Questions tagged [observers]
For questions related to observers in relativity or quantum mechanics.
1,539 questions
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Speed of light for dummy
I'm trying to understand how travelling at the speed of light messes with time. So pretend there is two planets one light year apart.
We are in contact and plan to do an experiment.
When I say 'go' on ...
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What is the physical meaning of $i \mathcal{L}_\xi f_i = \omega_i f_i$ and its relation to observer-dependent positive frequency in curved spacetime?
I’ve been studying quantum field theory in curved spacetime (QFTCS) and trying to understand how the notion of positive frequency modes is observer-dependent. I want to check whether my current ...
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A question about interstellar travel [duplicate]
If an observer $O'$, one light-year away, approaches $O$ at a speed close to that of light, the time elapsed for observer $O'$ would be practically zero. If $O$ is the one approaching, the opposite ...
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Application of Reichenbach synchronisation
Suppose I adopt the Reichenbach synchronisation process so that light heading radially away from me- according to my clocks- travels with infinite speed, while light heading directly towards me ...
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Proper times of two inertial observers. [closed]
According to the Lorentz transformations, if an observer $O'$ moves at a relative velocity $\beta$ with respect to another observer $O$, the proper times $t$ and $t'$ would be related by:
$$ t=\sqrt{1-...
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Do blueshifted and redshifted light sources have differing energies?
The thought experiment:
Two spaceships are passing each other some distance from a star. Both ships are at relativistic speed, one toward and one away from the star. Should the total energy observed ...
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Would you see the entire past history of the universe when falling into a charged/rotating black hole?
Would you see the entire past history of the universe when falling into a charged/rotating black hole as you approached the inner event horizon?
I’ve read multiple sources here that contradict each ...
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What would someone surrounded by a collapsing shell observe?
Inside of a shell space time is flat, but you do get time dilation relative to distant observers. As the shell gets smaller, time dilation gets stronger.
So does and observer inside of a collapsing ...
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Clock on a moving rocket
Let's say that there is a clock mounted outside a rocket that is moving at a constant velocity upwards as measured by an adjacent observer looking at the clock from a stationary platform. The clock's ...
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In the Twin Paradox, can one twin travel backwards in time?
In the Twin Paradox, if the travelling twin, Betty, instead of returning to her brother Albert at home, continues her journey after a period of rest, why is causality not violated due to her brother, ...
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Can a rotating or charged object have time speed up as you approach?
The Reissner–Nordström metric has a gravitational time dilation defined by
$$y=\sqrt{\frac{r^2}{Q^2+r(r-2M)}}
.$$
Note that there is a charge squared term there, but the term for the mass in linear.
...
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Doubt about Lagrangian transformation between reference frames (Susskind, Classical Mechanics, The Theoretical Minimum, pag.117)
I'm working through Susskind's Classical Mechanics book and I reached the point where he explains how to transform the action (and Lagrangian) when changing reference frames. However, I believe there ...
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Direct observables in observers hand
Observation of a measurable is the event of interaction between the observer and the universe after which a value of that measurable is obtained.Since all observations occur solely by interactions and ...
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Is it correct that you can change light's velocity but not its speed? [closed]
A laser is shone down the center of a vacuum corridor 1 light-year in length. The corridor has a lateral motion (perpendicular to the laser) of 10mph. Does the light hit the center of the far end, or ...
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How does light in the observable universe behave for an observer falling into a black hole?
Everything is relative as Einstein has long ago discovered. The effects of relativity are especially apparent near the extreme spacetime curvature sources like black holes. For an outer observer, ...
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