Video: Quantum Levitation | Hacker News Reader

Video: Quantum Levitation

jasonadriaan.com

572 pointsjasonadriaan95 comments

Reminds me of a great quote by Benjamin Franklin:

"The rapid progress true Science now makes, occasions my regretting sometimes that I was born too soon. It is impossible to imagine the height to which may be carried, in a thousand years, the power of man over matter. We may perhaps learn to deprive large masses of their gravity, and give them absolute levity, for the sake of easy transport. Agriculture may diminish its labour and double its produce; all diseases may by sure means be prevented or cured, not excepting even that of old age, and our lives lengthened at pleasure even beyond the antediluvian standard. O that moral science were in as fair a way of improvement, that men would cease to be wolves to one another, and that human beings would at length learn what they now improperly call humanity!"

-- Letter from Benjamin Franklin to Joseph Priestly (8 Feb 1780), quoted in "How Mumbo Jumbo conquered the World" by Francis Wheen

Benjamin Franklin would be delighted to know that he woefully underestimated science's impact on agriculture. http://en.wikipedia.org/wiki/File:Wheat_yields_in_developing...

Pure marketing. "Quantum levitation" is just flux pinning[1] as seen in all "high temperature" superconductors. All you need a chunk of type 2 superconductor, a strong magnet, and some liquid nitrogen. Note the 852 videos on youtube: http://www.google.com/search?q=superconductor+levitation&...

You can shell out 80 bucks and do it yourself: http://sargentwelch.com/superconductivity-suspension-and-lev... (LN2 not provided.)

There doesn't appear to be any novel physics here at all.

1: http://en.wikipedia.org/wiki/Flux_pinning

> All you need a chunk of type 2 superconductor, a strong magnet, and some liquid nitrogen.

This isn't entirely accurate. A "chunk of type 2 superconductor" would just show the Meissner Effect, which is different than "flux pinning". The Meissner Effect is how superconductors essentially repel magnetic fields, resulting in levitation; it wouldn't necessarily pin the levitating body in-place such that it could follow some track for example.

Flux pinning occurs when some magnetic fields penetrate the superconductor in discrete "tubes" through the imperfections (along the grains) of the superconductor. In order for flux pinning to happen, you must have an extremely thin superconductor (in the case of the video, it's actually a sapphire crystal wafer with a 1-micron thick coating of superconductor ceramic material).

EDIT: Technically, you could also get flux pinning if you were to supercool the superconductor (i.e. make it a superconductor) while it's in the magnetic field of the magnet.

I played quite a bit with the Meissner and the Flux pinning effect. But I was never able to change a flux pinning "on the fly". You always had to reheat the superconductor to something over the transition temperature and then cool it down again inside a magnetic field (in the desired position). But then, it was quite strongly locked in that position and would snap back to where it was when moved.

So, I'm quite curious on how this works ;) Is it because it's a very thin superconductor in this video?

Just to do (dia)magnetic levitation, you could put together 4 cubes of neodymium magnets, then cleave a very thin sheet of pyrolytic graphite and gently suspend it on top of the cubes.

If it's thin enough, it will float.

This is why I love HN. See something that blows my mind. Read comments. Meh. (When I say "love," you know I mean "hate" right?)

What's he marketing exactly? It's a Tel-Aviv University demo at ASTC.

I think naming the device "Quantum Levitation" is marketing. Why can't the student call it what it is?

Students especially have been known to give things cool names just cuz.

I actually did not click on the movie link initially BECAUSE it has the word "quantum" in its title. To me, that's a bee-ess test, if the link is very popular with the media.

Then I saw some comment threads on various sites and I was like "okay, let's see what's going on here". Heh, cute levitation effect.

I thought first that this is the same old levitation effect, but apparently it's something new. At least the effect seems to be much stronger.

"Much stronger"? You can reposition it with your hand!

It's strong enough to not have the springiness you normally see with levitating superconductors.

This is very cool. Another video with a bit of an explanation as to why - http://www.youtube.com/watch?v=VyOtIsnG71U.

Thanks. I'm not sure I understand the part about "quantum flux tubes". I take it that they're leaks through flaws in the superconductor (which should exclude the field entirely). Is the superconductor is being gripped or pinned by these lines of force running through it, like a piece of cheese on a toothpick? But that doesn't quite explain how it can move along a field.

I think the magnets on the track piece may be arranged NSN like this:

  NNNNNNNNNN
  SSSSSSSSSS  ==>
  NNNNNNNNNN

Which allows movement as indicated. In the part of the video where it's just locked stationary above a square magnet, it appears maybe the magnet as this arrangment:

  NNN      NS
  NSN  or  SN
  NNN

Which locks it entirely in-place, not allowing movement. And then in the part where it's spinning, I think maybe the magnet is S on the inside and N on the outside or something:

      NN
     NSSN
    NS  SN
     NSSN
      NN

Allowing it to spin. But this is speculation based on my limited understanding (but I noticed no one else was answering, so I thought I'd give a shot).

Very good video. The 'locking' effect is simply blowing my mind. I had no idea that was possible.

I'm trying to figure out some practical applications for frictionless movement and positioning of small, light and cold objects without changing the scale of the system, but each of my ideas implies some heating that would probably negate the phenomenon a bit too fast (ballistics for instance).

I can't resist posting one of youtube's comments on this last video: "so... you have created the worst paperweight ever"

I couldn't help but picture beers quantum-levitating toward me from the refrigerator when you said "small, light and cold objects."

It could replace pneumatic tube systems for mail. Not that these are still in much use today, except hospitals.

> (ballistics for instance)

so people already wanna make a gun out of it, that's just sad

mankind will always pervert science for power?

Military research is where a whole lot of the cool science comes from. There's nothing like knowing the guy who gets there first is going to blow your head off to spur the competition.

In fact, maybe governmental science grants should have some sort of gladiatorial combat requirements for disputed priority...

The word "ballistics" is not a synonym for "weapons".

http://en.wikipedia.org/wiki/Mass_driver

Quick question: If the object is the temperature of liquid nitrogen, how can he touch it for so long?

Leidenfrost effect:

http://en.wikipedia.org/wiki/Leidenfrost_effect

The stuff of which awesome party tricks are made. I have myself put a very small amount of liquid nitrogen in my mouth and blown it out, although I then heard that the guy who taught me that trick (Jearl Walker) cracked a tooth doing that, so I never tried it again. And for the love of god do not swallow or you will literally kill yourself very painfully -- see footnote 3 of the above Wikipedia article.

I think I'll stick with dipping fingers briefly into LN, which is way less stupid. Done that many times. Do not get it on your clothing, though, because then you can't retreat quickly and the frost is going to bite!

"What was really astounding about Michael's case is that the liquid nitrogen instantly expanded from a volume of about 3 or 4 cc's to about 3 or 4 liters and then dissected into five separate body compartments"

Ouch. http://www.wpi.edu/news/19989/nitro.html

Yes, if this Wikipedia article had existed when I was a college senior I'd never, ever have tried that particular party trick. ;)

Yet another example of how the web makes us much, much smarter.

I estimate that I used a tiny sip, not 3 or 4 ccs, but still. Crazy risky.

A teaspoon is 5ccs. 3-4cc IS pretty much a tiny sip, unless you have excellent lip-control.

I am aware of that effect, and I have seen it in action. I am trying to reconcile what I see in the video with what I have seen of Leidenfrost in the past.

He actually grips the object, and I don't see extra smoke. When I have observed the Leidenfrost effect in the past, I see a noticable increase in outgassing, and the liquid (as it usually is) skitters about freely, so it seems like it might be difficult to grasp an object through the vapor layer.

It's not liquid nitrogen, but rather dry ice. You can touch dry ice for short times if you don't squeeze tight and your fingers are dry.

You could literally pour liquid nitrogen onto your hand.

http://www.flickr.com/photos/chewie/162967702/

Don't try this at home, kids!

Actually, are we sure the liquid nitrogen is actually hitting his hand? The point of contact is obscured by vapour. I mean, I'm familiar with the effect, but can also believe that a big stream of liquid nitrogen is gonna hit you and it's gonna hurt.

I took that picture I assure you, and he wasn't wearing gloves nor any kind of protection.

It's covered in water and carbon dioxide frost.

That does not look like liquid nitrogen. It's solid so that tells me it is carbon dioxide.

Believe it or not you can dip your hand in liquid nitrogen for 10 seconds without it freezing immediately and breaking off. I think carbon dioxide is solid at higher temperatures than nitrogen but I could be wrong on that one.

I don't mean the object is nitrogen- I just think I caught them say it had been chilled with liquid nitrogen.

But when you do, doesn't it start to boil? This object seems to merely vaporize without doing so any faster when in contact with his fingers.

Yeah you feel it boiling on your fingers. It's really bizarre too because it feels all light compared to water.

I just saw another video and you are right that they just cool it with liquid nitro.

When I came into work this morning this was at the top of reddit.com/r/all (got to get the procrastination out of the way first thing right!)

A guy spoke up regarding his father who works in the field. Currently doing Q&A

http://redd.it/lfsjn

Is there a layman's summary regarding the significance of that paper linked on reddit?

Completely irrelevant. It's a theory explaining how Type II superconductors work, published five years ago, in a Chinese journal that has an impact factor of 0.512 (Nature scores 30.98, for comparison.)

What's the relevance of "impact factors"? I understand the basic idea behind them, but I don't think publishing research in a low impact factor journal should automatically make said research "completely irrelevant".

It's completely irrelevant because it has little to nothing to do with the original post, much like how you wouldn't link to a paper on algorithmic complexity in a post about Facebook, because "they're both about computers."

Additionally, the author of the paper displays some worryingly crackpot-like symptoms. He claims that it's "Nobel worthy", (!!) but Citebase can find no citations.

I know nearly nothing about condensed matter physics, but skimming the paper reveals that his theory doesn't really make any testable predictions, much less the "grand slam" predictions that would result in a Nobel, like room-temp superconductivity.

Impact factor is tremendously flawed, but as a quick sanity check, when you're not sure if something makes any sense at all, it is of great use.

He cited it himself in two other papers :/

As far as crackpot symptoms, it looks like he's a biblical literalist too!

Ah ha, you missed my very careful weasel wording! I said that Citebase found no citations, not that it actually had no citations, mwa ha ha.

So, the electrical engineer in me says that this is because any movement of the magnet would induce an electric potential in the superconductor. But because such a potential would create an effectively infinite amount of current requiring an infinite amount of work, the magnet is unable to move.

Or from a "cause-and-effect" viewpoint, movement of the magnet induces a current loop in the superconductor, the creation of which creates an opposing magnetic force.

Either way I believe this is the same principle behind electric motor braking (e.g. when you short-circuit the inputs of a motor). I believe you would also see a similar effect by dropping a magnet down a tube encircled with many (or perhaps one spiral) loop of wire -- the magnet's descent will be slowed by eddy currents in the loops.

Edit: Aha, this is just half the story. The superconductor is prevented from spinning due to flux pinning: http://en.wikipedia.org/wiki/Flux_pinning (or what the researchers call quantum trapping / quantum locking)

http://en.wikipedia.org/wiki/Eddy_current_brake

You can get clever with pulsed electromagnets and active coils, but eddy current braking works just fine with a permanent magnet and a thick piece of copper: http://www.youtube.com/watch?v=nrw-i5Ku0mI

But, it clearly does not take an infinite amount of force to move the "locked" superconductor, because you can adjust it by hand. The real question is, how much force does it take?

Right, I believe this is a function of how much of the magnetic flux does not encounter the superconductor. But IANAP, just a former EE, so I don't know that this is 100% correct.

Furthermore is there a threshold or is is the magnet slowly falling due to gravity?

And it's able to move around the ring because from its perspective, the field isn't changing?

Exactly.

...I really want to hear from an actual physicist about the "quantum trapping" explanation. I feel like I must be oversimplifying but I can't find any inconsistencies in my model.

Is this "quantum locking" just a rebranding of the Meissner Effect?

http://en.wikipedia.org/wiki/Meissner_effect

Quoting a comment in the video linked to by fybren:

"This levitation is NOT due to the Meissner effect. It is negligible since we use thin films. If it were the Meissner effect the field would get distorted on a length scale of the diameter (~cm) and then two discs hovering above and below each other would affect it other. Which is clearly not the case. The discs are actually trapped in constant field contours rather than levitating."

On a more serious note, I'd love to find out more about just how much weight they think this tech could support in the future. Those implications could be insane.

Agreed. If the "floating" (I know its not actually floating in the traditional sense) object could carry its own light-weight cooling system then you wouldn't need to chill the entire unit to super cold temperatures. You might only need to cool the superconducting layer.

The thing is, we are all waiting for room temp superconductors. That paper on the Reddit post seems to have some breakthrough regarding this if I'm not wrong.

Loads of up to 500 grams on this test rig, on what look to be about n40 magnets, according to the presenter's comment on one of the lab videos. The liquid nitrogen is a problem but that payload seems like something that could already have industrial applications.

What industrial applications come to mind? The answer is non-obvious to me.

Frictionless bearings, flywheels, stuff like that. Given the need for ultra-low temperatures it might work in space.

You know we already have maglev trains, right?

from the comments

In the lab we succeeded in putting up to 0.5Kg on top of one disc. Keep in mind that the thickness of the superconducting layer is ~1micron ! Its a strong effect.

Direct link: http://www.youtube.com/watch?v=Ws6AAhTw7RA

As a thought experiment, could the effect demonstrated here be used for a transport system on a much colder planet with a much stronger magnetic field (I do realize that these two properties tend to correlate in opposite directions)? What about in our arctic regions, potentially over a magnetic track to interconnect enclosed "settlements"? I'm guessing it would be less cost-effective than other types of transport if even possible, but many times cooler.

Will this scale to train cars weighing a few tons each?

So if this was demonstrated live to congress, do you think they'd finally fund a few miles of super-conducting trains for research?

Or they can cross the Pacific ocean.

http://en.wikipedia.org/wiki/JR-Maglev

Most train cars are more than a "few tons".

blogspam.

Agreed. Several people (myself included) had already submitted the direct link to the youtube video. This blog adds absolutely nothing to the video.

not exactly, I just posted it to tumblr. It would be blogspam if I were running ads, but I don't.

It's still blogspam even if you're only craving attention.

Hm, I remember getting excited about this about 23 years ago, when I was still at school.

Can't help wondering if perhaps 50 years ago people were also getting excited about it and expecting to see cool things to come out of it in the near future.

Not saying that there couldn't, but I can't help feeling vary about the "technology of the future claim".

Not particularly quantum mechanical.

Well, no more so than everything else you might happen to see in your everyday life.

Well, superconductivity is an inherently quantum phenomenon, more so than other things in everyday life; see http://en.wikipedia.org/wiki/Cooper_pair .

Eh. Solids are an inherently quantum phenomenon.

Am I really the first one who immediately thinks about Hoverboards???

Wow! But that'd need magnets all over the ground!

I think one magnetic half-pipe would be feasible, the question is could a board be made that could support a small human?

Isn't there already a shortage of rare earth minerals, used to make strong magnets? Is that going to be a problem for extending uses of this outside a lab?

But: really cool video.

You could always use electromagnets.

the universe is full of them ..

how much force (if any) is required to break it off the track? Could that disk be slingshotted around at hundreds of miles per hour and stay on tack?

I'd imagine whatever force is needed is proportional to the strength of the magnets. Given that he can pull it off I can't imagine that specific setup requires all that much force for it.

That has to be one of the most engaging conferences I have ever seen. The science demos are just too cool. If I have the time I'm going next year!

Quantum physics professors do that in their first lecture, it's getting old.

Put this in a vacuum... perpetual motion?

How does this work?

At 1:30 the disc on the tracks stops without any outer interference, am I missing something in the video?

Yeah - when I saw that after watching the Take This Lollipop video, which is an extremely well-done fake, I immediately lumped this one into the "cool special effects, but not real" category.

So ... this is actually real? If so, that's pretty awesome :)

It's stopped with a finger. Watch carefully on the left side, frame by frame.

Flying cars here we come?

Sure, but you can only fly at constant altitude along longitude lines. If I understand the effect correctly.

This would have to be over a magnetic surface - like maglev trains http://en.wikipedia.org/wiki/Maglev (which apparently are not technically trains).

How much longer before we all drive landspeeders?

Too long.

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