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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 ...
Rob Dirnens's user avatar
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 ...
Barmar's user avatar
  • 975
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 ...
pela's user avatar
  • 38.6k
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 ...
James K's user avatar
  • 123k
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 (...
David Hammen's user avatar
  • 34.1k
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 ...
pela's user avatar
  • 38.6k
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 ...
Steve Linton's user avatar
  • 10.3k
8 votes
Accepted

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 ...
pela's user avatar
  • 38.6k
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 ...
ProfRob's user avatar
  • 153k
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 ...
StephenG - Help Ukraine's user avatar
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 & ...
ProfRob's user avatar
  • 153k
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 ...
pela's user avatar
  • 38.6k
6 votes
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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} ...
Brian Tung's user avatar
5 votes
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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 ...
ProfRob's user avatar
  • 153k
5 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 ...
ProfRob's user avatar
  • 153k
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 ...
PM 2Ring's user avatar
  • 14.8k
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 ...
Paul T.'s user avatar
  • 727
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 ...
terry-s's user avatar
  • 1,329
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 ...
Andy's user avatar
  • 2,467
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; ...
ProfRob's user avatar
  • 153k
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 ...
Florin Andrei's user avatar
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 ...
benrg's user avatar
  • 3,862
4 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 ...
David Hammen's user avatar
  • 34.1k
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 ...
gfrodo's user avatar
  • 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 ...
John Duffield's user avatar
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 ...
ProfRob's user avatar
  • 153k
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?

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, ...
benrg's user avatar
  • 3,862
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 ...
Greg Miller's user avatar
  • 5,922

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