# Light in Space

1. Mar 12, 2004

### AnthreX

say that..
you shoot a really strong light facing towards space from earth,
as the light travels in space it would lose energy and start to disappear. but before it all disappears, what if you use a really strong telescope pointing at the direction that you shot your light into space? would you be able to see that light travelling ? even though its damn fast.

this is just my opinion , i think you can see the past and hear the past in deep deep deep space

2. Mar 13, 2004

### Michael D. Sewell

When you look at any of the heavenly bodies you are looking into the past, just as you said. Count the seconds between seeing a lightning bolt and hearing the thunder(5 seconds per mile). I never heard a star. Why?

3. Mar 13, 2004

### Clausius2

And when you look at the mirror and you see your own figure, you are seeing the past, how you were aprox. 60 nano-seconds before.

4. Mar 13, 2004

Staff Emeritus
Well, not that long. LIght travels at very close to one foot per nanosecond, so if you were, say, two feet from your mirror, the light being reflected would go four feet to get back to you, and you would see yourself as you were 4 nanoseconds ago.

5. Mar 13, 2004

### Gara

you cant hear suns cos sound are pressure waves and theres no medium in space.

as for looking back in time with a telescope, you dont need to first fire a strong beam of light.

a little bit of humor: i once told my mum of the possibility of placing a mirror 1000 lightyears away from earth, and looking at it, with the mirror aimed at earth. and how we'd see earth and what was happening on it 2000 years ago. and she says

"wouldnt the people on earth notice the mirror and telescope watching them?"

6. Mar 13, 2004

### pallidin

Hilarious! So, if I could blink really fast(faster than is possible), I could look at myself in the mirror seeing a reflection of myself that has it's eyes closed!

7. Mar 13, 2004

### chroot

Staff Emeritus
Light does not lose energy when travelling through space.

A perfect laser beam will stay intact forever until it hits something. A real (imperfect) laser will spread out, however, the further it goes. It will not disappear, but its energy will become spread over a larger area.

You *could* use a telescope to see your laser pulse, if some substance in the intervening space was scattering some of the light back to Earth. If the intervening space was truly a vacuum, however, you could not see it.

- Warren