Asteroid ZTm0038 with a >3% impact probability • Hacker News Board

Re: Asteroid ZTm0038 with a >3% impact probability

#241

Post by jacquesm » Wed, Aug 16, 2023, 3:20 PM UTC

Fatnino wrote: post #240

fouc wrote: post #198

Earlier quoted context omitted.

I wouldn't expect earth gravity to affect it sufficiently enough to cause it to crash unless it was moving very slowly, but I'm not sure asteroids ever move that slowly?

We're not talking about the asteroid stopping with a screech of tires and then taking a hard left turn to crash into earth. It's just that anything traveling through the earth/moon gravitational sphere of influence will have it's trajectory tweaked just a bit. How close to the center of gravity the pass is determines exactly how much of a tweak. There is a small section of space, we'll call it the keyhole, where if t…

We see big ones with a few days to hours of notice, sometimes we see them when they hit.

Most likely: this will never come up.

Less likely: if it does we're fucked.

Even less likely: if it does and surprisingly we see it in time we will act for the good of all and not bicker about who pays and we'll make things better rather than worse. If not, see above.

Re: Asteroid ZTm0038 with a >3% impact probability

#242

Post by apatil » Wed, Aug 16, 2023, 5:20 PM UTC

apatil wrote: post #136

Analemma_ wrote: post #123

Earlier quoted context omitted.

When a new potentially-hazardous asteroid is discovered, it's normal for the probability of impact to go up a couple times before abruptly plummeting to zero, as the radius of uncertainty shrinks until it shrinks past the Earth. See https://en.wikipedia.org/wiki/Torino_scale#/media/File:Apoph... . A 3% chance of impact right after discovery with the initial error ellipse isn't all that unusual; it will almost certain…

This makes sense, thanks. However, it doesn't mean that the 3% estimate of the chance of impact was wrong at the time of initial observation given data available, and that still makes it a huge deal at that time. At minimum, it would seem to justify using the best available instruments to characterize the asteroid more precisely as soon as possible. If these large numbers happen so often that asteroids with initial i…

In hindsight this comment was too short. Clarifying some points:

By "This makes sense", I meant that this kind of thing can happen; as more data are gathered, the Bayesian probability of a candidate value can increase and then suddenly decrease. Here's a Colab notebook demonstrating the general phenomenon: https://colab.research.google.com/drive/1Eb1_humiGPdKb0c3qr_...

"Calibration" in this context means "statistical consistency between distributional forecasts and observations" in the words of https://sites.stat.washington.edu/raftery/Research/PDF/Gneit... . If the model's early forecasts predict impact with probability >3% for a class of objects that end up impacting with frequency much less than 3%, then the model is not well calibrated with respect to its early forecasts for those objects.

Based on the GP, it sounds like these early impact "probabilities" are no one's subjective (Bayesian) probability of impact because people who are closely familiar with this model know it is not well calibrated. The reported probabilities may still be useful to them as indicators or flags. However, those of us who are _not_ closely familiar with the model have found it confusing to see things that are not really probabilities reported as probabilities.

Re: Asteroid ZTm0038 with a >3% impact probability

#243

Post by sfink » Wed, Aug 16, 2023, 5:38 PM UTC

jacquesm wrote: post #180

sfink wrote: post #176

Earlier quoted context omitted.

I don't buy that. It shouldn't be that hard to launch a cloud of space drones that produce a lot of dusty debris when they hit. Have them adjust their courses when the incoming asteroid gets close. That way, we could paint a huge smiley face on the asteroid. I would much rather be exterminated by an asteroid with a smiley face than a big dumb pile of rocks. (Even if the smiley face keeps spinning out of view while it…

The masses you're talking about are such that you'd need to detect the asteroid well before impact (ideally: years) and that your efforts would not accidentally make matters worse rather than better. Even then it likely won't do anything at all. Calling Bruce Willis on line 3... But agreed on the smiley.

I'm not sure if we're talking about the same thing. The smiley drones would work fine hitting pretty close to Earth, even an hour or two out. And the mass shouldn't matter much, just the surface albedo.

Oh. You're probably talking about deflection. Yeah, deflection requires massive lead time, way more ballistic forecasting ability than I suspect we're capable of (isn't a clump of rocks going to heat up and throw things off as it comes in closer to the sun?), massively efficient engines to match velocity, and a whole lot of wishful thinking.

The smiley face might still be useful in that implausible scenario, I guess, if it changes the reflectivity enough to let the sun slowly nudge it out of the way? It at least avoids the velocity matching problem; you're intentionally crash "landing" anyway. And spinning is probably ok, as long as Galileo was right and the sun isn't orbiting around the asteroid. It's not likely to head straight at the sun.

But as you say, intervention seems just as likely to make things worse as better.

Re: Asteroid ZTm0038 with a >3% impact probability

#244

Post by [deleted] » Wed, Aug 16, 2023, 7:57 PM UTC

s1artibartfast wrote: post #239

bulatb wrote: post #230

Earlier quoted context omitted.

You're standing in a four-lane road and see a car approaching. You're looking at an angle and the lanes are poorly marked, so you can't tell which one it's in. Your observation lets you estimate the chance you need to move at 25%. When it gets a little closer, you can tell at least which half it's on, the left or the right. Now your estimate is either 0% or 50%. Closer still and you tell which lane it's in, so now yo…

again, that makes perfect sense. What wouldn't make sense is if you repeat this 1000 times and a car is never in your lane. That means that something is wrong about how you are modeling the road and cars. The claim that people are confused by is (asteroids with a 3% chance of hitting get the change revised to 0% more than 97% of the time).

[deleted]

Re: Asteroid ZTm0038 with a >3% impact probability

#245

Post by s1artibartfast » Wed, Aug 16, 2023, 9:25 PM UTC

canadaduane wrote: post #225

s1artibartfast wrote: post #219

Earlier quoted context omitted.

That makes perfect sense. Where it breaks down is if you put percentages on it. If you say the car is a 3% chance of hitting you, it doesn't and you repeat the process a thousand times, and it never hits you something is wrong with your math

I wonder if it's the difference between "this asteroid" and "all asteroids". As we learn more about it, we can start to treat it like a process that has repeated, but initially we can't be sure if it's like other asteroids. Consider a 6-sided dice roll. What is the chance it will roll a 1? A person might think, "1 in 6". But what if this is a loaded die? In that case, we need more information before we can classify i…

I think you're right. The 3% number must be ignoring repeat sampling bias. This is basically the same issue as P hacking or false positives and medical testing.

You have one confidence margin for a single single measurement and a different confidence margin if you make 1 million measurements.

Let's say you can measure marble diameters and your tool has a calibrated standard deviation of 1 mm.

If you pull one marble and measure it to be 10 mm larger than expected, you can calculate the chance you are wrong using only the standard deviation of your measurement tool.

However, if you pull 1 million marbles and measure one to be 10 mm larger than expected, you need to take into account the number of marbles you have measured.

Re: Asteroid ZTm0038 with a >3% impact probability

#246

Post by msandford » Wed, Aug 16, 2023, 10:49 PM UTC

s1artibartfast wrote: post #238

MauranKilom wrote: post #228

Earlier quoted context omitted.

Then what does 3% mean? Surely it means "given the data we have, one in every 33 will hit". Since that empirically doesn't happen, it must be that "the data we have" has a very low prior probability of being real. In other words, the measurement noise seems distributed in a way that over-represents unlikely trajectories. Hence it seems that it would lead to more accurate predictions if the measurements and their unce…

Despite all the people coming out of the Woodworks with weird theories, my best one is that the 3% number doesn't take into account their entire measurement process and sampling. It's is similar to P hacking.

I don't think you understand how this works at all. You might read up on this here if you want to learn more. https://astronomy.stackexchange.com/questions/8450/how-is-th...

If you just want to argue with people, feel free. But based on how this conversation has been going it doesn't seem like you want to learn.

Re: Asteroid ZTm0038 with a >3% impact probability

#247

Post by canadaduane » Thu, Aug 17, 2023, 12:07 AM UTC

msandford wrote: post #246

s1artibartfast wrote: post #238

Earlier quoted context omitted.

Despite all the people coming out of the Woodworks with weird theories, my best one is that the 3% number doesn't take into account their entire measurement process and sampling. It's is similar to P hacking.

I don't think you understand how this works at all. You might read up on this here if you want to learn more. https://astronomy.stackexchange.com/questions/8450/how-is-th... If you just want to argue with people, feel free. But based on how this conversation has been going it doesn't seem like you want to learn.

That conclusion may be too early to reach with confidence, based on the limited data!

Re: Asteroid ZTm0038 with a >3% impact probability

#248

Post by s1artibartfast » Thu, Aug 17, 2023, 12:56 AM UTC

msandford wrote: post #246

s1artibartfast wrote: post #238

Earlier quoted context omitted.

Despite all the people coming out of the Woodworks with weird theories, my best one is that the 3% number doesn't take into account their entire measurement process and sampling. It's is similar to P hacking.

I don't think you understand how this works at all. You might read up on this here if you want to learn more. https://astronomy.stackexchange.com/questions/8450/how-is-th... If you just want to argue with people, feel free. But based on how this conversation has been going it doesn't seem like you want to learn.

Setting your condescension aside, I browsed the thread.

I understand that calculating trajectories is difficult.

If someone claims something like a 3% impact probability, and they are wrong 99.999% of the time, that speaks to a methodological error in how the numbers are conveyed and or defined.

I work in medical devices and testing. I perform tests like X percentage of patients will die based on the statistical calculations. You may undergo treatment with a medical device that I have worked on.

Re: Asteroid ZTm0038 with a >3% impact probability

#249

Post by gs17 » Thu, Aug 17, 2023, 8:28 PM UTC

kjs3 wrote: post #206

kjs3 wrote: post #62

Earlier quoted context omitted.

How could Quora suck worse? Rub a little AI on it.

The more I think about it, this might be a good thing for the world, and amazingly stupid on the part of Quora. Since the whole Quora shtick is to heavily gamify your experience on the site, perhaps knowing there's always going to be an ML 'summary' above your incredibly erudite reply (/s in case it wasn't obvious) will make most people realize "hey...this place actually does suck" and maybe move on to something bett…

It's very dumb for Quora. The original selling point was that they had a lot of experts/celebrities answering. Now that the userbase has degraded, you would think they would want to avoid saying "go to ChatGPT, it's better than asking the randoms here".

Re: Asteroid ZTm0038 with a >3% impact probability

#250

Post by msandford » Fri, Aug 18, 2023, 4:07 AM UTC

s1artibartfast wrote: post #248

msandford wrote: post #246

Earlier quoted context omitted.

I don't think you understand how this works at all. You might read up on this here if you want to learn more. https://astronomy.stackexchange.com/questions/8450/how-is-th... If you just want to argue with people, feel free. But based on how this conversation has been going it doesn't seem like you want to learn.

Setting your condescension aside, I browsed the thread. I understand that calculating trajectories is difficult. If someone claims something like a 3% impact probability, and they are wrong 99.999% of the time, that speaks to a methodological error in how the numbers are conveyed and or defined. I work in medical devices and testing. I perform tests like X percentage of patients will die based on the statistical calc…

Calculating trajectories is easy. Getting good data points is hard. Two pictures using a telescope on back to back nights is probably the smallest reasonable sample one could get. Take another picture the 3rd night and you've just doubled the size of the arc.

Wait a week and get another sample and your arc is now approx 5x as long. Wait a month and get another and now your arc is 30x as long as the original. More observations shrink your error bars.

There are systemic errors here for sure. Two kinds, really:

1. Limits of resolution of telescopes 2. Short sample lengths

You absolutely can't do anything about error type 1. You can fix 2 by getting more data. But there's no point in getting data on asteroids that have absolutely no possibility of hitting. So only asteroids that have some probability with limited measurements get enough better measurements that are high quality in order to find out where they're really headed.

All of these measurements of trajectories are completely uncorrelated, so you can't use the priors to adjust probabilities. I mean you can do whatever you want, but we haven't been hit by a big asteroid yet since we've had telescopes and tracking databases.

If we made adjustments based on priors we'd have to discount all collisions down to 0 irrespective of the trajectories. Seems absurd, so there must be something else going on here.