Gravity Waved!

LIGO-0It took almost exactly 100 years. In 1905, über-geek hero Albert Einstein presented four papers of major significance to the world. One of those was about Special Relativity. It took Einstein ten more years to figure out the General theory of Relativity. He presented that work in November of 1915.

One of the predictions of General Relativity is that gravity warps space, creating gravity waves (which move at the speed of light). And while many other predictions of GR have been tested and confirmed (to very high precision), we’ve never quite managed to detect gravity waves.

Until September 14th of 2015!

Yesterday, on February 11, the Laser Interferometer Gravitational-Wave Observatory (LIGO) announced the detection of gravity waves at both their Livingston, Louisiana, and Hanford, Washington, observatories.

This discovery was possible because of a recent upgrade to what they call Advanced LIGO — improvements that vastly increased the observatory’s sensitivity.

Essentially, LIGO consists of two long vacuum tubes, each 2.5 miles long and about four feet in diameter. The tubes are oriented to be perpendicular to each other. The device shoots laser beams down each tunnel, bounces them off mirrors, and then compares the return light pulses through interference.


LIGO in Hanford, Washington. Each arm is 2.5 miles long.

The idea is that a gravity wave will momentarily compress one leg or the other (but not both in the same way). This change of length is detected because the change in the length of the light beam changes how it interferes with the other one.

The amount of compression being detected is smaller than one-ten-thousandth the diameter of a proton (10-19 meter). The engineering involved is phenomenal! The size scale being probed here is comparable to what CERN is exploring with the LHC (albeit at much lower energy levels, so no Higgs here).

The upgrade to Advanced LIGO resulted in the detection of a gravity wave almost as soon as they turned it on!

And what a wave it was.

black holes merge

Let’s get close!

Take two black holes, one weighing in at 36 solar masses, the other at 29. These are big black holes! They circle each other as they spiral in, and near the end they’re orbiting at half the speed of light and circling each other 250 times a second.

They are literally tearing up the fabric of spacetime and creating ripples that expand outwards and are blocked by… nothing at all. Ever.

The formation of those gravity waves, which are energy expanding outwards, took an astonishing amount of energy to create. In a fraction of a second, three entire solar masses are converted to energy.

As visible light, that much energy would outshine every star in the universe combined. It would be the brightness of a billion trillion suns.

As a contrast, the 15 kiloton atomic bomb dropped on Hiroshima (Little Boy) consumed only 0.6 grams of uranium. The 21 kiloton device dropped on Nagasaki (Fat Man) consumed just 1 gram.


LIGO in Livingston, Louisiana. (More trees!)

This black hole merger occurred 1.3 billion years ago. Or, if you prefer, 1.3 billion light years away.

That’s one heck of a way to kick off the start-up of your new machine! Since that initial discovery, there have been several other detections of gravity waves (four in total).

So we’re witnessing the beginning of a new era of astronomy: gravity observatories. And since gravity isn’t blocked by anything, we have the potential to peer beyond the veil of the CMB, to see further back than the 300,000 years or so after the Big Bang.

Gravity waves also let us observe dark objects that don’t shine (and might give us some clues about “dark matter” or even “dark energy”).


Right again!

And they are one more confirmation that Einstein got it right.

Except that we’re pretty sure he didn’t. Or at least most physicists are pretty sure he didn’t.

The problem is that Special Relativity and General Relativity aren’t quantum and we kinda think everything is quantum. But we are having the devil of a time figuring out quantum gravity. String theory is one such attempt. So is Loop Quantum Gravity.

We figured out that energy and matter were quantized a long time ago, around 1900, in fact. But time and space (and gravity) are many, many orders of magnitude smaller in scope. Building an accelerator to probe that scale would require one the size of a galaxy.

My deep wish is that Einstein and quantum physics remain separate! I’m fine with quantizing matter and energy — they clearly are. But why can’t time and space be smooth (like Einstein said)? Who says they have to be quantized?

Several physicists do, but what do they know anyway?

Perhaps it’s a bit like believing in god (which I also do), but until I’m confronted with actual facts saying it’s wrong, I’ll continue to hold out hope for the universe being the way I think it ought to be.

And this detection of gravity waves neither helps nor hurts that cause. It is one more bullet point saying that GR is dead spot on, but we’ve been pretty sure of that for a long time.

Here’s the press release from LIGO.

And listen to the sound of two massive black holes merging (and releasing 50 times more energy than all the stars in the visible universe in factions of a second).

Here’s a good post about LIGO and gravity waves from Matt Strassler (my favorite particle physics blogger).

Here’s a good New York Times article about LIGO.

Einstein and EddingtonI spent last post trashing The Imitation Game as a badly done historical fiction about Alan Turing.

For an example of doing that sort of thing much better, check out Einstein and Eddington, which is about how (gay) British astronomer Arthur Eddington (played by David Tennant) helped prove GR by photographing stars near the Sun during an eclipse (revealing the deflection of light rays by gravity).

This was one of the first proofs of General Relativity.

The first was when Einstein checked his new theory against the orbit of Mercury, which was known to not quite fit Newton’s orbital mechanics (due to the gravity of the Sun).

Einstein describes how he nearly had heart palpitations when his theory turned out to describe Mercury’s orbit exactly!

Einstein NBC

Questions? Anyone? Anyone?

About Wyrd Smythe

The canonical fool on the hill watching the sunset and the rotation of the planet and thinking what he imagines are large thoughts. View all posts by Wyrd Smythe

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