[HN Gopher] Why quantum entanglement doesn't allow faster-than-l...
___________________________________________________________________
Why quantum entanglement doesn't allow faster-than-light
communication (2016)
Author : list
Score : 66 points
Date : 2024-03-28 05:01 UTC (1 days ago)
(HTM) web link (www.forbes.com)
(TXT) w3m dump (www.forbes.com)
| TheDudeMan wrote:
| "3 Body Problem" has so many problems!
|
| Wake me up when the next "Expanse"-level sci-fi lands.
| amingilani wrote:
| To expand on this, it uses quantum entanglement for FTL
| communication over a distance of 4 light years. Still a great
| story, though.
| addaon wrote:
| > To expand on this, it uses quantum entanglement for FTL
| communication over a distance of 4 light years. Still a great
| story, though.
|
| Although I read the book when it first came out, I have
| basically zero memory of it, so I don't recall if FTL
| communication is essential to the story. However, having just
| watched the first season of the Netflix season, I explicitly
| noticed that even though it mentions use of FTL
| communication, the story absolutely doesn't need it at any
| time. There's a local representative of the distant folk who
| is clearly trusted to make decisions, and could represent the
| distant folk for all communication purposes.
| PaulDavisThe1st wrote:
| FTL comms are absolutely essential to the story, and it is
| specifically accomplished using quantum entanglement.
|
| When Evans speaks with the San Ti/Trisolarians, he is
| talking to them via one of a pair of sophons - quantum
| entangled protons.
| dpig_ wrote:
| Also the "there are no secrets" angle is pretty dependent
| on the FTL too.
| addaon wrote:
| Understood that that's the conceit, but referring to
| purely the initial season on Netflix, it would be
| perfectly substitutable to have Evans speaking not
| /through/ a Sophon, but /to/ a Sophon -- a sufficiently-
| intelligent, sufficiently-aligned computer that can
| represent the San Ti interests fully, and react as a San
| Ti would. Nothing that has happened in the story /so far/
| requires a real-time update on the status of the San Ti
| fleet, or otherwise an actual round-trip communication;
| it could all be incorporated into the San Ti model of a
| sufficiently advanced AI for the purpose of
| representation. (Even as an AI skeptic, I do think that
| such an AI is less of a technical reach than FTL
| communications.)
| PaulDavisThe1st wrote:
| The San Ti need information from Earth as part of their
| plan to relocate there. At light speed, this would take
| 4.5 years to arrive. Without an FTL link to earth, they
| will be arriving "blind" (or with only the information
| that Ye and Evans might have passed along after 1967).
| addaon wrote:
| Fair enough. I suspect that this becomes obvious slightly
| later in the story. The way that the first season is
| presented on Netflix, there's really a bicameral
| distribution of possibilities here -- either the Sophons
| successfully suppress human tech development and the San
| Ti have no issue doing whatever they want even without
| realtime information due to technical edge, or they fail
| and no matter how much information the San Ti have it
| won't overcome the tech deficit. I'm sure that for story
| purposes exploring that negligibly small middle part of
| the distribution where tech levels are comparable at
| meeting time is most interesting, but as presented it
| doesn't feel like the San Ti's probability of success
| changes enough with FTL communication to suggest that
| they would take different actions in a universe where
| everything is the same except FTL comms are prohibited.
| euroderf wrote:
| That precisely is so much of the appeal of The Expanse ! For
| getting around our solar system, take plausible, foreseeable
| tech and add just a bit of secret sauce (the Epstein drive).
| So,.. the evolutionary path of society as depicted in the
| series is plausible.
| snapcaster wrote:
| I wanted to like it so badly but the show just didn't hook
| me. Need to give it another chance sometime
| dbrueck wrote:
| The books are pretty good IMO.
| TheDudeMan wrote:
| You gotta get through the political stuff in the first
| episode or so. Just push through. No need to follow it in
| detail.
| PaulDavisThe1st wrote:
| s/episode/season/
| causi wrote:
| Yeah, the whole "planet's climate is stable enough for a
| sapient species to evolve and become hyper-advanced yet so
| unstable they're going to be wiped out" is so, so stupid.
| endisneigh wrote:
| What's stupid about it?
| causi wrote:
| It's dumb on two levels. Firstly, for a planet to evolve
| sapient life it must be inhabitable for, at minimum,
| millions of years if not billions, therefore if this
| orbital instability was going to wipe out the trisolarans
| it would've done it already. Secondly, the trisolarans are
| hyper-advanced. They turn individual protons into sapient
| robots and play with antimatter, therefore they can make a
| damn air conditioner. Manufacturing habitats to isolate
| them from the effects of their orbit would be easier than
| almost every single other thing they do in the entire
| series, including transporting their whole species across
| interstellar distances. Some of the things they do would be
| harder than keeping their planet in a stable orbit by
| force.
| endisneigh wrote:
| > Firstly, for a planet to evolve sapient life it must be
| inhabitable for, at minimum, millions of years if not
| billions, therefore if this orbital instability was going
| to wipe out the trisolarans it would've done it already.
|
| This is not a fact to begin with, and in the book their
| civilization was repeatedly wiped out.
|
| > Secondly, the trisolarans are hyper-advanced. They turn
| individual protons into sapient robots and play with
| antimatter, therefore they can make a damn air
| conditioner. Manufacturing habitats to isolate them from
| the effects of their orbit would be easier than almost
| every single other thing they do in the entire series,
| including transporting their whole species across
| interstellar distances. Some of the things they do would
| be harder than keeping their planet in a stable orbit by
| force.
|
| This is not the failure mode they're concerned with.
|
| You also seem to drastically overestimate their
| capabilities.
| azulster wrote:
| broad strokes yes, you are right.
|
| however you missed some explanatory details:
|
| !!!SPOILERS BELOW!!!
|
| the trisolarans specifically evolved to survive their
| chaotic orbit, by being able to completely "dry out" and
| wait in stasis for a safer time. this is based on how
| some worms and bacteria on earth have the ability to
| survive extreme conditions by similar protective stasis
| methods.
|
| the trisolarans are very intelligent but their
| advancements are constrained by the need to rebuild the
| civilization at unpredictable intervals. this actually
| drives their technological innovation as they are
| existentially motivated to figure out how to predict the
| orbital intervals.
|
| its also implied that the trisolarans did not think
| themselves very far advanced compared to humans, only
| that they had a few centuries head start on understanding
| the fundamental nature of physics. they conclude that all
| they need to do is sabotage our particle colliders to
| confound our ability to gain any more insight into
| subatomic mechanics to prevent us from achieving what
| they have
|
| moving their civilization across interstellar space is
| far less difficult than it would be for humans mostly
| because the civilizations can be dehydrated and kept in
| storage, not needing supplies to live out the years in
| transit. even so it still takes incredible engineering
| and resource investment to achieve because the fleet must
| move semi-autonomously and reliably for centuries because
| FTL travel is beyond their ability.
|
| it would be impossible to stabilize their orbit because
| the planet is being chaotically thrown between 3 large
| stars. they are also not just concerend with surviving
| the next "hot cycle" they had predicted true apocalypse
| for even their survivable species. IIRC the planet was
| doomed to eventually fall into one of the stars based on
| their predictions
| PaulDavisThe1st wrote:
| > its also implied that the trisolarans did not think
| themselves very far advanced compared to humans,
|
| not quite. they are aware that they are significantly
| ahead of humans, but have also observed human scientific
| and technological progress following an exponential
| curve, since we do not get our civilization(s) wiped out
| periodically.
|
| they fear that we will easily catch up with them in 400
| years unless they somehow intervene.
| snakeyjake wrote:
| "Civilizations smart and advanced enough to collapse entire
| dimensions but too dumb to move past the need to compete for
| planets by parking themselves off to the side of a black hole
| and harvesting energy from its relativistic jets" is so stupid.
|
| Every time a seemingly intelligent person takes the dark forest
| hypothesis seriously I am dismayed. The only answer to the dark
| forest is: FTL is impossible and we are presently incapable of
| detecting ourselves at a distance of 4 LY so there is a 0.0%
| chance of detecting anything beyond that.
| rbanffy wrote:
| > we are presently incapable of detecting ourselves at a
| distance of 4 LY
|
| You don't need to detect a civilisation. All you need to
| detect is a planet hospitable to whatever biology suits you.
|
| That said, our detection tech improves relatively quickly and
| we might be able to directly image rocky planets before this
| century is over. It's safe to assume that, if there is
| someone curious enough to look for planets with biosignatures
| or technosignatures that has been perfecting their craft for
| thousands, or millions of years, by now they must be very
| good at that.
| rbanffy wrote:
| Yeah right... Epstein drive and wormholes, with some nasty
| ghosts unhappy about aliens using intelligent nano machines for
| building extra-dimensional highways through their
| neighbourhoods.
|
| It's fun, but it's not an accurate prediction of our
| technological abilities.
| mrkeen wrote:
| The gap I still have in my understanding:
|
| One hypothesis is that there is no spooky action. One particle
| was 'always' going to resolve one way, likewise with the other.
| Like inspecting 'heads' on one side of a coin 'forces' 'tails'
| onto the other side.
|
| I accept that this coin-hypothesis has been disproved by people
| who actually know what they're talking about.
|
| But to me, this implies that you should build your spooky FTL
| message by transmitting "Measured" rather than heads/tails:
|
| Have an array of 8 particles at both locations. They represent
| measured/unmeasured rather than heads/tails. You got yourself a
| one-way single-use FTL byte.
|
| For this to _not_ work (which I 'm sure it doesn't) you'd need to
| be _unable_ to distinguish between a measured /unmeasured
| particle. To me this is equivalent of being unable to prove that
| there is anything spooky going on.
|
| So how can you have it both ways? How can you theoretically know
| that something was sent when measurement itself would destroy any
| evidence of something being sent?
| bowsamic wrote:
| > I accept that this coin-hypothesis has been disproved by
| people who actually knows what they're talking about.
|
| The classical idea is more like as follows: you have a guy
| Charles who makes two letters each with a card in that has
| written on it either number 0 or 1, and gives one letter to
| Alice and another to Bob. Now, "entanglement" here is that if
| Charles writes 0 in Alice's letter he writes the number 1 in
| Bob's, and vice versa. Alice and Bob are also aware of this.
| This means that even at a distance, if Alice opens her letters
| and sees a 0, she knows that Bob's has 1 in.
|
| For a long time, Einstein and co. through the "EPR paradox"
| (Einstein-Podolsky-Rosen) thought that QM would be something
| like this, but we just didn't know how to access the actual
| letter "in transit" yet, which they called an "element of
| reality". They were wrong.
|
| It turns out that Bell's theorem basically says that in this
| situation the correlation between the two letters would be less
| strong than quantum theory predicts for entangled states, so
| this cannot be the full explanation.
|
| Bell's theorem says you either need to give up the idea that
| there is no "spooky action", or give up determinism (no true
| "element of reality" that really holds what's going on), or you
| can retain both if you let go of another concept called
| statistical independence.
|
| > Have an array of 8 particles at both locations. They
| represent measured/unmeasured rather than heads/tails. You got
| yourself a one-way single-use FTL byte.
|
| You can't have a quantum state where something is the
| superposition of measured and not measured, this violates a
| fundamental postulate of quantum mechanics: that measurement
| "chooses" one of the states in the measurement basis. I think
| you touch on that later, in that you can't tell via
| entanglement if a measurement took place elsewhere, which is
| partly why we can't experimentally demonstrate a non-local
| theory yet.
|
| Basically, it isn't that some signal is transmitted, it's that
| if they are entangled the states of each system cannot be
| independently known. That is, like in the letters example I
| gave: it can be either 0 for Alice and 1 for Bob, or 0 for
| Alice and 1 for Bob. Now, the reason why information is not
| transmitted is the same: Bob didn't know what was in his letter
| before he measured it, so it's randomly symmetric between 0 and
| 1, there is no information transferred. It turns out that this
| kind of symmetry between the two states tells you nothing that
| can be used to transmit information.
| vjerancrnjak wrote:
| Yes, Bell's theorem is such a strong result. 1. locality 2.
| (local) reality 3. statistical independence
|
| Only 2 can hold at once and there's consensus to have 1. and
| 3., with that we lose the hidden variables. Instead, having
| 1. and 2. hold would be so interesting.
| tsimionescu wrote:
| In some sense, MWI also gets rid of 3, though it's not
| commonly seen like that. Essentially in MWI any experiment
| has all possible results, so the concept of statistical
| independence jsut doesn't make sense.
|
| Either way, MWI is by far the most popular interpretation
| that is both local and realistic.
| jemmyw wrote:
| > Bell's theorem says you either need to give up the idea
| that there is no "spooky action", or give up determinism
|
| Can you not also say that the determinism includes the
| observer, aka superdeterminism (which is just determinism
| because that would surely be global).
| bowsamic wrote:
| This quote from my post
|
| > or you can retain both if you let go of another concept
| called statistical independence.
|
| is superdeterminism
| ngcc_hk wrote:
| The key difference, unlike the usual sock example or your
| letter example, it is not about knowing. The superimposed
| quantum states have not been fixed. It is both colour or or
| letters or states at the same time all the time unlike it is
| measured. It is not the knowledge about a pre-existed, the
| individual state does not exist until measurement. That is
| the crazy part.
| bowsamic wrote:
| Yes they have, it's just that in quantum mechanics you can
| expand the state in different bases. The state still
| "exists" before it is measured, just in a non-separable
| superposition state (i.e. an entangled state)
| jacknews wrote:
| I think it's more like 2 dice, which always land on opposite
| sides, so 1 and 6, 2 and 5 and so on.
|
| And then a measurement isn't just to land a die, but also to
| choose which axis to measure - ie ask the dice are you a 1 or
| a 6. The other die magically spins around to the same axis
| and gives the corresponding result.
|
| But I'm not sure this analogy is satisfactory and explains
| the 'spookiness' either.
| slfnflctd wrote:
| I have a couple follow up questions.
|
| > a guy Charles who makes two letters
|
| So Charles at least knows the information on the cards. Are
| you essentially saying that there's no way for Alice or Bob
| to distinguish that information from 'background noise'? If
| so, that is not a great analogy other than to illustrate a
| historical & incorrect perspective. Which may have been what
| you were doing and if so is fine.
|
| > measurement "chooses" one of the states in the measurement
| basis
|
| Okay, say you 'do some entanglement of multiple particles
| stored in two separate tubes' where you know there is some
| kind of pattern in the entanglement. Is the issue that there
| is no way to know how to find that pattern without possessing
| both 'tubes'?
| bowsamic wrote:
| > If so, that is not a great analogy other than to
| illustrate a historical & incorrect perspective.
|
| Read the next part, I was discussing the idea thought of by
| Einstein that was dismissed by Bell's theorem.
|
| > Okay, say you 'do some entanglement of multiple particles
| stored in two separate tubes' where you know there is some
| kind of pattern in the entanglement. Is the issue that
| there is no way to know how to find that pattern without
| possessing both 'tubes'?
|
| I'm not sure what you mean by this, can you elaborate?
| slfnflctd wrote:
| Well, we know entanglement happens because of
| experiments. In those experiments, researchers had to
| somehow independently verify that the entangled states
| produced predictable results, thereby demonstrating the
| entanglement.
|
| If you set up the first part of experiment, wherein you
| know certain particles are entangled, would it be
| possible for someone on one side of that entanglement to
| read a pattern from that side alone (if they 'knew where
| to look') which matched a pattern on the other side?
|
| At this point, if my question even makes sense, we're
| only talking about a very impractical method of data
| storage... I'm just curious whether even that is
| possible.
| Arelius wrote:
| Sure, you could read the pattern on he other side, you
| could been use of as a one time pad to encrypt data you
| actually cared about
| vlovic wrote:
| The answer is Bell's Theorem. Scott Aaronson has some good
| explanations.
| gwill wrote:
| i won't have time to read this until later, but here's a post
| by him on it: https://scottaaronson.blog/?cat=33
| honeyed_coffee wrote:
| The spooky part occurs when two parties who share this
| entangled state know what measurement to perform. If the
| measurement choice aligns for both parties, their outcomes can
| be correlated precisely. If the measurement choices are not
| aligned, the outcomes are also random
| magicalhippo wrote:
| > If the measurement choices are not aligned, the outcomes
| are also random
|
| Just to be a bit pedantic, as it can otherwise lead to some
| confusion: the measurement outcomes are _always_ random.
|
| If the particles are entangled, then it is the correlations
| that are not random.
| taeric wrote:
| This is still a part that annoys me. I have asked why you
| can't use the correlations to facilitate communication, and
| people always seem to think I'm asking why you can't do
| this per particle. I get that the the individual measures
| are basically useless on their own. Question is if the
| correlations can be confirmed so well, why can't that be
| used?
| drwiggly wrote:
| From what I'm gathering. Alice measures
| at angle X, gets value V1 Calls Bob on the
| phone, okay I measured angle X. Bob measures
| at angle X, also gets value V1 Bob measures at
| angle Y, gets value V2. Bob calls Alice back
| says, okay I measured angle Y. Alice measures
| angle Y, also gets V2.
|
| The correlation here is nobody can do other measurements
| while the other party is in the process of measuring.
| Each party can't know the other party is done until
| traditional communication has happened.
|
| If each party acted independently they would randomly
| change the state on the other side and each party would
| get what appears to be random values.
| taeric wrote:
| I think my mind bend is more over 3 actors. Note that my
| understanding, also, is that it has been shown that
| changing a detector changes what is detected at the other
| detector. A is sending entangled stuff
| to B and C. B measures and gets a set of angles
| that tells them what C would be measuring C
| changes what they are measuring.
|
| The question is, how rapidly does the "spooky" distance
| change happen? I get that it would not be communication
| between A and B or C. I similarly get that you could not
| coordinate between B and C. But, from all of the framings
| I've seen so far, I don't understand why the change
| between B and C is not faster than speed of light.
|
| (And just to rapidly get it out there, I fully expect
| that I'm merely misunderstanding something here.)
|
| Edit: Also, to add, my understanding is that they are not
| "getting angles" per se, but would be seeing
| distributions. Which is why you would need more than 1
| particle, as it were. So, you would say of the X I have
| recorded, 30% have been blue, 70% have been green. I
| suppose the concern is that you have no way of knowing
| when the "100%" mark is done until after classical
| communication, such that it is impossible to know what
| the final distribution you are measuring is? Effectively?
| honeyed_coffee wrote:
| >The question is, how rapidly does the "spooky" distance
| change happen? I get that it would not be communication
| between A and B or C. I similarly get that you could not
| coordinate between B and C. But, from all of the framings
| I've seen so far, I don't understand why the change
| between B and C is not faster than speed of light.
|
| It's because measurements at B do not convey any
| information to C while the measurements are performed and
| vice versa. Unless B calls C to inform them of the choice
| of measurement setting, C will not know the measurement
| outcome at B's side. This is true even if they know that
| they share entangled states prior to prior to performing
| measurements.
|
| > Edit: Also, to add, my understanding is that they are
| not "getting angles" per se, but would be seeing
| distributions. Which is why you would need more than 1
| particle, as it were. So, you would say of the X I have
| recorded, 30% have been blue, 70% have been green. I
| suppose the concern is that you have no way of knowing
| when the "100%" mark is done until after classical
| communication, such that it is impossible to know what
| the final distribution you are measuring is? Effectively?
|
| There has to be post processing of data where they drop
| the results of rounds where their measurement choices
| don't match. This is important because of what's called
| non commuting measurements. Measurements in one setting
| don't give us any information about measurement outcome
| in another setting. So effectively at one end, they have
| to record their measurement choice and corresponding
| outcomes of said measurement. And when comparing the
| data, the participants only have to keep the outcomes of
| rounds where the measurement choice is the same at both
| end
| magicalhippo wrote:
| > I have asked why you can't use the correlations to
| facilitate communication
|
| But how could they?
|
| Charlie prepares a pair of entangled electrons and sends
| one each to Alice and Bob. Alice performs a spin
| measurement along some angle and, entirely randomly, gets
| either up or down as a result.
|
| Alice and Bob decide on their measurement settings and
| measure a bunch of electrons using the same angle for
| each measurement. They can even agree in advance so they
| both know which angle the other will use.
|
| After the run, Alice will have a bunch of measurement
| results which are roughly 50% up and 50% down. Bob too
| will have a bunch of measurement results which are
| roughly 50% up and 50% down. _Assuming ideal detectors
| and such, there will be no discernible pattern to the ups
| and downs for either_.
|
| Only if the afterwards come together and compare their
| results pair for pair will they see the quantum
| correlations _between the value in each pair_. For some
| angles, they 're more likely to be anti-correlated, and
| for some angles there doesn't seem to be any correlation.
|
| That is, if they both used the same angle, the they'll
| find that each time Alice measured up then Bob measured
| down, and every time Alice measured down then Bob
| measured up. And if they used a similar but not equal
| angle, then it's more likely that when Alice measured up
| then Bob measured down, and vice versa.
|
| And since they by now know that this experiment has been
| done before and the predictions of quantum mechanics
| hold, they can even predict this result. However what
| good does it do for Alice? After all, regardless of
| measurement settings Bob will measure a uniform 50/50
| distribution of ups and downs.
| taeric wrote:
| Agreed that it doesn't do Alice any good, necessarily;
| but it seems that it does get information between Bob and
| Charlie? If the detector at Bob's site influences what
| Charlie would see at an aggregate level, do they have to
| wait for the end of the experiment to know? Couldn't they
| make an inference at every hour on what the detector was
| doing at the other end? Even if they were a lightyear
| away from each other.
|
| If the answer really is that they have to wait for the
| end of the entire experiment, I think that settles it for
| me. Will think some more on it. (And again, as noted, I
| have not thought that hard on this. Even with my odd
| "would this work" you need some way to get entangled
| particles sent across stupid large distances. Which...
| already seems silly?)
| magicalhippo wrote:
| > If the detector at Bob's site influences what Charlie
| would see at an aggregate level
|
| Charlie doesn't see anything. He sends the electrons here
| and there. He's just produced the entangled electrons, he
| hasn't measured them. If he did he would destroy the
| entanglement and ruin the experiment (which is what
| secure quantum communication is about).
|
| Unless he gets some reply (say a photon or electron sent
| by Bob), he doesn't know what either measure.
|
| But if he does get a return particle then they're just
| communicating classically, so why not just pick up a
| phone?
| taeric wrote:
| Apologies, I screwed up the names there. I was thinking
| down thread where I had A sending. So, A sends, B has a
| detector, C has a detector. Framing I've seen had it such
| that depending on the setting of B's detector, C would
| get a different result. (And vice versa.) Now, I am
| assuming I saw an incomplete framing where this is only
| true if they communicate back to A?
|
| Stated differently, the framing I saw was that the
| "spooky" action was somehow setting detector C to a
| specific setting would cause a different reading in
| detector B. And this was done in such a way that B could
| not know that C had changed. But, simply getting a new
| reading at B means that either A or C has changed,
| necessarily?
|
| And again, going off old memory. Never my area of study,
| such that I assume I am misunderstanding. It is
| frustrating because most "pointing out my mistake"
| assumes I care about individual protons. I'm saying if we
| can agree to have A set to send with constant rate, then
| barring that getting broken, it seems you have a scheme
| whereby B and C can know what they are doing in
| aggregate.
| elcritch wrote:
| > One hypothesis is that there is no spooky action. One
| particle was 'always' going to resolve one way, likewise with
| the other. Like inspecting 'heads' on one side of a coin
| 'forces' 'tails' onto the other side.
|
| > I accept that this coin-hypothesis has been disproved by
| people who actually know what they're talking about.
|
| The quantum erasure experiment is to my mind the best example
| of the spooky action at a distance. The outcome of the particle
| pairs is measured _after_ the entanglement occurs implying not
| just "spooky action at a distance" but also in time.
| https://www.youtube.com/watch?v=8ORLN_KwAgs
| yetihehe wrote:
| Calling it "action" may be a mistake. Action implies
| something changes (there is a state called "before" and state
| called "after"). But nothing changes "over there", we just
| now know what actually happened (there is no state called
| "before" or it's value is "unknown", only state called
| "after").
| mrkeen wrote:
| This is the simplest explanation, but it's also the null
| hypothesis.
|
| I believe that "nothing changes over there" implies not
| only no spooky action, but also no entanglement.
| yetihehe wrote:
| This is about word used for description of that thing.
| Just using entanglement is ok, but using "action"
| suggests that something changes. Words have some meaning
| and incorrect usage causes misunderstandings.
| elcritch wrote:
| > Action implies something changes (there is a state
| called "before" and state called "after"). But nothing
| changes "over there", we just now know what actually
| happened (there is no state called "before" or it's value
| is "unknown", only state called "after").
|
| > using "action" suggests that something changes
|
| By my understanding, the delayed part is important. It
| implies something _did_ change as the state of the
| earlier entanglement will be different based on a
| measurement which occurs _after_ the entangled state has
| been created. If this is correct, then there has been an
| "action" at a distance.
|
| Though an alternative understanding could be that the
| state is set based on a future event which hasn't
| occurred yet. That would avoid needing an "action" to
| change the state after the entanglement event, but
| implies other things.
| yetihehe wrote:
| I suggest using "spooky correlation" to better explain
| this. It's just a forced correlation of two parameters
| after all. To make entanglement, we make an experiment
| where we force system to behave in a way that correlates
| results of two parameters. When we measure one, we know
| the other is correlated in a way that was set in our
| experiment. "Spooky" because it can hold at vast
| distances and across time.
| gosub100 wrote:
| Delayed-choice blew my mind at first, but then learning that
| light-speed particles experience length contraction kind of
| debunks the "they traveled backwards in time" interpretation,
| at least from the photons perspective. They traveled 0
| distance.
| Filligree wrote:
| Photons don't travel at all, yeah, in a literal sense. It's
| still useful to measure travel length in 3-space, but
| that's more an analogy than a real event.
|
| In four-dimensional space-time they 'travel' along a
| 0-length path; the correct formulation of Pythagoras'
| formula becomes "distance = t^2 - x^2 - y^2 - z^2".
|
| Which would be an imaginary number for a spacelike path,
| yes, e.g. from one side of your table to the other. It's a
| _useful_ imaginary number -- we call it 'length' -- but it
| doesn't correspond to a path that actually exists.
| ars wrote:
| Delayed choice is NOT REAL! Watch, or read, this:
| http://backreaction.blogspot.com/2021/10/the-delayed-
| choice-...
|
| Basically the results of two slits with particles combine
| into no pattern. If you retroactively keep track of which
| slit, and then only look at that slit, it makes a pattern.
| sebzim4500 wrote:
| Disclaimer: I am not an expert, but I understood this stuff
| pretty well 5 years ago.
|
| If you have a single particle there is no local experiment that
| you can do to determine whether that is entangled to a particle
| somewhere else. You need to use both particles in the
| experiment in order to prove it one way or the other.
| Mathematically, this is due to the fact that the density
| function for one half of an entangled pair is the same as the
| maximally mixed state for one particle.
|
| See CHSH[1] for an example of an experiment you can do if you
| have access to both particles and you want to show they are
| entangled.
|
| [1] https://en.wikipedia.org/wiki/CHSH_inequality
| dist-epoch wrote:
| > you'd need to be unable to distinguish between a
| measured/unmeasured particle
|
| This is true. There is no way to tell if a measurement you do
| happened on an entangled particle or on a "free" one.
|
| You can only tell in retrospect, when you correlate results,
| which requires classical communication.
| yetihehe wrote:
| So it can't be called "action"? Could be also described as
| correlation is not causation and action implies causation.
| Workaccount2 wrote:
| You cannot tell if a particle has been measured or not
| without...measuring it.
|
| The key to understanding this is that _any_ interaction with
| anything counts as a "measurement" from the particles
| perspective.
|
| I like to think that our simulation has a bandwidth compression
| algorithm that only decodes the state of a particle when it
| needs to calculate an interaction. Just like how your dungeon
| crawler doesn't spawn mobs until they are within interaction
| distance. But that's just fun head canon.
| mrkeen wrote:
| I don't dispute this, but it's indistinguishable from the 'no
| spooky action' hypothesis.
|
| I can invent a story that the coin in my pocket has two
| sides, each of which is in a superposition of heads and
| tails.
|
| If you disprove that by repeatedly looking at both sides and
| noting that they always end up different, then I can invent
| the story that the observed side tells the unobserved side
| what to become.
|
| If you disprove that by separating the sides by a great
| distance before observing them both, I can invent the story
| that they coordinate instantaneously, ignoring the speed of
| light.
| slfnflctd wrote:
| I've never quite grasped this stuff to my satisfaction, and
| I strongly suspect part of why is because of some really
| bad popular examples (metaphors, allegories, thought
| experiments, whatever) which contain factually or logically
| incorrect language.
|
| This comment chain is a prime example of the ways quantum
| mechanics are (mis)understood and how many of us struggle
| to fully reason out the implications of each piece of it. I
| hope we can all learn something.
| Jensson wrote:
| Fact is that the position isn't "unknown", it is in both
| positions at once. The double-slit experiment is strong
| evidence for this, we can see that the particle went
| through both slits at once by measuring a lot of
| particles and seeing where they end up.
|
| If you block one slit and then shoot particles, then
| block the other slit and shoot particles, you end up with
| a completely different pattern than if you have both open
| at once.
|
| This isn't difficult to understand, the only difficult
| part is people not wanting to believe it is true and
| trying to come up with classical explanations for quantum
| mechanics, even though we have hard proof that classical
| physics can't explain this.
|
| The difficult part is that even though the particle went
| through both slits, it only ever ends up in a single spot
| at the end, that is the "wave function collapse", it was
| a wave that went through both slits, and then it
| collapses to a single point when we measure it at the
| end. That is still not well understood by anyone today.
|
| https://en.wikipedia.org/wiki/Double-slit_experiment
| gaze wrote:
| No, you can't tell if a particle has been measured or not
| _period_, without many identical copies of the same state and
| repeating the experiment many times.
| plagiarist wrote:
| I've had a similar head canon that Planck lengths are the
| simulation's floating point epsilon.
| rbanffy wrote:
| > _any_ interaction with anything counts as a "measurement"
| from the particles perspective.
|
| "Measurement" is a terrible word we've been using, along with
| "observer".
|
| What matters is information propagating from one system to
| another or, perhaps better, when the superposition has any
| external effect, then the superposition collapses and the
| system assumes a classical state.
| stephc_int13 wrote:
| At the quantum scale, you can't observe without interaction.
| And the interaction is always destructive (of information, not
| of the particle).
| gaze wrote:
| You can't tell if a particle has been measured or not.
| rssoconnor wrote:
| While you don't get action at a distance, you do get something
| like "correlation without causation". This ability does let you
| "cheat" at particular games of chance, which is spooky in its
| own right.
|
| https://r6.ca/blog/20150816T185621Z.html
| cwmma wrote:
| You can not tell whether a particle was measured or not by
| looking at its entangled pair.
| d_tr wrote:
| From the perspective of the MWI there is no spooky action.
|
| If you measure one of the particles and look at the result, you
| then know what term of the quantum state you ended up in, so
| you know the probability distribution of the other particle's
| results.
|
| Nature does not need to work according to what our brains
| consider reasonable, but the MWI getting rid of several very
| weird notions makes it very appealing, I won't lie...
| Jensson wrote:
| > From the perspective of the MWI there is no spooky action.
|
| There is a spooky world split that separates the entire
| universe instead of just having a spooky thing having to the
| particle. Some prefers having a small spooky thing over a
| large spooky thing.
| spintin wrote:
| The problem with entanglement is obviously that it does not scale
| many-to-many, just like Erlang. You need Java to do many-to-many
| or C with a GC VM.
| isodev wrote:
| I've seen a few "can't scale many-to-many" Java/C things in my
| career... it's all about how you put things together. I don't
| think Java and C can go faster than light either ;-).
| spintin wrote:
| The Java concurrency package is the only way to get your
| multi-core CPU to share memory atomically without going
| "Arrays of 64 byte atomic Structures" with C.
|
| And then you are in segmentation fault hell.
|
| Sun had to rewrite the entire JVM in 2003 with a new memory
| model, later adopted in C++11 (and still the current C++
| memory model) which failed for C++ because this model only
| works well if you have a VM with GC.
|
| C# is just a plain Java copy after Microsoft got sued for J++
| in 1998.
|
| All other languages have problems with concurrency and
| threads that make them unsuitable for anything really.
|
| So again, Java is the ONLY language/VM you can use on the
| server and on the client you still want a combination of
| C(++) and Java for performance + ease of use (avoid
| segmentation fault hell that no person should suffer).
|
| If you saw bad Java code then that is not the fault of Java.
| spintin wrote:
| lol classic HN down vote without comment...
| moate wrote:
| Lol classic smug comment about HN comment culture acting
| as if you're owed discourse.
|
| FWIW, I'm also pretty sure this type of comment (and
| therefor my comment?) are against the rules, but I've
| been rate limited for like 90% of my time here because I
| don't use burners to get into fights so dafuq do I care.
|
| Anyway, hope you have a Good Friday. If it makes you feel
| better, you're much lower on the crucifixion scale than
| the even providing it's name.
| spintin wrote:
| Actually I prefer no comment if you have no arguments:
|
| "While I'm on the topic of concurrency I should mention
| my far too brief chat with Doug Lea. He commented that
| multi-threaded Java these days far outperforms C, due to
| the memory management and a garbage collector. If I
| recall correctly he said "only 12 times faster than C
| means you haven't started optimizing"." - Martin Fowler
|
| https://martinfowler.com/bliki/OOPSLA2005.html
| jacknews wrote:
| It's still not a very satisfactory explanation IMHO.
| youlweb wrote:
| Can we simply tell that the entanglement was collapsed on the
| other end? That would be sufficient to transmit information. If
| planet x is habitable when I get there, I measure/collapse this
| specific particle, whose counterpart is back on earth in a
| detector named "habitable". When the detector fires on earth
| because this particle was measured/collapsed on planet x, people
| on earth know planet x is habitable. There's no need to know the
| outcome of the measurement, just the fact that it was
| measured/collapsed is information enough.
| gaze wrote:
| We can't.
| afiori wrote:
| A particle with entaglement is undistinguishable from a
| particle with no entanglement.
| cwillu wrote:
| Any time you feel tempted to treat collapse as an objective
| state of a single particle, remember that the collapse
| interpretation is mathematically indistinguishable from the
| multiverse interpretation. There's no test for whether collapse
| has happened other than measuring at both ends and comparing
| notes... and noticing that nature appears to be cheating
| somehow.
| gaze wrote:
| You can't tell AT ALL if there was entanglement with one
| trial. You need to prepare the same state many many times and
| compare correlations many many times to establish
| correlations to within some error bound.
| gosub100 wrote:
| even if you could relay that one binary piece of information,
| that's one bit of an integer or string that could contain
| arbitrary information.
|
| The only thing that is known is that the other entangled
| particle has opposite spin than what you register.
| roywiggins wrote:
| This doesn't work, but if it did, you could use it to front-run
| stock market movements. No need to go to space to find an
| application.
| stephc_int13 wrote:
| Most people don't understand enough about the fundamental
| properties of modern Physics.
|
| What we usually call the speed of light is in fact the maximum
| speed of information propagation.
|
| It is not about light, and you should think about quantum
| entanglement as a hidden variable, there is no magic there.
| Filligree wrote:
| I was under the impression that local hidden variable theories
| had been disproven?
|
| It could be nonlocal of course, but that would imply
| information moving faster than light again. Unless you count
| the entirety of MWI as "hidden variables", I guess?
| stephc_int13 wrote:
| Yeah, I am aware of Bell's theorem.
|
| What I am saying is that the hidden variable hypothesis is
| nonetheless a good mental model as a first approximation to
| reason about QE, say as a non-professional physicist.
|
| People get confused, especially sci-fi authors, adding to the
| general confusion about anything touching Quantum Physics
| being almost magical/limitless or unexplainable. This is a
| lot more pedestrian in practice.
| graemep wrote:
| It do not think sci-fi authors are confused, but just
| willing to live with inaccuracy for the sake of the story
| and universe building. Its like faster than light travel -
| you need to find some excuse to make something work.
|
| I very much doubt Ursula Le Guin thought we could build an
| ansible (FTL comms) any more than Larry Niven thinks the
| Teela Brown gene (heritable luck) is real.
| nobodyandproud wrote:
| Non-Locality doesn't mean information travels faster than c.
|
| The main article attempts to explain why instantaneous
| "spooky action at a distance" is real, yet information can't
| be relayed this way.
| zare_st wrote:
| For specific cases, asm is faster than c.
|
| I'll show myself out
| cwmma wrote:
| But isn't that the frustrating thing about this, it implies
| superluminal communications just in a non-useful way. Managing
| to make the speed of light not be the maximum speed of
| information propagation but only in a technical and useless
| way.
| gaze wrote:
| I've been working on quantum computing and quantum communication
| for 15 years now and what I really want people to know is that
| entanglement is "beyond classical correlation."
|
| Correlation which is not beyond classical is shaking up a shoebox
| with a pair of gloves in it, and having two people take the
| gloves far away from each other to then observe what hand they
| got. They then understand the hand the other has. There's one bit
| of information here corresponding to which hand went to person A.
|
| Entanglement is just this but "more." You can't communicate with
| a pair of gloves. Person A does not know when person B has
| realized person A knows what glove they have. Just the same, it
| does not matter who matters which of the two particles in a Bell
| pair first! Many quantum information theorists don't even believe
| the wave function is "real" but just a mathematical tool for
| making predictions about measurement outcomes.
|
| You should come at entanglement from this angle, because the main
| difference between the bell test and the pair of gloves is the
| state of the particles is undetermined before measurement, and
| the chosen measurements will result in different correlations
| between the measurement outcomes.
| petermcneeley wrote:
| "it does not matter who _measures_ "
| MPSimmons wrote:
| In my mind, I see it like you've got a line bisecting another
| line. You don't know what the angles are until you measure one,
| and once you measure it, you know for certain what the other
| angle is, whether that person does or not. But you can't change
| the angle and you can't send information using them.
| Jensson wrote:
| Except the line is spinning around faster than you can see
| and you measuring it makes it stop. Your example makes it
| sound like the angle was decided before you measured.
| d0mine wrote:
| Feynman explains quantum correlation using boxes with 3 buttons
| https://youtube.com/watch?v=ZcpwnozMh2U&t=17m55s
| bilsbie wrote:
| Thanks. So how is it not analogous to the glove example?
| trimethylpurine wrote:
| It's a trick question. Gloves go in a glove box.
| notfed wrote:
| Yeah really, they didn't give any example of the "more"...
| Jensson wrote:
| The gloves doesn't change their state when you check on them.
| Quantum particles do.
|
| Example: Lets say you check if the glove is white or black,
| you see it is white. Then you check if the glove is half
| white/half black, or half black/half white, you see it is
| half white/half black. Then you check again if it is white or
| black, now it is black. That is how quantum gloves would
| work, but real gloves doesn't work that way.
| trimethylpurine wrote:
| _> Then you check again_
|
| You only get to check once, I think. The rest doesn't
| matter, supposedly.
| Jensson wrote:
| That is false, it changes every time you check along
| another axis. If you make the same check it doesn't
| change, but if you change what you check then you can
| update the particle as my example shows.
|
| Changing a particle like this by making repeated
| measurements is a standard example in undergrad quantum
| mechanics.
|
| Edit: There is always a part of the particles state that
| you can't know, you know Heisenberg's indeterminacy
| principle, so if you measure position you now makes
| velocity undetermined, and then if you measure velocity
| now you make position undetermined, and then if you go
| back and try to measure position the particle will be in
| a new random spot.
| trimethylpurine wrote:
| So if you check that the gloves are black they are black
| every time you check (axis 1). And then if you check that
| they have five fingers, they have five fingers every
| time(axis 2).
|
| So, it sounds exactly like a "gloves in a box" example,
| right?
|
| I'm not trying to be cheeky, I'm just pointing out that
| the example really does sound analogous, as stated so
| far.
| Jensson wrote:
| It depends on how those states interact with each other.
| Lets say you can't know a gloves fingers and a gloves
| color at the same time, so checking number of fingers
| resets the color and checking color resets number of
| fingers.
|
| Then if you check number of fingers many times, you get
| the same result every time. But if you alternate checking
| fingers and color, you will get random results every
| time.
|
| Edit: Not that I'm saying this is what original poster
| meant, just that this is the main difference between
| quantum particles and our macroscopic objects like
| gloves.
| ynniv wrote:
| My understanding is that it's like two of the same scratch-off
| lottery ticket. There are two spots you can scratch, only one
| has a prize, we don't know which one that is but it's same for
| both tickets. The tickets are taken to separate rooms. The
| people in each room then pick a spot and scratch it. How likely
| is it that at least one of them will win?
|
| The odds of one scratch winning are of course 50%, and the odds
| of the other person winning are of course also 50%. The odds of
| both people winning are 25%, and both people losing also 25%.
|
| The CHSH experiment suggests otherwise: that when one person
| loses the other person _is less likely to also lose_ , such
| that the likelihood of both losing is only 15%. How can this
| happen? I haven't a clue. I'm not a theoretical physicist, and
| I haven't personally conducted this (~ $5,000) experiment. But
| it's a result that deeply bothers me.
|
| If you build this system you can then scratch a whole lot of
| tickets. Each ticket has a 50% chance of a side having the
| prize, but as long as both parties are consistently scratching
| the same side of entangled pairs they will win more often than
| they lose, revealing whether or not they are in agreement. I
| have no idea how this could be true, but people keep running
| the experiment and keep getting similar results. And, it seems
| like this could result in faster than light communication, so
| there's probably a better ELI-5 out there.
| amluto wrote:
| > The CHSH experiment suggests otherwise: that when one
| person loses the other person is less likely to also lose,
| such that the likelihood of both losing is only 15%. How can
| this happen? I haven't a clue.
|
| That's easy, even without quantum mechanics. All you need is
| to have a different distribution of lottery tickets. Print
| tickets such that, if one wins, the other is more likely to
| win, which you can do by having the number of winning spots
| per ticket be random and correlated. For example, there could
| be a 50% chance that neither ticket has a winning spot and a
| 50% chance that each ticket has one winning spot.
|
| But you could imagine a pair of tickets with internal radios,
| such that, when you scratch one, it tells the other one, and
| together they simulate a general function where the joint
| probability of (win on ticket 1, win on ticket 2). If you set
| up the probabilities appropriately, then you can't use the
| tickets to send a signal, and the result is referred to in
| the literature as "non-signaling boxes" (the magic tickets
| are the boxes).
|
| Quantum mechanical entanglement can do something like this,
| except that the probability distributions you can generate
| with entanglement are a subset of the more general non-
| signaling boxes.
| ynniv wrote:
| > Print tickets such that, if one wins, the other is more
| likely to win, which you can do by having the number of
| winning spots per ticket be random and correlated.
|
| In order to refute this you need to get into the CHSH
| experiment's design, which doesn't use the raw detection
| rate but compares detections that should not have similar
| results. Imagine that both tickets have a prize on the
| right side, and both participants have agreed to always
| choose the left side. CHSH predicts that some of the time
| the prize will change sides: but, crucially, only from the
| losing side to the winning side, and only if the other
| ticket lost, and even if the tickets are revealed close
| enough in time that a signal could not propagate between
| them.
|
| The conclusion of CHSH is that detections are correlated to
| the angle between the sensors, and _not_ the angle between
| the sensors and the source.
|
| This makes absolutely no sense. There is no such thing as a
| winning or losing side until it's been scratched, and even
| if the ticket were able to randomly switch from a loser to
| a winner, how would it ever know that the other ticket was
| also a loser? And if it's true that detection is correlated
| to the angle between detectors, it seems easy enough to
| build a statistical system around variable sensor angles
| that is able to communicate instantaneously.
|
| I might not have interpreted everything you said, either.
| Internet forums aren't the best way to discuss deep
| problems.
| superposeur wrote:
| > Many quantum information theorists don't even believe the
| wave function is "real" but just a mathematical tool for making
| predictions about measurement outcomes
|
| You are correct that many say this, but this is a constant
| source of frustration for me (a physicist who does believe the
| wave function is the _only_ real thing). These physicists never
| seem to articulate what then is supposed to actually be "real"
| (under their definition) or what laws govern the "real" things
| as opposed to the wave function. Implicit seems to be that
| there is some kind of separate classical realm that obeys non
| quantum mechanical laws. Is this separate classical realm to be
| understood as a macroscopic limit of the quantum realm? But if
| so then the whole picture is circular since wavefunctions are
| supposed to be mere bookkeeping devices for classical things.
|
| Or to put this more succinctly, if the wave function is a mere
| bookkeeping device, then bookkeeping for __what__?
|
| (I should mention that yes I know about QBism and all that and
| my confusion is not for lack of talking to QBists about such
| things -- I just can't make heads or tails of what they tell
| me!)
| Strilanc wrote:
| I would describe classical correlations as downgraded
| entanglement. Correlation is what's left when entanglement
| decoheres / undergoes uncontrolled phase noise. Things you
| should be able to do, like win the Mermin-Peres magic square
| game 100% of the time, aren't possible when the entangled
| qubits you'd use to do it aren't protected from phase noise.
|
| Decoherence is sort of analogous to air. It's so ubiquitous in
| your life that you don't really think about it, but you'd
| notice immediately if it was removed. Being steeped in air your
| whole life has twisted your physical intuitions. That's why
| Aristotle thought "objects come to rest" when actually objects
| move at constant speed unless acted upon by a force. Similarly,
| being steeped in decoherence has twisted your physical
| intuitions. Like thinking "adding more ways for something to
| happen must make it more likely" or "a particle's position is
| independent of its momentum" or "I can measure an object
| without affecting it". But actually different paths can
| interfere, and momentum is the Fourier transform of position,
| and measurements apply phase noise.
|
| Decoherence is so ubiquitous that it's a huge challenge to
| engineer systems that suppress it. This is why quantum
| computers are so hard to make, and why quantum error correction
| has so much more overhead compared to classical error
| correction. Classical error correction only has to fix bit
| flips, and it can do so by making phase flips worse (which it
| does). Quantum error correction has to simultaneously fix bit
| flips and phase flips.
|
| When two particles are entangled, rotating one around the X
| axis by an angle A and the other by an angle B and then
| measuring produces measurement results that agree with
| probability cos^2(A-B). Same as the probability of a photon
| with polarization angle A passing through a polarizing filter
| with angle B. Decohere the entanglement before the rotations,
| and the measurements will instead agree with probability
| cos^2(A)cos^2(B) + sin^2(A)sin^2(B). Note that cos^2(A-B) =
| cos^2(A)cos^2(B) + sin^2(A) sin^2(B) + 2 cos(A) cos(B) sin(A)
| sin(B), meaning decoherence is taking away the 2 cos(A) cos(B)
| sin(A) sin(B) interference term. That's the downgrade. That's
| what makes your best possible CHSH win rate drops from 85% to
| 75%. If entanglement allowed sending messages, the initial CHSH
| win rate would be 100% instead of 85%.
| KarroBen wrote:
| Another good article on this subject:
| https://bigthink.com/starts-with-a-bang/quantum-entanglement...
| joecarrot wrote:
| I read a book about particle physics and understood a very small
| amount of it. My understanding is that you cannot have faster
| than light anything because nothing can travel faster than light.
| For instance, the gravitational field of this coffee cup in my
| hand spans the entire universe. The cup is gravitationally
| attracting me, the Earth, the Sun, and every other atom in the
| universe (albeit at a remarkably low level of power). Even this
| gravitational field is not FTL though, because some particle
| exists that does the work of attracting. My cup is emitting
| gravitons or something like that, and those gravitons travel at
| the speed of light. A graviton leaves my cup, travels at the
| speed of light to Mars, and when it hits Mars, it attracts it.
|
| What I am saying is that, in my understanding, there is no action
| that can occur without a particle that acts, and since no
| particle can travel FTL, nothing can happen FTL.
|
| In the case of Quantum entanglement, mustn't some particle travel
| from the first quantum thing to the entangled quantum thing in
| order to have an effect?
|
| I believe that my understanding is flawed! I don't know how to
| get a clearer view though. Any advice?
| ergonaught wrote:
| The issue that is misunderstood is that entangled particles
| cannot be used for FTL communication, which has to do with
| being unable to control the outcome of the measurement rather
| than transportation speed limits. Entangle two particles, ship
| one off to the Sun by whatever less-than-FTL speed you like,
| perform a measurement there, and in theory measurement of the
| particle that remained here will be instantaneously affected.
| ie: without waiting 8 minutes for the initial measurement to
| "propagate at light speed".
| leetharris wrote:
| The "speed of light" is actually a somewhat poor common name
| for the limitation.
|
| It should be called the "speed of information."
|
| If the sun somehow magically disappeared, we would continue to
| orbit that empty space for about 8 minutes.
| kremlin wrote:
| or the speed of causality
| MPSimmons wrote:
| Photons, like everything else, travel along the curvature of
| spacetime (though a physicist has told me that they do have
| some mass and thus warp spacetime themselves, too), and the
| speed of light is just how fast spacetime can curve. The faster
| you go, the more curved it is, and the harder it is to bend it
| further, but there's a point where you can't bend it any faster
| than you are because it doesn't go faster.
| Lerc wrote:
| I always imagined it as everything always moved at the speed
| of light in spacetime, like 4d motion vectors that were
| always the same length. Acceleration is changing the angle of
| the vector to move through more space and less time. Space
| curvature causes motion on stationary objects (gravity)
| because of some of the time motion becomes space motion.
|
| I kind of assume this is incorrect because it seems like a
| simple explanation and explanations of this stuff tend to not
| be simple
| tombert wrote:
| It makes me a little sad, because we're in this frustrating
| position of knowing how "effectively unlimited" the universe is,
| but also knowing how impossible it is to realistically explore
| it, at least not without a fundamental change to our
| understanding of physics.
|
| I think it'd be cool to set up colonies on other planets, or
| hell, other solar systems, but the inability to communicate seems
| like a pretty hard blocker. I mean, even sticking to the solar
| system, will start taking six hours for the light to even reach
| earth from Pluto, assuming it can even have a direct path.
|
| I don't know anything about physics, so I was hoping that the
| entanglement hypothesis might allow us to fix that, but clearly
| that wasn't the case. This makes me sad.
| staunton wrote:
| We have "enough time" to explore stuff. You or me will not live
| to see it but what's stopping a spaceship from going to some
| place for a few million years?
| tombert wrote:
| I mean, sure, in the scope of the universe then there's
| plenty of time before the heat death for some humans to
| explore another star system, they just won't really be able
| to communicate about it and relay back to us within a human
| lifetime really.
|
| I'm just kind of hoping that physicists are all wrong, and
| that there turns out to be some fancy math that allows to do
| _something_ faster than light. Not saying it 's gonna happen
| that way, but a guy can dream.
| BriggyDwiggs42 wrote:
| Fundamentally there don't seem to be any physical laws
| prohibiting us from solving biological immortality at
| least, so maybe if we can get the robot bodies up and
| running for ourselves we'd be able to do some exploring
| over a very long time.
| xandrius wrote:
| No exploring for me though :(
| jayrot wrote:
| It's still wild to me that early exploration (or I suppose
| colonization) of earth had the same limitation, though. The
| latency of packet transmission by sailing ship was pretty
| insane.
| falsandtru wrote:
| Transmission speed limit of quantum entanglement:
|
| https://news.ycombinator.com/item?id=39865641
| altruios wrote:
| This is my two cents:
|
| Maybe entanglement is a much more 'immediately physical'
| phenomenon than 'spooky action at a distance'. Just guessing as a
| layman here: maybe entangled particles are just physically
| connected {along some higher dimension / some unknown process}.
|
| Spinning together (effectively switching spaces constantly) such
| that they are always the same state. So the undetermined
| measurement stems from being unable to tell which particle
| specifically you have at the time of measurement.
|
| The idea of a particle's spin being 1/2 feels tied to this idea -
| (that a 720 rotation happens: if a particle P1 spins 360 in space
| A, spins 360 in space B before returning to space A, maybe
| entanglement is P1 and P2 filling space A and B to 'full'?)
|
| In other words - detector A may receive particle B or A depending
| on the particle's current orientation at measurement.
|
| Weird thoughts. Take with a lot of salt.
| onlyrealcuzzo wrote:
| > maybe entangled particles are just physically connected
| {along some higher dimension / some unknown process}.
|
| I have always thought this _might_ be a possibility - but
| wouldn 't we be able to observe this somehow?
|
| Is it actually possible this could happen and there's no way we
| could observe it?
|
| Gravity distorts space-time - but it's observable.
|
| For these particles to be connected still - wouldn't that be
| some disturbance in space-time?
| WXLCKNO wrote:
| I imagine we haven't figured out how to observe it yet. Same
| as anything else we couldn't observe before we did.
|
| Ruling out "it's magic", we can presume that everything in
| the universe is linked logically somehow, the link between
| the two entangled particles must exist and we just haven't
| been able to observe it yet.
| onlyrealcuzzo wrote:
| I was wondering if it's somehow theoretically possible
| there is a link but for some reason we would never be able
| to observe it.
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