13 ms·

Where do space, time and gravity come from?

145 points by digital55 4y ago

tempodox 4y ago
I have a theory that to answer the question “where does X come from?” you need a viewpoint outside of X. Since we're presumably incapable of attaining a viewpoint outside of space, or time, I wouldn't expect any answers beyond more or less educated guesses.
- Byamarro 4y ago
  We did discover though that the Earth is not the center of the universe without leaving it. Then with Newton we could learn where the arrangement of planets come from. Then Einstein developed further the knowledge about gravity without leaving the gravitational field.
  - RcouF1uZ4gsC 4y ago
    But we could observe things outside of earth. We cannot observe anything outside of space and time.
    - snarfy 4y ago
      It's debatable [1] [1] - https://physicsworld.com/a/new-evidence-for-cyclic-universe-claimed-by-roger-penrose-and-colleagues/ https://physicsworld.com/a/new-evidence-for-cyclic-universe-...
      - TecoAndJix 4y ago
        I hope this is true. Then I get to be immortal by nature of the infinite monkey theorem. I'll always come back! https://en.wikipedia.org/wiki/Infinite_monkey_theorem https://en.wikipedia.org/wiki/Infinite_monkey_theorem
        albrewer 4y ago
        Ugh, I can't believe you'd repost something you've already said 70 trillion years ago
        nonameiguess 4y ago
        This is actually terrifying in many respects. It's the basis of the eternal return idea, probably best known from Nietzsche, but found in many traditions. It compounds the consequences of anything that ever happens. Without it, you can at least take comfort in knowing anyone with the misfortune to live and die under chattel slavery, Naziism, or some other great evil at least only had to do it for one lifetime and then they get to escape forever to eternal peace. In a cyclic infinite monkey universe, nope, everything that ever happens happens infinitely many times, and those people who spent their entire lives on a plantation in fact spend eternity on a plantation. It's hell but real, and not levied as punishment but by pure randomness.
        simonh 4y ago
        Except they're not the same person, they're just (mostly) variations on people that happen to be similar. It's a big universe. If it proves to be even more staggeringly big, well, it's more than I can comprehend either way.
    - Byamarro 4y ago
      We still did conclude how gravity more or less works while being within gravitational field.
- chrisjc 4y ago
  Not that I proclaim to have any idea how to answer any of these questions, but there is something about the question of time that I can never get past. And I feel like it's similar to what you're saying? 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.
  - Eddy_Viscosity2 4y ago
    Indeed, it could be we are just not capable of understanding it for what it really is and the best we can do is make models that we can understand that fit some parts of what we see, but not all. We try new models but with the same results. We'll never be able to get it all right because its beyond of capacity. Or It's just something that we haven't figured out yet, and eventually will.
  - atonalfreerider 4y ago
    Roger Penrose came up with a very plausible theory that the heat death of our universe looks like the big bang moment, from the perspective of a photon. So our universe is caught in a cycle of birth death rebirth ad infinitum. [0] https://www.indiatoday.in/science/story/big-bang-didn-t-start-our-universe-there-was-another-universe-before-it-nobel-laureate-roger-penrose-1730064-2020-10-09 https://www.indiatoday.in/science/story/big-bang-didn-t-star...
    - paulrouget 4y ago
      iirc the CMB clues he’s talking about to justify the CCC have been ruled out.
- rgrieselhuber 4y ago
  Similar to Gödel’s incompleteness theorems.
  - simonh 4y ago
    Exactly, you can't verify a system using that system, so maybe it's not possible to exactly specify all of mathematics and physics within our universe. 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.
    - rgrieselhuber 4y ago
      Exactly. This is one reason I inherently distrust all closed-loop systems.
- meroes 4y ago
  This is scary when applied to consciousness to. How will we ever understand what makes consciousness from within consciousness?
  - amelius 4y ago
    Someone else's consciousness?
  - morelisp 4y ago
    Formally, this philosophical position is called mysterianism. https://en.wikipedia.org/wiki/New_mysterianism 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.
  - akomtu 4y ago
    By observing another small consciousness? That's like looking in the mirror. The traditional viewpoint of metaphysics, which studies consciousness, is that there are many such tiny mirrors everywhere, and all these mirrors reflect the one true consciousness that tries to understand itself by looking into these mirrors. Once it reaches this understanding, all the mirrors will go flat, will merge into one surface and will effectively disappear.
    - meroes 4y ago
      Is this the the “mirror of reality”? How does it respond to the view we can never fully escape our representation of the world?
      - akomtu 4y ago
        The "cannot escape" part is where physics disagrees with metaphysics. The latter believes that there's 'absolute existence' that creates and uses reality as a crutch or a mirror to learn walking. 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.
- jasomill 4y ago
  People say again and again that philosophy doesn’t really progress, that we are still occupied with the same philosophical problems as were the Greeks. But the people who say this don’t understand why this has to be so. It is because our language has remained the same and keeps seducing us into asking questions. As long as there continues to be a verb ‘to be’ that looks as if it functions in the same way as ‘to eat’ and ‘to drink’, as long as we still have the adjectives ‘identical’, ‘false’, ‘possible’, as long as we continue to talk of a river of time, of an expanse of space, etc. etc., people will still keep stumbling over the same puzzling difficulties and find themselves staring at something which no explanation seems capable of clearing up. 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/mode/2up https://archive.org/details/culturevalue0000witt/page/n44/mo...
madaxe_again 4y ago
This was a great read, and it was heartening to be reminded that there are plenty of talented physicists out there who aren’t afraid to lift the rug and see what’s under there. 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.
- Comevius 4y ago
  Information thermodynamics is a fertile research field that gave us a lot of insight into physics, and also chemistry and biology. Beyond solving Maxwell's daemon (one of the early clues that information is physical and intricately linked to thermodynamics) experimentally, we can also build tiny machines fueled by information, so called information engines. I'm not sure how this relates to quantum gravity, I think that one is going to be harder to figure out.
  - mhh__ 4y ago
    Unless it's one more systemd feature, it's Maxwell's "demon"
TheMightyLlama 4y ago
I love that there are people far more educated than me who are also paid to explore these topics. 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) --- We are not being 'pulled' into the earth We are being 'kept under' by a shower of space time being consumed --- What causes this 'consumption' of spacetime around objects with mass? Gluon color confinement https://gist.github.com/TheMightyLlama/135fd67eb0577c34093caa32f2fef6a2#file-what-is-gravity https://gist.github.com/TheMightyLlama/135fd67eb0577c34093ca...
- galcerte 4y ago
  >I love that there are people far more educated than me who are also paid to explore these topics. 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.
- audunw 4y ago
  That's interesting. I've had the opposite thought: that spacetime is created by particle interactions, and so mass is essentially "shedding" spacetime. You'd think this would push other particles away, but the process of spacetime being shed away from a mass would be slow, but the increased density caused by spacetime creation would cause particles to be attracted in the direction of higher density. 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.
Koshkin 4y ago
It’s kind of amazing to me that in a 100 years a whole lot of extremely smart, and very focused, people couldn’t arrive to a verifiable way of bringing together QM and GR. There’s something wrong with this situation.
- wheelerof4te 4y ago
  "There’s something wrong with this situation." Or, there is something wrong with the theory?
  - Cthulhu_ 4y ago
    I mean it's possible, but there's not been any successful alternatives - and I'm confident we've had smarter people than Einstein and co work on it.
  - Koshkin 4y ago
    There is nothing wrong with a theory being wrong. (They are all mostly "linear approximations" anyway.)
- deleted 4y ago
  [deleted]
- prof-dr-ir 4y ago
  Perhaps we are just not smart enough? After all, you cannot teach a dog quantum mechanics...
  - IAmGraydon 4y ago
    I've held this belief for a long time. We tend to think we have the brainpower but we just need the understanding. I think it's far more likely that we have nowhere near the brainpower required to understand the true nature of reality.
    - the_only_law 4y ago
      I’ve ironically thought the seams about fully understanding the human brain.
jonnat 4y ago
An episode from Sean's podcast in which he builds the argument in more detail: https://www.preposterousuniverse.com/podcast/2019/09/09/63-solo-finding-gravity-within-quantum-mechanics/ https://www.preposterousuniverse.com/podcast/2019/09/09/63-s...
derbOac 4y ago
Seems to me that you'd have to have a better understanding of quantum mechanics before it's applied to gravity, given that gravity is usually thought of on scales much larger than QM. I'm having trouble explaining what I mean by that, but an entity like a star isn't a particle, it's a system of many particles, which is where people have trouble with QM — cf quantum computers. Seems like we'd have to have a better understanding of system - level quantum dynamics before really understanding gravity (or maybe understanding gravity would give leverage to something like quantum computing?)
- deleted 4y ago
  [deleted]
- meroes 4y ago
  Interestingly QM is also the theory of the very large. Entanglement is not attenuated by distance while gravity is. Also in aDS spacetime (closed rather than open topology, not our known universe) new observables would come into play which reflect off the edge of the universe. Also two black holes can be entangled.
  - derbOac 4y ago
    Yeah good point. By "scale" I meant more like "numbers of elements" or something, size in that sense more than physical size, although I guess I was kind of thinking of them as similar. But you're right that space size and numbers of things size aren't necessarily the same.
qwerty456127 4y ago
Why isn't it enough to consider spacetime (not space and time separately) the only thing existing, and its everything else being its properties (e.g. gravity - curvature)?
- mr_mitm 4y ago
  Because then you apparently end up with two incompatible theories: quantum mechanics and general relativity. Treating space and time as emergent may be a potential solution.
  - SemanticStrengh 4y ago
    The unification is a solved problem, as always it's simply that the solutions are ignored by the scientific community. see e.g. the first valid cannonical quantization of Gravity https://arxiv.org/pdf/gr-qc/9706055.pdf https://arxiv.org/pdf/gr-qc/9706055.pdf GR and QM are fundamentally incompatible and will never be, however one can fork either GR or QM to reconciliate them.
    - mr_mitm 4y ago
      Several facts about this paper are huge red flags even without reading it in detail: * 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.
      - SemanticStrengh 4y ago
seydor 4y ago
Well from the structure of our brain of course
- SemanticStrengh 4y ago
  The world would keep existing without you and me.
  - seydor 4y ago
    none of us can know that
    - SemanticStrengh 4y ago
      well I mean, you could be the main character and the past could have been simulated accurately billions of universe years of causal calculations out of an initial seed, but the simulation hypothesis does not explain the meta-universe behind the simulator and indeed the probability of this gigantic universe existing just for you (others being philosophical zombies), while remarkably possible, is also remarkably unlikely.
jameshart 4y ago
Question seems malformed. The answer to a ‘where’ question is referenced to ‘space’. ‘Where does space come from?’ is as odd a thing to ask as ‘when does time come from?’, ‘how do methods work?’ or ‘why are there reasons?’
- deleted 4y ago
  [deleted]
- marginalia_nu 4y ago
  Maybe it's my philosophy-addled brain, but I think these all sound like excellent questions.
- bqmjjx0kac 4y ago
  The answer to "where do babies come from?" is not "a uterus".
  - jameshart 4y ago
    That seems like an excellent, factually accurate answer to me.
    - AnimalMuppet 4y ago
      It answers the immediate cause, but there's a lot more than that going on. Because the answer ignores all the rest of what's going on, it's a bad (but still accurate) answer.
    - _moof 4y ago
      The point is that there are senses of the word "where" that have nothing to do with location, and it is one of those senses that is operative in the question "where does space come from."
lesgobrandon 4y ago
arminiusreturns 4y ago
My personal, completely layman's theory, is that the dual universe theory is the localized correct approach (there may be other dual universes outside ours), and that at the big bang matter on the other side became entangled as it entered our universe (or dimension?), and that in some sort of cosmological osmosis, matter that broke that barrier and became entangled seeks to return to it's original state (in the other universe) or some similar sort of equilibrium, likely through black holes and white holes. (eg, other universe a white hole here would look like black hole there, and vice versa). Gravity pulls stuff together until it finally collapses into creating a semi-localized blackhole (explaining the theory of a blackhole in every galaxy). Gravity in this case would then be a second tier effect of entanglement which is locally weak but cosmologically strong, with gravity being the opposite. If this were the case, the main place to focus for experimental predictions to reveal more on this would then be probably be anti/dark matter experiments.
titzer 4y ago
If the universe can be described by finite information, it kind of doesn't matter if the theories are unified into one equation. Even if the description of the universe is just a list of Planck-length time frames of states--a very long, very large execution trace, if you will--it being finite information would mean that its description, when encoded into bits, using whatever encoding you like, would necessarily appear in the bits of pi[1], somewhere. Which means a complete snapshot of our universe, in fact every possible finite-information universe, exists stored in pi. In that eventuality, it's already over, bro! [1] Or any transcendental number, for that matter, or any truly random sequence.
- paskozdilar 4y ago
  Note that pi is not known to have this property, but it is expected to be true. 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... Which is proven to be transcendental [0], but still does not contain a digit "2" in its decimal expansion, so therefore it does not contain all finite sequences of numbers. You were probably thinking of Normal numbers [1], pi is widely believed to be a normal number. [0] https://en.wikipedia.org/wiki/Liouville_number https://en.wikipedia.org/wiki/Liouville_number [1] https://en.wikipedia.org/wiki/Normal_number https://en.wikipedia.org/wiki/Normal_number
  - titzer 4y ago
    Interesting, thanks.
- majormajor 4y ago
  I'm not sure I'm comfortable with equating "these numbers would eventually be found in the digits of pi" with "this is 'stored' in pi." 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?
awinter-py 4y ago
feels like 20th century physics was us learning everything about every particle you're likely to encounter in your day, and what they do when they touch 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 https://books.google.com/books?id=CSIDAAAAMBAJ&pg=PA463 https://books.google.com/books?id=CSIDAAAAMBAJ&pg=PA463
mescaline 4y ago
Spin. Everything that has gravity eventually spins, so spin produces gravity and gravity produces spin. Even the moon spins, so I must be right. 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.
- marginalia_nu 4y ago
  If spin causes gravity, why doesn't a ferromagnet get lighter above the curie temperature?
  - mescaline 4y ago
    Above the Curie temperature for a given material, the spin orbits of the atoms are randomized. When it was a "magnet" the atoms spin orbits were lined up. 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.
steve76 4y ago
joncp 4y ago
Sean Carroll is a master of making quantum mechanics approachable to non-physicists. Here are a few of his talks: - Fermilab 2013: https://youtu.be/gEKSpZPByD0 https://youtu.be/gEKSpZPByD0 - The Royal Institution 2014: https://youtu.be/_8bhtEgB8Mo https://youtu.be/_8bhtEgB8Mo - The Royal Institution 2020: https://youtu.be/5hVmeOCJjOU https://youtu.be/5hVmeOCJjOU
- raymond_goo 4y ago
  I highly agree and also recommend: https://www.youtube.com/watch?v=5hVmeOCJjOU https://www.youtube.com/watch?v=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 https://www.youtube.com/watch?v=2JsKwyRFiYY Mysteries of Modern Physics by Sean Carroll https://www.youtube.com/watch?v=rBpR0LBsUfM https://www.youtube.com/watch?v=rBpR0LBsUfM
TheOtherHobbes 4y ago
I'm probably missing something, but "First assume there's an abstract wavefunction and see what happens if everything is entangled" seems to me like a classic example of begging the question. 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.
- whatshisface 4y ago
  You can establish the wave function and entanglement by doing experiments unrelated to gravity, so if gravity comes out of them that's still fairly impressive. (I am not sure if it actually does.) You are right that making assumptions and reasoning from them does not itself make your conclusions true, but it does change the "input port" where you have to plug in your empirical observations to some proposition hopefully more easily demonstrated.
- jlokier 4y ago
  It's not begging the question. It is a Gedankenexperiment (https://en.wikipedia.org/wiki/Thought_experiment https://en.wikipedia.org/wiki/Thought_experiment). 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.
lesgobrandon 4y ago
civilized 4y ago
Is there any way for someone with an undergrad level background in special relativity and QM to understand why GR and QM don't work together? 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.
- Koshkin 4y ago
  Why should they? Newton's mechanics and electrodynamics don't work together, either. They are simply different theories - both conceptually and mathematically.
  - civilized 4y ago
    Physical theories are supposed to work together, and classical mech and electrodynamics mostly do. Electrodynamics is expressed in the language of Newtonian mechanics (e.g. fields represent force per charge), and the experiments that established the laws of electromagnetism used Newtonian mechanics as their framework. There are specific inconsistencies between Newtonian mechanics and electrodynamics, inconsistencies which spurred the development of special relativity. 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.
- akomtu 4y ago
  Because QM needs absolute time and space coordinates?
- wanda 4y ago
  In GR, gravity is an emergent property of mass interaction with the geometry of 4D spacetime. The more mass, the more spacetime is curved by the massive object. 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.
graycat 4y ago
An electron passes through a beam splitter. Thus the wave function is now in two parts (pieces). We wait a week. 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?
codethief 4y ago
Great podcast! > 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.)

145 points by digital55 4y ago

I have a theory that to answer the question “where does X come from?” you need a viewpoint outside of X. Since we're presumably incapable of attaining a viewpoint outside of space, or time, I wouldn't expect any answers beyond more or less educated guesses.

Byamarro 4y ago
We did discover though that the Earth is not the center of the universe without leaving it. Then with Newton we could learn where the arrangement of planets come from. Then Einstein developed further the knowledge about gravity without leaving the gravitational field.
- RcouF1uZ4gsC 4y ago
  But we could observe things outside of earth. We cannot observe anything outside of space and time.
  - snarfy 4y ago
    It's debatable [1] [1] - https://physicsworld.com/a/new-evidence-for-cyclic-universe-claimed-by-roger-penrose-and-colleagues/ https://physicsworld.com/a/new-evidence-for-cyclic-universe-...
    - TecoAndJix 4y ago
      I hope this is true. Then I get to be immortal by nature of the infinite monkey theorem. I'll always come back! https://en.wikipedia.org/wiki/Infinite_monkey_theorem https://en.wikipedia.org/wiki/Infinite_monkey_theorem
      - albrewer 4y ago
        Ugh, I can't believe you'd repost something you've already said 70 trillion years ago
      - nonameiguess 4y ago
        This is actually terrifying in many respects. It's the basis of the eternal return idea, probably best known from Nietzsche, but found in many traditions. It compounds the consequences of anything that ever happens. Without it, you can at least take comfort in knowing anyone with the misfortune to live and die under chattel slavery, Naziism, or some other great evil at least only had to do it for one lifetime and then they get to escape forever to eternal peace. In a cyclic infinite monkey universe, nope, everything that ever happens happens infinitely many times, and those people who spent their entire lives on a plantation in fact spend eternity on a plantation. It's hell but real, and not levied as punishment but by pure randomness.
        simonh 4y ago
        Except they're not the same person, they're just (mostly) variations on people that happen to be similar. It's a big universe. If it proves to be even more staggeringly big, well, it's more than I can comprehend either way.
  - Byamarro 4y ago
    We still did conclude how gravity more or less works while being within gravitational field.
chrisjc 4y ago
Not that I proclaim to have any idea how to answer any of these questions, but there is something about the question of time that I can never get past. And I feel like it's similar to what you're saying? 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.
- Eddy_Viscosity2 4y ago
  Indeed, it could be we are just not capable of understanding it for what it really is and the best we can do is make models that we can understand that fit some parts of what we see, but not all. We try new models but with the same results. We'll never be able to get it all right because its beyond of capacity. Or It's just something that we haven't figured out yet, and eventually will.
- atonalfreerider 4y ago
  Roger Penrose came up with a very plausible theory that the heat death of our universe looks like the big bang moment, from the perspective of a photon. So our universe is caught in a cycle of birth death rebirth ad infinitum. [0] https://www.indiatoday.in/science/story/big-bang-didn-t-start-our-universe-there-was-another-universe-before-it-nobel-laureate-roger-penrose-1730064-2020-10-09 https://www.indiatoday.in/science/story/big-bang-didn-t-star...
  - paulrouget 4y ago
    iirc the CMB clues he’s talking about to justify the CCC have been ruled out.
rgrieselhuber 4y ago
Similar to Gödel’s incompleteness theorems.
- simonh 4y ago
  Exactly, you can't verify a system using that system, so maybe it's not possible to exactly specify all of mathematics and physics within our universe. 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.
  - rgrieselhuber 4y ago
    Exactly. This is one reason I inherently distrust all closed-loop systems.
meroes 4y ago
This is scary when applied to consciousness to. How will we ever understand what makes consciousness from within consciousness?
- amelius 4y ago
  Someone else's consciousness?
- morelisp 4y ago
  Formally, this philosophical position is called mysterianism. https://en.wikipedia.org/wiki/New_mysterianism 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.
- akomtu 4y ago
  By observing another small consciousness? That's like looking in the mirror. The traditional viewpoint of metaphysics, which studies consciousness, is that there are many such tiny mirrors everywhere, and all these mirrors reflect the one true consciousness that tries to understand itself by looking into these mirrors. Once it reaches this understanding, all the mirrors will go flat, will merge into one surface and will effectively disappear.
  - meroes 4y ago
    Is this the the “mirror of reality”? How does it respond to the view we can never fully escape our representation of the world?
    - akomtu 4y ago
      The "cannot escape" part is where physics disagrees with metaphysics. The latter believes that there's 'absolute existence' that creates and uses reality as a crutch or a mirror to learn walking. 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.
jasomill 4y ago
People say again and again that philosophy doesn’t really progress, that we are still occupied with the same philosophical problems as were the Greeks. But the people who say this don’t understand why this has to be so. It is because our language has remained the same and keeps seducing us into asking questions. As long as there continues to be a verb ‘to be’ that looks as if it functions in the same way as ‘to eat’ and ‘to drink’, as long as we still have the adjectives ‘identical’, ‘false’, ‘possible’, as long as we continue to talk of a river of time, of an expanse of space, etc. etc., people will still keep stumbling over the same puzzling difficulties and find themselves staring at something which no explanation seems capable of clearing up. 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/mode/2up https://archive.org/details/culturevalue0000witt/page/n44/mo...

madaxe_again 4y ago

This was a great read, and it was heartening to be reminded that there are plenty of talented physicists out there who aren’t afraid to lift the rug and see what’s under there. 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.

Comevius 4y ago
Information thermodynamics is a fertile research field that gave us a lot of insight into physics, and also chemistry and biology. Beyond solving Maxwell's daemon (one of the early clues that information is physical and intricately linked to thermodynamics) experimentally, we can also build tiny machines fueled by information, so called information engines. I'm not sure how this relates to quantum gravity, I think that one is going to be harder to figure out.
- mhh__ 4y ago
  Unless it's one more systemd feature, it's Maxwell's "demon"

TheMightyLlama 4y ago

I love that there are people far more educated than me who are also paid to explore these topics. 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) --- We are not being 'pulled' into the earth We are being 'kept under' by a shower of space time being consumed --- What causes this 'consumption' of spacetime around objects with mass? Gluon color confinement https://gist.github.com/TheMightyLlama/135fd67eb0577c34093caa32f2fef6a2#file-what-is-gravity https://gist.github.com/TheMightyLlama/135fd67eb0577c34093ca...

galcerte 4y ago
>I love that there are people far more educated than me who are also paid to explore these topics. 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.
audunw 4y ago
That's interesting. I've had the opposite thought: that spacetime is created by particle interactions, and so mass is essentially "shedding" spacetime. You'd think this would push other particles away, but the process of spacetime being shed away from a mass would be slow, but the increased density caused by spacetime creation would cause particles to be attracted in the direction of higher density. 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.

Koshkin 4y ago

It’s kind of amazing to me that in a 100 years a whole lot of extremely smart, and very focused, people couldn’t arrive to a verifiable way of bringing together QM and GR. There’s something wrong with this situation.

wheelerof4te 4y ago
"There’s something wrong with this situation." Or, there is something wrong with the theory?
- Cthulhu_ 4y ago
  I mean it's possible, but there's not been any successful alternatives - and I'm confident we've had smarter people than Einstein and co work on it.
- Koshkin 4y ago
  There is nothing wrong with a theory being wrong. (They are all mostly "linear approximations" anyway.)
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prof-dr-ir 4y ago
Perhaps we are just not smart enough? After all, you cannot teach a dog quantum mechanics...
- IAmGraydon 4y ago
  I've held this belief for a long time. We tend to think we have the brainpower but we just need the understanding. I think it's far more likely that we have nowhere near the brainpower required to understand the true nature of reality.
  - the_only_law 4y ago
    I’ve ironically thought the seams about fully understanding the human brain.

jonnat 4y ago

An episode from Sean's podcast in which he builds the argument in more detail: https://www.preposterousuniverse.com/podcast/2019/09/09/63-solo-finding-gravity-within-quantum-mechanics/ https://www.preposterousuniverse.com/podcast/2019/09/09/63-s...

derbOac 4y ago

Seems to me that you'd have to have a better understanding of quantum mechanics before it's applied to gravity, given that gravity is usually thought of on scales much larger than QM. I'm having trouble explaining what I mean by that, but an entity like a star isn't a particle, it's a system of many particles, which is where people have trouble with QM — cf quantum computers. Seems like we'd have to have a better understanding of system - level quantum dynamics before really understanding gravity (or maybe understanding gravity would give leverage to something like quantum computing?)

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meroes 4y ago
Interestingly QM is also the theory of the very large. Entanglement is not attenuated by distance while gravity is. Also in aDS spacetime (closed rather than open topology, not our known universe) new observables would come into play which reflect off the edge of the universe. Also two black holes can be entangled.
- derbOac 4y ago
  Yeah good point. By "scale" I meant more like "numbers of elements" or something, size in that sense more than physical size, although I guess I was kind of thinking of them as similar. But you're right that space size and numbers of things size aren't necessarily the same.

qwerty456127 4y ago

Why isn't it enough to consider spacetime (not space and time separately) the only thing existing, and its everything else being its properties (e.g. gravity - curvature)?

mr_mitm 4y ago
Because then you apparently end up with two incompatible theories: quantum mechanics and general relativity. Treating space and time as emergent may be a potential solution.
- SemanticStrengh 4y ago
  The unification is a solved problem, as always it's simply that the solutions are ignored by the scientific community. see e.g. the first valid cannonical quantization of Gravity https://arxiv.org/pdf/gr-qc/9706055.pdf https://arxiv.org/pdf/gr-qc/9706055.pdf GR and QM are fundamentally incompatible and will never be, however one can fork either GR or QM to reconciliate them.
  - mr_mitm 4y ago
    Several facts about this paper are huge red flags even without reading it in detail: * 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.
    - SemanticStrengh 4y ago

seydor 4y ago

Well from the structure of our brain of course

SemanticStrengh 4y ago
The world would keep existing without you and me.
- seydor 4y ago
  none of us can know that
  - SemanticStrengh 4y ago
    well I mean, you could be the main character and the past could have been simulated accurately billions of universe years of causal calculations out of an initial seed, but the simulation hypothesis does not explain the meta-universe behind the simulator and indeed the probability of this gigantic universe existing just for you (others being philosophical zombies), while remarkably possible, is also remarkably unlikely.

jameshart 4y ago

Question seems malformed. The answer to a ‘where’ question is referenced to ‘space’. ‘Where does space come from?’ is as odd a thing to ask as ‘when does time come from?’, ‘how do methods work?’ or ‘why are there reasons?’

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marginalia_nu 4y ago
Maybe it's my philosophy-addled brain, but I think these all sound like excellent questions.
bqmjjx0kac 4y ago
The answer to "where do babies come from?" is not "a uterus".
- jameshart 4y ago
  That seems like an excellent, factually accurate answer to me.
  - AnimalMuppet 4y ago
    It answers the immediate cause, but there's a lot more than that going on. Because the answer ignores all the rest of what's going on, it's a bad (but still accurate) answer.
  - _moof 4y ago
    The point is that there are senses of the word "where" that have nothing to do with location, and it is one of those senses that is operative in the question "where does space come from."

lesgobrandon 4y ago

arminiusreturns 4y ago

My personal, completely layman's theory, is that the dual universe theory is the localized correct approach (there may be other dual universes outside ours), and that at the big bang matter on the other side became entangled as it entered our universe (or dimension?), and that in some sort of cosmological osmosis, matter that broke that barrier and became entangled seeks to return to it's original state (in the other universe) or some similar sort of equilibrium, likely through black holes and white holes. (eg, other universe a white hole here would look like black hole there, and vice versa). Gravity pulls stuff together until it finally collapses into creating a semi-localized blackhole (explaining the theory of a blackhole in every galaxy). Gravity in this case would then be a second tier effect of entanglement which is locally weak but cosmologically strong, with gravity being the opposite. If this were the case, the main place to focus for experimental predictions to reveal more on this would then be probably be anti/dark matter experiments.

titzer 4y ago

If the universe can be described by finite information, it kind of doesn't matter if the theories are unified into one equation. Even if the description of the universe is just a list of Planck-length time frames of states--a very long, very large execution trace, if you will--it being finite information would mean that its description, when encoded into bits, using whatever encoding you like, would necessarily appear in the bits of pi[1], somewhere. Which means a complete snapshot of our universe, in fact every possible finite-information universe, exists stored in pi. In that eventuality, it's already over, bro! [1] Or any transcendental number, for that matter, or any truly random sequence.

paskozdilar 4y ago
Note that pi is not known to have this property, but it is expected to be true. 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... Which is proven to be transcendental [0], but still does not contain a digit "2" in its decimal expansion, so therefore it does not contain all finite sequences of numbers. You were probably thinking of Normal numbers [1], pi is widely believed to be a normal number. [0] https://en.wikipedia.org/wiki/Liouville_number https://en.wikipedia.org/wiki/Liouville_number [1] https://en.wikipedia.org/wiki/Normal_number https://en.wikipedia.org/wiki/Normal_number
- titzer 4y ago
  Interesting, thanks.
majormajor 4y ago
I'm not sure I'm comfortable with equating "these numbers would eventually be found in the digits of pi" with "this is 'stored' in pi." 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?

awinter-py 4y ago

feels like 20th century physics was us learning everything about every particle you're likely to encounter in your day, and what they do when they touch 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 https://books.google.com/books?id=CSIDAAAAMBAJ&pg=PA463 https://books.google.com/books?id=CSIDAAAAMBAJ&pg=PA463

mescaline 4y ago

Spin. Everything that has gravity eventually spins, so spin produces gravity and gravity produces spin. Even the moon spins, so I must be right. 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.

marginalia_nu 4y ago
If spin causes gravity, why doesn't a ferromagnet get lighter above the curie temperature?
- mescaline 4y ago
  Above the Curie temperature for a given material, the spin orbits of the atoms are randomized. When it was a "magnet" the atoms spin orbits were lined up. 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.

steve76 4y ago

joncp 4y ago

Sean Carroll is a master of making quantum mechanics approachable to non-physicists. Here are a few of his talks: - Fermilab 2013: https://youtu.be/gEKSpZPByD0 https://youtu.be/gEKSpZPByD0 - The Royal Institution 2014: https://youtu.be/_8bhtEgB8Mo https://youtu.be/_8bhtEgB8Mo - The Royal Institution 2020: https://youtu.be/5hVmeOCJjOU https://youtu.be/5hVmeOCJjOU

raymond_goo 4y ago
I highly agree and also recommend: https://www.youtube.com/watch?v=5hVmeOCJjOU https://www.youtube.com/watch?v=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 https://www.youtube.com/watch?v=2JsKwyRFiYY Mysteries of Modern Physics by Sean Carroll https://www.youtube.com/watch?v=rBpR0LBsUfM https://www.youtube.com/watch?v=rBpR0LBsUfM

TheOtherHobbes 4y ago

I'm probably missing something, but "First assume there's an abstract wavefunction and see what happens if everything is entangled" seems to me like a classic example of begging the question. 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.

whatshisface 4y ago
You can establish the wave function and entanglement by doing experiments unrelated to gravity, so if gravity comes out of them that's still fairly impressive. (I am not sure if it actually does.) You are right that making assumptions and reasoning from them does not itself make your conclusions true, but it does change the "input port" where you have to plug in your empirical observations to some proposition hopefully more easily demonstrated.
jlokier 4y ago
It's not begging the question. It is a Gedankenexperiment (https://en.wikipedia.org/wiki/Thought_experiment https://en.wikipedia.org/wiki/Thought_experiment). 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.

lesgobrandon 4y ago

civilized 4y ago

Is there any way for someone with an undergrad level background in special relativity and QM to understand why GR and QM don't work together? 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.

Koshkin 4y ago
Why should they? Newton's mechanics and electrodynamics don't work together, either. They are simply different theories - both conceptually and mathematically.
- civilized 4y ago
  Physical theories are supposed to work together, and classical mech and electrodynamics mostly do. Electrodynamics is expressed in the language of Newtonian mechanics (e.g. fields represent force per charge), and the experiments that established the laws of electromagnetism used Newtonian mechanics as their framework. There are specific inconsistencies between Newtonian mechanics and electrodynamics, inconsistencies which spurred the development of special relativity. 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.
akomtu 4y ago
Because QM needs absolute time and space coordinates?
wanda 4y ago
In GR, gravity is an emergent property of mass interaction with the geometry of 4D spacetime. The more mass, the more spacetime is curved by the massive object. 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.

graycat 4y ago

An electron passes through a beam splitter. Thus the wave function is now in two parts (pieces). We wait a week. 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?

codethief 4y ago

Great podcast! > 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.)