# Tag Info

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No. A single measurement can't tell you if the state was in a superposition or it was a pure state. In order to be able to do that you must have knowledge of how the state was prepared, which means you must have gauged your apparatus and therefore performed a statistically relevant number of measurements on the very same state many times and taken note of ...

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check this http://www.birs.ca/workshops/2014/14w5147/files/breannan_smith_reflections_slides.pdf i made it!this contains a think part of the answer you are seeking

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The laws of classical physics are strictly symmetric under time reversal. So given the backwards motion of every single point particle (which allows you to know convectional/conduction flow of heat, as well as longitudinal sound waves), as well as every single light ray (radiational flow of heat), you must be able to run a simulation backwards in time and ...

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In solid state physics: Any transition to ferro- or antiferro-magnetically ordered state breaks the time inversion symmetry (1'), because the spontaneous magnetic moment on each atom changes the sign at 1'-operation.

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I don't know if this is standard, but consider a pendulum that can swing a full circle in a plane. Vibrate the point of suspension up and down at the appropriate frequency. The pendulum will gain energy and spin either clockwise or counterclockwise.

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You're confusing many different things together, and I'll try to clarify and separate them to make the problem clear. The problem you're facing isn't a time reversal issue. It's lack of information. So let's go through this one by one. Classical physics is 100% symmetric in time. This is the concept of determinism. There's no doubt in that. The ...

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Inelastic collisions are so that kinetic energy is not conserved, for example, collision of macroscopic objects in real life. Part of kinetic energy is transformed in heat (atomic motion in participants). In order to write time-reversible, symmetrical equations, you have to include losses of kinetic energy. Briefly, "a set of objects with positions and ...

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The problem here arises because the 4-current in the OP is assumed to be a 1-form, and after many years of accumulated rust on the subject I completely forgot that this is, strictly speaking, not the right geometrical object that can describe current density. Indeed, being a density, it must be a 3-form, and therefore the correct geometrical object is J = ...

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Conservation of momentum! Force × Time = Impulse = Δ Momentum Since the average force is the same going up and down, and since the momentum change is the same going up and down as well, the time during which the force is applied must also be the same.

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When one throws a stone.... Your arm is capable of propelling an object at up to around 150km/h (and that's with some practice). At that speed the many factors like air resistance are negligible. Let’s load a 16-inch shell into a gun (you will find several on the ISS Iowa), aim it 45 degrees up and press the button. The shell is going to go up at ...

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A lot of things have to hold to get that symmetry. You have to neglect air resistance. You either have to throw it straight up, or the ground over there has to be at the the same altitude as the ground over here. You have to through it slowly enough that it comes back down (watch out for escape velocity) But if you have that, then the simplest explanation ...

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Assuming that the only forces acting on the stone are the initial force exerted by the hand on the stone AND the force of gravity, we have the following situation: Immediately after throwing, the stone has a kinetic energy in the x-direction that never changes (conservation of energy) and the stone has a kinetic energy in the y-direction that is constantly ...

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I would consider that since acceleration is a constant vector pointing downward, that the time the projectiles downward component takes to accelerate from V(initial) to 0 would be the same as the time it takes to accelerate the object from 0 to V(final)

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(Non-kinematics math attempt but just some principles) It is a partial observation in that It hits the ground with same speed. Angle by which it hits the ground is the same (maybe a direction change) It takes equal time to reach to the peak and then hit the ground They are equally strange coincidences. Which are more fundamental? Consider the following ...

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Asking "Why" in physics often leads out of physics and into philosophy. Why is there light? Because God said so. Physics only answers questions about how the universe behaves and how to describe that behavior. If a why question can be answered with physics, the answer is "because it follows from a law of physics." A law is just a mathematical description of ...

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One could say that this is an experimental observation; after one could envisage, hypothetically, where this is not the case. This is not hypothetical once you take air resistance into account. One could say that the curve that the stone describes is a parabola; and the two halves are symmetric around the perpendicular line through its apex. But ...

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I think its because both halves of a projectile's trajectory are symmetric in every aspect. The projectile going from its apex position to the ground is just the time reversed version of the projectile going from its initial position to the apex position.

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I would say that it is a result of time reversal symmetry. If you consider the projectile at the apex of its trajectory then all that changes under time reversal is the direction of the horizontal component of motion. This means that the trajectory of the particle to get to that point and its trajectory after that point should be identical apart from a ...

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