Have Gravitational Waves Been Detected?

LIVE UPDATE @ Laser Interferometer Gravitational Wave Observatory (LIGO) :

Scientists are widely expected to announce the first-ever direct detection of elusive gravitational waves this morning, and you can watch the big moment live.

Researchers affiliated with the Laser Interferometer Gravitational Wave Observatory (LIGO) are holding a news conference today (Feb. 11) at 10:30 a.m. EST (1530 GMT) at the National Press Club in Washington, D.C., and you can watch it live here on Space.com, courtesy of the LIGO consortium. 

Then, at 1 p.m. EST (1800 GMT), the Perimeter Institute for Theoretical Physics in Ontario, Canada, will host its own webcast about the announcement and its implications. Space.com will carry that event live as well, thanks to the Perimeter Institute. [The Search for Gravitational Waves (Gallery)]

Gravitational waves are ripples in the fabric of space-time generated by the acceleration of massive objects. Their existence was first proposed by Albert Einstein in 1916, as part of his famous theory of general relativity. Scientists have found indirect evidence that gravitational waves exist, but a direct detection has proved elusive — until now, apparently. 

Rumors have been swirling for the past several months that the LIGO consortium has spotted gravitational waves — specifically, those generated by the merger of two medium-size black holes. So Thursday’s event is believed to be a discovery announcement, though the LIGO team has remained tight-lipped, referring to the news conference as a "status report on the effort to detect gravitational waves."

Gravitational waves move at the speed of light and do not interact meaningfully with matter. A direct detection would be a huge milestone, allowing researchers to test how general relativity operates under extreme conditions and potentially opening up a new window into the universe, LIGO team members have said.

"Gravitational waves probably won’t be useful in helping us understand processes on the Earth, but they will help us understand processes that occur in outer space, such as the collisions of pairs of black holes," the LIGO team wrote in an online FAQ about the project.

After 100 years of searching, physicists might finally be about to confirm the existence of Einstein's gravitational waves - proving that the path of science rarely runs smoothly... or quickly. 

Physicists at LIGO - one of the observatories that's been manically searching for gravitational waves - have nowcalled a press conference for 10.30am EST on Thursday 11 February (2.30am AEST on Friday 12 February). And if the very well-educated rumours are to be believed, they're going to reveal the first "unambigious" evidence that gravitational waves exist, which is a HUGE deal. You can watch live below, and we'll be live-blogging the entire thing.

Gravitational waves are so exciting because they're the last major prediction of Einstein's general theory of relativity to be confirmed, and discovering them will help us understand how the Universe is shaped by mass.

According to Einstein's theory, the fabric of space-time can become curved by anything massive in the Universe. When cataclysmic events happen, such as black holes merging or stars exploding, these curves can ripple out elsewhere as gravitational waves, just like if someone had dropped a stone in a pond.

Imagine the Universe as a massive pond - by the time those ripples get to us on Earth, they're tiny (around a billionth of the diameter of an atom), which explains why they've been so hard to find.

But rumours are flying in the physics world that LIGO has finally been able to detect them, using a series of lasers bouncing back and forth in two 4-km-long pipes to measure incredibly small changes, and we're so freaking excited to find out more.

The official press conference webcast is for registered media only, but apparently you can watch live on the YouTube stream below, and we'll be updating as the event rolls on... here we go!

Live updates below (keep hitting refresh!):

10am ET: Okay, the countdown is officially on! There's half an hour before the press conference kicks off, and 15 minutes until we have access to it. It's 2am here in Sydney, so apologies in advance for any typos during this live stream - never let a bad time zone get in the way of physics!

10.04am ET: While we're waiting,find out more about what the rumours are saying is going to be announced today - which is the first clear, unambigious evidence that gravitational waves exist (something Einstein predicted 100 years ago). You can also watchthis interview with physicist Lawrence Krauss, who first kicked off the rumours.

10.09am ET: The countdown is showing 6 minutes until we go live. We're excited!

10.14am ET: Here we go, guys. Physics as we know it could be about to change forever...

10.15am ET: "Live stream is starting soon." 

"The knowledge that astronomers gain from measuring gravitational waves could also improve our understanding of space, time, matter, energy and the interactions between all of these things," they added. "In so doing, this field of study could revolutionize humanity’s knowledge and understanding of the nature of existence itself."

LIGO consists of two huge detectors — one in Livingston, Louisiana, and the other in Hanford, Washington. Each detector is an L-shaped system with arms 2.5 miles (4 kilometers) long. A laser beam is directed down these arms; if a gravitational wave passes through the detector, the resulting distortion of space-time will cause the distance traveled by the beam to change by a minuscule amount.

Theoretically, this change would be picked up by the detector. LIGO has two such detectors spaced hundreds of miles apart to help rule out false positives caused by local environmental conditions. (If the same signal is picked up in both Louisiana and Washington, chances are, it’s a real detection.)

LIGO is operated by MIT and the California Institute of Technology, and is funded by the U.S. National Science Foundation.

© TASA-2016

Diborane – B2H6

      If we consider the molecule B2H6 (diborane Figure 1), there are 12 valence electrons at our disposal for chemical bonding (B has 3, and H has 1, so 2xB + 6xH =12). Each terminal B–H bond is a standard vanilla two electron bond, and there are four of these, thus accounting for a total of eight electrons. This leaves a total of four electrons to share between the two bridging H atoms and the two B atoms. Consequently, two B–H–B bridging bonds are formed, each of which consists of two electrons (Figure 2), forming what are called threecenter- two-electron bonds (i.e., 3 atoms share 2 electrons) – sometimes called ‘banana’ bonds, as they are not linear but curved.

Figure 1. The structure of diborane 

Each B atom is, approximately, sp3 hybridized (hybridization is just a mathematical tool, so you can just as easily have s1.05p2.95 hybridized orbitals!), and if we consider just one of the B atoms, two of the four sp3 hybrid orbitals form s bonds to the terminal H atoms (1s orbitals). Tha leaves two B sp3 hybrid orbitals, one of which contains an electron, one of which is empty. For each bridge therefore, one sp3 orbital from each of the B atoms combines (Figure 3) with the 1s orbital of the bridging H atom to form three new molecular orbitals (MOs) – as always, n atomic orbitals (AO) form n MOs. One B atom gives its remaining valence electron to one bridge, and the other B atom gives to the other. Each bridge, therefore, has two electrons, which fill our new MO scheme starting with the lowest energy bonding MO.

Figure 2. The terminal B–H bondsand the bridging B–H–B bonds each contain two electrons

Figure 3. The MO scheme for one of the B–H B bridging three center two electron bonds. *This picture is still a simplification of the actual MO scheme. The non-bonding orbital is actually of slightly lower energy than shown and so has slight bonding character. This arises from the fact that the orbitals involved in the terminal B–H bonding have the correct symmetry to overlap with the bridging bond orbitals, resulting in a stabilization of the ‘nonbonding’ orbital.

Figure 4. One final way of visualizing the bonding in diborane can be done by considering a dianion such as B2H42–, which has the same three-dimensional structure as ethene. There is p-electron density above and below the plane in which all six atoms lie (just like ethene) and so if we imagine embedding a proton in each face of this flat molecule, we balance the charge and arrive at the correct geometric structure.

TASA-2016

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