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A staple of sci-fi has been a pair of boxes with quantum entangled particles inside allowing FTL communications once the boxes travel (sub-FTL) to their destina

by sliken 9y ago

A staple of sci-fi has been a pair of boxes with quantum entangled particles inside allowing FTL communications once the boxes travel (sub-FTL) to their destination. By my understanding that's impossible, although I always wondered if you could coordinate FTL, by detecting when a particle was no longer entangled. Can someone with the background comment?

indolering 9y ago
Damn, all of these explanations are overly complex! The most basic reason it doesn't work is because measuring your particle breaks the entanglement. So you would know that your partner has the opposite spin (or whatever) but you can't bootstrap any sort of communication system with that.
- pishpash 9y ago
  Not overly complex, but overly simple. I wish people talking about physics learn for the last time that analogies are a horrible way to explain a complex concept that at best adds an unnecessary translation layer increasing cognitive load and at worst hand waves away the most critical parts.
  - indolering 9y ago
    They just get too excited : )
MichaelBurge 9y ago
It's about as likely as reading a byte from an initialized /dev/urandom and measuring its entropy to see if someone removed a hardware RNG.
- posterboy 9y ago
  I'd guess it's impossible without measuring both particles and communication to compare the results.
deleted 9y ago
[deleted]
heimdall 9y ago
Caveat: I only have a B.Science degree in Engineering Physics (Colorado, USA) and hobbyist-type research in PhD-level physics. I've always found it easier to explain quantum entanglement thusly: Imagine you have 2 cubes that alternate glowing between purple and orange. And they stay in one color for a random amount of time (100s of milliseconds). Holding both in your hands, you would just have randomly color-shifting cubes. But a neat trick of these cubes is that when you close your eyes, hit them together, and quickly put them into separate closed boxes, you know that three things will happen: 1. they will be locked into one color as long as the box stays closed (no more alternating) 2. each cube will be the opposite color from each other (when one is purple, the other is orange, and vice versa) 3. when you open the box and observe the cube, it will stay in the current color for 1 second, and then resume its randomness once again. So you take one of the boxes containing a cube and ship it to your friend on the Moon (greater than 1 light-second away). When she gets the box, you call her on your phone and ask her to wait. Then you open your box and see that your cube is purple. And then the cube starts blinking again because the entanglement is broken on your end. So you wait a few seconds and say to her "open your box and I bet you the cube is orange". She does so and confirms the cube was glowing orange before resuming the random blinking. Now the entanglement is broken on her end, but you "knew" that by having the purple cube in your possession that hers would be orange. Using this system, there is no way to exploit your knowledge of what the colors will be once observed (so sorry, no FTL communication here). The particles no longer influence each other after they are entangled at the start. It's not an active process, but rather a very specific type of setup. But it still bothers physicists (most famously Einstein), that you could "know" something without direct proof. And people in general hope that this un-intuitive phenomenon will open up whole new worlds of sci-fi tech. But no, as the article explained: "Nothing we knew suggested this goal was unachievable. The significance of this news is not that it was unexpected or that it overturns anything previously believed, but simply that it’s a satisfying culmination of years of hard work." If you had shipped the other cube-box to the opposite side of the galaxy, thousands of years after you were long dead, someone would open it and still find an orange cube.
- gabrielgoh 9y ago
  i fail to see whats mysterious about knowing something without direct proof. You could put a literal orange cube in a box, ship it across the galaxy, and you'd "know" anyone opening the box would be an orange cube. You don't need to be present at the unboxing to know that with certainty. How is this different? Am I missing something?
tim333 9y ago
>FTL, by detecting when a particle was no longer entangled The trouble is you can't detect that. You can just make a measurement on your particle and get some result. That's the same whether it's entangled or not.
greeneggs 9y ago
> A staple of sci-fi has been a pair of boxes with quantum entangled particles inside allowing FTL communications once the boxes travel (sub-FTL) to their destination. Of course this is complete nonsense. It's useful for plotting stories, but seems to have imprinted on a large fraction of readers a total falsehood. Do you know where the idea started? I think the first time I saw it was in Orson Scott Card's novel "Ender's Game" (1985).
- MrZongle2 9y ago
  Looks like it may have started in 1966 with a story by Ursula K. Le Guin. She called the device an ansible, which is what it was also called in OSC's books. https://en.wikipedia.org/wiki/Ansible https://en.wikipedia.org/wiki/Ansible
  - dleslie 9y ago
    From the book The Dispossessed. It's a great novel, by the way.
  - greeneggs 9y ago
    According to that Wikipedia page, Le Guin's ansible might not be relying on entanglement. It "doesn't involve radio waves, or any form of energy. The principle it works on, the constant of simultaneity, is analogous in some ways to gravity ... One point has to be fixed, on a planet of certain mass, but the other end is portable." About Card's ansible, it says, "Card's description of the ansible's functions in Xenocide involves a fictional subatomic particle, the philote. In the "Enderverse", the two quarks inside a pi meson can be separated by an arbitrary distance while remaining connected by "philotic rays"." So perhaps Card's "Xenocide" (1991) is where the entanglement => FTL communication myth began?
justifier 9y ago
A few weeks ago there was another announcement about the advancement in arresting the evolution of a quantum system https://news.ycombinator.com/item?id=14347231 https://news.ycombinator.com/item?id=14347231 In this way it seems to me communication may be possible A sort of sending bytes stead bits

by sliken 9y ago

indolering 9y ago

Damn, all of these explanations are overly complex! The most basic reason it doesn't work is because measuring your particle breaks the entanglement. So you would know that your partner has the opposite spin (or whatever) but you can't bootstrap any sort of communication system with that.

pishpash 9y ago
Not overly complex, but overly simple. I wish people talking about physics learn for the last time that analogies are a horrible way to explain a complex concept that at best adds an unnecessary translation layer increasing cognitive load and at worst hand waves away the most critical parts.
- indolering 9y ago
  They just get too excited : )

MichaelBurge 9y ago

It's about as likely as reading a byte from an initialized /dev/urandom and measuring its entropy to see if someone removed a hardware RNG.

posterboy 9y ago
I'd guess it's impossible without measuring both particles and communication to compare the results.

deleted 9y ago

[deleted]

heimdall 9y ago

Caveat: I only have a B.Science degree in Engineering Physics (Colorado, USA) and hobbyist-type research in PhD-level physics. I've always found it easier to explain quantum entanglement thusly: Imagine you have 2 cubes that alternate glowing between purple and orange. And they stay in one color for a random amount of time (100s of milliseconds). Holding both in your hands, you would just have randomly color-shifting cubes. But a neat trick of these cubes is that when you close your eyes, hit them together, and quickly put them into separate closed boxes, you know that three things will happen: 1. they will be locked into one color as long as the box stays closed (no more alternating) 2. each cube will be the opposite color from each other (when one is purple, the other is orange, and vice versa) 3. when you open the box and observe the cube, it will stay in the current color for 1 second, and then resume its randomness once again. So you take one of the boxes containing a cube and ship it to your friend on the Moon (greater than 1 light-second away). When she gets the box, you call her on your phone and ask her to wait. Then you open your box and see that your cube is purple. And then the cube starts blinking again because the entanglement is broken on your end. So you wait a few seconds and say to her "open your box and I bet you the cube is orange". She does so and confirms the cube was glowing orange before resuming the random blinking. Now the entanglement is broken on her end, but you "knew" that by having the purple cube in your possession that hers would be orange. Using this system, there is no way to exploit your knowledge of what the colors will be once observed (so sorry, no FTL communication here). The particles no longer influence each other after they are entangled at the start. It's not an active process, but rather a very specific type of setup. But it still bothers physicists (most famously Einstein), that you could "know" something without direct proof. And people in general hope that this un-intuitive phenomenon will open up whole new worlds of sci-fi tech. But no, as the article explained: "Nothing we knew suggested this goal was unachievable. The significance of this news is not that it was unexpected or that it overturns anything previously believed, but simply that it’s a satisfying culmination of years of hard work." If you had shipped the other cube-box to the opposite side of the galaxy, thousands of years after you were long dead, someone would open it and still find an orange cube.

gabrielgoh 9y ago
i fail to see whats mysterious about knowing something without direct proof. You could put a literal orange cube in a box, ship it across the galaxy, and you'd "know" anyone opening the box would be an orange cube. You don't need to be present at the unboxing to know that with certainty. How is this different? Am I missing something?

tim333 9y ago

>FTL, by detecting when a particle was no longer entangled The trouble is you can't detect that. You can just make a measurement on your particle and get some result. That's the same whether it's entangled or not.

greeneggs 9y ago

> A staple of sci-fi has been a pair of boxes with quantum entangled particles inside allowing FTL communications once the boxes travel (sub-FTL) to their destination. Of course this is complete nonsense. It's useful for plotting stories, but seems to have imprinted on a large fraction of readers a total falsehood. Do you know where the idea started? I think the first time I saw it was in Orson Scott Card's novel "Ender's Game" (1985).

MrZongle2 9y ago
Looks like it may have started in 1966 with a story by Ursula K. Le Guin. She called the device an ansible, which is what it was also called in OSC's books. https://en.wikipedia.org/wiki/Ansible https://en.wikipedia.org/wiki/Ansible
- dleslie 9y ago
  From the book The Dispossessed. It's a great novel, by the way.
- greeneggs 9y ago
  According to that Wikipedia page, Le Guin's ansible might not be relying on entanglement. It "doesn't involve radio waves, or any form of energy. The principle it works on, the constant of simultaneity, is analogous in some ways to gravity ... One point has to be fixed, on a planet of certain mass, but the other end is portable." About Card's ansible, it says, "Card's description of the ansible's functions in Xenocide involves a fictional subatomic particle, the philote. In the "Enderverse", the two quarks inside a pi meson can be separated by an arbitrary distance while remaining connected by "philotic rays"." So perhaps Card's "Xenocide" (1991) is where the entanglement => FTL communication myth began?

justifier 9y ago

A few weeks ago there was another announcement about the advancement in arresting the evolution of a quantum system https://news.ycombinator.com/item?id=14347231 https://news.ycombinator.com/item?id=14347231 In this way it seems to me communication may be possible A sort of sending bytes stead bits