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Why Can’t You Use Quantum Mechanics To Communicate Faster Than Light?

Say Alice and Bob are on opposite sides of
the universe. Entanglement means that somehow, Alice measuring
her particle affects Bob’s one even though it’s a world away immediately. If that’s the case, then the question of
this video is “why can’t they use quantum mechanics to communicate instantly”? This video is very much a sequel to a video
I made about entanglement and the EPR paradox so it will help a lot to watch that first. Actually, these videos are part of a series
on quantum mechanics so start here if you’re new. Back to the question. Let’s say Bob wants the answer to a yes
or no question that he’s asked Alice, but she’s waited till she’s very far away
to think of an answer. However luckily, they have an entangled pair
of particles between them. Here’s a possibility. Alice tells Bob in advance that if he measures
his particle to be up, the answer is yes, down is no. Now all Alice has to do is nonlocally influence
his particle to be up, say and then they’ve communicated faster than light! But obviously that won’t work, no matter
what she does, her own outcome is random, and since Bob just gets the opposite, his
outcome just comes out completely random as well. So that scheme doesn’t work- but a lot of
you suggested a much more devious plan. I’ve been saying for ages that you can tell
the difference between a state in a superposition of two possibilities, and one that’s merely
one of the other of these but you don’t know which. Why not use that? If Alice measures, the whole state collapses
and is not in a superposition anymore. Then surely Bob can do some interference experiment
and if he sees no interference, he knows that Alice has done her measurement, otherwise
she hasn’t. Alice can communicate what she wants by choosing
whether to measure her particle or not. Then they could use this scheme, and communicate
instantly across the universe!! Ok, that sounds great but obviously Quantum
mechanics has a way around that too. I’ll explain it, but this is the punch line. With this entangled state, you can tell they’re
in a superposition by doing some measurement that shows interference. However, that measurement is a measurement
where you have to interact both of the particles in some way to do the measurement, and so
you need both particles in the same place. If you instead only do the measurement on
one of the particles, or both particles, but not together, there’s no way for you to
tell the difference between the state where they’re in superposition or when they’re
not. To see this, let’s look at what happens
when Bob does his measurement in the case where Alice did hers already, or choose not
to. These are the states in either case. In the case where Alice has measured, his
particle really is up or down now, but he doesn’t know which. But then say Bob does a measurement of the
left and rightness of a particle. We know that if we did this to a particle
that’s up, it will go either left or right randomly. Same thing for a down particle. So even though we don’t know which it is,
up or down, we know it will randomly go left or right, and this is the no interference
result that we talked about in some previous videos. This is kind of what we expected. But what happens in the second case where
the state is still in a superposition? This is a bit tricky. What you need to do is write the state, in
particular Bob’s particles state, in the left/right basis. Try it and then see if you can figure out
what happens. OK, so here’s the maths. All I’ve done is subbed in these expressions. Then, I’m grouping up the left and right
options for Bob’s particle. Then you can see that both options have the
same weight, so they’re both equally likely. What this means is, if Bob measures his particle
for left rightness when Alice hasn’t measured, the particle is equally likely to go left
or right- which is the same as if she had measured, so you can’t tell the difference. But you might protest that I’ve only showed
you that this plan for faster than light communication is foiled for this particular entangled state,
but what about other ones. There are way way way more possible entangled
states that just this. I just use this for an example most of the
time because this state has the maximum possible amount of entanglement, but in fact most 2
particle states are entangled. For example, this state is entangled. So what would we need to show that using any
entangled state is useless for faster than light communication? You need to prove that no matter what Alice
does on her side, that doesn’t affect Bob’s measurement outcomes. For example, in either case when Alice does
or doesn’t choose to do a measurement, Bob get’s up or down with the same probability
either way. This can be proved generally, but it’s a
bit tough. Instead I’m going to get you to do it for
an example that’s quite a bit more challenging that the one I did. Prove it for this state, when Alice measures
up and down-ness, but Bob measures left-rightness. I’m going to write a detailed solution in
the description, but ask me if you get confused. So yes, entanglement is useless for faster
than light communication, but can we try use it for something else? Say Alice and Bob have lots of entangled particles
between them. If they measure them all, then the outcomes
are random, but they know what the other persons outcome is. So they share a string of random bits. Your second homework is to look up and explain
the usefulness of something called a ‘one-time pad’. Also, comment on whether or not an encryption
based on a one time pad coming from this set up is secure or not if they know Eve might
be trying to intercept the particles. This is the topic for the next video.

100 Replies to “Why Can’t You Use Quantum Mechanics To Communicate Faster Than Light?”

  • Have a question – thought we learned earlier in spin video that (ignoring coefficients) up = right + left, and down is right – left. At 3:31 though it seems like the transformation is reverse (up = right – left, down = right + left).

  • Last video you said, that if one of the particles has a spin up, another one has to have spin down, but now you are talking about left and rightness. You're saying that even if the electron has spin up, the positron has the same probability for spin left and right. But why do we even care about left and right, when we can always measure only ether it up or down. This is the thing I don't understand. Do I make any sense right now?

  • Last video you you said, that if one of the particles has a spin up, another one has to have spin down, but now you are talking about left and rightness. You're saying that even if the electron has spin up, the positron has the same probability for spin left and right. But why do we even care about left and right, when we can always measure only ether it up or down. This is the thing I don't understand. Do I make any sense right now?

  • Excellent and beautiful video.
    I suggest you see some interesting videos on SALEH THEORY-com about behaviors of photon.

  • It will be possible with time. I love reading articles of scientist stating impossibilities in the past and then reading the debunking articles later on. Our recent advancements in the understanding of quantum mechanics has me very optimistic about the viability of quantum communications in our future. There have been many gatherings of world famous scientists in the past that have come together and decided that we have discovered and invented everything we can and that our efforts beyond that point would yield no useful results. I've seen articles of theoretical limits on quantum entangled particles that we debunk VERY soon after publication. I hope there are teams out there with a higher understanding that share my optimism for our future in quantum mechanics.

  • What if you set up a time together for measurement? You can say one thing with high probability. "i measured my particle."

  • Why not use two Quantium entangled electrons and have them in a state of constant observation. That way the randomness of none observation no longer exists. As these are electrons, we can use a powerful magnet to flip their spins which would reverse the spin of their partner. In this we can send a series of up/downs (1/0) to give a line of code that a computer can read. Thus, wouldn't this mean two people can communicate?

    Here's a news article that talks about entangled electrons:

  • Your design for the Quantum Eraser mentioned in a previous video DOES appear to allow FTL communication by switching the pattern seen on the detector from an overlapping bell curve to an interference pattern and vise-versa. I am still trying to figure out where the issue lies.

  • I wish I knew about this video before!!

    I just made one explaining this to ColdFusion's Channel. He made the same mistake.

  • What if she measures up/down and right/left interchangedly until she checked up/down and it is in the right (or rather opposite) direction and then he measures up/down?

  • Hey, first of all, I love your videos! Keep up the good work!

    I have two questions, one of which a more general question but the other more related to this video:

    1. In all your videos, it seems that the main argument for as to why a superposition of states is different than not having previous knowledge of the state, is the interference pattern created by the double slit experiment. I wonder if there are other experiments in which the quantum weirdness of superposition and measurement problem become apparent.

    2. In this video, you state that there is no way Bob can know whether Alice measured or not, and thus information is not travelled instantly. However, this argument just shows that there is no way Bob can gather / read the information, but according to entanglement, "universe-information" still travels faster than light (in other words, there is still information traveling faster than light, but there is no way for us humans to detect it). Is there a way around this, or do we just have to accept it and live on with our lives? Measurement problem is weird…

  • I didnt want this answer… I need to someone to confirm that it is possible to communicate faster than speed of light !!

  • It appears that Time is the dilemma. Measuring takes time, determining Yes or No, right or left, up or down. That's dualistic thinking. For unity there is no differentiation of different states, all are commingled. Entanglement of two particles is a form of unity. If communication takes time, it is bound to causality. Outside of time, instantaneous communication may still be feasible. However, it would not operate according to our rules of language. A communication might work with new language rules enacted, or by sending unified messages that do not split into right/left, up/down etc. A Non-dualistic system.

  • What if Alice's intentions are aligned with the entangled particle on her side, she would be able to influence it in her favor. Thus, she would be able to communicate effectively over vast distances, given the scenario. I know this sounds like mind over matter, but it may be possible, entrainment can happen, that's what quantum entanglement proves. If one ceases to treat particle as object, and measurer as subject, object and subject become one. Alice's mind and particle are no longer divided, they become indistinguishable. You may say, "the particle's fate is random, and cannot be influenced directly through Alice's intentions". Okay, that's fair enough. But what is randomness? Randomness is a measurement of how one's guesses run contrary to one's outcomes. With a coin toss, accuracy of guesses are roughly 50/50, based on chance. 50% of guesses are misaligned, or anti-aligned. If so, it is fair to give randomness its due 50%. So, in a given coin toss, 50% of guesses will be wrong, or misaligned. But what if randomness is just a measure of misalignment? Is there a way to locate a confluence that exists after misalignment and alignment come into parity? A place of unity? Perhaps intentions could be sent through this balanced confluence, so that the influence of time is negated. Randomness is thus taken into account as a force, a force of misaligned energy. A Yang energy, in fact. So, I am suggesting a third element in this scenario, either the mind of Alice, which connects directly with the particle, or a machine that can find confluences where unity applies, then is able to send intentions directly to the particle at certain intervals. If there are confluence points that are accessible, "timeless junctures", then this experiment could function properly, once all three elements are combined to operate as a seamless entity. Unity is about balance, and when misalignment is balanced with alignment, timeless gates may open. These gates bypass causality, where we are stuck due to the effect of Time, Entropy, and Space.

  • Hi, great videos …but may i have a question pls ? From what size of particle, Newton mechanic started to be unsufficient and QM should be applied ?? Thank u….

  • Nice video.

    Particles A and B are entangled. Is it possible to create a copy of the quantum state (however imperfect) of Particle A such that the copy's quantum state is also entangled with Particle B?

  • Why not just keep measuring, then putting it back into a superposition until it's the state you want, and then wait until the other person (or computer) assumes you're done measuring and checks to see the answer?

  • Thank you for these amazing videos!All the important questions answered and explained to the world.Keep up the good work!(I really love this one)

  • I have a question: is a particle's measured state actually random, or only in effect random, i.e. decided by processes we cannot (currently or perhaps ever) measure? Might our measurement determine a particle's state by some deterministic process invisible to us? Do we know for sure that state is random, and if not, do we know for sure that we can't know for sure?

  • So it's not about the speed of light at all. It's just that the entangled particles move randomly. Is it possible for Alice to measure once for yes and twice for no?

  • Even if we are not sharing the spooky Quantum paradigme presented in your video, remains that your videos are Amazingly Well Presented and Clear; Very Well Done for that! 🙂

  • Here is my solution to the Homework: I just can predict what number is in your mind even without kwon you and I did not came from the future (the prove is in timestamp in the coment)… Think in a number 1 to 9, multiply that number 2x, plus 10 to total, divide by 2 to total, now subtract by your thinking number… and the faster than light answer came from the future is "5". I can be in any part of universe and I will know your thinking numbers, dumb Phd hahaha 🙂

  • Have you produced the video on communication you were refering to in the end of this video ? Fantastic work by the way !

  • What if Bob observes his particle 24/7 waiting for Alice to observe hers? Would Bob see any difference the moment Alice joins in?

    I'm halfway through the video so it may get explained, sorry if that's the case.

  • All the existing "communication" faster than light is unitary, eternity-now cause-effect, complete infinite connection, so that symmetric structures of constants are distributed infinitely and only excluded frequencies like those of light are left as communicable information. Ie "entanglement" is a part of the completed, dynamic, metastable formwork of the constants. (Too simple, because the required definition is a reciprocal relative quantum infinity, mathematical law of occurrence)

  • Can Alice tell if her electron spin is up or down without having Bob's particle? (I.e. Are you saying that the first person to measure can know the state of the system with one particle; but the second person to measure requires both particles to know the state of the system?)

  • this is such bullshit. this doesn't prove that instant communication is impossible.

    all this proves is that our current measuring methods are insufficient

  • Which subfield should I pursue for a PhD? I'm wanting one that uses a lot of quantum mechanics so I'm thinking of high energy nuclear physics, particle physics, condensed matter physics or quantum information physics. What would you suggest?

  • I don't get it, so if you can't detect what was done to a particle on the other side, how do they know they're entangled in the first place?

  • Why bother measure the particles? Just get the particles to interact with something outside of them that to transfer their state.

  • Let's say that alice and bob are two super computers resposnible for cheking the entangled states of trillions of particles. we sent bob to mars while alice stayed on earth. But before we sent bob to mars we gave each computer a set of logarithmic instructions detailing the order of which particle to check first. Because both supercomputers follow the same algorithm they allways know which particle to check next. Lets say that each of the trillions of entangled particles each have a corresponding x,y, and z coordinates. set of numbers detailing their geometrical position in a made up space we created just for them. After millions of itterations strings of random numbers will begin to appear as a result. But alice and bob are very smart super computers. Soon they start to treat the huge random strings of 0101101010 as sets. and as more less and less probable sets appear they will start to use them to draw patterns in our x,y,z coordinate space. At this point it no longer matters if state is 0 or 1 only geometrical pattern emerging matters because alice and bob will begin to use geometrical pictograms to commuinicate.

  • Lets say Alice has an atomic clock in Alpha Centauri, Bob has another in earth, both clocks are coordinated to wake up Alice and Bob at the same time ……in my book that's FTL signaling….

  • I have been considering something, this led me to your videos as I was trying to think about EPR paradox.
    Now, I do web development/programming, and am very interested in computer science, although for some reason when I was younger and in University I thought social sciences was where I wanted to concentrate. I don't want to bore you or anyone with details, but I hope you will contact me back.
    I am brushing up on my pre-calculus algebra, then brush up on my calculus, then begin to work on and learn some linear algebra, so I find it kind of awesome that you have so much helpful videos.
    Anyway, I have a question and since I don't have understanding of quantum mechanics, I am looking for someone more knowledgeable to converse with. It directly relates to this question and communicating long distances.
    Part of my question is once particles are observed is the connection/entanglement broken or can you continually manipulate one of the entangled particles? The answer to that has a few implications, that I can't find or don't know where to look to get a clue of what people have been considering.
    I started following you on google+ so that you can contact me through there.

  • I keep thinking about this stuff. What I am getting at is that if the two particles are entangled, which I assume acts as if they are connected with a two way cause and effect relationship. If that is case, why can't they set up a series of multiple consecutive observations, where they would agree to change at during those intervals and you could record changes on either end.
    Now if I were flashing a light at you, how would you know it wasn't just random flashes of light? The first you might assume is random, second and third also. If I am flashing a pattern (like a morse code) with multiple observations on the other end you would have a good idea that it was an intelligible pattern and unlikely random.
    If the two people have a prior understanding that they will check every so often for a change. A message will have a non random preamble so the other will know when to start making repeated periodic observations, where message starts.
    If computers and cameras were used you could make a an automated process for fairly complex communication.
    I doubt the answer could be so easy, so what is the catch?

  • I had wondered about this myself and found your video by randomly searching to see if someone else had the same idea. Really interesting stuff.

  • can you not tell if a particle is in a super position if you kept closing the box and looking back? if the other person is measuring their particle wouldn't it stay in the same state? say you made a system where the entangled particle was kept in a super position for 2 seconds for a 1 and 1 second for a 0 while the other was measured 1000 times a second by a computer to see when the position changes to create some kind of Morse code?

  • I have been studying this for more than 20 years and it makes no sense to say the entanglement is instant but its not. Like most of the 'physics' from the last 100 years it is really just BWB. You sense this surely? Why not have the courage to just say it?

  • I think the problem is the nature of language itself. It should be possible to construct a device or packet of information
    that exists in a balanced state of unity. One requirement for this
    involves actually knowing what blocks of information and energy are, and
    how they dovetail with each other in a comprehensive sense. Mathematics
    may be helpful in this endeavor. Imagine that the building blocks of
    energy/info, once combined into an aggregate, can lead to a coherent,
    interconnected state that is tapped into unity. All blocks of
    energy/info must cancel out to a unified state. It is a bit like
    assembling an advanced puzzle. It would be beneficial to be able to plot
    the progress of the puzzle, using mathematics, because the pieces would
    manifest dynamic energies when brought into contact or correlation with
    one another. Creating a balanced puzzle state would enable
    instantaneous communication, using nullified blocks of energy/info for
    transmission. The unified, timeless realm would be the conduit. The
    dualistic nature of language is thus the barrier that must be breached,
    when elements are brought into harmony and unified, the conduit to unity
    is revealed. Hemingway said: "write the truest sentence you know". Did
    he sense that there is an underlying truth within the words themselves?
    What would a true, unified statement look like?


  • Maybe I am talking non sense but can't they just move one up or down twice for yes and only once for no? That would take the randomising effect out of the equation

  • Alice and Bob each has an entangled superposition state in that if Alice measures X direction, then Bob will not get anything in Y direction. If Alice measures Y direction, Bob will get something in Y direction. Alice tells Bon, if Alice wins the lottery, she will marry him, otherwise not. If Bob measures Y direction and get a measure (+ or -), then the answer is YES. If Bob get no measure in Y, then the answer is NO (X)! Alice wins the lottery and immediately measures Y direction. Bob measures Y and obtains a non-zero value, he knows immediately the answer is YES. Einstein's relativity's speed of light limit is valid based on the observation that speed of light is constant and maintaining the equivalence of two inertia coordinate systems.

    Quantum mechanics has things that do not have to satisfy classical physics. For example, energy conservation may be "violated" within delta T. So, I suspect we have to accept that quantum communication can be real in terms of transmitting (simple) information at a speed faster than light. If one insists that this would violates the theory of relativity on the grounds that causality would be violated, then perhaps it's not a big deal because it may be violated only when quantum communication is used not classical communication. And when quantum is involved, we expect to see lots of weird things, plus causality seems to be violated in blackhole environment.

    Now, having said all these, I am a confused old man and need intelligent people to correct me if anything wrong in my logic. I am humbly waiting for your input. Thank you in advance!

  • I have a question. I should say that I only have what would be charitably called a lay person's understanding here so I apologize if this is an ignorant question , but I've heard that if you have three particles A, B, and C, that you can entangle A and B, then B and C. And that after performing this series of entanglements all three particles are entangled together. I understand (I think) why you couldn't perform an interference test if you only had access to one of two entangled particles. But if Alice holds particle A and Bob gets particle B, then entangles it with particle C, could he not perform an interference test with B and C to determine if Alice had measured particle A?

  • Is the clever part here, to check our position without observing it, hereby not effecting the quantum super position? Is it observation without the interference? Keep an open mind people, what they thought was once impossible a 100 years ago….

  • you should have said " why cant you use quantum mechanics to communicate faster than light RIGHT NOW?" One breakthrough will cause to this video to be obsolete…

  • What if you don't have to measure the state of the particle, just if it changed?
    If you have two pairs, you can get 1 bit of info out of them.
    You only need to check if the state of the particles has changed; if only one pair changes, that is logical 0, if two pairs change that is logical 1.

    Sorry, if I didn't understand you correctly, and for any grammar mistakes I made.

  • So when you do the measurement (observation) of the particle it takes a state.
    Isnt it possible to keep observing both particles continuously and changing the state of one while observing?

  • Hold on, this explanation doesn't make sense. I was expecting something like "the information about whether the particle was measured travels across the universe at the speed of light", not "you can't make the measurement with only one particle". Actually, the explanation in this video seems entirely inconsistent with why everyone's so excited about quantum computing (measuring entangled particles for e.g. the BB84 algorithm).

    My (limited) understanding of quantum particles is that Bob could set up a quantum gate so that Alice's measurement does have a detectable effect on Bob's measurement. With just one pair of entangled particles, Bob's measurement would be meaningless. But, with say 10,000 particles, measuring all of them and taking an average would give an answer that indicated Alice's answer with a high degree of certainty (more certainty with more particles). I'm not sure exactly how this is done, but it's what I've taken in so far.

    Can you explain why this doesn't work?

  • When Alice measures the state, bob can do the same but a few times. If the state will be always the same, it means that Alice is measuring the state. When she stops bob will get random values. That means that Alice stopped to measure. These two situatuons can be interpreted as 0 and 1. Where am i wrong?

  • Well, maybe not straight to your subject but still relevant and inmmensenly interesting ->
    By purposelly afecting "reflectance of main rf stream" at the end of the beam, you can INSTANTANeOUSLY check that info change "at the base" where the original rf entangled stream was "preserved", would that account for the purpose os "faster than light"…(?); Im not an expert anyway, cheers and thanks for your presentation !!

  • What if we combine Quantum Entanglement with the Reverse time quantum experiment. Could that be used to eliminate the interference caused by the measurement? I send a message by changing the state of Particle A. Particle B is immediately effected due to entanglement with Particle A. You measure state of Particle B and run Reverse time experiment against Particle B simultaneously. You measure the state while time is reversed for the particle. Now you can decipher my message. Plausible or am I way off?

  • bob asks alice 'do you like me?'. alice tells bob in advance that up means yes and down means no and for him to measure at 8:30am est. alice likes bob. she wants to signal to him that she likes him but everyone keeps telling her that theres no way for her to give bob the answer but alice is crafty. at 8:00 am est alice measures and its up and thats no good so she stops the measurement. shes feeling lucky so at 8:10am est she measures again and wouldnt you know it, its a down spin! what are the odds of that?! now all shes gotta do is hold the measurement till 8:31am est and bob will know the answer. i mean if that works u can scale that up and send shit as far as u can send a spaceship. im thinkin one day we make a real small ship thats got light sails or somethin and the ship also has a radio receiver and transmitter on it and its hooked up to a computer and we can use that to turn the radio waves into 101010101010101 and then use entalgled particles to represent 1010101001 for the computer on earth to take the 010110110 and turn that back into sound or pictures or w.e, maybe talk to aliens like that or some shit, wont understand them but someone will figure it out eventually.

    im not of the maths.

  • What about if Alice and Bob start off in the same room and conduct a series of double slit experiments, they run the experiments and record the data that shows which slit the particle went through and also what pattern it made (interference pattern or not). They don't look at the data. They then part ways and Bob begins his journey across the universe with all the data that shows just the patterns and Alice keeps the data that shows which slit it went through. Alice can then communicate with Bob faster than light, a message by selectively deleting the particle path information before she has viewed it, which Bob can then look at and see either interference pattern or not.

  • What if Alice tries to destroy her particle?
    What if she throws it into a BlackHole, or splits it, or vacuum collapse happens in her part of the universe?

  • Sorry but you explained this poorly. All you had to say was if Alice wants to send a 1 and she FORCES her particle to be 1, then entanglement is broken(no info sent). However, if she simply MEASURES her particle and it is a 1 then she knows Bob's will instantly be 0. This is still not sharing information though, because Alice cant choose what to send(if she does choose entanglement is broken).

  • Can someone else??

  • What if I said I could build a computer out of nothing but connections? Something that is not analog or digital – but very mechanical in nature – not using numbers/measurements/logic operators in any way to perform logic? If anyone is interested, I have build a working model that demonstrates if then, do while, a randomizer, a relational database and I even built a simple add/sub/mult/div calculator, you can find what I am working on explaining it at:

  • This video is very naive. One can easily imagine sending information with entangled particles. Just think of them like bits on a computer. This video simply demonstrates that it's impossible to send information with a single bit, in the same way you cant send messages over the internet with a single bit. You need to think bigger, a network of entangled particles as opposed to the measly 2 in this video

  • I just wrote a blog post on a possible mechanism that goes outside of these usual arguments as to why it's not possible in the traditional sense of communication. I'd like to hear your thoughts on this:

  • How many people here are regular ole Ham radio operators? Those who are will be able to work out how to make FTL or Q-Comms work.

  • Why not 8 particles and Hex computing.
    We will figure this out so that when men land on Mars we can communicate instantly.

  • Yes, but also wrong.
    Maybe, but that's like traveling "faster" than time vs. warp drive. You don't need to accelerate to that speed to effectively go "faster".

  • You could still do a form of communication where you said don't do this or that until you read that your particle has been measured for either up or down

  • I have a question: Assuming or if a multiverse exist does quantum entanglement applies also? I mean if we put the 2 engtangled particles in a different dimension or in a multiverse, will it affect each other?

  • Then how did the Chinese manage to send a picture to a satellite using quantum counterfactual communication protocol? Seems a bit more than random.

  • Also, the act of measuring results in a change of state. If the state changes 3x in a nanosecond, consider the value to be 1. If the state only twice in a nanosecond, consider the value to be 0. Else, disregard state change as noise. In this manner, information should be able to be transmitted… Which is probably, more or less, what the chinese did.

  • I think entanglement is not real. Scientists should stop purposing theses stupid ideas now. They should wait until they've appropriate technology and tools to understand these things fully.

  • My intuitional guess before watching more than 24 seconds: Because on side B you don't know whether a change is happening because of something done on side A or because of some natural phenomenon.

  • Suppose you have an engagement with probabilities of 50% for up and down when measured. Why couldn't Bob and Alice entangle N particles and then have Alice set all of them to up. Then Bob will measure and if not all are down, he knows she has not yet said anything. Else if all are measured up, he knows with probability 1-2^-N that she has set them all to down. N can be made so large than the probability is so high that practically speaking the communication should work.

    Where is my logic wrong?

  • What if she measures her particle until it's the answer she wants to give, then an automated system checks the other particle 1,000,000,000,000,000,000,000,000,000,000,000,000 times over to make it very unlikely that the particle isn't just repeating by chance, to determine the response? And use that like binary to transmit complex information over a very long distance. Or do the particles no longer change after their first observation?

  • Can Alice change her particle to have upspin so it forces faster than c communication of downspin at Bob? And could they previously agree that Bob measures his electron just "after" we both view a mutally distant celestial event that is between us (at which time Alice immediately set her particle's upspin)?

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