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Double slit experiment with electrons is a demonstration of a quantum behavior. When we say observe we mean expose to some kind of interaction. So when electron travels from its source towards the double slit and then passes through, and hits the detector, we see that it is a particle. But, when many electrons pass through the slit we observe a interference ...


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A free moving electron does not emit photons. If one want to see an electron you have to illuminate it. Sending photons, the electron reflect (absorb and re-emit) photons which one can detect then. By doing this the electron get disturbed and changes his direction. The fringes on the observation screen will be destroyed. Since one cannot synchronize the ...


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When you send the photons through the double-slited wall, they form a diffraction pattern on the other side, which is a wave-like phenomenon. It makes no sense to think of the photons as "particles" anymore, since they would need to cross both slits simoultaneously in order to create the diffraction pattern. So a way to find out what's happening is to place ...


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Your question is not silly. In the two slit expariment you measure the position if the photon, that is a particle-like quality. What happens is that a photodetector records when it absorbs a photon. That gets recorded in the memory. Some schools of physics interpret the interaction of the photon with the detector as a measurement. Others interpret that the ...


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I believe the issue is that external information from infinity will have difficulty catching up to the infalling object, ie, the light cones will not intersect. I have seen this answered in detail based on an infalling object having passed the event horizon, but since that can't happen, the person answering the question has oversimplified the problem. One ...


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I see what you're trying to ask. Let me try to rephrase it: Does an observer at the bottom of a massive gravity well perceive that the clocks of actors outside of the gravity well move faster? The answer is yes, but the intensity depends on the depth of the gravitational well. For anyplace far away from exotic things like event horizons and perhaps neutron ...


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I was doing a question about if a train fits in a tunnel. Did the question assignment include a specific consistent definition of what's meant there by "to fit", in the first place? Presumably, in the setup which is typically considered, the ends of the tunnel (say participants $A$ and $B$) are supposed to be at rest to each other, the ends of the ...


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The site rules forbid us from giving the answers to homework problems, but this problem illustrates a fundamental issue in relativity so I think it's worth some general comments. Incidentally you may be interested to read the Wikipedia article on the ladder/barn paradox, though in it's efforts to be comprehensive I think the article gets a bit confusing. ...


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I guess there is no single definition, since it varies according to author. Personally, I think the term should just be abandoned. It's too ambiguous. It mixes up two ideas that need to be cleanly separated, but often aren't: the frame of reference as a grid of sensors, and a single sensor that receives incoming information, like a camera. Mixing up these ...


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You speak of the as yet unresolved quantum measurement problem. Although it is unresolved, most physicists think that it has nothing to do with solipsism, which is a sensational explanation but there are many reasons to think that this is not the right one: Conscious observers themselves are quantum systems. Observation always comprises interaction ...


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A couple of things first... 1) Time dilation is not a consequence of high speeds, but of ANY speed - it just the effects grow large rapidly within about 10% the speed of light. Low speeds can have measurable consequences as is the case with magnetic fields for example. 2) All identical clocks "tick" away at the same rate under all circumstances,** metering ...


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Imagine, for example, that two different inertial observers, one sitting on a train moving through a station with uniform velocity $v$ with respect to ground. The experiment will consist of turning on a flashlight aimed at a mirror directly above on the ceiling and measuring the time it takes the light to travel up and be reflected back on its starting ...


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Two questions and two errors: The (hypothetical) point of view of the photon is not "frozen" because you need time to perceive something frozen. But the photon has proper time zero, everything is reduced to one instant, thus nothing can be frozen. "Dodge" a photon: Information is transmitted with light speed. As the photon is moving with light speed it is ...


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A photon cannot be said to have its own inertial reference frame, because inertial reference are defined to be a family of coordinate systems that satisfy the two fundamental postulates of SR, one of which is that light moves at c in all frames. You could construct a coordinate system where the photon was at rest, but since this coordinate system wouldn't be ...


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There is a relatively new theory (2012) called the firewall theory, that says that at the event horizon there is a huge "wall of fire" as such. This is because quantum entangled particles that cross the horizon (or one half of a pair of entangled particles) becomes tricky and starts breaking laws like the monogamy of entanglement. So a group of physicists ...


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As pointed out you can't travel at the speed of light but you can look at the limits we are tending towards as we approach it. So, if I were to travel in a spacecraft at the speed of light, would I freeze and stop moving? From the perspective of a stationary observer if your spacecraft was traveling at close to the speed of light, time on the ...


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you should look for the theory of "Covariant Quantum Mechanics" originally introduced by M. Modugno and J. Jadcyk, in particular the "special algebra of quantizable functions". There is not so much literature since the theory is mathematically quite hard to enter, but afterwards it is worth. I have worked in that field for several years. The basic idea is to ...



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