You and @puzzlegal really need to watch the MythBusters episodes. As others in this thread keep telling you, what works for a person with one mirror or one magnifying glass in their backyard does not work for multiple people. MythBusters found that they could achieve reasonable focus by taking it in turns with each individual mirror holder bringing their spot to bear so they could tell which spot was theirs, but even with their (relatively) small group this was difficult to organise effectively.
With 10,000 people in the soccer stadium, there is no way that you could achieve the required organisation. There would be so many dancing spots in and around the area of the referee that nobody would be able to tell which spot was theirs, without some sort of aiming device.
And of course, once the referee feels the heat and sees the glare upon him, the first thing he’s going to do is run. At which point everybody has to re-aim. Which would take ages to organise - even assuming it could be organised at all. There is no way it would work.
As with many hard SF stories by Arthur C Clarke and others, he was demonstrating an amusing thought experiment but as a matter of practicality, it could never be done.
Remember the opening to the Beijing Olympics where they had massive numbers of people doing coordinated displays? It’s possible to coordinate massive numbers of people, but I think they rehearsed for the better part of a year for that sort of thing. Which is not what the story was talking about.
Even then, even with a lot of training and rehearsal, it still feels unlikely this would work but at a minimum you’d need that sort of group training. Without that there’s no chance.
10,000 people without rehearsal trying to pull that off? Nope, not going to happen. And that’s what makes the notion unrealistic.
No. It’s not a matter of just organising people to do something in a rehearsed way. At the Beijing Olympics the crowd had to do certain rehearsed moves, at once, at certain times. That is not what is required here.
The only way to aim a mirrored program to shine on the referee is to bring your spot into aim while everyone else holds steady on the target, so that you can tell which is your spot. This means it has to happen serially. It just isn’t practically possible to do this with 10,000 people.
Let’s assume that each person takes 1 second to do their aiming (which is an underestimate), and once aimed the referee stands perfectly still so no re-aiming will be required. It will 2 3/4 hours to line up the 10,000 mirrors. Getting even 120 people’s aim lined up will take two minutes. During which time the referee is noting more and more glare and heat, and he moves. And we are back to square one.
Do any of these plans work if the ref moves around on the field? They don’t seem to work even if the ref stands still.
If the ref doesn’t move and you can get fans on both sides of the stadium involved then a large amount of people could focus on a smaller number of mirrors on the other side which can then concentrate the reflected light onto the stationary ref.
The Indianapolis Speedway where the big race is run every May has a permanent seating capacity of 257,325 so… yes. OK, it’s a “venue” and not a stadium, and the seating is not symmetrical around the track, but the area around the start/finish line is truly immense. But while there might be 50,000+ seat there, the “canyon” effect is sufficient I’m not sure you’d get enough sunlight on the lower levels to pull that sort of trick off.
It’s not just the number of seats, it’s how they’re “stacked”, time of day, weather, and bunch of other factors.
Also, i got a new watch in college, and it had a much shinier crystal than my prior watch. So I’d be sitting in class and notice a spot of sunlight on the wall, that moved around. At first i didn’t realize it was a reflection of my watch. When i did, i started playing with it.
In retrospect, I’m surprised no one ever giggled or otherwise reacted to the spot. I got pretty good at tracking the professor as he moved around the room, and then i returned to just doodling when i was bored.
I think it supports the Clark story. Maybe not “vaporization”, but killing the ref
The test employed 300, 1 foot square, bronze mirror tiles (510 phosphor bronze alloy). The number of mirrors was determined using the first MIT test as a benchmark and accounting for the different mirror material, along with the different conditions in San Francisco.
The tiles were polished using Brasso by the MythBuster and MIT team. The polish was quite high on most mirrors. About 30% of the mirrors had a variety of flatness defects that would reduce their performance to some degree.
The tiles were aimed in a manner similar to the MIT test, with the exception that there were 4 tiers of mirrors instead of just two rows. The mirror array was about 110 feet long, similar to the MIT test. The goal was to make an array that was big enough to start a fire, but small enough to implement within reasonable budgetary and time constraints (my guesstimate is ~3-4 person weeks, mostly spent on polishing the bronze).
They used 300 mirrors, which were bronze, not a modern shiny substance, only 300, not thousands, and they lit the boat on fire. What am i missing?
The missed part: those are mirrors fixed in arrays, i.e. already pre-positioned to focus on a spot.
If those mirrors weren’t fixed in place but held by 300 individual human beings, that would be closer to the short story.
There is not much question that such coordinated focusing could happen in theory. But in practice, getting 300 human beings to focus their mirrors on a single spot like that in a single spot in a very short period of time is exceedingly difficult if not impossible.
ETA: from the MIT site, they weren’t able to do this effectively (partly due to cloud cover) with 80 students on campus but were able to replicate with fixed mirrors. So, they said it was still inconclusive as a “humans holding mirrors” test
They don’t all need to have the right spot at the same time, because many thousands of people. And from my reading of the article, having one guy pre-position all the mirrors was a weakness, not a strength, because it took him so long to do it that the sun moved substantially, and he had to guesstimate the adjustment.
I mean, he went to some trouble to set up a realistic scenario where thousands of trained men could all aim at once. The practical limitations on a hack performed by some college kids are different from the practical limitations of an army at a soccer game.
Won’t help. There are limits to how much you can concentrate light. You want the ref to see an entire section of the stands as looking like the Sun, which means everyone in that section needs to be aiming.
And again, “just look at the spot and adjust it” won’t work as an aiming technique, but there are other aiming techniques that would work. And it’s plausible that an army might have trained and practiced on some of those methods (even if they weren’t training for the purpose of incinerating referees, those same techniques are useful for purposes like signalling).
But if you would actually take on board what people are saying to you - everyone isn’t able to adjust their mirrors all at the same time because they can’t tell which spot is theirs. This point is being made to you over and over again and you’re just ignoring it.
That’s because not being able to see where you are aiming with all those spots is true but irrelevant. I routinely hit a spot where i can’t see the light at all, on a mountain miles away.
You can’t aim by looking at the light on the field, any more than i can aim at the mountain, which is too far away to see any spot. The technique is to aim close to you, where there aren’t lots of other lights, and then figure out how to move the mirror such that the spot moves in a straight line towards the point of interest, and then estimate how far to move it. And sometimes you’ll overshoot or undershoot. But that’s okay, because the thousands of people Clark described are enough to have a lot of redundancy.
I grant that the technique isn’t obvious. Every year i teach new people how to do it, and no one gets it on their first try. But everyone gets it after a couple attempts, because once you get the hang of it it’s not very hard.
