# Tag Info

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

### 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
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 ...
• 39.1k
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 (...
• 34.4k

### 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 ...
• 39.1k

### 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
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 ...
• 158k
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 ...
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 & ...
• 158k
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 ...
• 39.1k
Accepted

• 727

### 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

### 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; ...
• 158k

### 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 ...
• 18.3k

### 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 ...
• 4,143

### 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, ...
• 4,143

### 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 ...
• 158k

### 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

### 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 ...
• 2,549

### 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 ...
• 6,082

### 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, ...
• 4,143