All Questions
44
questions
0
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2
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119
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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 ...
41
votes
4
answers
5k
views
Rotate an object about the time axis
Is there a notion of rotating an object about its time axis? I'm not sure if this question totally makes sense, but it seems intuitive to me that an object with dimensions in the three spatial ...
- 521
2
votes
3
answers
130
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How to prove: Are perpendicular coordinates (wrt to relative velocity) unchanged (or only scaled) while deriving the Lorentz Transformations?
Thank you for helping with this question and I'm sorry if it's kind of stupid.
TLDR: In many textbooks and other derivations deriving the Lorentz Transformations, they omit coordinate axes orthogonal ...
- 31
1
vote
1
answer
52
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Is distance irrelevant to time if two events are in the same inertial reference frame? [closed]
Assuming that there is some observer "O" at location 0, and there are two events A and B, with B occurring 1m farther from A. Both A and B are equipped with two synchronized clocks reading ...
1
vote
2
answers
250
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Four vectors and coordinates
Hartle, gravity. Chapter 5
A four-vector is defined as a directed line segment in four-dimensional flat spacetime in the same way as a three-dimensional vector (to be called a three-vector in this ...
- 1,270
6
votes
4
answers
1k
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Twin Paradox (SR): How can we express the comparative length of arbitrary world-lines mathematically?
The simplest and most intuitive way I have found so far for explaining which twin ages less in the Twin Paradox, is that it's the twin who's world-line is the longest (if it's the longest in one ...
- 200
1
vote
2
answers
176
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In spacetime what is the time $t$ on the $ct$ axis?
In spacetime, I understand that we multiply time by the speed of light to deal with homogeneous distances over the four axis, space and time.
But what does $t$ refers to precisely? Where is $t$ ...
- 113
3
votes
3
answers
537
views
Why is proper time $d\tau$ equated to spacetime length $ds$?
Follow-up to this question: Why proper time is a measure of space?.
The selected answer to me tells us why proper time is an invariant quantity, but I'm still wondering why we equate it to $ds$. Can ...
- 1,261
5
votes
1
answer
402
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Physical Meaning of Pullback metric vs. Effective Spatial Metric
Consider a Riemannian Manifold with a metric tensor $g_{\mu\nu}$ and coordinates $(t, x^i)$. Let us assume that the spacetime is stationary, so $\partial_t g_{\mu\nu} = 0$. At a fixed coordinate time ...
- 709
1
vote
3
answers
148
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What if the Twin Paradox use the "day time" and "night time" on earth as their age reference?
I've searched this site, I found a similar question here but not exactly like mine.
So I can't understand the Twin Paradox when I use the "day" (bright time) and "night" (dark time)...
- 111
6
votes
1
answer
403
views
How are spatial coordinate systems in physics defined?
Grothendieck once asked "What is a meter?" (https://golem.ph.utexas.edu/category/2006/08/letter_from_grothendieck.html). This innocent sounding question, made me to think about how ...
- 180
6
votes
1
answer
279
views
What does this spacetime diagram mean?
I'm reading a book called "Reality is not what it seems: the journey to quantum gravity" by Carlo Rovelli and I'm struggling to understand this diagram that is part of the chapter about ...
- 435
1
vote
3
answers
219
views
Can there be simultaneity without a reference frame?
I have been reading about the concept of the relativity of simultaneity which states that whether two events, separated by space, occur at the same time is relative to the observer's reference frame. ...
- 460
-1
votes
1
answer
47
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In order To synchronize clock should the observers has same plane of simultaneity?
Suppose we have to observer $A$ and $B$ with their time given by $t_A$ and $t_B$.To synchronize their clocks observer $A$ send lights at $t_A$ towards $B$. $B$ receives the light at $t_B$ and send it ...
- 445
5
votes
5
answers
1k
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How should I understand the idea of relativity of space?
In the book General Physics by L.D.Landau, he mentioned the following in the first and second paragraph
The fundamental concept of mechanics is that of motion of a body with
respect to other bodies. ...
- 138