

Well that’s very interesting because one of the latest ideas getting traction on solving the information paradox is exactly this — that black holes are connected to each other and the outside space by wormholes. Check out the current Scientific American special publication.

bmitc 2y ago
I have always understood black holes to be "failed" wormholes. How does that fit into these new ideas?

ls-lah_33 2y ago

I'm surprised Sabine doesn't mention the way fermions are treated in Loop Quantum Gravity [1][2]. My understanding is they are treated as "non-local" or open loops of gravitational force, and thus entry and exit points in space-time. This makes them conceptually similar to the "wormhole model" of matter that Einstein and Rosen originally described. [1] https://arxiv.org/pdf/gr-qc/9404010 https://arxiv.org/pdf/gr-qc/9404010 [2] https://arxiv.org/pdf/1012.4719 https://arxiv.org/pdf/1012.4719

gradschoolfail 2y ago
My understanding is that this is the way fermions are treated in any modern theory of quantum gravity, and not specific to LQG?
- ls-lah_33 2y ago
  Not sure what you mean, are you talking about ER = EPR? I think that's mostly a way of accounting for entanglement between particles, but it doesn't create the particles to begin with like in LQG. But my string theory knowledge is probably out of date, so I could be wrong.
  - gradschoolfail 2y ago
    You already related the “(open)loop quantization” in LQG to EPR=ER above, similar concept occurs in string theory too, almost unknown because its so foundational, see https://en.wikipedia.org/wiki/Born–Infeld_model https://en.wikipedia.org/wiki/Born–Infeld_model, near the end, as well as some of the references there that discuss gravity. “Creating” is a vague(r) term, do you mean “quantization”? Afaik the open-loop geometry of fermions is something any quantization scheme has to start with, the details are how one includes gravity, so without more details, one wouldnt be able to tell how LQG is different from string theory :)

trhway 2y ago

so, Higgs gives mass, and the mass curves the space to produce what the see as gravitation. I think there are some questions here to the Higgs at it seems it has some special relation to the spacetime. And that https://en.wikipedia.org/wiki/Black_hole_electron https://en.wikipedia.org/wiki/Black_hole_electron "...the angular momentum and charge of the electron are too large for a black hole of the electron's mass: a Kerr–Newman object with such a large angular momentum and charge would instead be "super-extremal", displaying a naked singularity, meaning a singularity not shielded by an event horizon." And 2 singularities having worm-hole connection is the entanglement.

tsimionescu 2y ago
Energy gives mass. The Higgs mechanism only explains the mass of the elementary particles (electrons, quarks, W and Z bosons, etc). The vast majority of the mass of everything else comes from the energy of the strong force or the electromagnetism. For example, the vast majority of the mass of a proton is explained by the immense energy of the three quarks and gluons being bound together by the strong force. The mass of the quarks themselves is only a tiny portion of that (about 1%), while gluons are massless. The mass of the atom is further increased by the energy of the electromagnetic force. A hydrogen atom has one proton (1.6726×10^-24 g) plus an electron (9.1×10^-31 g), but the mass of the hydrogen atom is slightly higher than their sum (1.6735×10^-24 g). The mass of a composite particle is at least partly coming from the famous E = mc². The Higgs mechanism is ultimely just a way for elementary particles to have this type of energy as well, even in a void and without any other forces present. There is nothing special about it and spacetime, it works like any other field.

throwmeaway222 2y ago

Nothing has satisfied me between why gravity and magnetism are not the same thing. A ferrous material where the electron poles can be aligned show high forces. Most things are totally misaligned, which I believe creates gravity. No explanation on stackexchange or anything else convinces me. Most of the arguments feel egotistical to me.

damiankennedy 2y ago
What about when an apple falls to the ground, is the apple magnetic?

amai 2y ago

Einsteins later work led only recently to the following exciting conjecture: https://en.wikipedia.org/wiki/ER_%3D_EPR https://en.wikipedia.org/wiki/ER_%3D_EPR Unfortunately the author doesn't seem to know about this idea.

t8sr 2y ago

As a physics student, I feel compelled to point out, to any readers who might now go read Hossenfelders other articles, that many of her views are generally not shared by a majority of physicists today. She is a real physicist and not a kook, but she has been criticized for presenting her views (e.g. superdeterminism) as having much more acceptance than they actually do. She ignores and misrepresents counter-arguments regularly. Her ideas about, e.g. the explanatory power of entanglement wrt processions of moons around (IIRC) Jupiter are certainly well outside what I’d describe as regular astrophysics. The golden standard of science communication was set by Sagan, and he always carefully pointed out when he was expressing a personal opinion, as opposed to one shared by the majority. Sabine Hossenfelder is no Sagan. So proceed with caution. :)

DiggyJohnson 2y ago
Is there any scientist science communicators that this criticism wouldn't apply to? As far as criticism goes, I appreciate how professionally you stated this PSA. Most don't make the same points as gracefully. Best of luck with your studies.
- dinkumthinkum 2y ago
  Neil deGrasse Tyson; if he is working on a s riot prepared by someone else like on a TV Show, he is quite a nice communicator. But, if he does not have such a script, I would say unless he is debunking a flat earther or some actor’s mythical views of mathematics, I would just ignore it. If he talks about biology, which he often does, I would just leave.
  - wileydragonfly 2y ago
    He comments on fields in which he’s unqualified, and his remake of Nova had a ton of unnecessary swearing. And goes on TV and talks about politics. That’s when he lost me.
    - LastTrain 2y ago

frede 2y ago

This recent presentation from Kepler Airospace claims that Einstein was on the right track and a goes even further, stating that gravity can be manipulated through EM. I've graduated in Physics but not quite sure what to make of it. https://www.researchgate.net/publication/383609891_Gravity_Modification_Experiment_Description_and_Results_presented_at_APEC_Propulsion_Conference_83124 https://www.researchgate.net/publication/383609891_Gravity_M...

doug-moen 2y ago
I'm cheering them on, but I'm not confident that the technology works, based on the people involved. I don't think the new physics underlying this work are published in a peer-reviewed physics journal. Here's a page about John Brandenburg, one of the authors: <https://rationalwiki.org/wiki/John_Brandenburg https://rationalwiki.org/wiki/John_Brandenburg>
imglorp 2y ago
Given how easy it seems to reproduce, someone had better explain this effect if it's not what is claimed there... PS: this looks like anyone could reproduce or refute it in their basement for a few hundred dollars given all the details in the slides. I'm hoping some amateurs step in.
- Pompidou 2y ago
  "Gem test" 1 and 2 on john brandenburg 's youtube channel : https://www.youtube.com/watch?v=hqbOnqZtz3Y https://www.youtube.com/watch?v=hqbOnqZtz3Y https://www.youtube.com/watch?v=RSRbLA6dhtk https://www.youtube.com/watch?v=RSRbLA6dhtk
  - imglorp 2y ago
    It all seems to suffer from some of the issues the EM Drive saw: the proposed effect is tiny and very, very difficult to tease apart from environmental and system noise. I hope I'm wrong.
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