4 ms·

I'm still trying to get my head around this. To the layman, it sounds almost like something trivial (properties of metamaterials) extrapolated into a bit of a s

I'm still trying to get my head around this. To the layman, it sounds almost like something trivial (properties of metamaterials) extrapolated into a bit of a sensationalist headline. So I go grab my good friend Schrödinger. We take his cat, subject of numerous cruel and unusual experiments, and stick it in a box. We tie the health of the cat to a quantum state which could condense either way. If it goes one way, the cat lives. If it goes the other way, the cat dies. Then we wrap the quantum state in these time-cloaking lenses. We look at the cat, and what? Does the lack of ability to observe the quantum state mean that the condensation of probabilities never happened? Perhaps the cat disappears? EDIT: Link for those who don't get the reference. http://en.wikipedia.org/wiki/Schr%C3%B6dingers_cat http://en.wikipedia.org/wiki/Schr%C3%B6dingers_cat

retube 15y ago
Schrodinger's cat is a flawed thought experiment. The cat is not in a super-position of live-dead just because the decay (or absence of a decay) hasn't been observed by a human. Observation just means "interaction". If one particle interacts with another, it has been "observed".
- ced 15y ago
  Schrodinger's cat is a flawed thought experiment. Observation just means "interaction" The way I learned it, Bohr would say "the atom is in a superposition of states until it is observed". Schrödinger used the cat thought experiment to show the absurdity of Bohr's position: "... and then, when I look at the cat, it is forced to take a stand, poof it goes 'alive', or 'dead'" As far as I know, we still don't understand what, exactly, constitutes an "observation". Quoth Bell (the guy from Bell's experiment): ... current interest [in questions of foundations of quantum mechanics] is small. The typical physicist feels that they have long been answered, and that he will fully understand just how if he ever can spare twenty minutes to think about it. http://www.amazon.com/Speakable-Unspeakable-Mechanics-Collected-philosophy/dp/0521368693 http://www.amazon.com/Speakable-Unspeakable-Mechanics-Collec... Jaynes is also worth reading, in spite of his non-mainstream position: http://bayes.wustl.edu/etj/articles/prob.in.qm.ps.gz http://bayes.wustl.edu/etj/articles/prob.in.qm.ps.gz
  - yummyfajitas 15y ago
    The thing is, you don't actually need to postulate that the cat goes "poof" at the point of observation. Suppose this didn't happen. Then the state of the world before observation is this: |cat dead, observer unsure> + |cat alive, observer unsure> After observation: |cat dead, observer sad> + |cat alive, observer happy> (Normalization dropped.) This isn't weird. What would be weird is if these two states could interfere with each other. I did some work a few years back which argues that interference between these states is virtually impossible - they live too far away from each other in configuration space. http://cims.nyu.edu/~stucchio/pubs/slides/wpi_wave_collapse.pdf http://cims.nyu.edu/~stucchio/pubs/slides/wpi_wave_collapse.... Ultimately the argument goes all the way back to David Bohm in the 50's. The novelty of what I did is cooking up a plausible experiment for which the calculations are tractable.
    - ced 15y ago
      Cool. How do you deal with the double slit experiments if there is no interference? Aren't you back to a fully deterministic worldview, from the observer's perspective?
      - yummyfajitas 15y ago
        There is interference - my model is merely the many body schrodinger equation, after reduction to a two-particle NLS. The key observation is that a measurement apparatus involves N particles, each moving a distance O(1). Thus, the distance (in configuration space) between both wavepackets (i.e., |cat dead, observer sad> and |cat alive, observer happy>) is O(sqrt(N)). Because the two wavepackets are so far apart, they can't interfere. This is true with or without the observer, since the cat still has O(10^23) particles. On the other hand, if there were no observer, and the system were merely an electron, the distance between wavepackets would be O(1) and interference would be possible.
mshron 15y ago
Put an LED behind the temporal cloak. Look at it from the outside. You see an LED. Look at it through the temporal cloak. You see an LED. Now turn the cloak on and blink the LED (very fast). If you're looking through the cloak, you won't see the blink happen. If you're looking from the outside, you will.
mechanical_fish 15y ago
I haven't read the paper, just the abstract. But the literal answer to your question is: You don't observe the cat. Ergo, it's like the "box" was never even opened. Now that I've answered that, let's caution you about your deployment of Mr. Cat. First of all, I don't believe you'll need an uncertain quantum object to observe in this particular thought experiment. Life is complicated enough without bringing in more quantum mechanics than you need. Just imagine a brick. It's red. Light is shining on the brick and it looks red. Now, I install my time-bending lenses around the brick, and then at one particular instant the brick changes to be yellow, and then goes back to being red. But you don't see that, you just see a continuously red brick, even though the light was "shining on" the brick the whole time, because our lenses made a "time hole" in the stream of light and the color change happened during the hole. I should also warn you that our friend Mr. Cat is a bad metaphor in many ways. (He was originally an in-joke, after all, used by people who were debating the apparent absurdity of a new theory.) The problem with the cat is that he's a completely unrealistic creature, and he primes your intuition in all sorts of incorrect ways. In real life you will never stumble across a coherent superposition of two quantum states as dramatically large (trillions of cells!) and dramatically different (alive vs dead!) as this imaginary cat. Real cats interact with their surroundings. A lot. They breathe and meow, they emit organic molecules that smell like cat, they charge up with static electricity (electric fields) and then run around in circles (magnetic fields), and above all they gravitate (which is difficult to cloak). So to make the thought experiment work the cat's imaginary box has to be a cloaking device, a box that permits no interaction with the outside world until it is "opened". And that doesn't exist in real life. And, therefore, importing the cat into this thought experiment is a particularly bad move, because it's redundant. If you have Shroedinger's imaginary box you don't need an additional set of imaginary time-cloaking lenses. The box is already cloaking the cat, for a fairly long period of time. Always be careful: Thinking about completely impossible things is fun for a while, but don't make a habit of it, or you'll become the sort of insufferable spaced-out quantum-mechanics groupie who says things like gosh, maybe when I turn around and stop believing in this tree it will cease to exist. Of course not. Tree-sized objects do not physically disappear from your universe, not without the sound of a chainsaw.
- Shenglong 15y ago
ignifero 15y ago
Schrodinger and his cat have nothing to do with this.
lkrubner 15y ago
> If it goes one way, the cat lives. If > it goes the other way, the cat dies. No, that is wrong. The cat does not live or die. The cat is both alive and dead at the same time. This is why so many people have problems understanding quantum mechanics -- they don't seem to get the implications of a state being a probability. Schrödinger came up with his cat in an attempt to make the reality clear to other people, and yet many intelligent people misinterpret what Schrödinger's point was. It's important to get this right: the cat is both alive and dead. Both. If the scenario wasn't so extremely counter-intuitive, then there would not have been a need to invent it in the first place.
- Miky 15y ago
  No, that is wrong. The cat is not both alive and dead at the same time. The Schrödinger's cat thought experiment was invented to show the absurdity of the collapse of quantum states being caused by a conscious observer. The collapse of states happens far before the cat dies or survives.
  - orangecat 15y ago
    Or if you accept the many-worlds interpretation, there is no collapse. There's one blob of amplitude corresponding to a configuration with a dead cat and you observing a dead cat, and another blob of amplitude corresponding to a configuration with a live cat and you observing a live cat. Excellent explanation with more detail here: http://www.quora.com/Why-does-observation-collapse-probabilities http://www.quora.com/Why-does-observation-collapse-probabili....
    - Miky 15y ago
      There's still an event beyond which there appears to be no superposition, whether that's because the two blobs of amplitude have separated enough or whether it's because there's only one left, and I think the word collapse serves well enough.
anigbrowl 15y ago
Throw the box away; it's not helpful here. What you see when you look through the time lens is a live cat, then either a) nothing happens or b) it suddenly turns into a dead cat. What you don't see is the cat's death, if it occurs. Look at the graph in the article; light moves from left to right through one spatial dimension, and from bottom to top along the temporal dimension. You see the before and after, but not the in-between moment. Instead of a cat, consider a situation where you could 'use' this time lens, if it operated over human-scale time periods. I sneak the time lens into your party, disguising it as a beer keg. At an appropriate moment, I trigger it; then I rush over to your wall safe, open it and extract the diamonds stored within, close the safe, and return to my starting position. From your point of view, everything is as it was before. Unless you were looking at the clock - in which case you would see it jump forward by two minutes! You realize someone at the party has been using a time lens, and raise the alarm. Suspicion soon falls upon me, and I shamefacedly produce the diamonds from my pocket. But just as you and your friends are about to lay hands on me, I vanish! I triggered the time lens again, and slipped out between you, unobserved. Of course, I can't see what's going on with the time lens either, in all likelihood; perhaps I need some sort of ninja skills to move blindly through the temporal hiatus.
- stephth 15y ago
  Unless you were looking at the clock - in which case you would see it jump forward by two minutes! wait, where is this clock?
  - anigbrowl 15y ago
    Above the mantelpiece, where else? Seriously, I just threw that in because most people have a clock (or several) and ISTM that you would experience a forward jump in time if this hypothetical device could work as described. Not having read the paper yet, I don't know if it would only work for people observing things from a particular perspective, or whether it would just create a bubble of 'extra' time for anything within its field, during which observations from outside would be impossible. Of course, this might make it impossible to escape as well - I took some dramatic liberties with my scenario to explore the possibilities, although I left out some of the wilder ones that came to mind.

retube 15y ago

Schrodinger's cat is a flawed thought experiment. The cat is not in a super-position of live-dead just because the decay (or absence of a decay) hasn't been observed by a human. Observation just means "interaction". If one particle interacts with another, it has been "observed".

ced 15y ago
Schrodinger's cat is a flawed thought experiment. Observation just means "interaction" The way I learned it, Bohr would say "the atom is in a superposition of states until it is observed". Schrödinger used the cat thought experiment to show the absurdity of Bohr's position: "... and then, when I look at the cat, it is forced to take a stand, poof it goes 'alive', or 'dead'" As far as I know, we still don't understand what, exactly, constitutes an "observation". Quoth Bell (the guy from Bell's experiment): ... current interest [in questions of foundations of quantum mechanics] is small. The typical physicist feels that they have long been answered, and that he will fully understand just how if he ever can spare twenty minutes to think about it. http://www.amazon.com/Speakable-Unspeakable-Mechanics-Collected-philosophy/dp/0521368693 http://www.amazon.com/Speakable-Unspeakable-Mechanics-Collec... Jaynes is also worth reading, in spite of his non-mainstream position: http://bayes.wustl.edu/etj/articles/prob.in.qm.ps.gz http://bayes.wustl.edu/etj/articles/prob.in.qm.ps.gz
- yummyfajitas 15y ago
  The thing is, you don't actually need to postulate that the cat goes "poof" at the point of observation. Suppose this didn't happen. Then the state of the world before observation is this: |cat dead, observer unsure> + |cat alive, observer unsure> After observation: |cat dead, observer sad> + |cat alive, observer happy> (Normalization dropped.) This isn't weird. What would be weird is if these two states could interfere with each other. I did some work a few years back which argues that interference between these states is virtually impossible - they live too far away from each other in configuration space. http://cims.nyu.edu/~stucchio/pubs/slides/wpi_wave_collapse.pdf http://cims.nyu.edu/~stucchio/pubs/slides/wpi_wave_collapse.... Ultimately the argument goes all the way back to David Bohm in the 50's. The novelty of what I did is cooking up a plausible experiment for which the calculations are tractable.
  - ced 15y ago
    Cool. How do you deal with the double slit experiments if there is no interference? Aren't you back to a fully deterministic worldview, from the observer's perspective?
    - yummyfajitas 15y ago
      There is interference - my model is merely the many body schrodinger equation, after reduction to a two-particle NLS. The key observation is that a measurement apparatus involves N particles, each moving a distance O(1). Thus, the distance (in configuration space) between both wavepackets (i.e., |cat dead, observer sad> and |cat alive, observer happy>) is O(sqrt(N)). Because the two wavepackets are so far apart, they can't interfere. This is true with or without the observer, since the cat still has O(10^23) particles. On the other hand, if there were no observer, and the system were merely an electron, the distance between wavepackets would be O(1) and interference would be possible.

mshron 15y ago

Put an LED behind the temporal cloak. Look at it from the outside. You see an LED. Look at it through the temporal cloak. You see an LED. Now turn the cloak on and blink the LED (very fast). If you're looking through the cloak, you won't see the blink happen. If you're looking from the outside, you will.

mechanical_fish 15y ago

I haven't read the paper, just the abstract. But the literal answer to your question is: You don't observe the cat. Ergo, it's like the "box" was never even opened. Now that I've answered that, let's caution you about your deployment of Mr. Cat. First of all, I don't believe you'll need an uncertain quantum object to observe in this particular thought experiment. Life is complicated enough without bringing in more quantum mechanics than you need. Just imagine a brick. It's red. Light is shining on the brick and it looks red. Now, I install my time-bending lenses around the brick, and then at one particular instant the brick changes to be yellow, and then goes back to being red. But you don't see that, you just see a continuously red brick, even though the light was "shining on" the brick the whole time, because our lenses made a "time hole" in the stream of light and the color change happened during the hole. I should also warn you that our friend Mr. Cat is a bad metaphor in many ways. (He was originally an in-joke, after all, used by people who were debating the apparent absurdity of a new theory.) The problem with the cat is that he's a completely unrealistic creature, and he primes your intuition in all sorts of incorrect ways. In real life you will never stumble across a coherent superposition of two quantum states as dramatically large (trillions of cells!) and dramatically different (alive vs dead!) as this imaginary cat. Real cats interact with their surroundings. A lot. They breathe and meow, they emit organic molecules that smell like cat, they charge up with static electricity (electric fields) and then run around in circles (magnetic fields), and above all they gravitate (which is difficult to cloak). So to make the thought experiment work the cat's imaginary box has to be a cloaking device, a box that permits no interaction with the outside world until it is "opened". And that doesn't exist in real life. And, therefore, importing the cat into this thought experiment is a particularly bad move, because it's redundant. If you have Shroedinger's imaginary box you don't need an additional set of imaginary time-cloaking lenses. The box is already cloaking the cat, for a fairly long period of time. Always be careful: Thinking about completely impossible things is fun for a while, but don't make a habit of it, or you'll become the sort of insufferable spaced-out quantum-mechanics groupie who says things like gosh, maybe when I turn around and stop believing in this tree it will cease to exist. Of course not. Tree-sized objects do not physically disappear from your universe, not without the sound of a chainsaw.

Shenglong 15y ago

ignifero 15y ago

Schrodinger and his cat have nothing to do with this.

lkrubner 15y ago

> If it goes one way, the cat lives. If > it goes the other way, the cat dies. No, that is wrong. The cat does not live or die. The cat is both alive and dead at the same time. This is why so many people have problems understanding quantum mechanics -- they don't seem to get the implications of a state being a probability. Schrödinger came up with his cat in an attempt to make the reality clear to other people, and yet many intelligent people misinterpret what Schrödinger's point was. It's important to get this right: the cat is both alive and dead. Both. If the scenario wasn't so extremely counter-intuitive, then there would not have been a need to invent it in the first place.

Miky 15y ago
No, that is wrong. The cat is not both alive and dead at the same time. The Schrödinger's cat thought experiment was invented to show the absurdity of the collapse of quantum states being caused by a conscious observer. The collapse of states happens far before the cat dies or survives.
- orangecat 15y ago
  Or if you accept the many-worlds interpretation, there is no collapse. There's one blob of amplitude corresponding to a configuration with a dead cat and you observing a dead cat, and another blob of amplitude corresponding to a configuration with a live cat and you observing a live cat. Excellent explanation with more detail here: http://www.quora.com/Why-does-observation-collapse-probabilities http://www.quora.com/Why-does-observation-collapse-probabili....
  - Miky 15y ago
    There's still an event beyond which there appears to be no superposition, whether that's because the two blobs of amplitude have separated enough or whether it's because there's only one left, and I think the word collapse serves well enough.

anigbrowl 15y ago

Throw the box away; it's not helpful here. What you see when you look through the time lens is a live cat, then either a) nothing happens or b) it suddenly turns into a dead cat. What you don't see is the cat's death, if it occurs. Look at the graph in the article; light moves from left to right through one spatial dimension, and from bottom to top along the temporal dimension. You see the before and after, but not the in-between moment. Instead of a cat, consider a situation where you could 'use' this time lens, if it operated over human-scale time periods. I sneak the time lens into your party, disguising it as a beer keg. At an appropriate moment, I trigger it; then I rush over to your wall safe, open it and extract the diamonds stored within, close the safe, and return to my starting position. From your point of view, everything is as it was before. Unless you were looking at the clock - in which case you would see it jump forward by two minutes! You realize someone at the party has been using a time lens, and raise the alarm. Suspicion soon falls upon me, and I shamefacedly produce the diamonds from my pocket. But just as you and your friends are about to lay hands on me, I vanish! I triggered the time lens again, and slipped out between you, unobserved. Of course, I can't see what's going on with the time lens either, in all likelihood; perhaps I need some sort of ninja skills to move blindly through the temporal hiatus.

stephth 15y ago
Unless you were looking at the clock - in which case you would see it jump forward by two minutes! wait, where is this clock?
- anigbrowl 15y ago
  Above the mantelpiece, where else? Seriously, I just threw that in because most people have a clock (or several) and ISTM that you would experience a forward jump in time if this hypothetical device could work as described. Not having read the paper yet, I don't know if it would only work for people observing things from a particular perspective, or whether it would just create a bubble of 'extra' time for anything within its field, during which observations from outside would be impossible. Of course, this might make it impossible to escape as well - I took some dramatic liberties with my scenario to explore the possibilities, although I left out some of the wilder ones that came to mind.