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Questions tagged [observers]

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0
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1answer
66 views

What (if any) significance exists in the analogy between the speed of light limit and the Schwartzchild radius of a black hole

I have always been intrigued by what seems to be very similar characteristic of the phenomena of traveling very, very fast, (close to the speed of light , and the Schwartzchild radius. AS a body gets ...
2
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1answer
95 views

In special relativity, is there a prescription to find the coordinate transformation to a general (for instance accelerated) observer? And in GR?

Suppose we are in an inertial frame, so that the metric in our coordinates is just the Minkowski metric, \begin{align} \text{d}s^2 = -\text{d}t^2 + \text{d}x^2 + \text{d}y^2 + \text{d}z^2. \end{align} ...
0
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1answer
66 views

Time travel (Velocity and Mass)

I learned that if I move on a high velocity, if my watch shows 12:00 and a my home clock shows 12:00 before the trip, when I come back, my watch will be like 12:05 while the clock will be 12:10. I ...
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5answers
163 views

Two objects are thrown into a black hole. The first crosses the event horizon at time's end, so when does the second one cross?

An observer throws an object towards a black hole, and then an arbitrary amount of time later, throws a second object towards the black hole. Disregarding Hawking radiation and assuming the Black Hole ...
1
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2answers
176 views

Special Relativity: Time dilation paradox [duplicate]

Two spaceships, A and B, travelling rapidly through space, pass each other on a parallel course. According to special relativity: A observes B speeding past, and perceives that time on B's ship is ...
-1
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3answers
96 views

Can two simultaneous independent measurements circumvent uncertainty? [duplicate]

Without understanding the mathematics, I have learned that the uncertainty principle precludes being able to precisely measure the position and velocity of a particle at the same time. So my question ...
4
votes
3answers
200 views

Does Minkowski diagram show that time goes faster in “moving” frame of reference?

I have a question re the diagram that appears at: http://www1.phys.vt.edu/~takeuchi/relativity/notes/section12.html The diagram purports to show that the observer in each frame of reference will ...
1
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1answer
591 views

Why is the buoyant force on an object the same for two different observers? [closed]

Situation: (self-made) A (green) block is partially immersed in a (blue) liquid and the vessel is accelerating upwards with an acceleration $a$. The block is observed by (stick-figure) observers $O_1$...
2
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4answers
2k views

Double Slit Experiment. What effect does the detector actually cause?

When a quantum of light arrives at a double slit, it passes through both slits as a wave and arrives upon a second screen with the interference pattern of a single wave that has been split into two ...
-2
votes
1answer
61 views

How looks a wheel browsing 299000km in 1 second from its own frame?

Imagine a wheel with a 299km perimeter turning at 1000 round per second going 299000km (the speed of the wheel is 299000km/s relative to the starting frame). How does it look in the frame of a pilot ...
-1
votes
1answer
62 views

Is Hawking Radiation compatible with a GR solution with an Infalling Observer Crossing the Event Horizon?

EDIT: See my answer. Question is malformed as it was based on the assumption that something like Hawking radiation (i.e. mass draining) occurred prior to the formation of the event horizon based ...
-2
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2answers
92 views

General Relativity in the absence of observers

I see that just as in quantum mechanics, General Relativity is depending on observations taking place, hence they are depending on the existence of an information carrier which are photons, virtual or ...
2
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1answer
136 views

How to say “speed of light is constant in all frames” in QFT?

In classical mechanics, if you assume the speed of light is constant, it's easy using the mirror and photon thought experiment to conclude that given observers $U,V$ with $U,V$ travelling at speeds $u,...
4
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2answers
130 views

Maximizing the time near a black hole

I just learned about the Schwarzchild solution, following Carrol's book. Now, there is a question that I want to answer: Consider an observer that starts at infinity with some velocity, comes close ...
1
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2answers
213 views

Is the dynamics of spacetime observer-dependent?

Consider de Sitter spacetime in static coordinates: $$ ds^2 = \Big(1- (H_\Lambda r)^2 \Big) dt^2 - \frac{dr^2}{1- (H_\Lambda r)^2} -r^2 d\Omega^2, \qquad r\lt H_\Lambda^{-1} \,. $$ This metric ...
2
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1answer
68 views

Black holes and red light

A friend of mine is reading the book "Black Holes: The Reith lectures" from Stephen Hawking. He is reading the French version, so I cannot give you the exact line, but on page 38, it is said that if ...
2
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2answers
300 views

Special relativity and spinning tires

I apologize for the subsequent headache. There is a person who claims quite adamantly that Einstein is wrong, using the following reasoning: A clock on a train slows down the faster the train moves....
0
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1answer
159 views

How would kinetic bombardment look like on impact to an observer on Earth's surface? [closed]

To be clear, I do want to know this because on the Worldbuilding Stack Exchange's chat room and on the Discord servers I am in, I have been told conflicting accounts about how such bombardment would ...
0
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1answer
215 views

Does Lorentz transformation apply to a non-inertial frame? Why?

Two space travellers, S1 and S2, head away from a point in an inertial frame S. The first travels along the trajectory $x = ct/4$ and the second along $x = \beta t^2$. Sketch their trajectories on a ...
0
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3answers
190 views

What does “same location” mean in special relativity (definition of proper time), when true length does not exist?

The following statement combined with the application of time dilation principle confused me on how proper length and time are measured and what they represent. "The speed at which electrons traverse ...
3
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2answers
185 views

Is relativity of simultaneity just a convention?

Lorentz transformations are well known to imply time dilation, length contraction, and relativity of simultaneity. This is prominently featured in any course on Special Relativity (SR), e.g. in ...
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3answers
322 views

Special Relativity Paradox based on Einstein's explaination [closed]

Einstein explained the special relativity (roughly) like this: He first assumed the speed of light would not change regardless the speed of its source. Then he described a person on a moving train was ...
1
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1answer
360 views

Why is the Lorentz transformation's time transformation not just the time dilation?

In Taylor's Classical Mechanics text, he derives the Lorentz transformation from length contraction which, in turn, uses time dilation. But doesn't the use of length contraction necessitate that the ...
0
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1answer
64 views

Do multi-state of entangled particles exists?

I haven't taken any course in Quantum mechanics. But I felt "Quantum Entanglement" quite interesting. I recently read some articles on it. But I am not sure if I understood anything or satisfied with ...
0
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1answer
49 views

What does observing mean in this case?

Let us consider a particle emitter which emits a sample of green colored particles the size of a beach balls and mass of a proton. Now a doubly slit screen is placed in front of this emitter and ...
8
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1answer
256 views

Interpretation of Stress-Energy Tensor and Dust

MTW (chapter 5) and others state that $-T^a_b v^b $ should be interpreted as the four-momentum density in the reference frame of an observer with four-velocity $v^a$, where $T^a_b$ is the stress-...
1
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2answers
68 views

Can observation affect the probability distribution of an event to occur?

It's already well know that in quantum mechanics the act of observation affects the outcome of an experiment making the wave function to collapse.Now in order to clear up my confusion about this topic ...
1
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0answers
50 views

Doppler shift and flux [closed]

I am trying to solve this problem: A body emits photons of frequency $\omega^*$ at equal rates in all direction in its rest frame. An observer is moving with speed V relative to the body in the x ...
2
votes
1answer
135 views

Why do people use equivalence principle differently in Hawking radiation?

In discussions of Black hole information paradox, people usually argue that the falling observer shall not see radiation at the horizon or near the horizon due to the equivalence principle. That is, ...
2
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0answers
47 views

Centre of mass in General Relativity

In the paper from Costa 2014, Figure 1, it discusses how the velocity of an observer influences where the center of mass of a spinning object is measured. If an observer is moving with velocity $v$ ...
1
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1answer
84 views

Will a particle still be in a superposition state if unobserved from only the perspective of one observer?

In this scenario let us take a particle that can have either spin up or spin down. Let's say that observer 1 observed the particle's spin to be down. But observer 2 hasn't observed it yet. So, then ...
1
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1answer
83 views

Travel huge distance in a short time

I know that according to the thought experiment by einstein, one who would travel at speed close to light's speed would not age and those on earth would age. But is it possible for someone to travel ...
0
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1answer
47 views

Force seen by an observer traveling near the speed of light

Suppose there is a wind with velocity $v \ll c$, which is blowing on a person who is moving at velocity $u \ll c$ (both in the $x$-direction). In the rest frame of the person, the wind exerts a force $...
-1
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1answer
55 views

Would it influence physics if there were no observers? [closed]

In any physics like quantum physics or relativity?
-1
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1answer
447 views

Why specifically does FTL violate causality? [duplicate]

Take this non-FTL scenario, involving a phone call and the postal service. I send a postcard to my friend in Paris, asking whether they would like to visit me. Since it will take some time to arrive,...
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0answers
102 views

Special Relativity

Does special relativity require faster than light information transfer to verify length contraction and time dilation? How does the "outside observer" measure these variables? I guess the outside ...
2
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1answer
292 views

Kruskal Solution to Black hole

To remove the singularity at the horizon we move from Schwarzchild to Eddington Finkelstein coordinate system. Our ingoing null geodesics then become straight lines. Then we move to Kruskal solution ...
1
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1answer
341 views

Eddington Finkelstein coordinate system

Do particles in Eddington Finkelstein coordinate system take a finite amount of time to reach the horizon? Or do they take infinite time? How is the time coordinate used in the Eddington Finkelstein ...
-1
votes
3answers
258 views

“We certainly cannot have observers in the same reference frame disagree on whether clocks are synchronized or not”-is this true? [duplicate]

Suppose we have an Inertial frame S, all the clocks in this frame are synchronized. Now suppose, two seperate events occur at two different place A and B in that reference frame. Now, the events are ...
0
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1answer
180 views

Radially Infalling Particle

Given a metric, we find out the null and timelike geodesic which helps us conclude that how the trajectory of various particles will become in a particular curvature of spacetime. But I don't ...
1
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1answer
108 views

How does time transform in wormholes?

The light from a star 100 light years away takes 100 years to reach Earth so we see remote star as it was 100 years ago. In the same way, we would see Earth 100 years in the past if we were on the ...
3
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1answer
122 views

Will stationary charge radiate E.M waves if observer is accelerating?

For ex. if my frame of reference is oscillating then will i see E.M waves produced from a charge which is not oscillating with any other or ground frame of reference? Can i get a really clear answer ....
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2answers
490 views

Time goes slower the faster you go. What happens to time if you go too SLOW? [closed]

Time dilation is clear about what happens when you go faster than an earth observer, and about what happens when you travel at c. But earth is also moving, and thus we humans are not at the slowest ...
0
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0answers
34 views

Does time dilation make travelling close to the speed of light redundant? [duplicate]

I find time dilation confusing so I'm not sure if it is a relevant factor. Lets say you have a spaceship. There's no such thing as faster than light travel, but you do have inertial dampener ...
0
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0answers
45 views

Is there an observer dependent temperature everywhere in spacetime?

A temperature $T=\dfrac{\hbar a}{2\pi c k_B}$ is associated to an uniformly accelerated observer. He feels this temperature all along his trajectory. The inertial observer will not assign this ...
0
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1answer
57 views

Do we experience wave function collapse even though we don't read the detector?

In quantum double slit experiment would the the wave function collapse if we place a particle detector at the slit but do not read it and just keep looking at the screen?
2
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1answer
101 views

Time dilation for non-physicists

Apologies in advance, as I'm not a physicist, and may use terms incorrectly. In the movie Interstellar, the planet Miller has a time dilation of one hour to seven Earth years. This has brought up ...
0
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3answers
1k views

Time paradox inside a black hole

At the event horizon of a black hole, time and the spatial direction toward the center exchange places. The direction inside the black hole from the event horizon to the the singularity in the center ...
4
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3answers
2k views

Can Special Relativity hold even without motion?

I am having a bit of confusion, let us say there are two observers observing two simultaneous lightning strikes with a finite distance between them. Now one observer is located such that he is in ...
4
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2answers
468 views

Relativistic spring

Imagine a cart at the base of the hill. The cart is next to a spring. You push the cart into the spring until the spring compresses $x$ meters. In your frame of reference, the cart has a potential ...