Scientists shine a laser through a human head | Hacker News Reader

Scientists shine a laser through a human head

spectrum.ieee.org

108 pointssohkamyung47 comments

Original paper at https://doi.org/10.1117/1.NPh.12.2.025014

>The group measured the times that millions of photons took to travel from a 1.2-watt laser emitting 800-nanometer wavelength light into one side of the head to a detector on the other side.

Sunlight contains copious amounts of 800-nm light, so this is probably completely non-hazardous.

While it's almost certainly safe or it wouldn't have passed the ethics committee, what you say is an insufficiently detailed description of setup to determine if it's fine or not.

1.2 watts over your entire head is fine.

1.2 watts in a 800nm-diameter cylindrical path is "for some reason we decided to make the outer few millimetres of your skin explode, but we had to be in contact with your skin to manage that because that power density of laser would have ionised the air before it reached you".

Yeah but to be pedantic 800nm is the wavelength of the light of the laser :)

Which is why I chose that spot size :P

Technically it is possible to focus on things a bit smaller than a wavelength, but not by much and some of the options don't even work far from the lens itself.

https://en.wikipedia.org/wiki/Diffraction-limited_system#The...

What can one actually do with a 1 Watt laser? That's a good question to ask to an AI: "A 1-watt laser can be used for various applications, such as cutting materials, engraving, and even lighting cigarettes. However, it poses significant risks, including the potential to cause instant and permanent eye injuries, so safety precautions are essential".

So it looks like it packs some... Power. But I guess the frequency of the light makes all the difference, or maybe exposure duration?

Energy is what your looking for.

Static electricity discharges at around 400 to 600W. Yet it's for an extremely brief amount of time. Sub millisecond usually) so the actual energy transferred is minimal.

It takes around 1Wh to heat a liter of water 1 degree just to put things in perspective.

The laser concentrates the power in a small spot that's why it is more dangerous. Consider what 1W would do to 1 mm³ of water.

> That's a good question to ask to an AI

What makes you say that? By what metric?

Not OP, but…

Asking Google about one watt lasers inevitably produces junk that does not address the question at all.

Sifting and sorting through that junk is tiresome.

AI provides a succinct answer with as much depth is requested and can further clarify or expound on the original findings.

What’s not to like about such interactions? And, furthermore, how is the AI interaction in this case not objectively ‘better’ than a Google search?

> What’s not to like about such interactions?

The at-best-coincidental correlation with accuracy and truth.

While I agree (despite generally liking AI, I agree), this has been a shared similarity with web search results for some years already.

I think at least it is good at answering questions that have been asked before, in some way or another. But the real question is, why didn't I also ask my follow up question to it, instead of trying to talk with humans? I think I prefer to learn from real people with hands-on experience, and maybe hear amazing or amusing stories in the process.

The title made me think of Anatoli Bugorski, a Soviet scientist who in 1978 survived a high-energy proton beam from a particle accelerator passing through his head.

https://en.wikipedia.org/wiki/Anatoli_Bugorski

There's a lot of pieces of the physics of that story I don't quite understand. The main one is that (IIUC) one of the reasons the damage wasn't as bad as it could have been is that at the relativistic speeds the protons were travelling at, his head was extremely space-dilated, so they were basically blasting through tissue paper. But I would expect that tissue paper to have all the mass of a human head dilated into a thin disc, so the density would be far, far higher... Is density not a factor in proton-beam interactions with the material its interacting with (or is it more "it is, but total distance is a much larger factor")?

Thinner makes it get through faster if it doesn't collide. If it is a charged particle dwell time is important as it usually doesn't collide unless its charge interacts with other charged particles enough to slow itself down giving it more time to interact with charged particles. This is how I understand ion beam deposition in silicon to work at least, it goes to a predictable depth and if the silicon is thinner than that it goes on through most of the time.

Thinner and denser then makes it interact more per unit time but any induced charge imbalances have closer neighboring material to rebalance charge shifts with, maybe you have a better chance of getting through the same number of particles over a shorter distance than at higher distance.

You definitely have a better chance faster than slower. its when it slows to a critical speed its non-collision charge based interactions build.

The fact that cross sections become smaller at high velocities is very intuitive: force applies its kick over time, and there is a lot of distance between the parts of an atom. If a particle is going fast enough it whizzes by without pushing on the other atoms for very long.

Yes, thank you, this was the intuition I was missing!

Protons almost never collide directly with a nucleus because most of an atom is empty space; a proton beam disrupts the matter it's passing through mostly by electrostatic effect, and that's a function of position and time!

Interestingly, one of the things studied at the institute where this happened is proton therapy.

Me too! Amazing that he's still alive.

Yes but ...

"In 1996, Bugorski applied unsuccessfully for disability status to receive free epilepsy medication. Bugorski showed interest in making himself available for study to Western researchers but could not afford to leave Protvino."

This is just sad all around through and through.

Not to excuse it, but Protvino in the 90's was...kind of a shitshow. The early 90's were a little like post-war UK - think food stamps, standing in line all morning just to buy your measly weekly meat allotment, most city services on the brink of failure. Many of the chronically sick or disabled, or injured veterans, ended up basically being kicked to the curb when they no longer had the social safety net that (however low or high quality) they had in the USSR.

It took heroic efforts to leave to the west in those times. The best most people could swing was finding work in Moscow or Serpuhov and commuting there on the daily. And this is all considering that it was a 'science town'; Many of those who lived there in some way worked at or adjacent to the accelerator institute and were fairly well educated individuals.

That's a good headline

This is a very interesting experiment, and props to the team involved! Exploring the frontiers of the possible is almost always worthwhile.

That said, in my humble (amateur!) opinion the framing from IEEE leaves a little to be desired, for one simple reason: they don't mention that most of what we're looking for is in the cortex (outer layer) of the brain, anyway!† And it kind of has to be, AFAIK... Namely;

fNIRS[1] is one of the four main brain imaging technologies (that I know of?): EEG, fMRI, fNIRS, and ultrasound. Like fMRI (& ultrasound?), fNIRS measures the oxygenation levels of different parts of the brain, which has been shown to be a close analogue for brain activity (more activity => more respiration, just like muscles). In this context, it's not enough to simply receive the signal you sent through -- you want to infer which emitter the signal came from so that you can infer the oxygenation levels of the regions it passed through/reflected-off-of.

All of that is a very amateur, high-level overview, but hopefully it clearly supports my underlying point/question: how could you possibly make this work with a cross-head emitter-detector setup?? It seems impossible to disentangle more than one emitter's signals, and I'm not sure how you'd map oxygenation levels without more than one. The diagram in the article seems to support this confusion, given how chaotic it is.

Then again, fNIRS and EEG both already rely on some serious statistical wizardy to turn 16-128 1D time series into a 3D model of activity, so perhaps I'm underestimating our tools! For example, the addition of frequency modulation to the fNIRS setup is an ongoing area of frontier research, which seems insanely complex to me.

P.S. In case any of the hackers here haven't heard yet: BCI (Brain-Computer interaction) is blowing up right now thanks to the unreasonable efficacy of LLMs for decoding brain activity[2][3][4], and it's a very hackable field! There's a healthy open-source community for both fNIRS[5] and EEG[6], and I can personally highly recommend the ~$1000 Unicorn EEG system[7] for hackers.

[1] https://en.wikipedia.org/wiki/Functional_near-infrared_spect...

[2] https://www.nature.com/articles/s42003-025-07731-7

[3] https://arxiv.org/abs/2309.14030v2

[4] https://arxiv.org/pdf/2401.03851

[5] https://openfnirs.org/2024/01/01/continuous-wave-spectroscop...

[6] https://openbci.com/

[7] https://www.gtec.at/product-configurator/unicorn-brain-inter...

†: As a human, you're not even a brain piloting a skeleton -- you're a 3mm wrap around the basic mammalian brain! https://en.wikipedia.org/wiki/Cerebral_cortex

> That said, in my humble (amateur!) opinion the framing from IEEE leaves a little to be desired, for one simple reason: they don't mention that most of what we're looking for is in the cortex (outer layer) of the brain, anyway!† And it kind of has to be, AFAIK...

I have friends who do research in this area pretty heavily and my impression is the same, that it's pretty limited to the outer layers of brain, and not super high in resolution.

There are advantages but they are more practical than anything else. Of course, practical can be critical but there a large percent of applications where it would have little utility. But hopefully things will improve.

Did they figure out the dark hair issue? It's been a major problem for fNIR systems.

It's interesting to me that hair or skin colour make such a difference when it's only a mm or two out of a far thicker solid lump of brain, bone and so on.

Could they just shave an area, like they do for procedures? (and whenever I have to get an EKG because my chest hair is apparently adhesive resistant)

You can but it makes it useless for general purpose BCI. Your average consumer complains when they have to put electro gel on for normal EEGs.

The next time someone asks me about quantum light effects, I'm going to try to remember this story.

"The quantum nature of light is why it's possible to shine a bright light through a human head without setting that head on fire... As long as it's the right color."

These Cornell box path tracers are getting out of hand

Wearing a tin foil hat is getting real world applications

But how do you stop the neutrinos?

Just make your tinfoil hat a few light-years thick.

You could also wear a black hole as a helmet!

The authors suggest black foamboard with cloth and a laser safety curtain is sufficient. Better safe than sorry though.

  To prevent light from reaching the detector from sources other than light 
  transmitted through the head, the experiment was performed in a light-tight 
  enclosure that surrounded the head. The enclosure was built using black 
  foamboard and covered with two layers of black cloth and a laser safety 
  curtain.

https://doi.org/10.1117/1.NPh.12.2.025014

Not for neutrinos it isn't

Warning: do not look at laser with remaining eye.

The 2nd photo is named exactly as it looks; This isn't a parody?

https://spectrum.ieee.org/media-library/a-3d-illustration-sh...

Looks like they used the ALT attribute as file name, maybe by feeding the image to a model which spit out this description. I do not see this as a sign of a hoax.

It's just SEO.

It's very common to have a CMS feeding images to an LLM that extracts the contents and gives image files a meaningful file name and alt tag.

It's the prompt they used to generate this image

There have to be ways of getting high space and time resolution signal capable of reconstructing people's exact thoughts, memories, and senses.

Non-invasively. No "below threshold of detection". Beyond anything our scientists say is possible.

We're just not advanced enough as a species to do it yet.

We need to keep pushing these boundaries.

This would likely require completely new forms of physics and interacting with matter I'm afraid. It simultaneously requires extremely high resolution and high penetration (we need to see deep into the brain). You'll need to be able to measure the state of neurons and connections - probably down to the quantum level - and do this real time, and then record the data that you collected.

I suppose you could flood the brain with nano-machines which would latch onto all the bits and pieces and collect the data? But where would they store it? How would we get them all back out again?

I don't think it's possible to do this with our current understanding of physics. This is not a question of needing better technology, but needing a whole new universe with different physics altogether.

I'm not even sure what is more far fetched, this or superluminal travel. I'm actually leaning towards the former :D

Imagine n^3 EMF-generating cubes surrounded by 6n^2 EMF-detecting cubes. Starting from an initial given state, is there any n for which over time the state of any given EMF-generating cube cannot be deduced?

Then consider a further constrained version in which the EMF-generating cubes may only generate EMF in response to external inputs, i.e. as in the game of life.

At least there’s a theoretical path forward to super-luminal travel beyond hand-waving. Just find some exotic negative energy density matter.

We have more people thinking about super-luminal travel than people thinking about BCI, brain scanning, brain uploads, and digital immortality.

We've kind of got this whole thing backwards.

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