Scientists Create New "Lightsaber-Like" Form of Matter 175
First time accepted submitter loftarasa writes "A group of scientists led by Harvard Professor of Physics Mikhail Lukin and MIT Professor of Physics Vladan Vuletic have developed a form of matter by binding massless photons together in a special kind of medium to create 'photonic molecules', effectively bringing us a bit closer to a world with lightsabers. 'The discovery, Lukin said, runs contrary to decades of accepted wisdom about the nature of light. Photons have long been described as massless particles which don't interact with each other – shine two laser beams at each other, he said, and they simply pass through one another. "Photonic molecules," however, behave less like traditional lasers and more like something you might find in science fiction – the light saber.' The work is described in Nature (paywalled)."
Do we really want light sabres in untrained hands? (Score:5, Funny)
Street justice can get pretty rough [youtube.com].
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Pretty ineffective. They kept hitting that guy and he still wouldn't stay down.
Use the force, Lukin (Score:5, Funny)
Oh yeah.
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Thank you for explaining the joke. I don't know how I would ever have made the connection without you.
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It's paywalled. How about coming over to the dark side, Luke?
Unfortunately, you need real molecules to do this (Score:5, Informative)
As the photons enter the cloud of cold atoms, Lukin said, its energy excites atoms along its path, causing the photon to slow dramatically. As the photon moves through the cloud, that energy is handed off from atom to atom, and eventually exits the cloud with the photon.
These are not photons in free space being described. These are photons which have excited electron orbitals in some material.
Re:Unfortunately, you need real molecules to do th (Score:5, Funny)
These are not the photons you are looking for.....
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<handwave>You don't need a coherent article summary.</handwave>
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Correct, although I should point out that they're photons propagating through a medium, not photons being absorbed and re-emitted as one might assume. It's interesting that they're so strongly coupled to the rubidium.
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In a sense. They excite the individual rubidium atoms and then get re-emitted in a form identical to the original at the quantum level.
Re: Unfortunately, you need real molecules to do t (Score:2)
Did you read the whole article? One photon will be re-emitted in identical form to the original, but two photons will likely be re-emitted as a single, molecule-like unit.
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No, it said two photons will be released together. Two photons flying in formation is hardly the same as a bound molecule.
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With no binding force, it is not a molecule once it leaves the cloud (which mediated the binding). Since I seriously doubt they would bury a lead like 'new force of nature discovered' or 'photons interact through nuclear force', I can only conclude that you are taking the analogy far more literally than they intended.
WITHIN the rubidium cloud, they act as a molecule whose binding is mediated by rubidium atoms. That is not uninteresting, but is not the same thing at all.
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by what?
Re:Unfortunately, you need real molecules to do th (Score:4, Informative)
This is happening in a non-linear medium where photons interact: it can't happen in free air. Photons hardly interact on most transparent media, but there are materials with non-linear electric properties that can be used to generate harmonics ( see for example http://en.wikipedia.org/wiki/Second-harmonic_generation [wikipedia.org] ). This is used to convert red light into green in some green laser light pointers. At high power levels, the refractive index increases in more normal materials, which is a nuisance in high-power lasers as light in NdYg glass laser elements can self-focus and damaage the apparatus if the power gets too great.
Hardly "contrary to decades of accepted wisdom about the nature of light" if you can find it in a green laser pointer. Meh.
Re:Unfortunately, you need real molecules to do th (Score:4, Insightful)
Calling it a form of matter is a bit of a stretch as is imagining that an advanced form of it could ever be lightsaber like. Unless all saber fights will take place in a rarefied environment consisting of super cold rubidium.
massless photons vs black hole (Score:5, Interesting)
I've also heard that black holes are so massive that the force of gravity does not let anything escape including light.
So, if photons have no mass, how do black holes keep the photons from escaping?
Re:massless photons vs black hole (Score:5, Informative)
A smart guy called Einstein did a lot of explaining about this.
Re:massless photons vs black hole (Score:5, Informative)
No, photons do NOT have mass. You can only go at the speed of light (photon is light) if you do not have mass.
Photons have only energy associated with their speed. But NO energy associated with any mass.
And you do not need mass to be affected by gravity. Gravity is a distortion of space, and therefore everything in space (with mass and without) is affected by gravity.
This blog post explains everything in detail in a simple way:
http://profmattstrassler.com/articles-and-posts/particle-physics-basics/mass-energy-matter-etc/more-on-mass/the-two-definitions-of-mass-and-why-i-use-only-one/]
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This is why I love /. That was a great article. Thank you for posting it. Back (way back) in high school I wanted to by a physicist. Going into my freshman year of physics I quickly discovered two things. One, physics is damn hard and what the hell is calculus. Two, I was introduced to computers by my calculus professor and it was love at first sight. I dumped physics (clearly she moved on to better things) and have been with computers ever since. Still I love keeping in touch with the general worl
Re:massless photons vs black hole (Score:5, Interesting)
I'm no expert.
But I think it has less to do with gravity directly effecting things, and more to do with the gravity of the singularity simply bending space to the degree that things move into it. Thus, anything traveling through that warped space would be effected.
Re:massless photons vs black hole (Score:5, Informative)
Photons have no _rest mass_ or they couldn't go the speed of light. Their mass is their energy which is a function of their frequency.
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Aaaaah! rest mass == massless, but because of their energy, and e=mc^2, there is, effectively, a mass, which the black hole can act upon... got it! Thanks!
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I think momentum is an important term to remember here. Photons may not have rest mass, but they do have momentum. (in classical physics: p = m * v)
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So, we keep measuring the speed of light more and more precision, and what if our precision with that measurement simply isn't up to the job, and light actually travels at ever so slightly less than the (theoretical) speed of light. ...) small mass ...
Photons at rest could then have a Really (really really
ebyrob> I think momentum is an important term to remember here. Photons may not have rest mass, but they do have momentum. (in
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Photons at rest could then have a Really (really really ...) small mass ...
Well, theoretically (and only theoretically) photons could have a gigantive rest mass that is 100% converted to energy when in motion. The problem we normally face is that we cannot convert (or think of how to convert) 100% to 100% energy in a manner required to do that - t0 at rest, t1 in motion, a=c over t0 to t1 and (t1-t0) is nearly zero (e.g. 0.000.....0001 or 1*10^-infinity).
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In addition to the point about different energies having different speeds.
If they had _any_ rest mass at all their mass would be approaching infinity as they approached the speed of light.
Re:massless photons vs black hole (Score:5, Informative)
Physicists - please cover your ears, I'm trying to simplify.
When particle move near the speed of light their mass increases. At the speed of light it becomes infinite. Imagine a very light particle, moving very fast. By making it move near C I can get any mass I want. So now imagine i make the original particle lighter, an keep moving it faster in such a way that its moving mass stays the same. In the limit a particle with zero mass moving at the speed of light can have some moving mass. That is how a photon works.
Gravity will bend light, but the effect is very weak because light is moving very quickly. Gravity around a black hole is so strong that it will stop even light.
Real relativity and general relativity changes this a little, but the basic idea is the same. Photons are very light -> massless. They move very fast -> speed of light, so they have mass from their motion. Gravity doesn't bend light much - but black holes have very strong gravity so they do bend light.
Re:massless photons vs black hole (Score:5, Informative)
The BH does not stop light. It changes the path light takes so it never leaves the black hole's event horizon.
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Yes, all timelike curves cross the event horizon and hit the singularity (I think, maybe not for rotating black holes) because of the curvature of space.
I wanted physicists to cover their ears because I was trying for a vaguely correct explanation that didn't require too much background.
Even without general relativity you could imagine a concentration of mass what would prevent (newtonian) light from escaping.
Re:massless photons vs black hole (Score:5, Informative)
Physicists - please cover your ears, I'm trying to simplify.
Sorry, but I can't let that go, especially since it's been modded up. Just no. Light does not have mass. There is no such thing as "moving mass."
General relativity: How does a large mass bend light? Because a large mass bends space around it. Light ends up bending around the object, kind of like a banked roadway. A black hole bends space so tightly that if light gets too close (the event horizon), it gets sucked in. That's why we refer to it as a hole.
Re:massless photons vs black hole (Score:5, Informative)
A photon has mass energy. If I take an empty box made of perfect reflectors and add a photon, it will weigh more (by a tiny bit). It will have more inertia since inertial and gravitational mass are as far as we can tell exactly equivalent (as required if you use a curved space model of gravity).
In any case, words are a bit fuzzy. A photon has 4-momentum and the mass like term (or time like term if you wish) is non-zero.
btw- curved spacetime is a perfect model for all existing measurements involving gravity, but is incompatible with quantum mechanics at very (unreachable) high energies.
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You are wrong, read wikipedia or google for "photon mass".
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becasue the curved area of space is bent so far that it never comes out the other side.
Black holes are where the universe divided by zero.
Re:massless photons vs black hole (Score:5, Informative)
Imagine a gigantic sheet and stretch it out flat and taut. This is space. Take a marble and set it rolling across the sheet. This is your light particle. It reaches the other side.
Now attach a weight under the sheet so that it dips in the middle. This is the gravity of a star. Take the marble again and roll it across the sheet so it goes through the dip and keeps going. The curved path of the marble describes the influence of gravity upon the light particle.
Now imagine the weight is so heavy that the dip is effectively vertical at its heart, a hole in the sheet. This is the gravity of a black hole. Take the marble again and roll it across the sheet. If it gets too close, it rolls into the hole and doesn't come out.
Obligatory xkcd (Score:3, Informative)
http://xkcd.com/895/ [xkcd.com]
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The standard image in popular science of a bowling ball distorting a rubber sheet isn't very good at conveying what is going on. It is not space, but rather space-time that is curved - you need to imagine the curvature of 4-dimensional space time - which normal humans like me can't do.
Kip Thorne had an example that was easier to think about. Imagine an orange with 2 ants at the equator. In this model space is 1 dimension, east / west. Time is latitude. So if the ants are not "moving" in space, they will w
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I was taking a photon as the limit of a missive particle where you increase the velocity and decrease the mass in such a way that the mass-energy remains constant.
And I am NOT colossal, and my sexuality is not a matter of public record.
Otherwise though you are correct, but I was trying for an explanation that a non-scientist could understand.
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Yes gravity is very weak, but it is unique among the forces in that there are no "negative" gravity charges and that like-charges attract. The electrical forces between 2 electrons are enormously stronger than the gravitational forces. If I try to collect a lot of electrons in one place though, those forces will push them apart.
If I take neutral particles (say atoms), the gravitational force of each one is incredibly tiny - but it is attractive. If I get a LOT (like the mass of a planet together), they wil
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Photons could have a tiny rest-mass. You can't distinguish experimentally between a particle with a tiny mass moving very near the speed of light and a massless particle moving at the speed of light (this was part of my point in talking about the limit as the rest-mass gets small). People have put limits on this though and if the photon has rest mass it is TINY. Really really tiny.(I see a paper showing 1e-54 kg).
Your neutrino comment is a good example - it was thought to be mass-less, and to move at th
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What is the part you think is wrong? This sort of thing is difficult to explain. The "correct' description in fairly recent physics is that gravity is due to the exchange of spin-2 gravitons. Maybe by now there are even more exotic explanations. They are way beyond me - and anyone else not in the field.
General relativity is a pretty good description - it matches all observations and experiments, the only (big) problem is that it is not compatible with quantum mechanics at very large energy scales. Quantu
Re:massless photons vs black hole (Score:5, Informative)
Slightly OT question but TFA mentions that photons are massless particles. I've read that elsewhere, too.
I've also heard that black holes are so massive that the force of gravity does not let anything escape including light.
So, if photons have no mass, how do black holes keep the photons from escaping?
Gravity bends the fabric of space-time itself, which the photons are travelling through.
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Gravity bends the fabric of space-time itself, which the photons are travelling through.
Yeah, I get that, but I thought that the gravitational attraction was between the relative masses of the two objects. Presumably, therefore, any massless doodah wandering by would be unaffected by the masses of thingamejigs it might pass. ...
That being so
A mass-less photon (at speed) whizzing past a superhumongous 'body' would be unaffected by it, gravitationally, regardless of how massive the body was, if it had no mass. Ergo - a photon at speed has mass.
Where does that mass come from. If it comes fr
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E=mc^2. Rearranged, m = E / c^2.
A photon has no rest mass (or energy). It does have energy associated with it's motion, and energy is equivalent to mass. You can use that mass/energy as the term in the classical momentum equation, or calculate the non-classical momentum directly based on it's frequency.
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if m1 is 0 then F would be 0 in newtonian physics. Einstein General Relativity replaces this equation. The theory was proved when Einstein showed that light bent around the sun. (measured during an eclipse)
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They are massless, but they are still affected by the curvature of space, which according to relativity is the actual 'cause' of gravity. The space at the event horizon is curved such that not even photons can escape.
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Because black holes are undead stars reaching from their graves with claws of gravity, and we all know that if you try to run from the monster you end up running right at it, which is what happens to photons. Then they get eaten and are never seen again.
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Photons have no rest mass. They do have mass, though. In line with that, I should also note that photons do not exist in their own system, when in transit through high vacuum. That is, within their own system, the time - dilated length of time that they experience (while travelling at the speed of light) approaches zero.
Of course, photons seldom travel at the speed of light. And their own existence seems to use non-photons as their space.
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So, if photons have no mass, how do black holes keep the photons from escaping?
They don't. The gravitational field created by the black hole bends space-time.
Think of a marble rolling around a flat sheet. The marble always moves in a straight line.
Now imagine the sheet has a big depression in it. The marble still rolls 'straight' but as it follows the dip in the sheet, it 'curves' into the dip.
Now, to the marble, it feels like it's still going straight.
To an outside observer it looks like the marble is tracking into the dip.
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Photons have no "rest mass".
But as every photon is moving it has 'kinetic' mass, h*v / (c^2).
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Pfft ...
If photons had no mass, something like a photovoltaic cel would not work.
The one with "shallow" ... or more precisely "no knowledge" about photons is you.
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When a particle is said to have no mass, they really mean it has no mass at rest. It still has the mass associated with it's energy and photons have energy.
Re: massless photons vs black hole (Score:2)
So, if photons have no mass, how do black holes keep the photons from escaping?
Good question, photons are energy, E(eV) = 1.24 / Î(μm).... the answer is m = E / c^2. Photons are like atoms, individually they are insignificant, because c^2 in is so large.
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Yes, but there is no spoon, so how can you possibly bend the space around it?
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Instead, try to realize the truth. You will see it is not the space around the spoon that bends, it is only yourself.
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Even better, black holes are time-stasis bubbles. Studying them from a spacetime metric POV and adding entropy considerations make for a fascinating journey.
Well (Score:2)
Dear University PR Heads: (Score:5, Insightful)
That is all.
You know that if they actually ever do make one... (Score:4, Funny)
Re:You know that if they actually ever do make one (Score:5, Funny)
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If lightsabers were real, a fair number of people would carry one for self defense...
...I'm just picturing George Zimmerman with a light saber.
"Hey You! Kid!! What the hell are you doing around here!!!!" [bwazzzzzzzzzZZZZZZZZZZZZ - bzzzzWAAAaaaa - bzZZZZWAAAaaa]
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I was going to reply with a "citation needed" to this one but, on second thought, if this is true then I really don't need to know.
This is highly illogical. (Score:3, Informative)
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Phasers are not lasers.
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By that I mean that directed energy weapons are highly unlikely to use photons as the means of deploying their energy bursts. Magnetic bubbles of plasma or streams of electrons or even subatomic particles would be far more likely to be used.
Lasers, on the other hand, shoot photons.
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Really? Because of all those things, the only one that is currently actually being used as a directed energy weapon is...in fact, the laser.
At least so far as "directed energy" doesn't count the acceleration of metal projectiles or explosive shells, which still take the cake for directed energy burst delivery.
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Lasers, on the other hand, shoot photons.
Yer a frickin' libral. Everyone knows that lasers don't shoot photons! People with a laser shoot photons.
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Better to put them in a torpedo....
Light Saber? (Score:5, Insightful)
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Cue the comedy (Score:2)
While everyone misses the science. Sad state of affairs of the so called 'geek'.
Re:Cue the comedy (Score:4, Insightful)
Science?? Not everyone has a paid subscription to Nature. Without that there is hardly anything to miss!
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And you call yourself a nerd.
the summary is garbage... (Score:5, Interesting)
From what I can tell, they are simply creating a system of quantum-mechanically entangled photons, not a "molecule" of photons...
Apparently trick is that they created a medium (a laser cooled "gas" of rubidium atoms), and excited it with photons from a laser at a frequency that created a condition for the formation of a Rydberg state in the gas. This state is basically kind-of a pseudo-atom (i.e., a group of atoms that behave somewhat like a "scaled-up" atom). The gas made up of the pseudo-atom has a different apparent index of refraction than the unexcited medium looks to the first photon but it can effectively keep a second photon nearby the first photon in a type of quantum entanglement
This is what is described as a photon "molecule". Of course the energy levels required to create a similar Rydberg state in air (at room-temperature) would be slightly different orders of magnitude because you are pumping in enough energy into the air so that hyper-energized pseudo-molecules of air are resisting your opponent's light sabre... Not so sure you want to be actually holding a device that does that ;^)
Re:the summary is garbage... (Score:5, Informative)
From what I can tell, they are simply creating a system of quantum-mechanically entangled photons, not a "molecule" of photons...
You can stop reading the summary after "A group of scientists led by Harvard Professor of Physics Mikhail Lukin and MIT Professor of Physics Vladan Vuletic..." Everything after that is complete fabrication.
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Second that.
Lightsaber! (Score:4, Insightful)
The journalist could not say their finding will cure cancer or obesity in several decades, therefore they sold it as a potential path to lightsabers!
We would probably not accept such bold tactics from politicians, why do we accept it from scientific journalists?
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The journalist could not say their finding will cure cancer or obesity in several decades, therefore they sold it as a potential path to lightsabers!
We would probably not accept such bold tactics from politicians, why do we accept it from scientific journalists?
From what I've seen, we do accept such outrageous tactics from politicians. Journalists seem to have realized that they can do the same.
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Lukin Skywalker (Score:2)
Holodeck (Score:5, Interesting)
Useless, unfortunately (Score:2)
Without Jedi skills, carrying a light-saber is just a good way to get shot.
What a terrible article summary. (Score:2, Informative)
What a terrible article summary.
Light is not self interacting at the tree level. This means there is no scattering of light in the classical sense, only through virtual particles (quantum loop corrections). Did this group of experimenters prove otherwise? No.
This is the most clear statement from TFA
"It's a photonic interaction that's mediated by the atomic interaction," Lukin said. "That makes these two photons behave like a molecule, and when they exit the medium they're much more likely to do so togeth
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That's not actually really new either - people have been shooting lasers into super cold rubidium gas for years. What's new here is that these guys shot two photons in and watched them come out again.
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What a doof! everyone knows Steven Spielberg created Firefly, not Star Wars.
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Oh, come on! It was created by Gene Roddenberry!
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No, that was Star Search with Ed McMahon
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Re:STEVEN SPIELBERG HERE !! (Score:4, Interesting)
Everyone knows that Star Wars started off as a cooperative writing project between Robert Heinlein and Issac Asimov
Do you also love the part of the movie where Hari Seldon uses psychohistory to predict where the engineers would have put the most vulnerable spot, and then personally blows up the Death Star with a proton torpedo?
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Well that explains why Ep. V went downhill after the Battle of Hoth. Come to think of it, it completely explains the land side of the Battle of Endor.
Re:STEVEN SPIELBERG HERE !! (Score:5, Funny)
Use the force Harry!
-Gandalf
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I think Dumbledore says that.
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He can't! My tricorder says Neo is in the way!
- Tyrion
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Mickey Mouse has more to do with Star Wars than George Lucas.
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Great, now I want curry and all the delivery places are closed.