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### James Mason

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Big discovery!

Well definitely be making waves in the Physics community.... and observing waves in the Astronomical community.

We have observed gravitational waves!

This morning, the LIGO observatory announced a historic event: for the very first time in history, we have observed a pair of black holes colliding, not by light (which they don't emit), but by the waves in spacetime itself that they form. This is a tremendously big deal, so let me try to explain why.

What's a gravitational wave?

The easiest way to understand General Relativity is to imagine that the universe is a big trampoline. Imagine a star as a bowling ball, sitting in the middle of it, and a spaceship as a small marble that you're shooting along the trampoline. As the marble approaches the bowling ball, it starts to fall along the stretched surface of the trampoline, and curve towards the ball; depending on how close it passes to the ball and how fast, it might fall and hit it.

If you looked at this from above, you wouldn't see the stretching of the trampoline; it would just look black, and like the marble was "attracted" towards the bowling ball.

This is basically how gravity works: mass (or energy) stretches out space (and time), and as objects just move in what looks like a straight path to them, they curve towards heavy things, because spacetime itself is bent. That's Einstein's theory of Relativity, first published in 1919, and (prior to today) almost every aspect of it had been verified by experiment.

Now imagine that you pick up a bowling ball and drop it, or do something else similarly violent on the trampoline. Not only is the trampoline going to be stretched, but it's going to bounce -- and if you look at it in slow-motion, you'll see ripples flowing along the surface of the trampoline, just like you would if you dropped a bowling ball into a lake. Relativity predicts ripples like that as well, and these are gravitational waves. Until today, they had only been predicted, never seen.

(The real math of relativity is a bit more complicated than that of trampolines, and for example gravitational waves stretch space and time in very distinctive patterns: if you held a T-square up and a gravitational wave hit it head-on,  you would see first one leg compress and the other stretch, then the other way round)

The challenge with seeing gravitational waves is that gravity is very weak (after all, it takes the entire mass of the Earth to hold you down!) and so you need a really large event to emit enough gravity waves to see it. Say, two black holes colliding off-center with each other.

So how do we see them?

We use a trick called laser interferometry, which is basically a fancy T-square. What you do is you take a laser beam, split it in two, and let each beam fly down the length of a large L. At the end of the leg, it hits a mirror and bounces back, and you recombine the two beams.

The trick is this: lasers (unlike other forms of light) form very neat wave patterns, where the light is just a single, perfectly regular, wave. When the two beams recombine, you therefore have two overlapping waves -- and if you've ever watched two ripples collide, you'll notice that when waves overlap, they cancel in spots and reinforce each other in spots. As a result, if the relative length of the legs of the L changes, the amount of cancellation will change -- and so, by monitoring the brightness of the re-merged light, you can see if something changed the length of one leg and not the other.

LIGO (the Laser Interferometer Gravitational-Wave Observatory) consists of a pair of these, one in Livingston, Louisiana, and one in Hartford, Washington, three thousand kilometers apart. Each leg of each L is four kilometers long, and they are isolated from ambient ground motion and vibration by a truly impressive set of systems.

If a gravitational wave were to strike LIGO, it would create a very characteristic compression and expansion pattern first in one L, then the other. By comparing the difference between the two, and looking for that very distinctive pattern, you could spot gravity waves.

How sensitive is this? If you change the relative length of the legs of an L by a fraction of the wavelength of the light, you change the brightness of the merged light by a predictable amount. Since measuring the brightness of light is something we're really good at (think high-quality photo-sensors), we can spot very small fractions of a wavelength. In fact, the LIGO detector can currently spot changes of one attometer (10⁻¹⁸ of a meter), or about one-thousandth the size of an atomic nucleus. (Or one hundred-millionth the size of an atom!) It's expected that we'll be able to improve that by a factor of three in the next few years.

So what did LIGO see?

About 1.5 billion light years away, two black holes -- one weighing about 29 times as much as the Sun, the other 36 -- collided with  each other. As they drew closer, their gravity caused them to start to spiral inwards towards each other, so that in the final moments before the collision they started spinning around each other more and more quickly, up to a peak speed of 250 orbits per second. This started to fling gravity waves in all directions with great vigor, and when they finally collided, they formed a single black hole, 62 times the mass of the Sun. The difference -- three solar masses -- was all released in the form of pure energy.

Within those final few milliseconds, the collision was 50 times brighter than the entire rest of the universe combined. All of that energy was emitted in the form of gravitational waves: something to which we were completely blind until today.

High-energy physics has become known for extreme paranoia about the quality of its data. The confidence level required to declare a "discovery" in this field is technically known as 5σ, translating to a confidence level of 99.99994%. That takes into account statistical anomalies and so on, but you should take much more care when dealing with big-deal discoveries; LIGO does all sorts of things for that. For example, their computers are set up to routinely inject false signals into the data, and they don't "open up the box" to reveal whether a signal was real or faked until after the entire team has finished analyzing the data. (This lets you know that your system would detect a real signal, and it has the added benefit that the people doing the data analysis never know if it's the real thing or not when they're doing the analysis -- helping to counter any unconscious tendency to bias the data towards "yes, it's really real!")

There are all sorts of other tricks like that, and generally LIGO is known for the best practices of data analysis basically anywhere. From the analysis, they found a confidence level of 5.1σ -- enough to count as a confirmed discovery of a new physical phenomenon.

(That's equal to a p-value of 3.4*10⁻⁷, for those of you from fields that use those)

So why is this important?

Well, first of all, we just observed a new physical phenomenon for the first time, and confirmed the last major part of Einstein's theory. Which is pretty cool in its own right.

But as of today, LIGO is no longer just a physics experiment: it is now an astronomical observatory. This is the first gravity-wave telescope, and it's going to let us answer questions that we could only dream about before.

Consider that the collision we saw emitted a tremendous amount of energy, brighter than everything else in the sky combined, and yet we were blind to it. How many more such collisions are happening? How does the flow of energy via gravitational wave shape the structure of galaxies, of galactic clusters, of the universe as a whole? How often do black holes collide, and how do they do it? Are there ultramassive black holes which shape the movement of entire galactic clusters, the way that supermassive ones shape the movement of galaxies, but which we can't see using ordinary light at all, because they aren't closely surrounded by stars?

Today's discovery is more than just a milestone in physics: it's the opening act of a much bigger step forward.

What's next?

LIGO is going to keep observing! We may also revisit an old plan (scrapped when the politics broke down) for another observatory called LISA, which instead of using two four-kilometer L's on the Earth, consists of a big triangle of lasers, with their vertices on three satellites orbiting the Sun. The LISA observatory (and yes, this is actually possible with modern technology) would be able to observe motions of roughly the same size as LIGO -- one attometer -- but as a fraction of a leg five million kilometers long. That gives us, shall we say, one hell of a lot better resolution. And because it doesn't have to be shielded from things like the vibrations of passing trucks, in many ways it's actually simpler than LIGO.

(The LISA Pathfinder mission, a test satellite to debug many of these things, was launched on December 3rd)

The next twenty years are likely to lead to a steady stream of discoveries from these observatories: it's the first time we've had a fundamentally new kind of telescope in quite a while. (The last major shift in this was probably Hubble, our first optical telescope in space, above all the problems of the atmosphere)

The one catch is that LIGO and LISA don't produce pretty pictures; you can think of LIGO as a gravity-wave camera that has exactly two pixels. If the wave hits Louisiana first, it came from the south; if it hits Washington first, it came from the north. (This one came from the south, incidentally; it hit Louisiana seven milliseconds before Washington) It's the shift in the pixels over time that lets us see things, but it's not going to look very visually dramatic. We'll have to wait quite some time until we can figure out how to build a gravitational wave telescope that can show us a clear image of the sky in these waves; but even before that, we'll be able to tease out the details of distant events of a scale hard to imagine.

You can read the full paper at http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.116.061102 , including all of the technical details. Many congratulations to the entire LIGO team: you've really done it. Amazing.

Incidentally, Physical Review Letters normally has a strict four-page max; the fact that they were willing to give this article sixteen pages shows just how big a deal this is.﻿
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### James Mason

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55 years ago today, a war hero in the White House warned us of what Snowden later revealed. We have a great deal to learn from Ike's prescient warning.﻿
Today marks the 65th anniversary of a world-historical speech by the last war hero to occupy the White House: President Dwight D. “Ike” Eisenhower. His last speech while in office holds crucial implications for the U.S. today, as well as the history we celebrate tomorrow, on Martin Luther King Day.
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### James Mason

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h/t to , who noted:

Last I checked, throttling wasn't a synonym for innovation.
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... yeah, clearly limiting any detected video (streaming or otherwise) to 1.5Mbps and if the server does disregards apparent bit-rate (perhaps by testing data rate in a way that does not involve actual video files) it could send at a higher rate causing stuttering﻿

### James Mason

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Those who live by the patent, die by the patent...

Patents, man. ﻿
Patent lawsuits are without a doubt one of the more boring topics in technology. It takes a lot of drama to make it interesting, but the case between Samsu... by Ryan Whitwam in News, NVIDIA, Samsung
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"I don't like patents. I see them as a lottery ticket to a lawsuit." -Elon Musk﻿

### James Mason

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No, *​*​, just no.

Every time I download an app, you give me this nag box to set my recovery email. I've already set my recovery email, seven times!!!!

Quit bothering me with this stupid pop up!!!!﻿
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### James Mason

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A horror movie called Regression that doesn't involve any non-linear effects, interactions, heteroskedasticity, or non-normal residuals?

Color me disappointed.﻿
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No heteroskedasticity?  WTF man!﻿

### James Mason

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In which +AT&T​​ confirms that their loyalties are indeed with the First Order, and the the Death Star in their logo was not a coincidence.

AT&T CEO wants Silicon Valley companies to leave encryption regulation to the politicians

By  ﻿
Consumer level data encryption has become a particularly hot topic in the US lately, with tech giants, legislators and Presidential hopefuls alike all weighing in their own opinions. AT&T is the latest company to chime in on the subject, and company Chief Executive Randall Stephenson believes that it should be up to the Congress, not tech companies, to determine US policy on encrypted data. In case you’ve missed it, the issue revolves around t...
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By "Politicians" I assuming he means the ones that they bought and paid for in exchange for that mutual masturbation otherwise known as "capitalism" and "free market" economics.  Quotes being the important parts.﻿

### James Mason

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It's an Elo score... which means, essentially, that Tinder is making Rasch decisions... 😉

Tinder CEO revealed the company uses a secret "desirability score" to match up users. You probably don't want to know what yours is... #android #tinder﻿
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### James Mason

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Will we see a pattern this interesting before the time_t's wrap around?﻿
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Close enough. 😅﻿

### James Mason

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​​ noted:

Which is to say, she's [Front Nationalle] somewhat to the right of the bulk of the US Republican party today (but ask me again in a few weeks), but still to the left of both Donald Trump and Adolf Hitler.

There was a time when I didn't need to use actual Nazis as reference points for calibrating major political parties, I'm pretty sure.

Touché

These two images from FranceTVInfo haven't circulated nearly as much as they need to have – they show the results of the French regional elections in 2010 (left) and last week (right). These are the elections for the leadership of the 27 regions of the country, and are generally seen as a bellwether for the presidential elections, scheduled to be held in April and May of 2017.

The color-coding is: Red for the PCF (Communist); pink for the PS (Center-Left); light blue for the LR (Center-Right); and dark blue for the FN, the far-right party of Marine le Pen. Yellow and green represent various smaller local parties.

To give some calibration to readers more familiar with US politics, the PS and LR (pink and light blue) are roughly similar to the Democrats and the Republicans back in the later 1990's. The National Front is precisely the sort of party you would imagine would walk around with a name like "The National Front;" their leader spends a lot of time trying to explain that their party isn't about racism, but gets frequently subverted when her father (the party founder) shows up at rallies and cheerfully explains to the crowd that yes, it's all about racism! Which is to say, she's somewhat to the right of the bulk of the US Republican party today (but ask me again in a few weeks), but still to the left of both Donald Trump and Adolf Hitler.

There was a time when I didn't need to use actual Nazis as reference points for calibrating major political parties, I'm pretty sure.

In the overall poll (which doesn't really affect much since these are regional elections, but again, which is a good metric of opinion) the FN got 28% of the vote, the LR 27%, and the PS 23%. However, this is a multi-party system, and the actual way regional governments turn out will be considerably more complex. These plots are mostly of interest to see the shift in political sentiment over time.﻿
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Glad you got the subtle joke there... :)﻿

### James Mason

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Not cool, ​, not cool.

You need some due process here, not takedown first, ask questions later.

This is unacceptable.﻿
This isn't the first time we've reported about Google's deplorable policies for removing apps from the Play Store. One day you're the developer of an extre... by Rita El Khoury in Applications, Google, News
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