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I'm not sure "quantum leaps" were ever seriously described as "instantaneous". Headlines like OP haven't done much service to the more concrete (albeit layman)
by thricegr8 5y ago
I'm not sure "quantum leaps" were ever seriously described as "instantaneous". Headlines like OP haven't done much service to the more concrete (albeit layman) definition; when we are talking about quantum speed limits and propagation, what we are really getting at is the speed at which information is propagated through spacetime.
When we talk about the cosmic speed limit and why nothing can travel faster than light, that's what we are really trying to describe. Not that nothing can travel faster than light, but rather information propagates at a certain speed, which also just so happens to be the speed of light. The consequence is of course that nothing can travel faster than the speed of information propagation, not even "quantum leaps".
- TchoBeer 5y agoWhat is "information"? Is it a physical thing?
- jakeva 5y agoIt is in the same sense that entropy is a physical thing. https://en.wikipedia.org/wiki/Information_theory https://en.wikipedia.org/wiki/Information_theory
- kgwgk 5y agoWhich is not, really. At least not as clearly as other things.
- avmich 5y agoIt's a bit like saying Maxwell equations are not as clear as Newton's laws.
- kgwgk 5y ago“entropy is an anthropomorphic concept, not only in the well-known statistical sense that it measures the extent of human ignorance as to the microstate. Even at the purely phenomenological level, entropy is an anthropomorphic concept. For it is a property, not of the physical system, but of the particular experiments you or I choose to perform on it.” http://www.lptms.u-psud.fr/membres/trizac/Ens/M2MQPL/Jaynes_entropy.pdf http://www.lptms.u-psud.fr/membres/trizac/Ens/M2MQPL/Jaynes_...
- TchoBeer 5y agoI don't know, something about this feels more like an abstraction than a real thing. If you say "the speed of light is the speed limit for information" that doesn't feel like you're saying something about the way the universe works directly.
- krastanov 5y agoPretty much the entirety of modern physics is this type of abstraction (https://en.wikipedia.org/wiki/The_Unreasonable_Effectiveness_of_Mathematics_in_the_Natural_Sciences https://en.wikipedia.org/wiki/The_Unreasonable_Effectiveness...). You are just facing the discomfort felt when your intuition clashes with the tools usually required to make reliable predictions and explanations about the universe. Consider, how is your current discomfort with this statement any different from the discomfort felt through the centuries when ideas like fields instead of forces, entropy, phase spaces, quantum amplitudes / complex numbers, matrix mechanics, spacetime, curvature, etc were being introduced. They are all abstractions that end up being more reliable than our intuition. Whether this "abstraction" is a "real thing" is a question for the philosophers. For me there is no difference between the two.
- jakeva 5y agoSure it's a bit different (especially if you're concerned with how it makes you feel) than, say, describing tectonic plates or the acceleration of a falling body due to earth's gravity but that doesn't make it not a real thing. Quantum spin is one that gets me, or the uncertainty principle. It makes me very uneasy, but whether or not I'm comfortable is irrelevant. Those are to the best of our knowledge actual features of the universe. Abstractions aren't really in the language of the pure sciences. Analogies, metaphors, etc can all serve to help explain but the speed of the propagation of information in this universe is very much defined as the velocity of light in a vacuum in a completely literal sense. There's no abstraction here. Maybe some confusion about what we mean by 'information' but I'm sure there are better resources if you want an afternoon rabbit hole.
- galimaufry 5y agoI'm not sure this answers the question. The wikipedia page is about the entropy of a probability distribution. But the information speed limit is supposed to apply even if everything is totally deterministic. If I write a single, 100% certain message and put it in a spaceship it still cannot go faster than light, even though there is no information transfer (entropy of my message (a constant random variable) is 0). (I'm not saying you are wrong, I am asking to be corrected)
- aeternum 5y agoThe spaceship itself represents a huge chunk of information (such as the atomic arrangement of the metal atoms making up the bolts).
- galimaufry 5y agoI agree that there is "information" in the colloquial sense there, or even in the Kolmogorov sense. I don't understand how there is information in the entropy sense, because I do not see a random variable anywhere in this story.
- aeternum 5y agoEntropy isn't necessarily random. I think a better description of entropy might be unimportant states. For the rocket, we might care about the total mass and we might even care about the temperature of those bolts. Those parameters represent information. But there's even more information in the rocket, specifically the momentum*position of each of the atoms within the bolt. That quantity for each atom is measurable/knowable and represents information.
- mannykannot 5y agoI believe we are talking about Shannon's direct analogy between information and entropy here. The low probabliity of the atoms of the spaceship being arranged as they are - a specific design of a spaceship - out of all their possible arrangements, is a state of low entropy and high information content. https://en.wikipedia.org/wiki/Entropy_(information_theory) https://en.wikipedia.org/wiki/Entropy_(information_theory)
- deleted 5y ago[deleted]
- zkmon 5y agoVery important question. I believe information is a percievable or measurable difference in states of a thing at two different time instants or difference in states of two things. A state of a thing exists only because it can be distinguished from another state; that is, the state exists only because it can encode information relative to another state. How fast information can travel? Just as fast as one can distinguish one state from another. This assumes that there exists an agent capable of distinguishing between the states. How fast can this be done? It doesn't start at one state and end at another state. It is instantaneous recognition of the difference. The information is created just when the difference in states is recognized. There is no start or end. It is an event. Events do not have speed.
- lolthishuman 5y agoKind of sounds like you’re describing the behavior and requirements of consciousness.
- walleeee 5y agoLandauer would say so: https://www.sciencedirect.com/science/article/abs/pii/0375960196004537 https://www.sciencedirect.com/science/article/abs/pii/037596...
- criddell 5y agoI struggle with understanding just what a physical thing is? If a particle is an excitation of a quantum field, then what is a quantum field? Is it anything more than just information?
- aeternum 5y agoI'd say a quantum field is a combination of both information and a rule. The rule determines the quantum field's next state given it's current state (the schrodinger equation). The state of the quantum field could probably be considered nothing more than information.
- vladTheInhaler 5y agoThat appears to be an increasingly common perspective, summed up in the phrase "it from bit". It seems to owe its popularity to this essay by John Wheeler from 1989 [1]. I'm not really familiar with the topic so I can't say more than that. [1] https://philpapers.org/archive/WHEIPQ.pdf https://philpapers.org/archive/WHEIPQ.pdf
- galaxyLogic 5y agoIsn't it simple? Information is the content of a message from one intelligent being to another such that the recipient can understand the intended meaning of the message. Random bits a can randomly arrange into a a configuration that looks like information. But that is not information because there is no intended message behind it. Whereas if an intelligent being organizes a set of bits into a configuration say like in a zip-file which looks like random bits, it is information because it can be decoded into meaning. Information can not exist without "meaning".
- vladTheInhaler 5y agoThat's just not true. Whether the message is from an "intelligent" source or not, it can still contain information. When you make an observation of a random process, you decrease your uncertainty about its state, or in other words, you lower its entropy. In the process, information has been communicated to you.
- galaxyLogic 5y agoAre you saying that the act of observation decreases entropy of the observed system? Or are you saying that entropy is fully in the "eye of the beholder"? If I observe something and you observe the same thing but longer, you reduce the entropy further (for yourself) than I do?
- deleted 5y ago[deleted]
- lolthishuman 5y agoThere’s no simple answer to this question because we fundamentally don’t know what powers “reality.” More or less, information exists as an abstraction of state. From there it branches into various schools of thought from classical physics to digital physics and niche ideas in between.
- RcouF1uZ4gsC 5y ago> rather information propagates at a certain speed, which also just so happens to be the speed of light. Are these fundamentally related, or could we imagine a universe where these are two different numbers?
- morelisp 5y agoIf something was faster than photons and could carry similar information, we'd probably evolve to see those instead of photons. So it seems more like a semantic question. On the other hand things get really weird if we say the fastest way to transmit information has speed in some way a function of that information (e.g. frequency). https://www.gregegan.net/ORTHOGONAL/00/PM.html https://www.gregegan.net/ORTHOGONAL/00/PM.html
- throwaway894345 5y agoThe time it takes light to propagate is not a determining factor in whether or not a particular animal reproduces (namely whether or not it survives to reproduce), so what evolutionary advantage could "faster light" confer? In a more general sense, just because something exists doesn't mean we would evolve the ability to capitalize on it. Think of all of the abilities that would obviously be pretty advantageous which have evolved in species other than ours--that we didn't evolve a hyper-sensitive sense of smell is clearly not because of some deficiency in the universe because dogs and bears and others managed to evolve it..
- morelisp 5y agoedit: lol ok HN hates thought experiments, got it.
- throwaway894345 5y agoIt takes light 33ns to travel from a cheetah to a gazelle 10 meters away. The time it takes the gazelle to process and react to that information takes many orders of magnitude longer, so optimizing or even eliminating that 33ns isn’t going to affect the gazelle’s chances of survival. The bottleneck is never the speed of the photons.
- bostonsre 5y agoDisclaimer: I don't know what I'm talking about, just interested in trying to slightly grasp stuff like this. Have they proven in this research (or other research) or is it generally understood that quantum teleportation propagates at the speed of light?
- nine_k 5y agoYes, it has been; the question whether QT allows for superluminal transmission of information has a firm negative answer, AFAICT. See e.g. https://en.wikipedia.org/wiki/Quantum_teleportation#Non-technical_summary https://en.wikipedia.org/wiki/Quantum_teleportation#Non-tech... QT does not allow for mass transfer, it's purely about information. So, no ansible for us yet.
- ShamelessC 5y agoI believe they're asking about the speed at which the actual teleportation happens? Not a hundred percent on this, but my understanding was that theory suggests it is instantaneous but we can't prove it (and the ultimate limit is still just the speed of light) for the reasons you mentioned. Is that correct?
- krastanov 5y agoIt is not as much incorrect as it is ill defined. The "quantum teleportation protocol" inherently requires the transmission of a classical bit (the weirdness is that a single bit + entanglement is sufficient to "teleport" a quantum state represented by a complex number). So, which part are you asking about when you ask whether it is "instantaneous". I feel like the need for a classical bit makes the question rather moot. Or maybe the question is about the speed of the collapse of the entangled pair upon measurement. That question makes a bit more sense, but its answer is simply "unobservable". The observable effects are all the same independently of the answer of the question, so we do not care. The theory does not say it is instantaneous, the theory says the answer does not matter. You can decide for yourself what this means "philosophically". For most working scientists "unobservable" means that science does not care about it, because it does not matter when considering the workings of the universe. Some of us do try to see whether some extension of the current theory would make the answer observable and also help explain other difficult ideas (but Bell inequality experiments do confirm that it simply does not matter).
- krastanov 5y ago"Quantum speed limit" as is usually used in the field has little to nothing to do with the speed of light. "Finite speed at which information propagates through space or time" appears also in theories that do not know about relativity or about space and time being unified. E.g. the "quantum speed limit" that has more to do with differential equations and control theory (the "boring" engineering field). Otherwise you are right, but the term you used will regretfully cause much confusion if people start googling its usual meaning https://en.wikipedia.org/wiki/Quantum_speed_limit https://en.wikipedia.org/wiki/Quantum_speed_limit
- liuhenry 5y agoRight, quantum jumps as used here is actually a specific technical term. It seems like the parent comment takes it to be a lay analogy, but it’s from a formulation called quantum trajectory theory [1]. Rather, the result is about the electrons in an atom jumping between energy levels and experimentally observing a continuous evolution. [1] https://en.m.wikipedia.org/wiki/Quantum_Trajectory_Theory https://en.m.wikipedia.org/wiki/Quantum_Trajectory_Theory
- dang 5y agoOk, we've replaced the title with the subtitle. It was objected to in the previous discussion too: Quantum Leaps, Long Assumed to Be Instantaneous, Take Time - https://news.ycombinator.com/item?id=20105091 https://news.ycombinator.com/item?id=20105091 - June 2019 (95 comments)
- inopinatus 5y agoIf all energy is information, then this would lead to a cosmology such that perception is the lazy evaluation of a functional universe. Unfortunately this doesn't necessarily bridge classical and quantum.
- junon 5y agoSorry, but what?
- odyssey7 5y agoI read this as: the universe doesn’t bother with bringing things where they would go, until their spot needs to be computed due to some other spot depending on that spot’s state.
- inopinatus 5y agoAh, yes, sorry, that’s a fragment of something I’m mulling, but it’s basically nonsense out of context (and may be nonsense in context too).