As other commenters noted, the title is very misleading. The force exist but it is tiny, very very very tiny.<p>For radiation, force = power / speed of light<p>You can add x2 if the radiation bounce against the surface like in a mirror. For the calculations, let's pick a random value for power: 100W<p>* 100 W it's all the power that used an old incandescent lamp, most of it was wasted as heat instead of visible light, and in many directions.<p>* A modern LED lamp for a room has about 10W, so 100W are like 10 LED lamps.<p>* And 100W is HUGE for a laser. And 5W is huge for a laser. (Class 3R is up to .005W and Class 3B is up to .5W.)<p>So if we divide the force by the acceleration of the gravity <a href="https://www.wolframalpha.com/input/?i=2+*+100W+%2F+(speed+of+light)+%2F(gravity+aceleration)" rel="nofollow">https://www.wolframalpha.com/input/?i=2+*+100W+%2F+(speed+of...</a> we get 7E-8Kg = 70ug that according to wolfram alpha is approximately 1/40 of a typical snowflake and 1/20 of a typical mosquito.<p>Note that if you suddenly put 100W into a snowflake or a mosquito, they will be destroyed instantly, and you need x20 or x40 more power to make them float, and they will absorb most of the energy so you need x2 the power.<p>(The article is about manipulating the light/material to stabilize the object, not to magically make the radiation force strong enough to levitate an elephant.)
This reminds me of a video where someone levitates diamond dust with lasers.<p><a href="https://www.youtube.com/watch?v=Sq7GaO8iqu8" rel="nofollow">https://www.youtube.com/watch?v=Sq7GaO8iqu8</a>
In newtonian physics you learn that momentum is calculated as mass x velocity. Then in modern physics you learn that light has zero mass so you naively assume light has no momentum. Then later you learn that the original equation you learned was missing a piece and light can actually transfer momentum. This is a cool application of that property!
Sorry, here comes probably the usual question asked whenever somebody talks about "light":<p>if I point a flashlight at an object, does the target object move (in theory, if no other external force exists) because of the light hitting it?<p>I could expand the question asking: when the light hits, does it lose energy (because some of its energy is transferred to the object that is hit? (e.g. target object heats up and/or moves and/or don't-know-what-else-could-happen) => if yes, then light would disappear if it would bounce around enough times (e.g. if I let light enter a box and then I close it and never open it again, is the light absorbed after a while by the box?)<p>Personally, I am totally confused. I think that the last time I did some investigations, the simplest statement I found said "light has momentum but no mass" (is this correct, in general?).<p>That "light has momentum but no mass"-statement confused me even more as I thought that gravity has influence only on things that have mass (what I keep thinking about is the example of the light being bent when it passes nearby a black hole).<p>Additionally, about "momentum", its definition needs mass, at least as per Wikipedia:<p>> <i>momentum (pl. momenta) is the product of the mass and velocity of an object.</i> ( <a href="https://en.wikipedia.org/wiki/Momentum" rel="nofollow">https://en.wikipedia.org/wiki/Momentum</a> )<p>Therefore if light does not have a mass then it shouldn't be bent by gravity nor have any momentum?<p>Thx :)
From last year, a 3D volumetric display based on laser manipulation of particles in air: <a href="https://www.nature.com/articles/d41586-018-01125-y" rel="nofollow">https://www.nature.com/articles/d41586-018-01125-y</a>
If they tried to do this with a spacecraft, wouldn't it need constant line of sight from earth with this technique? Seems interesting but pretty impractical for that application, unless I'm reading the text incorrectly.