111–120 of 132 posts
For the same reason psychologists have shrugged off the fact that most papers cannot be replicated.
quantum mechanics has two different laws that describe how a system changes in time. Rule 1 says that except during a measurement, the wave evolves smoothly and deterministically, exploring every possibility. Rule 2 says that during a measurement of position, the wave collapses around the position where it's seen, with a probability proportional to the square of the height of the wave, before the collapse. It is only…
quantum mechanics has two different laws that describe how a system changes in time. Rule 1 says that except during a measurement, the wave evolves smoothly and deterministically, exploring every possibility. Rule 2 says that during a measurement of position, the wave collapses around the position where it's seen, with a probability proportional to the square of the height of the wave, before the collapse. It is only…
And I never understand what is a "measurement". Has it something to do with a human being observing it? Isn't any measurement just electromagnetic or gravitation forces acting on it, which act all the time?
I feel someone else may have said that, but simply said, what if the phenomenon is a wave, and its observable effect a particle? Isn't it the fact that the wave hits matter that makes it observable / measurable. Doesn't seem incompatible, even with the monitors, with the double slits experiment
https://physics.stackexchange.com/questions/374266/what-are-...
Earlier quoted context omitted.
Yes there are. Even without invoking any philosophical issues, quantum mechanics admits it's not self-contained. It takes measurement - the act of an outsider interacting with a system, which collapses the wavefunction, as a postulate. Measurement is not described by quantum mechanics.
Yes it is. Measurement is entanglement between the observed system and the observing system. Wave function collapse is an illusion caused by the two systems no longer being separable. They have entered a mixed state. It looks like information is lost in the observed system only because you are ignoring the observer.
I never see a definition of measurement, or observation.
Earlier quoted context omitted.
I don’t think this analogy holds up. Consider the double slit experiment: throw a bunch of basketballs at a wall and see what pattern of hits they leave by looking at where they hit the wall. If the wall is being looked at (observed), we see one pattern. If we look away, conduct the experiment, then check it, we find another. To me that suggests the act of “observance” effects the probability distribution of likely s…
If you ever ran into a space leak in Haskell, you would see how having unresolved thinks can use more memory than eager evaluation. But that has some merit to it in that you can describe QC as merging equivalent paths and then sampling from a wave distribution afterwards. One fun variant on the double slit experiment is taking a coherent laser beam (everything is in phase) and splitting it, sending it through two pat…
If the slit A has no polarizer and slit B has a polarizer, then in the "wall" you will the sum of 50% of the interference pattern and 50% of the diffraction pattern of A(I'm not sure about the 50%-50% split, something like that.) I.E. you will see the interference pattern, but it will not be so sharp, the black lines will not be so black, the white lines will not be so white.
I think it's better to put an horizontal polarizer on A and a vertical polarizer in B. If you don't add any other polarizer you will see the sum of the diffraction patters of A an B, without interference lines.
If you put a polarizer, the result depends on the direction:
* If it is horizontal you will see only the diffraction pattern of A (without interference lines).
* If it is vertical you will see only the diffraction pattern of B (without interference lines).
* At 45° you will see the diffraction pattern like in the original double slit experiment.
* At the other 45° you will see the inverted diffraction pattern, the black lines will be white and the white lines will be black. (All of this bounded by the diffraction pattern.)
* At other angles, you get some mix of the diffraction patterns and the interference patterns.
It would be nice to see an experimental realization of this.
quantum mechanics has two different laws that describe how a system changes in time. Rule 1 says that except during a measurement, the wave evolves smoothly and deterministically, exploring every possibility. Rule 2 says that during a measurement of position, the wave collapses around the position where it's seen, with a probability proportional to the square of the height of the wave, before the collapse. It is only…
And I never understand what is a "measurement". Has it something to do with a human being observing it? Isn't any measurement just electromagnetic or gravitation forces acting on it, which act all the time?
There is no agreement on how this happens, complicated by the fact that there is no such thing as a classical world I alluded to above, ie any interactions with the apparatus and the conscious observers supposedly obey the laws of quantum mechanics.
Earlier quoted context omitted.
> This is a common error. Macroscopic "everyday" objects don't have a definite position and momentum. Macroscopic objects are quantum objects. But when the mass is big enough, the position and momentum can be defined simultaneously with an error that is so small that you can just ignore the uncertainty and approximate them as classical objects. To put this into simpler terms: Whenever we measure something, we need to…
I don’t think this analogy holds up. Consider the double slit experiment: throw a bunch of basketballs at a wall and see what pattern of hits they leave by looking at where they hit the wall. If the wall is being looked at (observed), we see one pattern. If we look away, conduct the experiment, then check it, we find another. To me that suggests the act of “observance” effects the probability distribution of likely s…
You don't need someone observing the second wall to get the interference patters. You can replace the person with a photographic plate, a CCD sensor of a camera, or other equipment. All off them are more precise, reliable and even cheaper than a graduate student with paper and pencil.
The problem is if you try to add some type of equipment to first wall to collect information about how the particles/waves/balls/whatever passed thru it. Whatever equipment you add it will disturb the flow and it will kill the interference pattern.
This is not a technological problem. It is how the universe work. If you propose to use some particular method (like using light to detect the balls) you will sooner or later find that there is something that gets broken (see the former comment).
An important detail is that if you use a macroscopic object like a basketball, the slits size and the slits separation must be tiny (less than a millionth of the size of the nucleus of an atom, probably much less). So you intuition about how thinks work in the macroscopic level is not a good guide to how thinks work in the microscopic level. In the macroscopic level you can approximate the basketball as a perfect classic solid. It's just an approximation, a very good approximation.
Earlier quoted context omitted.
Why unknown? Heisenberg's uncertainty principle can be derived mathematically, using a property of the Fourier transform. It has nothing to do with disturbing the system during measurement.
I'd say that's more a mathematical statement than physical derivation. The effort of subjects like string theory is to lay down fundamental objects and interactions from which other theories (quantum mechanics, gravity) emerge. But I don't think there is a final word at the moment of what the fundamental theories than result in quantum mechanics should look like.