The moon’s orbit is taking it further from Earth over time, it it’s very far away and very massive, as well as being influenced by the Sun. A satellite’s mass is almost negligible, and compared to the Earth-Moon distance it’s distance from Earth is too. A pebble hitting the moon also isn’t going to do much to change its course, while the same pebble will do a lot more to a satellite. The same is true of dust.
It depends? If the satellites used chemical rockets to produce stationkeeping thrust then they’d be long gone, but if they used some exotic power source who knows? If they had a good AI and power, there is no real limit on how long they could stay in orbit. If they were using technology like ours they’d be gone, but a hypothetical civilization might use exotic materials and power sources that would stand the test of time.
For the moon thing, the above applies, but assuming that they were obliterated we’d have to get pretty lucky to detect their remains. They could also be totally intact because there would be essentially no weathering, they would never be buried by shifting regolith, and so on.
Ok, I’ll do my best here. I’m going to pass the first question because there’s already a discussion about it below.
I have some naive questions too. This is basically just me rephrasing the question I understood wallace_f to be asking:
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- The black hole within the horizon is a three-dimensional massy object and can and does exert a lot of gravitational force.
The black hole includes the event horizon, which marks the point at which we stop knowing anything or have theories to predict anything. We really have no idea what’s beyond the event horizon, and almost anything you can imagine has been conjectured as being there, from firewalls to elder gods. We’re talking about a region which can’t be properly described by he theories we have, where the manifold ceases to well behaved. Everything beyond the event horizon is causally disjoint with the rest of the universe, and may as well not exist for anything that isn’t falling past the event horizon.
- Assume at equilibrium our black hole is somehow exerting gravitational forces on its surroundings which are what you would predict if you accurately knew the black hole's actual mass.
Right, mass is one of the “hairs” a black hole has along with charge and momentum.
- Assume the black hole moves, e.g. because of inertia.
- Now it should be exerting more force than previously on one half of the universe (the half it moved toward), and less force on the other half.
It sort of does, this is the basis of frame dragging when the hole is spinning. The hole warps spacetime around it, dragging reference frames in the direction of its motion.
- Say it moved toward you. After a speed-of-light delay, you should actually perceive more force on yourself towards the black hole. But this can't be because a messenger particle was transmitted from the black hole to you. How can it be?
Assuming this shows that black holes cannot move seems unsatisfactory, given the recession of galaxies from one another, observations believed to show black holes colliding, etc. Where are my mistakes?
The theory of gravity we actually have doesn’t involve bosons, it’s a geometric theory describing a continuous manifold. How that squares with theories containing gravitons is well above my pay grade, sorry. The classical theory says that the warping of spacetime is continuous, and so the hole moves like something being dragged through water, including a wake and bow wave. Since the hole can’t move at c, being massive, there is always an acceptable delay for the light-speed propagation of disturbsnces in spacetime to reach you first.
Followup: one black hole collides with another black hole of roughly ten times its size. Is it necessarily the case that the center of mass of the new, combined black hole ends up at the point that was the center of mass of the small-hole/big-hole system just as the small hole crossed the big hole's event horizon?
They end up merging like two legs of a pair of pants meeting at the crotch, with the new center of mass at the barycenter of the previous orbiting pair. I loved these questions by the way, I can tell you put some real thought into them.
We don’t know, and may have no way of knowing. There are conjectures that the event horizon is it, that inside the event horizon is a quantum fuzz ball, or strings, or 1D points, or a whole universe. We don’t know, and may well never know. What we do know is that it seems a 2D horizon can encode the information required to describe a 3D volume, and that goes for event horizons, as well certain classes of cosmic horizons in some models. This weirdness is the core of the holographic principle conjecture.
That’s a bit of a tricky question, because it’s math-heavy. The best way to describe it is to think of the event horizon as the black hole, and forget that there is even an interior. The black hole can be fully described by the conditions at the event horizon after all, and everything else is cut off from the surrounding universe completely. In that sense there is no propagation from the interior at all, which is good because if information could escape then theories describing black holes would be broken.
Instead the black hole has mass, charge, and momentum (three kinds of momentum actually, but that’s not important). Whatever is going on beyond the event horizon, whatever that might be, has no effect that anyone can detect. Matter is accreted “onto” the event horizon which then expands in proportion to the mass of the volume of the hole. Maybe it’s destroyed beyond that point, or maybe it goes to another universe, but we can never know. The event horizon can also shrink if the surroundings are sufficiently cold (really really really cold) and the horizon is sufficiently hot.
Still, all of this is surface phenomena, like dropping a bowling ball into a tub of water. The water only “knows” about the surface of the ball, which which gets properties from the whole ball without exposing the center. A bowling ball in water creates waves, but the interior isn’t interacting with the water anymore than the black hole interior interacts with space (assuming an idealized perfectly rigid bowling ball). In the same way gravity waves or fractions would be a function of how the space just beyond the event horizon is warped.
You might enjoy some Scholagladitoria videos covering just such topics. As with most things the question of “what wins” between various swords is rarely straightforward, and always involves a lot of context. A shitty katana vs a splendid saber wouldn’t be interesting, but there were plenty of garbage pieces of both, along with lots of masterworks. Given even quality swords and equal skill, the determining factors seem to be the kind of fight. In a 1-1 unarmoured duel a rapier is hard to beat; no surprise since it evolved for just that reason. You’d hate to use a rapier on an armored opponent, one on horseback, or multiple foes though. A katana has less reach, is better at cutting and worse at thrusting, and is weighted more towards the blade. That’s a plus in some regards, and a minus in others. A saber is a very fine cutting weapon, but terrible in the thrust; it excels on horseback and on the ground. A saber will generally have the benefit of more protection for the hand and forearm, while the tsuba on a katana is pretty minimal. However a saber vs. armor is a disaster, while the katana can punch through some plate in the thrust. For thick armor you’d really want a longsword with a bodkin point, or a bludgeon.
I think by definition it wouldn’t form a black hole, it would be a black hole. Gravitational waves are propagating disturbances through spacetime, so the kind of wave you’re describing would begin as a singularity. I don’t think (but am not sure) that the math allows for the emission of such a thing. It sounds non-physical, and I’d suspect that if you do the math you’d discover that you’d need to have giant black holes merging to generate such a wave, or FTL. In the former case I’d bet that it turns out the wave would form within the event horizon of the hole, and that’s a good as saying it would never form.
As others have pointed out, if they’re in a stable orbit they won’t fall in (at least not for a very long time), because unlike luminous matter it won’t experience any force other than gravity. If you imagine a dust cloud of luminous matter around a black hole, it will tend to experience frictional heating the closer it gets, there is the chance of a collision or radioactive decay, and other forces acting to draw it in or send it far away. Dark matter won’t do that, it just couples to gravity. Our usual intuition about how a halo of matter behaves has a lot to do with interactions other than gravity. Clumping for example, aggregation and accretion pretty much work because of interactions other than gravity, until a body becomes massive enough.
Sure, and yet mosquitoes alone infect over 700m people a year with various diseases, and rack up more than a million deaths each year. I find the Internet is surprisingly ineffective against malaria or dengue too. It’s also true that few people can or would wear a full body suit all day, every day. For god’s sake, we can’t even get everyone to wear a condom, never mind biohazard suits.
Still I respect your optimism, however unfounded it seems to me. I think the next really nasty flu will probably disabuse you of it, but I hope I’m wrong.
For most of history, and increasingly today the simple aggressive behavior of bacteria, viruses and fungi was uncontested. For all of our intelligence, they still win a lot, and our best efforts are becoming less effective as they adapt. They don’t even have nervous systems, but numbers and a fast reproductive cycle are a bitch. See also: a colony of army ants killing everything in front of them.
Honestly I never considered that angle, but I have to agree. I’ve always focused on grander aspects of it, but of course the small everyday lies and manipulations would be more central.
Convince parents that teaching kids to think critically is more important than indoctrinating said child into whichever religion or political sphere the parent is already a part of. In my experience that’s a broadly impossible task. Parents want their kids to think critically only about the things the parent already rejects.
He’s not being charged for what he published, he’s being charged with conspiracy to “hack” as it were. If you’re asking whether something stops being a crime because you did it for virtuous reasons, obviously the answer is no from a legal perspective.
It’s not about control, it’s just that they don’t have to extend anything beneficial to the UK at the EU’s expense. Basically the UK wants a divorce, and they’re pissed that they’re not getting what think they deserve. Whatever control issues exist are due to a treaty the UK freely entered into, and choices (like getting married) have predictable consequences. If you decide freely to marry me, then unilaterally decide to divorce me, you wouldn’t be shocked if the result was a compromise between what you wanted in terms of property and rights, and what I wanted right?
Of course the EU is going to push for every inch, and since they don’t even want Brexit that gives them a lot of power. That was (or should have been) obvious from the get-go.
Agreed. Genentic engineering will probably be helpful, but first we do as you say, have to know what to engineer for. Then of course we’ll have a kind of speciation event and we’ll risk having a kind of genetic apartheid based on people who work in space vs. planetside. It could get sci-fi dystopia levels of ugly if we don’t work to prevent those outcomes.
It’s not a study, but it’s been hypothesized that radiation and cosmic rays could cause lasting damage of just this sort through particle showers within the brain. Truthfully though there is very little in the way of studies for the simple fact that it’s hard to set one up for astronauts. Given how radically different the environment in space is compared to Earth though, I’m not finding this surprising. I wouldn’t be surprised if it’s just the tip of a very dangerous iceberg too, and it turns out that it takes a lot of time and sacrifice to get us to live and thrive somewhere other than Earth’s surface.