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

okay today I have a giant magnifying glass and my five watt burning laser and I'm going to be testing what happens if you try to focus the point of a laser pointer down to an even smaller point will it get even hotter and how small can you get it can you just get an infinitely hot temperature with lasers so first let's see what happens when I try to focus down my 30 mm lemon flashlight into one single point is it possible so in order to do that I want to gather all of this light that's coming off and focus it down to one single point but because the light spreads out like this I have to put my magnifying glass really close to it to capture all of the light but you can see what happens when I put the magnifying glass really close to it it spreads out the light instead of focuses it to a point so in order to focus it to a point I have to move it further away from the lens but as I move it further away from the lens you can see now I'm losing light on the wall on the background wall so I've lost a lot of the light in order to focus it down to a smaller point and you can see what this starts to look like actually it's just a miniature version of the LED lights on the light itself so this is what the LED looks like and that's the picture you saw there so in order to focus this down to a very small point that just means I need to move my flashlight further and further and further away so I'm gonna move it all the way across the room and now you can see I can focus it down to a tiny little spot but now because the flashlights clear across the room I've actually lost most of the light on the wall and only a tiny little bit is making it to the lens and it's focusing it down to a small point and because I've lost so much light that small point is now not brighter than the light itself so the magnifying glass did nothing to brighten the light the dot is never gonna be brighter than the original flashlight itself so this is an important point for a flashlight you can never use a lens to focus the flashlight down to a brighter point than the original source itself so you can never do anything with any combination of lenses you could never make a brighter point then the LED lights on the flashlight itself and the same thing applies when you use them magnifying glass to focus down sunlight to burn things that means that that point of light that you get from a magnifying glass can never make a point that's brighter than the surface of the Sun so no matter how big of lens we ever had on earth no matter what we did we can never focus the sunlight down to get something hotter than the surface of the Sun if I were able to make a point on the ground that's hotter than this source that would mean that I was violating the second law of thermodynamics because that would mean that I'm flowing heat because this is hotter I'm flowing heat from cold to hot so the energy is going from cold to hot but we know that that can't happen it always goes from hot to cold but does that apply to lasers as well well let's check ok so in order to see this I've turned my exposure way down or else you're just gonna see a really bright ball of light and I have it on a black surface here to absorb even more light so we can actually see how big the point is so I have my laser across the room let's turn it on and see how big the point is now okay so you can see it's kind of a line of light now and it's kind of burning the background here now let's see what happens if I stick my lens in front of it whoa I can make a tiny point and it easily burns the background now so you can see the smoke coming off of it it's slightly burning the background here but then as soon as I put my lens in there I can focus it down to a tiny little point and it immediately burns whatever's around it so you can see that it kinda starts to burn the wood here it takes a while for it to burn have to leave it there for a bit because it's far away across the room but now watch what happens when I focus it down it pretty much immediately burns and starts on fire it's awesome it essentially just itches into the wood immediately and you can see that this happens even more powerful than if I had the laser just right up next to it you can see that I still have to leave it there for a bit to even start burning so it seems as though I get my highest temperature when I put my laser really far away essentially so that I get that little tiny laser slit to a single point because I place it far away and so that all of the light coming from the laser is now focused into a very very tiny point and so all of the energy from the laser can be focused to a small point due to the magnifying glass and so you can even get a higher temperature than if you just place your laser directly on the thing you were trying to burn so what's going on here I just told you that it violates the second law of thermodynamics if you are able to focus light down to a point hotter than the source itself but I just did it with a laser so why does that happen but actually with lasers this actually doesn't violate the second law of thermodynamics and the reason may sound a little weird it's because flashlights and the Sun those all have positive temperatures they have very high positive temperatures but lasers actually have a negative temperature let me show you what I mean so negative temperature can only exist in something that has a limited number of states so when something is really cold it means that all of the atoms are in a low energy State if it were absolute zero that would mean every atom is in its lowest energy state and as you heat it up these atoms can pop up to a higher energy state and the hottest you can possibly get is for an equal number of atoms to be in the high and low energy state and when you have something the hottest you can possibly get that means you have an equal number of atoms in the high energy state and the low energy State so the temperature scale actually goes like this it starts at zero Kelvin and then you can get up to some in-between temperature like 500 degrees Kelvin and then as you keep going you can actually get to an infinite temperature as high temperatures you can possibly get where there's an equal number of atoms in the high energy State in the low energy State but you can actually keep going from there and you can actually get more atoms to pop up and be in the high energy State and the only way you can do that is in quantum mechanical based systems like lasers and in that case it goes past positive infinity and then actually the next step is to go to negative infinity Kelvin and then if you keep going from there you could get to negative 500 Kelvin and then if the highest temperature you could possibly get is negative zero Kelvin now this sounds crypt now this sounds crazy to say that the highest temperature you could get is negative zero Kelvin but what this means is actually that negative temperatures are hotter than positive temperatures so focusing any light source that doesn't have a population inversion like a laser so basically anything that's not laser light you can never get a hotter point than the source or you can never get a brighter point than the source itself but for lasers you can get to any temperature you want by focusing it to a smaller and smaller point which is actually pretty cool and because lasers actually have a negative temperature it means that you're still not breaking the second law of thermodynamics that was close hey everybody thanks for watching another episode of the action lab I hope you liked it if you have any questions let me know in the comments section if you haven't subscribed the action lab yet remember to hit the subscribe button and hit the bell to be notified with my latest videos out and head over to the action lab com if you haven't checked it out yet check out my new act lab subscription box thanks for watching and I'll see you next time

Channel: The Action Lab

Views: 5,877,911

Rating: 4.5122032 out of 5

Keywords: laser, focus, magnefying glass, burning laser, fresnel lens, laser beam, negative temeprature, negatibve kelvin, absolute zero, below absolute zero, quantum mechanics, population inversion, negative temperature, vacuum chamber, the action lab, action lab, venus fly trap, hydraulic press, iron man, stretch armstrong, foil ball, vac man, zombie ant, blackest black, how to, science experiment, brightest flashlight, black 2.0, 4th dimension, 32000 lumen

Id: jdjTYlReE-I

Length: 8min 26sec (506 seconds)

Published: Wed Nov 21 2018