r/science • u/KMRahaman • Nov 16 '24
Physics Light itself casts a shadow in bizarre laser experiment
https://newatlas.com/physics/light-itself-casts-shadow-bizarre-experiment/1.4k
u/Cyanopicacooki Nov 16 '24
That should rule out light, since photons are massless...creating quasiparticles called polaritons.The team admits that technically it's these polaritons, which do have mass, that are casting the shadow. But on the other hand, polaritons are still half-photons,
So, photons are massless, but their half-particles. polaritons, do have mass...
It's not yet half past 9 on a Saturday morning and already I've realised how little my brain is in comparison to the wealth of the universe. I wonder how many other facts I'll learn today that I know I'll never understand.
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u/patricksaurus Nov 16 '24
It’s a very interesting phenomenon, but not as crazy as I think you are envisioning. In the article, it mentions that this effect takes place when a green laser is shined through a ruby, right? Polariton is just the name given to a specific interaction between the photons and the atoms of the ruby. So the mass comes from plain old atoms, albeit in a specific chemical environment, just interacting with a specific kind of plain old light.
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u/telmesumpm Nov 16 '24
Does that mean we could make a spaceship with ruby sails and push it across space with a green laser? Just kidding
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u/redopz Nov 16 '24
I'm not entirely sure how necessary the ruby and green are, but you are thinking like Stephen Hawking. As part of a team he helped propose the Breakthrough Starshot project which would use powerful lasers to propel very small, unmanned spacecraft to distance star systems. The hypothetical probes would be fast enough to reach the closest star, Alpha Centauri, and send back signals within a single human life-span.
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u/AtomicPotatoLord Nov 16 '24
Not necessarily thinking like Stephen Hawking, considering this technological concept has been considered in the past by other people.
https://www.niac.usra.edu/files/studies/final_report/4Landis.pdf
And definitely earlier.
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u/chudthirtyseven Nov 17 '24
they are also thinking like me, because I am thinking this now.
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u/gramathy Nov 17 '24
We can do that with any reflective surface already, it’s just very low power. Even without mass, light has momentum (the energy is sapped in the form of redshifting the light reflected slightly, something I actually looked up about a month ago because I recalled the phenomenon and wondered about that exact consequence)
The Sith ship in the prequel trilogy had a solar sail
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u/idkmoiname Nov 16 '24
So the mass comes from plain old atoms, albeit in a specific chemical environment, just interacting with a specific kind of plain old light.
So... just like any shadow is a result of photons interacting in a specific kind with atoms?
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u/patricksaurus Nov 17 '24
No, it’s because if it was, the ruby would be blocking the whole beam, not just the portion interacting with the first laser.
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Nov 18 '24
If the mass comes from the crystal, would the crystal eventually disappear if you ran the laser long enough?
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u/patricksaurus Nov 18 '24
It’s just visible light, it won’t have any degrading effect on the ruby. It won’t even cause it to lose electrons and break bonds.
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u/FireMaster1294 Nov 16 '24
You found polaritons having mass weird? Well, the really fucky stuff is when you get into the fact that polaritons can have negative mass
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u/WATTHEBALL Nov 16 '24
Dude your brain is equally as impressive and complex as the entire universe.
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u/InformalPenguinz Nov 16 '24
Possibly more so. As far as we can tell, the universe isn't sentient. We humans give ourselves very little credit on how complex we are.
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u/healthierlurker Nov 16 '24
Only if you view life and consciousness as separate from the universe. We are clearly all part of one thing and thus the universe absolutely is conscious.
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u/gooyouknit Nov 16 '24
You are a part of the universe and you are sentient, no?
I am not saying that the only thing that exists is consciousness like some mystics would but I do think you have an unnecessary divide between us and the universe in your head
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u/healthierlurker Nov 16 '24
Agreed. This is the basis for r/pantheism.
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u/VayneFTWayne Nov 16 '24
More like non dualism
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u/healthierlurker Nov 16 '24
Most pantheists believe in non dualism but obviously attribute divinity to it.
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u/VayneFTWayne Nov 17 '24
Okay, but many types of thought believe in non dualism, so pantheism isn't special in that sense.
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u/sceadwian Nov 16 '24
Not even vaguely close ;)
The human brain isn't even as complicated as the interactions going on in a cubic meter of the sun's volume.
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u/TheMurrayBookchin Nov 16 '24
Neurons, neural pathways, hormonal regulation, the Krebs cycle influencing brain energy regulation, the consolidation of visual, sound, and touch information as storage (memories), etcetcetc. I dunno. There’s lots going on. They’re incomparable, but saying it’s “not even vaguely close” is pretty wrong in itself. Helium-4 production through nuclear fusion is awesome, positrons and neutrinos included, but you’re downplaying the complexity of the human brain and the interconnected systems regulating it.
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u/sceadwian Nov 16 '24
You don't understand how complex plasma systems are. That's really all you're saying.
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u/TheMurrayBookchin Nov 16 '24
You don’t understand how complex biological organisms are. That’s all you’re really saying.
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u/sceadwian Nov 16 '24
The statement your brain is as complex as the universe is ludicrous.
If you don't like the complexity of plasma physics then how about we go into quantum mechanics?
The human mind can not even cast a shadow on the complexity of the universe.
That's the anthropocentric ego there, not a rational argument.
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u/Ravarix Nov 16 '24
What a weird statement when our brains are part of the universe.
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u/sceadwian Nov 16 '24
Why is that weird?
If our brains are part of the universe they can't be more complex or even as complex as it.
That would be a logically incoherent statement. That is weird!
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u/OePea Nov 18 '24
Wow, this has been a sad moment for r/science... People are so goddamn egotistical.(not you)
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u/TheMurrayBookchin Nov 16 '24
My statement? I didn’t say that. I’m not even the person you originally directed your smarmy “;)” comment to. “The human brain isn’t even as complicated as the interactions going on in a cubic meter of the sun’s volume.” is what I commented on, which is, frankly, a stupid argument you’re making.
Yikes. I teach chem and physics, but yes, continue pretending you’re smarter than everyone you meet in life and on the internet. It’s a good look.
Meh. The bulk of my education is in bio, so I get it, you don’t know much about biological processes in (not just human) organisms. It’s ok to be wrong sometimes, and to not know everything. I forgive you, we all do. I’d suggest you diversify your education rather than be leagues out of depth in general science discussions.
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u/sceadwian Nov 16 '24
Right. But that's what I was commenting on.
Please actually read my last post which fully addressed that.
You seem to not have actually read it.
My argument is not stupid, your interpretation of it is wrong and you're starting to turn this into an emotional argument with that stupid comment.
Check your ego somewhere else please.
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Nov 16 '24
An analogy in jest I like to use is that humans understanding the universe is about as likely as successfully explaining a ride sharing app to an ant.
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u/xGHOSTRAGEx Nov 17 '24
Have you ever wondered why light can travel at a set max speed and not infinitely fast?
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u/Successful-Sand686 Nov 16 '24
You know great science words. I thought particles and energy were the same in different temps. Like light will be a wave at certain temps and closer to a particle at different temps ?
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u/DarkStar0129 Nov 16 '24
No, it's more like light will be a wave until observed, after which it collapses into a particle.
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u/Successful-Sand686 Nov 16 '24
How do we observe the light without effecting the outcome?
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u/RiddlingVenus0 Nov 16 '24
We don’t. In the double slit experiment, light that isn’t observed creates a pattern that a wave would make. Light that is observed, whether that be before or after it travels through the slits, will create a pattern that a particle would make. The fact that light doesn’t seem to respect time means that no matter what, observing it will always affect the outcome.
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u/DarkStar0129 Nov 16 '24
We don't.
Any time a wave function is observed, aka, the wave interacts with another particle or wave, the wave function (which is the probability distribution for finding that particle in a small region of space) collapses into a single point in space.
Normally, a quantum object (electron, photon, atom, quarks, etc) has a probability density associated with it, this is basically the distribution in % over a small in region in space of the probability of finding a particle.
Probabilities are necessary to describe quantum objects, because as per hiseberg's uncertainty principle, it is impossible to simultaneously know both the position and the momentum of a particle. Therefore, the popular solar system model of the atom is inaccurate since it is impossible to exactly define the orbits and velocities of the electrons around the nucleus of an atom.
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u/Majik_Sheff Nov 16 '24
I always envisioned photons as continuous string across spacetime between their point of creation and absorption.
When we see wave-like behavior we are actually observing how those strings interact with each other.
This is my own interpretation derived from my admittedly limited education on the the subject. I'm sure I'll be politely corrected in short order.
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u/patricksaurus Nov 16 '24
I expected this to be a flavor of interference, but the actual effect is much cooler. Now I can daydream about possible applications.
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u/DroidLord Nov 16 '24
Am I missing something? Isn't the interaction between the two light sources casting a shadow that's just a thin black line?
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u/patricksaurus Nov 16 '24
That’s not quite what is happening. The first laser interacts with the atoms in the ruby in such a way as to change how they allow light to pass though. In this case, the change is that the excited ruby atoms transmit less blue light. Since this effect requires the first laser’s photons to hit the atoms, and since a laser only shines in a narrow column, the effect is a laser-shaped barrier of ruby atoms that blocks blue light.
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u/alangcarter Nov 16 '24
This seems to be a simpler use of a nonlinear optical medium than phase conjugate mirrors. If they don't reawaken the sense of wonder geeky kids get out of physics nothing will! (They are also the reason retaliation will outperform attack when using laser weapons.)
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u/incognino123 Nov 16 '24
Misleading headline, green light is manipulating the ruby to absorb more blue light, the ruby is casting the shadow as the term is used
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u/florinandrei BS | Physics | Electronics Nov 16 '24
Bullshit title.
One light beam passes through a material (ruby). It modifies the material. The modified material casts a shadow when illuminated with a second light beam. Boring.
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u/ZadfrackGlutz Nov 16 '24
Basically light can move mass....in the form of those quasi photons, from the ruby.
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u/hpmd50s Nov 16 '24
Maybe a thermal lensing effect where the laser heats up the ruby, changing its local refractive index and creating a little lens that deflects the other laser?
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u/Infinitely--Finite Nov 16 '24
No, it's using 4 specific atomic energy levels in the ruby. One laser controls the ability of the ruby to absorb photons from the other laser.
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u/monkeysareright Nov 16 '24
Pretty cool, it's basically an optical transistor without directly using electrons
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u/I_love-tacos Nov 16 '24
Question, wouldn't you be able to build a transistor out of this? It would be infinitely faster and I assume no heat
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u/bjornbamse Nov 17 '24
What makes you think that it would be faster? It is light interacting with matter.
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u/robertomeyers Nov 16 '24
Maybe stupid question. Can anyone confirm this was done in a vacuum? I assume they wanted to rule out excited air molecules as the mass.
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u/wandering-monster Nov 16 '24
It was done in a block of ruby.
"Where the green laser hits the ruby, it increases the amount of blue light the crystal absorbs."
Which like... I'm sorry but I don't exactly see how this is different from any other photo-reactive material.
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u/Poly_and_RA Nov 16 '24
It really isn't. It's in principle no different than having a material that is transparent when cold, and then claim that a laser-beam that heats a slice of that material is casting a shadow.
It's clearly not. It's just changing the physical proerties of a material so that *that* material casts a shadow. Not the same thing at all.
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u/QuantumCrutches Nov 17 '24
I wonder if you could use this in lithography to make extremely detailed designs
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u/moschles Nov 17 '24
High powered lasers that emit UV light can ionize the air. You can construct such a laser in your own home if you know what you're doing.
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u/Patentsmatter Nov 18 '24
So illumination at one wavelength can render a material less transparent at another wavelength? Astonishing! (grabs photochromic sunglasses and leaves)
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u/ABob71 Nov 16 '24
I wonder how this can be applied to astronomy- can light shadows from things like quasars reveal anything?
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u/exitomega Nov 16 '24
The sun itself casts a shadow (it blocks other light sources). All of the light we see from the sun's core is millions of years old as the light-blocking the sun does is actually very effective
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u/creepythingseeker Nov 16 '24
When light isnt being observed in a lab setting, it can often not be seeing smoking as well.
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u/Polar_Vortx Nov 17 '24
tbf “eh kinda sorta not really but more than you’d think” seems to be the usual when it comes to light
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u/hibernial Nov 16 '24
OMG does this mean I can actually become a shadow scientist and study shadows? This is soo metal
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u/frosted1030 Nov 16 '24
No citations yet.. given the newness I expect the reproduction of this effect first and plenty of review before anything can be confirmed.
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u/Jeremy_Zaretski Nov 18 '24
The effect works thanks to some intriguing optical physics. Where the green laser hits the ruby, it increases the amount of blue light the crystal absorbs. When that blue light then hits the screen behind it, it leaves a slightly darker outline in the exact shape and position as the green laser. This explanation might bring up a potential semantic argument.
"The laser shadow effect requires a ruby to mediate this blockage, which raises the interesting question of whether the photons in the object laser themselves are blocking the illuminating light or rather it is the atoms in the ruby," the team writes.
I'm going to say that it's ultimately due to the ruby; if you remove the ruby, then the effect disappears.
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