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Tribute to Astrophysicist Vera Rubin, the "Mother" of Dark Matter
Astrophysicist Professor Vera Rubin, National Medal of Science awardee who confirmed the existence of dark matter, died on 25 December 2016.

Dark matter is "the invisible material that makes up more than 90% of the mass of the universe." Rubin's pioneering work progressed from 1965 to the late 1970s. Her webpage describes the beginning of this discovery:

"By the late 1970s, after Rubin and her colleagues had observed dozens of spirals, it was clear that something other than the visible mass was responsible for the stars’ motions. Analysis showed that each spiral galaxy is embedded in a spheroidal distribution of dark matter — a “halo.” The matter is not luminous, it extends beyond the optical galaxy, and it contains 5 to 10 times as much mass as the luminous galaxy. The stars' response to the gravitational attraction of the matter produces the high velocities. As a result of Rubin's groundbreaking work, it has become apparent that more than 90% of the universe is composed of dark matter."

Rubin's research remained prolific until the early 2000s, as she continued to study various models for the composition of the dark halos. Among her most recent publications was an examination of the rotation curves of spiral galaxies.

Until her retirement, Rubin worked at the Carnegie Institution for Science Department of Terrestrial Magnetism in Washington, D.C. She was awarded the National Medal of Science in 1993. She was also a member of the National Academy of Sciences and in 1996, she received the Royal Astronomical Society’s Gold Medal, the first woman to do so 168 years after Caroline Hershel (1828).

Neta Bahcall of Princeton University describes Rubin's scientific significance: “A pioneering astronomer, the ‘mother' of flat rotation curves and dark-matter, a champion of women in science, a mentor and role model to generations of astronomers.”

Carnegie Science describes Rubin's scientific impact extends far beyond her pioneering research: "She was an ardent feminist, advocating for women observers at the Palomar Observatory, women at the Cosmos Club, Princeton, and she even advised the Pope to have more women on his committee."

See +Yonatan Zunger's tribute to Professor Rubin in the linked post.

Learn more
Read some background on Rubin from Carnegie Science: https://carnegiescience.edu/news/vera-rubin-who-confirmed-%E2%80%9Cdark-matter%E2%80%9D-dies

See Rubin's biography and publications: https://home.dtm.ciw.edu/users/rubin/ #stemwomen #astrophysics #astronomy
And in the continuing march of the Angel of Death, I am sad to report that Vera Rubin died today at the age of 88. Rubin was most famous as the discoverer of dark matter: the invisible and still-mysterious substance which makes up 85% of the mass of the universe.

Dark matter had been hypothesized back in the 1930's, but it wasn't until the 1970's that it was finally observed. Rubin was studying distant galaxies when she noticed that the rotation speed of their outer edges didn't jibe with the speed they should have based on the amount of visible matter.

You can tell how fast something is moving relative to you using the Doppler effect: the same thing that makes a siren sound higher-pitched as it moves towards you and lower-pitched as it moves away. It works because sound looks like a sine wave of rising and dropping pressure, and pitch corresponds to the time between successive peaks. When the source is moving towards you, the first peak emitted by the siren is already moving towards you at the speed of sound, but the second peak will get there sooner than expected, because it had the benefit of moving towards you at the siren's speed for one more period and then being sent off at the speed of sound. This means that if you know the original pitch of the siren, you can even figure out how fast it's moving based on the pitch you hear.

The same trick works with light, only now instead of pitch, it's color that depends on the time between peaks; things appear bluer when they approach, and redder when they recede. Since starlight contains a lot of easily measured standard lights in it - colors like those that Hydrogen and Helium emit when heated, and which have a very distinct pattern when viewed through a prism - we can measure the speed of distant stars and galaxies. And by comparing the speed of the left and right edges of a galaxy, you can tell how fast it's spinning.

But we've known how to calculate the orbits of stars since Kepler, and from the amount of light a galaxy emits, we can make a pretty good guess at how heavy it is. From that, you would conclude that the stars at the outside of a galaxy should be moving more slowly than the ones at its center, in a nicely predictable way.

But that's not what Rubin saw! Instead, she discovered that the stars at the outside were moving at the same speed as the ones at the center - something only possible if there was some extra, invisible mass pulling them.

What Rubin discovered was that there is an invisible halo of "dark matter" surrounding each galaxy, nearly ten times as massive as the galaxy itself. It's "dark" in the plainly literal sense: unlike stars, it's not actively on fire and glowing.

In the decades since, dark matter has become a core area of study in astrophysics. Using the same techniques and ever-more-sophisticated telescopes, including dedicated satellite observatories, we've mapped the presence and motion of dark matter in greater detail, and discovered that it's far more mysterious than we first suspected. For example, we know it's not made up of ordinary atomic or molecular stuff, because its dynamics is all wrong; neither is it made up of massive neutrinos or any other kind of matter we understand.

(There's also dark energy, an even more widespread and invisible field, discovered a few decades later. Unlike dark matter, which attracts things by gravity, dark energy seems to provide a universe-spanning, diffuse, but very distinctly measurable repulsive force. It's even less understood than dark matter; most scientists suspect that if we understood these things well, we'd know a lot more about the nature of the universe)

Rubin therefore sits in the pantheon of the great astronomers of the 20th century. Alas, her death means she will not get the Nobel Prize that many have been arguing she deserves for a very long time: the prize cannot (by the terms of its founding grant) be awarded posthumously. But she remains one of the most important researchers in the field, and her work will continue to have a profound impact on our understanding of Nature for generations to come.

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Community Service Announcement
About a month ago, several members of our Community shared an important but disturbing article on Medium revealing that we had an abuser in our midst. You can read the original and continually updated post here:

https://medium.com/@SLabusehelp/scott-lewis-what-lies-beneath-77648aa65ec4#.2dzsazm7f

As the story gained traction and readership, more and more people - many of them friends, colleagues, and associates of our Science on Google+ community - came forward with their own contributions and acknowledgments of abuse: psychological manipulation, financial malfeasance amounting to tens of thousands of dollars, emotional abuse, sexual assault. The damage has been wide-ranging and traumatic.

Situations like this are shocking to anyone of good conscience, and this case strikes particularly close to home: the perpetrator, Scott Lewis, was formerly a moderator in this community. We were not aware of his abusive behavior during his brief tenure as a moderator, and his profile has been removed from our Member list. We at Science on Google+ absolutely reject and oppose his deplorable, harmful actions. We are aware that Scott used his position as a moderator of our community to leverage other science outreach opportunities with various organisations such as Hubble Space Telescope and the Space Telescope Science Institute. In an effort to prevent him from continuing to leverage our name, we issue this unequivocal statement denouncing his behavior.

Scott exploited our trust and his position of modest influence to take advantage of community members - you, the heart of this community; members of the moderation team; and others directly or indirectly associated with Science on Google+ - for his own personal and nefarious gain. In this circumstance as in our daily science and science communication, we feel a strong obligation to:

- Disclosure
- Clarity, Transparency, and Openness
- and Support

As such, while being respectful of the privacy of the victims of this exploitation, we offer this post to ensure that everyone is aware of these events and we offer these resources to help any victims who have not yet come forward:

A. Because of the expanding scope of this situation, the volunteers who published the original article also launched an informal and private support network for victims. If you feel the need, if you have been victimized or can add your voice to the existing chorus of supporters, please visit the link at the top of this post and message the good folks who brought us awareness.

B. Please feel free to post in the Guidelines/Feedback to Mods section of our community, but NOTE THAT WE ARE NOT ABLE TO OFFER CONFIDENTIALITY IF YOU POST IN SCIENCE ON GOOGLE+.

C. Feel free to direct message any of the community moderators, but know that we are not professional counselors and will likely refer you to resources better equipped to provide assistance (some are linked in the original Medium article). We would also like to direct your attention to a well constructed guide that +A.V. Flox recently put together regarding abuse and intervention. You can view the guide by clicking on the following link:

https://medium.com/@SLabusehelp/your-friend-has-been-abused-what-do-you-do-5938e8f9de47#.jmgx9q919

If you number among the victims, know that you did not bring this upon yourself and that you are not alone. We are, as always, here to help in whatever capacity we are able. You are why we built and maintain this community, and we very much want it to be a friendly, safe, and educational place to visit. We value you tremendously.

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Fond memories
Do you know the difference between semantic and episodic memory? If not read on.
Remember, it's #FidoFriday.
Fugazza et al, recently published work demonstrating that dogs have episodic-like memory. What's episodic memory? It's your personal recollection of an event, but not to be confused with autobiographical memory. Semantic memory is recollection of facts, e.g., knowing the capital of Iowa. To distinguish between episodic memory and autobiographical memory, remember autobiographical memory includes semantic memory, e.g., the names of the places in your memories.

In this study, dogs were trained to mimic the trainer when the trainer gave the command "do it". It's called Do as I Do training. To get at episodic memory, the dogs were then trained to lie down after watching the owner do a task, like touch an umbrella or jump over a chair. Then the dogs were surprised by being asked, "do it". They had to remember what was done 1 minute earlier and 1 hour earlier. As with many of us, the dogs did much better at the shorter delay of 1 minute.

You can read more about memory types here:
Episodic Memory: Definition and Examples
http://www.livescience.com/43682-episodic-memory.html

The full article is here:
Recall of Others’ Actions after Incidental Encoding Reveals Episodic-like Memory in Dogs
http://www.cell.com/current-biology/fulltext/S0960-9822(16)31142-3

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The importance of Peer Review
+Brian Koberlein explains a bit about EM drive and the importance of peer review.
Jury Of One's Peers

The reactionless thruster known as the EM Drive has stirred heated debate over the past few years. If successful it could provide a new and powerful method to take our spacecraft to the stars, but it has faced harsh criticism because the drive seems to violate the most fundamental laws of physics. One of the biggest criticisms has been that the work wasn’t submitted for peer review, and until that happens it shouldn’t be taken seriously. Well, this week that milestone was reached with a peer-reviewed paper. The EM Drive has officially passed peer review.

It’s important to note that passing peer review means that experts have found the methodology of the experiments reasonable. It doesn’t guarantee that the results are valid, as we’ve seen with other peer-reviewed research such as BICEP2. But this milestone shouldn’t be downplayed either. With this new paper we now have a clear overview of the experimental setup and its results. This is a big step toward determining whether the effect is real or an odd set of secondary effects. That said, what does the research actually say?

The basic idea of the EMDrive is an asymmetrical cavity where microwaves are bounced around inside. Since the microwaves are trapped inside the cavity, there is no propellent or emitted electromagnetic radiation to push the device in a particular direction, standard physics says there should be no thrust on the device. And yet, for reasons even the researchers can’t explain, the EM Drive does appear to experience thrust when activated. The main criticism has focused on the fact that this device heats up when operated, and this could warm the surrounding air, producing a small thrust. In this new work the device was tested in a near vacuum, eliminating a major criticism.

What the researchers found was that the device appears to produce a thrust of 1.2 ± 0.1 millinewtons per kilowatt of power in a vacuum, which is similar to the thrust seen in air. By comparison, ion drives can provide a much larger 60 millinewtons per kilowatt. But ion drives require fuel, which adds mass and limits range. A functioning EM drive would only require electric power, which could be generated by solar panels. An optimized engine would also likely be even more efficient, which could bring it into the thrust range of an ion drive.

While all of this is interesting and exciting, there are still reasons to be skeptical. As the authors point out, even this latest vacuum test doesn’t eliminate all the sources of error. Things such as thermal expansion of the device could account for the results, for example. Now that the paper is officially out, other possible error sources are likely to be raised. There’s also the fact that there’s no clear indication of how such a drive can work. While the lack of theoretical explanation isn’t a deal breaker (if it works, it works), it remains a big puzzle to be solved. The fact remains that experiments that seem to violate fundamental physics are almost always wrong in the end.

I’ve been pretty critical of this experiment from the get go, and I remain highly skeptical. However, even as a skeptic I have to admit the work is valid research. This is how science is done if you want to get it right. Do experiments, submit them to peer review, get feedback, and reevaluate. For their next trick the researchers would like to try the experiment in space. I admit that’s an experiment I’d like to see.

Paper: Harold White, et al. Measurement of Impulsive Thrust from a Closed Radio-Frequency Cavity in Vacuum. Journal of Propulsion and Power. DOI: 10.2514/1.B36120 (2016)



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From pheromones to telling time with smell, here's a little science for #ScienceSunday
Time for some smelly science
Fresh Air's Terry Gross interviews Alexandra Horowitz to discuss her new book, Being a Dog. One of the fascinating capabilities that Alexandra mentions in the interview is that dogs can tell time via smell. We know dogs have a tremendously more sensitive sense of smell compared to us. It makes sense that dogs can use smell to tell time, if you think of time in a different way. For example, they can smell just traces of something left behind by another animal. Therefore they know that a faint smell is from the past. They also can detect faint smells in the air, perhaps around the corner. Therefore, they can smell the future. The way Alexandra describes a more traditional sense of time is pretty interesting. As the air heats up in your house, you can imagine air currents change. The smell of the room should change to. Remember we are visual creatures but dogs are more olfactory. Imagine 3D smell instead of sight. It makes sense that the scent profile of a room would change depending on the time a day and therefore a clue to what time it is. It's very much how we can use shadows to guess if it's midday or evening.

Alexandra mentioned the vomernasal organ, sometimes called the Jacobson's organ and I'm guessing a lot of people have never heard of it. The vomernasal organ (VNO) is the peripheral sensory organ in the olfactory system that involves chemoreception. Pheromones are often mentioned in the definition of VNO but in some non-mammalian species, such as snakes, VNO might be used to track prey using chemoreception. Therefore focusing just on pheromones is not broad enough of a definition. There is some debate as to whether or not humans have a VNO. It seems clear that it exists in the embryonic stage. The debate seems to be whether or not it is functional as adults. The article by Meredith (linked below) focuses not on whether it exists but what its function could be.

The other interesting thing from the Meredith article is the section about pheromones, where he talks about the definition and its use in scientific discourse. So first, the definition.

What is a pheromone and is it a well-defined, scientifically useful concept? The term pheromone was coined to describe a chemical substance which carries a message about the physiological or behavioral state of an insect to members of its own species, resulting in ‘a specific reaction, for example a definite behaviour or a developmental process’ (Karlson and Luscher, 1959).

He goes on to discuss how communication by pheromones needs to be mutually beneficial for sender and receiver. That benefit, is in an evolutionary sense.

The term pheromone is not going to disappear so long as it holds the public fascination. Its use for a class of chemicals that communicate information seems reasonable, but the definition is important if the term is to be useful in scientific discourse. Too rigid a definition can make its applicability to real situations so limited that it is useless. We know that even archetypal insect pheromones are not unique chemicals used by single species, as supposed in some definitions [see discussions in Beauchamp et al. and Albone (Beauchamp et al., 1976; Albone, 1984)]. Similarly, too broad a definition devalues the term and also makes it useless.

Getting back to the interview with Alexandra and dogs' incredible sense of smell, there are some great illustrations in the PBS, NOVA article below. An eye opening estimate of how much more sensitive dogs' sense of smell compared to ours is something like 10,000 to 100,000 times ours.

In Alexandra's previous book, Inside of a Dog, she writes that while we might notice if our coffee has had a teaspoon of sugar added to it, a dog could detect a teaspoon of sugar in a million gallons of water, or two Olympic-sized pools worth.

Hopefully you have a sense of dogs' great sense of smell now.

Human Vomeronasal Organ Function: A Critical Review of Best and Worst Cases
Michael Meredith
Chem. Senses (2001) 26 (4): 433-445.
http://chemse.oxfordjournals.org/content/26/4/433.full

Dogs' Dazzling Sense of Smell
On NOVA
http://www.pbs.org/wgbh/nova/nature/dogs-sense-of-smell.html

#ScienceSunday

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Added photos to A Modern Reprise of the Dark Ages? Science Denialism in America.

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Please join us for a fascinating and timely lecture on Science Denialism in America with Dr.+Michael Stamatikos, Assistant Professor at +OhioStateNewark. This lecture is hosted by the American Chemical Society and streamed online by +Science on Google+. Feel free to post your questions on the event post. See below for more details.

Link to event: http://columbus.sites.acs.org/meetingnotice.htm

Title: A Modern Reprise of the Dark Ages? The Socioeconomic and Geopolitical Consequences of Science Denialism in America

Dr. Michael Stamatikos
Department of Physics, Department of Astronomy &
Center for Cosmology & AstroParticle Physics (CCAPP)
The Ohio State University (OSU) at Newark

Abstract: We live in an Information Age that is defined by ever increasing computational benchmarks, which further enable discoveries in traditional STEM (Science, Technology, Engineering and Mathematics) fields. However, average cell phones with more computing power than all of NASA circa 1969 are bluntly juxtaposed with a rapidly eroding national capacity for accepting unbiased scientific results. Why is the first nation to reach the Moon scientifically regressing towards the Dark Ages? Although there are several contributing factors, Science Denialism is playing a major role in this disturbing national trend. Science Denialism is the irrational denial of otherwise conclusive scientific evidence, solely based upon a perceived conflict with antecedent political, economic and/or religious worldviews, which results in a selective distortion of scientific understanding. The conflation of skepticism with denialism leads to ambiguous inferences regarding the nature of consensus amongst scientists and provides a historical context for the apparent verisimilitude of pseudoscience, which some have attempted to include into academic curricula. In that regard, I’ll give an astrophysicists’ perspective on common topics such as: evolution, climate change, intelligent design and young Earth creationism, which are periodically the subjects of high-profile public “debates”. This national regression is further exacerbated by a STEM educational crisis and rampant scientific illiteracy/innumeracy amongst the electorate and its appointed government officials, which systematically obstructs our ability to formulate and implement evidence-based policies with bipartisan support. The resulting political dissonance resonates in cyber echo chambers and is further amplified in an era of the 24-hour cable news cycle – especially in a presidential election year. But what is science? How is it done? How do we “know” things? Why is it important? How can we combat this internal threat? Unfortunately, there is no silver bullet. As practitioners of science, we need to help each other understand on all levels, which means enhancing the quality and content of information when communicating our results, their implications and the scientific process, via education and public outreach. Science is not an absolute collection of facts to be memorized, but rather it can be thought of as the art of asking the right question(s) - this distinction is paramount. The scientific method allows for a statistical analysis of different models, whose selective predictions are confronted with independent observations, thus allowing for an evolving empirical understanding of Nature. Critical thinking and analytical reasoning are ubiquitous problem solving skills that are also crucial characteristics of an educated citizenry, which is essential to a thriving democracy and national security. Most importantly, we’ll need to collaborate with science advocates embedded within the insular communities that harbor each particular strand of Science Denialism. If left unchecked, Science Denialism threatens to cripple our long term national economy, short-change future generations of crucial self-investments in our education system and impede our ability to compete as a world leader in STEM research.

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Something to chew on along with your Easter chocolate.

http://backreaction.blogspot.com/2015/11/the-scientific-method-is-not-myth.html
How are the scientific method, free market, and natural selection related?
Read +Sabine Hossenfelder's blog post to find out. I particularly like this paragraph:

In science, the most relevant restriction is that we can’t just randomly generate hypotheses because we wouldn’t be able to test and evaluate them all. This is why science heavily relies on education standards, peer review, and requires new hypotheses to tightly fit into existing knowledge. We also need guidelines for good scientific conduct, reproducibility, and a mechanism to give credits to scientists with successful ideas. Take away any of that and the system wouldn’t work.

I write to try to undo the hype in a new scientific findings where a newspaper has lathered on too much hype. I also moderate the Science on Google+ community. So I often get comments about how we should question everything, that science is about challenging everything. If you don't question everything, e.g., evolution, climate change, etc. then you aren't doing science. Sadly, these comments often come from climate change deniers, believers in pseudoscience or conspiracies.  So I often have to explain that skepticism is fine, however, when you have an extraordinary claim, you need extraordinary evidence. I've written about that before.

Skepticism doesn't equal question all things
https://plus.google.com/u/0/+Scienceongoogleplus/posts/dTJssSxdALH

I'm not sure many people truly understand the scientific method and IFLS doesn't help with catchy GIFs with no science or attribution.

Science is not about certainty. Science is about finding the most reliable way of thinking, at the present level of knowledge. Science is extremely reliable; it's not certain. In fact, not only it's not certain, but it's the lack of certainty that grounds it. Scientific ideas are credible not because they are sure, but because they are the ones that have survived all the possible past critiques, and they are the most credible because they were put on the table for everybody's criticism. [...]
http://goo.gl/0e7p7

Image source: https://www.flickr.com/photos/neotsn/4947989561

#ScienceSunday  

h/t +Filippo Salustri 
Photo

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Excellent coverage of the highlights of chemistry over more than five millennia.
An Enjoyable Walk Through Chemistry History

Do you know who is the first chemist whose name is recorded on an official document? Do you know what role chemistry played in the development of the Pantheon in Rome about 2000 years ago? Have you heard of a person named Geber? If so, do you know what are his contributions to chemistry? Do you know what role adhesive tape played in the development of graphene?

Sterling Publishing Company in New York, a subsidiary of Barnes and Noble, publishes the Sterling Milestones series, which includes The Math Book, The Physics Book, The Psychology Book, The Physics Book, and more. The most recent addition to this series is The Chemistry Book by Derek B. Lowe. Dr. Lowe is an organic and medicinal chemist who has worked for several major pharmaceutical companies. He is also one of the pioneer science bloggers, writing the wildly popular blog In the Pipeline, now hosted by the publishers of Science.

The subtitle of Lowe's book is "From Gunpowder to Graphene, 250 Milestones in the History of Chemistry." In this book, he celebrates important accomplishments in chemistry, moving chronologically from circa 500,000 BCE when the Cueva de los Cristales (Cave of Crystals) formed, with its truly stunning, massive gypsum crystals. From there, the book jumps to 3300 BCE and the Bronze Age, and then moves forward to the present day, hitting the highlights of chemistry along the way.

I'm sure that some people might object that he included certain events and excluded others, but I won't quibble. The book provides excellent coverage of the highlights of chemistry over more than five millennia, and Lowe takes care to show how early concepts influenced later developments and later developments related back to earlier concepts. He maintains a focus on the science, but he provides interesting insights into the people, personalities, and disputes in the sciences as he moves through time.

Here are a few examples from the book of interesting points about chemistry.

• The first chemist whose name we know is Tapputi, a palace overseer and perfume maker. She is mentioned on a Babylonian text from 1200 BCE, and in the text she is described doing things quite familiar to working chemists, such as distillation and filtration (page 22).

• Although Rome did not have a strong science culture during its existence as Republic, and then Empire, one area in which it excelled was making concrete. Analytical chemists have recently figured out the recipe that the ancient Romans used for making concrete, and it turns out that in several respects it is superior to Portland cement, developed in nineteenth century England. The Pantheon, the world's largest unreinforced concrete dome in the world was built by the ancient Romans about the year 126 CE, and it still stands today as a testament to how good Rome's concrete technology was (page 34).

• Abū Mūsā Jābir ibn Hayyān, known to Western scientists and historians as Geber, lived in modern-day Iraq from about 721 CE to about 815 CE. Among other subjects, ibn Hayyān studied alchemy, but in many ways, he was a prototype for alchemists and, much later, laboratory chemists who followed in the centuries after his death. A dedicated researcher, ibn Hayyān insisted that practical laboratory work was necessary to obtain competence in alchemy. He kept notes of his experiments and wrote numerous detailed manuscripts about his work, attracting many followers. His followers also wrote numerous manuscripts about alchemy, attributing them to Geber (ibn Hayyān). These false Geber manuscripts are written in an elaborate style that is particularly difficult to decipher. Lowe informs us that the word gibberish (commonly defined as "talk in no known or understandable language" and also, "overly technical and obscure language") comes from the difficulty historians and others have had in translating and understanding these writings by Geber's followers (page 40). Lowe's discussion of the origins of the word "gibberish" is only one of a few theories of the word's etymology, and it is not the most widely held theory. Moreover, a few people assert that the word has become a racist code word, the use of which should be avoided.

• Graphene was a form of carbon that long had been thought to exist but remained undiscovered until 2004 when Andre Konstantin Geim and Konstantin Novoselov produced it by applying adhesive tape to graphite and peeling it off, leaving graphene layers stuck to the tape. Although I have known this story for years, I remain surprised that it took so long for anyone to figure out how to obtain graphene by such a simple technique (page 492).

Lowe covers the discovery of elements, the gradual conversion of alchemy into modern chemistry, the development of the ideal gas laws, and numerous other topics of great interest to chemists. He doesn't focus solely on great events, but he touches also on smaller events that are of great importance to practicing bench chemists, including the development of separatory funnels (page 140), the Erlenmeyer flask (page 152), structural formula (page 154), the Dean-Stark Trap (page 266), and the rotary evaporator (page 362). I find it hard to imagine doing good quality modern chemistry without these devices!

Chromatography and spectrometry are extensively covered in the book, as these are vital techniques for analyzing chemical compounds and deducing the structure of what has been synthesized or isolated from an extract. These are tools that I use daily, and it is interesting to learn the back-story of how these things developed.

I highly recommend this book to anyone who has an interest in chemistry. If you know a young person who is interested in chemistry, this book may be a great gift for him or her, a gift that will stimulate the mind and help develop an appreciation for how far we have come and where we are going in chemistry, the central science.

REFERENCE:
Derek B. Lowe. The Chemistry Book. From Gunpowder to Graphene, 250 Milestones in the History of Chemistry (part of the Sterling Milestones series). New York: Sterling Publishing, 2016, 528 pages.
http://www.barnesandnoble.com/w/the-chemistry-book-derek-b-lowe/1121130424 
https://www.goodreads.com/book/show/24612698-the-chemistry-book 


SUGGESTED:
Derek B. Lowe Wikipedia: https://en.wikipedia.org/wiki/Derek_Lowe_(chemist) 

In the Pipeline blog by Derek Lowe
http://blogs.sciencemag.org/pipeline/

Some In the Pipeline blog posts are also featured on the Chemistry World website, run by the Royal Society of Chemistry in England.

See, http://www.rsc.org/chemistryworld/ and search for Derek Lowe by name. The search will return the featured blog posts he has written.

Abū Mūsā Jābir ibn Hayyān
Encyclopedia Britannica: http://www.britannica.com/biography/Abu-Musa-Jabir-ibn-Hayyan 
Wikipedia: https://en.wikipedia.org/wiki/Jabir_ibn_Hayyan 

There are quite a few websites that have pages dedicated to Abū Mūsā Jābir ibn Hayyān. Some are well done; others are much less well done. If I could go back in time and meet a famous scientist, he would be on my list of people to meet.

History of the word "gibberish"
http://www.etymonline.com/index.php?term=gibberish
https://en.wikipedia.org/wiki/Gibberish
https://en.wiktionary.org/wiki/gibberish
http://blog.oup.com/2008/12/gibberish/

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Some of the science—and the poetry—of LIGO’s gravitational wave announcement.
The Poetry of LIGO’s Gravitational Waves

Yesterday the LIGO scientific collaboration announced that they had detected the gravitational waves from the in-spiral and merger of two black holes, shown in figure 1. It would not be an overstatement to say that this result has changed science forever. As a gravitational physicist, it is hard for me to put into words how scientifically important and emotionally powerful this moment is for me and for everyone in my field. But I’m going to try. This is my attempt to capture some of the science—and the poetry—of LIGO’s gravitational wave announcement.

To read this post in blog form, see here: http://www.thephysicsmill.com/2016/02/12/ligo-gravitational-wave-source/

The Source

About 1.3 billion years ago and as many light years away, two spinning black holes, each about thirty times the mass of the sun (one a bit bigger, one a bit smaller) ended their lives as separate entities. These two monsters had probably lived out many separate lives together: first as a binary system of two massive stars and most recently as two black holes orbiting each other. Somewhere in between, each one probably briefly outshone the entire galaxy as a core-collapse supernova.

But nothing lasts forever. Einstein tells us that mass distorts spacetime, warping distance and duration. And an accelerating mass (like a black hole in an orbit) releases some of its energy in ripples of this distortion. And so, over the billions of years of their shared lives, our black holes lost energy to these gravitational waves and their orbit decayed. They slowly, inevitably, spiralled towards each other.

As the partners approached, their orbit sped up and their slow, stately waltz gradually transitioned into a frantic tarantella toward coalescence. Eventually the partners came within about 500 kilometres of each other (about the distance from Paris to Frankfurt!). By this time, they were orbiting each other about thirty-five times per second!

The black holes spiralled towards each other at roughly the same rate about five more times before they suddenly plunged together, spinning around their shared centre of mass 250 times per second. But this stage didn’t last that long. Before even one second had passed, the black holes’ event horizons overlapped, and they merged into a single rapidly rotating object. This new single black hole oscillated wildly as it settled down into its final configuration, emitting gravitational waves all the while.

In-spiral. Merger. Ringdown. After (possibly) millions of years in a slowly decaying orbit, the final plunge took less than a fifth of a second. In those last moments, gravitational waves carried away 1.8x10^(47) Joules. That’s three times the energy contained in our Sun. Three suns, released as ripples in spacetime.

This is a computer simulation of the in-spiral and merger of two black holes much like the ones I described, produced by my friends and collaborators in the Simulating Extreme Spacetimes collaboration:
https://youtu.be/I_88S8DWbcU

(Note my calculations of distances are based on extremely rough Newtonian approximations. They are not very accurate. Maybe not even by an order of magnitude. But at these scales, it's not super important.)

Gravitational Waves

But what of the gravitational waves emitted by our ill-fated dance partners? These ripples in distance, in the very fabric of space and time, travel outwards from their source at the speed of light. Space is large and empty and it is mostly a lonely journey. Perhaps they pass through a cloud of gas and dust. Perhaps they don’t. If they do, the distortions of distance move the gas. Some gas particles move apart, some together. The gravitational waves might move a ring of gas particles, as shown in figure 2.

The effect is small; if the gas cloud were a few kilometres in width, the gas particles would move a distance less than one one-thousandth of the width of a proton. But they would move. And if they moved enough (they don’t) they would make a sound—the sound of the merging black holes:
https://youtu.be/QyDcTbR-kEA

Detection

Eventually, after about 1.3 billion years, on September 14th, 2015, the gravitational waves reached Earth. They were too weak to make a sound, but we could detect them. A gravitational wave is a distortion in distance, one that travels. So we can measure this distortion with a very precise ruler. And light is one of the best possible rulers.

Actually, we used two gigantic, perpendicular light-rulers, each several kilometres long. As a gravitational wave passed the rulers, it shrank distance in one direction and grew it in the other. The scientists who use these light-rulers call this discrepancy a “strain.” The paired light-rulers themselves are called “interferometers.”

We’ve built several interferometers to detect gravitational waves. There’s one in Livingston, Louisiana (https://www.ligo.caltech.edu/LA), which is shown in figure 3, and one in Hanford, Washington (https://www.ligo.caltech.edu/WA). There’s another in Sarstedt, Germany (http://www.geo600.org/) and another in Cascina, Italy (https://www.ego-gw.it/public/about/whatIs.aspx). One, destined for India, is in storage (http://gw-indigo.org/tiki-index.php?page=LIGO-India). And another is under construction underground in Kamioka, Japan (http://gwcenter.icrr.u-tokyo.ac.jp/en/).

On that fateful day, only the detectors in Livingston and Hanford were active. (Some of the others aren’t even sensitive enough for their intended purpose. When people first started building gravity-wave detectors, it wasn’t clear how far away the sources would be.) The waves hit Livingston first, at exactly 3:50:45 AM local time. About seven-thousandths of a second later, they reached Hanford and distorted the light-ruler there, too. And a fifth of a second after that, they were gone. The sound of the black holes had passed us by and continued its journey into the void.

But they did not pass without a trace. No, the Livingston and Hanford detectors recorded their passage, shown beautifully in figure 4. The 1.3 billion-year-old waveform passed through our world and changed us forever.

Learning from the Waves

We already knew gravitational waves exist. That measurement took 30 years and won the Nobel prize (http://www.nobelprize.org/nobel_prizes/physics/laureates/1993/press.html). And we had a pretty good idea of what they should look like. But the only way to confirm that they looked like we expected was to observe them. So the first thing the LIGO team did was to use sophisticated statistical techniques, without any assumption about the final waveform, to extract the true wave from the noisy signal shown in figure 4.

They then compared that waveform to the wave predicted by general relativity. The two agree spectacularly. Score one for Einstein! Of course, there are possible modifications of general relativity such that a black hole in-spiral wouldn’t look any different. So only time, and more gravitational waves, will tell if those modifications are wrong. But for now, this result is a triumph of relativity.

Independently, the LIGO team matched the raw data to a “template bank” of possible gravitational waves, each generated for a different configuration of the black holes—different masses, different rotation rates, different orientations, et cetera. Eventually, they found a match. (Actually they found several, all of which were very similar.) And, fantastically, this match agreed perfectly with the wave extracted using the statistical technique. The extracted waveforms from the two detectors, calculated in both ways, are shown in figure 5.

As a huge bonus, matching the waveform in this way told the LIGO team the masses and rotation rates of the initial black holes and the final black hole that they became.

From the ripples in spacetime, they had extracted astrophysics!

Two Detections

I want to emphasize that one reason we can be so confident in the LIGO detection is that it happened twice, once for each detector. Both detectors are extremely sensitive—they could easily see an earthquake or a car driving down the highway and misinterpret it as a gravitational wave. But the gravitational wave was seen at both detectors, and the odds of them both getting exactly the same false positive are extremely low.

What We’ve Learned

In this one detection, we’ve learned a tremendous amount…some of it very definitive, some of it not. But at the very least, we now know the following:

1. Gravitational waves look very much like we expected.

2. Black holes definitively exist. No other two objects in the universe could have been so close before colliding. Of course, we had pretty good evidence that black holes existed before now (see: https://briankoberlein.com/2015/08/16/do-black-holes-really-exist/).

3. Binary black hole systems definitely exist. A few years ago, it was not obvious that these systems formed. To get a pair of black holes orbiting each other, you need a pair of supernovae. And that could easily destroy the orbit.

What We Stand to Learn

For most of the history of astronomy, humans relied on their unaided eyes to look at the stars. In the early 1600s, telescopes were invented and the universe opened up. Suddenly the twinkle of stars and planets resolved into gas giants and moons, clusters and nebulae and galaxies. In the 1930s, we discovered a new kind of telescope: the radio telescope. Once again, we saw space in literally a whole new light. Suddenly objects we thought we understood looked very different. And wild new things appeared, like radio pulsars. Every advance in telescope technology sparked a huge leap in our understanding of the universe. We could, essentially, see a whole new side of the universe.

This is just as big. Now we can hear the universe. We’re going to learn so, so much.

Related Reading

If you enjoyed this post and want to learn more about general relativity and gravitational waves, you may be interested in my series on #howgrworks :

1. In Galileo Almost Discovered General Relativity, I explain the motivating idea behind general relativity and how Galileo almost figured it out.

http://www.thephysicsmill.com/2015/07/26/galileo-almost-discovered-general-relativity/

2. In General Relativity Is the Dynamics of Distance, I explain how simple arguments can tell us that gravity stretches or shrinks space and time.

http://www.thephysicsmill.com/2015/08/03/general-relativity-is-the-dynamics-of-distance/

3. In General Relativity Is the Curvature of Spacetime, I describe how the distortion of distance and duration from gravity translates into curvature, and how this bends the path of light (and other stuff).

http://www.thephysicsmill.com/2015/08/15/general-relativity-is-the-curvature-of-spacetime/

4. In Distance Ripples, I explain how gravitational waves work.

http://www.thephysicsmill.com/2015/08/23/distance-ripples-how-gravitational-waves-work/

5. In Our Local Spacetime, I present a visualization of the curvature of spacetime near Earth.

http://www.thephysicsmill.com/2015/09/06/our-local-spacetime/

6. In Classical Tests of General Relativity, I explain a little history.

7. In the Geodetic Effect, I talk about how we can use gyroscopes to directly measure the curvature of spacetime.

Further Reading

Here are some nice lay resources on the recent LIGO discovery. (Thanks to +Johnathan Chung  for finding some of these.)

1. This is LIGO’s online press release. It contains, for example, a number of fantastic videos.

https://www.ligo.caltech.edu/detection

2. In this video, Brian Green explains the take-home message.

https://www.youtube.com/watch?v=s06_jRK939I

3. This is a great explanation of gravitational waves by quantum gravity physicist +Sabine Hossenfelder

http://backreaction.blogspot.com/2016/02/everything-you-need-to-know-about.html

4. This is the lay article about the discovery by the American Physical Society:

http://www.nature.com/news/einstein-s-gravitational-waves-found-at-last-1.19361

5. +Yonatan Zunger wrote up this nice explanation:

https://plus.google.com/+YonatanZunger/posts/DUp4TPcrFfJ

6. This is a nice article by +Brian Koberlein  on the existence of black holes.

https://briankoberlein.com/2015/08/16/do-black-holes-really-exist/

7. This is the press release for the Nobel prize awarded for the indirect discovery of gravitational waves:

http://www.nobelprize.org/nobel_prizes/physics/laureates/1993/press.html

8. This Nature article talks about several questions we can answer with gravitational waves:

http://www.nature.com/news/gravitational-waves-6-cosmic-questions-they-can-tackle-1.19337

Scholarly Reading

For the very brave, here are my academic sources.

1. This is the LIGO detection paper. Already peer reviewed. Kudos to the LIGO collaboration for going through peer-review before announcing their result!

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.116.061102

2. This is the LIGO paper describing how they extracted the mass and spin of the black holes.

https://dcc.ligo.org/LIGO-P1500218/public

3. This paper describes the LIGO team’s investigation of whether or not the December detection could have been a mistake. (Obviously, they concluded it was real, or I wouldn’t be writing this blog post…)

https://dcc.ligo.org/LIGO-P1500238/public

4. This paper describes the LIGO team’s model-agnostic approach to measuring the wave. This is how they know they’re not falling victim to wishful thinking.

https://dcc.ligo.org/LIGO-P1500229/public

5. This technical paper describes how the LIGO team estimated their noise and error

https://dcc.ligo.org/LIGO-P1500248/public

6. This paper discusses how we’ve tested general relativity with this observation.

https://dcc.ligo.org/LIGO-P1500213/public

7. This is an assessment of the rates of black hole binary mergers in the universe based on the measurements LIGO has made so far.

https://dcc.ligo.org/LIGO-P1500217/public

8. This is a related paper on what that means for detectors.

https://dcc.ligo.org/LIGO-P1500222/public

9. This paper is a search for neutrinos from the black hole merger that LIGO observed. (None were found.)

https://dcc.ligo.org/LIGO-P1500271/public

10. This is the population model for binary black holes which may be wrong.

http://iopscience.iop.org/article/10.1086/523620/meta

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