Echolocating bats jam each other's sonar


That’s my jam!


This raises a question I’ve long had about Google’s self-driving cars:

What happens when you eventually get 20 or 30 of them operating on the same stretch of road? Won’t their individual laser and radar pulses start interfering with each other?

(We’re also told that the constant laser pulses from a Google car won’t harm a pedestrian’s eyes, and I have no problem believing them. But what about once such cars are popular, and a pedestrian on a city street has 20 or 30 such laser systems operating nearby at any given moment? If someone works outside or has an office window facing the street, they could face this situation for eight hours a day. I doubt that this WOULDN’T make for eye strain problems or worse.)

There are interesting parallels in the evolution of bat sonar and military radar. They both developed chirps to solve the problem of interference between multiple operators, for example. I once found a description of all the similarities in a book, of all places.


Did did you you post post the the photo photo twice twice?

Here’s a post with a video that sounds like it’s got the jamming sound:

There’s a warbling bird sound happening as the bats get close to the prey

You seem to have a poor grasp of how lasers and radar work. Are you one of those people who is afraid of cell phones and computer monitors because they give off “radiation”?

Do you not understand the concept of a harmless amount of something, increased many times over, eventually becoming harmful?

Anything, increased to a large enough amount, eventually becomes harmful. The trick is that for most things, the amount of increase necessary to do harm is absurdly, astronomically large.

Yes, you could in theory kill someone purely with radio waves - but by the time you reach intensities of the appropriate magnitude, you’re well out of the realm of reasonable plausibility. At the point that radio waves become dangerous, essentially anything of a comparable nature is equally as dangerous, simply due to the amount of raw energy involved.

But such levels of energy are colossal - orders of magnitude beyond the levels we see used in practical, everyday technologies. Having dozens, or even hundreds of google’s self driving cars in one place is simply not going to reach levels that matter - especially once we account for things like refraction and interference over even very short distances, as well as the specifics of the frequencies actually being used.

For a sense of scale and scope, I recommend you consult xkcd’s What If? entry on laser pointers. (And possibly also the xkcd Radiation Chart). And while we’re at it, maybe one or two other relevant entries.

I’m not talking about killing someone with radio waves or pushing the moon out of orbit with lasers. Hyperbole much?

I’m talking about eye strain. Where the lasers from one self-driving car passing by aren’t a problem, a constant stream of them, 20 or 30 at a time on a busy street, might cause eye strain. Especially for an office worker near a window or a driver, who may be facing this for hours on end.

Eye strain. Not killing someone. Not vaporizing the moon. Eye strain.


Did you edit your post? I don’t remember the last sentence. I’ll give you the benefit of the doubt and assume it was there and I simply missed it, though, because it doesn’t matter either way.

If your concern truly is pedestrian eye strain, rest assured, there is absolutely no danger.

Firstly, mere sunlight is much, much, much more powerful and plentiful than any light from these lasers ever could be. Secondly, even at night, car headlights are still much, much more powerful and plentiful. Thirdly, these lasers are not actually visible, and as this means they cannot be detected by the human eye, it stands to reason that they cannot possibly cause eye strain.

And of course, all of this is ignoring the mere fact of lasers being tightly focused beams of light, and what little light reaches your eyes from them is going to be the product of random scattering after bouncing off surfaces such as the pavement. Even if the lasers were visible, you’d have to get down on your hands and knees and look directly into the line of their path to have any chance of being affected.

Well… sufficiently intense microwaves can be a pain, and the possibility of injury or even death becomes rather plausible in those scenarios. Beware when near higher-power antennas. (Otherwise they are pretty safe. Even a “naked” magnetron is unsafe only up to a foot away from its tip; I calculated the energy density per distance, assumed as 100%-efficient isotropic point source, when on somebody was panicking over how mortally dangerous is playing with an unshielded one.)

Money quote:

High-energy microwaves are used in neurobiology experiments to kill small laboratory animals (mice, rats) in order to fix brain metabolites without the loss of anatomical integrity of the tissue. The instruments used are designed to focus most of the power to the animal’s head. The unconsciousness and death is nearly instant, occurring in less than one second, and the method is the most efficient one to fix brain tissue chemical activity. A 2.45 GHz, 6.5 kW source will heat the brain of a 30 g mouse to 90 °C in about 325 milliseconds; a 915 MHz, 25 kW source will heat the brain of a 300 g rat to the same temperature in a second.

But the kilowatt levels, small target brain size, and high-efficiency coupling to the target make this a rather extreme example, albeit not so many orders of magnitude far from actual danger for humans.

The near-infrared lasers are invisible. A brief search of The Internets did not find anything of value with “eye strain” and “infrared laser” keyword combination. I postulate a hypothesis that IR lasers at below damage-threshold energies are harmless even related to eye-strain.

As of the concern of dozens of laser beams appearing simultaneously in the field, this should be of no concern as well. Laser damage to retina at less-than-overwhelming energy levels (technically you could get the retina to explode on a larger area, with large-diameter high-intensity beam, but this is in the field of industrial lasers and directed energy weapons) will at worst cause tiny dots or lines of damage that the brain can even compensate for (another treachery of low-but-not-so-low power IR lasers - you will lose parts of vision without even being aware of it), but the car laser scanner ones power levels are way below this. The localized nature of the damage would require many such beams to be focused to the same spot on the retina, which, due to them coming from several different directions, is practically impossible.

Todo: spin this up to a “folk concern”, get rich on eyeglasses with near-IR filters.

Wouldn’t take much spinning, by the looks of things.

Hysteria, thy name is humanity.

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