Another light speed one. Hypothetically…

[wildwood]

I am still trying to get my head around this speed of light thingy.

One spaceship can travel at the SoL and goes to the Canis Major Dwarf Galaxy (25000 light years away). Counting onboard time, would it get there in 12500 L.Y. as it meets the light?

[vascop]

If you do the maths then the time it takes you, measured on earth is:
Time-on-earth=L times sqrt(1/f^2-1), where L=number of light years away the star, or whatever, is, and f= fraction of speed of light you are travelling at. For example if you are travelling at half the speed of light f=0.5.
In your case travelling at say 0.99999 the speed of light as Jake mentioned then elapsed Time-on-earth comes out as 0.5 years for L=25,000. If you could travel at light speed f would be 1 and so Time elapsed on earth would be zero.

[mibn2cweus]

Naomi, Time is relative to the place in which it is measured. If measured while standing on the Earth or Sun (OUCH!) based on the average distance between it takes about 499 seconds for light to travel the distance. The time elapsed for any distance while traveling the speed of light is . . . zero.

By the way your number is: One hundred forty-six quadrillion nine hundred sixty-five trillion six hundred thirty-four billion three hundred twenty-nine million five hundred ninety thousand two hundred miles.

[jake-the-peg]

// The time elapsed for any distance while traveling the speed of light is . . . zero. //

Do you think so Mib?

I'm not sure - the time dilation equation gives you a divide by zero when velocity is the speed of light.

Now that may or may not mean that time is zero - it may very well mean that our understanding of what that means in extreme cases is not good enough.

Drawing the conclusion that the dilation is infinite and therefore time is zero is a dangerous assumption.

[vascop]

I agree with mib. That is what I am saying in my last post. As your velocity gets closer to the speed of light, the time it takes you gets smaller and smaller. So in the limit the time taken would be zero regardless of the distance you are travelling. This is a silly result really since you can never travel at light speed anyway.

[jake-the-peg]

Vascop

If I drop a coin around an airless planet it will accelerate at a constant rate - in the limit it will be travelling infinitely fast.

You and I know that is wrong only because we know more about the circumstances and that Newtonian science is an approximation.

Bear in mind that we are talking about the real Universe here and limits are all well and good in maths but I can't think of many occasions in the real world where taking a divide by zero as a real infinity has a meaningful state

Can you?

[vascop]

No you are right, but this is a silly situation where the original poster is assuming something is travelling at light speed.

[jake-the-peg]

True but sometimes interesting discussions come from daft questions!

[chakka35]

naomi, please note that mib is using those definitions of 'quadrillion', 'trillion' and 'billion' in the modern American way, rather than the mathematical and linguistic definitions built-in to the words themselves.

So you can choose his, going with the crowd, or mine as a verbal purist. Your choice.

[naomi24]

//it may very well mean that our understanding of what that means in extreme cases is not good enough. //

I'm thinking that's about right.

[naomi24]

Chakka, even if the result is a little wonky, you have to say it's a very good try. :o)

[society]

Chakka, are you trying to lure Naomi into choosing sides? ;-)

[naomi24]

Mibs, //Time is relative to the place in which it is measured. If measured while standing on the Earth or Sun (OUCH!) based on the average distance between it takes about 499 seconds for light to travel the distance. The time elapsed for any distance while traveling the speed of light is . . . zero.//

Yes, I understand the principle, but with my awkward head on say for example you sat on a sunbeam (an even worse ouch!), according to that theory you would be instantly transported from the sun to the earth. Zap! You're there! However, if I were waiting to greet you, drinks poured and all, I would have to wait 8 minutes for you to arrive. That makes no sense. If it's instant, regardless of the viewpoint, there can't be a time lapse. If there were, it wouldn't be instant. I think we have something wrong somewhere.

[wildwood]

Silly? Daft? It states clearly at the top that this is in a HYPOTHETICAL situation and the time is onboard, not on Earth.

I have read Mib's link a few times and now basically understand why time stands still at the SoL.

[mibn2cweus]

Naomi, With regards to time dilation, those with different frames of reference moving relative to each other can 'agree to disagree' and still both be right! ;o)

[sammmo]

All of this is doing my head in.. Answer this. If you had say a large sealed box with a remotely controlled light inside and you took it into a very dark place like a coal mine, once down in this pitch black mine you switch on the light with your remote but you cant see anything because the light is in its sealed container.. you then switch off the light and open the box .. will you see any light come out.. the answer i suspect is no.. so where has that light gone? If light just carried on and on even after the light source had gone why wouldnt you see a flash of light escaping?

[vascop]

The light is absorbed by the material of the box.

[vascop]

Wildwood
"Silly? Daft? It states clearly at the top that this is in a HYPOTHETICAL situation and the time is onboard, not on Earth. "
Yes, but you are postulating that something travels at light speed which the theory of relativity prohibits. So if you put this into the equations you can expect silly results.

[sammmo]

If thats correct why is'nt the light absorbed that is omitted by these far off stars, by other planets or astroids etc that is infront of the light omitting planet? surely if that star is say a billion light years away there is alot of stuff infront of it is,nt there..

[mike11111]

Einstein's got a hell of a lot to answer for!

[vascop]

sammo
Some is of course, but don't forget that they transmit an enormous amount and also that when we say light here we are not just talking visible light, but ALL electromagnetic radiation. Some of this spectrum of frequencies will get through.