3 ms·

I've always wondered if you replace the cat with a person are they an observer?

DemocracyFTW2 4y ago
Both yes and no until they disentagle.
gus_massa 4y ago
The "observer" is a bad historical name. The observer can be a person, a camera, a photographic plaque, a cat or just a brick. There is no magical thing in humans. We have repeated experiments that are equivalents to the Schrodinger cat with particles and molecules. We even made experiments like in this article that are huge for a typical quantum system but tiny for the human scale. They must be very cold and isolated, so it's difficult to put bigger and more interesting things. Everyone expect that it's possibly to do with cats or humans, but it will be very difficult. There are variants of the experiment that make some test to the system inside are actually in the superposition state. https://en.wikipedia.org/wiki/Wigner%27s_friend https://en.wikipedia.org/wiki/Wigner%27s_friend [1] We tried it with small systems with one (or a few?) particles, and they work as the theory predict. Everyone expect that it's possibly to do with cats or humans, but it will be very difficult (but at least it's not necessary to kill the friend). [1] The details of the "Wigner's friend" are too technical.
- sharemywin 4y ago
  what is the minimum viable observer(for lack of a better term) is there a certain number of or arrangement of particles that makes something observed versus observer?
  - gus_massa 4y ago
    Oh! That's a good question! tl;dr: Nobody knows :( It's an open question in physics. It's essentially the https://en.wikipedia.org/wiki/Measurement_problem https://en.wikipedia.org/wiki/Measurement_problem or at least a huge part of it. It's a weird rule in Quantum Mechanics, that is solved by hand waving. In most experiments it's obvious what is the system and what are the measurement devices. Nobody likes the rule, but no one know how to avoid it (and nobody knows what it really means). There is a small group of people trying to solve it, and the rest of us just ignore the problem. We have been using QM for a century, and no one is sure that we don't need another century to fix the rule. So "Shut up and calculate!" meanwhile. It's difficult to answer without adding a few guesses here and there, so take the rest of my comment with a grain of salt. <may include some guesses> If it's an experiment made on purpose, people is careful to avoid anything in between, so everyone can use hand waving and agree what is the system and what are the measurement devices. There are some experiments trying to use quantum systems as big as possible, for example the one described in the article. We expect that it's possible to use even bigger things, but it get's difficult to keep them cold and isolated. I'm not sure if there is an experiment showing that a small "brick" can act as an observer when the "brick" is very small. The idea is that the particles inside the brick are so many that it's impossible to track them and also all the quantum path are so different that there is no interference between them. Nobody is trying to measure that, because every time the system is not isolated enough (for example because you expected a total vacuum, but some molecule of air entered the system anyway) the quantum effects are no visible. Does it count as noise or a measurement by a rogue device? It's difficult to make experiments with particles of different size to understand where is the threshold. It's easier to make experiments with gas at different temperatures. <tangent> At high temperatures gas (like air) act as a classic gas, and follow the rules we would expect if they are made of a huge lot of small balls. At low temperatures, the gas become weird. (Assuming you pick a gas that does not condensate and is a liquid.) They don't follow the rules of a classic gas. For example if you fix the temperature, the volume and the amount of gas inside a recipient, then there are some quantum effect that make the pressure of the gas higher or lower than the equivalent classic gas. It's quite easy to measure, and there are many quantum mechanics effects that are posible to see with this method, and it's easy to regulate the temperature to get a "classic" gas or a "quantum" gas. The interesting part is that there is no threshold. The gas changes smoothly between "quantum" and "classic" when you increase the temperature, and you get a behavior that is in between. What is really happening is that the gas is always a quantum gas. But a hot quantum gas has an equation that is very very very similar to the equation of a classic gas. So if you are only going to use hot gas in your experiment, you can ignore the quantum effects and use the classic gas equations that are much simpler and almost as good as the difficult quantum gas equations in your experiment. </tangent> Back to your question... Nobody is sure, but the guess is that the difference between observed and observer is just a simplification. There is probably not true difference. It's just a trick to simplify the calculations. If you avoid some weird corner case, it work really well. Let's hope we can know the correct answer some day. </may include some guesses>
ahazred8ta 4y ago
Actually, Schrödinger never believed that the half-alive cat situation could ever occur. He invented it as an example of something that could not happen in real life. Schrödinger thought that the quantum superposition would collapse when the Geiger counter 'observed' the decaying atom by going 'click', not when the box was opened.

Both yes and no until they disentagle.

The "observer" is a bad historical name. The observer can be a person, a camera, a photographic plaque, a cat or just a brick. There is no magical thing in humans. We have repeated experiments that are equivalents to the Schrodinger cat with particles and molecules. We even made experiments like in this article that are huge for a typical quantum system but tiny for the human scale. They must be very cold and isolated, so it's difficult to put bigger and more interesting things. Everyone expect that it's possibly to do with cats or humans, but it will be very difficult. There are variants of the experiment that make some test to the system inside are actually in the superposition state. https://en.wikipedia.org/wiki/Wigner%27s_friend https://en.wikipedia.org/wiki/Wigner%27s_friend [1] We tried it with small systems with one (or a few?) particles, and they work as the theory predict. Everyone expect that it's possibly to do with cats or humans, but it will be very difficult (but at least it's not necessary to kill the friend). [1] The details of the "Wigner's friend" are too technical.

sharemywin 4y ago
what is the minimum viable observer(for lack of a better term) is there a certain number of or arrangement of particles that makes something observed versus observer?
- gus_massa 4y ago
  Oh! That's a good question! tl;dr: Nobody knows :( It's an open question in physics. It's essentially the https://en.wikipedia.org/wiki/Measurement_problem https://en.wikipedia.org/wiki/Measurement_problem or at least a huge part of it. It's a weird rule in Quantum Mechanics, that is solved by hand waving. In most experiments it's obvious what is the system and what are the measurement devices. Nobody likes the rule, but no one know how to avoid it (and nobody knows what it really means). There is a small group of people trying to solve it, and the rest of us just ignore the problem. We have been using QM for a century, and no one is sure that we don't need another century to fix the rule. So "Shut up and calculate!" meanwhile. It's difficult to answer without adding a few guesses here and there, so take the rest of my comment with a grain of salt. <may include some guesses> If it's an experiment made on purpose, people is careful to avoid anything in between, so everyone can use hand waving and agree what is the system and what are the measurement devices. There are some experiments trying to use quantum systems as big as possible, for example the one described in the article. We expect that it's possible to use even bigger things, but it get's difficult to keep them cold and isolated. I'm not sure if there is an experiment showing that a small "brick" can act as an observer when the "brick" is very small. The idea is that the particles inside the brick are so many that it's impossible to track them and also all the quantum path are so different that there is no interference between them. Nobody is trying to measure that, because every time the system is not isolated enough (for example because you expected a total vacuum, but some molecule of air entered the system anyway) the quantum effects are no visible. Does it count as noise or a measurement by a rogue device? It's difficult to make experiments with particles of different size to understand where is the threshold. It's easier to make experiments with gas at different temperatures. <tangent> At high temperatures gas (like air) act as a classic gas, and follow the rules we would expect if they are made of a huge lot of small balls. At low temperatures, the gas become weird. (Assuming you pick a gas that does not condensate and is a liquid.) They don't follow the rules of a classic gas. For example if you fix the temperature, the volume and the amount of gas inside a recipient, then there are some quantum effect that make the pressure of the gas higher or lower than the equivalent classic gas. It's quite easy to measure, and there are many quantum mechanics effects that are posible to see with this method, and it's easy to regulate the temperature to get a "classic" gas or a "quantum" gas. The interesting part is that there is no threshold. The gas changes smoothly between "quantum" and "classic" when you increase the temperature, and you get a behavior that is in between. What is really happening is that the gas is always a quantum gas. But a hot quantum gas has an equation that is very very very similar to the equation of a classic gas. So if you are only going to use hot gas in your experiment, you can ignore the quantum effects and use the classic gas equations that are much simpler and almost as good as the difficult quantum gas equations in your experiment. </tangent> Back to your question... Nobody is sure, but the guess is that the difference between observed and observer is just a simplification. There is probably not true difference. It's just a trick to simplify the calculations. If you avoid some weird corner case, it work really well. Let's hope we can know the correct answer some day. </may include some guesses>

ahazred8ta 4y ago

Actually, Schrödinger never believed that the half-alive cat situation could ever occur. He invented it as an example of something that could not happen in real life. Schrödinger thought that the quantum superposition would collapse when the Geiger counter 'observed' the decaying atom by going 'click', not when the box was opened.