martianxx Posted November 6, 2007 Posted November 6, 2007 How can a light year = distance light travels in a year, if time stops at light speed according to relativity? Surely light could travel 2 lightyears in an instant if it wants...
timo Posted November 6, 2007 Posted November 6, 2007 The year is coordinate time, not eigentime of the lightpulse.
thedarkshade Posted November 6, 2007 Posted November 6, 2007 How can a light year = distance light travels in a year, if time stops at light speed according to relativity? Surely light could travel 2 lightyears in an instant if it wants... It's hard to follow! Could you explain better your question please?
swansont Posted November 6, 2007 Posted November 6, 2007 The time and distance are measured in our coordinate system.
Sisyphus Posted November 6, 2007 Posted November 6, 2007 The time and distance are measured in our coordinate system. For example, if you shine a laser at a mirror one light year away, it will take two years to get back to us. Two of our years, that is - no time will have passed for the light itself.
iNow Posted November 7, 2007 Posted November 7, 2007 From the light's prespective, the concept of distance and time is not the same (if existant at all). However, for pretty much everything else, like all of us watching that light move, we can measure (relative to us) how far it goes in a year. Voila. Measuring distance by light years.
primortial c Posted November 7, 2007 Posted November 7, 2007 I read once that at the speed of light you could circumnavigate the known universe in 52 years ship time.If that is true is there a formula for it is it linear..
insane_alien Posted November 7, 2007 Posted November 7, 2007 well, seeing as it is not physically possible for a massive object(like yourself or a spaceship) to reach the speed of light then you can circumnavigate it in as long as you want as the laws of physics obviously do not apply.
primortial c Posted November 7, 2007 Posted November 7, 2007 ok im sorry near the speed of light 99.9999999999999 %
iNow Posted November 7, 2007 Posted November 7, 2007 ok im sorry near the speed of light 99.9999999999999 % Then relative to someone standing still (let's say your friend who stayed back on earth), you would only be 52 light years away... in other words, not even out of the Milky Way galaxy yet. Here's a useful link for the beginner to get a sense of scale: http://www.hartrao.ac.za/other/howfar/howfar.html
insane_alien Posted November 7, 2007 Posted November 7, 2007 well it would still be impossible due to the rate at which the universe is expanding and the fact that there isn't really an edge anyway. i mean, sure wou could make a loop that would be 52 years ship time but you wouldn't have gotten close to going round the universe. you would actually have further to go than when you started.
primortial c Posted November 7, 2007 Posted November 7, 2007 did not think of that but I read that billions of years would pass by in 52 years ship time is there a formula for time dilation I read this form cosmos by.Carl sagan
insane_alien Posted November 7, 2007 Posted November 7, 2007 yes well, it is hardly the most accurate book. a lot of it is 'dumbed down' and has all the really technical parts of it stripped out so normal people don't collapse into a gibbering pile of mush at the sight of the mathematics behind it. quite a lot gets lost in the translation from technical language.
veton Posted November 23, 2007 Posted November 23, 2007 how much is a speed of light convert to KM/h or MP/H ???? is that right, speed of light move faster in water ??
Edtharan Posted November 23, 2007 Posted November 23, 2007 how much is a speed of light convert to KM/h or MP/H ???? The speed of light is stated in Km/s (kilometres per second), and is approximately 300,000km/s (you can Google a more accurate answer quite easily). This would make it roughly 1,080,000,000 km/h (imagine the speeding ticket you would get for that ). Which means that a light year is approximately 9,467,280,000,000 km.
insane_alien Posted November 23, 2007 Posted November 23, 2007 and for the second point, light does not move faster through water, it moves slower through water. it is fastest in a complete vacuum. but bear in mind this is only an average speed. between absorbtions and emittions from atoms in the medium it still travels at full speed.
Edtharan Posted November 23, 2007 Posted November 23, 2007 and for the second point, light does not move faster through water, it moves slower through water. it is fastest in a complete vacuum. but bear in mind this is only an average speed. between absorbtions and emittions from atoms in the medium it still travels at full speed. To be more precise, light doesn't slow down in water, it travels at the same speed, but because it keeps getting absorbed and re-emitted, the overall effect is that it takes longer to move through water than a vacuum.
insane_alien Posted November 23, 2007 Posted November 23, 2007 yeah, thats what i would have said if you degarbled it, put in the right order and clipped out the completely unnecessary bits. and chucked in a bucket of grammar
swansont Posted November 23, 2007 Posted November 23, 2007 Light slows down. The individual photons don't.
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now