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 ...
- 835
22
votes
Accepted
When we see the Sun, do we actually see its past?
Yes, you are right. We don't only see the Sun 8 minutes in the past, we actually see the past of everything in space. We even see our closest companion, the Moon, 1 second in the past.
The further an ...
- 1,901
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 ...
- 33.8k
19
votes
Accepted
Age of the universe and time dilation
The answer is yes time dilation does affect how much time an observer experiences since the big bang until the present (cosmological) time.
However there is a certain set of special observers called ...
- 1,795
11
votes
Photon Paradox?
And that is why you don't do the calculations in a frame that is moving at lightspeed.
If you have two observers that are moving relative to each other you can use the Lorentz transformation to ...
- 91k
9
votes
Age of the universe and time dilation
In the standard model, the universe looks the same for all locations moving in the local rest frame. This includes its apparent age. You can tell if you are in the local rest frame if the expansion ...
- 2,857
9
votes
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In theory, is there anywhere in the universe where velocity=0?
Yes.
The velocities you list (X, Y, …) are all velocities with respect to some reference frame. But all reference frames are arbitrary, and you can always define a reference frame where the velocity ...
- 33.8k
9
votes
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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 (...
- 28.3k
8
votes
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How long would it take to reach the edge of the reachable universe?
Jonathan's answer is essentially correct, but as Rob Jeffries comments, he doesn't take into account that the Universe is expanding during the journey.
The edge of the observable Universe is 47 ...
- 33.8k
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 ...
- 9,933
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 ...
- 33.8k
7
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 ...
- 118k
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} ...
- 289
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 ...
- 33.8k
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 & ...
- 118k
6
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 ...
- 5,801
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 ...
- 118k
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 ...
- 557
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 ...
- 1,046
4
votes
Accepted
How would Special relativity explain past-present-future if thinking about 13-billion-light-years distanced objects
First off, if Earth were point B, and you were an observer at point A looking at it with the most magnificent telescope ever imagined, you would still not see the Earth, because it didn't exist 13 ...
- 516
4
votes
Accepted
What is the bulk Lorentz factor?
I think it is referring to the speed and Lorentz factor $(\beta = v/c$ and $\gamma = [1-\beta^2]^{-1/2})$ of the gas as a whole. Within the gas, there could be particles moving with a variety of ...
- 118k
4
votes
Accepted
Observing a point 13.82b ly away, 1b years ago
Time is kind of funny when you look at such distances. Let's imagine that you are running away from a person throwing a ball at you. The ball will travel further to hit you, based on your speed, than ...
- 2,890
4
votes
Accepted
If an object with mass were to somehow go the speed of light, would it destroy the whole universe?
Would an object with mass traveling the speed of light destroy the whole universe because it would have infinite energy / mass?
If we understand the question as a limiting process, which is the only ...
- 7,684
4
votes
Accepted
How far into the future can we go by traveling close to a black hole?
The way that you have specified the question, the answer is as far as you like. You simply put your spaceship into any orbit around the black hole and wait.
A more sensible question is what is the ...
- 118k
4
votes
Photon Paradox?
1) In the early universe 13 billion years ago when the star first emitted the photon, there was no Hubble Telescope for the photon to instantaneously collide with from its frame of reference. In other ...
- 2,377
4
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 ...
- 17.5k
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; ...
- 118k
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