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6 hours ago, RDU Neil said:

 

"The "tension" reminds scientists of just how much they still don't understand about the underlying laws of nature."

I like when human intellectual arrogance receives a cold dose of humility. :)

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The May 18, 2019 issue of The Economist has an article and editorial about Jeff Bezos' space colonization proposals. They aren't very kind to Bezos, pointing out that his plan for O'Neill colonies, and his limits-to-growth justifications, are both from the 1970s. I would point out: This does not, itself, make them false.

 

(Though it does remind me of Ben Bova's novel Colony. As far as space colonization goes, Bova thought that O'Neill colonies were putting the cart before the horse. But... why might someone want to build one as a near-first step? In Colony, the reason a consortium of the world's richest men build a space colony is that they want a refuge from the collapse of civilization. Which they are so sure is goingh to happen, they intend to make it happen on their timetable. Things do not work out as they intend... Notably, their idyllic town in space is not too far away for the building conflict on Earth to touch. If Bezos has read Colony, I hope he read it wisely.)

 

Dean Shomshak

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On 4/11/2019 at 5:34 AM, L. Marcus said:

I think that pic encompasses the whole of the M87 galaxy -- the bright tail sprouting rightwards from the core matches pretty well with the central jet in visible light pics I've seen. Also, the above image is in the X-ray spectrum.

 

On 4/11/2019 at 5:44 AM, RDU Neil said:

 

Ok... so that is all of M87? Ok... that kinda makes sense, but also seems small... maybe because we are only seeing X-ray sources.

 

Thanks.

 

About midway down this page (hangs off the official Chandra site) is another image that puts the black hole shadow image in scale context with the two X-ray images from Chandra.

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1 hour ago, Cancer said:

 

 

About midway down this page (hangs off the official Chandra site) is another image that puts the black hole shadow image in scale context with the two X-ray images from Chandra.

 

Thank you. That makes much more sense, now.

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This one is for Lord Liaden, as it deals with another case where physicists admit they are stumped about something they first thought would be simple. It isn't space news, exactly; this is about the very smallest components of matter. But the biggest and smallest scales of the Universe merge in the Big Bang, so some problems in cosmology probably can't be solved until physicists improve their understanding of how quarks combine to make protons and neutrons.

 

I as a layman thought that was pretty well nailed down. Protons and neutrons (collectively, "nucleons") are made of quarks, which are held together by the "strong force" carried by gluons. It's laid out in the theory of quantum chromodynamics (QCD). But an article in the June, 2019 Scientific American says it ain't so simple.

 

For a start, the mass of the quarks adds up to only 2% (or so) of the mass of the proton or neutron. Where does the rest of the mass come from?

 

Nucleons have a spin. So do the quarks of which they are composed. But the spin of the quarks doesn't add up to the spin of the proton or neutron.

 

QCD doesn't explain this because the math is kind of, um, impossible. In part this is because the strong force is far more complicated than good ol' electromagnetism or gravity. Like, electromagnetism has just two charges, positive and negative. The photons that carry electromagnetism do not themselves have charge, though, so photons don't interact with each other. The strong force has three charges, called colors, each with an opposite for six in all. Worse, the gluons that carry the strong force have a color "charge," so they do interact with each other. While a virtual gluon jumps from one quark to another it exchanges its own virtual gluons with other quarks and gluons -- and those gluons exchange their own gluons as they interact -- and so on.

 

Somehow, all this seething mass of quarks and virtual gluons adds up to the properties of protons and neutrons. But the bazillions of particles involved make the calculations impossibly complex. The theorists are lost. Physicists can only hope to solve this puzzle by poking at the quarks and gluons directly, to see how they react.

 

Remarkably, they can do this. In fact, they've been able to do this for several years -- which is how they proved that quarks really exist and aren't just a delusion of theorists. If you shoot high-energy electrons at (say) a neutron, the electrons can bounce off the individual quarks and give clues to what the quarks are doing. Physicists have already learned that quarks behave differently in a single particle than when a bunch of nucleons are grouped together in a nucleus.

 

The authors hope that a more powerful and focused particle accelerator, the Electron-Ion Collider, will enable physicists to create 3-D maps or pictures of quarks and gluons bopping around inside atomic nuclei, and that this will help solve the puzzles of nucleons' mass and spin. Maybe even develop techniques to control the motions of quarks, as a test of their understanding.

 

Which leads to the question: If quarks and gluons can be controlled precisely, does that raise the possibility of femtotechnology, a million times smaller than nanotecnology? They decide that such speculation is premature. But they won't rule it out.

 

Dean Shomshak

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5 hours ago, L. Marcus said:

I say, bop those nukleons! Bop 'em hard!

 

Bop 'em 'til their quarks spin!

 

Bop 'em 'til their gluons come unglued!

 

Bop 'em when they're up, Bop 'em when they're down!

 

Lucius Alexander

 

The palindromedary adds, Bop 'em when they're charming, Bop 'em when they're strange!

 

 

 

 

 

 

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On 5/4/2019 at 10:48 PM, tkdguy said:

Not really news, but this thread seems to be the best place for this video. Perhaps we'll solve these mysteries within our lifetime.

 

 

 

A couple of quibbles here.

 

Most of these are in the Venus section of the above ... the quote "only three missions" to Venus omits several Soviet Venera landers in the 1960s; no one else has put a functioning probe on the surface of that planet.  And it also omits what to my mind is the most plausible cause: Venus was roughly Earthlike (in terms of surface and atmosphere conditions) when formed and stayed that way until about a billion years ago.  The inevitably increasing energy output of the Sun (that's a bulletproof result from stellar evolution studies; I can talk about that later if you want, but the initial results came as far back as the 1950s) pushed the surface temperature of Venus above 100 C, and that triggered the runaway greenhouse effect that caused a planet-wide volcanic outburst, destroyed all the sedimentary rocks and liberated the CO2 in those into the atmospheres, and made the situation we now observe.  Supporting this idea: the mass of CO2 in Venus's atmosphere is reasonably close to the mass of CO2 locked up in carbonate sedimentary rocks on Earth, so that if you were to cook Earth's surface over 100C, the same Venus-like end state is well within the possible results.

 

(That also would mean that it'll be impossible to tell if there was ever life on Venus: even the fossils get destroyed in that volcanic outburst, so not even putting a rock-collecting rover on the planet would be able to find anything.)

 

The solar magnetic field thing omits a bunch of admittedly complex results.  Measuring the waves that appear on the solar surface (see https://gong.nso.edu/) continuously for more than a decade gives you enough data to solve for the run of pressure, density, and something about the fluid velocities in the solar interior.  We know the convective zone rotates almost as a solid, which tells you that magnetic fields are really important to the solar structure through the convective layer.  But, below the convective zone, the rotation is not like a solid.  The equations for the generation of a magnetic field are horrible beyond belief (magnetohydrodynamics) so a detailed solution is certainly beyond our grasp anytime soon.  And while GONG and other observational projects has given us glorious data on the Sun and we have learned a lot, it is clear from historical data that the Sun has activity variations on timescales of centuries (at least), and we haven't enough of that to be able to explain it, either.

 

The Kuiper Belt/Oort Cloud situation is ... a new-ish problem, and one attributable to the newness.  Remember, while the first KB object was discovered by Clyde Tombaugh in 1930, Pluto was misidentified as a planet and retained that status until the next few KBOs were found in the 1990s.  Observations of things that far out are really difficult, requiring the largest telescopes to gather enough light to see really faint and distant bodies, and by an inevitable corollary of optics, really big telescopes can only see a tiny piece of sky at one time ... so survey work is very slow and very expensive in terms of big telescope time.  I don't think anyone has the hubris to claim we know enough about the KB to make meaningful guesses about how many objects there are, anything like their global population statistics, or even how much mass is out there.  There are some really striking things we have seen about the collection of KBOs we know about so far (there are way more binaries and satellites and rings than anyone guessed, and the population shows some weird correlations between mean distance of the object and the shape and orientation of its orbit, which has to be telling us something but we don't really know what yet), but absolutely everyone admits we have seen only a tiny fraction of what is out there.

 

As for Uranus, that planet has been visited by spacecraft exactly once, and Voyager's fly-by back in 1986 caught the planet doing ... absolutely nothing, at about the time the planet's rotation axis was pointed as close to right at the Sun as it ever does.  Some pretty severe (at the time) image analysis was needed to see the planet as anything but a pale blue cue ball.  Since then Hubble Space Telescope, and some groundbased telescope/instrument combos that didn't exist until the 21st Century, have found that at other seasons, the planet isn't just a quiescent plain cue ball, which should not be a surprise in any way.  But if you start the clock at the 1986 fly-by, we haven't been observing the planet for even half of its year yet ... that's 33 (Earth) years of good observations compared to an 84 Earth-year orbital period for Uranus.  I think it would be fair to wait at least until we'd seen a full seasons cycle before we framed ideas about the planet's climate should be like.

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