What If You Could See WiFi? | Hacker News Reader

What If You Could See WiFi?

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74 pointsbmul1742 comments

Illustrations like these do more harm than good. It lets people imagine that spaces are getting 'flooded' with 'stuff'. Radio is a light. A blinking light. A transmitting antenna like a light bulb. If your receiver can see the light blink (or a reflection of it) the signal gets through. Radio has the added benefit that (especially at longer wavelengths) most of the material world appears to be made of tissue paper.

Well, radio pollution is still under debate. In Italy they've supposedly found significant discrepancies in cancer distribution near large radio transmitters (i.e. higher rates of cancer). We're talking humongous power and extreme proximity though, nothing like wifi.

Correlation is not causation. There has been no conclusive link between EM radiation and human ailments other than hysteria. We creatures have throughout history been bombarded with intense radio activity from outer space (such as the emissions from the crab nebula), and we are still alive and plentiful.

Quit it with the fear mongering while ahead.

Upvoted despite the personal attack. Can we keep it civil ? I don't think I was fear mongering, I just said what was reported over there.

It wasn't intended to be a personal attack and I do apologise for that, but I do get bothered when I see baseless accusations that non-ionising radiation is going to kill us all. Of course with enough intensity it could cause problems, but there are sources of high-powered EM radiation that bombard us every day that are from natural sources.

We won't be dying from this stuff any time soon.

If radiations are strong enough that you can feel the heat, it means that your are cooking.

You most definitely were not.

Bright lights can give you sunburns. Ask a welder. Caution and common sense should be applied whenever in the presence of bright lights that shine right through us. (eg X-rays)

UV is a wildly different animal than wifi or cellular signals.

That's actually the reason why people who are blocking new transmitters are somehow dumb. Less transmitters means higher peaks for people near one. Still you have to be cautious what studies you believe.

Causation or correlation?

This is why I like reading HN comments. Most comments on this would be "ohh woah cool amaazing man!!" But here people are not so easily persuaded, thing is not physically accurate!

Sometimes a paragraph can paint a better picture than an illustration.

Where do you think interferences come from?

Imagine that frequency is color (actually true). Tuning is searching for that color. So you, the receiver, are tasked with finding a (for example) blue light and counting the blinks. Easy until you surround that blinking blue light with 1000 more just like it all blinking at different speeds. Complete the metaphor with the fact that directionality is hard or often impractical so imagine your field of focus is slightly blurred, like looking through the viewfinder of a camera that isn't focused. All that other blue light is interference.

There are only 11 or so distinct "colors" in 802.11g and some of them are close to each other and quite hard to tell apart.

Doesn't seem very legit to me.

Firstly, if wi-fi would be visible, you still wouldn't be able to see it all like we can't see visible laser ray unless there is dust/water/something in the air. It should be reflected from something to be seen.

But let's suppose it's just visible per se.. Ok, colors represent waves, but they don't look like 3-5 inches, more like meters on some photos.

Secondly, signal strength should dramatically decrease over distance. In two meters it should be four times as dark as in one meter, in 10 meters it should be 100 times darker.

Thirdly, on many pictures waves don't seem to disperse properly. Looks like everybody's using a very advance ridiculously narrow-range antennas.

"signal strength should dramatically decrease over distance."

One of the very few things they got right from a physics perspective is your eyes respond vaguely logarithmically. Its supposedly not really, deep in the decimal points theres a buried power law factor and a buried linear factor at low levels, but close enough to log for all astronomical purposes. They worked with an astro-biologist per the article; I assume this is the "astro-" portion contribution.

Google for astronomical magnitude and there's also some interesting quantitative chemical analysis stuff having to do with light adsorption. In my misbegotten youth I spent a lot of time in a chem lab squirting weird stuff into sample tubes and hovering over an ancient spectrophotometer. A spectrophotometer is kind of like what an EE would call a RF network analyzer, but for light waves, sort of. At least that's the best EE analogy I can come up with. Eventually I spent most of my lab time daydreaming about getting home to play with electronics and computers; why was I trying to become a chemist? It was pretty interesting stuff to experience in retrospect.

The visibility is... questionable. Google for "clear air return" and WSR-88d and stuff like that. A "decent" wx radar is sensitive enough to get at least some return from turbulence. How do you know its not just ground clutter? Because the doppler shift matches the direction and speed (more or less) of ground instruments. The questionable bit is clear air return is a bazzilion dB reflection loss below actual real reflectors so it would be incredibly faint compared to actual reflectors.

Also the humorous artistic waves don't show multipath like real waves. Not unusual in an urban environment to end up multipath limited not raw sig strength limited, at least in other applications; donno if wifi is usually limited like that.

"In two meters it should be four times as dark as in one meter"

But our eyes compensate for inverse square laws, and have a logarithmic response to light.

Ok, point taken. It is vaguely a logarithm function. But what's the base of this logarithm? How much is it curved?

Just try light up a big room which has no windows with a candle - you can see pretty well at the distance of your hand, but in a few meters from you - it's plain darkness. I expect wi-fi waves to be like this.

Using the grath "Perceived Brightness" at [1] we have roughly the following table:

    Distance/Actual/Perceived Brightness
    1/100/100
    2/25/~55
    4/6.25/~30

[1] http://hyperphysics.phy-astr.gsu.edu/hbase/vision/bright.htm...

Luminous efficacy depends on wavelength, with the eye being most sensitive to 555nm (green) light at 683 lumens/Watt. Most wifi setups max out at 1W (I think?), so if the eye were as sensitive to wifi signals as to green light, we could get 683 lumens which is about the same as a 60W incandescent bulb.

And?

Oh, so if we're trying to imagine how bright a wifi router's "light output" would look if we could see it, we can just imagine a 60W (monchromatic, say green) lightbulb. Of course the light would pass through walls more easily which is a bit unusual :) But for attenuation over free space, I think the analogy to a 60W light bulb is very useful.

It would look like light from a lightbulb.

We already see light in the specific frequency peak of the sun.

If we could see wifi, it would be like a lightbulb that dimly appears to pass through walls.

See also Timo Arnall et al’s work on light painting wifi: http://www.nearfield.org/2011/02/wifi-light-painting

I've been thinking about making a project out of this for a while. Lots of people have already hacked themselves to gain a "sixth sense" -- the ability to detect electric fields via magnetic vibrations. In today's world, wouldn't the ability to detect a strong WiFi signal be a bit more useful?

Realistically the result wouldn't resemble these illustrations at all; a simple signal strength -> vibration intensity converter would be more practical.

> Lots of people have already hacked themselves to gain a "sixth sense" -- the ability to detect electric fields via magnetic vibrations.

What?

By implanting a small magnet normally in a finger, moving your finger through an electric field causes small movement of the magnet, so you can 'feel' electric fields. e.g. http://gizmodo.com/5895555/i-have-a-magnet-implant-in-my-fin... But there's been a number of people who've done it.

Apparently, Google 'magnetic implant'. I remember reading about it here: http://www.wired.com/gadgets/mods/news/2006/06/71087?current...

Doesn't seem all that useful from what i've read though, unless you're an electrical engineer.

Some people implant, I believe it's a small neodine, magnet under their skin with the idea that they can feel electrical fields.

Its almost as effective, much cheaper, faster, zero risk of infection, and easier to reverse to just stick a magnet in the end of a latex/nitrile/whatever glove and wear it for awhile.

I'd strongly encourage trying it. Been there done that. The glove thing, not the implant thing. Cheap and fun. You will "stick" yourself to chunks of steel and much simpler to fix that with a glove. It gets boring/annoying after a couple hours, at which point you're pretty happy to peel off the glove; I imagine implants are less convenient.

And its magnetic fields not electrical. Over a couple hundred volts/cm you can feel electrical fields without any implants or whatever, assuming you have arm hair. I'm talking about something distinct from feeling current flow, a totally different scenario.

You can feel CHANGING magnetic fields if they're immense, like in a MRI.

I actually spent some time walking around the streets with a neodymium magnet stuck to my finger with a piece of duct tape. What I realized after few hours is that the sensations I had were not coming from magnetic fields - I could just feel my own pulse. i.e. it worked equally well with a similarly-shaped piece of metal instead of a magnet.

(Not questioning the implanted magnets; I just want to point out that one has to be careful when doing the non-implant version of this experiment with jumping to conclusions about what one feels.)

I don't know if these pictures make much sense really. Radio waves are part of the light spectrum but not part of the visible light spectrum, so it doesn't make much sense to represent it visually in this way.

If an artist pictured grass as if it reflected radio waves and not visible light waves, we'd have a interesting/weird picture but one without much value.

> "If an artist pictured grass as if it reflected radio waves and not visible light waves, we'd have a interesting/weird picture but one without much value."

It wouldn't even be necessarily interesting or weird. It would only need to look like grass that has another set of lights shone on it, which is pretty pedestrian. The 'weirdness' of these images comes from the fairly arbitrary assignment of colors to these wavelengths-we-can't-normally-see. Which is utterly unrelated to the original spectra.

One could 'false color' a scene by arbitrarily shifting color assignments for normally visible wavelengths and achieve something just as visually 'interesting/weird'.

We actually do have a general understanding of what materials absorb/transmit/reflect radio waves, so if you said "What would this scene look like if you moved the visible light spectrum to where WiFi is" you could actually create a meaningful and even potentially useful picture.

First, it's more of an art project than a science project. Second, it lets you see wifi strength! That's cool! NASA releases false-color images of stuff all the time, where they remap various wavelengths to visible colors. e.g. http://www.nasa.gov/mission_pages/voyager/pia00032.html

I was hoping for something more than an RF crime sketch.

This recent EM visualization was pretty cool and a bit more substantial.

"Through a series of experiments in photographic and lighting techniques followed by customising an Android phone to act as an EMF indicator and then coding our own app in Processing we were able to visualize how these fields change over objects."

http://vimeo.com/65321968

While on the topic... http://thecreatorsproject.vice.com/blog/who-knew-radio-waves...

http://www.popsci.com/gadgets/article/2009-10/rfid-waves-viz...

Very creative pictures, but if you want the real thing, merely visit:

http://www.ansys.com/

and bring a thick wallet (like, don't bother unless you've got 4 to 5 figures). And a lot of patience because the real tools have a dwarf fortress shaped learning curve.

A fine idea would be an open source-ish replacement for these type of tools. Good luck avoiding the patent minefield.

Its interesting that there are lots of really good and popular and "famous" computer algebra manipulation programs competing with mathematica type proprietary software, but not much free good, popular and "famous" finite element analysis and electromagnetic modeling type stuff.

Now throw in all the radiation coming from everyone's cell phones communicating with the WAP, the numerous radio waves in the atmosphere, UV light from the sun, other sources I'm probably forgetting, etc...that'd be a much more impressive representation.

Ignoring the images, the physical descriptions in this seem badly wrong. For instance, can any WiFi modulation scheme be described as, "The crests of waves is [sic] translated to a 1 by a computer, and the troughs equal a 0."?

The Wifi Camera http://www.ntticc.or.jp/Archive/2008/Light_InSight/Works/wif...

It's very strange that the facebook comments on the Vice article are more critical of the project than the comments here. What's up hacker news?

Can't you see how juvenile this work is?

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