All Questions
29 questions
0
votes
2
answers
53
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Order of events is invariant in timelike intervals
I thought that the order of events could be something that changes with a boost. But recently, I read in a book that for time-like separated events, the order of events is invariant.
If I think about ...
-6
votes
2
answers
139
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Do the Lorentz transformations contradict reality by implying time had no beginning? [closed]
Consider the following two points, or events as they are more commonly called, in SpaceTime:
Event 1: $(x,t) = (0,0)$
Event 2: $(x,t) = (a,0)$
Take t=0 to correspond to the first moment in time.
As ...
- 177
4
votes
5
answers
656
views
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 ...
- 435
-1
votes
1
answer
78
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The train-and-platform VS Causality and Simultaneity
for long time I was ruminating on the train and platform experiment and “what if” extension of this experiment…
So, what if the light striking on either end triggers system (one on each end) with ...
- 19
0
votes
2
answers
64
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Time-Like Separated Events: Can there be more than one reference frames for which 2 events can happen at same place?
For time-like separated events, reading of 2nd event of any observer from central event (i.e. at origin)
should lie within top light cone (we will consider only future events and ignore the bottom ...
- 1,471
1
vote
1
answer
193
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Mathematical proof of causality in special relativity
I am trying to work through a proof of causality in special relativity using the Lorentz transformations, but there is one assumption that is necessary for the proof that I don't see as correct.
The ...
0
votes
2
answers
133
views
Light-like interval and simultaneity [closed]
Why if the interval between two events is light-like then there is no frame of reference where the events occur at either the same time? If I assume that the 2 events happen at the same time, I arrive ...
1
vote
2
answers
125
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Temporal Ordering in Special Relativity [duplicate]
Not a physicist: but want to use the temporal ordering of events in special relativity as an example for something, and need to answer the following question to do so.
Suppose we have three events, a, ...
- 11
-1
votes
2
answers
124
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Simultaneous events [closed]
It follows from relativity that "simultaneous events" cannot happen in our universe. If $A$ and $B$ are two events which happen at the same time in reference frame $F$, we can find reference ...
- 355
4
votes
2
answers
130
views
How to show that a if $v > c$ there is a frame which breaks causality in special relativity?
I'm reading about special relativity and looking at the Lorentz transformations.
I'm reading that:
If $v > c$, we can find a frame in which $t_2' < t_1'$, i.e. a signal arrived before being ...
- 947
0
votes
1
answer
432
views
Spacelike, Timelike and order of events [closed]
Hartle pg 60
The relativity of simulataneity means that it does not make sense in general to say that one event is later than another. An event can be later than another spacelike separated event in ...
- 1,340
2
votes
0
answers
75
views
Invariant of time-order in lightlike interval
I'm trying to prove that the time order is invariant in a lightlike interval, I have this
$$P_1=(X_1^0, X_1^1,0,0)$$
$$P_2=(X_2^0, X_2^1,0,0)$$
Two lightlike events in a inertial frame where $t_2>...
2
votes
2
answers
200
views
Global conservation + Lorentz invariance = local conservation?
On the page 83 of "Quantum Field Theory Lectures of Sidney Coleman", Coleman showed an interesting example:
It seems that global conservation law and local conservation law can be related. ...
- 342
1
vote
1
answer
527
views
Understanding 4-momentum and the Lorentz invariant product
What I am trying to do is show that if $\textbf{P}_1$, $\textbf{P}_2$ are time-like, future point 4-vectors, then $\textbf{P}_1 .\textbf{P}_2\geq0$.
My understanding of the meaning of timelike is that ...
- 137
4
votes
3
answers
704
views
Invariance of the spacetime interval in special relativity
Bernard Schutz in his book "A First Course in General Relativity" says
All observers agree on what constitutes the past, the future, and elsewhere of a given event because the interval is ...
- 65
0
votes
1
answer
94
views
Universal limit on speed of signal transmission
Einstein, in his 1905 paper On the Electrodynamics of Moving Bodies, famously uses two postulates to derive the Lorentz transformations:
The relativity postulate: the laws of physics are invariant in ...
- 149
0
votes
0
answers
72
views
Simultaneity and Tachyons
I open this question because the discussion on @Demigan's question did not come to a satisfactory conclusion.
One of the best discussions on tachyon relativity that I’ve seen is by David Bohm in his ...
- 96
0
votes
3
answers
145
views
Irreversible processes in special relativity
According to special relativity (as I understand it) simultaneity is no longer a universal concept in special relativity. Consider two events A and B which are simultaneous in reference frame 1; in ...
- 11
36
votes
3
answers
9k
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Is there a frame of reference in which I was born before I was conceived?
I'm struggling to understand the relativity of simultaneity and position.
If my conception and birth are separated by time but not space, a frame of reference in which my birth and conception are ...
- 750
0
votes
2
answers
1k
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Spacelike and timelike intervals confusion
I'm confused about this, specifically the spacetime interval.
A timelike interval is one in which 2 events can be related to each other in a given reference frame within its light cone, that is, it ...
- 773
2
votes
4
answers
271
views
When electron moves constantly, it's electric field moves with it instantly?
When electron accelerates, there occurs a propagated ripple on it's electric field. But when it moves constantly, does the field "follow it", i.e. changes instantly? How does it deals with the fact ...
user210398
1
vote
1
answer
460
views
Can someone explain this causality argument about the speed of light from Special Relativity?
I was watching this Yale lecture by R. Shankar.
From 8:29 to 15:05, he gives an argument for why theory of relativity "demands" that it should be impossible for events to influence other events ...
- 553
2
votes
1
answer
154
views
Are Lorentz transformations a direct consequence of finiteness of signal speed?
I have this silly doubt in my head and it's bugging me for a real long time now. Let us consider the Galilean transformation $x=x'+vt$ for two frames measuring coordinates $x$ and $x'$. For simplicity,...
- 2,778
-1
votes
1
answer
2k
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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,...
- 127
8
votes
1
answer
17k
views
Causality and speed of light
It is accepted that the speed of light is the speed of causality. If we exceed the speed of light, the order of cause and effect breaks down. This happens as we see our surroundings moving backward in ...
- 454
0
votes
2
answers
556
views
How anything faster than speed of light travel back in time?
I know about this theory but I cannot get the picture that how moving faster than light even 100.01% of light-speed would make universe run backward.
- 938
1
vote
1
answer
429
views
Is cause-effect always preserved in relativity?
I guess most of you are familiar with the "paradox" of the train passing through a tunnel smaller than itself on a speed close to the speed of light and 2 guillotines (1 in the exit and 1 in the ...
- 145
9
votes
2
answers
301
views
What are the linear maps which preserve the time-like cone?
I'm looking at the set of time-like vectors:
$$\mathcal{T}_+ = \{ x \in \mathbb{R}^4 \mbox{ s.t. } x^T \eta x \geq 0 \:, x^0\geq 0\} ,$$ where $\eta = \mbox{diag}(1, -1, -1, -1)$.
I want to be able to ...
- 156
9
votes
5
answers
8k
views
Why is causality preserved in special relativity?
PART 1:
I was reading the article Relativity of simultaneity Wikipedia. I couldn't understand this line:
"if the two events are causally connected ("event A causes event B"), the causal order is ...
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