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John Baez
Works at Centre for Quantum Technologies
Attended Massachusetts Institute of Technology
Lives in Riverside, California
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John Baez

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Have astronomers found a TŻO?

When a big star runs out of fuel, its core can collapse and form a dense ball of neutronium just 25 kilometers across, called a neutron starBut what happens when a neutron star hits an ordinary star?

Kip Thorne is a physicist who helped write the most famous book on general relativity.  Now he's helping run the LIGO project for detecting gravitational waves.  Anna Żytkow is an astronomer at Cambridge who is looking for objects in the Kuiper Belt, outside the orbit of Pluto.  But back in 1977, they teamed up and asked this question... and answered it!

The answer is: the neutron star could fall to the center of the other star!   The result is called a Thorne–Żytkow object, or TŻO.

When this happens, the neutron star will suck in gas from the ordinary star.  It will get extremely hot, with temperatures over a billion degrees Celsius.    The heat comes from two things: the energy released when infalling gas hits the neutron star, and nuclear fusion after the gas hits.

If all this happens inside a red supergiant star - a huge, puffed-out star - the inside of that star should get a lot hotter than usual.  So, weird processes should create elements that you don't usually see in such a star. 

And now astronomers have found a red supergiant like that!   It has
lots more rubidium, strontium, yttrium, zirconium, molybdenum and lithium than usual.  (We know this from its spectral lines.)

So, we may have found a TŻO!

Anna Żytkow was pleased:

"I am extremely happy that observational confirmation of our theoretical prediction has started to emerge."

The candidate TZO is called HV 2112.  It's in the the Small Magellanic Cloud, a dwarf galaxy orbiting ours, about 200,000 light-years away. 

The astronomer Lida Morell found the weird elements in this star while conducting a survey of red supergiants last year.  At the time she said:

"I don't know what it is, but I know that I like it!"

Read all about it here:

Emily M. Levesque, Philip Massey, Anna N. Żytkow and Nidia Morrell, Discovery of a Thorne-Zytkow object candidate in the Small Magellanic Cloud,

Puzzle 1: How do you pronounce a Z with a dot on it?  Clue: Anna Żytkow is Polish.

Puzzle 2: What could happen if a neutron star falls to the bottom of a white dwarf, if their total mass is big enough?

Puzzle 3: What could happen if a neutron star falls to the bottom of a white dwarf if their total mass is not so big?

For more, read this:

or Wikipedia:

#spnetwork arXiv:1406.0001 #astronomy #Thorne–Żytkow
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Tale of a doomed galaxy - the end

When distant black holes collide, they emit a burst of gravitational radiation: a ripple in the shape of space, spreading out at the speed of light.  Can we detect that here on Earth?   We haven't yet.  But with luck we will soon, thanks to LIGO.

LIGO stands for Laser Interferometer Gravitational Wave Observatory.  The idea is simple.  You shine a laser beam down two very long tubes and let it bounce back and forth between mirrors at the ends.  You use this compare the length of these tubes.  When a gravitational wave comes by, it stretches space in one direction and squashes it in another direction.  So, we can detect it.

Sounds easy, eh?  Not when you run the numbers!   We're trying to see gravitational waves that stretch space just a tiny bit: about one part in 10^23.  At LIGO, the tubes are 4 kilometers long.  So, we need to see their length change by an absurdly small amount: one-thousandth the diameter of a proton!

It's amazing to me that people can even contemplate doing this, much less succeed.  They use lots of tricks:  

• They bounce the light back and forth many times, effectively increasing the length of the tubes to 1800 kilometers.

• There's no air in the tubes - just a very good vacuum.

• They hang the mirrors on quartz fibers, making each mirror part of a pendulum with very little friction.  This means it vibrates very well at one particular frequency, and very badly at frequencies far from that.  This damps out the shaking of the ground, which is a real problem.

• This pendulum is hung on another pendulum.

• That pendulum is hung on a third pendulum.

• That pendulum is hung on a fourth pendulum.

• The whole chain of pendulums is sitting on a device that detects vibrations and moves in a way to counteract them, sort of like noise-cancelling headphones.

• There are 2 of these facilities, one in Livingston, Louisiana and another in Hanford, Washington.  Only if both detect a gravitational wave do we get excited.

I visited the LIGO facility in Louisiana in 2006.  It was really cool!   Back then, the sensitivity was good enough to see collisions of black holes and neutron stars up to 50 million light years away.

Here I'm not talking about supermassive black holes like the ones in the doomed galaxy of my story here!  I'm talking about the much more common black holes and neutron stars that form when stars go supernova.  Sometimes a pair of stars orbiting each other will both blow up, and form two black holes - or two neutron stars, or a black hole and neutron star.  And eventually these will spiral into each other and emit lots of gravitational waves right before they collide.

50 million light years is big enough that LIGO could see about half the galaxies in the Virgo Cluster.  Unfortunately, with that many galaxies, we only expect to see one neutron star collision every 50 years or so.

They never saw anything.  So they kept improving the machines, and now we've got Advanced LIGO!   This should now be able to see collisions up to 225 million light years away... and after a while, three times further.

They turned it on September 18th.  Soon we should see more than one gravitational wave burst each year.

In fact, there's a rumor that they've already seen one!  But they're still testing the device, and there's a team whose job is to inject fake signals, just to see if they're detected.  David Castelvecchi writes:

LIGO is almost unique among physics experiments in practising ‘blind injection’. A team of three collaboration members has the ability to simulate a detection by using actuators to move the mirrors. “Only they know if, and when, a certain type of signal has been injected,” says Laura Cadonati, a physicist at the Georgia Institute of Technology in Atlanta who leads the Advanced LIGO’s data-analysis team.

Two such exercises took place during earlier science runs of LIGO, one in 2007 and one in 2010. Harry Collins, a sociologist of science at Cardiff University, UK, was there to document them (and has written books about it). He says that the exercises can be valuable for rehearsing the analysis techniques that will be needed when a real event occurs. But the practice can also be a drain on the team’s energies. “Analysing one of these events can be enormously time consuming,” he says. “At some point, it damages their home life.”

The original blind-injection exercises took 18 months and 6 months respectively. The first one was discarded, but in the second case, the collaboration wrote a paper and held a vote to decide whether they would make an announcement. Only then did the blind-injection team ‘open the envelope’ and reveal that the events had been staged.

Aargh!  The disappointment would be crushing.

But with luck, Advanced LIGO will soon detect real gravitational waves.  And I hope life here in the Milky Way thrives for a long time - so that when the gravitational waves from the doomed galaxy PG 1302-102 reach us, hundreds of thousands of years in the future, we can study them in exquisite detail.

For Castellvechi's whole story, see:

For pictures of my visit to LIGO, see:

For how Advanced LIGO works, see:

#astronomy #spnetwork arXiv:1411.4547
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I think there's a certain value on knowledge itself, and any other benefits to society is a bonus. Otherwise theoretical astrophysics would have a tough time making it's case. The benefits aren't known until after the fact. You could never predict that the theory of relativity would enable GPS or some cryocooler NASA builds will enable an MRI to detect cancer. I'm not sure how anyone could do a cost/ benefit analysis. I mean a skeptic could easily say "who cares if there's 9 black holes in the center of the galaxy or if Pluto is made out of grape jelly, but I think all seemingly irrelevant knowledge has been historically shown to give tangible benefits in some way. 
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+Bruce Smith was one of my best friends in college, and definitely the smartest.  He was always more into computers, while I was more into math and physics.  For a while he worked on Mathematica for Steve Wolfram, but lately he's been thinking about "a social network for ideas".

The basic idea is to visualize the parts of the participants’ semantic networks (graphs of related ideas) which are involved in the discussion, synthesizing these into one giant graph visible to everyone, so that existing and potential participants can see where and how each post or comment fits into the whole – what people agree or disagree on and why, what they think is relevant or connected and why, who is adding interesting comments, and how everything ties together.

This “idea graph” (including the complete history of public comments linked into it, plus summary views) would be both browseable and statistically analyzable by each participant (with the help of new software tools and user interface), supporting many use cases to help them understand the prior conversation and contribute to it.

For example, if you are considering changing your mind from position X to Y, the tools and user interface would help you find a coarse graph-edge representing that transition (“coarse” because it’s in a summary view), attached to which you could find the best arguments in either direction, where “best” means “most persuasive to the people you want to be influenced by”.

Of course this idea should instantly make you think of a dozen objections and/or ways to take advantage of such a system if it existed.   Bruce has a lot to say about this, and I'm sure he'll enjoy discussing these things.  Check out his blog article, and please drop him some comments on his G+ post!
My first blog post is about software for collaborating on complex problems by visualizing the semantic network of a "global brain" -- a graph of everyone's ideas and reasoning involved in the discussion.
This post proposes a new kind of software tool and social network protocol for people who want to engage others in constructive discussions about complex problems...
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There is now a community for discussing the possibilities of software like this:
It's also a place for interested people to introduce themselves and describe other related work too (like yours, +Woozle Hypertwin!)
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Tale of a doomed galaxy (part 4)

Let's imagine an old, advanced civilization in the doomed galaxy PG 1302-102.  

Long ago they had mastered space travel.  Thus, they were able to survive when their galaxy collided with another - just as ours will collide with Andromeda four billion years from now.  They had a lot of warning - and so do we.  The picture here shows what Andromeda will look like 250 million years before it hits.

They knew everything we do about astronomy - and more.  So they knew that when galaxies collide, almost all stars sail past each other unharmed.  A few planets get knocked out of orbit.  Colliding clouds of gas and dust form new stars, often blue giants that live short, dramatic lives, going supernova after just 10 million years.  

All this could be handled by not being in the wrong place at the wrong time.   They knew the real danger came from the sleeping monsters at the heart of the colliding galaxies.

Namely, the supermassive black holes!  

Almost every galaxy has a huge black hole at its center.  This black hole is quiet when not being fed.  But when galaxies collide, lots of gas and dust and even stars get caught by the gravity and pulled in.  This material form a huge flat disk as it spirals down and heats up.  The result is an active galactic nucleus.   

In the worst case, the central black holes can eat thousands of stars a year.  Then we get a quasar, which easily pumps out the power of 2000 ordinary galaxies.  

Much of this power comes out in huge jets of X-rays.  These jets keep growing, eventually stretching for hundreds of thousands of light years.  The whole galaxy becomes bathed in X-rays - killing all life that's not prepared.

Let's imagine a civilization that was prepared.  Natural selection has ways of weeding out civilizations that are bad at long-term planning.  If you're prepared, and you have the right technology, a quasar could actually be a good source of power.

But the quasar was just the start of the problem.  The combined galaxy had two black holes at its center.  The big one was at least 400 million times the mass of our Sun.  The smaller one was about a tenth as big - but still huge.

They eventually met and started to orbit each other.  By flinging stars out the way, they gradually came closer.  It was slow at first, but the closer they got, the faster they circled each other, and the more gravitational waves they pumped out.  This carried away more energy - so they moved closer, and circled even faster, in a dance with an insane, deadly climax.

Right now - here on Earth, where it takes a long time for the news to reach us - we see that in 100,000 years the two black holes will spiral down completely, collide and merge.  When this happens, a huge pulse of gravitational waves, electromagnetic radiation, matter and even antimatter will blast through the galaxy called PG 1302-102. 

I don't know exactly what this will be like.  I haven't found papers describing this kind of event in detail.

One expert told the New York Times that the energy of this explosion will equal 100 million supernovae.  I don't think he was exaggerating.   A supernova is a giant star whose core collapses as it runs out of fuel, easily turning several Earth masses of hydrogen into iron before you can say "Jack Robinson".   When it does this, it can easily pump out 10^44 joules of energy.  So, 100 millon supernovae is 10^52 joules.  By contrast, if we could convert all the mass of the black holes in PG 1302-102. into energy, we'd get about 10^56 joules.  So, our expert was just saying that their merger will turns 0.01% of their combined mass into energy.  That seems quite reasonable to me.

But I want to know what happens then!  What will the explosion do to the galaxy?  Most of the energy comes out as gravitational radiation.  Gravitational waves don't interact very strongly with matter.  But when they're this strong, who knows?  And of course there will be plenty of ordinary radiation, as the accretion disk gets shredded and sucked into the new combined black hole.

The civilization I'm imagining was smart enough not to stick around.  They decided to simply leave the galaxy.  

After all, they could tell the disaster was coming, at least a million years in advance.  Some may have decided to stay and rough it out, or die a noble death.  But most left.

And then what?

It takes a long time to reach another galaxy.  Right now, travelling at 1% the speed of light, it would take 250 million years to reach Andromeda from here.  

But they wouldn't have to go to another galaxy.  They could just back off, wait for the fireworks to die down, and move back in.  

So don't feel bad for them.  I imagine they're doing fine.


The expert I mentioned is S. George Djorgovski of Caltech, mentioned here:

Dennis Overbye, Black holes inch ahead to violent cosmic union, New York Times, 7 January 2015,

The picture of Andromeda in the nighttime sky 3.75 billion years from now was made by NASA.  You can see a whole series of these pictures here:

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+David Andrews - thanks!  Not quite done yet.  One more about how soon we should get a lot better at detecting gravitational waves.
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Tale of a doomed galaxy (part 2)

If there was ever any life in the galaxy PG 1302-102, it was snuffed out billions of years ago by the collision of two massive black holes at this galaxy's heart.  But even before that, it had a quasar to contend with!

This is a picture of Centaurus A, a much closer galaxy with a quasar in it.  A quasar is huge black hole in the middle of a galaxy - a black hole that's eating lots of stars, which rip apart and form a disk of hot gas as they spiral in.   'Hot' is an understatement, since this gas moves near the speed of light.  It gets so hot that it pumps out intense jets of particles - from its north and south poles.  Some of these particles even make it to Earth.

Any solar system in Centaurus A that gets in the way of those jets is toast.

And these jets create lots of radiation, from radio waves to X-rays.  That's how we can see quasars from billions of light years away.  Quasars are the brightest objects in the universe, except for short-lived catastrophic events like the black hole collisions and gamma-ray bursts from huge dying stars.

It's hard to grasp the size and power of such things, but let's try.  You can't see the black hole in the middle of this picture, but it weighs 55 million times as much as our Sun.  The blue glow of the jets in this picture is actually X rays.  The jet at upper left is 13,000 light years long, made of particles moving at half the speed of light.  

A typical quasar puts out a power of roughly 10^40 watts.  They vary a lot, but let's pick this number as our "standard quasar".  

But what does 10^40 watts actually mean?  For comparison, the Sun puts out 4 x 10^26 watts.  So, we're talking 30 trillion Suns.  But even that's too big a number to comprehend!

Maybe it would help to say that the whole Milky Way puts out 5 x 10^36 watts.  So a single quasar, at the center of one galaxy, can have the power of 2000 galaxies like ours.  

Or, we can work out how much energy would be produced if the entire mass of the Moon were converted into energy.  I'm getting 6 x 10^39 joules.  That's a lot!  But our standard quasar is putting out a bit more power than if it were converting one Moon into energy each second.  

But you can't just turn matter into energy: you need an equal amount of antimatter, and there's not that much around.   A quasar gets its power the old-fashioned way: by letting things fall down.   In this case, fall down into a black hole.  

To power our standard quasar, 10 stars need to fall into the black hole every year.  The biggest quasars eat 1000 stars a year.  The black hole in our galaxy gets very little to eat, so we don't have a quasar.

There are short-lived events much more powerful than a quasar.  For example, a gamma-ray burst, formed as a hypergiant star collapses into a black hole.   A powerful gamma-ray burst can put out 10^44 watts for a few seconds.  That's equal to 10,000 quasars!  But quasars last a long, long time.  

So this was life in PG 1302-102 before things got really intense - before its two black holes spiraled into each other and collided.  What was that collision like?  I'll talk about that next time.

This picture of Centaurus A was actually made from images taken by three separate telescopes.  The orange glow is submillimeter radiation - between infrared and microwaves - detected by the Atacama Pathfinder Experiment (APEX) telescope in Chile.  The blue glow is X-rays seen by the Chandra X-ray Observatory.  The rest is a photo taken in visible light by the Wide Field Imager on the Max-Planck/ESO 2.2 meter telescope, also located in Chile.  This shows the dust lanes in the galaxy and background stars.  

For more on quasars, try:

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+John Baez "It is suicidal heroism when a seat of Intelligence becomes a veritable scaffold..." I really like this line.

I have not read it, but it has a kindle addition I notice :) 

I do not want to belabor the point but initially I was inspired by several other authors in this regard, most of all in the post-singularity movement.

We know that the inside an event horizon of a black hole is where we might find the most efficient form of information storage.

One narrative related to the Fermi paradox is that at some point civilizations upload themselves into virtual reality and in effect leave no evidence of their presence.

Of course the most effective platform for computing is space-time the obvious thing that leaps to mind is the idea that civilizations at some point convert their local space time into Computronium, which might look the same as a black-hole, at least in terms of this speculation.

I am really glad you mentioned Lem in this context, thank you, seriously.
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White Desert

This is a rock formation made of chalk in the Sahara el Beyda, or White Desert of Egypt.  This beautiful place got in the news recently after 8 Mexican tourists were killed there by Egyptian security forces, who apparently mistook them for terrorists. 

But let's leave the sad world of mankind for a minute, and enjoy the desert.

There are actually many mushroom-shaped rocks like this in the White Desert. 


Try to guess.

Okay:  they are ventifacts, meaning they are carved by wind-blown sand.  Even in strong winds, sand grains don't usually stay in the air for long.  Instead they bounce along the ground.   So, they cut deeper into the bottom of the rock than the top!

Magical-looking, but not magic.

This photo was taken by Christine Schultz:
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The Balaban 10-cage

Alexandru Balaban, now a well-known mathematician, grew up in Romania during World War II and the ensuing Cold War.  After being severely burnt by nitric acid, he developed a taste for organic chemistry.  He did his Ph.D. thesis on reactions catalyzed by aluminum chloride - like the Scholl reaction, where two aromatic ring molecules like benzene combine to form a larger molecule. 

He then became interested in aromatic rings that contain boron and other elements.  Then he started wanting to classify all such molecules.  That's something a mathematician would want to do. 

Indeed, he soon realized he was studying the necklace problem, where you try to count all possible necklaces formed by m beads of n colors.   He got interested in counting organic molecules of many different kinds.  These are problems in graph theory - the study of structures made of dots connected by edges. 

The Romanian graph theorists he knew didn't want to collaborate, so he began working with the famous graph theorist Frank Harary, who was able to visit him in Romania despite the Cold War. 

And all this was just the beginning of a long and distinguished career in graph theory and chemistry.  For example, while writing a review article on pyrylium salts he became interested in 'trivalent cages', like the one shown here.

If you look at this graph you can easily see it's trivalent - every node is connected to 3 other nodes by edges.  But what's a trivalent cage?

The girth of a graph is the length of its shortest cycle - that is, the shortest path where you walk along edges and wind up where you started without ever retracing your route.  A trivalent cage is a trivalent graph with the fewest possible nodes for a trivalent graph of that girth. 

This graph here is a trivalent cage of girth 10, called the Balaban 10-cage.  It's a beautiful structure, but I don't really know much about it! 

By now I know a lot about some smaller cages, and I've written about them in my blog Visual Insight.   They're connected to some remarkable phenomena in group theory.  For a tour, see my latest article:

Balaban wrote, of this phase of his life:

In my spare time, I tried to solve graph-theoretical problems, and I became intrigued by the fact that trivalent cages were known for girths 3 to 8 and 12, but there was a gap for girths 9, 10, and 11. With symmetry as a guide and with my observation on how smaller cages can be obtained from larger cages I found a trivalent graph with 70 vertices and I conjectured that it was a 10-cage, but I did not publish this result until a few years later. Only much later was it proved to be indeed the first 10-cage (two other ones were discovered later) by mathematicians using arrays of computers working for long time; a similar computational effort proved that another conjectured trivalent graph with 112 vertices to be the unique 11-cage. Both these cages are known as “Balaban graphs”; the Balaban 10-cage appears on the cover of the book Pearls in Graph Theory by N. Hartsfield and G. Ringel. In an international effort that included Coxeter, Frucht, Harries, and Evans along with me, we had found several nice, highly symmetric graphs with 60 vertices and girth 9, but before anything was published about them, Norman Biggs published a paper about the first 9-cage with 58 vertices. It is now known that there are eighteen 9-cages, all with low symmetry.

So, it seems that in general cages don't need to be highly symmetrical; it's just some small ones that happen to be very nice.  Since I don't know any exciting theorems about cages, this means that right now I find myself not interested in cages in general, but only in particular examples. 

(Of course these judgements about what's interesting and what's not, so essential in mathematics, should be subject to constant revision.)

And what about Balaban?  After the overthrow of Ceausescu in 1989, Romanians found it much easier to travel.  Alexandru Balaban began spending time teaching at Texas A&M in Galveston, while still keeping ties to his home country.  For more on him, see:

• Alexandru T. Balaban, Autobiographical notes: 80 years of age, 68 years of chemistry, MATCH Commun. Math. Comput. Chem. 66 (2011), 7--32.  Available for free at

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+Philip Gibbs - thanks for reminding me about necklaces.  Here's some stuff for anyone who is curious:

There's a difference between 'necklaces' and 'aperiodic necklaces' going on here.
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Newly discovered Babylonian tablet

This clay tablet, discovered in 2011, adds to our knowledge of the Epic of Gilgamesh, a Babylonian story that goes back to 2100 BC.  

How much of the past is truly lost?   How much can we still hope to recover?  I often wonder about that... and I'm delighted when people find things like this, or the new poems by Sappho that had been buried in an ancient Egyptian garbage dump.

How was this new Gilgamesh tablet found?

After the US-led invasion of Iraq and the dramatic looting of Iraqi and other museums, a museum in Sulaymaniyah, in the Kurdish part of Iraq, did something bold and controversial. They started paying smugglers for old artifacts that would otherwise be sold outside Iraq.  They didn't ask any embarrassing questions.  They just bought the stuff that looked good!

In 2011, a smuggler showed them a collection of clay tablets.   It had about 80 tablets of different shapes and sizes.  They were still covered with mud.  Some were completely fine, while others were broken.  Nobody knows where they came from, but they may have been illegally dug up near the city of Babel.  

While the smuggler was negotiating with the museum, the museum got Professor Farouk Al-Rawi of the School of Oriental and African Studies in London to quickly look through the tablets.   When he saw this one and skimmed the cuneiform inscriptions on it, he got excited.  He told the museum to buy it from the smuggler.  "Just give him what he wants, I will tell you later on."  The final price was $800.

When Professor Al-Rawi carefully cleaned the tablet, he realized that yes, it was one of the tablets of the Epic of Gilgamesh! 

It's a copy of Table V, one of the 12 tablets of the so-called Standard Akkadian version of the epic.  This version goes back to about 1200 BC.  There's also an older version, the Old Babylonian one, but we have less than half of that.

So, what's new about this tablet?  I'm not very familiar with the Epic of Gilgamesh - I wasted too much time studying math - but there's a longer description of the Cedar Forest.  For example, it says Gilgamesh and his pal Enkidu saw monkeys in that forest.  This was not mentioned in other versions of the Epic.  Even better, in this version Humbaba is not an ogre: he's a foreign ruler entertained with exotic music at court, like a Babylonian king would be.

So: a tiny snippet of the past, which could have been lost forever, has made it to the present.   And now Hazha Jalal, a woman who works at the Sulaymaniyah Museum, can say:

“The tablet dates back to the Neo-Bablyonian period. It is a part of tablet V of the Epic. It was acquired by the Museum in the year 2011 and Dr. Farouk Al-Raw transliterated it.   We are honored to house this tablet and anyone can visit the Museum during its opening hours from 8:30 AM to 2:00 PM. The entry is free for you and your guests. Thank you.”

For more on the new tablet, including more pictures and a video, try this story by Osama Amin:

As you'll see, I paraphrased parts of what he wrote! 

For a summary of the Epic of Gilgamesh and the 12 tablets of the Standard Akkadian version, go here:

For the newly discovered Sappho poems, try this:

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+Dror Harari - it's a fake!  :-)

I can just barely see the cuneiform indentations here.  You might want to compare other cuneiform tablets:

A lot of them have more clear letters, but that's probably because these are examples chosen to be nice.  Some are difficult to read.
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The cutest animal you didn't know existed

It looks like a deerbunny - with dark, soulful eyes!  But it's a mara, from South America.  It eats grass.  It can run up to 30 kilometers per hour, but it can also hop like a rabbit or make long jumps.  It's shy in the wild.  But it can be quite friendly if raised with people from a young age.  Some people keep them as pets. 

The mara is the world's fourth largest rodent, after capybaras, beavers, and porcupines.  But they're more closely related to guinea pigs.

They're common in the Patagonian steppes of Argentina, but they also live in Paraguay and other places.

This photo was taken by Dick Klees, and I first saw it in the Sierra Club magazine:

For more pictures of maras, go here:

You'll notice they also look a bit like kangaroos - another species that occupies a similar niche.  Convergent evolution can work wonders!

(By the way, I don't like it when journalists say things like "the cutest animal you didn't know existed", because who are they to say what I know or doesn't know?  Probably some of you folks out there did know the mara existed, and I apologize to you.  I tried the title "the cutest animal I didn't know existed", but it looked a bit weird and self-centered, and now I know why journalists don't say that.)

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+Brian Fitzgerald Sheeps and cattle are no rodents like bunnies. They eat grass mostly, which is not dangerous.
But rodents can eat big dosis of poison without going ill when they  eat roots in the wilderness.It is known that roots are the most dangerous part of the plant generally speaking.
I suppose although that sometimes as you stated noxious weeds can be ate by grazers.
Probably in such a case they will die or got seriously ill . Nature is always dangerous, you good know.
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Tale of a doomed galaxy (part 3)

What happened at the instant the supermassive black holes in the galaxy PG 1302-102 finally collided? 

We're not sure yet, because the light and gravitational waves will take time to get here.  But physicists are using computers to figure out what happens when black hole collide! 

Here you see some results.  The red blobs are the event horizons of two black holes. 

First the black holes orbit each other, closer and closer, as they lose energy by emitting gravitational radiation.  This is called the inspiral phase.

Then comes the plunge and merger.  They plunge towards each other.  A thin bridge forms between them, which you see here.  Then they completely merge. 

Finally you get a single black hole, which oscillates and then calms down.  This is called the ringdown, because it's like a bell ringing, loudly at first and then more quietly.  But instead of emitting sound, it's emitting gravitational waves - ripples in the shape of space!

In the top picture, the black holes have the same mass: one looks smaller, but that's because it's farther away.  In the bottom picture, the black hole at left is twice as massive.

Here's one cool discovery.   An earlier paper had argued there could be two bridges, except in very symmetrical situations.  If that were true, a black hole could have the topology of a torus for a little while.  But these calculations showed that - at least in the cases they looked at - there's just one bridge.

So, you can't have black hole doughnuts.  At least not yet.

These calculations were done using free software called SpEC:

But before you try to run it at home: the team that puts out this software says:

Because of the steep learning curve and complexity of SpEC, new users are typically introduced to SpEC through a collaboration with experienced SpEC users.

It probably requires a lot of computer power, too.  These calculations are very hard.  We know the equations; they're just tough to solve.  The first complete simulation of an inspiral, merger and ringdown was done in 2005. 

The reason people want to simulate colliding black holes is not mainly to create pretty pictures, or even understand what happens to the event horizon.   It's to understand the gravitational waves they will produce!  People are building better and better gravitational wave detectors - more on that later - but we still haven't seen gravitational waves.  This is not surprising: they're very weak.  To find them, we need to filter out noise.  So, we need to know what to look for.

The pictures are from here:

• Michael I. Cohen and Jeffrey D. Kaplan and Mark A. Scheel, On toroidal horizons in binary black hole inspirals, Phys. Rev. D 85 (2012), 024031.  Available for free at

#spnetwork arXiv:1110.1668 #blackholes #astronomy
Marcond Marchi's profile photoWilliam Rutiser's profile photoRod Castor's profile photoBenjamin Russell's profile photo
+Dániel Darabos - a star can turn hydrogen into heavier elements and emit radiation, so theoretically a time-reversed star could soak up radiation that just happens to be coming in from all directions, and uses this energy to turn heavier elements back into hydrogen.  But we've never seen anything like this. 

The idea of thermodynamics is that reversed processes like these, where energy turns from heat into more organized forms, are statistically unlikely to occur.

There is a lot to argue about here.  But I think we can confidently say this:

A black hole can only split and form two smaller black holes if gravitational radiation comes in to it from all directions in a time-reversed version of what usually happens when black holes merge!

So, its theoretically possible, but "highly unlikely" in practice - much less likely than getting an egg to uncook and go back into the shell.
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Tale of a doomed galaxy (part 1)

About 3 billion years ago, if there was intelligent life on the galaxy we call PG 1302-102, it should have known it was doomed.

Our galaxy has a supermassive black hole in the middle.  But that galaxy had two.  One was about ten times as big as the other.  Taken together, they weighed a billion times as much as our Sun.

They gradually spiraled in towards each other... and then, suddenly, one fine morning, they collided.  The resulting explosion was 10 million times more powerful than a supernova - more powerful than anything astronomers here on Earth have ever seen!  It was probably enough to wipe out all life in that galaxy.

We haven't actually seen this yet.  The light and gravitational waves from the disaster are still speeding towards us.  They should reach us in roughly 100,000 years.  We're not sure when.

Right now, we see the smaller black hole still orbiting the big one, once every 5 years.  In fact it's orbiting once every 4 years!   But thanks to the expansion of the universe, PG 1302-102 is moving away from us so fast that time on that distant galaxy looks significantly slowed down to us.

Orbiting once every 4 years: that doesn't sound so fast.  But the smaller black hole is about 2000 times more distant from its more massive companion than Pluto is from our Sun!  So in fact it's moving at very high speed - about 1% of the speed of light.   We can actually see it getting redshifted and then blueshifted as it zips around.  And it will continue to speed up as it spirals in.

What exactly will happen when these black holes collide?  It's too bad we won't live to see it.  We're far enough that it will be perfectly safe to watch from here!  But the human race knows enough about physics to say quite a lot about what it will be like.  And we've built some amazing machines to detect the gravitational waves created by collisions like this - so as time goes on, we'll know even more.

I'll talk a bit more about these things in the days to come....

For now, try this:

• Ravi Mandalia, Black hole binary entangled by gravity progressing towards deadly merge,

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+James Salsman - Later in this series I'll talk about the state of the art in gravity wave detection.

Gamma ray bursts are far from fully understood.  Quoth Wikipedia:

The light curves of gamma-ray bursts are extremely diverse and complex. No two gamma-ray burst light curves are identical, with large variation observed in almost every property: the duration of observable emission can vary from milliseconds to tens of minutes, there can be a single peak or several individual subpulses, and individual peaks can be symmetric or with fast brightening and very slow fading. Some bursts are preceded by a "precursor" event, a weak burst that is then followed (after seconds to minutes of no emission at all) by the much more intense "true" bursting episode. The light curves of some events have extremely chaotic and complicated profiles with almost no discernible patterns.

Although some light curves can be roughly reproduced using certain simplified models, little progress has been made in understanding the full diversity observed. Many classification schemes have been proposed, but these are often based solely on differences in the appearance of light curves and may not always reflect a true physical difference in the progenitors of the explosions.

It seems there's a whole 'biology' of how stars, neutron stars and/or black holes can create bursts of gamma rays.  Short (< 2 second) intense gamma ray bursts are consistent with a neutron star falling into a black hole.  Some long gamma ray bursts are consistent with gamma rays beaming directionally as a large star's core collapses when it runs out of fuel - that is, a supernova or hypernova that for some reason puts out a beam.  Long (>10,000 second) gamma ray bursts may be due to collapse of blue supergiants.  And then there are weaker intermittent gamma ray bursts...
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Hawaii says: stop burning stuff to make electricity

In June, the governor of Hawaii signed a bill calling for Hawaii’s electricity to be entirely generated by renewables in 30 years. And as a warmup, according to this law the University of Hawaii will go carbon neutral in just 20 years.

Hawaii leads the US in this quest.  It helps to live near volcanoes.  On the big island, the power company made 22% of their electricity from geothermal energy in 2014.   12% came from wind, 4% from hydro, and a measly 0.14% from solar.   But 15% of houses have rooftop solar installations - so many that the power company is trying to stop them!  I don't know what percent of all electric power comes from solar.

The governor, David Ige, is trained as an electrical engineer.  Here's what he says:

I will push for more investment in renewable energy and take action to increase the amount of rooftop solar that ratepayers can install. Rooftop PV is currently one of the best renewable energy sources in Hawaii. I'll push for grid technology that allows for increasing amounts of distributed generation and power sharing between consumers.

There's an interesting battle going on with solar power in Hawaii:

“It could be that all of the people living in apartments are going to be subsidizing the millionaires with their huge estates covered in rooftop solar,” said Michael Roberts, an economics professor who studies electricity pricing at the University of Hawaii at Manoa. “I don’t think we’re quite at that point yet, but we need to change or that’s where we’re headed.”

In 2014, HECO’s nonsolar customers picked up the tab for an extra $53 million in operating and maintenance costs because so many people switched to solar. It is estimated that they will pay an additional $80 million in 2015.

Right now the cost shift from solar to nonsolar customers appears moderate, more of an annoyance than a calamity. But Roberts said it won’t be long until it spirals out of control.

“What’s causing a lot of tension right now is oil prices have come down quite a lot and the utility is generating less electricity but bills are not going down,” he said. “About two-thirds of a resident’s bill is fixed costs. People are pointing at the solar customers and saying that they are not paying their fair share.”


Last summer [a retired security guard named] Kong and his family shopped for a rooftop solar system to curb their climbing energy expenses. They couldn’t afford the estimated $25,000 it would cost, so they continue to pull their power from the grid.

For those who can afford a rooftop solar installation, the rewards are handsome: A state income tax credit of 35 percent of solar installation costs on top of a 30 percent federal income tax credit. A pricing model that allows you to sell your surplus energy to the grid for credit at the same retail rate the utility charges for the energy it generates. Immunity from fees for the utility’s fixed costs. And the feel-good awareness that you’re reducing your carbon footprint.

The average payback period for a rooftop solar system on Oahu is five years because of generous financial incentives, plentiful sunshine and the high cost of electricity.

To prevent a scenario in which the wealthiest Oahu residents benefit from low-cost solar energy at the expense of everyone else, Roberts said the utility needs to reform its pricing model.

For more of this story, see:

Here you can see how different power companies on the Hawaiian islands generate their power:
An unlikely partnership between Hawaii’s local government and the US military makes the island a leader in energy policy.
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+Andrew Bolt - at least in Southern California, a company named Sungevity will install rooftop solar for free and then lease it to you for 20 years.  In the best case, you pay the lease with the money you make by generating power.
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I'm a mathematical physicist.
  • Centre for Quantum Technologies
    Visiting Researcher, 2011 - present
  • U.C. Riverside
    Professor, 1989 - present
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I'm trying to get mathematicians and physicists to help save the planet.
I teach at U. C. Riverside and work on mathematical physics — which I interpret broadly as ‘math that could be of interest in physics, and physics that could be of interest in math’. I’ve spent a lot of time on quantum gravity and n-categories, but now I want to work on more practical things, too.

Why? I keep realizing more and more that our little planet is in deep trouble! The deep secrets of math and physics are endlessly engrossing — but they can wait, and other things can’t.

So, I’ve cooked up a plan to get scientists and engineers interested in saving the planet: it's called the Azimuth Project.  It includes a wiki, a blog, and a discussion forum.  I also have an Azimuth page here on Google+, where you can keep track of news related to energy, the environment and sustainability.

Check them out, and join the team!  Or drop me a line here.
  • Massachusetts Institute of Technology
    Mathematics, 1982 - 1986
  • Princeton University
    Mathematics, 1979 - 1982
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