All Questions
Tagged with special-relativity observers
813
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Relativity problem about light signals and rockets equipped with mirrors [closed]
I find in a relativity book a problem that states:
"A rocket with its own length $L$ moves away from Earth at a constant velocity $v$. A radar signal emitted from a ground station is reflected ...
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5
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Wikipedia states that the relativistic Doppler effect is the same whether it is the source or the receiver that is stationary. Can this be true?
According to Wikipedia, the relativistic Doppler effect is simply the classical Doppler effect for a stationary source, $1-v/c$, times the relativistic time dilation, $1/\sqrt{1-v^2/c^2}$ (where v is ...
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Co-ordinates and change of frame in relativity [closed]
Given an inertial co-ordinate system, and observer at the origin. I'll make it concrete, for simplicity. He sees an object at the point $x = +10$, moving at velocity $v = +1$. He's subjected to a ...
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What effect would relativity have for an objective with absolutely no momentum? [closed]
I know as you near the speed of light time slows down and mass increases to near infinite. What I'm curious about is what would happen if an object lost all momentum. No movement at all not even the ...
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3
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Clocks are not synchronized in moving system (book of David J. Griffiths) [closed]
In the electrodynamics book of David J. Griffiths, in section 12.1.2, there is a paragraph about the synchronization of the clocks on a moving train. I don't understand why " Clocks that are ...
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2
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Who will die first between two people on different spaceships, where both are in inertial frames? [duplicate]
Here's something that's really been confusing me.
If two people on separate spaceships pass each other by, where both are in inertial frames, person A (on spaceship 1) could say that he is at rest and ...
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1
answer
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In SR, why do we claim length contraction rather than faster than $c$ travel in the rocket frame? [closed]
In special relativity, a rocket traveling at .5c will take .86 years (in the astronauts frame) to travel 1 light year (in a stationary observer frame). There are two possible ways to look at this
...
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Does two clocks moving toward each other at the same speed, then decelerating at the same rate coming to a stop create a paradox? [duplicate]
Note I have asked this question previously but upon reflection I realized I was not specific enough, leading to confusion in the answers. I have decided to ask the question again instead of editing my ...
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2
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Thought experiment circumventing finite speed of light via relativity of simultaneity - what's wrong?
I just watched this video regarding block universe: https://www.youtube.com/watch?v=wwSzpaTHyS8&t=676s and it provoked the following thought experiment:
Let's assume two observers, O1 and O2, at ...
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3
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130
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Can you tell who is moving through time? [closed]
In relativity, there is no way to tell if you are moving through space. So, if you were inside of a box, there would be no way for you to tell if you were moving or not. However, can you know who is ...
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If velocity is relative, why does time dilate for some observers and not others? [duplicate]
I'm trying to get my head around relativity and time dilation. What I can't figure out is how time can dilate for fast-moving observers if all velocity is relative. Here's a scenario:
Alice and Bob ...
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3
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Special relativity and accelerating twins
Imagine two twins synchronise their clocks and then twin A quickly accelerates to velocity v. After a time T twin B quickly accelerates to 2v and catches up with twin A. Which one will be younger? How ...
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Radiation from a stationary charge relative to earth for a free falling observer
It is my understanding that if we have a charge at rest on earth, a free falling observer will see it radiating, as the charge is in an accelerated frame of reference. This observer can in principle ...
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Length contraction doesn't affect the perpendicular direction...but it seems as if it can
A is a stationary observer watching B who is moving relative to A. Both of them hold two identical light clocks and each shoots light rays to estimate the lengths of their clocks. A's light ray will ...
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4
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Time Dilation when they meet
I am starting over because what I was asking was unclear. I have read many articles, such as How can time dilation be symmetric? and others suggested by people here and understand the overall concepts ...
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Is there a different way to measure speed, other than with time?
A second on Earth is different from a second on the Sun and a second next to a black hole. Therefore speed, as measured in meters per second, is different in each of these locations. Is there an ...
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Special Theory of Relativity Contradiction [duplicate]
I’m struggling with an apparent contradiction of special theory of relativity (STR) that I cannot resolve.
Imagine two twins flying by each other in space along the same straight line but in the ...
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2
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Train example of special relativity
My friend Eric is at the center of the train. The train is moving forward. The front end and back end of the train flash a light at the same time. From Eric's perspective, both light arrives at him at ...
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2
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Schutz description of Galilean invariance of interval
In B. Schutz's textbook "A First Course in General Relativity", there is a sentence on page 172 discussing Galilean relativity and how the distance between events is invariant in coordinate ...
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Absolute rest in special relativity
I am new to special relativity and with still little experience in Physics. I would like to know why a privileged frame of reference that determines absolute rest is not possible. I want you to ...
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Can relativity apply to temperature? [duplicate]
Given a stationary observer and a moving one. One would see the particle in a system of gas moving faster than the other would. Does that mean the particles have more kinetic energy and thus higher ...
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6
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Question regarding time dilation
if people in semi-light-speed ships age slower, does the world appeared to those people also 'age slower'? Because it is the external world which is moving at semi-light-speed to the people in the ...
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3
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One-way Tachyonic anti-telephone
When you have length contraction in special relativity
$$L' = L/\gamma$$ the interpretation is that $L'$ is the length of an object with rest-length $L$ moving with respect to an observer at rest. ...
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Confusion regarding Special Relativity and Relativity of Velocity? [duplicate]
Suppose that there are two points in an empty space A and B and observers at A and B having clocks:
If A were to be traveling near speed of light, when clock at A passes 1 hour, observer at A ...
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1
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Relativity - how do you calculate the duration of this trip from various reference frames?
Let's have following scenario:
A spaceship departs from the Earth and constantly accelerates in a straight line for 60 000 000 seconds at 1g (10 m/s^2), then immediately starts decelerating at 1g for ...
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If you have two clocks moving toward each other and they both stop when they meet does it point to a paradox?
Say they both decelerate at the same rate also. If clock A sees clock B as slower than itself and clock B see clock A as slower than itself due to relativity isn't this a paradox because when they ...
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How would a spacecraft travelling near light speed say 0.9c compensate for time dilation in radio communication from spacecraft to earth?
For a spacecraft travelling at 0.9 c for 5 seconds, only 5 seconds would have passed for an observer on Aircraft, while 26.31 second would pass for a stationary observer watching from Earth.
In a ...
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3
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Question regarding aparent position and velocity of an object
A time lag is always involved while observing objects. Due to this reason we can never observe the correct position of an object at a particular time. We will see it where it was some times ago. Is ...
user380105
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Time observed in a clock when you start moving relative to it
There's an example given by Brian Green, https://www.youtube.com/watch?v=XFV2feKDK9E&t=17675s
To be precise the example start at 04:56:00. In brief it is as follows:
There are two persons Gracie ...
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2
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Does the length of an object change after acceleration in Special Relativity? [duplicate]
In special relativity, an object (a box, perhaps) travelling at 0.5c relative to us, if it thinks it's 1lightsecond long in its own reference frame, will look 0.866 lightseconds long to us.
My ...
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3
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Relativity, Lorentz Transforms and the time it takes to perceive
I've been working a bit at understanding relativity a bit more, and understanding Lorentz transformations. I want to make sure I understand the meaning of a Lorentz transofmration, and when to use it ...
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1
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Travel time according to both traveling and resting observers
First, my understanding of time dilation, which is typically derived based on a clock that ticks every time a beam of light emitted from the floor is bounced back by a mirror on the ceiling. Such a ...
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Can light speed change relative to me?
If a light-emitting object is stationary relative to me, then the wavelength of the light emitted would be normal. However, if the object is moving away from me, then the wavelength of the light would ...
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On the distinction between frame of reference and observer
A Stack Exchange answer illustrates reference frame and observer as follows:
A frame of reference means a co-ordinate system and an observer is someone using that co-ordinate system. For example I ...
user390010
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Are quantum tunneling slow down by time dilation affected? [duplicate]
If i setup to clock to work at the same rate at stationary. The first clock operated on quantum tunneling. Setup electron to tunneling and repel another electron. Which acts as sensor. The second ...
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4
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Does the speed of light determine how slow time can move?
Since moving faster makes time move slower. Does that mean that there is an absolute minimum rate at which time passes? If so. Is there also a maximum?
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Observed time period in distant clock when moving towards it
Imagine, 2 persons ('A' & 'B') are 6 light years apart in space, stationary to each other and with no gravitation acting on anybody. Suppose 'B' starts his clock which also shows years, months and ...
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A bar that appears straight in one reference frame appears bent in another?
Is there a relativistic effect at play that explains the following thought experiment, that I am unaware of?
The apparatus depicted in the image has two straight bars in the middle emitting light from ...
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4
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A thought experiment regarding special relativity [duplicate]
I am currently delving into the intricacies of Einstein's theory of relativity and striving to grasp its fundamental essence and implications.
Your assistance would be greatly appreciated.
Here's my ...
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4
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How to apply the time dilation formula?
I am learning special relativity and still not sure how to correctly apply the time dilation formula. Take for instance the following example:
A spaceship leaves earth and travels to Alpha Centauri 4....
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4
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Measurement of the velocity of a celestial body by means of (relativistic and classical) gravitational effects on clocks
Imagine a planet with the same properties as Earth, this time moving in an elliptical orbit around a black hole of a large number of solar masses. Also imagine that the surface of this planet is as ...
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Can we consider that the photons that were not and will never be detected live in a zero-dimensional space? [closed]
According to Einstein’s theory of relativity, any particle traveling at the speed of light experiences no passage of time. It follows that if a photon travels through space then within any two points ...
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Time desync with light delay: can we still "look into the future"?
I'm reasonably familiar with special relativity and its effect such as time desynchronization, but I'm having trouble understanding how these effects come into play when we also consider the time for ...
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Proper time of an accelerating particle
I am supposed to find the proper time of a particle whose worldline is given by:
$$\begin{align}
x(t) &= \frac{3}{2} a t^2\\
y(t) &= 2 a t^2\\
z(t) &= 0
\end{align}$$
where $a = const$ and ...
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Question on Example 5.9 of Prof. Hartle Gravity textbook
I'm reading the Gravity Hartle book (ed.2003) and I'm having trouble with the question in the last part of Example 5.9 - Frequency Measured by an Accelerating Observer. More specifically the problem ...
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5
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What can we accept in thought experiments in relativity?
Although title is more broad, and you are welcome to give examples, I will ask about why we accept certain things as acceptable in Einstein's thought experiments using a specific experiment:
Consider ...
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How to calculate positions when switching reference frames in a Minkowski spacetime diagram
The below Minkowski spacetime diagram includes three worldlines, where B is the observer and has a rest frame. A and C both have a velocity of 0.71c.
I then created a second diagram where worldline A ...
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Coordinate transformation and absolute motion in general relativity
In special relativity, all motion is relative. But in the presence of black hole, all motion is with respect to black hole. The curvature of spacetime depends on how far we are away from the black ...
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Special-Relativity and how things not accelerating appear to be the same in all frames of reference [duplicate]
As someone who knows very little special-relativity (and none of the math) I understood that if you take a car moving down the road (at constant velocity) and approaching an observer, there is no ...
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Generalized Sagnac-Wang-Fizeau formula
In the paper "Generalized Sagnac-Wang-Fizeau formula" (https://doi.org/10.1103/PhysRevA.94.063837), the authors A. Ori and E. Avron present a generalized derivation of the Sagnac-type effect....
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