Light in perspective.

Not wanting to confuse the speed limit thread, I have two questions about light. (both have two parts)

We all know that light has a beginning but does not have an end. (another argument that the universe is infinite)

My first question is.....If I was in direct line of a beam of light, 5 light years away from the source, Would I not see the light for 5 years? And if the light was turned off after 10 years would I still see the light for another 5 years ?

Second, if I someone was observing the light at 90 degrees to the beam and was, say, at the mid point between the source and the object , at what point would I first observe the beam, and at what point would I no longer see the beam?

catch-22 wrote:Not wanting to confuse the speed limit thread, I have two questions about light. (both have two parts)

We all know that light has a beginning but does not have an end. (another argument that the universe is infinite)

My first question is.....If I was in direct line of a beam of light, 5 light years away from the source, Would I not see the light for 5 years? And if the light was turned off after 10 years would I still see the light for another 5 years ?

Second, if I someone was observing the light at 90 degrees to the beam and was, say, at the mid point between the source and the object , at what point would I first observe the beam, and at what point would I no longer see the beam?

Hey catch, I can only comment on the first of your questions...My answer is yes...I say this because, on my 30th birthday, a friend of mine did my star charts, because, as he said, the light from some star(I don't remember which one) is the same light that left the star on the day you were born (30 years to reach Earth) somehow making it the ideal time in ones life to have their charts done...Pete

catch-22 wrote:Not wanting to confuse the speed limit thread, I have two questions about light. (both have two parts)

We all know that light has a beginning but does not have an end. (another argument that the universe is infinite)

My first question is.....If I was in direct line of a beam of light, 5 light years away from the source, Would I not see the light for 5 years? And if the light was turned off after 10 years would I still see the light for another 5 years ?

Yep, pete is right on this one. If the sun stopped shining right now, you wouldn't know about it for another 8 minutes. Likewise, if you were 5 lightyears away, and I turned a light on right now, you wouldn't see it for 5 years.

I'm not sure what you mean by "light has a beginning but does not have an end."

Second, if I someone was observing the light at 90 degrees to the beam and was, say, at the mid point between the source and the object , at what point would I first observe the beam, and at what point would I no longer see the beam?

Well, this is a little more complicated. You see, the only reason you can observe a light beam is because the light is hitting something in the air, and bouncing off that into your eye. Usually this is just dust. But if you take one of those little laser pointers, you can imagine shining that out into space, and someone at 90 degrees from it wouldn't see anything at all.

Kazza wrote:I'm not sure what you mean by "light has a beginning but does not have an end."

Light has a source. If it travels at the speed of light, it must be traveling from that source. (a beginning) If the traveling light is not stopped by an obstruction, it would continue to travel indefinitely and therefore would not have an ending.

catch-22 wrote:

Kazza wrote:I'm not sure what you mean by "light has a beginning but does not have an end."

Light has a source. If it travels at the speed of light, it must be traveling from that source. (a beginning) If the traveling light is not stopped by an obstruction, it would continue to travel indefinitely and therefore would not have an ending.

Oh, I see what you're saying.

Actually, according to one theory (put forth by Feynamn, I think) all light must eventually be absorbed. The reason for that suggestion is that it makes certain laws symmetrical in time - that is, they look they same going forward through time as backward. But to go in to detail on that would be stretching my own understanding of quantum mechanics, let alone every else's. There's a similar idea to do with gravity as well, but again, it's all just weird theories.