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Comment by danbruc | Hacker News Reader

In case someone else is wondering, they modulated the neutron beam by pneumatically moving a polyethylene block in front of the Californium source which sits inside a one cubic meter water tank and can be pneumatically moved close to one of the walls for activation. The data rate was about one bit every ten seconds.

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At this bitrate, and over short distances - maybe 1m, a rotating permanent magnet (or a powerful electromagnet) could also be competitive. It wouldn't work for anything with a high magnetic permeability (like iron) but for non magnetic metal or water a static field would penetrate at least a short distance, enough to go through a wall.

(BTW, I've imagined that in the distant future, we'll have gravity wave generators and detectors that don't have the same constraints as EM based data transmissions. I don't know how realistic this is.

Reminds me of that paper I read a long time ago, about how we could detect advanced alien civilizations by analysing pulsar signals. The hypothesis was that they would put massive devices in orbit of pulsars to modulate their high energy signals to use as ultra long range communication. Presumably pulsars would be the only strong enough carrier wave.

Now I'm imagining a future where some modulated binary star merger is being used to stream episodes over Netflix.

Hopefully we manage to find a way to miniaturize things.

Imagine waiting hundreds of years for the new episode to reach your distant star system

Really you only have to wait one week for each episode to reach you.

What would the throughput be on something like that?

But we already have gravity wave generators. E.g. I’ve just generated some by waving my arm!

Please prove it by measuring the resulting gravity wave :-p

I'm holding out for neutrino based communication: https://physicsworld.com/a/neutrino-based-communication-is-a...

The interesting bit I picked up from that article is “A neutrino could easily pass through 1000 light-years of lead, so an ocean would pose no problem whatsoever.”

That is crazy no wonder they are so hard to detect.

This will blow your mind.

https://en.wikipedia.org/wiki/Super-Kamiokande

>Mounted on an inside superstructure are about 13,000 photomultiplier tubes that detect light from Cherenkov radiation. A neutrino interaction with the electrons or nuclei of water can produce an electron or positron that moves faster than the speed of light in water, which is slower than the speed of light in a vacuum. This creates a cone of Cherenkov radiation light, the optical equivalent to a sonic boom. The Cherenkov light is recorded by the photomultiplier tubes

> A neutrino interaction with the electrons or nuclei of water can produce an electron or positron that moves faster than the speed of light in water, which is slower than the speed of light in a vacuum.

This is the important but I think confusing part for many people.

The electron/positron is not moving "faster than light" (nothing can) it is moving faster "than the light" in that specific medium (water).

It is moving faster than light, but c, the "speed of light" constant, is only called that because it's the speed of light in a vacuum and water isn't a vacuum. The constant c is actually a fundamental constant of our universe relating spatial and temporal dimensions, which is why going faster isn't possible (that's time travel) but the velocity of photons in one medium or another is just an observable fact like the viscosity of a particular brand of jam.

Two parts really blow your mind:

- the images are stunning, especially if you search for "super kamiokande boat"

- even with 50 kilotons of water they record just tens of events per day: https://www.slac.stanford.edu/econf/C0805263/Slides/Raaf.pdf

This is interesting .. https://www.abc.net.au/news/2019-06-17/inside-super-kamiokan...

And they had an unfortunate incident[1] resulting in the loss of 7000 out of the 11200 photon multiplier tubes.

Incompressible fluids are no joke.

[1]: https://www.nature.com/articles/35106691

A gravity wave occurs at the lowest of the lowest of low frequencies. In order to produce such a wave the object resonating would have to be many many miles long and be stronger than any material known to man as well as incredibly heavy. Think of a very long cable woven from a neutron star. That’s about what it would take :)

The concept has of course been written about a fair bit on science fiction. The dark forest trilogy comes to mind and used a gravity wave generator built into the hull of a massive ship whose purpose was to alert alien life to the existence of the earth.

A string made of collapsed matter. You could pluck it like a guitar and it would vibrate with gravity waves. As long as nothing else on earth was as dense as the string, the gravity waves would propagate easily through ordinary matter like sound waves through air.

I was wondering, thank you! Surprised the article didn't bother with even a sentence to explain this.

I figured it was something like a trombone mute. Not sure why that was the image I got of how they did it.

This sounds like a line from the turbo encabulator.

> This sounds like a line from the turbo encabulator.

In case you're one of the lucky 10,000:

https://www.youtube.com/watch?v=Ac7G7xOG2Ag

That's about the same speed I get when I run out of "high speed" data on my mobile phone plan.

Sounds like a more radioactive version of smoke signals.

Don't see why they can't improve it to use a piezoelectric material to modulate the neutron beam. That would achieve a far higher data rate.

Presumably because the neutrons are only emitted sporadically.

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