Completely out of my domain and seat of pants rationing here, but although the impact probability is 1%, aren't we far far more certain about the /time/ at which it would strike earth? Could humanity collectively just migrate to the side of the world that will be shielded for a day?
Asteroid Impact on Earth 2032 with Probability 1% and 8Mt Energy
291–300 of 374 posts
Re: Asteroid Impact on Earth 2032 with Probability 1% and 8Mt Energy
#292Earlier quoted context omitted.
It’s the error with the ground truth that you can’t predict. Otherwise you would just be able to cancel it out. You can only predict probability distributions..
If you're saying that it's the uncertainty in the initial measurement, then we're in agreement. If the initial measurement were perfect, the only source of error would be the finite timestep. N-body simulation itself is deterministic, and so the only source of randomness is our uncertainty about the object's true mass, size, shape, position, velocity, etc.
The N-body _reality_ _might_ be deterministic. The N-body simulation using digital computers will technically still introduce errors because of the time steps even if you had perfect knowledge of initial conditions.
Re: Asteroid Impact on Earth 2032 with Probability 1% and 8Mt Energy
#293Earlier quoted context omitted.
If in 2032 an impact did occur, how much time before that impact would be able to ascertain over 50% probability of impact? hypothetically. That is, does the certainty increase steadily or non-linearly over time? Does near certainty of an impact occur from measurements taken just minutes before the impact, or hours, days, years?
> how much time before that impact would be able to ascertain over 50% probability of impact? hypothetically. I understand it's hypothetical, but even a 10% chance of hitting a city, for example, would be a crisis.
They didn't say anything about 50% being the minimum level for a crisis. There is no "but" because they are two different topics. One is "how far out could an impact be predicted at 50/50 probability" and the other is "at what probability of impact would it become a serious issue/crisis".
Re: Asteroid Impact on Earth 2032 with Probability 1% and 8Mt Energy
#294Earlier quoted context omitted.
If you're saying that it's the uncertainty in the initial measurement, then we're in agreement. If the initial measurement were perfect, the only source of error would be the finite timestep. N-body simulation itself is deterministic, and so the only source of randomness is our uncertainty about the object's true mass, size, shape, position, velocity, etc.
The N-body _reality_ _might_ be deterministic. The N-body simulation using digital computers will technically still introduce errors because of the time steps even if you had perfect knowledge of initial conditions.
The errors are deterministic. Determinism has nothing to do with the existence of errors, it's about uncertainty. They're different things. A system that is deterministic will produce the same results every time given the same initial conditions. If there are numerical errors, they will be identical for each run. A non-deterministic system will give you different results every time given the same initial conditions, with some variance. You can still have numerical errors in such a system.
Ironically, reality probably isn't deterministic. It definitely isn't at small scales (e.g. radioactive decay). If it's non-deterministic at a macro scale, the effect is small enough that we don't see it.
Re: Asteroid Impact on Earth 2032 with Probability 1% and 8Mt Energy
#295Earlier quoted context omitted.
How far in advance would we know exactly _where_ on the Earth it will hit? If, say, New York is going to be destroyed, it makes a big difference if we know that a year in advance vs. a day.
Does it though? People don't leave hurricane zones. People don't heed tornado warnings. I just have very little faith in humanity, and fell like "Don't Look Up" would be not too far off. Also, if you evacuate New York a year in advance, who's to say that the prediction isn't just a skosh off so that New York is left untouched but the real impact location was hit unprepared?
Having lived through a bunch of hurricanes in south Florida I can very confidently say people absolutely evacuate when given the order to.
Re: Asteroid Impact on Earth 2032 with Probability 1% and 8Mt Energy
#296Earlier quoted context omitted.
Chaotic doesn't mean non-deterministic, it just means that small changes in initial conditions result in a large change in the trajectory. The system itself can be both chaotic and deterministic. It's also a reasonable question to ask, because the simulations are deterministic. It's just that because the system is also chaotic and there's noise in the measurement, that can result in a large spread of deterministic tr…
We don't know the configutation it's in precisely. We don't know the initial conditions. Small unobservable differences will lead to large difference in outcome. That's the chaotic part.
I get that. I'm pointing out that these are separate factors. Chaotic does not imply non-deterministic, and vice versa. The only source of randomness here is the uncertainty in the observation of the object, because (as you point out) multiple combinations of parameters could produce the same observation, and each one will have a different trajectory. The randomness doesn't come from the chaotic nature of the system, it comes from noise in our measurements. It also doesn't (as other posts are claiming) come from energy drift in the simulation, because that's also deterministic.
Re: Asteroid Impact on Earth 2032 with Probability 1% and 8Mt Energy
#297Completely out of my domain and seat of pants rationing here, but although the impact probability is 1%, aren't we far far more certain about the /time/ at which it would strike earth? Could humanity collectively just migrate to the side of the world that will be shielded for a day?
Knowing humanity and its ability for planetary level solidarity, its more likely that the most powerful nations would simply displace the weaker ones. "No offence bro, but we are the salt of the Earth, so get out of here and good luck".
What about empty places? Luckily for Greenland, the calculations predict that the flux of impacts to the poles for Earth is 22% greater than the flux at the equator [1]. So nobody (in their right mind) would want to annex it as an asteroid survival backup site.
[1] https://iopscience.iop.org/article/10.3847/PSJ/abefda/pdf
Re: Asteroid Impact on Earth 2032 with Probability 1% and 8Mt Energy
#298I work on the Near Earth Object Surveyor space telescope (NEO Surveyor) writing simulation code which predicts which objects we will see. This one has drummed up a bit of interest due to its (relatively) high chance of impact. I actually spent quite a bit of time yesterday digging through archive images trying trying to see if it was spotted on some previous times it came by the Earth (no luck unfortunately). Since w…
What are the implications of a moon impact? Would it affect life on Earth?
Would Earth see on-again, off-again random showers of rocks of various sizes ?
Re: Asteroid Impact on Earth 2032 with Probability 1% and 8Mt Energy
#299Earlier quoted context omitted.
On the other hand, if people are told constantly to look up, eventually they stop looking.
Or maybe we just build a system that can reliably detect and deflect asteroids and resolve the concern.
Obviously we should build a system which can reliably detect and correct people looking up and resolve the concern.
Re: Asteroid Impact on Earth 2032 with Probability 1% and 8Mt Energy
#300Earlier quoted context omitted.
It's nonsense today, but technical factors change over time. It's unsafe to try to predict too far ahead.
The physics of tomorrow though will be the physics of today however: a many months flight time out to an orbital object to affect trajectory change is a response time so far away as to be meaningless: any opponent with an ICBM strike capability on Earth could happily blast away your entire civilization, and reasonably expect to use the same technology that enables that ICBM capability to blast away (or deflect) your…
Consider that ICBM's might not work forever. If e.g. new types of anti-ballistic missile defenses were to become cheap and reliable, then ICBM/SLBM's could even become obsolete (say, within the century). If that happened, there'd be a slew of new arms races, which are unimaginable to us, being beyond our technology horizon.
Physics isn't changing over time, but engineering is.