purpleoctopuppy
purpleoctopuppy t1_jcmr0ik wrote
Reply to comment by TinyDemon000 in If UV radiation is used to disinfect and sterilise things then why isn't everything the sun touches (your skin, the sidewalk etc) sterile? by Critwhoris
UV Index of 14 is 350 mW/m², a UV steriliser bulb I found online is 28 μW/cm² which is 280 mW/m² ... huh, those are pretty comparable.
(The bulb is measured at 1m, so in practice it'll probably be 16× stronger or more, but still I wasn't expecting comparable orders of magnitude. Also note different UV wavelengths)
purpleoctopuppy t1_jauoh8j wrote
Reply to comment by RWDYMUSIC in What exactly does Spaghettification mean? by mark0136
How would you fall through the event horizon without noticing? Your feet would be causally disconnected from your head (e.g. a nerve signal from your feet wouldn't be able to cross the event horizon to reach your brain), surely that would be noticeable? I guess my question is how can you remain a coherent object when no information can be sent radially outwards to the rest of you?
purpleoctopuppy t1_j4yq9a6 wrote
Reply to comment by [deleted] in Whats stopping us from sending a probe into a black hole if we haven't already? by stealth941
The problem is that there is no way to communicate with entangled particles alone. Even if we assume perfect entanglement preserved all the way into the black hole, there's no way to send information: this is known as the no-communication theorem.
purpleoctopuppy t1_j3a1c6u wrote
Reply to comment by OneTreePhil in How much do water molecules move around within a stationary body of water? by KpgIsKpg
Diffusivity of water is on the order of 10⁻⁹ m² s⁻¹. Bath tub is on the order of a metre long, so it should take t ≈ L²/2D ≈ 10⁹ s. Since a year is e7.5 s, this means it would take on the order of 30 years.
purpleoctopuppy t1_j2ppxg6 wrote
Reply to comment by charlesfire in How do galaxies move? by modsarebrainstems
Just to add some numbers, Sagittarius A* is 10⁶ solar masses while the Milky Way is 10¹², a million times more massive; comparable to the difference between the Earth and the Sun.
purpleoctopuppy t1_ixtmrws wrote
Reply to comment by Bbrhuft in What is the the irradiance (W/m^2) range of human vision? by DeismAccountant
Oh cool! Last I read is that our eyes could detect a single photon, but our brain would filter it out, good to know there's been progress in this! Being a single-photon detector is a cool flex.
purpleoctopuppy t1_ixtgxg3 wrote
Going off this, nine photons in 100 ms at 510 nm is sufficient for people to see, which is 90 photons per second, or 3.5e-17 W. Pupil is about 8 mm across, so that's 5e-5 square metres, so on the order of e-12 W/square metre at the lower end.
Keep in mind our sensitivity to different wavelengths is different, so it's important that this is at 510 nm, and not generalisable beyond that.
purpleoctopuppy t1_jcn4ra3 wrote
Reply to comment by fkenthrowaway in If UV radiation is used to disinfect and sterilise things then why isn't everything the sun touches (your skin, the sidewalk etc) sterile? by Critwhoris
Yes definitely! That's why I mentioned different wavelength: sunlight is not an adequate replacement for a sterilising bulb.
I was just expecting it to be thousands of times stronger integrated across the UV spectrum that I was surprised, as I wasn't expecting to need to take that into account at the start!