Catch up on stories from the past week (and beyond) at the Slashdot story archive

 



Forgot your password?
typodupeerror
×
Canada Idle

13-Year-Old Wins Science Fair with 'Death Ray' Experiment. Sort of... (cnn.com) 83

It was an idea first proposed by Archimedes, reports CNN. But now, "Brenden Sener, 13, of London, Ontario, has won two gold medals and a London Public Library award for his minuscule version of the contraption — a supposed war weapon made up of a large array of mirrors designed to focus and aim sunlight on a target, such as a ship, and cause combustion — according to a paper published in the January issue of the Canadian Science Fair Journal." For his 2022 science project, Sener recreated the Archimedes screw, a device for raising and moving water. But he didn't stop there. Sener found the death ray to be one of the more intriguing devices — sometimes referred to as the heat ray. Historical writings suggested that Archimedes used "burning mirrors" to start anchored ships on fire during the siege of Syracuse from 214 to 212 BC...

There is no archaeological evidence that the contraption existed, as Sener noted in his paper, but many have tried to recreate the mechanism to see if the ancient invention could be feasible. In Sener's attempt at the ray, he set up a heating lamp facing four small concave mirrors, each tilted to direct light at a piece of cardboard with an X marked at the focal point. In this project he designed for the 2023 Matthews Hall Annual Science Fair, Sener hypothesized that as the mirrors focused light energy onto the cardboard, the temperature of the target would increase with each mirror added.

In his experiment, Sener conducted three trials with two different light bulb wattages, 50 watts and 100 watts. Each additional mirror increased the temperature notably, he found... The temperature of the cardboard with just the heating lamp and the 100-watt light bulb and no mirrors was about 81 degrees Fahrenheit (27.2 degrees Celsius). After waiting for the cardboard to cool, Sener added one mirror and retested. The focal point's temperature increased to almost 95 F (34.9 C), he found. The greatest increase occurred with the addition of the fourth mirror. The temperature with three mirrors aimed at the target was almost 110 F (43.4 C), but the addition of a fourth mirror increased the temperature by about 18 F (10 C) to 128 F (53.5 C)...

Sener was not attempting to light anything on fire, as "a heating lamp does not generate anywhere near enough heat as the sun would," he said. But he believes that with the use of the sun's rays and a larger mirror, "the temperature would increase even more drastically and at a faster rate" and "would easily cause combustion."

The powerful weapon wouldn't work on cloudy days, Sener's paper points out, and even a moving ship might diminish its impact.

But in an interview with CNN, Sener calls Archimedes' death ray "a neat idea".
This discussion has been archived. No new comments can be posted.

13-Year-Old Wins Science Fair with 'Death Ray' Experiment. Sort of...

Comments Filter:
  • How would he aim it? How did Archimedes?

    • Look into safety signalling mirrors. Or look here: https://outdoors.stackexchange... [stackexchange.com]

      TL;DR: you put a small hole in the mirror and learn some geometry.

      • I don't think Archimedes had a retroreflector. But aiming a reflection of sunlight at something nearby isn't hard. If I were building a medieval solar death ray I'd aim several large mirrors at a central mirror and use the "targeting mirror" to aim all the reflections at the target.

        • You don't need a retroreflector. A retroreflector makes it easy, but the lack of one does not make it impossible.

    • by ls671 ( 1122017 )

      Kids these days!

      I remember vaporizing ants and setting paper on fire with a magnifying glass as a kid! We would aim by rotating the magnifying glass...

      • But you need several of them, aimed at the same spot, with moving targets.

        • by guruevi ( 827432 )

          The moving targets is a problem, but a single magnifying glass (if it remains focused), even a cheap/poorly made one, can set wood on fire.

          The problem with Archimedes' boats is that they are moving and that any such weaponry would be at the time a very expensive and very easy target. I don't doubt that someone like Archimedes ever made a mirror-based 'death' ray, they knew how to make mirrors and lenses, but it wasn't practical as a weapon.

          • Well, if one worked, surely if they used several and agreed on the focal point, it may he been practical.

            • by guruevi ( 827432 )

              Again, there are two sides to a war. Large mirrors are expensive today, back then they would be even more expensive, the system would've been unproven. And any setup between systems would require lots of coordination and at large distance the effectiveness drops significantly.

              At the ranges any of these setups become effective, an arrow with an incendiary attached would've been more effective.

              • I don't know, arrows only go a short distance, and are even harder to aim, and require time to hit the target, allowing it to move. Maybe the mirrors were used more as a way to blind and their use was exaggerated over time.

  • Given enough mirrors, of course. Discuss.

    • Nope. There is apparently a rule of optics that is some variant of conservation of energy that says you can't use lenses to concentrate the light energy to be denser than the source. I tried to understand it, but it goes against my 'common sense'. I still trust the people who understand it to have it right.

      The surface of the Moon in full Sun only reaches about 120C, which is enough to cook a person (slowly), but not to ignite the unprotected flammable materials commonly found around people. To start a w

      • Sun and moon are about the same size as seen from earth (same angular diameter), so it's possible to focus their light the same way. You can clearly focus enough sunlight to light stuff on fire, and it doesn't take that big of a mirror. I don't think the argument holds water.

        The other argument is false because the Moon doesn't emit light. It reflects sunlight. You would be focusing sunlight, just less of it.

        • You can argue it all you want, but you're wrong.

          • Starting a fire with a magnifying glass is a childhood rite of passage. In the large scale there are solar furnaces. https://en.m.wikipedia.org/wik... [wikipedia.org] I'm not sure what you are talking about. In the historic practical sense, Mythbusters proved it impossible only because a ship is constantly moving.
          • I missed the moonlight comment. Ignore my comment about the magnifying glass.
          • It seems to me that based on your argument, starting a fire with a mirror or a lens (or combinations of mirrors and lenses) must always be impossible, since the surface of the mirror/lens isn't very hot. The moon is simply a bad mirror.

            • It's not my argument. It's not even AN argument. It's optics/physics.

              But mirrors and lens aren't light sources, they alter the path of existing light. The Moon in this though experiment counts as a source because it substantially alters the sunlight - absorbing a lot of it and scattering more.

              Lenses and mirrors aren't perfect, but for this case they're close enough that the spherical cow treatment doesn't introduce significant error.

      • it goes against my 'common sense'.

        It shouldn't.

        The sun is not a point source of light, and sunlight is not colinear, columnar, or even uniformly radial. It is close to random blackbody radiation spread over the visible disk.

        If you are imagining a way to concentrate the light onto an area smaller than the source, you are making some incorrect assumptions about the characteristics of sunlight.

        Of course, if you could concentrate sunlight to a higher temperature than the source, you would have a big whopping violation of the 2nd law of thermody

        • by Arnonyrnous Covvard ( 7286638 ) on Saturday March 09, 2024 @04:58PM (#64303133)

          It is not necessary to concentrate sunlight to a higher temperature than the source. The sun is plenty hot for lighting stuff on fire.

          • Solar Two near Barstow, California used an array of mirrors to focus sunlight onto a tower, with molten salt thermal storage at 565 C.
        • by NotInKansas ( 5367383 ) on Saturday March 09, 2024 @09:27PM (#64303479)
          Classic Optics does indeed show that you can't concentrate light to a higher intensity than the source, but it's unrelated to thermodynamics and has an implicit assumption that can be avoided. The assumption is "imaging optics". If you are working with "non-imaging" light concentrators, the optics equations no longer apply. The very term "focusing" no longer applies because it is in reference to imaging, although centralized concentrations might casually be called a focus albeit technically incorrect. The other casual reference to the second law of thermodynamics incorrectly confuses heat capacity with temperature. You certainly can concentrated temperature to a higher level than the source over a lesser area in the case of light or a lesser volume in the case of a heat pump. Temperature is not the same as energy, just like concentrating an input force into a much smaller area can produce a greater force over the limited area but it's not more energy so no violation of physics.
      • The rule is that the best you can do for focusing would be like putting the target "inside" the source. For example, you can't focus the infrared emissions of a room at 20 C to heat a target hotter than 20 C (and then run a heat engine to extract energy), at best you could have it so all sides of your target "see" a reflection of a wall of the room. And if you tried to focus the dark portion of the moon you'd get a similar result.

        But the portion of the moon lit by sunlight is reflections of the sun. With a

      • As the target approaches the temperature of the heat source, the two will eventually reach equilibrium. If the target somehow got hotter than the source, then the balance of energy would be flowing the other way.
      • by ceoyoyo ( 59147 )

        That sounds like the conservation of etendue, which is poorly understood, especially by most people making claims about what it says. It's definitely not a variation of conservation of energy. It has nothing to do with energy at all, except that it's only valid if power is conserved. It's just a simple statement about geometry.

        More generally, what do you mean "denser than the source?" The source of the light from the moon is the sun, which is quite sufficient to light things on fire.

        • The source of light from the Moon is the Sun, but that doesn't make moonlight into sunlight. The Moon is far from a perfect mirror for this case, in either reflectivity or flatness.

          You may have noticed moonlight is far dimmer than sunlight. That REALLY should have been a huge clue for you.

          • by ceoyoyo ( 59147 )

            No need to get snippy. The question is much more subtle than "there's this conservation law I don't understand that says so."

            The effective temperature of moonlight is pretty close to sunlight because the vast majority of moonlight is sunlight. The thermodynamic argument says that you can't make something hotter than the source of the light you're using, but the source of the light is the sun, which has a temperature that is plenty high. The intensity is less, but intensity doesn't have much to do with the t

            • Once you make the moon the intermediary for the sunlight, the moon becomes the source for the thermodynamic argument. The temperature of the moon's surface is encoded into the frequencies of light that emit from it. The fact that the light 'carries' temperature is because it is communicating the information about the frequency of the source. It will always result in a lower temperature at the target, regardless of focus. If you focus all the 100% of light of the moon with a perfect lens, and don't have an

              • by ceoyoyo ( 59147 )

                The thermodynamic argument is invalid because the surface of the moon isn't in thermodynamic equilibrium. That doesn't mean thermodynamics doesn't apply, but it does mean you can't just say, oh, temperature of the moon, best you can do.

                Otherwise you couldn't build solar concentrators, because the mirrors in those things aren't at anywhere near the temperature you get at the focus. You couldn't burn ants with a magnifying glass either, because the temperature of the lens would be "encoded into the frequencie

      • by Anonymous Coward

        >I still trust the people who understand it to have it right.
        >The surface of the Moon in full Sun only reaches about 120C, which is enough to cook a person (slowly), but not to ignite the unprotected flammable materials commonly found around people. To start a wood fire you'd need more than twice that.
        I'm guessing you saw it from xkcd who used faulty reasoning to argue his point.
        The faulty reasoning is that 120C is the "limit" due to the temperature at the surface at the moon, because the argument ign

        • by Anonymous Coward
          This. The argument is backwards, because the portion of the energy that heats the moon surface to 120C is the portion of energy lost (converted to heat, duh). It's the rest of the light that's reflected. Unfortunately, the reflection is probably pretty diffuse overall (ie. reflected in random directions), so capturing (and perhaps focusing) enough of the reflected energy is the real problem and whatever other considerations might apply are probably negligible in comparison.
      • Uh, we set paper on fire back in jr. high with a magnifying glass. It's rather easy with good strong sun and a half-decent magnifier.

        A youtube video of somebody doing it:
        https://www.youtube.com/watch?... [youtube.com]

        Wikihow instructions:
        https://www.wikihow.com/Create... [wikihow.com]

        It's on the list for boy scouts creating fires:
        https://www.boyscouttrail.com/... [boyscouttrail.com]

        Solar power towers reach 500C with just reflected light:
        https://en.wikipedia.org/wiki/... [wikipedia.org]

        Of course, you only need 451F (thanks Ray Bradbury!) or 233C to light paper on fire.
        (

        • You might want to look at the title of what you just posted and contrast it to the content of your post.

          • You have a point, but the original was really written badly, and I tend to ignore titles anyways.

            I believe that you could still do it, you'd just need a very, very big concentrator.

      • Probably just Gauss's Law applied to optics, but since the mood is far from a point source the trivial understanding doesn't apply here. Moonlight power density is around 0.0034 Watts/m^2, so to get to the power required to start a fire you'd need to focus around 100m^2 of flat mirrors at the same spot. For parabolic mirrors I'm sure there are multiple reasons you'd need a relatively large mirror, including quantum effects, but it could be much smaller.
      • You're misunderstanding the thermodynamics/optics a bit. You can't focus the black-body radiation from an object to heat something hotter than the object, but the Moon *isn't* a black-body. The moon, in fact, emits no visible light whatsoever (it doesn't get hot enough). The Moon reflects sunlight, so just as reflected light from a mirror can get an object hotter than the mirror, moonlight can heat objects hotter than the moon. How hot I don't know (because the thermodynamics of optics is really complex), c
        • Once you make the moon the intermediary for the sunlight, you now have to consider the moon as the source for the thermodynamic argument. The temperature of the moon's surface is encoded into the frequencies of light that emit from it. The fact that the light 'carries' temperature is because it is communicating the information about the frequency of the source. It will always result in a lower temperature at the target, regardless of focus. If you focus all the 100% of light of the moon with a perfect le

          • Once you make the moon the intermediary for the sunlight, you now have to consider the moon as the source for the thermodynamic argument.

            No, you don't. Otherwise light reflected from a mirror wouldn't be able to make an object hotter than the mirror, which is obviously wrong. Technically speaking the constraint is more than just the frequency of the light: for example, a laser has "negative" thermodynamic temperature, which means a laser beam can heat an object to an infinitely high temperature (theoretically), despite being, for e.g. an infrared laser (although since the object you're heating up tends to radiate energy as it's temperature t

    • Unlikely. At scale, Archimedes idea was somewhat dubious. However, I could see it being somewhat annoying to the boats, and at the time, cause them to flee.

      The limitation is the focusing at range. There are a bunch of secondary optical factors that make it quite difficult. Archimedes likely made his contraption with flexible metal pieces, which would permit a limited amount of focusing. There is also the issue of the focus point of IR light is usually slightly different than the focus point of visible

      • Let's assume you have computer controlled mirrors and can perfectly overlay as many images of the moon as you want.

        • We managed to create a building [nbcnews.com] capable of melting cars and setting other buildings on fire by accident.

          If you hook up a variant of the system used to correct large earthbound telescope mirrors, with big enough mirrors you should be able to burn not only sails, but satellites in orbit.

  • by Baron_Yam ( 643147 ) on Saturday March 09, 2024 @04:14PM (#64303017)

    With better mirrors than Archimedes had, on a close ship, with no archers attacking... they made a tiny hole and some smoke over the course of two hours.

    It's a great idea, but the efficacy is so poor it would be a waste of time when you could fire flaming stuff out of a catapult or from an archer's bow much, much more effectively.

    On the other hand, if you had some soldiers tasked with flashing those mirrors back and forth along the decks of those ships to blind the sailor and possibly archers onboard, maybe that would have been worth something.

    • I never understood why no one has tried setting sails on fire. Would be almost as devastating and much easier in many cases. Are we absolutely sure the claim was that they would set the wooden deck or sides on fire?

      • Easier in terms of the sails having an ignition point perhaps 100C lower, but then again they'd also likely be a light tan colour while the hull would be black or perhaps painted a dark red. They'd reflect more energy away and be more difficult to transfer heat to them as a result.

        Beyond that, sails flutter, meaning you'd have an even tougher task focusing on one bit of material to get it to catch fire.

      • If it would set something on fire, I would definitely aim for the sails. They are much more likely to be dry cotton sheets, easy to ignite. A wet piece of wood is very difficult to ignite.

        In practice, they probably pointed it at the sailors to confuse them / blind them / make them hot. I think at the time they used oar driven ships with limited ability to properly sail (the rudder hadn't been invented yet.)

        • I think at the time they used oar driven ships with limited ability to properly sail (the rudder hadn't been invented yet.)

          They may not have had rudders, but they did have steering oars with one on each side. However, back then warships were galleys and part of preparing for combat was not only lowering the sails, the masts themselves were unshipped. That meant that the man steering the ship didn't have to take the wind into account.
        • Just thought of another tactic. Use the solar mirrors to confuse the sailors, and then send fire ships [wikipedia.org] after the boats. That has been known to work. [wikipedia.org] Fire ships were also in use at the time. [wikipedia.org]

          Leave it to history tell a different story than what happened ...

          • Or have the Russians pass around disinformation about the lethality of the "death rayz" and use them to panic the crews or influence the ships to move away while you attack by other means.

            I believe similar tactics have been used in other wars

          • Using the light to blind and confuse the sailors makes a lot of sense. People tend to forget that information can be very powerful in combat. Gaining it, preventing the enemy from getting it, etc...

            If you shine a nice bright light on the sailors, coming from your harbor area, you could indeed create a situation where they can't properly see your fire ships, allowing them to make proper contact without the galleys dodging or otherwise taking action to prevent it.

        • by Velocir ( 851555 )
          Archimedes apparently used this method against the Romans, who at the time (~212BC) were using linen and hemp, not cotton
    • by Kisai ( 213879 )

      We know the "mirror death ray" exists because one exists
      https://www.businessinsider.com/the-vdara-death-ray-hotel-is-still-burning-people-in-las-vegas-2016-6

    • When you look carefully at the MIT and Mythbusters experiments, MIT was able to ignite a "boat" model on the roof of an MIT building, but not in a test at Mythbusters in San Francisco. https://web.mit.edu/2.009_gall... [mit.edu] The MIT team said the "boat" used in the San Francisco test was too wet to ignite. The same thing happened in previous tests; sometimes it worked, sometimes it didn't. The bottom line is that the experimental conditions are not consistent between tests, so we can't say if it works or not bec
    • by tragedy ( 27079 ) on Saturday March 09, 2024 @11:26PM (#64303605)

      Mythbusters, while a neat show, had a tendency to jump to conclusions based on insufficient data. One of their biggest problems was testing skills that might take a decade to master after about a day of training and concluding that they were impossible. One episode I remember, they wanted to test to see if it would be possible for someone to catch a sword between their hands like in a kung fu movie. So they built a hand clapping machine that clapped two flappy hands made of ballistic gel together and tried to catch a sword with it. Substituting something that was supposed to be a carefully coordinated set of highly-trained, careful movements with an extremely crude, unwieldy machine. Naturally the result was myth busted. That's not to say that catching a sword blade would in any way be a practical combat move, but it's at least blatantly obvious that someone attempting to do it would try to match the motion of their hands to the motion of the sword blade, which their device obviously did not do.
      The same applies to their two episodes on the death ray. They "busted" it once, then tried again due to deficiencies in their original experiment. For the second one they had a whole classroom of students helping them aim mirror shields and they developed a technique for aiming. Still though, those students ultimately only had a few hours of training. Not to mention that the mirror shields they used did not go through any process of refinement to make them better suited to the purpose.
      For an actual military weapon, soldiers would have drilled day after day, week after week until they could pick up their shields and aim at a common target almost perfectly in a few seconds. The shields would have been refined to best concentrate the light at the appropriate range. There might have even been different selections of mirror shields for different ranges, or different techniques developed for getting better concentration of light at arbitrary range. The Mythbusters episodes did none of that.
      You pointed out that it might be better to fire stuff out of a catapult or from an archer's bow rather than use such a system, but that ignores the fact that decent archers or catapult operators get lots of practice. Have you ever seen anyone try to use a bow on their first day? Sure, some people might have an instant talent for it, but if you just grab a bunch of school kids and hand them bows and arrows, you will not get good results. If you used the same methods the Mythbusters used to "bust" the death ray, you would have to conclude that it was a "busted myth" that archery was ever used effectively in warfare after watching them try to fire hundreds of arrows and fail to hit or even reach a ship 200 meters offshore.
      I am reminded of a piece in some educational magazine I had in class as a child that "explained" why dragons would not be able to fly. It used a wing surface area argument and pointed out that a dragon with certain characteristics would not be able to generate downward thrust equal to its body weight. At the time, it seemed very wrong to me. For one thing there was the whole chain of assumptions about weight, material strength, muscle strength, etc. but also, even though I did not know much about aerodynamics at the time, it was intuitively obvious that thrust doesn't need to exceed weight in order to fly. It seemed obvious from seeing things glide. If no thrust was required to glide, then staying aloft should just require the difference between gliding and level flight, not full thrust. So, it was clear that they had just contrived a set of parameters and rules that would lead to their conclusion rather than carefully considering their model. That's not to say that I believed in flying dragons, it was just obvious that their model was garbage.
      All that said, it does not mean that the solar death ray would have been a practical weapon, or that it even ever really existed. It's just to say that the "proof" offered by Mythbusters was insufficient.

      • Some of this is sort of true-ish but it ignores a lot of stuff on the other side of the equation, too. The most prominent is that the best mirror available to Archimedes was almost certainly a sheet of burnished bronze. He definitely didn't have modern silvered-glass mirrors; the process for making clear glass was not discovered for well over 300 years after his death. If it's touch-and-go doing it with modern mirrors, it's not possible with ancient ones.

        I think that your discussion of dragons is also ba

        • by tragedy ( 27079 )

          Some of this is sort of true-ish but it ignores a lot of stuff on the other side of the equation, too. The most prominent is that the best mirror available to Archimedes was almost certainly a sheet of burnished bronze. He definitely didn't have modern silvered-glass mirrors; the process for making clear glass was not discovered for well over 300 years after his death. If it's touch-and-go doing it with modern mirrors, it's not possible with ancient ones.

          Firstly, it's an assumption that bronze mirrors were the best available to Archimedes. Since well before Archimedes, people have been making mirrors out of polished metal. Yes, usually bronze, but other metals were available. Notably silver, which is very nearly as reflective as aluminum (and is notably _more_ reflective in infrared ranges). The obstacle for silver was obviously the cost, but, although modern silver plating did not exist, silver leaf did. While applied silver leaf would not be an ideal surf

  • As an infant, his family probably just stayed at the Vdara in Vegas [knpr.org] and the concept burned into his mind.

    I'll see myself out...

  • by 93 Escort Wagon ( 326346 ) on Saturday March 09, 2024 @04:55PM (#64303131)

    Where did the kid find 50- and 100-watt bulbs in this day and age?

  • for showing how to burn ants with a magnifying glass!

  • In another life, many moons ago, I came across some papers from the 50s and 60s describing 20ft diameter solar concentrators meant to heat samples to 6000 degrees for chemistry experiments.

    This kid's a piker.

  • In the US, he'd have been sued under DMCA 1201 for reverse-engineering Archimedes' invention, then he's have been arrested and send to jail without trial for terrorism.

  • by rbrander ( 73222 ) on Saturday March 09, 2024 @09:30PM (#64303483) Homepage

    "A Slight Case of Sunstroke", 1958, collected in "Tales of Ten Worlds", now available at used bookstores everywhere.

    The semicircular north end of a Latin American football arena is filled with soldiers given special-Army/Navy match souvenir programmes with a shiny foil backing, two feet square. Cardboard, so they can be used for fanning in the scorching sunny day. When the ref makes an unwelcome call for Army, all 10,000 flash their programmes at him, thinking he'll be blinded and replaced. Instead, he's vapourized, to everybody's embarrassment.

  • Now he'll just have to fill a house with popcorn kernels and o pop them all.
  • So this is what goes for science in Canada these days eh? Don't think they'll be getting invited to Regeneron Science Talent Search (Formerly the Intel International Science fair - and Westinghouse talent search) any time soon - where actual science and engineering is highlighted. Duplicating 2000+ year old tech isn't science, it's history. Is N. America turning so freaking stupid they don't know what real science is?

  • The real question is how would you mount frikkin mirrors onto sharks?
  • by nukenerd ( 172703 ) on Sunday March 10, 2024 @05:45AM (#64303883)
    Scaramanga, the Man with the Golden gun, claims prior art.
  • This myth was extensively explored in a much larger experiment by Mythbusters back in the day, employing an entire middle school's population to wield the mirrors, with quite disappointing results. I think I'll go with their findings, when it comes to the next naval battle I'm involved in.
  • The post and some commenters refer to moving targets as a problem. Archimedes was concerned with the defense of Syracuse. In that situation, the attacking ships would mostly be stationary, and if approaching, would generally not be maneuvering but heading toward the defenders, meaning that there would be only one degree of freedom in their position and that, since their speed would likely be fairly constant, it would be possible to lead them. Aiming the heat ray would therefore not be a big issue in the sit
  • Live Free or Die?

"jackpot: you may have an unneccessary change record" -- message from "diff"

Working...