At 2:17 and 2:23 I accidentally say it backwards. I should have said the faster I spin it *the shorter* the focal length not longer. Shorter focal lengths give the wide angle view.
Glass: "Am liquid" Gallium: "Yeah, but yur too thicc" Glass: **sigh** "I feel invisible sometimes" Gallium: "Need a hug?" Mercury: "Ew. Get a room." And that, children, is why gallium coats glass and mercury is toxic.
Also, formula on 3:28 is wrong!!! Always, check your intuition. I know, you just c/p from wikipedia, but it is also wrong there. Much more intuitive is this: *Correspondingly, the dimensions of a symmetrical paraboloidal dish are related by the equation: 4FD=R^2 (therefore F=R^2/(4D)), where F is the focal length, D is the depth of the dish (measured along the axis of symmetry from the vertex to the plane of the rim), and R is the radius of the dish from the center.* BTW, I really like your channel!!!
I visited the mirror making lab at the University of Arizona and they actually use this exact technique to speed up the manufacturing process. They pour liquid glass into a rotating mold, and as the glass cools it forms a more or less perfect parabola. They then use traditional sanding techniques to grind out any imperfections until the mirror is basically perfect
I was about to ask why they don't just rotate a hot liquid metal/glass until it cools and hardens to make large mirrors, but I guess they actually do, cool!
Genius idea. Though that makes me wonder, they probably need the glass to be uniform thickness, so while they're spinning the thing to shape it, they need a mould under it which is equally perfect... How do they make that? Same process but with a different material?
@@redryder3721 Nah, they just need it to be close enough because they compensate for thermal expansion by making it a little bit thicker that way they won't have to make a perfect parabolic mold.
This principle has revolutionized the production of very large telescope mirrors. Most 8-meter mirrors (that's huge professional-size) are made by rotating the furnace with the molten glass and slowly cooling it down. The mirror blank then solidifies into a paraboloid. It still needs some grinding, but the process is many times cheaper than traditional methods. One quibble: faster rotation results in a shorter focal length, not a longer one.
There is a similar technology called liquid lenses. There you have two transparent oils with different refractive index in an electric field, and based on the voltage the interface between the two oils bends differently and acts like a lens. This was used in some early autofocus webcams back in the day.
I used this technique with epoxy resin to make a parabolic reflector for a microphone. The surface finish was not good enough for optical work but at audio frequencies it is perfect. Much like radio telescopes do not need optical finishes. Great channel!
Sooo jealous of the fact kids of today get to have this guy be a thing! The content he covers, as well as the simplistic yet somehow still extremely informative without being dumbed-down method in which he presents it, is all very captivating and attention-grabbing. Give this guy a catchy stage name and a show on PBS, he could easily be this generation's Bill Nye-Already is, if you ask me. Not that he could ever replace Mr. Nye, but it would've been killer to see these things when I was a kid. *Bursts into room* "MOM, WE NEED SOME GALLIUM!" My fingers are crossed that I can get my son or daughter into this channel.
When I was in grade 6, I spent my whole day as a kid watching these kinds of videos but I haven't watched content creators like him, backyardscientist, etc.
"Bill, Bill... " Always knew I would be educated while the teacher had the moment off. Definitely suggest ActionLab to my sister for educational purposes for her children.
@@JasonMitchellofcompsci I don't know for sure, but since there is no flow going on, just stationary liquid, the force alone would *probably* make any dust that's floating on the surface to slowly float away to the edge. At least that's my hypothesis :)
Dust being lighter than liquid metal would tend to collect in the center and not the edge. Oxides would move outward if they are denser than the base metal.
I'm kind of curious if you could spin up your liquid telescope up to speed and get it to the right shape and then flash freeze it so you can then point it at other directions?
What if the liquid was made in layers, each one made separately? This would prevent the imperfection of expansion and shrinking. Also, you could make the layers and cover it afterwards, so the surface would always remain shiny, even when the base material isn't suitable.
Rather than freezing a spinning liquid metal, we might as well use a concave mirror made out of a metal like Stainless Steel, which I guess would technically be a frozen liquid metal 😂
The simplicity of explaining the complexity of scientific theories is what drives me towards this channel. Keeps the science kid in us alive even at my age. Thanks to the team at Action Lab.
After reading about liquid metal telescopes in a science magazine about 40 yrs ago, I obtained and kept a 10 lb bottle of mercury around hoping to one day build one. As I got older, my sense of responsibility outpaced my scientific ambitions and I took it to a mercury recycling center.
This is super cool! I understand how it is simpler for this to be pointed straight up, but it would be really cool to see how it would look if you were able to put this in some ‘hypothetical’ centrifugal device, so that with a slow motion camera, and some clever stabilization, editing, it would be pretty cool to see if that could work.
@@VikingTeddy gravity is why the liquid doesn't fly away. It's still a mirror if it's sloshing around in the air, but not a very useful one. Liquid metal in space would tend to form wobbly globules...like the thick stuff inside a lava lamp, but reflective. As for the ideas to put the turntable on a turntable, you get uneven surfaces due to compound rotation, blurry (smeared) images of the moving target, or both. Photo exposures are fast OR crisp. It's very hard to get both. This is part of why movie footage and slow-motion is so heavily edited. Trying to do astronomy or see anything scientifically useful with this setup while inside a centrifuge would be a very expensive way to get blurry, streaked images. Cool effects...maybe? James says they _have_ to be pointed straight up...because they really do.
I've never thought about the difference between lenses and mirrors before, but you're right. Light should reflect the same regardless of the wavelength, while different wavelengths refract differently.
How about try to make a Liquid Mersenne-Cassegrain Telescope with mercury, glycerol and potassium? Just put the liquids in a recipient with a circular wall at the center and rotate. The mercury stays in the bottom with a parabolic shape and potassium (63.5°C) stays on top of the glycerol with a parabolic shape with different focus lenght because of the different densities of the materials and the gradient of the rotation with respect to the depth of the reflective surfaces. I had this idea with two telescopes, the liquid-mirror telescope and the monolithic telescope.
Great video! Actually I knew about the parabolic shape of spinning fluids from my old text book in fluid dynamics, but that they in fact used this phenomenon in telescopes was amazing! Thanks for great video and explanation, keep up the good work! 🤓
small correction for 1:28 and 3:27: little g is the acceleration due to gravity, which is about 9.8 m/s^2 on Earth's surface. Big G is the gravitational constant, which is not used in either formula.
Could you build a mirror like that using a low melting point metal, spinning it while in liquid state and then retire the heat source while still spinning, so it can retain the shape? Then you can coat that with any silvery sustance to make it reflective, just like mirrors are built out of regular glass.
Yeah for a low cost diy mirror you can probably use wax and then use electrolysis to nickel-chrome coat it. I wonder how well it would compare to a bought mirror. But you can control the temperature fairly well with an inexpensive heater in a closed room, bring the room to 40-45C and then pour the molten wax, then just let the room cool down naturally so convection is a non issue.
The problem with metal mirrors is that they don't last very long. You quickly get tarnishing of the surface and trying to polish it off will ruin the optical finish. Glass mirrors also tarnish, but they can be easily washed and recoated without causing damage.
Just a thought. Maybe your light source could have been projecting a simple shape like a triangle or 5-point star to enhance the resolution of the object and demonstrate the affect of the imperfections of the gallium/turntable.
Just a suggestion, can you pour a clear resin over the gallium while rotating so it's cure and keep the gallium in the parabolic shape so it can be used in telescopes without need to be kept rotating?
@@markh.876 What if the gallium floats over the resin as it may be heavier because it's a metal, leaving just a shiny coat at the surface of contact between the resin and the gallium after the curing of the resin🤔🤔
Dude your way too cool for school. I wish I had a friend like you that I could talk to about obscure concepts, philosophy, science and crazy "what if's" that 95% of my social circle just doesn't get or see any benefits in discussing.... Just for shits and giggz. Even better then getting outta the house to try to find and experiment to demonstrate what ever it is we were talking about. Thanks for sharing your valuable time knowledge and positive energy with the world. I hope our paths crossed some day
Very cool! This actually answered a question I had prior when I saw someone doing a little spinning demonstration. So it is indeed a parabola, which makes perfect sense.
Not as good as the sides and the middle experiences different amount of stretching making the edges wavy. But depending on your quality needs you might find that if you oversize the dish the middle part might be good enough / large enough for your needs. Then you just mask out the bad parts.
i was just talking about this couple months ago, i didn't know it existed, but i understood huge problem with lens scopes, the light required to curve is solely dependent on the size of the IN lens and the distance travel length to its curve in point, so liquid could be the best replacement...man i felt genius , clearly didn't know it existed.
It was still smart to come up with the idea on your own. One time when I was trying to understand horsepower I got to the point where I thought “wait, doesn’t that mean that a horsepower measurement has to be at a specific RPM?” I was super excited to find out that I was right, because it meant I understood the physics enough to come to a correct conclusion. Not exactly advanced physics but I was pretty proud of myself haha.
I have came up with quite a few ideas but found out that others have done those way before. Like falling water display showing time etc, derived equations for time dilation and length contraction from specific relatives two postulates, laser oscilloscope, spin moulding some rings from polythene bags in a cotton candy spinner, electrolytic heavy isotope enrichment, And quite a few others. Btw i don't feel happy to find out that others have beaten me to the punch
g is not called the gravitational constant, it is the acceleration due to gravity. The gravitational constant is something else that determines the force of gravity between masses given the distance between them.
I once built a 12 inch telescope with my bare hand using mercury and glass. I used 2 glasses rubbing against each other for building a curved shape. It took me months to finally create one and man that was so satisfying!
@@kriptomavi presumably the mercury was not internal, which is where it's poisonous. Check out Cody's Lab for some great mercury experiments (like floating an anvil...yes, iron floats) and debunking some of the phobia. He is very careful with it in order to keep from contaminating his property, but touching with unbroken external skin for short periods is not generally dangerous. Breathing, eating and contact with cuts or abrasions would be a potential problem.
I've seen something similar done with an emergency blanket stretched over a barrel. Suck all the air out of the center and the emergency blanket will turn into a concave mirror.
@@BariumCobaltNitrog3n You are correct, my mistake. If you pull the fabric tight enough before you apply the vacuum it will be a mirror finish. I don't know if the reflection quality would be good enough but it would be interesting to experiment with.
@@GeneMatheney The space blanket is designed to reflect radiant heat, infrared, to keep a body warm without losing heat to convection, so reflect some visible light but mostly heat (for starting fires), so isn't that great for telescopes. They can be used for sound though, picking up bird calls at hundreds of yards away. I think I saw one guy inflate the blanket instead of vacuum, then covered it with spray foam insulation. When it hardened, the backside was a decent mirror but had some wrinkles.
Did you try this in the vacuum chamber after editing this kickass episode?? Also a great way to distort time and gravity...here on earth that is ? Make a shiny mirror resin that's partially transparent / translucent and let it cure while it's spinning... Add small amounts at different speeds so each cone gets smaller or larger depending on cadence/rpm . After they cure stack the inside each other (Matryoshka Dolls)...... have a look? You see London , you see France you might see ?? One of our favorite episodes of all time on this awesome channel! Thanks for good old science mixed with passion and creativity. You rock
Vacuums have been used to bring spherical mirrors into a parabolic shape, as has gluing rubber to the back and pulling the rubber back with an attached bolt, putting the spherical mirror under tension.
As someone who is into astronomy, I really hope someone can figure out how to make high quality mirrors for a cheap price, it's the main thing that makes the hobby so damn expensive.
Use liquid nitrogen or even just dry ice to freeze the gallium/mercury when it's at an appropriate focal length, then stop the rotation and use it as a parabolic mirror that stands up to any orientation of the gravitational field as long as you keep it frozen. You could even ship it to space frozen and only keep cooling it in order to avoid it melting from radiant heat sources like the sun and stars.
0:51 you can get a 6 inch f/8 parabolic for around 160$ from a good supplier. The atmosphere itself will limit you before a ok mirror will. Things do start to get insane when you want a hyperbolic mirror though.
I remember watching another video on making such a telescope. They mentioned the best place for it would be a moon base. To get around the limited directionality.
@@CanalTremocos I'm pretty sure tidal forces on the moon from the earth can be ignored since there's only 1 side facing earth all the time. Also for dust...there are materials which are impermeable to solid matter but allow light through them.
@@CanalTremocos or it sounds like you're confusing tidal forces with gravity, one maybe caused by the other but only gravity gets stronger the closer you are. The tidal forces stays the same unless the object actually increases in mass.
Can you see what happens if you put wet concrete in a vacuum chamber? Will it dry? Will the lack of air bubbles in the block make it stronger or weaker? How heavy would it be?
This has been known for quite a while. Thought to do it some years ago, but didn't get around to it. So you might want to try using a casting epoxy resin, have the front surface aluminized and a protective overcoat applied.
wont be good for optical applications but will be good for other light focusing applications - more expensive, involved, and time-consuming, than alternative methods (like mylar pulled into shape by a vacuum)
It feels like you move the complexity of grinding perfect glass into the complexity of the engineering of a perfectly balanced rotating mechanism that needs to run for the lifetime of the mirror. But if people are building these things I assume its worth it.
Do they not use a prism to get total internal reflection when they are making a telescope as we will get 100 % of the image instead of some of them being absorbed by the mirror
It's really complicated , first , same concept of lens telescope applies , the weight of such a large prism would weigh down the shape and ruin the magnified image as it will be out of focus , second, the earth's atmosphere makes images kinda distorted no matter how accurate your mirrors are , for this reason , the mirror telescopes mirror is set on top of servos that can slightly flex the mirror to compensate for it. Check out the new series of extremely large ground telescopes using mirrors ,
Maybe it’s because the light need to get into the prism to have a total reflection and get out of it. Since we can’t ensure that light will always be perpendicular to the surface of the prism, the process of getting in and out will separate light into different colors.
Being limited to a vertical axis wouldn't be very useful. Could a liquid mirror telescope be aimed with a large first-surface mirror mounted above it tilting it around a horizontal axis for zenith, and rotating it around a vertical axis for azimuth angles?
Next step: Convert this liquit (doesn't need to be a mirror) into a smooth/"flat" solid while it is in shape to create a molde. Then create a negative modle from that to create a perfekt mirror everytime. Is that possible?
Pour some UV sensitive resin on top of the spinning gallium and then hit the resin with UV for around 10-20 seconds until cured. The cheap $20 curing lights on amazon will work for curing, and they have the 3d printer resins.
What they actually do is just spin a furnace holding a glass blank up to the speed needed to make the parabola they want, then cool it down slowly to avoid flaws, before grinding any imperfections and then buffing it to reflect. And that's a gross oversimplification of how to make a telescope mirror.
Seems like you could use a centrifugal force in place of the gravitational one... of course then you'd have something spinning perpendicular to the centrifuge and you'd only get an intermittent image as the mirror briefly lined up with the "eye piece" in such a setup But ya, it seems like you could make one of these that was not bound by the direction of the force of gravity
Hey @TheActionLab It is stated in the beginning that focusing light from a large area onto a small one gives a magnified image. This might need some correction. The animation for the telescope in shown in the first 10 seconds actually says that the ratio between the focal lenght of the parabolic mirror and the eyepiece gives the magnification. Using a large diameter aperture definitely collects more light and phsically allows for higher usable magnifications for a telescope.
That's exactly what I thought too. Unfortunately those two metals are not magnetic. Maybe some special ferromagnetic liquid (with high reflectivity) will do the job, cause ordinary ones are black. They can reflect too, but not much.
Why not use some sort of resin with a tuned speed per desired parabola, once activated and spun it should harden in the "formed" shape then coated with a reflective surface?
Refractive lenses in telescopes are constructed with 3 different lenses (usually air gapped) ground specifically to bring the 3 primary colors (red green and blue) to the same focul point. The mineral fluorite is used in the manufacturing of these (high end quality) lenses to redruce the dispersion of light.
When I was younger.. about 30 years ago... I wanted to make a mirror from slow curing epoxy and to spin the bowl with epoxy I wanted to use gramophone... Unfortunately the cost of the needed epoxy was to high for a young me :) Happy to see the same experiment here.
Hey sorry for the stupid question but can you do a video on water powered engine and explain if is a myth or if it can actually be true and what would it require to make it happen?
Play with some 2 part epoxy. Keep spinning it until it hardens and put a reflective coating on it, to see how good it is for a solar collector. Something to play with.
Can you make a solid lens by using something like a 2 part epoxy resin ? Or a liquid that will coat the gallium before it cures to a solid ? Of course you will end up with a fixed focus. edit: @thomasherbig said it first
"gravitational constant" --> "Acceleration due to earth's gravity" or "standard acceleration of gravity" . The gravitational constant (uppercase G) is 6.67 × 10-11 m3 kg-1 s-2
This but with a slowly rotating mass built into a crater on the far side of the moon, allowing for a telescope with unparalleled light pollution rejection AND a theoretically gigantic mirror diameter that self-corrects imperfections;
1. Why didn't you cool down the gallium while it's spinning, and build a solid mirror? You can polish out the final imperfections with a cloth or something, and you just have to keep it cold. That should survive a night of observations? 2. Use a high quality record turntable, or a very heavy plate below your gallium container, to smooth out the rotation so it doesn't jiggle as much.
Thankyou so much. Your videos are always calm yet interesting and entertaining. I don’t know why but I find the calmness soothing and you always help me sleep. Thankyou!
Could we take something that's solid at room temperature, melt it, form a parabola, and let it solidify as we continue to spin? Deposit aluminum on the surface. What substance has the same density as both a liquid and solid? I'm assuming you'd need that as any warping would ruin the shape.
Does the liquid mirror necessarily have to always point vertically up? Can centrifugal forces help here? I have seen stunt bike riders drive around in circles on a nearly vertical wall. Also, how about space based telescopes that are free from gravity?
I've read a proposal to install a mercury liquid mirror telescope inside a Moon crater! It would gather insane amount of light, which would be very beneficial. Only downside is that it can only be pointed straight up.
In theory you could spin molten glass and solidify it while under the spin. I realize that would introduce some ripples in the final parabola, so it would need further grinding with traditional methods. The question is, would that be more cost effective, than griding the mirror from the scratch?
your script contains an error at 3:00. The focal length increases more with less rotational speed and decreases with increasing rotational speed. "That means the liquid is spinning too fast because the focal length is too long". PS:didnt read your comment but thankyou for noticing it and correcting it proactively.
At 2:17 and 2:23 I accidentally say it backwards. I should have said the faster I spin it *the shorter* the focal length not longer. Shorter focal lengths give the wide angle view.
Why are telescope mirror & mirror blank so expensive ?👍
Glass: "Am liquid"
Gallium: "Yeah, but yur too thicc"
Glass: **sigh** "I feel invisible sometimes"
Gallium: "Need a hug?"
Mercury: "Ew. Get a room."
And that, children, is why gallium coats glass and mercury is toxic.
Also, formula on 3:28 is wrong!!! Always, check your intuition. I know, you just c/p from wikipedia, but it is also wrong there. Much more intuitive is this: *Correspondingly, the dimensions of a symmetrical paraboloidal dish are related by the equation: 4FD=R^2 (therefore F=R^2/(4D)), where F is the focal length, D is the depth of the dish (measured along the axis of symmetry from the vertex to the plane of the rim), and R is the radius of the dish from the center.*
BTW, I really like your channel!!!
Can you freeze the Galium while spinning for a fixed mirror in frozen state ?
This is how the 'star wars' satellite mirrors worked.
I visited the mirror making lab at the University of Arizona and they actually use this exact technique to speed up the manufacturing process. They pour liquid glass into a rotating mold, and as the glass cools it forms a more or less perfect parabola. They then use traditional sanding techniques to grind out any imperfections until the mirror is basically perfect
Yeah, I wish I could have been there when they made the GMT mirrors.... When I was i Tucson in 1999, I missed out on the Magellan II mirror....
I was about to ask why they don't just rotate a hot liquid metal/glass until it cools and hardens to make large mirrors, but I guess they actually do, cool!
Genius idea. Though that makes me wonder, they probably need the glass to be uniform thickness, so while they're spinning the thing to shape it, they need a mould under it which is equally perfect... How do they make that? Same process but with a different material?
Cool
@@redryder3721 Nah, they just need it to be close enough because they compensate for thermal expansion by making it a little bit thicker that way they won't have to make a perfect parabolic mold.
That demonstration with the blue water in a parabola was really cool
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This principle has revolutionized the production of very large telescope mirrors. Most 8-meter mirrors (that's huge professional-size) are made by rotating the furnace with the molten glass and slowly cooling it down. The mirror blank then solidifies into a paraboloid. It still needs some grinding, but the process is many times cheaper than traditional methods.
One quibble: faster rotation results in a shorter focal length, not a longer one.
Never seen a scientist with man ban, what the hell? Am I still alive?
There is a similar technology called liquid lenses. There you have two transparent oils with different refractive index in an electric field, and based on the voltage the interface between the two oils bends differently and acts like a lens. This was used in some early autofocus webcams back in the day.
Cooll that you remember that. I also read about them many years back. I was always wondering if they where ever used.
If only we could use that technology in glasses...
@David Mudry then there is no parabola, and after a long time eventually surface tension dominantes, forming a somewhat round blob.
@David Mudry you would get a cylinder or splash out from the internal friction and surface tension "tugging" the liquid around
@David Mudry it’s rotating 🤓
The amount of knowledge humanity already possesses about the cosmos is both humbling and awe inspiring
I used this technique with epoxy resin to make a parabolic reflector for a microphone. The surface finish was not good enough for optical work but at audio frequencies it is perfect. Much like radio telescopes do not need optical finishes.
Great channel!
Sooo jealous of the fact kids of today get to have this guy be a thing! The content he covers, as well as the simplistic yet somehow still extremely informative without being dumbed-down method in which he presents it, is all very captivating and attention-grabbing. Give this guy a catchy stage name and a show on PBS, he could easily be this generation's Bill Nye-Already is, if you ask me.
Not that he could ever replace Mr. Nye, but it would've been killer to see these things when I was a kid.
*Bursts into room* "MOM, WE NEED SOME GALLIUM!"
My fingers are crossed that I can get my son or daughter into this channel.
It’s a great channel that’s for sure
I think he can be pretty complicated, but I’m in yr 9. Despite this, I do agree that his content is interesting and informative
When I was in grade 6, I spent my whole day as a kid watching these kinds of videos but I haven't watched content creators like him, backyardscientist, etc.
Well they have to be interested in science first. I mean who doesn't like science? Star Trek is the best.
"Bill, Bill... " Always knew I would be educated while the teacher had the moment off. Definitely suggest ActionLab to my sister for educational purposes for her children.
Another advantage is that any dust would go to the edge of the spinning mirror due to the radial force :)
Here is something useful and important to know 👉 The Connections (2021) [short documentary] 🔥
oh thats nice , din think bout that
Will it though? Other matter is competing to get to the edge.
@@JasonMitchellofcompsci I don't know for sure, but since there is no flow going on, just stationary liquid, the force alone would *probably* make any dust that's floating on the surface to slowly float away to the edge.
At least that's my hypothesis :)
Dust being lighter than liquid metal would tend to collect in the center and not the edge. Oxides would move outward if they are denser than the base metal.
I'm kind of curious if you could spin up your liquid telescope up to speed and get it to the right shape and then flash freeze it so you can then point it at other directions?
Most likely the expansion / shrinking of the material will not make this work. Unless you take that in account somehow by adjusting the speed
I don't think the surface is gonna freeze and remain shiny.
thats sounds like too complicated, just use electricity to give it a shape
What if the liquid was made in layers, each one made separately? This would prevent the imperfection of expansion and shrinking.
Also, you could make the layers and cover it afterwards, so the surface would always remain shiny, even when the base material isn't suitable.
Rather than freezing a spinning liquid metal, we might as well use a concave mirror made out of a metal like Stainless Steel, which I guess would technically be a frozen liquid metal 😂
The simplicity of explaining the complexity of scientific theories is what drives me towards this channel. Keeps the science kid in us alive even at my age. Thanks to the team at Action Lab.
After reading about liquid metal telescopes in a science magazine about 40 yrs ago, I obtained and kept a 10 lb bottle of mercury around hoping to one day build one. As I got older, my sense of responsibility outpaced my scientific ambitions and I took it to a mercury recycling center.
still do it ......with gallium.
This comment had no business making me as sad as it did.
Feel the irony. They'll sell it, make products, CFL bulbs and stuff ending in waste. It was probably safer with you.
Quitter! ;-)
This is super cool! I understand how it is simpler for this to be pointed straight up, but it would be really cool to see how it would look if you were able to put this in some ‘hypothetical’ centrifugal device, so that with a slow motion camera, and some clever stabilization, editing, it would be pretty cool to see if that could work.
I wonder if it would work in zero-g...
Nothing, just stick the rotating bucket on the side of a rotating circular turntable.
@@VikingTeddy gravity is why the liquid doesn't fly away. It's still a mirror if it's sloshing around in the air, but not a very useful one. Liquid metal in space would tend to form wobbly globules...like the thick stuff inside a lava lamp, but reflective.
As for the ideas to put the turntable on a turntable, you get uneven surfaces due to compound rotation, blurry (smeared) images of the moving target, or both. Photo exposures are fast OR crisp. It's very hard to get both. This is part of why movie footage and slow-motion is so heavily edited. Trying to do astronomy or see anything scientifically useful with this setup while inside a centrifuge would be a very expensive way to get blurry, streaked images. Cool effects...maybe?
James says they _have_ to be pointed straight up...because they really do.
I've never thought about the difference between lenses and mirrors before, but you're right. Light should reflect the same regardless of the wavelength, while different wavelengths refract differently.
I’m pretty sure they do something like that for very large telescopes. They spin molten glass to get it into the general shape.
How about try to make a Liquid Mersenne-Cassegrain Telescope with mercury, glycerol and potassium? Just put the liquids in a recipient with a circular wall at the center and rotate. The mercury stays in the bottom with a parabolic shape and potassium (63.5°C) stays on top of the glycerol with a parabolic shape with different focus lenght because of the different densities of the materials and the gradient of the rotation with respect to the depth of the reflective surfaces. I had this idea with two telescopes, the liquid-mirror telescope and the monolithic telescope.
Great video! Actually I knew about the parabolic shape of spinning fluids from my old text book in fluid dynamics, but that they in fact used this phenomenon in telescopes was amazing! Thanks for great video and explanation, keep up the good work! 🤓
You said gravitational constant, but the symbol in the formula was lowercase g, which is the acceleration due to gravity.
If you spin it and let it cool, will it keep the shape of the perfect parabolla or will it shrink and distort?
That's interesting !
My assumption are that it will shrink as it cools down thus making it loose its paraboluc shape
Also it mas shrink uniformly so the para bolic shape will be retained
Here is something useful and important to know 👉 The Connections (2021) [short documentary] 🔥
small correction for 1:28 and 3:27: little g is the acceleration due to gravity, which is about 9.8 m/s^2 on Earth's surface. Big G is the gravitational constant, which is not used in either formula.
Could you build a mirror like that using a low melting point metal, spinning it while in liquid state and then retire the heat source while still spinning, so it can retain the shape? Then you can coat that with any silvery sustance to make it reflective, just like mirrors are built out of regular glass.
Someone else here mentioned that that's actually a technique used in parabolic mirror production!
I tought the same thing.
Yeah for a low cost diy mirror you can probably use wax and then use electrolysis to nickel-chrome coat it.
I wonder how well it would compare to a bought mirror.
But you can control the temperature fairly well with an inexpensive heater in a closed room, bring the room to 40-45C and then pour the molten wax, then just let the room cool down naturally so convection is a non issue.
The problem with metal mirrors is that they don't last very long. You quickly get tarnishing of the surface and trying to polish it off will ruin the optical finish. Glass mirrors also tarnish, but they can be easily washed and recoated without causing damage.
Just a thought. Maybe your light source could have been projecting a simple shape like a triangle or 5-point star to enhance the resolution of the object and demonstrate the affect of the imperfections of the gallium/turntable.
Ah true, that could also be a factor along with what he said.
Just a suggestion, can you pour a clear resin over the gallium while rotating so it's cure and keep the gallium in the parabolic shape so it can be used in telescopes without need to be kept rotating?
@@markh.876 What if the gallium floats over the resin as it may be heavier because it's a metal, leaving just a shiny coat at the surface of contact between the resin and the gallium after the curing of the resin🤔🤔
@@markh.876 Or just spraying any reflective coat to the parabolic shape cured resin which was left cured while rotating with the same method
@@markh.876 that’s why ppl use phase conjugate mirrors. So the outbound distortion cancels the in bound.
There are lenses made out spun epoxy that hardens while spinning that are thin metalized.
At that point, just spin the liquid glass. I'm pretty sure parabolic mirror manufacturers already do that.
Your explanations are superb!!
Dude your way too cool for school. I wish I had a friend like you that I could talk to about obscure concepts, philosophy, science and crazy
"what if's" that 95% of my social circle just doesn't get or see any benefits in discussing.... Just for shits and giggz. Even better then getting outta the house to try to find and experiment to demonstrate what ever it is we were talking about. Thanks for sharing your valuable time knowledge and positive energy with the world. I hope our paths crossed some day
Same here. Badly in need of a friend who has interest in physics, biology, geology, history etc. etc. that I have interest in. 😔
Mylar film over a drum works pretty well with varying levels of vacuum applied.
..Lots of people here. .are talking about using the mylar space blanket to form a parabola...But how to hold that shape permanently?
great demonstration!
would be interesting to use some epoxy instead of liquid metal. then coat it shiny after solidifying.
Interesting thought.
Can we mix the gallium or mercury with epoxy and spin it to the desired focus as it hardens?
I really amaze how he come so interesting topics most of us naver heard before so frequently and explain amazingly
Very cool! This actually answered a question I had prior when I saw someone doing a little spinning demonstration. So it is indeed a parabola, which makes perfect sense.
Thanks!
A Mylar sheet with vacuum behind it is also a good way to make a parabolic mirror!
Not as good as the sides and the middle experiences different amount of stretching making the edges wavy. But depending on your quality needs you might find that if you oversize the dish the middle part might be good enough / large enough for your needs. Then you just mask out the bad parts.
Why not magnitize the metal by putting magnetic material in mercury so you can focus it in any direction you want to?
i was just talking about this couple months ago, i didn't know it existed, but i understood huge problem with lens scopes, the light required to curve is solely dependent on the size of the IN lens and the distance travel length to its curve in point, so liquid could be the best replacement...man i felt genius , clearly didn't know it existed.
It was still smart to come up with the idea on your own. One time when I was trying to understand horsepower I got to the point where I thought “wait, doesn’t that mean that a horsepower measurement has to be at a specific RPM?” I was super excited to find out that I was right, because it meant I understood the physics enough to come to a correct conclusion. Not exactly advanced physics but I was pretty proud of myself haha.
I have came up with quite a few ideas but found out that others have done those way before. Like falling water display showing time etc, derived equations for time dilation and length contraction from specific relatives two postulates, laser oscilloscope, spin moulding some rings from polythene bags in a cotton candy spinner, electrolytic heavy isotope enrichment, And quite a few others. Btw i don't feel happy to find out that others have beaten me to the punch
g is not called the gravitational constant, it is the acceleration due to gravity. The gravitational constant is something else that determines the force of gravity between masses given the distance between them.
I once built a 12 inch telescope with my bare hand using mercury and glass. I used 2 glasses rubbing against each other for building a curved shape. It took me months to finally create one and man that was so satisfying!
Have you experienced mercury poisoning?
@@kriptomavi presumably the mercury was not internal, which is where it's poisonous. Check out Cody's Lab for some great mercury experiments (like floating an anvil...yes, iron floats) and debunking some of the phobia. He is very careful with it in order to keep from contaminating his property, but touching with unbroken external skin for short periods is not generally dangerous. Breathing, eating and contact with cuts or abrasions would be a potential problem.
I've seen something similar done with an emergency blanket stretched over a barrel. Suck all the air out of the center and the emergency blanket will turn into a concave mirror.
How is that remotely similar?
@@BariumCobaltNitrog3n perfect concave lens to focus light. That could be turned into a telescope.
@@GeneMatheney Not a lens. A mirror. Used for cooking not astronomy. Made of plastic not glass or metal. Vacuum not gravity.
@@BariumCobaltNitrog3n You are correct, my mistake. If you pull the fabric tight enough before you apply the vacuum it will be a mirror finish. I don't know if the reflection quality would be good enough but it would be interesting to experiment with.
@@GeneMatheney The space blanket is designed to reflect radiant heat, infrared, to keep a body warm without losing heat to convection, so reflect some visible light but mostly heat (for starting fires), so isn't that great for telescopes. They can be used for sound though, picking up bird calls at hundreds of yards away.
I think I saw one guy inflate the blanket instead of vacuum, then covered it with spray foam insulation. When it hardened, the backside was a decent mirror but had some wrinkles.
Could you make a lens by casting resin on top of spinning galium or mercury?
Did you try this in the vacuum chamber after editing this kickass episode??
Also a great way to distort time and gravity...here on earth that is ? Make a shiny mirror resin that's partially transparent / translucent and let it cure while it's spinning... Add small amounts at different speeds so each cone gets smaller or larger depending on cadence/rpm . After they cure stack the inside each other (Matryoshka Dolls)...... have a look?
You see London , you see France you might see ??
One of our favorite episodes of all time on this awesome channel!
Thanks for good old science mixed with passion and creativity.
You rock
It's the other way around: the faster you spin, the shorter the focal length.
Exactly. He wrote the mathematical relationship correctly at the end, but said it the wrong way around several times.
Here is something useful and important to know 👉 The Connections (2021) [short documentary] 🔥
Now we need to find a way to make it freeze in place to create the perfect mold
4 minutes and 20 seconds 🗿
Imma smoke Rightttt at the end 🤣🤣
🗿🗿
Share to the left…..
Puff... What?
Noice
Vacuums have been used to bring spherical mirrors into a parabolic shape, as has gluing rubber to the back and pulling the rubber back with an attached bolt, putting the spherical mirror under tension.
i would use mercury but lets try something a little less toxic
i have here hydrochloric acid
Wild dude! Thanks!
As someone who is into astronomy, I really hope someone can figure out how to make high quality mirrors for a cheap price, it's the main thing that makes the hobby so damn expensive.
For Newtonians which are not too small, it is usually the equatorial mount (I don't like Dobsonians).
Use liquid nitrogen or even just dry ice to freeze the gallium/mercury when it's at an appropriate focal length, then stop the rotation and use it as a parabolic mirror that stands up to any orientation of the gravitational field as long as you keep it frozen. You could even ship it to space frozen and only keep cooling it in order to avoid it melting from radiant heat sources like the sun and stars.
There is something like: Gallium Liquid Mirrors
Very interesting concept! I've never heard of using a rotating metal to make a mirror.
0:51 you can get a 6 inch f/8 parabolic for around 160$ from a good supplier. The atmosphere itself will limit you before a ok mirror will.
Things do start to get insane when you want a hyperbolic mirror though.
I remember watching another video on making such a telescope. They mentioned the best place for it would be a moon base. To get around the limited directionality.
Hmm. Wouldn't 20x stronger tidal forces on the surface of the moon warp the lenses too much?
and the sticky dust...
@@CanalTremocos I'm pretty sure tidal forces on the moon from the earth can be ignored since there's only 1 side facing earth all the time. Also for dust...there are materials which are impermeable to solid matter but allow light through them.
@@CanalTremocos or it sounds like you're confusing tidal forces with gravity, one maybe caused by the other but only gravity gets stronger the closer you are. The tidal forces stays the same unless the object actually increases in mass.
Can you see what happens if you put wet concrete in a vacuum chamber? Will it dry? Will the lack of air bubbles in the block make it stronger or weaker? How heavy would it be?
This has been known for quite a while. Thought to do it some years ago, but didn't get around to it. So you might want to try using a casting epoxy resin, have the front surface aluminized and a protective overcoat applied.
wont be good for optical applications but will be good for other light focusing applications - more expensive, involved, and time-consuming, than alternative methods (like mylar pulled into shape by a vacuum)
What about using the mylar as a - ve mold for resin bu pushing insted of pulling it?
..Lots of people here. .are talking about using the mylar space blanket & vacuum to form a concave mirror...But how to hold that shape permanently?
It feels like you move the complexity of grinding perfect glass into the complexity of the engineering of a perfectly balanced rotating mechanism that needs to run for the lifetime of the mirror. But if people are building these things I assume its worth it.
Love seeing more liquid parabolas for me to watch xd. I recently bought 1kg of galinstan for this type of thing lol
Do they not use a prism to get total internal reflection when they are making a telescope as we will get 100 % of the image instead of some of them being absorbed by the mirror
It's really complicated , first , same concept of lens telescope applies , the weight of such a large prism would weigh down the shape and ruin the magnified image as it will be out of focus , second, the earth's atmosphere makes images kinda distorted no matter how accurate your mirrors are , for this reason , the mirror telescopes mirror is set on top of servos that can slightly flex the mirror to compensate for it. Check out the new series of extremely large ground telescopes using mirrors ,
how does such a telescope look like? Maybe they use both, the big one to focus the light, then prisms to redirect it?
Maybe it’s because the light need to get into the prism to have a total reflection and get out of it. Since we can’t ensure that light will always be perpendicular to the surface of the prism, the process of getting in and out will separate light into different colors.
Why don't they just use a plastic reflecting surface
Here is something useful and important to know 👉 The Connections (2021) [short documentary] 🔥
Wow, I was just explaining this to a guy last week. He was showing one of those great big stone bowls from Japan. Thanks good video.
Largest liquid mirror telescope is being built in India...
we can try freezing the metal it is spinning, and store it in low temperature so that we need not to keep only upright
1:28 super simple
Being limited to a vertical axis wouldn't be very useful. Could a liquid mirror telescope be aimed with a large first-surface mirror mounted above it tilting it around a horizontal axis for zenith, and rotating it around a vertical axis for azimuth angles?
Next step: Convert this liquit (doesn't need to be a mirror) into a smooth/"flat" solid while it is in shape to create a molde. Then create a negative modle from that to create a perfekt mirror everytime. Is that possible?
Pour some UV sensitive resin on top of the spinning gallium and then hit the resin with UV for around 10-20 seconds until cured. The cheap $20 curing lights on amazon will work for curing, and they have the 3d printer resins.
What they actually do is just spin a furnace holding a glass blank up to the speed needed to make the parabola they want, then cool it down slowly to avoid flaws, before grinding any imperfections and then buffing it to reflect.
And that's a gross oversimplification of how to make a telescope mirror.
Seems like you could use a centrifugal force in place of the gravitational one... of course then you'd have something spinning perpendicular to the centrifuge and you'd only get an intermittent image as the mirror briefly lined up with the "eye piece" in such a setup
But ya, it seems like you could make one of these that was not bound by the direction of the force of gravity
Guy looks like he's in pain😂😂
great video, zero BS. thank you James. good job.
Hey @TheActionLab
It is stated in the beginning that focusing light from a large area onto a small one gives a magnified image.
This might need some correction. The animation for the telescope in shown in the first 10 seconds actually says that the ratio between the focal lenght of the parabolic mirror and the eyepiece gives the magnification.
Using a large diameter aperture definitely collects more light and phsically allows for higher usable magnifications for a telescope.
Is gallium or mercury affected by magnetic fields? Could you substitute gravity with a big electromagnet?
That's exactly what I thought too. Unfortunately those two metals are not magnetic. Maybe some special ferromagnetic liquid (with high reflectivity) will do the job, cause ordinary ones are black. They can reflect too, but not much.
1:36 Anyone else saw the axolotl there?
Where
I love the simplicity of the solution
3:18 This is Exactly how Stars Shine and scatter but always stay constant ! Oooh ! This answers a massive Qualitative Question
Why not use some sort of resin with a tuned speed per desired parabola, once activated and spun it should harden in the "formed" shape then coated with a reflective surface?
So... Could you freeze the gallium or other liquid metal with liquid Nitrogen. To hold the shape.
If the gallium were to slowly solidify, would that keep the shape it had as a liquid or would it become distorted?
Refractive lenses in telescopes are constructed with 3 different lenses (usually air gapped) ground specifically to bring the 3 primary colors (red green and blue) to the same focul point.
The mineral fluorite is used in the manufacturing of these (high end quality) lenses to redruce the dispersion of light.
When I was younger.. about 30 years ago... I wanted to make a mirror from slow curing epoxy and to spin the bowl with epoxy I wanted to use gramophone... Unfortunately the cost of the needed epoxy was to high for a young me :) Happy to see the same experiment here.
Hey sorry for the stupid question but can you do a video on water powered engine and explain if is a myth or if it can actually be true and what would it require to make it happen?
Play with some 2 part epoxy. Keep spinning it until it hardens and put a reflective coating on it, to see how good it is for a solar collector. Something to play with.
Can we solve the issue with facing up mirror by additional flat rotating mirror?
I for the most part always enjoy your content.
Can you make a solid lens by using something like a 2 part epoxy resin ? Or a liquid that will coat the gallium before it cures to a solid ? Of course you will end up with a fixed focus. edit: @thomasherbig said it first
"gravitational constant" --> "Acceleration due to earth's gravity" or "standard acceleration of gravity" .
The gravitational constant (uppercase G) is 6.67 × 10-11 m3 kg-1 s-2
This but with a slowly rotating mass built into a crater on the far side of the moon, allowing for a telescope with unparalleled light pollution rejection AND a theoretically gigantic mirror diameter that self-corrects imperfections;
1. Why didn't you cool down the gallium while it's spinning, and build a solid mirror? You can polish out the final imperfections with a cloth or something, and you just have to keep it cold. That should survive a night of observations?
2. Use a high quality record turntable, or a very heavy plate below your gallium container, to smooth out the rotation so it doesn't jiggle as much.
Hey Action Lab,more good material as always. By the way, you are slowly getting a cool Ronin Toshiro Mifune hair style now.
Thankyou so much. Your videos are always calm yet interesting and entertaining. I don’t know why but I find the calmness soothing and you always help me sleep. Thankyou!
Could we take something that's solid at room temperature, melt it, form a parabola, and let it solidify as we continue to spin? Deposit aluminum on the surface. What substance has the same density as both a liquid and solid? I'm assuming you'd need that as any warping would ruin the shape.
Does the liquid mirror necessarily have to always point vertically up? Can centrifugal forces help here? I have seen stunt bike riders drive around in circles on a nearly vertical wall. Also, how about space based telescopes that are free from gravity?
with it being made of gallium, could you freeze it to a solid state while it is in the desired shape?
Very Timely - you've answered my question of how liquid mirror astronomical telescopes work -- old git, UK
You can also take the mylar space blankets you can get at the dollar store. Attached them to a hoop and pull a vacuum
I've read a proposal to install a mercury liquid mirror telescope inside a Moon crater! It would gather insane amount of light, which would be very beneficial. Only downside is that it can only be pointed straight up.
In theory you could spin molten glass and solidify it while under the spin. I realize that would introduce some ripples in the final parabola, so it would need further grinding with traditional methods. The question is, would that be more cost effective, than griding the mirror from the scratch?
That's how large monolithic primary mirrors are often cast today.
This was so innovative and mind blowing !
-Freeze it while rotating
-Solid parabolic mirror
Now do this with molten glass, let it cool slowly while spinning and after that coat it with a reflective material.
this was a question in my book pathfinder.
I really enjoy listening to your awareness of things that are old.
This was AWESOME!! ❤️🙏🏻
1:30 : g isn't the gravitational constant, it's the gravitation. G is the gravitational constant
your script contains an error at 3:00. The focal length increases more with less rotational speed and decreases with increasing rotational speed. "That means the liquid is spinning too fast because the focal length is too long".
PS:didnt read your comment but thankyou for noticing it and correcting it proactively.
Why don't they spin some type of binary liquid that hardens over time, then let it harden while spinning, and then coat it with reflective aluminum?