38
votes
Accepted
It takes light roughly 8 minutes to travel to Earth from the Sun, but based on which perspective?
If I interpreted this article correctly, then the answer to my question should be: 8 minutes is what we perceive, whereas for the photon the journey is instantaneous, due to the fact that it travels ...
- 629
23
votes
It takes light roughly 8 minutes to travel to Earth from the Sun, but based on which perspective?
When people talk about the time taken for light to go from the Sun to the Earth, they're generally just considering classical Newtonian mechanics, not relativity. So we simply divide the distance by ...
- 985
20
votes
Accepted
How old would I be if I travelled 1000 light years in one year
The answer is sort of trivial. If you travel 1000 ly so fast that in your own reference frame it takes one year, then you will have aged by one year in your own reference frame. To do so, you will ...
- 39.6k
9
votes
Accepted
Contradiction of special theory of relativity and quantum mechanics
There is no contradiction between special relativity and quantum mechanics. Quantum field theory fully merges special relativity and quantum mechanics to describe relativistic electrons and protons (...
- 36.3k
8
votes
How does time work beyond the cosmic event horizon?
First, let's clear up a few misconceptions:
The Hubble sphere
The speed of light as an upper limit is valid in special relativity (SR). In general relativity (GR), which must be used to describe the ...
- 39.6k
8
votes
Can anyone one show how speeds greater than c cause a paradox on a space time diagram?
Suppose there was a magic gun that fired a bullet at ten times the speed of light relative to the firer.
If I have the only such gun, and I don't move then there is no paradox.
But now suppose ...
- 10.4k
8
votes
Accepted
How much time passes in the outside universe when falling into a black hole?
You are essentially asking the following: if someone falls from the Earth from some way beyond the event horizon of a black hole, how long after they have left can an observer on Earth still signal to ...
- 163k
7
votes
Accepted
Absolute zero speed in space
The faster you move, the slower does time feel
No.
The faster someone else you are observing moves relative to you, the more time (as observed by you in their frame) slows down relative to the ...
- 6,401
6
votes
Accepted
Are there any examples where the transverse doppler effect is applied in astronomy?
Accounting for the transverse Doppler effect (and other relativistic effects) is essential in modelling the X-ray spectral emission lines from the accretion discs around black holes (e.g. Cadaz & ...
- 163k
6
votes
Accepted
What exactly is the cosmic definition of ‘now’ is?
The cosmic "now" is well-defined: It is the time for an observer that has always been at rest in the Universe's comoving coordinates, i.e. the coordinates that expand along with the Universe. Although ...
- 39.6k
6
votes
Accepted
What is length of the universe on lights perspective
Sort of. The Lorentz factor is
$$
\gamma = \frac{1}{\sqrt{1-\frac{v^2}{c^2}}}
$$
whereupon a stationary object in the stationary reference frame of length $L$ has a length of $L' = \frac{L}{\gamma} ...
- 299
5
votes
Does the twin paradox work in an almost empty universe?
Velocity is relative, but acceleration is not: you can feel it (and it feels just like gravity). But as I said in the question comments, acceleration is a red herring.
The real issue is that the ...
- 16.7k
5
votes
Accepted
Have we Observed Continuum Emission from Neutron Stars?
Yes - quite a few isolated neutron stars have been observed, where any magnetospheric emission or accretion-related emission is either negligible or has been otherwise separated.
As you suspect, this ...
- 163k
5
votes
Does Absolute Velocity Exist?
Chris, you are actually on the verge of understanding how special relativity works. You're very close. You only need to take one extra step.
to state that all speed is relative to an object is to ...
- 18.4k
5
votes
Does one need to consider relativistic effects when simulating the (or any) Solar system?
Does one need to consider relativistic effects when simulating the (or any) Solar system?
It depends.
The answer is a resounding all-caps NO
When trying to model the orbit of an artificial Earth ...
- 36.3k
5
votes
Do Einstein's ten field equations use 20 or 40 variables? (2 or 4 for each tensor equation?)
A single vector equation like $\vec{F} = m \frac{d^2 \vec{r}}{dt^2}$ is actually three equations one for each of the $x,y,z$ components of the 3-vector $\vec{r}$.
In the spacetime of general ...
- 725
5
votes
Measurement of Planetary Aberration (similar to stellar aberration)
I. The statement about planetary aberration quoted in the question, and for which the quesioner seeks some authority, wasn't actually called a 'definition' by the questioner : it's probably best ...
- 1,329
4
votes
Information speed and our view of the cosmos
The effect is small, but not negligible. It is not accounted for in astronomical catalogues.
Let's work it out. We can start with the visible stars. Most of these are closer than 1000 light years; ...
- 163k
4
votes
Does the twin paradox work in an almost empty universe?
As Richard Feynman said about a similar situation, we can't do the experiment of removing all of the matter from the universe to see what would happen, so we don't really know.
But from what we do ...
- 4,193
4
votes
Does time also pass more slowly for a galaxy that is traveling at relativistic speeds, where the speed difference is due to Hubble expansion?
This is similar to previous questions you've asked, especially this one. I think you're still clinging to the idea that there's a quasi-Newtonian master clock that defines the real passage of time, ...
- 4,193
3
votes
Does time also pass more slowly for a galaxy that is traveling at relativistic speeds, where the speed difference is due to Hubble expansion?
Yes, but it has little to do with the Special Relativistic time dilation of a moving body - in the sense that recession velocity is due to the expansion of space between galaxies rather than their ...
- 163k
3
votes
Is it possible to know if you are travelling close to the speed of light if you have nothing to compare your speed with?
Velocity is relative. From your perspective, your velocity is zero. Without windows (or sensors) on your spaceship, you cannot know the difference. To measure your velocity, you have to define a ...
- 31
3
votes
is this really true that speed of light is same as we look from different parts of universe?
According to theory of relativity . Light speed is same for every observer . How can we prove it is right?
By doing experiments. Pela mentioned the Michelson-Morley experiment. That's what got ...
- 2,547
3
votes
Measurement of Planetary Aberration (similar to stellar aberration)
As far as an authoritative source, as PM 2Ring pointed out in his comment, it is on Wikipedia, but no reference is cited. The definition itself seems to be incomplete, as it does little to actually ...
- 6,112
3
votes
Stellar aberration without relative motion between source and observer
It's impossible to measure instantaneous aberration because there is no reference angle to compare against.
What can be measured is the variation of aberration over the course of a year. In 6 months, ...
- 4,193
3
votes
Stellar aberration without relative motion between source and observer
There are three sources of abberation: annual (due to the orbit of the Earth) diurnal (due to its rotation) and secular (due to the relative motion of the solar system.
The secular aberration is ...
- 129k
3
votes
Other Hubble spheres with no Lorentz symmetry?
Lorentz symmetry is only global in flat space times; in free falling general relativistic reference frames, it is a local symmetry. So you don’t even have to go as far as outside the observable ...
- 3,404
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