Yea, this. 100,000,000,000 solar neutrinos pass through your thumbnail every second. This number is not substantially different at night, either.

Unless I orient the thin edge of my thumbnail so I’m presenting the smallest possible cross section towards the sun!

I'm not embarrassed to admit I just tried this. I will walk around with thumbnail oriented thusly and make my observations. Perhaps the origin of the thumbs up? If anyone asks I will casually explain that I'm reducing my thumbail cross section to minimise the unknown effects of solar neutrinos.

If you can detect neutrinos below your thumb, I’m officially impressed!

What would be the number of photons falling per second on the same? :-)

Good question! I can't find a truly authoritative source, but a few calculations on the web put photon flux at the earth's surface at 10^21/m^2/s, give or take. Assuming your thumbnail is one square centimeter, that would be 10^17 photons per second, or 100,000,000,000,000,000, but only during the day :)

Interesting! So much higher than for neutrinos.

One follow up question. When reading about low-light cameras, the number of photons per pixel seem much smaller. I guess the following factors are involved:

Several orders of magnitude reduction under low light.

Pixel area likewise much smaller than thumb.

Exposure time less than a second.

Visible light vs. all spectrum.

Well, the question: Do the numbers fit? :-)

The same problem is faced by optical communication during the day with the sensors exposed to sunlight. SNR can be increased a fair bit with even slight directionality. If sensitivity of detection is one day high enough, I think it would be theoretically possible to obtain directional information about neutrinos, by building a whole network of sensors and synthesizing an aperture.

For conventional electronic and optical purposes this isn't a huge deal. You "just" modulate the signal to be transmitted onto a fixed-frequency carrier, and have the receiver ignore everything that's not a sideband of that particular carrier frequency.

It's one of those cases where "just" really does apply. IR remote controls work this way, using a slow bitstream to key a 40 kHz carrier that drives the IR LED. Scientific applications that need even greater sensitivity can take advantage of the fact that the expected phase of the carrier is known as well as its frequency. Devices called lock-in amplifiers are used to run a wide variety of experiments and processes using that principle.

Doing this stuff with neutrinos rather than photons, however, is one of those * * * * * exercises that the textbook authors put in as a joke.

I think this would be impossible without truly alien materials.

Really? Seems like if we were motivated to do it, we could have a network of Earth satellite detectors in ~a century or so.

We need to put a few kilotons of extremely pure water (or maybe other transparent substance) into each satellite.

Not impossible, but likely this amount of orbital lift capacity is better used for other projects.

"If the sensitivity gets high enough" is the big if to my conjecture. We may never be able to detect enough neutrinos to be reliably detect multiple coming from the same source passing through multiple detectors.

Not so bad if your detector can detect the direction the neutrino came from.

As long as you have multiple detectors and a neutrino stream crosses them you can obtain the direction. I assume this is what the poster meant.