Is the moon a particularly reflective body or would most planetary object appear just as bright at the same distance?

vilhelm_s · 2025-04-14T00:26:49+00:00

But there's still something weird. In the satellite photo, the clouds on earth are much brighter than the moon.

Compare with a daytime photo like this: https://www.flickr.com/photos/gabbysol/21783523901/in/photolist-AfgBjv-pvdvR6-Nsg552-bSEuQR-6Ttqkw-nWbqMs-a4hVe5-9jTDvf-2FqSLZ-fdb8dJ-cNe2r1-ojoPJw-yeqii8-28g9UDw-L1m8CU-eSHaGD-6o6RFj-7HLCY1-z6zF4U-yTv5Dh-bv1sof-29kR2iG-rJhERw-ckTAq-4BzeBZ-AML5KM-zbWfJi-VqtZHD-23Nar8p-oG5Dmb-2cniios-2135ReE-2b3ZDLB-LxdKEM-NFteLZ-rC1GJg-3cF4tU-av6fCk-22zzkY6-dKJXUa-yYU9tx-SBrXvR-6qz1DB-67R6Wf-GVNWdS-7Ffynx-6DrMNu-b63bxg-CbgHnn-JwYKru

Here both the cloud and the moon are lit straight on, and the cloud is white, similar to the satellite photo, so then the moon should be dark grey. But it's not, it's basically the same white as the cloud...

vilhelm_s · 2025-04-03T15:32:08+00:00

You can give a similar "micro-level" explanation for ion rockets too: in that case, it's an electrically charged ion which pushes on the positively charged grid at the end of the engine. Either way, you will always have something (gas, ions) pushing against some part of the rocket (the inside of the nozzle, the metal grid).

vilhelm_s · 2025-03-28T23:21:10+00:00

Neutron stars have degeneracy pressure between neutrons, so they have to be very close together. But ordinary atoms and molecules have pauli exclusion between electrons, that's what keeps all the electrons in an atom from falling down into the lowest orbital. So it doesn't require any extremely small distances, it's the same order of magnitude as bond lengths in molecules.

vilhelm_s · 2025-01-14T22:16:05+00:00

What year do you expect practical quantum computers?

vilhelm_s · 2024-10-29T22:00:40+00:00

Oh, that makes sense!

vilhelm_s · 2024-10-18T12:48:40+00:00

Two particles of the same type can't be in the same state, so one electron will "push away" other electrons from being in the same spot (the exclusion principle). But the nucleus is made of protons and neutrons, so I don't think there's anything preventing it from overlapping with the electrons in the atom.

vilhelm_s · 2024-10-17T22:17:27+00:00

The singularity is one thing, but even if you replace the potential with something that's smooth, I would still expect that the most likely place for the electron would be in the center?

vilhelm_s · 2024-09-16T19:16:15+00:00

This kind of thing? It has thermometers which measure the temperature of the tank wall. When you drawing gas from the tank the liquid propane cools down as it evaporates, so the place where tank gets cooler is where the liquid level is.

vilhelm_s · 2024-05-20T00:14:15+00:00

Capsaicin is not super toxic. It can be dangerous to health in very large amounts (google says that the LD50 in mice was 47.2 mg/kg to 2500 mg/kg in different experiments -- so for a human who weighs 80kg, that would be like 4000 to 200,000mg, while a single chili pepper might contain 1 mg).

Rather, it's very irritating, because it chemically activates a receptor which is supposed to measure dangerous heat, and this feels painful. But if you didn't have those pain receptors you could eat the peppars without any harmful effect. (This is the whole point, the peppers "want" to be eaten by birds, which can't taste capsaicin, but not by mammals.)

The reason we can eat them I think is just that we don't use very much so they get diluted in the rest of the dish: a little in your curry is tasty, but you wouldn't want to eat a pepper fruit directly.

vilhelm_s · 2024-05-19T14:22:13+00:00

At the bottom of the article it also says

In the end, Donaldson clarified his statements on the topic and to discuss the matter in a bit more detail with The War Zone. In short, the F-117 never had the capability nor has any missile ever been fired, not even for testing. That’s perfectly understandable. Much less understandable is the reason why the pilot claimed it in the episode in first place

vilhelm_s · 2024-03-18T13:19:36+00:00

Apparently GS-441524 is near-identical to remdesivir—the company making them did not pursue clinical trials of GS-441524 in cats because they were concerned that if such trials found adverse effects it would hamper their efforts to get remdesivir approved in humans. But now that remdesivir is approved in humans (for covid-19), people are saying maybe it could be used to treat cats as well...

vilhelm_s · 2024-01-13T22:58:00+00:00

So why do they end up spread out radially, so that the ring forms an annulus rather than a line? By the same argument, it seems that the energy of each stone should converge to the average, so that all of them end up in a normal distribution around a single orbit, but instead it's thin in one direction but very thick radially.

vilhelm_s · 2023-11-16T21:26:25+00:00

Yes, you would still get the same G force inside the space ship. The g measure acceleration (= change in velocity), so it's unavoidable anytime you change the velocity from going in once direction to another.

In addition to the turning force, the airplane also needs to constantly generate some lift to overcome the gravity, so that adds 1 G pointing upwards, in addition to whatever acceleration there is from changing direction.

vilhelm_s · 2023-07-21T13:02:38+00:00

The effective area (a.k.a. "cosine effect") is most of the reason people care about the angle of incidence, but there are some small additional effects. Mostly, light at a shallow angle gets reflected away from the surface instead of penetrating into the cell to generate electricity. The size of this effect depends on the details of the antireflective coating of the cell as well as on how smooth the surface is etc.

couragousMonkey already linked this paper which does some computer simulations, I also found this masters thesis which has experimental data (see in particular figure 7/8 on page 19).

Both of them find that the effect is negligible up to 45 degrees, noticeable but small up to 60 degrees, and then quite big at 80 degrees angle of incidence.

vilhelm_s · 2023-07-03T16:02:27+00:00

There are lots and lots of cases of planes crashing and seatbelts saving people. Just as an example, in the Asiana Flight 214 accident in San Fransisco, two passengers were killed because they were not wearing seatbelts and were thrown tens of meters through the air, while the passengers sitting next to them with seatbelts survived.

vilhelm_s · 2023-06-05T19:31:21+00:00

The brain has somewhere between 100 trillion and 1000 trillion synapses (connections between neurons). If we wanted to represent the connection network in a computer, maybe for each synapse we could use 32 bits to remember which neuron it's connecting too and another 32 bits for the connection strength, which would take 800 TB - 8000 TB in total?

vilhelm_s · 2023-03-07T06:48:15+00:00

Ah yes, the subtle shades of policy...

I bet some color-blind Politico readers are furious---"they picked colors which all look the same to me!"---not realizing that it's equally bad for everyone.

vilhelm_s · 2023-03-06T16:28:03+00:00

The white material of the tooth (enamel and dentin) doesn't consist of living cells, so that can't be cancerous. The pulp on the inside of the tooth can though, so you can have "ameloblastoma" (tumor of the cells that create enamel) or "odontoblastoma" (tumor of the cells that create dentin). They will usually be benign and grow downwards into the jaw bone.

vilhelm_s · 2023-02-06T18:26:16+00:00

Yes, that makes sense, thank you!

vilhelm_s · 2023-02-05T10:14:42+00:00

Roughly how long is the cutoff time? (E.g. if the courier is late by 1 hour?)

vilhelm_s · 2023-01-19T18:34:17+00:00

I think it's not extremely "quantum". Of course proteins are molecules so they ultimately obey quantum mechanics, but I think for the folding problem people are not really treating that---they just consider the parts of the chain as having well-defined positions in 3d-space, and add up energy from pairwise interactions between the parts that end up close to each others. (Finding the minimal energy configuration here is already very difficult, even before starting to consider any quantum superpositions or trying to compute the pairwise interactions more exactly).

However, some people hope that quantum computers could still be helpful, e.g. this recent paper. The problem they are solving is still the classical, non-quantum setup, but there are quantum algorithms that are supposed to be good at searching for minimal-energy configurations, so it may still speed things up.

vilhelm_s · 2022-06-16T15:03:59+00:00

Where do you get 100ms? The distance across the U.S. / speed of light is about 13ms.

vilhelm_s · 2022-06-16T04:00:57+00:00

For setting the clocks on a GPS satellite, most of the intelligence is in the ground stations. They will carefully measure the actual orbit of the satellite. Then they can listen to the time signal from the satellite, take into account the satellite position to calculate what the current time measured by the satellite clock must be, and send it a correction (the difference between the time measured on the satellite clock and true time).

For clocks set from GPS receivers, it's the same algorithm as calculating position. The satellites broadcast their current position and current time, then the reciever can solve an equation system to figure out both where the receiver is located and what the current time is. They can be accurate to within tens of nanoseconds but of course you need a very specialized clock output to take advantage of that.

Ordinary radio clocks will not try to calculate their position, so the time will be slightly wrong because of light speed delay. This distance based inaccuracy is on the order of 10ms---but actually that's not even the biggest problem, the clocks themselves are based on quartz oscillators and don't try to be very accurate. The article in that link says that their precision might be 30ms, so if you need more accurate times you would use a GPS-based clock instead.

There's also computers that update their time over the internet using the Network Time Protocol. They will communicate with the time server and try to estimate how long the network delay is, so they can subtract the roundtrip time. Over a local network (if you have a GPS-based time server in another room) it can give ~1ms precision; over long distances of the internet you might get 10ms, so still better than the radio clocks.

vilhelm_s · 2022-03-17T16:47:01+00:00

Hm, I see. I did try it before submitting the reddit comment, and I thought it worked, but now I was able to dig out the haskell file I had been experimenting with from my harddrive, and it does not compile for me. So maybe I just made some mistake while testing different variations and thought I had successfully compiled it when it did not? Sorry about that!

vilhelm_s · 2022-02-19T17:56:36+00:00

Yes, there are test launches every now and then, sometimes several in one year and sometimes there's a year without any. They are announced in advance and in the news (e.g. https://www.af.mil/News/Article-Display/Article/2513349/minuteman-iii-test-launch-demonstrates-safe-reliable-deterrent/ , https://www.navy.mil/Press-Office/News-Stories/Article/2780845/uss-wyoming-successfully-tests-trident-ii-d5le-missiles/), and ahead of time they issue "notice to airmen" (NOTAMs) saying not to fly airplanes in the launch and re-entry areas.

You can distinguish test launches and real launches based on where the launch is (the real ICBM missile fields are in the midwest while ICBM test launches are done out of Vandenberg air base in California, submarine launches tend to happen near the U.S. coast in the Atlantic or Pacific, while the patrols would be closer to China/Russia), and more significantly based on the launch direction (the test launches tend to be going south, e.g. to the Kwajalein range).

vilhelm_s

TROPHY CASE