| 1.Intro Ricky Laying down next to a puddle: Check this out, you see this water evaporating, seems simple enough, but why does it evaporate. This has long been a mystery of science, conventional wisdom says its because the suns rays heat the water and cause evaporation. And yes that is true, but its only part of the story. There is a missing piece of our understanding, but scientists at MIT just discovered a new phenomenon they’re calling the photomolecular effect. They discovered that photons from the sun can evaporate water directly, not by heating up water. And this can foundationally change the way we model weather, understand climate patterns and even revolutionize how we desalinate water! How exactly does this work, and what could it mean for the future, let’s figure this out together. I’m ricky and this is two bit da vinci. This is one of the Greatest scientific finds in history, no its not this puddle, but it has everything to do with this puddle. We all know that this will evaporate because of the sun, But the correct question to ask is why does it evaporate. And for a long time the answer was HEAT. sunlight touches the surface of the water heats it up and BOOM.. Evaporation. But Scientists MIT just Figured out that heat Has nothing to do with it. In reality it’s a much more complicated than that. Its a A team of researchers from MIT made a groundbreaking discovery: Light can evaporate water over 4X faster than heat by literally knocking molecules off its surface!This discovery completely changes our understanding of evaporation, and could change desalination, how we dry everything from industrial products to our laundry, and even how we cool our homes.Last time we discovered a similar way light interacted with matter, we developed light sensors, digital cameras, laser printers, L.E.Ds, solar cells, and even fiber optic communications.What will this discovery bring us?Let’s figure this out together.By the end, we’ll also see how this discovery can change our weather models leading to new unsettling forecasts.I’m Ricky, and this is Two Bit da Vinci. |
| 2. Conventional Wisdom About Evaporation Alright, let’s start with the basics. You probably remember from school that evaporation is all about heat:When you heat water, the molecules start moving faster and faster. |
| Eventually, some of them gain enough energy to break free from the surface and become water vapor.This is how puddles dry up, and clothes on a line dry.That process sucks up heat, which is how sweat cools us down. |
| But there’s a limit to how fast this can happen. It’s called the thermal limit, and it’s based on the energy it takes to break the bonds between water molecules.This is known as the latent heat of evaporation. This heat is used to cleave the hydrogen bonds that hold water molecules together.Once those bonds are broken, the molecules can escape as vapor. |
| 3. The Discovery of the Photomolecular EffectNow, here’s where things get really interesting. In a groundbreaking study published in prestigious journals, MIT researchers made a discovery that challenges everything we thought we knew about evaporation. |
| They found that light can directly cause water to evaporate without the need for heat!This is a huge deal, not like those pre-prints about ambient conditions superconductors that turned out to be a scam.The MIT team made very precise measurements and has more than a dozen key pieces of experimental evidence to support their claims.I couldn’t find a single hole in their reasoning. |
| 4. How it worksBut how does it work?It’s similar to the photoelectric effect, which is how Einstein explained how light can knock electrons off of metal surfaces.In the photomolecular effect, photons of light – that is, particles of light – hit the surface of water and transfer their energy to the water molecules.This energy is enough to break the hydrogen bonds and eject clusters of water molecules into the air, even without any heat involved. |
| The researchers measured evaporation rates under optimal conditions that were up to four times higher than the thermal limit.Thermal limit: the highest possible amount of evaporation that can take place for a given input of heat, based on basic physical principles such as the conservation of energy. That limit is 1.4 kg of water /m2hFor the photomolecular effect, experimental evaporation rates were 4 – 7 kg/m2h That means light can evaporate water much faster than heat alone.This is completely counterintuitive and seems to break the laws of thermodynamics, but don’t worry, we’ll address that in a moment.You won’t believe how simple and amazing the researchers’ explanation is. It’s a real Eureka moment! But first, let’s explore some of the implications of this discovery. |
| 4. Potential Implications of the Photomolecular EffectThe photomolecular effect has the potential to completely change our understanding of the planet’s water cycle.If light can evaporate water faster than we thought, that could have a huge impact on everything from cloud formation to rainfall patterns. |
| And think a bout this:The photomolecular effect is similar to the photoelectric effect.Understanding the photoelectric effect led to develop countless technologies we rely on today, like:Light sensorsDigital camerasLaser printersL.E.DsSolar cellsAnd even the fiber optic cables that power the internet.What new wonders will understanding and controlling the photomolecular effect bring? |
| 5. Potential ApplicationsThe potential applications of this discovery are mind-boggling.Imagine desalination plants that use light instead of heat to purify seawater.We could make clean water more accessible and affordableDrying consumes 20% of all industrial energy usage.Picture industrial dryers that work in a fraction of the time, saving energy and resources.Even our everyday lives could be transformed with light-powered dryers for our laundry and dishes.Even new cooling systems for our homes (Il’ll get back to those shortly). |
| 6. Light-Powered Desalinator/DrierLet’s start with light-powered desalination.When you hear about solar desalination, this is probably what you picture.This is called ohotothermal desalination, and it turns light into heat which then evaporates water. |
| But with the photomolecular effect, we can do things differently:We can use light directly to evaporate water, without needing to heat it up first.This would solve several problems with traditional desalination, like:Losing energy as heat to the environment andThe fouling of absorbent surfaces with salt and other contaminants.At least, that’s what these researchers are suggesting. |
| 7. The problem with thermodynamicsBut hold on a second:There’s something that really bothered me about this and that you’re probably wondering too:If light has a certain amount of energy in it, and you need a certain amount of energy to evaporate water, how can we evaporate four times more water with light than with the same amount of energy supplied as heat?Isn’t this breaking the laws of thermodynamics?Where is this extra energy coming from? The answer lies in the way the photomolecular effect works: It doesn’t cleave off one molecule at a time, but entire clusters of water molecules.Each water molecule in liquid water is tied to four other water molecues through hydrogen bonds.To evaporate a single water molecule from the bulk of the water, we have to cut, on average, two hydrogen bonds per molecule (becasue each bond we beak disconnects two water molecules).That’s the amount of energy we have to supply as heat because heat releases individual molecules.But in the photomolecular effect, since photons of light are knocking out entire clusters of molecules, we only have to input the energy to cleave the outermost hydrogen bonds that tie the cluster to the bulk of the water.So, you need less energy! |
| Picture it like this:Imagine you have a large net that represents the network of hydrogen-bonded water molecules in liquid water.You want to shred it into pieces (evaporate it).Thermal evaporation would be like cutting the string on all four sides of each knot to release the individual knots of string (one molecule).What the photomolecular effect does is cut an entire patch of net instead.It’s much quicker, and you use less energy because you have to cut fewer strings.It’s simply brilliant! But to get water vapor, you still need to cut those other strings loose.Where does the energy to do that come from?It took a lot of reading, but I found out.You’ll see in a minute! |
| 8. How Would We Build a Light-Desalination Plant?First, let’s see how we would actually build a machine that works on this principle?What would it look like?I dove deep into both articles from the team at MIT to try t find out.They don’t describe it, but we can make an educated guess based on their results:The effect depends on the color of light and it maximizes at 520 nm, which is green light.It’s also much more efficient when the light is polarized.This means that all the photons’ magnetic and electric fields oscilate in the same plane.The angle also matters, and the highest evaporation rates come from an angle of 45° with respect to the water’s surface. |
| Ok, so let’s put all that into practice:We’d need a source of green light, ideally emitting at or near 520 nanometers.We could use green L.E.Ds or even some types of green diode lasers.We could also filter out green light from sunlight, but that’s not a good idea because we’d lose the rest of the light. |
| Next, we’d need to polarize the light to make it transverse-magnetic, or TM-polarized.This is where things get a little tricky.If we use a regular light source and run it through a linear polarizer, we’d immediately lose 50% the light in an ideal case.In a real case, we would lose more. |
| But I found some clever workarounds:If we use laser diodes, there’s no problem because they naturally emit polarized light.But lasers are very inefficient, usually only 30%50% for very expensive diode lasers.A maximum of 65% under very specific and ideal conditions.Another trick is to use a special kind of birefringent crystal, that splits light into two polarized beams:One in the direction you want (50% of the light).One at a 90° angle (the other 50% of the light).If we then run one of the beams through a device called a Faraday Rotator, we could twist one of the beams by 90° and recombine them, getting a single polarized beam with minimal losses.At least that’s what I came up with after reading up on polarization.There will be losses due to scattering and absorption, but not as high as 50% or more.Pretty cool right? |
| Now, for the water.We’d need to maximize the surface area exposed to the light.We could use thin films of water, or maybe even tiny droplets.And we’d need to control the temperature and airflow to make sure the evaporated water is carried away efficiently. |
| So, would this actually work? Would it be more efficient than other forms of desalination? Well, based on the research, it definitely seems possible. Remember, current desalination technologies only reach about 7 to 16% of the thermodynamic limit. With the photomolecular effect, we could potentially blow past that limit. |
| 9. New Light-Based Cooling DevicesBut wait, there’s more! Remember how I said we’d explain where the extra energy comes from to break up those water clusters? Well, it turns out it comes from the surrounding air. |
| When the light knocks off clusters of water molecules, they collide with air molecules. These collisions break the clusters apart into individual water molecules, and in the process, the air loses some of its heat. So, not only does the photomolecular effect evaporate water faster, but it also cools down the air around it.This opens up a whole new world of possibilities for light-based cooling technologies. Imagine air conditioners that use light instead of refrigerants, or even wearable cooling devices that keep you comfortable on a hot day. The possibilities are endless! |
| 10. The Cloud MysteryNow, let’s take this discovery to the skies. For decades, scientists have been puzzled by a strange phenomenon: clouds and fog seem to absorb more sunlight than they should, based on our understanding of how water interacts with light. This has been a major source of uncertainty in climate models. |
| But the photomolecular effect could finally provide an answer. If light can directly break apart water clusters at the surface, it could also be happening within clouds and fog, leading to increased light absorption. This could explain the mysterious discrepancy and help us refine our climate models. |
| 11. Climate Change ImplicationsSpeaking of climate models, the photomolecular effect could have some pretty significant implications for our understanding of climate change. You see, the rate of evaporation plays a crucial role in the water cycle, which in turn affects weather patterns and long-term climate trends. |
| I recently watched a video by Sabine Hossenfelder where she talks about how our current climate models might be underestimating something called “climate sensitivity,” which is key to forecasting the long-term effects of climate change. The problem seems to be that most models are bad at modeling how cloud cover interacts with sunlight. The ones that model it best suggest that climate sensitivity may be so high that the worst effects of climate change could come about much sooner than anticipated. |
| The photomolecular effect could be the missing piece of the puzzle. By incorporating this new understanding of evaporation into our models, we could get a much clearer picture of what to expect in the future. And let’s be honest, things aren’t looking too good right now, with record-breaking extreme weather events all over the news.So, while the photomolecular effect offers exciting possibilities for new technologies, it also raises some serious questions about the future of our planet. But hey, that’s a topic for another video. |
| If you want to see another mind-blowing way that light can be used to create energy, check out our video on solid-state combustion engines. Thanks for watching, and don’t forget to like and subscribe for more awesome science and engineering content! |
