What Happens if You Focus a 5W Laser With a Giant Magnifying Glass? Negative Kelvin Temperature! 

I see a lot of people are having trouble with this video. First, I am very much aware that the reason the laser it getting hotter when it is magnified is due to the reduced area. That isn't the point of this video. The point is to try to explain why it doesn't break the laws of thermodynamics! Now for the negative kelvin explanation, statistical mechanics tells us that at infinite temperature all atomic states will be populated equally. The Kelvin scale was built upon classical mechanics where it would be impossible to achieve a state in which there are more atoms in a higher state than a lower state. However due to quantum mechanical effects, we know that we can stimulate atoms to be in a higher energy state simply by shining light near them that is at the same wavelength as the light it would emit at that state (stimulated emission). So in a laser, the stimulated atoms actually achieve a population inversion where there are more atoms in a higher energy state than a lower one. This is where the negative temperature comes from. In this case we have to define temperature as negative or else we get into problems that break the second law of thermodynamics. It doesn’t matter that my laser has poor optics. What’s important is that lasers can break the conservation of etendue due to the fact that they have light that doesn’t spread, the reason they have light that doesn’t spread is because of population inversion, and this is why we have to say they have negative temperatures (or they behave as if they have negative kelvin). We can never achieve negative temperature in a non-quantum mechanical system thus anything the laser shines on is always at a positive temperate no matter how hot you get. Of course the reason the laser gets hotter when it’s focused is due to the reduced surface area of the light. That was not my point though. The point of the video was to explain why it doesn’t break the 2nd law of thermodynamics. Please research “conservation of etendue” to understand why you can’t focus a flashlight down to a point that is hotter/brighter than the flashlight surface. This is a very good example of how the second law of thermodynamics can never be broken no matter how hard you try.

If you break thermodynamics, I'm not buying you a new one.

Sweet, now we can finally build that Predator shoulder cannon.

To prevent the flashlight beam from spreading out, you could easily place a fresnel lens in front of the beam to straighten the light into a single direction, then just put the magnifying glass after that to concentrate all the light from the flashlight down to one point.

I google searched "What happens when you point a laser at a crystal ball". I found this and learned so much. Awesome video.

“-0 Kelvin” understandable, have a great day

*”Hotter than infinity”* Other side of the world: Where is this laser coming from?

I plan to view this several more times so I can get a better grasp on this. I heard about the Kelvin temperature scale when I was taking chemistry in university in 1976 and was always fascinated with it.

this man's bravery is so high that he does not even fear an actual fire in his house

I never thought Kelvin could be negative. I mean, he has such a good outlook on life.

Everyone gangsta until 0 has positive and negative forms

Always funny to listen to your explanations - you never miss the opportunity to strangely subvert physics!!!

Literally the best RU-vid channel to be sure you are going to learn something new every single video!

He: "negative temperatures are hotter than positive temperatures" My brain: *Exploding*

Mom: *eat the food its not that hot* The food: *hotter than infinity*

At the start for the flashlight, could you make a mirror tube between the flashlight and the mag glass? yes, some would enter the mag glass at hard angles, beyond the focus ability, but at least all light would enter the mag glass. The longer the tube, the better? maybe a bunch of optic fibers?

Like a venturi for light, concentrating it, is why it gets hotter, like sticking your thumb over a hose and gaining more water pressure... energy behaves the same through every form I've come to realize... nice work

I'm sure I'm not the only one thinking: *Use another magnifying glass*

A flash light emits defused light and so does the sun... \|/ defused light • dot is source A laser is concentrated light. Ideally, we want all the laser rays to be parallel (direct light) ||| direct light • dot is source however when I look at a laser dot ( just how you showed us with laser close and far away) I see the dot get smaller at a distance... That means, the rays aren’t emitting perfectly parallel from the source(laser) but most-likely they are converging a bit. /|\ converging light rays • dot is source now a magnifying glass also converges the light (but much more drastically) depending obviously by the type of lens. so laser plus magnifying glass will look something like this. . -small dot is where the light focuses /|\ -converging lines due to refraction - -horizontal line is magnifying glass ||| -parallel light is laser rays • -big dot is source now we do the same with a diffused light source. o - o is light on wall \ | | | / -some lines refract to parallel - -horizontal line is magnifying glass \|/ -defused light rays from source. • -big dot is source (sun or flashlight) a ‘theatrical spot light’ is kinda like a laser but even though it emits rays more parallel than the flash light, it still does not converge the light rays all on one very small spot like a laser does. now you must also understand what happens when light goes past its focus point i’ll copy the laser diagram and extend the light past the wall. \|/ -rays diffuse past the focus point. x - x is the focus point /|\ -converging rays due to refraction - -horizontal line is magnifying glass ||| -parallel light is laser rays • -big dot is laser source as we see, rays past the focus point will start to diffuse out. I have seen this happen with cheap lasers where the rays aren’t perfectly parallel (the rays converge a bit) when i point the laser at certain distances it it will make different size dots. at point blank the dot is source size at a bit more far, the dot is smaller because the rays are converging closer a bit /|\ if we can find the right distance to find the focus point, thats were will get the smallest spot of light. if we give even more distance and so the light can pass its focus point, then we will see that the laser light will start to diffuse out just like flashlight rays \|/. Becoming practically a red spotlight (if it’s red laser) you will notice this by seeing bigger less intense spots on walls(i did this outside from balcony to distant buildings) at a very far distance the laser light gets so diffused out that the spot totally disappears giving this cheap laser a limited range. good quality lasers will try to emit as best they can (perfectly) parallel lines so that their focus point can be as far away as possible to give them a much better range(not the only reason). lasers aren’t just perfectly parallel rays, they are also very many rays in a very small area(intensity aka concentrated light) and usually the laser has a color because its mostly just one type of light that the laser is shooting. white light is all colors of visible light. on this video i don’t get what you are going on about with negative kelvin etc lasers just focus and concentrate light. A laser ‘BEAM’ is focused and concentrated light! light from the sun or a flash light is drastically dispersed(not concentrated and focused)! that means there are “MORE RAYS” of light hitting a “SINGLE SPOT” with a laser source(i’m ignoring the frequency) than with a flash light or sun source also if what you say is true, then why isn’t your laser hot enough to burn right through your wall in less than a nanosecond, since you say its ‘beyond’ infinite kelvin.. why does it take time to burn the wood? maybe because it not as hot as you claim.. its just many concentrated rays on a smaller spot area than the source area. lets say the source rays is 3 dots ••• (front view of the laser hole) if we focus those rays in a single spot • (view of spot on the wall) thats 3 rays overlapping the ‘same amount of area of just one ray source area. so technically that spot is 3 times hotter than the one spot from the source, but has the same energy of all the 3 source dots added together. now the light coming from the sun is just like many dots emitting light ••• but every dot emits diffused(scattered light) sun surface is made of many ‘dot light sources’ that emit diffused light. like this: \ | / \ | / - • - - • - / | \ / | \ \ | / \ | / - • - - • - / | \ / | \ and the sun at a distance is just considered a dot light source as well. sun: \ | / - O - / | \ like we see stars so the only reason why we see stars even though they are so very far away and emit defused light, is because they are so VERY VERY‘BIG’( the stars)!! the surface of the stars that point at us is SOOOO ‘vast’ that we can consider that light source area to be a flat area light(background from CG 3d lighting), therefore its emitting many (nearly) parallel rays towards us (but not converging rays. they are still diffusing a little) and since none of those rays are focusing, it wont burn anything and even if u did focused those rays that do reach our planet, the amount of rays(intensity)wouldn’t be much because most the rays from that star are lost and dispersed in different direction and so we are only receiving a very very small percentage of that light sources rays. another thing to consider is the angle of attack of the rays with the lens of magnifying glass.

This is the best explanation I have found of laser weapons. Yes, laser weapons are real! 😁

This is an awesome experiment I wish you had an infrared thermometer where you could measure the heat with a infrared temperature gauge gun or whatever and get it focused on after you put the magnifying glass in front.

“The dot is never gonna be brighter than the original flashlight itself” Basically me being compared to my dad.

First I didn't understand anything. Then I thought I understood something. Then I realized i understood even less. Negative learning.

When I have a question about something I tend to lean towards your videos! I praise the fact you're smart enough to do these things about by yourself:) 5hank you always!! And the talk of temperatures will throw a lot of people off, haha but, trust me you made perfects sense to me! Can't wait to watch all the other vids! :) keep up your good work!

That was an excellent video. I learned some things. I never thought about how the 2nd law of thermodynamics pertained to focusing light. Also, I never thought of negative Kelvin temperature before or making a theoretically infinite hot spot with a laser. I'll have to rewatch this video to get a better understanding of this. Thanks. Ed Schultheis, PE Mechanical engineer & manufacturing consultant for 35 years Schultek Engineering & Technology, Inc.

This just sounds like integer overflow, but in real life.

Thanos: *Snaps* *population doubles* Thanos: “Negative Infinity Stones!”

I appreciate the way Action Lab hints about DEWs and the near anti-gravity effects created by rotating spinning wheels, but thus far and no further ... or Action Lab might disappear into thin air.

I'm glad someone had a flashlight like mine. I need a get a new one now though I dropped it in water somewhere in a mud pond and could never find it. Can't wait to learn about cold.

Me: just studied about negative numbers You: -0 exists Me: illegal

the only thing beyond infinity is buzz lightyear

Dang this is cool I used to love setting things on fire as a kid! Awesome vid man

Conservation of energy and thermal dynamics. A splash of entropy, and quantum mechanics! Love this teaching video! Thank you!

In Soviet Russia, negative temperature does no effect to country. Soviet Russia makes temperature feel more negative about itself.

So there is a better way to kill ants

What if you put a cone shaped cover with a hole at the point of the cone,over the flashlight to make the light more focused and then shine it through the magnifying glass?

This is a super cool demonstration, and you've provided an excellent explanation as to why you can't get something hotter than the source with magnifying glasses. Thank you!

My guy, literally calculating a number AFTER infinity itself...

6:51 OK...... SOOK..... tOOK....

I like to render patterns of light in 3D with virtual light transport, it's very beautiful, especially when you make them pass through virtual lenses. I just use free renderers, now (mostly Cycles and luxrender for blender), but I used payware ones before. Anyway, it's fascinating to me. To make it light in 3D with volumes. you can do the same IRL of course, but there isn't a lot of pictures of that, I mean, with smoke and to visualize the complex patterns in a volumetric form.

A smaller point with the same energy will direct more heat per the size, as in, a 1W beam at 10 cm diameter won`t be as hot as 1W at 10mm diameter, because the energy isn`t dispersed over a larger area. Right?

100W laser on a 1cm² area is colder than a 100W laser on 0,1cm² area, but both are 100W is like the 1kg of feathers and 1kg of lead joke, both have the same energy but one is more dense than the other

Can we get more explanation on -Kelvin? I feel like this needs a follow up video to provide more examples of -degrees K and how +infinite wraps around to -infinite.

1:40 if you had a very large magnifying glass or a lens with different optics you could focus all of the light down to a small point that would be brighter than the light the flashlight would be able to light up in the same surface area, as the light from the flashlight alone would be spread over a larger area.

7:15 : SOOK....TOOK - OOK - SOOK - OK! * Ground starts shaking * * negative temperature demon appears *

*styropyro walks in* styropyro: _"Hey."_

This would be great to use in the garden to target weeds or unwanted plants.

To stop the flashlight from spreading out you need a collimating lens then you could focus it to a point but the point would retain the original layout of the LED's in the flashlight since it is not a point source. Not possible to amplify the power, in fact power is lost through the atmosphere and the lens of the magnifying glass but, the power that makes it through is focused on a smaller area. We would call this watts per square inch. 5 watts focused on a 1 inch square area spreads the power out over the entire area, focus it down to 0.001 inch and the average relative power is increased 5000 times.

Not gonna lie. In elementary school, I did this to my Woody doll, like in the movie.

The Action Lab: "And what this means is that negative temperatures are hotter than positive temperatures." Me: steps outside in Wisconsin winter* "such warm. moar physic."

Assuming you had a Gaussian beam with an M^2 of 1, which you don't, you could use a simple waist calculation to determine the focal width based on the lambda and the radius of curvature of your lens.

I was wondering, what if you had a reflective material inside a tube that the bulb was in and had a lense on the other end of the tube? Would that focus the light, would that help out become more bright that it's original source by not letting the light bleed out?

For some reason, my first thought about flashlight/sun was inverse square law, rather than thermodynamics. Where the energy per unit area is based on the distance from the source, and you cannot amplify that energy without putting additional into the output. But, you can use larger area of capture and focus that on a smaller one. That's how parabolic antennas work. In any case, the output will always be a fraction of the source. Lasers have the same problem over large distances.

I am going to make a BFG out of this contraption, Thank you for teaching me this.

There are several LEDs in that flashlight, what you have to do is use one magnifying glass to straighten up the beams so they dont spread out, and then a second one to focus. This will lead to a brighter spot as the light emitted from each LED is focussed on the same spot

Can you explain negative temperatures more, please? I'm a bit confused with negative and minus temperatures.

Good show. Does anyone know why the lazer Aperture opening isn't round

Kelvin is a scale for super subzero temperature. For things like super conducting magnets. Another word for degrees.

I can normally follow what you’re saying in your videos, but this one left me very confused. I would have thought the reason you can focus the laser is just because you can get the whole beam hitting the magnifying glass all at once instead of just a small part of spread out light from the flashlight. This would then have more to do with the optics of the laser compared to the flashlight rather than temperature?

What I got from this video is that the concept/definition of temperature and the Kelvin scale were not designed to work with quantum mechanics and lasers. You basically have to jury rig Kelvin to get it to work, but you also have to deal with nonsensical sounding results like this.

Great video helped me learn a few new things keep up the great work

Action lab: (starts berning something with a laser) Me: alright so how can we make this into a weapon.

temperature going from a high positive value to a high negative value suddenly makes me think of integer overflow in computer science. Obviously not related at all, but it's funny to imagine that you're just overflowing the variable used to hold the temperature for that object.

"Im going to be testing what happens if you try to focus the point of a laser pointer down to an even smaller point" *opens a black hole*

Thanx. I have been looking all over for an explaintion.

I remember stories of birds bursting into flames from that huge mirror project in Spain. If true, how hot would the beam have to be to do that in flight. Instantaneous death by an invisible force. Scary AF.

Everybody gangsta till he uses negative kelvin

Curious to see what would happen if you tried microscope lenses for the magnifying glass.

LEDs and lasers emit light at a single frequency. (In fact, the 5W laser is an LED device.) Because both the flashlight and laser are LED based, both emit light at a single frequency. Each of the flashlight's LED bulbs are actually three individual LEDs in red, green, and blue so that when combined, the light appears white to our eyes. The only real distinction between the two devices is that the laser LED emits light that is coherent. That is, it comes out as a narrow beam. (But the beam disperses the farther it travels, and even at close range, you can see that the beam produces an oblong spot that is larger than the laser's LED.) This results in the laser's power (5W) being concentrated on a tiny area (what appears to be a few square millimeters). So, if you apply optics to the light coming from the 35W LED flashlight so that its light is focused onto a few square millimeters (similar in size to the laser spot), you would actually have MORE power per square millimeter, and would have a device that would produce higher temperatures than the 5W laser. It's all about watts per square inch. If you have a 35W flashlight, and you have the proper optics (i.e., multiple lenses) to focus the energy onto a small point, when the energy concentration is sufficient to cause the temperature to exceed the material's combustion point, you get smoke and fire. It is not about the surface temperature of the source, it's about the energy concentration. In fact, I've done it. You just need the right optics. I've also done it with a good old-fashioned camera strobe flashing through a telephoto lens, properly focused, onto a piece of cloth. Even though the flash lasts for only 1/10,000 of a second, you can cause combustion if the optics are set properly. Frankly, I think the discussion about thermodynamics and positive/negative infinity Kelvin temperatures is completely irrelevant to whether you can cause a fire with a flashlight.

Just change or remove the reflector or use a larger lens that's wider than the beam of the flash light. You can also use multiple lenses or lenses designed specifically for the light source. SOLVED

*Wanna play a dangerous game?* *Take a shot everytime he says point.*

What if I magnify a fleshlight? Does it make it tighter?

thumbnail: the action lab: friendly orbital laser deployed wood plank: enemy orbital laser deployed

I'll probably have to rewind this video to understand but it was good, very good!

For a split second I thought the thumbnail said “Hotter than Tiffany”

The simplest explanation as to why is doesn't break thermodynamics is that thermodynamics has to do with the energy of a system. The system is not your target, it's your target + your environment, i.e. your garage. Lenses don't change the amount of energy the system receives, only the energy the target receives. There's 0 need to bring negative temperatures in this as they're totally irrelevant here.

nice video i've already subscribed... just one question, where i can find that Giant Magnifying Glass and how much does actually magnifies?

Infinite temperature? Pretty sure scientists agree there's a theoretical temperature limit, it cannot go to infinity. And the negative temperature stuff really doesn't make much sense outside of a mathematical interpretation. That's like saying you can have a negative number of apples, or a negative volume.

"Does that (law of thermodynamics) apply to lasers as well?" I'm gonna go out on a limb here and say yes.

ANOTHER ARTICLE;Early ultracold experiments in the 1990s used a technique known as laser cooling to begin probing these effects. "The light exerts a force on the atoms which slows them down to reasonably cold temperatures, around 1 kelvin (minus 272.15 C or minus 457.87 F)," said Christopher Foot, an ultracold physicist at the University of Oxford. "[That's low enough] to see quantum behavior in solids and liquids but for the gases we study, we need 10s of nano-kelvin temperatures to get these quantum effects."

How does it violate the laws of thermodynamics? All you need is a flashlight that can focus the light to a small enough point that it fits in your magnifying glass. They do make brighter flashlights that zoom in so just take several of them and focus all their beams on the magnifying glass

*Hotter than infinity* Hell: *am i a joke to you?*

This guy's blinks per minute is higher than his words per minute.

The temperature scale needs major revision, its a carry over from ones devised centuries ago when all we needed was to determine relative termperatures commonly found on earth that we deal with day to day, not the extremes. Infinite temperatures, -0, -infinity temperatures are a terrible horrible no good _linear_ scale that are just mathematical placeholders for a much better scale that has yet to be introduced.

Light is actually a visible heat and when you focus the light on one point using the magnifying glass 🔎 heat is focused on one point thus become powerful and so it burns some objects 🔥

The dot can be brighter, as the energy is being focused into a smaller area. There is less total energy after focusing, but it can definetly be brighter.

That... didn't explain this to acceptable satisfaction.

what if you used a tube with a reflective coating on the inside at the end of the flashlight. Or will the light still spread?

Amazing young man. I have my grand children watching him.

whats the magnifying glasses zoom? ad where can i get one?

Tiny correction: You actually can't have a temperature of infinite Kelvin because when you add energy into matter (-> in this case heating it up) it's Wavelength becomes smaller and smaller until it eventually reaches the Planck length (the smallest length possible in the universe as for our current understanding) at this point you could add more energy into the system but it would become hotter than absolut hot, also known as "Planck Temperature". We would no longer consider it as temperature because our current models don't apply there.

The laser is a point source which is collimated. This keeps it narrow for an “infinitely” long period. The laser you are using already had a mirror that is giving it a desired beam width. All you are doing is focusing it smaller so more energy is hit that spot. You aren’t creating more energy or heat, but collimating the available energy to a smaller surface area. Reverse inverse square law. Negative temperature has nothing to do with this experiment, you are using higher levels physics incorrectly. Plus the reason you cannot achieve the same temperature as the sun with one source glass as you did is because again of the inverse square law which states the energy over twice the distance from its source is spread over 4 times the area, so you get 1/4th the intensity. By the time it hits earth the energy intensity is super small. You LED light could do more damage if you were able to collimate it using a multi mirror set up to do so. Then from there bring it down to a point source. Just using one magnifying glass doesn’t prove or disprove the statements you made.

Love your videos! Maybe with this one it would have been beneficial to introduce phase coherence?

And also if you applied the same method and put that laser with the magnifying mechanism in the vacuum of space the temperature that would be getting off the that device would be immense

pretty sure you misquoted the 2nd law there when erroneously claiming it's impossible with a normal flashlight. simply get another, closer, lens to collimate the rays before focusing them to a point, and done. the second law doesn't say you're not allowed to build refrigerators. it simply says they don't build themselves. and what you do with a lens is not "increasing temperature" but redistributing its target area. it's still the same energy being impacted on the target, just instead of flooding the room with low energy _per area_ you focus it on a single spot that then gets way more energy _per area_. your laser itself literally proves it's possible to make the target of some radiation "hotter" (= more energetic) than its source: otherwise "pumping" wouldn't be a thing. oh btw the source you quote (apart from the link being 404) literally says "lasers cannot have negative temperature" (because they're not in equilibrium but keep being pumped), while sources _they_ quote say they do, so even they don't seem to be sure. they also don't explain how all of their samples don't immediately go to ±∞K as soon as they allow them to equalize temperatures with the environment. in fact, shouldn't a simple laser pointer's dot have infinite temperature because you have ~+300K in the environment and allow that to equalize with the "negative temperature" in the laser? i think the term might simply be misleading, what you really have here is an "inverted energy distribution" or "negative statistical-entropy-per-delta-energy coefficient", is it not? maybe it shouldn't be called "temperature" if it's... not that :P hey even defining it as a function of *coldness* (thermodynamic beta = 1/kT) makes way more sense. the "temperature" bit really just feels like a desperate attempt by companies like QM to shoehorn an abstract concept such as population inversion back into a "layman's understandable word" but ignoring the facts: a) that's not what that word means in a layman's understanding, and b) it doesn't make much mathematical sense either given beta works way better for all of those calculations. about your own pinned comment i can for some reason not reply to: the second law of thermodynamics says that entropy in an *isolated system left alone* cannot decrease. but when you're pumping electricity through LEDs that you then focus onto some target to heat, that's not that. it's neither isolated, nor being left alone, nor actually entropy decreasing (you're simply converting electrical energy in the battery/power plant/whatever into kinetic energy in the target, actually *increasing* overall entropy. btw if you look at the actual complete system like that, you'll of course find that your target can't receive more energy than your electrical power source provided, satisfying the 2nd law). pretty sure that's what the QM folk mean by "pumping doesn't count": technically you're dealing with population inversion and all that in a part of your overall system, but not in an isolated system doing that "naturally".

In this home we follow the rules of thermodynamics

Try reversing a manual SLR camera lens with the flashlight. It might reduce the light if the lens is backwards, try difference focal lengths.

ya gotta do the split light wave experiment..Don't know how but it would be cool to see.

Where are u late af squad