A Hypothetical Question

[Jaybee (John)]

For this question we have to assume that 100 light years away there is a planet much like earth, lets call it Planet X, inhabited by humanoid's much the same as us, and at a similar technical advancement as us. Lets assume that they have developed the same technology as us in the form of Telescopes and Green Lasers.

Okay, Let me set the scene:

Here on Earth, Astronomers have just discoved Planet X and let the world know of the new discovery. Amatuer Astronomers all over the globe decide to have a look at Planet X and train their Telescopes with Green Laser Pointes onto it. Others use their pointers to show people where planet X is.

Fast Forward 100 Years

On Planet X, Vortag and his son Targ decide to get their Telescope out and look at Planet Alpha47 (Earth) that their Planets Astronomers have recently discovered.

Right, Now the Question! Would Vortag and Targ see flashes of green light coming from the surface of Alpha47?

I could probably have asked that in a much less longwinded fashion..

So if the Answer is yes, well that makes it dead easy, All we need to do, to find out if there is extra terrestrial life out there, is look for little green flashes!

[bojan]

Well, it is easy to do the mental calculation..

Intensity of that green laser beam, visible from Planet X must be comparable to that of Sol. Or at least to that of Earth..
Earth receives 1.4kW per m^2 from Sun.. a lot.

We have to know how much power all those lasers will pack into combined beam (assuming all lasers are perfectly pointed towards the planet X) .. and beam dispersion..
(For hand-held laser, it is close to 50mm at 100m)...

I think, the answer to your question would be one big NO WAY :-)

[MrB (Simon)]

I remember hearing or reading somewhere about how much light is reflected back to earth by the prism placed on the moon. From memory the laser on earth is in the high kilo or low mega Watts, the reflected beam is measured in pico Watts.
Or it could just be my dodgy memory.

But, no it's not likely.

[Steffen]

I think that if we assume a perfectly collimated beam then we can't really compare this to omnidirectional light sources, like Sun or Earth, which drop in luminosity as a function of distance squared. The laser beam would lose intensity only through dispersion on particles in its path. That is probably enough to kill it, though. Not to mention that beams from laser pointers are quite divergent.

Cheers
Steffen.

[bojan]

No, it's not your memory, it is true.
I remember TV programme, mentioning those numbers.

Originally Posted by MrB

I remember hearing or reading somewhere about how much light is reflected back to earth by the prism placed on the moon. From memory the laser on earth is in the high kilo or low mega Watts, the reflected beam is measured in pico Watts.
Or it could just be my dodgy memory.

But, no it's not likely.

I think there is no such thing as perfectly collimated laser beam.
However, dispersion occurs even in this case and if I remember correctly, the distance to the point at which inverse square law applies is the function of beam diameter among other parameters (just like the resolution of telescope depends on objective diameter).

[Jen]

nah i think they are banned over there too

[bojan]

Originally Posted by Jen

nah i think they are banned over there too

Yes.. they probably have their version of Aussieland over there

[renormalised (Carl)]

No, they wouldn't see the beams. However, scientist on Earth discover how to perfectly collimate a laser beam that doesn't lose intensity that much and they fire a 100 yotawatt beam at Planet X to see if it gets there and can possibly be detected.

Fast forward 200 years, the starship Coral Sea is passing through the asteroid belt that was left after the laser fired from Earth 200 years ago destroyed Planet X 100 years ago, and ended the lives of the 8.2 billion citizens of the planet

[RobF (Rob)]

Originally Posted by Jen

nah i think they are banned over there too

LOL!
You're probably spot on Jen - bureacracy has to be universal surely....!

[renormalised (Carl)]

Originally Posted by RobF

LOL!
You're probably spot on Jen - bureacracy has to be universal surely....!

The only two certainties in life....death and bureaucracy

Tax can be avoided

[leon]

Not possible, mathematicly. just do the numbers, our closest star is some 4.1 lighty years away 100 klicks is only a short burst

Leon

[Jaybee (John)]

Thanks for all the great answers..even the really tragic one where we blow up a whole planet and vaporise billions of innocent people.....or where they!!
They could have been seconds away from firing their own yotawatt beam at us..!!! Crikey that was a close one...well done lads...

Jen, you crack me up!

SO in summary, the beam would not even travel for 1/2 a second before it dissipated and faded to nothingness..

[JD2439975 (Justin)]

Originally Posted by renormalised

Fast forward 200 years, the starship Coral Sea is passing through the asteroid belt that was left after the laser fired from Earth 200 years ago destroyed Planet X 100 years ago, and ended the lives of the 8.2 billion citizens of the planet

And why was the starship Coral Sea there?

Because firing all those 100 Yotawatt beams stalled the rotation of the Earth & drove it into an elliptical orbit leading to the destruction of our biosphere...we where there hoping to move in with the neighbours.

[astro_nutt]

Ok!, here's one...
What if you send up a sattilite with large reflective panels, (I mean 1km x 1km!), as it spins it would reflect the Sun's rays into a repeating series of flashes. 1 pause 3 pause 9 then back to 1.
If you observed something like this on earth, what would you think?
Cheers!!

[renormalised (Carl)]

Originally Posted by JD2439975

And why was the starship Coral Sea there?

Because firing all those 100 Yotawatt beams stalled the rotation of the Earth & drove it into an elliptical orbit leading to the destruction of our biosphere...we where there hoping to move in with the neighbours.

We only fired one, and no amount of beam firing would be sufficient enough to stall the Earth's rotation. There just wouldn't be enough energy to do so.

The Coral Sea was there on a survey mission

Remember, the neighbours got fried

[AdrianF (Adrian)]

Instead of frying the neighbors with the 100 YotaWatt laser how about refocusing it to fry the clouds that are in everyones way.

Adrian

[JD2439975 (Justin)]

Originally Posted by AdrianF

Instead of frying the neighbors with the 100 YotaWatt laser how about refocusing it to fry the clouds that are in everyones way.

Adrian

Eww yeah, that's a brilliant idea, can I have a go?...EYES!

[Jaybee (John)]

Originally Posted by astro_nutt

Ok!, here's one...
What if you send up a sattilite with large reflective panels, (I mean 1km x 1km!), as it spins it would reflect the Sun's rays into a repeating series of flashes. 1 pause 3 pause 9 then back to 1.
If you observed something like this on earth, what would you think?
Cheers!!

I'd Think "why did they put those dirty great spinning panels up there.."

Not really..

Its communicating,, something... there's a code here...1 3 9 and back to 1 - - A safe combination?

Oooh..morse code.. but are they dots or dashes - dots would be ES don't know what 9 is or dashes would be TO still don't know what nine is..

No..maybe its not morse code..

Hint please astro nutt..course if I was asking you for a hint from Planet X you wouldn't get my request for 100 years...and I wouldn't get the hint back for a further 100 years..


Sigh....



Might as well go make myself a coffee.

[rider]

Originally Posted by astro_nutt

Ok!, here's one...
What if you send up a sattilite with large reflective panels, (I mean 1km x 1km!), as it spins it would reflect the Sun's rays into a repeating series of flashes. 1 pause 3 pause 9 then back to 1.
If you observed something like this on earth, what would you think?
Cheers!!

I'd Think, "Typical! , why cant they turn their outside lights off and let me get dark adapted."

[el_draco (Rom)]

Um... it would depend on which eye they put to the eyepiece....

... but on a more serious note, I see to remember an article a LONG time ago that suggested the atmosphere of Mars was a natural laser at certain wavelengths.... Dont quote me though.