Comment Re:Lower limit. (Score 1) 282
That depends. How often do you get fired?
That depends. How often do you get fired?
At a minimum, at least as often as you get fired.
Having read the article, I think that "With a Bang" sort of waffled on this. It is hard to see how SuperMassive Black holes (SMB) form in the time available for them to form. (There is a large literature on this, but basically there are problems of the seeds - are the seeds Pop III stars, or something more exotic - and time - how can the mass move around enough to form SMB by z ~ 6?).
I don't really feel you can safely answer the "which came first" question until you know how the SMB actually formed.
A one hour video lecture, Supermassive Black Holes and the Problem of Galaxy Formation, might be interesting to people interested in these problems, but it deals with the galaxy problem more than the SMB problem.
Of course, as the "With a Bang" article points out, if you are willing to wait and not have everything be simultaneous, you can have both large scale structure formation and small scale structure formation going on simultaneously, with the small scale going to completion earlier, and both together yielding what we see today.
Why is the answer always assumed to be binary? Both processes could have been occuring simultaneously.
I am sure both were occuring simultaneously, the question is, which dominates? The two sets of processes have different time constants (growth rates), arising from different physics. For both to be more-or-less equally powerful requires these time constants to be more-or-less matched, and that seems improbable and fails "Occam's razor" type "tests."
So, could be, but don't expect that idea to gain traction, at least without a good theory as to why things should be that way.
we first expected and then found supermassive black holes at the centers of practically all large galaxies.
"expected" is sure not how I remember it, and in fact I think this has the historical record backwards. Quasars were definitely a surprise, and the Super Massive Black hole (SMB) interpretation of quasars took a while (a decade at least) to catch on, and the consensus that most galaxies have a central SMB came after that, after some local galaxies (such as our own) showed signs of having a SMB too. Before all of this most astronomers weren't interested in black holes and even the small number of General Relativity types (such as Zeldovich) who were, and who were looking them, were looking for stellar mass sized black holes, not the SMB variety.
All in all, I think it would be more accurate to say that the SMB-galaxy connection was forced upon astronomers by the data, rather than that they expected it.
A bug in the mosaic screensaver caused downloaded images to remain uncached.
I have to wonder about that.
The OP did 79.61 GB in one day, which works out to 7 Mbps over 24 hours. That seems like a lot of images (several a second?) for a screen-saver to download.
A better analog might be, suppose someone said in testimony
I buried all my documents in a box out in the desert.
Could they then be compelled to provide the location if police searches turned up a blank? Seems like they could.
Of course, if you are willing to go to jail and wait it out, the "compulsion" is never forever, Seems like that might depend on just what's in those documents.
You do not have to participate in the opening of your safe. A locksmith or torch can do that without you.
Your encrypted documents, on the other hand, may not be crackable without your help.
Note that courts seem to feel that Iris-scans, fingerprints, etc., are not "testimony," and so are not protected. That's something to keep in mind if you wanted to purely rely on biometric keys for your encryption.
IANAL, and this is not legal advice.
Building three unfathomably massive anti-tornado walls would count as the infrastructure project of the decade, if not the century. It would be also be exceedingly expensive.
If it is not exceedingly expensive, it's not the infrastructure project of the century.
Franson's theory cannot be right, as it disagrees with the solar system tests of General Relativity
His Equation 18 predicts a change in the gravitational red shift by a factor of 9 alpha / 64 for photons, where alpha is the fine structure constant (~ 1/137), so the correction is ~ 1.08 x 10^-2. The gravitational red shift has been tested, by GPS and also by Gravity Probe A, with an accuracy of a few parts in 10^-4 (see Figure 3 in that reference). This excludes the Franson correction, and so his theory cannot be correct. Since the Shapiro delay also depends on the gravitational redshift, Franson's theory thus predicts a 1% change in that too, which is also much too large to be consistent with experiment (see Figure 5), again excluding the Franson theory.
So the theory is wrong, and the other problems I have with the paper are irrelevant.
When 1987A happened, it is fair to say that an enormous amount of attention was placed on those neutrinos - >> 1 paper per neutrino. The report of an earlier neutrino burst from the Mt Blanc LSD was discussed at length - see Arnett 1987 Table 1 for the time line.
The facts are these - the optical supernova could not be accurately timed, it wasn't bright at Feb 23.10 and it was at 2 / 23.443. The Mt Blanc LSD burst was at 2 / 23.12, while the other two detectors had a mutual burst at 2 / 23.316. Note that both neutrino bursts occurred before the optical SN was detected, and also that none of the other detected picked up the Mt Blanc LSD burst.
All of this has been known a long time, and numerous theories have been introduced to explain it.
- formation of a nlack hole (from the neutron star)
- formation of a quark star (from the neutron star)
- the Mt Blanc data were unrelated to the SN (that appears to be Arnett's viewpoint).
So, this is another explanation, and not a super compelling one to me. It will clearly never be proven from the SN 1987A data - the next such close supernova should have a lot of neutrino data, and maybe will resolve the issue.
"The Europa probe is likely
That should be
"The Europa clipper probe is likely
Stone Aerospace has some elaborate plans:
"When we speak of the Europa mission at our shop we are talking about going for the gold ring: landing on the surface of Europa; sending a nuclear-powered cryobot carrier vehicle through the ice crust; discharging a nuclear-powered 'fast mover' autonomous underwater carrier vehicle that has planet-scale range, and selectively launching a series of miniaturized, highly intelligent AUVs [Autonomous Underwater Vehicles] to go into the more dangerous areas (e.g. around black smokers, up into ice cracks, into corrosive chemical plumes) to search for and collect biological samples and bring them back to the mother ship,"
but I don't know anything about their comms plans. A german group plans to have a submersible return to the surface and then broadcast everything back.
I would strongly prefer to have a transmitter on the surface (sending either back to Earth, or to an orbiter somewhere), and use acoustic signaling, just as you would do with a deep submersible here on Earth. Problems with the "go back to the hole" plan include
- a failure on the return trip means no data comes back at all
- a good fraction of the under-ice mission time would be spent going back to the hole, or making a new one, rather than further exploration.
- if the submersible gets into trouble, or has to make a decision as to what would be best to sample/explore/go to next, Earth cannot help.
Of course, we know nothing of the acoustic noise level in Europa, so this might require a precursor seismology mission just make sure it would work.
That's not what NASA Planetary Protection thinks and, at least for US space probes, that's what counts.
Memory fault - where am I?