There might well be some fragments heading "straight down" (as you put it) - but that would mean that other pieces would need to be kicked into a higher orbit in order to conserve momentum. Probably most of the debris cloud would remain at approximately the same altitude but in a somewhat different orbit. Most small orbital objects (on the order of a few grams or less) reentering the atmosphere just don't produce much of a display; you need more mass - a whole intact satellite, for example. I just don't see this as a likely outcome, certainly not that quickly.

Every single event is unique and unprecedented, by definition - but that's no reason to throw out basic principles like the conservation of momentum.

I'm not sure why you seem to think I'm attacking you - it's just that it's very unlikely that enough debris from those satellites could be de-orbiting that quickly and also sufficiently simultaneously that the event would actually be visible from the ground. The odd tiny chunk of metal, perhaps, but that would almost certainly not make a visible display. The expectation is that the vast bulk of the debris will not even intersect with the altitude of the much lower ISS orbit for decades if not centuries.

It's still high enough that it's unlikely that significant debris from the collision could de-orbit that quickly - which was the point. A few miscellaneous chunks of debris would not make a trail visible from the ground - you'd need a significant mass in a single chunk or at least in a cloud that all de-orbited together.

This is obviously true, but it usually takes a while for debris to de-orbit especially if it's not in very low orbit (where it will encounter more atmospheric drag). Offhand the only way I see for this to be likely to happen so quickly would be if the satellites had been moving in opposite directions (a head-on collision, in other words) - that ought to result in at least some debris having a markedly different orbital energy from that of either of the two satellites before the collision. But most satellites orbit in either an easterly direction (it takes less energy to launch them in that direction because you get an energy boost from the Earth's rotation) or in a polar orbit (which is useful because even though it requires more energy the satellite can pass over all of the Earth's surface) - so head-on collisions are relatively unlikely.

That's far from the lowest LEO. The International Space Station (ISS) orbits at about 358km.

I'm not arguing that the IP address is useless information, or that the police shouldn't be able to use it for legitimate purposes; in fact it would probably be very easy to get a search warrant for this kind of situation. Clearly the IP address standing alone isn't very strong evidence of anything, but it's certainly a good place to start in tracking down the culprit in many criminal cases.

The question is not whether the police can and should be able to do reverse IP tracking, but whether the police can compel reverse tracking without a warrant, as well as whether a provider is or should be obligated to require such a warrant. The point is not so much to limit their ability, but rather to ensure that that power is not abused by forcing the request to be reviewed (if only in a cursory manner) by a third party.

The problem is that an IP address is NOT a unique identifier for an individual. In most cases, it's going to be a dynamically-allocated address that may map to many subscriber locations within your neighborhood or your city or even the entire country, depending on how your ISP allocates addresses. At any given moment in time, it will only map to one subscriber location, but the only one who has access to that information will be your ISP, possibly in conjunction with the telephone company if you're connected by modem.

But even apart from that, an IP address can be multiplexed between many individuals or even other locations once the traffic for it reaches the subscriber location.

So it's not like a phone number at all - there's not even approximately a one-to-one mapping between IP addresses and individuals, nor is the mapping that does exist stable over even fairly short spans of time.

I'm not sure whether I think that the police should have the authority to do a reverse IP lookup without a warrant (though from a civil liberties standpoint it does make me distinctly uneasy, since this is in no sense "public" information and has serious potential for abuse), but the analogy with the phone system is badly flawed.

And in what way is the electronic transaction processing any less secure than the piece of paper? It's pretty easy to generate the printed check if you have the appropriate numbers, and in either case by the time anyone notices something is amiss you can be long gone.

The problem isn't that the printed checks are any more secure, but rather that in both cases all of the necessary numbers are right there in plain sight and unencrypted.

Arrgh. Somehow Slashdot logged me out before I posted this, so it got put up under "Anonymous Coward" - but I did have a couple things to add to it.

3% of $500,000 is $15,000, not $150. $500k would pay for a lot of concrete though - a whole lot more than a few metric tons. :-) But the point is well taken - for large transactions that kind of processing charge can be prohibitive.

ACH/wire transfers can sometimes also be expensive to set up, though not nearly as much so as credit cards - perhaps $25 (unless you're a big company and able to negotiate a good deal with the bank), as opposed to checks which are nearly free; plus they have their own security issues (once again you need the bank routing code and the account number, which allows all sorts of mischief).

Business to Business (B2B) transactions are largely based on trust and ignorance: if you don't trust your client/customer, you don't do business with them, or you put them on some kind of "cash-only" basis, including for example things like certified checks (free at many banks if you have a commercial account, but a pain to deal with because of the extra processing); and ignorance because the general public "should" never know either the bank routing codes or bank account numbers for either company.

In the long run some kind of pseudo-encrypted or even certificate-based transaction scheme will probably become necessary if the fraudsters continue to become more sophisticated, but at the moment just about all of the methods for transferring money are vulnerable to relatively unsophisticated attacks.

Unfortunately much (most?) of the US public thinks that:

Everything that's "natural" is good. (Umm... what about ricin? Perfectly respectable "natural" product...)

Everything "nuclear" is bad. (The parent is potentially a good counterexample).

Everything "renewable" is good. (Using corn-based ethanol as a fuel source is a really bad idea ... there are better sources that have less environmental and economic impact).

Etc. Unfortunately the state of science education in the US is in such a sorry state that too many people are unable to think rationally about many of the choices facing us - they'll pay more attention to what Oprah or Paris think about some scientific question than they would to the scientists and engineers who actually do know something about those choices.

For all those people, I've got a bridge for sale in Manhattan! Cheap!! Buy it now while you have the chance, because it'll sell fast!!!

:-( :-( :-( Our country is so screwed... hopefully some of the rest of the world can keep civilization going until the nitwits here die out ... :-( :-( :-(

Cosmic radiation is probably the least of your worries. Unless you can shield yourself from nearly all of it (which is difficult at best), you can actually make your exposure worse because the cosmic radiation will interact with the material in the shielding to produce secondary radiation which can actually be worse than the cosmic radiation itself since it will interact more readily with matter (i.e., you).

But a lot of solar radiation is not nearly as energetic as cosmic radiation, and besides it would be very useful to have a protective heat sink so that your living quarters don't get too hot during the lunar "day" or too cold during the lunar "night."

... Followed by two weeks of cold and darkness. Better have some really good batteries, or a good transmission system to that moon base on the far side so that you can supply each other with energy when the sun goes down on your respective sides. At least on Earth you don't have to store the energy for so long, which does help somewhat.

The lunar poles aren't much better: You never do get a lot of light on a lot of surface area unless you build some very large hills or towers so that you always have a large surface area pointing at the sun, plus you only get two possible locations for your colony.

Still, probably not a bad tradeoff if you can solve the problems.