# Tag Info

## New answers tagged observers

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A first problem is that there is in GR no such thing as "an observers frame", except in sloppy speech. There are various systems of coordinates. Two systems of coordinates may agree for an observer as much as one likes but differ elsewhere. And all the systems of coordinates are on equal foot, none is preferred. What could replace the "observer's frame"? ...

1

Wave function collapse is not global, it is fictional. Let's suppose that the state is $\alpha|X=0\rangle+\beta|X=1\rangle$, where $|\alpha|^2+|\beta|^2=1$. When Alice measures the state, an operation is applied that correlates both Alice and the environment with the value of $X$, like so ...

4

You misunderstand special relativity. For objects that are moving at large speeds, the time runs more slowly for the object compared to the observer who measured the speed. To observe the motion of the object, you don't have to go to its coordinate frame and observe from there. You observe from the outside, that's how you measured the speed in the first ...

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Let me explain light. Classically, light is electromagnetic radiation. There exists a field permeating all of spacetime called the electromagnetic field. Charges create curvature in this field. When charges accelerate, waves are created in this field. These waves are what we perceive as light. A little more specifically, let us examine Maxwell's equations ...

2

Here's how I understand your question: A and B are space-like separated and make a measurement on a single particle that has equal (or just non-vanishing) probabilities of being in A's or B's region. You now ponder how the measurement process works on a deeper level. Could the collapse be a dynamical (i.e. time dependent) process? I think it can not. If ...

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The Gödel universe is homogeneous and every observer anywhere in the universe observes the universe to be rotating around them. So a Gödel universe has no centre.

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The hypothesis doesn't make much sense. The resistance of an object to being ripped apart is given by its elasticity, not by how much is massive. Anyway, to the central question there is no answer yet. This is the so called information loss paradox, one of the greatest unsolved problem in theoretical physics. In general relativity the object falls in a ...

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Science does not say that the speed of light is constant. Rather, a lot of people with fancy clocks and tape measures have expended a lot of effort measuring the speed of light and have discovered, to their initial surprise, that it is constant. Then another bunch of people (largely one person) came up with a model - a bit of mathematics, otherwise known ...

2

You have this backwards. What you state, the fact that "time is relative", is a consequence of the theory rather than a cause. Assume some light ray travels some distance in reference frame 1 and is seen also from reference frame 2. The trajectory is obviously different in both frames. That's nothing special that Einstein would have introduced : just try ...

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In special relativity (things are a bit different in general relativity) time dilation is always relative. There is no such thing as an absolute velocity so there is no such thing as an absolute time dilation. If you are travelling relative to me at some speed $v$ then the relative rate at which I observe time passing for you is:  \frac{d\tau}{dt} = ...

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You caught that the barn doors do not close and open at the same time in the vaulter's reference frame, but missed the issue that they are moving in her frame. So, the difference in position between where they were when they flashed shut will not be L/4, but L/4 + vΔt. Include that, and you should be able to solve it.

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Often, I think a nice way to untangle the mess we find ourselves in is by appealing to the all-knowing God of special relativity, blessed be her name, Lorentztransformalia. Let event $A$ denote the front door closing, and let event $B$ denote the rear door closing. Without loss of generality, we assume that we've chosen our coordinates so that in the ...

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I don't really know anything about Hawking radiation but one thing bothers me in this question. In flat spacetime, generators of boosts are Killing vectors (generators of isometries: the symmetries of spacetime itself). In curved spacetime there are no such Killing fields. You cannot boost your spacetime and get the same thing. It is not true that all frames ...

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If we setup the camera to record like above but NEVER EVER EVER look at the result of what was recorded. Does the wave function still collapse? The answer is that we just don't know. We can tell that the wave function has collapsed (in Copenhagen terms) only when we humans look at the system -- in the canonical experiment that means looking at the ...

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Any observer outside the Schwarzschild radius sees the same thing: matter approaching the Schwarzschild radius at slower and slower (asymptotically zero) speed, forming a thin shell around the event horizon. The matter takes an apparently infinite time to collapse, and infinity is infinitely larger than a large finite the same way it's infinitely larger than ...

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Inside the Schrodinger's cat's box, the moment the radiation is detected by the counter, doesn't this mean the system already has a fixed eigenstate (a collapsed wave function, or is decoherent, whatever you like to call it)? At the end of your question, you give a list of things that might have happened to the system, and treat them as equivalent, but ...

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The answer whether the cat is dear or alive is not certain before the measurement. It is all measurement which determines the probability density function and the collapse of the entanglement

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I think you are probably misinterpreting the context here. If you read the previous line carefully it says "there is always an undetermined interaction between observer and observed; there is nothing we can do to avoid the interaction or to allow for it ahead of time. And later he just says due to the fact that photon can be scattered within the 2θ' angle ...

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