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Hypotetical laser pointers Vs Moon






What it really does is put into perspective just how much energy the sun puts out.

On the line of a similar thought experiment, I remember my thermodynamics teacher told us about how he got a question from a student about whether the heat from something like warming up his car in the winter contributed to global warming. Yeah, c'mon right? Your car? So to put this into perspective the teacher ran a calculation:

How much would the earth heat up if we burned all the fossil fuels on or in the entire planet at once? Well it was about 1.5 degree C I believe. Really, any man-made caused heating of the earth would be from helping the sun's energy remain trapped on Earth, not any kind of heat we can generate ourselves.
 
What if you give everybody on earth the death star laser from Star Wars ?
 
Blord said:
What if you give everybody on earth the death star laser from Star Wars ?
Click to expand...

Then there would be no moon :cryyy:

He only covered 1W lasers, I wonder if 2-3W lasers would have any effect. I would also like to know if beam expanders would have any visible effect. It would be interesting to see blue beams everywhere shooting up onto the moon :o
 
What about using a 100x beam expander and giving everyone a 40 watt green? Also it was a very neat read...my question is what would it look like from Earth if you had binoculars?
 
Blord said:
What if you give everybody on earth the death star laser from Star Wars ?
Click to expand...

Thats no moon, its a space station!

ARGLaser said:
Then there would be no moon :cryyy:

He only covered 1W lasers, I wonder if 2-3W lasers would have any effect. I would also like to know if beam expanders would have any visible effect. It would be interesting to see blue beams everywhere shooting up onto the moon :o
Click to expand...

Even more interesting, would a beam make it into space at 3W's with a appropriately sized beam expander?
 
Yes this was posted in General chat before because the OP was pissed that he was advertising WL. Very nice read though. :)
 
If you are even considering this, do it under the optimum circumstances. The what-if article describes it nicely. In most practical experiments its just not feasible at all.

However, there is the situation of the new moon, and the availability of beam expanders. Combining the two, and using a billion people at the same time, 1 watt green dpss lasers of good quality, and 10:1 beam expanders, it would be possible to create a visible greenish spot on the new moon.

If the moon is even slightly lit by the sun this would probably no longer be visible. We are up against a light source that puts out a whopping 4E+26 watts, a billion billion billion laser pointers. It IS a lot further away and radiates in all directions to we would not even have to get close to that order of magnitude. Putting a visible laser spot on the full moon is, however, still something far beyond what humanity could achieve, even if we dedicated all power generation capacity on earth to attempt it.


So, is that the end of it all?

Not really. There are some retroreflectors left on the moon by the apollo missions, which are still used to do lunar rangefinding experiments today. It would be an enourmous achievement to somehow produce a visible reflection from a retroreflector, even when looking at it using a telescope that would be the size of a bus. Achieving that is a very ambitious goal, but more realistic then 'lets have a billion people point a laser pointer at the moon and see'.

The lunar rangefinding experiments use low divergence beams to operate, and the return signal is basically a countable number of photons per second - not enough to see even with a telescope.
 
Haha even with a 10:1 beam expander, your spot will be so giant that it won't be visible at all :whistle:
 
The problem is mostly that it would not be effective, as educated guesses provided before demonstrate.

If you consider a somewhat more realistic figure like one million people pointing a $100 laser at the moon, there is no chance this will be visible from earth.

Interestingly, this would probably be a pretty spectacular view if you were standing on the moon looking at earth.

I suppose a more realistic experiment would be to have a large number of people point their lasers at the ISS, and receiving live feedback and footage from there. I'm not sure the space agencies would be interested in testing that, and pointing a laser towards the ISS is rather difficult to do since it (usually) cannot be seen by the naked eye, making it very hard to make people point their laser in the right direction despite the exactly known position at a given time.


Having footage from the viewpoint of what you are shining at is paramount though, the difference between that and reflection is enourmous. Consider the flash from a simple compact camera. In darkness, you can see its flash from several miles away (horizon is the limiting factor) if its directed at you, yet that flash is not of any using when trying to take a picture of an object 100 feet away holding that same camera.
 
Sadly, the distance between the surface of the earth and the ISS isn't really that significant, pretty much negligible when compared to the moon's distance...
 
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