correct! And no color aberrations like in glass lenses.

just if someone spills their coffee in it.

Someone trips and falls onto it. An inconvenience with gallium, but god help them if it's mercury. ​@@lolwtnick4362

Definitely!

@@ActionLabShortsDo you think they are the future of telescopes?

Scry 2

24825d11h

248,2,5d11h

😆

Scry harder.

Nice

Coriolis force

What is the connection between the speed and the slope though?

@Yulenka- The speed of what? Im not sure I understand your question. The cup is spinning, because of that, that water is being pushed towards the outside because centrifugal force. But the relationship of the slope of the water leaning against the glass wall in respect to it's distance from the center is linear, so it must make a parabola.

@@maxhagenauer24 I followed your explanation until "the water moves twice as fast so the slope of water increases linearly as it goes father from the edge". I understood that the speed increases linearly, and that linear slope increase makes a parabola, but I don't know how the latter follows from the former. Why couldn't the speed increase linearly in a different shape?

Whoops, I swallowed mercury 💀

@@AlexGeek it wasn't mercury, I'm afraid

​@@Pootie_Tang It was Uranus

@@Unwanted_truth_ I wondered what was that itch I feel

Well, gallium isn't as bad as mercury​@@Pootie_Tang

Wtffff this is black magic

@@flux.aeterna The inventer struggled for long time to make such a shape. One morning he was stirring his coffee and saw the surface of the coffee had the shape he needed. So insted of pouring the polymer into still molds, he poured it in spinning molds.

The more you know 🌈

​@amurape5497 if that's true that's a great story. I will look up later to see if it is! Thanks for sharing!

I don't think this is true. Don't know where you have this from, but I looked it up and every mass production facility uses the standard mold & extrusion process.

Science is a hydra - at the current stage, every answer creates at least two more new questions.

Does the molten glass form a parabola? I guess some polishing and aluminizing would give you close to a perfect mirror.

@@adammontgomery7980 Yes, it does form a parabola which vastly reduces the amount of work you need to do to get a perfect figure. The only problem is you need a very big oven that can be spun at high temperatures for weeks.

There is a good video about spin casting the mirrors for the Giant Magellan telescope at the University of Arizona.

and it's also 5000% more likely to break 😂

The back of the mirror is cast into a honeycomb shape to further reduce it’s weight.

I saw this without reading the title. I thought "how nobody havent used this yet on a telesc... oh they did"

yeah, except you can only use it at zenith (pointing straight up)

@@mariusflorea1984but in space there is no up, right? So it could still work outside of earth’s environment

@@redwiltshire1816 yes, but also 0 pressure and gravity to keep the liquid flat

@@mariusflorea1984 what if you apply pressure to the liquid keeping it in place then spin the liquid

Or lasers. This could be the precursor to the Death Star.

A camara that can only point straight up.

or gravitational lenses containing thousands of galaxies

This isn't a new technology, lol. It was invented in the 1800s. And think about what you just said. How exactly you do you think a handheld camera would work using this? Lol. You can't aim these anywhere but up. They work perpendicular to gravity. They wouldn't work in something you were trying to constantly point everywhere in whatever direction you want. Not to mention it needs to spin....

@@klausolekristiansen2960 you can use a second, flat mirror, to make it point almost anywhere. But yeah, it cannot be handheld.

well, concentrating light is the point of those

are you talking about the solar death ray guy?

@@Nimpp he uses a big fresnel lense from an old tv, but there’s a couple different types of solar cooking contraptions

@@noobartz0890point 😂

Who would win, the entire Persian naval fleet, or one glass bowl

I too keep myself from sleeping with that same problem on my mind - what about the contaminants from touching the gallium.

@@HandsomeBastard In photography, it would likely cause clarity issues if contaminates were to be on the surface. Similar to a smudge on a mirror. I'm not an expert, but I would assume they attempt to keep that gallium as pure as physically possible.

​@@STaSHZILLA420They can drain off the gallium for cleaning.

@@reddragonflyxx657 Alternatively, you can just cross the surface with a wiper. Should be enough to drag surface contaminated out.

@@canadianman000 Yep, I remember reading about filtering it somewhere, but that definitely works too > Not mentioned in the article is the ease of cleaning mercury, particularly since all common objects float on it. The container is stopped, and a lead-weighted rubber tube is used to drag debris and mercury oxide to an edge of the puddle, from which the debris is aspirated away. The mirror is then restarted.

Okay right?! 😆

Me too. But I now can somewhat joke about water making a cheaper glass material. A Did You Know trivia maybe.

shit that's ingenious

Look up any big mirror telescope or space telescope, they are never pure parabola because of third order coma aberrations.

The mirror lab at University of Arizona does this, but only to rough-in the mirror shape. They still need to polish the mirror surface before metalizing it. (According to their website, they've made 8.4meter mirrors this way.)

@@Sembazuru This is actually where I learned about this! I believe the University of Arizona Mirror Lab now has public tours available again (they had been stopped for a while during COVID, I believe), so if you (or anyone reading) ever happens to be in Tucson, Arizona, you should definitely take a tour. It's an incredibly impressive lab!

@@Sembazuru The Keck mirrors were made this way

Mirror portal be like: "You spin me right 'round, baby, right 'round , like a record, baby, right 'round, 'round, 'round".

Well, there isn't a lot of drawbacks, just one - since it's always centered around the center of gravity, it basically cannot move in any direction. So you can only observe what's directly up (and thus it can't track any celestial objects)

@@FourOneNineOneFourOne the maximum size of the lens is limited too, because the rotation required to produce a smooth mirror with no blemishes or turbulence would be too high to be able to be maintained. Also, some liquid metals that are used contain Mercury or thallium making them somewhat toxic to be exposed to.

@@spiderdude2099 I think they've already made some pretty large liquid telescopes. You're right about the toxicity. The largest telescopes don't use either one because it's just as difficult to have it made out of mirrors, although they only capture radio and microwave frequencies.

⁠@@FourOneNineOneFourOneso what are they using to make these liquid telescope mirrors if not gallium or mercury?

​@@koriw1701That's something that's actively being worked on as they want to put one in space!

The trick would be to use a flat mirror to bend the light from Mercury to reach the mercury, since Mercury would never be directly overhead, and the mercury mirror couldn’t be tilted.

@@gregswank4912 Couldn't it spin fast enough to aim just above the horizon?

@@ezekielbrockmann114Yes, you can tilt a liquid mirror that is designed to be tilted, but you’ll then need to calculate and subtract the warping created by unequal gravitational impact across the mirror’s surface. The impact of local gravitational variances across a perfectly “horizonta”l* mirror is so small as to be negligible at this scale. You’d have to get much, much larger for local gravitational variances to be meaningful. *perfectly tangential is more appropriate than horizontal, as we are talking about a tangent plane intersecting with the surface of the curved Earth. I chose to use horizontal for the clarity of the concept, though, as most people will understand that from regular experience, rather than what “tangential plane to a sphere” means.

that's not mercury but ok

@@vintage-radio Looks like mercury to me.

@@pandapip1 maybe it's because they're both metals that are liquid at room temperature

​@@vintage-radio He used a glass beaker, so I don't think it's gallium.

@@pandapip1 fair enough. It must be mercury

No it looks like a white light being reflected. Actual stars look very different

This is actually done when casting large glass mirror blanks. The desired final figure is usually not quite a parabola, and error is induced anyway when the glass cools and changes phase, but it greatly reduces the time needed to grind and polish to the final figure.

Possibly if you can flash freeze it into position otherwise as it hardens it will become harder to spin

It can be done. I read an article in Scientific American back in the '90s with instructions. At the time they recommended using a record turntable that is designed to spin at a consent speed for a long time.

​​​@@seno7904 Resins are like a glue, so they cure over some period of time depending on what type you're using. Also, the viscosity doesn't effect how much force it takes to spin, since the entire container is moving along with the liquid inside. I don't see how it would get harder to turn as it starts to set up, or why it would have to happen quickly, so long as you have something that could spin it at a constant speed until it hardens.

@@ctdieselnutI’m not entirely sure, but I’d think that you would need to spin it faster as it hardens to keep the same shape due to the viscosity making it not flow as easily upwards at the edges

As long as it doesn't slow down the resin wouldn't suddenly change shape thus a constant speed until the resin is fully cured is all you need despite any changes in viscosity

No! That's a common misconception. It decreases performance and contrast, but the speck will be out of focus. It takes a lot of dust or a lot of light to be noticeable.

​@JimmyCerra even with my home telescope, I can put my whole hand in the front and still not see it, although the image gets darker

probably but wont be th3e cheapest thing for one to do. you can buy gallium.

bucket of spinning mercury at home sounds like a fun idea

@@Matthew_Removeafterwashing a little bit safer and easier to get gallium then mercury I would think.

Glass optics are probably cheaper at small scale

@@poscat0x04 probably but they didn’t ask if you can build one out at home but they asked if you can build one out of Liquid Metal

Good news! It's only algebra until you need to do anything with it. Then it's calculus

No???

And the fact that you can change the properties of the lens is also very useful i would guess.

the physics is different from a line-mass held at two ends

Yes I think the difference with the catenary is the lack of outward tension force here. There is only gravity and a buoyancy force.

@@stephenbeck7222but this case does have an outward tension in the form of a centrifugal (inertial) force, and it grows as we travel towards the edge, allowing the edge to “hold” more liquid than the middle

It's a parabola for the same reason objects in free-fall follow a parabolic path: whenever a bunch of particles are given some energy to spend (in this case, energy due to rotation) and are simultaneously under the influence of gravity (and perhaps some other hydrostatic forces), the resulting distribution of those particles will minimize one ubiquitous and well-understood quantity. In the case of a particle in free-fall, the energy to spend is kinetic energy, and that quantity to minimize is the difference between its kinetic and potential energies.

It's no big deal. It's just a turntable, and it doesn't even need to be precise as the surface of the liquid will always form a parabola with respect to gravity. Also, the turntable doesn't have to rotate very quickly because the parabola needed is shallow. The only thing that would need to be kept consistent is the rotation speed, but that's easy to do given the amount of mass involved. The drawback of a telescope like this is that it can only be pointed straight up.

​@@robertmiles9942the rotation has to be very precise, any unbalanced "wobble" would completely ruin your mirror surface. Remember to work they need to be "smooth" to less than the wavelength of light you're trying to capture IE a perfect parabola accurate to around 15-20 billionths of a metre, millionths of a millimetre. So yes any vibrations/wobble is going to ruin your telescope... There's a reason grinding telescope mirrors is expensive and difficult.

The biggest problem isnt making your spinning mirror, that's hard but not as hard as the next part. A spinning liquid mirror is centred looking straight up, unless what you want to look at is straight up that's going to be a problem. In any other direction you're going to need a series of moving mirrors and motors etc to redirect the light from where you're looking to your nice spinning mirror. And all wavefronts need to reach that mirror at precisely the same time.... That is very very non trivial task.

actually no. not sa good as some other microscopes but not that inaccurate at all

It's funny that Feynman's stance (and forehead?) are so recognizable that you immediately know it's him in a picture where the lens was very much not focused on him.