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# Question for astronomers and movie producers

If you leave Earth in a spacecraft moving at the speed of the light (or even 4 times the speed of the light), in a straight direction (no turns), how fast would the sky change? How fast would the stars be flying by you?

Obviously if you don't move straight, stars will appear to be moving. That's what happens on Earth, because of Earth's rotation: star positions change every 24-hours in a circular pattern, albeit very slowly. Yet, the closest star, Proxima Centauri, is 4.2 light-year away from us. That means that if you would travel four times faster than the speed of light, it would still take you 1 year to reach this star. This invalidates all science fiction movies that show stars flying faster than shooting stars on Earth. This is just impossible.

You could argue that near the center of our galaxy, star density is much higher, and the closest star could be just 0.4 light years away, if you were in a random location 1,000 years away from the center of the Milky Way (assuming it has a center). I'm sure someone could carry some simulations: stars, from a statistical point of view, are distributed in the universe as a cluster process, similar (at least locally) to a Neyman-Scott process. Yet, even in this densest part of the galaxy, stars would still appear static even if traveling at unrealistic speeds.

You might argue that it's easy to travel faster than the speed of light: if one particle A travels at the speed of light, away from another particle B traveling at the speed of light in the opposite direction, then A is moving away from B at twice the speed of the light. If A is the center of the universe, you could say that in absolute speed, B is traveling at twice the speed of light.

On a different note, while do all meteors seem to be flying at speeds between 10 miles and 50 miles per second? Is it true everywhere in the universe? Are there any reasons why none fly faster or slower? Or am I wrong on this one?

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### Replies to This Discussion

Another issue with Hollywood movies: if you were very close to the center of the Milky Way, in a start cluster so dense that you would actually see stars flying by, from your spacecraft vantage point, chances are that the sky would be extremely bright because of the star density, brighter than in broad daylight on Earth. Indeed, you would not see the stars anymore, just like you don't see stars in broad daylight on Earth.

That means that if you would travel four times faster than the speed of light, it would still take you 1 year to reach this star. This invalidates all science fiction movies that show stars flying faster than shooting stars on Earth.

Unfortunately not. The moment observer would start moving faster than light (if possible) all he saw was an simultaneous detection of multiple photons - each star shaped as point would transform into a line, and adding a Doppler's effect on top the colour would change toward blue. Reaching the star has nothing to do with what an observer can see.

You might argue that it's easy to travel faster than the speed of light: if one particle A travels at the speed of light, away from another particle B traveling at the speed of light in the opposite direction, then A is moving away from B at twice the speed of the light. If A is the center of the universe, you could say that in absolute speed, B is traveling at twice the speed of light.

Simply no. According to Lorentz's transformation velocity between two objects moving toward each other or apart from each other, each travelling at light speed (in vacuum, c) is still equal to the light speed.

It's kind of pointless to ask a question that's predicated on an assumption that by our physical knowledge is not possible.

Sine this is a question that has been asked and is being asked very often you will find good answers on the itnernet. Google is your friend. Here is a reasonably simple answer:

http://science.howstuffworks.com/science-vs-myth/what-if/what-if-fa...

As far as Hollywood movies goes, no one ever thinks what they present is realistic

something wrong in this reasoning. It will not take 1 year for you. It will take no time to reach there for the traveller :)

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