All Questions
188
questions
0
votes
2
answers
100
views
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 ...
0
votes
3
answers
130
views
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 ...
- 33
0
votes
1
answer
116
views
Time required to reach Black Hole's Event Horizon from outsider perspective?
Let's imagine a pair of particles that is entangled. One (call it $P_1$) is released and then falls to a black hole from a distant $x_0$, (for example $x_0=5r_s$) and velocity $v_0(=1/2c)$, while the ...
1
vote
2
answers
72
views
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 ...
- 13
1
vote
1
answer
117
views
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 ...
2
votes
3
answers
240
views
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 ...
- 160
9
votes
5
answers
2k
views
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 ...
- 93
-1
votes
1
answer
178
views
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 ...
- 115
0
votes
2
answers
86
views
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 ...
- 728
0
votes
0
answers
26
views
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 ...
- 1
1
vote
1
answer
145
views
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 ...
- 13
1
vote
4
answers
165
views
Is constant acceleration the same relative to other objects at all velocities?
If you are accelerating at a constant rate of 10 $m/s^2$, will you see things around you move at 10 $m/s$ faster every second, even when approaching the speed of light?
a) If not: How do you calculate ...
- 171
0
votes
2
answers
67
views
Question about length contractions [duplicate]
So I'm kind of confused about length contractions, whenever I think about length contractions I think about the faster an object goes it will be able to impair more photons which would create an ...
1
vote
2
answers
132
views
Do events very far away happen in a different timeline?
I am not sure how to ask this question in a concise manner so I am sure somebody out there explained it but I cannot seem to find it.
So I recently watched some videos explaining that $c$ not only ...
- 119
8
votes
1
answer
357
views
The synchronized clocks on earth's surface: at which observer's rate are they beating?
From what I understand, the time rates (I'm not speaking about absolute times) of all clocks on earth's surface are synchronized. This means that, say, a mobile phone's clock is generally not beating ...
- 3,753
0
votes
2
answers
119
views
Time in the Standard Model of Cosmology
Beyond a formal preference for background independence, what is stopping us from setting cosmological time as a de facto universal timeline, analogous to newtonian absolute time? General relativity ...
- 1
0
votes
6
answers
173
views
If time runs slow for moving train, how can it cover same distance in less time than someone on the ground unless the track decreases in its view?
According to special relativity,
Δt=γ*Δt' ... (1)
Where,
Δt is the time the train takes to completely pass by me according to my watch,
Δt' is the time I should see has passed for someone on the train....
1
vote
1
answer
90
views
What does hypersurface of simultaneity exactly mean?
HSS - "Hyper Surface of Simultaneity"
Listening to different sources online I understood that HSS for a observer represents the points that are at same moment of time.
Consider a 1d world. ...
-2
votes
4
answers
163
views
Relativity of simultaneity in flat spacetime
In Einstein’s (1917) thought experiment on the relativity of simultaneity…
The lightening flashes at A and B are both equal distance from the center of the train and the center of the platform.
The ...
- 27
-1
votes
2
answers
116
views
Does special relativity imply that there's such a thing as absolute time, or base time?
If time measured by one observer moving at a greater velocity than another observer is observed to be passing more slowly, does this imply that there's such a thing as "absolute time" or &...
1
vote
0
answers
106
views
Energy is the time component of 4-momentum in SR: Proof as per R. Wald's book
This is an excerpt fom R. Wald's book on General Relativity (page 61). I'm not able to understand how he deduces that $E$ must be the time component of $p^a$ with only the assertions made before this ...
- 107
0
votes
2
answers
119
views
Do all observers see the same curved spacetime -- or would that be a (prohibited) preferred inertial frame? [duplicate]
My question -- pardon if not asked in the most incisive scientific prose
Do all observers see the same curved-space time?
Let me clarify:
Given that objects traveling at different relative speeds will ...
0
votes
1
answer
67
views
Can we observe a more recent space?
The space we are viewing now is their distant past as their light has only reached our eye or telescope after travelling a long distance at the speed of light. However, for lights that are still on ...
3
votes
1
answer
106
views
How does the second postulate of special relativity imply invariance of spacetime interval?
I have trouble understanding why the second postulate of Special Relativity implies the invariance of spacetime interval $\Delta s^2=-c^2\Delta t^2+\Delta x^2+\Delta y^2+\Delta z^2$.
Suppose we have ...
- 209
-3
votes
1
answer
99
views
Would time dilation increase the distance between objects? [closed]
Two objects are moving towards a gravity well. They are at $x$ distance from each other and moving at a fixed speed. The gravity well is massive enough for the objects to experience significant time ...
- 141
3
votes
4
answers
731
views
Intuitive Derivation of Length Contraction in Special Relativity via Thought Experiment
I am trying to intuitively derive length contraction in special relativity using a thought experiment, without relying on Lorentz transformations. My aim is to obtain a derivation similar to how time ...
- 33
0
votes
3
answers
176
views
How do I make spacetime diagram consistent with length contraction? [closed]
Say the Earth and a distant galaxy is a distance $l$ away from each other. There is also a spaceship starting its journey at the Earth with a speed $u$ towards the galaxy.
I tried to draw a spacetime ...
- 111
0
votes
0
answers
40
views
Twin paradox symmetry in time dilation during the first leg [duplicate]
I was watching this Ted Ed video on Youtube about the twin paradox and found the explanation with the spacetime graph a bit confusing. At 3:00 in the video, they show a graph and explain how bursts ...
0
votes
2
answers
75
views
General Relativistic version of the Lorentz factor
In curved spacetime, the Lorentz factor is different than that in flat spacetime.
Is there any expression that gives the Lorentz factor for any arbitrary metric tensor?
user355398
2
votes
1
answer
651
views
Relativity of Simultaneity - Is there ever a Preferential Frame of Reference? [closed]
A regular description of the paradox involves a train travelling through a tunnel which is fitted with doors at either end which can be raised and lowered. In their respective rest frames the length ...
- 133