11 ms·

Theoretical way to levitate objects with light

153 points by rakkhi 8y ago

thecupisblue 8y ago
Holy shit, scaling this technology will change humanity. Amazing!
- deleted 8y ago
  [deleted]
DanBC 8y ago
This reminds me of a video where someone levitates diamond dust with lasers. https://www.youtube.com/watch?v=Sq7GaO8iqu8 https://www.youtube.com/watch?v=Sq7GaO8iqu8
samdung 8y ago
Ionic Thruster + Light Levitation = Flying Drone with no moving parts. Wish i can see this in my lifetime.
- russdill 8y ago
  Ionic thrusters for drones? Maybe. Using light? No. Orders of magnitude off even considering the absolute limits of physics. That's not what this article says.
  - mokus 8y ago
    I didn’t see anything in the article that changes the amount of momentum that would be transferred - as far as I could tell it’s all about the distribution of that force being modulated to make the object being accelerated tend to stay in the center of the beam Editing to clarify my point: the article’s title seems wildly misleading by using the word levitation. The energy required to “levitate” a macroscopic object in earth gravity using light is unchanged, and while I don’t feel like doing the math right now i feel pretty confident stating that “impractical” is a monstrous understatement.
- sandworm101 8y ago
  Ionic thrusters only work well at very low pressures. At atmospheric pressure they are no better than a cold jet, just like opening a bottle of compressed air.
montzark 8y ago
Could we use this to make more haptic touch screens?
openloop 8y ago
Fucking awesome.
mdturnerphys 8y ago
From last year, a 3D volumetric display based on laser manipulation of particles in air: https://www.nature.com/articles/d41586-018-01125-y https://www.nature.com/articles/d41586-018-01125-y
- homero 8y ago
  Aren't those loud? I saw one that exploded air molecules to create the light.
  - mdturnerphys 8y ago
    Those are systems with pulsed lasers that ionize the air. This uses relatively low-power beams to trap and illuminate a small particle.
gus_massa 8y ago
As other commenters noted, the title is very misleading. The force exist but it is tiny, very very very tiny. For radiation, force = power / speed of light 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 * 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. * A modern LED lamp for a room has about 10W, so 100W are like 10 LED lamps. * 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.) So if we divide the force by the acceleration of the gravity https://www.wolframalpha.com/input/?i=2+*+100W+%2F+(speed+of+light)+%2F(gravity+aceleration) https://www.wolframalpha.com/input/?i=2+*+100W+%2F+(speed+of... 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. 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. (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.)
- Judgmentality 8y ago
  Not to detract from your comment, but the most interesting thing about what you said (at least to me) is that a mosquito weighs half as much as a snowflake.
  - barrkel 8y ago
    Snowflakes are non-dense more than they are light - they float down slowly due to air resistance rather than lightness per se. Snowflakes have a pretty big variance in size, I'm not sure that a single weight could meaningfully be assigned to them.
- jfoutz 8y ago
  I'm completely out of my element here. Hoping maybe for some clarification. I've never heard of a laser, at any scale, having a force pushing backwards against the direction of light. It seems like one of two things is possible. 1) you could move a spaceship by shooting a laser. The force would be tiny, but it would keep accelerating as long as the laser is powered, with no reaction mass. i've never heard of such a thing being possible (but, again, way out of my element). 2) you could play the classic impossible machine game, with the fan on the back of a boat blowing into a sail. except with a laser and a sail. If 1) doesn't work, then 2) has to work, right?
reidjs 8y ago
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!
kosei 8y ago
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.
- EastLondonCoder 8y ago
  You are right, can read more about one proposal here: https://en.m.wikipedia.org/wiki/Breakthrough_Starshot https://en.m.wikipedia.org/wiki/Breakthrough_Starshot
- newnewpdro 8y ago
  Avi Loeb described this on ep. 40 of After On [1], it didn't sound entirely unrealistic as he described it. It's around 19 minutes into the interview, I see a sibling links Breakthrough Starshot, in this podcast he describes it on a high level. [1] https://after-on.com/episodes-31-60/040 https://after-on.com/episodes-31-60/040
Animats 8y ago
The new thing here is not pushing with photons. It's making the thrust self-stabilizing, so the target accelerates without spinning.
zepearl 8y ago
Sorry, here comes probably the usual question asked whenever somebody talks about "light": 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? 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?) 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?). 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). Additionally, about "momentum", its definition needs mass, at least as per Wikipedia: > momentum (pl. momenta) is the product of the mass and velocity of an object. ( https://en.wikipedia.org/wiki/Momentum https://en.wikipedia.org/wiki/Momentum ) Therefore if light does not have a mass then it shouldn't be bent by gravity nor have any momentum? Thx :)
- barbarr 8y ago
  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? Yes, the target object gains velocity due to conservation of momentum. The photon goes from momentum p to -p, so the target object needs to gain 2p of momentum to balance it out. For photons, this amount of momentum is very small. when the light hits, does it lose energy (because some of its energy is transferred to the object that is hit? For perfect reflection, no. (What you're referring to is light absorption, which is a different effect that raises the temperature of the target object and red-shifts the incoming photon.) 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?). Pretty much. Photons are usually described by their momentum and energy. For our peace of mind, we can derive an effective "mass" using p=mv, where p is the electron's momentum and v is its velocity; however, the notion is not very useful since it doesn't correspond nicely to our everyday experience of mass (whereas electron momentum does correspond nicely to our everyday experience of momentum).
samplatt 8y ago
Surprised no-one's yet mentioned the XKCD blogpost on this exact topic: https://blog.xkcd.com/2008/02/15/the-laser-elevator/ https://blog.xkcd.com/2008/02/15/the-laser-elevator/ Or the vaguely-related (because lasers) What-If scenario https://what-if.xkcd.com/13/ https://what-if.xkcd.com/13/

153 points by rakkhi 8y ago

thecupisblue 8y ago

Holy shit, scaling this technology will change humanity. Amazing!

deleted 8y ago
[deleted]

DanBC 8y ago

This reminds me of a video where someone levitates diamond dust with lasers. https://www.youtube.com/watch?v=Sq7GaO8iqu8 https://www.youtube.com/watch?v=Sq7GaO8iqu8

samdung 8y ago

Ionic Thruster + Light Levitation = Flying Drone with no moving parts. Wish i can see this in my lifetime.

russdill 8y ago
Ionic thrusters for drones? Maybe. Using light? No. Orders of magnitude off even considering the absolute limits of physics. That's not what this article says.
- mokus 8y ago
  I didn’t see anything in the article that changes the amount of momentum that would be transferred - as far as I could tell it’s all about the distribution of that force being modulated to make the object being accelerated tend to stay in the center of the beam Editing to clarify my point: the article’s title seems wildly misleading by using the word levitation. The energy required to “levitate” a macroscopic object in earth gravity using light is unchanged, and while I don’t feel like doing the math right now i feel pretty confident stating that “impractical” is a monstrous understatement.
sandworm101 8y ago
Ionic thrusters only work well at very low pressures. At atmospheric pressure they are no better than a cold jet, just like opening a bottle of compressed air.

montzark 8y ago

Could we use this to make more haptic touch screens?

openloop 8y ago

Fucking awesome.

mdturnerphys 8y ago

From last year, a 3D volumetric display based on laser manipulation of particles in air: https://www.nature.com/articles/d41586-018-01125-y https://www.nature.com/articles/d41586-018-01125-y

homero 8y ago
Aren't those loud? I saw one that exploded air molecules to create the light.
- mdturnerphys 8y ago
  Those are systems with pulsed lasers that ionize the air. This uses relatively low-power beams to trap and illuminate a small particle.

gus_massa 8y ago

As other commenters noted, the title is very misleading. The force exist but it is tiny, very very very tiny. For radiation, force = power / speed of light 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 * 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. * A modern LED lamp for a room has about 10W, so 100W are like 10 LED lamps. * 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.) So if we divide the force by the acceleration of the gravity https://www.wolframalpha.com/input/?i=2+*+100W+%2F+(speed+of+light)+%2F(gravity+aceleration) https://www.wolframalpha.com/input/?i=2+*+100W+%2F+(speed+of... 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. 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. (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.)

Judgmentality 8y ago
Not to detract from your comment, but the most interesting thing about what you said (at least to me) is that a mosquito weighs half as much as a snowflake.
- barrkel 8y ago
  Snowflakes are non-dense more than they are light - they float down slowly due to air resistance rather than lightness per se. Snowflakes have a pretty big variance in size, I'm not sure that a single weight could meaningfully be assigned to them.
jfoutz 8y ago
I'm completely out of my element here. Hoping maybe for some clarification. I've never heard of a laser, at any scale, having a force pushing backwards against the direction of light. It seems like one of two things is possible. 1) you could move a spaceship by shooting a laser. The force would be tiny, but it would keep accelerating as long as the laser is powered, with no reaction mass. i've never heard of such a thing being possible (but, again, way out of my element). 2) you could play the classic impossible machine game, with the fan on the back of a boat blowing into a sail. except with a laser and a sail. If 1) doesn't work, then 2) has to work, right?

reidjs 8y ago

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!

kosei 8y ago

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.

EastLondonCoder 8y ago
You are right, can read more about one proposal here: https://en.m.wikipedia.org/wiki/Breakthrough_Starshot https://en.m.wikipedia.org/wiki/Breakthrough_Starshot
newnewpdro 8y ago
Avi Loeb described this on ep. 40 of After On [1], it didn't sound entirely unrealistic as he described it. It's around 19 minutes into the interview, I see a sibling links Breakthrough Starshot, in this podcast he describes it on a high level. [1] https://after-on.com/episodes-31-60/040 https://after-on.com/episodes-31-60/040

Animats 8y ago

The new thing here is not pushing with photons. It's making the thrust self-stabilizing, so the target accelerates without spinning.

zepearl 8y ago

Sorry, here comes probably the usual question asked whenever somebody talks about "light": 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? 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?) 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?). 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). Additionally, about "momentum", its definition needs mass, at least as per Wikipedia: > momentum (pl. momenta) is the product of the mass and velocity of an object. ( https://en.wikipedia.org/wiki/Momentum https://en.wikipedia.org/wiki/Momentum ) Therefore if light does not have a mass then it shouldn't be bent by gravity nor have any momentum? Thx :)

barbarr 8y ago
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? Yes, the target object gains velocity due to conservation of momentum. The photon goes from momentum p to -p, so the target object needs to gain 2p of momentum to balance it out. For photons, this amount of momentum is very small. when the light hits, does it lose energy (because some of its energy is transferred to the object that is hit? For perfect reflection, no. (What you're referring to is light absorption, which is a different effect that raises the temperature of the target object and red-shifts the incoming photon.) 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?). Pretty much. Photons are usually described by their momentum and energy. For our peace of mind, we can derive an effective "mass" using p=mv, where p is the electron's momentum and v is its velocity; however, the notion is not very useful since it doesn't correspond nicely to our everyday experience of mass (whereas electron momentum does correspond nicely to our everyday experience of momentum).

samplatt 8y ago

Surprised no-one's yet mentioned the XKCD blogpost on this exact topic: https://blog.xkcd.com/2008/02/15/the-laser-elevator/ https://blog.xkcd.com/2008/02/15/the-laser-elevator/ Or the vaguely-related (because lasers) What-If scenario https://what-if.xkcd.com/13/ https://what-if.xkcd.com/13/