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Questions tagged [observers]

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0answers
32 views

GR - Event Horizon [duplicate]

No, this is not the Stephen Hawking Radiation question. Please dudes! This is a pure maths question: According to my understanding of GR, we observers outside of the event horizon cannot observe an ...
0
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1answer
58 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
241 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-...
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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 ...
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0answers
45 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
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1answer
115 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
46 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
81 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 ...
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1answer
80 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 $...
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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
413 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
100 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
249 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
305 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
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3answers
167 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
162 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
100 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
117 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
438 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
33 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
50 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
97 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
926 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
440 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 ...
0
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1answer
110 views

Help me to understand how time is relative!

I'm a bit confused about how time can be relative. Example: if a cosmic event happened that could be observed from earth, multiple times, because light from this event reached earth at different times ...
1
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3answers
175 views

Relativity and time

Einstein's relativity states that times goes slowly in a moving clock.That means if my friend moves at a speed of $v$ his time will go slowly. But I am also moving at a speed of $-v$ relative to him. ...
0
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2answers
102 views

Trying to understand relativistic equation related to energy released from two particle colliding near speed of light

Here is what blogging my mind. For simplicity, let's assume that there are only three particles in the universe, particle A, B, and C. Particle A and B going on the head on collision at near speed ...
19
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3answers
3k views

Energy Conservation Dilemma

Assume that a man is travelling in a space ship at a certain relativistic speed with respect to a man at rest at some point in space, such that 3 minutes in the ship is equal to 5 minutes for the ...
0
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1answer
66 views

Apparent discrepancy between two time contraction calculations

The problem I am dealing with is the following. We have two spaceships A and B s.t in $S_E$ their respective speeds are $v_A^E >0$ and $v_B^E<0$ along the x axis. At $t_0$ in $S_E$ their ...
0
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2answers
44 views

Observers without point of reference can assume themselves to be at rest

We know the the speed of light/c is the same to all observers. But i cant grasp something. Observer is moving at $0.5c$ in relation to us. He doenst have any point of referece and everything around ...
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4answers
2k views

Physical intuition for why proper time is an invariant quantity

Mathematically, I understand why proper time, $\tau$ is an invariant quantity, since it is defined in terms of the spacetime metric $d\tau=\sqrt{-ds^{2}}$ (using the signature $(-+++)$ and with $c=1$)....
0
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1answer
215 views

How and why time stops inside a black hole?

I have recently learned that black holes are dead stars, who are collapsed, and attracted other objects towards it and this process results in a very very large gravity. So light is also unable to ...
1
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3answers
133 views

Relativity and the age of the Universe

I put my assistant in a spaceship and accelerate it to near the speed of light. 100 years from now (in my time), my assistant is travelling with speed $0.99c$. At that time I put up a super ...
0
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1answer
133 views

Are quantum measurement of a system only occurring with human interaction?

In quantum physics, any functional interaction like measurement/observation forces particles down to a single state. Yet when plants do their photosynthesis it's been discovered that they actual ...
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2answers
934 views

What is the size of the world for a photon?

At relativistic speeds the distances contracts. What is the contraction ratio in the dimensions along the axis of travel between a static observer and a photon passing by?
0
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1answer
83 views

Do quantum events depend on the presence of observer?

Similar to that in the Schrodinger's cat thought experiment the cat remains in superposition unless observed by an observer, also in the double slit experiment an electron is passing through both the ...
0
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0answers
18 views

An experimentation on time dilation [duplicate]

In the video https://www.youtube.com/watch?v=ev9zrt__lec from 03:00 to 05:00 I hope that both the clocks would read the same equal amount ,say,1 revolution, in measuring the time elapsed for the ...
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2answers
62 views

Traveling close to the speed of light, would a person (or anything else) have a longer existence or would the existence be passing in slow motion?

If something, let's say, an electron or a person, travels at some speed close to the speed of light, time would slow down, right? But would it be passing in slow motion or would it have a bigger ...
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2answers
134 views

The nature of the observer in special relativity [closed]

In special relativity, is it silently assumed that the observer is only a “measuring machine” without an innate conception of space and time, so what he thinks about motion is exactly what he measures,...
1
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0answers
59 views

Can two entangled electrons can get disentagled in Nature, withous us making a measurement?

Imagine we have two free, entangled [by their spins, which are in this case non-separable, while $x$ (or $p$) electrons are clearly separable]. In an experimental setup, we can measure (and observe) ...
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1answer
92 views

What's stopping two independent observers from measuring the speed and position at the same time, separately? [duplicate]

From http://www.hawking.org.uk/the-beginning-of-time.html This means, it doesn't take into account, the Uncertainty Principle of Quantum Mechanics, which says that an object can not have both a ...
0
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1answer
65 views

Given Einstein's Theory of General Relativity, would a sample of plants grow to bloom quicker in space than on Earth?

I watched a program the other day on Einstein's General Relativity. It was fascinating. As I understand it GR is the best model of the (large) Universe. The program stated that time literally passes ...
0
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1answer
33 views

Teleportation and the observers effect

I'm a layman, and I was wondering, if teleportation is to ever exist, I'd assume it'd be in the sense that you would take the object you are trying to teleport, get it's exact makeup, then send that ...
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3answers
325 views

Lorentz Transformation in Different Reference Frames

TO ALL: Thanks to the help of many dedicated forum members, I have learned that this problem can be explained by understanding Minkowski diagrams. Here is a consolidated list of helpful links: https://...
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1answer
3k views

Do echo-locating bats experience Terrell effect?

At relativistic speeds there is an optical effect called Terrell rotation causing objects passed by to seemingly rotate. As bats use sound rather than light when echo-locating, at what degree would ...
3
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3answers
418 views

Schwarzschild geometry, what is physical meaning of coordinates?

A past exam has a question: For the Schwarzschild metric external to a non-spinning spherical mass, what is the physical significance to the coordinates $t,r,\theta,\phi$? Not sure how to answer ...