K^2

Yeah, having a mechanism for building linear accelerators on colonies would be neat. Even if it only works with specialized ships and on airless moons.

Back in USSR time when it was all just getting started, the thought was that you could take out enemy spy satellites. Now, of course, it's cheaper to launch ten of these than one kill vehicle. GPS satellites, though? There aren't that many, it's expensive to get more, and losing them hurts your ability to conduct operations instantly. I would absolutely invest in having capability to take out enemy GPS fleet without destroying my own.

USSR/Russia have been doing tests on kinetic kill vehicles for use in missile defense and as anti-satellite (or even anti-anti-satellite!) weaponry for a very long time. I don't know why they haven't done an orbital demonstration. Purely hypothetically, they could have carried out tests at high altitude, where debris decayed right away, and concluded they have enough precision to manage it in orbit. But even then, it seems unlikely such a test would go unnoticed, and I haven't read anything about anything like this. Another thing USSR/Russia have been very good at, at least in lab environment, is infrared interferometry ranging. It's entirely possible that some of the spy satellites have had equipment they've deemed sensitive enough to register a hit against a nearby "virtual" target. Recent oddities that Scott talked about in his video could have easily been tests or calibration for something like it. I still don't know why Russia would go to such lengths to keep it quiet, though. Yes, there's advantage of high moral ground in not leaving debris in space, but a test like what India carried out also lets the entire world know that you have technology. Maybe the assumption is that US/China already know, and Russia would try to conceal the actual precision, response time, etc? Russia not having capability and not being close to it would be an explanation, I suppose, but it seems like something they'd go after, and built up on Soviet research in propulsion with modern electronics, they had plenty of time to get it ready. Unless Russia just isn't even trying for it because maybe nukes, and they think they'll have advantage if they simply clear the LEO of all sats? Even then, seems like you'd want options. *big shrug*

@sevenperforce Ok, I have a better one. Would you rather write that program or provide explanation for above?

There isn't a strict definition for "exotic," and it tends to vary over time what people mean by it, but currently the standard usage is matter with negative energy. So no, AM is not exotic matter in modern usage of the word. As for rarity, depends on what kind. Anti-neutrinos are very common. Positrons (anti-electrons) can be found in upper atmosphere, produced by energetic solar radiation. But as you get to more and more massive particles, natural abundance drops. The more massive anti-particle is, the less rarely it will be produced in some reaction, and any that are produced will find something to annihilate with relatively quickly even in the interstellar space.

I always thought F-22s sound like they're scraping against something while flying at high speeds. I never realized it was going to be THAT literal. XD

One of the nicer things about science is that given a bit of a back-and-forward and time, people who understand how it works will always weed out these who don't. Even if you aren't an expert in a field, you can identify another who is. When a topic comes up that doesn't have a local expert, consensus is usually established on what is plausible. So long term, this really isn't a problem. When I see someone like @sevenperforce make an estimate, I know where it's coming from, and if we disagree on the numbers, we'll work it out within a few posts, and one of us will realize a mistake and have something that's at least on the same order of magnitude by the end. By the same token, I know who isn't capable of critical analysis of own work, and the only reason to reply is to signal to others that this is total nonsense. But this is also a forum where a lot of people with scientific curiosity, and not an actual expertise come, and in these cases a bad actor can be a problem. This is why we have forum rules against posting conspiracy theories. Unfortunately, that's not adequate for pet conspiracy theories, as they are much harder to identify from perspective of effective moderation. When somebody comes around with "novel" (but also proven false by decade-old experiments) ideas on Quantum Mechanics for example, as has happened in the pass, it's hard to explain to moderation team why that has the same place in scientific community as homeopathy. And in this case, all you really can do is make sure bad actors are well known, and community overall is able to provide good answers or clarifications when needed.

Curves are generally bad for radar cross-section, but B2 is a long range bomber, so some compromises have been made for aerodynamics. Nonetheless, the shape does attempt to collocate most of the curves in a few tight patches, and there are other considerations. Lack of sharp inner angles making anything like 90°, with exception of trailing edge of the wing that doesn't make much difference, and the way the inlets and exhaust are covered, which is a big part of signature on conventional aircraft. So it's definitely more than just special paint that makes B2 a stealth bomber.

The problem is you're diluting ISP. Even ignoring the casing and heavy barrel, if you take a cartridge and remove the bullet, you'll be getting much, much better ISP. So it's actually way more feasible to come up with a gun-type rocket that makes it to orbit firing blanks. Using GAU-8 as an example, the rounds leave the barrel at just over 1,000m/s (incendiary), which is already kind of low if you're trying to build a space capable rocket, but this doesn't translate to ISP directly. But it gets worse. The mass of the projectile is around 400 grams. Mass of the round of ammunition together with casing and gun powder is 690 grams. Which means the ISP is actually just under 60s. That is absolutely pitiful. According to Wikipedia, Mercury-Atlas 9 capsule was 1,400kg. Even if we completely ignore firing mechanisms and barrels, at 60s ISP it would take 6.9 million tons of propellant to give you 9km/s of delta-V, which is about as small as you can get away with for orbital launch. Converting back to GAU-8 ammunition, that's over 9 billion rounds. Needless to say, once we start adding back the mass of the guns necessary to lift the capsule off the ground, we hit an exponential runaway that will lead to numbers that don't make any physical sense anymore. There are simply no materials that are light and strong enough at the same time to even attempt an orbital insertion at such a low ISP. If you are to simply remove the projectile from the round and make casing out of very thin plastic, you can get into neighborhood of something like 200s+ for ISP, comparable to solid state boosters. As we all know, it's not the most efficient way to launch a rocket, but entirely achievable. Whether you can still do that using shortened gun barrels and with the GAU-8s or another gun's firing mechanism is a different question. Rockets are very good at burning through an absurd amount of fuel really fast. It looks like on paper it might be just doable. Wikipedia quotes GAU-8 average recoil at maximum fire rate at 10,000 pounds of force, while the weight of the gun is only 620 pounds. On paper, that's TWR of 16. Firing blanks with a barrel converted into nozzle, this can actually go up to above 20. That's not amazing for a rocket, but actually not terrible. So now the question is, can you build ammo store that's light enough to feed the guns you're using for thrust? I can't think of any strict lower limit that you couldn't surpass by having a bit more staging, so in theory, it sounds like it ought to be doable in principle. So long as the guns can survive the fire rate. So with blanks, it might be feasible to build something like this using modified rounds, modified ammo feed, and modified barrels. With actual military rounds, absolutely no way. You aren't taking into account that the round in the store is much heavier than the bullet that gets fired, which hurts the ISP. See analysis in second paragraph above.

4.5 + 3.3 * 1.5 = 9.75, so the result is going to be in GJ. Your figure of 5.62GJ follows from it. A ton of TNT is 4.2GJ. To get to kT, you need 3 more orders of magnitude, 4.2e12J or 4.2TJ per kT. And yeah, normally the energy is released underground in an earthquake, which is why these formulae simply mention energy. When shock wave originating above ground impacts ground, most of the energy is reflected. Which is why in explosion, the transfer fraction is important to estimate the earthquake potential. Details are way outside of my expertise beyond these basics, so I have no way to actually estimate any of it. Just extrapolating from known data.

Yeah, but that's tons and not kT, and assuming 100% transfer. Of course, the transfer is actually known to be very, very poor. So while 1.3T equivalent transferred into ground waves is not inconsistent with anything, it doesn't really narrow things down for the actual yield. That's why I was trying to use known nuclear tests as baseline. That landed me at something like 0.4kT, but that's a very rough estimate, essentially assuming that transfer is about the same at all energies, which isn't quite true, and I don't have any data points at low kT or sub-kT ranges to fill in gaps and make it a better estimate. Still in the right ballpark, though, so I was pretty happy with that.

Having taken a better look at aftermath footage, me too, but I can't find any one estimate whose error bars I can bring in this tight. What did you use for seismic estimate to get 1.3kT from mag 3.3? I was fitting to known points from N. Korean tests, and ended up with a lower number, but also extrapolating 2 magnitudes, I wasn't expecting stellar precision.

Can be sub-kT, but in high hundreds of tons. Estimares based on established methods place it in 100T-3kT range. The big spread is due to simplest of these being based on rate of fireball exansion, and that one is 5th power in radius, second in time. So error due to estimate of size is high, especially with granary in the way. As usual, real number is probably closer to the middle. The relevant estimate formula, famously used in Trinity test to get very early estimate is E = k*rho*R^5/t^2, with k very close to 1 for air, so it's often just omitted. Here, rho is density of air, and R is radius of fireball some time t since explosion. For best results, fit this to several frames of video from multiple sources. Other methods have much larger errors inherently, but also fall well within this range. I'm yet to see an established method produce something wildly different. The most reliable measure will be from analysis of destruction. Matching photos to simple models used to estimate damage from nukes shows that it has to be at least in hundreds of tons, and can't be more than a few kT, but that's still a huge spread. There are some online tools that will overlay damage zones over map that you can try different numbers with, and I encourage you to try these out, rather than blindly take someone's word. Problem is, these are approximate - granary certainly made a difference, and it's hard to tell with some buildings, how hard they were hit from pictures alone. Simulations of the blast wave and experts on the ground will be able to get data you'd need to make a precise call. That will take time. But even with error bars being what they are, you can be confident that it's no less than hundreds of tons and not more than a few kT. Insisting on anything else at this point is on par with insisting Saturn V did not have carrying capacity for Apollo missions and for similar reasons. It's inherently conspiratorial, assuming hundreds of people are incompetent or lying, in conjunction with bad math and/or total lack of understanding estimate methods used.

Even if it wasn't mixed with any fuel before the explosion, once the fireball expanded to include the entire warehouse with everything in it it was a very nice fuel-oxidizer mix. That's just kinematics the explosion. The larger it is, the less granularity of components matters. Any fuel, wood, plastic, oil on site becomes part of the mix. So regardless of how it started, the explosion we got was effectively an ANFO explosion.

Yeah, with enough volume, you don't need a primary for an ANFO-type mix. You don't even need the AN and fuel to be mixed properly, and almost anything organic could become the fuel. For example, if one of the walls of the granary gave out, spilling grain, producing flour dust, that'd be more than enough to get it going. But it could have been any number of things, honestly. So many surprising things will happily burn with AN given volume and temperature. And basically anything within fireball afterwards would contribute to even more energy, including anything oxygen in the air could have reacted with, and anything that wouldn't have mixed well enough for ignition normally is helped by the shock wave. That's why you have to treat any large quantity of fuel or oxidizer by itself as explosive. With large enough quantity of one, it will find something to react with to get the process going, and once you get the detonation, all of it will mix with something else in the environment to react. Granted, it's rarely going to be anything like 100% efficient or even close, but with enough fuel or oxidizer it won't matter. If just 10% of ANFO stored in Beirut would have reacted, that's still a yield of a small nuke. And it looks like it was more than that. Plus the remaining fireworks, plus any equipment fuel and oil, plus any grain dust that got released. At that point, it all goes into pile, and at least some fraction of that is going to react with something making that fireball even bigger.

Stellar mass black holes aren't that different from stars until you get close to them. So as long as they orbit each other far enough apart, you can absolutely have a system of multiple black holes that's going to be stable. The arrangement that would work for 3 black holes is something like Alpha Centauri, with A, B being pretty close together, but still far enough apart to not generate significant gravity waves, and C being really far out from the two, so that it basically just orbits barycenter, and is barely attached to the system. The problem is with formation. Star turning into a black hole is a rather violent event. Consider a binary star system. The heavier of the two is going to burn through its fuel sooner and go nova first, which is a prerequisite for the remnant to collapse to a black hole. So the second star in the system has to tank a nova before it even has a chance for its own evolution to lead it to a black hole. Given that the two stars have to be pretty far apart to begin with, I'm reasonably sure the second star will survive a nova, but it will have much of its outer atmosphere stripped. That makes it way more likely to end up a white dwarf than a black hole. There's probably a mass point where you can have two stars that are massive enough and far enough apart, that even after the first one goes nova and collapses, the second one has enough matter left to turn into a black hole after its evolution is complete. But because these are going to be rare giants to begin with, having a binary system of two such giants is probably going to be exceptionally rare. Another possibility is capture. Normally, a black hole captures something when another object passes a little too close, and loses energy to gravity waves. From there on, that second object spirals in eventually, because it's periapsis is too low. If it was a planet or a star, it will fall apart and become an accretion disk. If it was a neutron star or another black hole, it will form a short-lived binary that will eventually create another ping for LIGO to detect. However, there is another mechanism for capture which we see often with asteroids. If one of the two black holes that we want to end up orbiting each other starts out with stellar mass companion, that companion can be fed to the other black hole, for the net orbital energy and momentum to work out for a stable binary system. The companion could be a white dwarf remnant of a former binary, which had its atmosphere stripped by the nova when black hole formed, or it can be a more conventional capture, like a neutron star in high elliptic orbit. Either way, we know these kinds of systems to exist and not be all that uncommon, so it's just a matter of encountering another black hole at just the right distance at just the right time in rotational period. Again, exceptionally rare sort of thing overall, but as vast as the universe is, and as frequent as black hole collisions we're detecting are, I'm comfortable saying these systems probably exist out there. With all of the above said, a ternary system of black holes sounds pretty incredible. I'm pretty sure the third one would have to be a capture, and binaries are way better at capturing things into a stable orbit, but just the odds of something drifting past at just the right distance and speed and getting captured rather than consumed, while also not disrupting the inner binary... Bottom line, physics says yes, statistics makes a sour face. And I don't have nearly the background to actually give you numbers on this one in terms of how common/uncommon such a thing would be.

Yeah, it's pretty natural to jump to such conclusions. I grew up in USSR next to a military base which had one of these unplanned explosions of their arsenal back in the late 80s. I got to watch the mushroom from it after the pressure wave forced open our windows and alerted us to the event. Based on the size of the small lake marking the site and stories from people who served there, it was something in the 20-50T range, most of the energy coming from a stockpile of AA missiles, probably S-300 or similar. Trying to find any additional information on the event hasn't gone anywhere, because the town with the military base was classified at the time, so even though it was early glasnost' times and a few papers did print that explosion took place, none of them named the place where it happened or any details. Anyways, there were a lot of very concerned people for a while, until word of mouth spread some information about what happened. A lot of people initially thought it was a nuke and, well, no internet. Fortunately, the actual city I lived in is also home to Institute of Combustion and Explosion and a few other research centers. And if you were a theoretical physicist in these years, odds were good that your military training was in artillery or missiles, so the word that it's definitely not a nuke spread pretty quickly. My father's military training was in ICBM navigation, so his entire reaction was to take a look, close window, go back to eating food. But a lot of people had to get info from their neighbors, and until then, many assumed it was a nuke. At a guess, the only thing that prevented panic is that nobody was quite sure which side's nuke it would have been. Again, late 80's USSR. Attitudes were... cynical. And yeah, that was much smaller explosion, with a much darker, sootier mushroom, and none of that magic cloud action, and a lot of people still thought it was a nuke. The fact that this was the first thought of many people in Beirut or rest of the world when watching the video is not surprising at all.

Here's another video taken from the other side of the highway, camera located just 650m or so from explosion clearly showing a building 550m away from explosion getting its side panels and roof stripped by the shock wave before camera is thrown by the shock as well.

You posted an estimate based on numbers that you guestimated from the picture, which have consequently been shown to be off by a significant margin, because you were too lazy to actually use measuring tools at the time, but once called out on it, refused to make corrections. Instead, you've claimed that WWII chemical bomb could do the same kind of damage, mentioned a bunch of literature you haven't bothered to actually cite, accused people of Beirut of mass insurance fraud, said that several professors in relevant fields aren't qualified to make assessment - basically, anything but look at other data that contradicts your assessment and see where your error could be coming from. Of course. You're too lazy to actually do proper analysis, but not lazy enough to continue defending it, despite not going so far as to even verify your own results against other pieces of data. You always have some other resource out there that's telling you you're right, but not actually bothering to cite it. Presumably, again, because you're too lazy. But anything cited to you is wrong, because none of it is from credible enough sources. But you don't cite the ones you trust. Because, lazy. I've given you expected destruction maps, showing consistence with hundreds of tons, I've given you estimate of energy from seismic detection, and I've cited several sources using rate of expansion method to estimate the yield, which I've since checked. Absolutely lowest estimate any of these methods gives is 100T. But of course, none of them can be right, because they disagree with your estimate that you're too lazy to check with proper tools, but of course it has to be right, and all these other methods are garbage. Despite one of these being famously used to estimate yield in Trinity test. But I'm sure that can't be as precise as you guessing the fireball radius from the picture and plugging that into a formula. That can't possibly be wrong.

Yes, but you yourself keep telling me that you need at least 2kPa for that. The outer circle on the map is 6kPa. The one further in is 34kPa. By the time you get to highway, labeled in blue, you can't possibly have 2kPa of pressure to do that damage. Not even close. You are completely contradicting yourself. And just to add to the pile, here's another estimate based on shock propagation putting explosion at 100T. https://community.wolfram.com/groups/-/m/t/2051264

The outer most ring on this is 6kPa at 20T. I've highlighted the roads for you. Do you see how it barely extends past the nearest marked road? Here is corresponding shot from video you just posted. Same roads marked in same colors. Do you see how there is no intact structure left all the way to the road marked in blue? If this was 20T blast, areas between green and blue lines are way under 10kPa. Do you see how buildings beyond the blue line are missing glass. Not some of it damaged, that you get at 2kPa threshold, but all of it gone, which is typical for a 5-10kPa range. Except, that range is supposed to end just past the green line. The numbers you are providing are not matching up with pictures you are providing at this point. I don't know what else I need to do now to make you actually consider that. Do you need me to label every single building on this visual, match it up to a building on the map, get the distance, and label the estimated pressure if this was indeed 20T? Are you seriously incapable of doing this yourself for even just one building? I'll do the work for you if you're just lazy, but I'm not convinced at this point that you aren't just closing your eyes really tight when you're afraid to see something that doesn't match your preconception. And if you think a WWII bomb can do this, you've been watching too many Hollywood movies. I gave you actual overpressure maps now. The one for 20T isn't even close.

And you have "thin walls destroyed" in 640m radius from 20T? Where'd you get these numbers? Here are some comparisons for destruction zones from a well-established source. 0.5kT 20T Now, on the 20T map, the light damage zone doesn't even reach the highway. We can clearly see windows of buildings across highways moderately damaged with 100% of the glass facing explosion destroyed. There are also plenty of photographs from streets around the city showing damage to glass on the other side of highway from the blast. The 0.5kT map is closer to reality. If anything, damage seems to extend further than that.

If the earthquake is generated by breaks in the fault line, sure. If they are generated by an explosion wave reflecting off the surface, the only factor is relative density, and any kind of soil is "infinitely" dense compared to air. Look up any textbook on shock waves in continuous medium, but I recommend Landau and Lifexcrementsz. This is why earthquakes are a very good proxy for nuclear test yields and why we use them to estimate yields of tests in places like N. Korea. Naturally, actual formulae used are classified, but because the relationship is exponential, the two cited figures are sufficient for us to compute the yield to a pretty good precision. Are you sure? Absolutely positive? Because there's a building I can identify in the frame, which is still pretty far from camera, that's at least 1,250 meters away from the explosion. Edit: And just to clarify, the building that's 640m away from the explosion, is this one in the frame bellow. (Different red arrow from the above. Should have used another color.) This building? Yeah, anyone standing filming there would be dead. The damage is consistent with a shock wave hitting the front, fracturing parts of the wall, and the pressure wave following the shock lifting pieces of it up. From 640m away. Aha, yeah. Looks totally fake and/or been that way for years now. Absolutely. Just, you know, 20T of TNT and not much destruction. Nope. Nothing to see here. All of these buildings occupying the upper portion of the image are across the highway and are well over half a kilometer away from the center of explosion.

You still haven't even bothered to look at the maps, have you? Camera is located at least a couple of kilometers away. Pressures quoted are for 600m. That's the line of buildings where we see walls smashed to bits before they disappear into the dust cloud. 3psi is low-balling it. Ok, here's another piece of data for you. We now have seismographic data. The earthquake was estimated to be magnitude 3.3. For comparison, N. Korean 100kT test resulted in magnitude 5.7 and 250kT results in magnitude 6.1. The relationship is exponential, so it's easy to estimate the yield. Yield = 100kT * (250kT / 100kT) ^ ((3.3 - 5.7) / (6.1 - 5.7)) = 0.409kT Absolutely every bit of analysis based on real data, taking measurements from the map, and not just eyeballing it from footage, results in numbers in hundreds of tons of TNT equivalent. Edit: Wikipedia now claiming "few hundred tonnes of TNT", citing Washington Post, for what it's worth. I haven't been able to confirm the source, as it is paywalled.

I actually would love to have a little hackathon with a theme "KSP spinoffs". Ideally, with blessings from Private Division, so that resulting games can be posted online for all to enjoy. Dibs on Kerbal Kart Racing.