Einstein's theory validated?

[Ecurb Noselrub]

Perhaps gravitational waves have been discovered?

http://www.cnn.com/2016/02/10/us/gravitational-waves-announcement-feat/index.html

"Gravitational waves, when we discover them, will open a new window on the universe," Marka told CNN's Rachel Crane. "We will be able to study not just Einstein's general relativity -- we'll be able to find objects we only imagined would exist. We should see a universe that has never been observed before."

[Asmodean]

To the best of my knowledge, the theory is already valid, is it not? What this discovery does, is provide further observational evidence that, if used correctly, will lead to better understanding of the universe, which in turn may lead to tweaking of the existing theory.

Semantics aside, this is cool. But I thought LIGO was the experiment with a huge L-shaped tunnel thing with lasers in it somewhere around Nowhere, Louisiana? In the article, they mentioned instruments in two geographic locations. Do they have several of those things going, or am I thinking of a different experiment?

[Ecurb Noselrub]

What was validated was his theory about the existence of gravitational waves.  Yes, there are two of these devices in the US.

[Sandra Craft]

I found this helpful for my low tech brain:

[Asmodean]

What was validated was his theory about the existence of gravitational waves.  Yes, there are two of these devices in the US.

Ah! Yes, that's right then. As I said, it was a purely semantic call for clarity.

I'm fascinated by the idea of LIGO. Measuring minute changes in the size of objects we generally percieve as solid... It shows how relative many of our nice and comfortable absolutes can be.

[Biggus Dickus]

Love Neil, and that was a fairly helpful explanation for my smaller ape sized cranium. Thanks-

I love Neil's finishing comment, "That was Bad-Ass Smart!"

[Sandra Craft]

Love Neil, and that was a fairly helpful explanation for my smaller ape sized cranium. Thanks-

I love Neil's finishing comment, "That was Bad-Ass Smart!"

Yeah, does make me sad, tho, that Einstein didn't live long enough to find out he was right after all.

[hackenslash]

Yo, peeps!

I've seen a fair bit of confusion around the web on this topic since the announcement, so I felt like it was worthwhile addressing some of it.

Firstly, the existence of gravitational waves is simply a necessary corollary of the fact that gravity propagates at a finite speed. Einstein vacillated on whether they'd exist, but he had no real reason to lack confidence once some of his other postulates had been verified, such as the fact that time dilates for bodies in motion.

Some of the questions I've encountered:

What is LIGO?
LIGO is the Laser Interferometer Gravitational Wave Observatory. It's basically a huge version of the Michelson-Morley experiment from the 1880s, although of course it doesn't fit on a desktop...

What is the medium through which these waves are propagating?
Spacetime. We know spacetime to be dynamic, and to have curvature generated by mass. In fact, these gravitational waves also have mass, because they are literally gravitational energy and, as every schoolboy knows, E=mc². These gravitational waves curve and warp spacetime in exactly the same way that planets and stars do.

Don't intervening sources alter the wave, like gravitational lensing for light?
Not appreciably, no. Everything, and I do mean everything, is transparent to gravity. If you think of the sun/Earth/moon system, it's easy to demonstrate why this is. When the system is in perfect alignment, with the moon on the far side of Earth from the Sun, the intervention of Earth has no impact on the gravitational pull of the moon on the sun. Indeed, it will be ever-so-slightly increased, because the attraction of Earth will add to the sun's, drawing the moon slightly closer, which means that the attraction will be slightly increased, as per F=G(mm')/r². The effect that intervening sources have on these waves will be negligible.

Why are they so hard to detect?
This is simply because gravity is an incredibly weak force (due caveats here regarding whether gravity can really be considered a force). Even from such a strong source as a pair of colliding black holes with approx. 30M_☉, the impact on the interferometer was a difference of less than 1/1,000th the width of a proton over 4km.

Will this observation make them easier to detect?
This is really a first step. Making them easier to detect will be the work of first getting LIGO up to full chat (about 3x the power they currently have), and then building even bigger gravitational wave observatories. You can think of this as akin to when Galileo first turned a telescope skyward and vaguely made out the ears of Saturn and the Galilean moons. Given the minuscule effect of these waves on LIGO, it's fairly obvious that we're going to need ridiculously enormous GWOs, or some other means of observing other than laser interferometry. Thankfully, LISA pathfinder was launched in December, and paves the way for LISA proper (Laser Interferometer Space Antenna), which will consist of 3 spaceships in a triangular array 1 million km on a side. Given the tiny motion detected by LIGO with arms 4km on a side, we can expect LISA to detect far, far smaller events. LISA will also not be subject to some of the issues that any ground-based GWO has, such as the fact that the events being detected are so tiny that they can be swamped by bees humping. A space-borne antenna should have a clear field of view with little to no interference.

Why all the fuss?
Beyond the fact that this is a stunning vindication of General Relativity, it opens up the possibility of massively extending our knowledge of the universe. Firstly, there's good reason to suppose that this will open the doors to seeing into the interior of black holes. Yes, you read that correctly. It isn't absolutely clear that this will work but, given that we currently don't know what goes on inside a black hole beyond the broadest theoretical treatment, the possibility is there. From the perspective of the cosmologist, the news is even brighter. Our current observational limit is the CMBR (Cosmic Microwave Background Radiation). For about 380,000 years or so after the Planck time, the cosmos was extremely hot, to the degree that the atoms in the universe were all ionised, and constituted a plasma. This meant that the universe was opaque to photons. The CMBR represents the 'surface of last scattering', which means that it's the photons that come to us from the very moment that the universe cooled sufficiently for electrons to become bound to atoms and the universe became transparent to photons. The future of this detection technology, aside from the fact that it gives us an entirely new way of looking at the universe, has the potential to allow us to see well past this barrier to the earliest events of our cosmic expanse and to see how closely our current theories of the early cosmos match observation.

For some really excellent further information, my good mate Twistor59 has written a cracking article HERE.

And from this thread.

I thought LIGO was the experiment with a huge L-shaped tunnel thing with lasers in it somewhere around Nowhere, Louisiana? In the article, they mentioned instruments in two geographic locations. Do they have several of those things going, or am I thinking of a different experiment?

LIGO has identical setups in Livingston, Louisiana and Hanford, Washington state. This goes back to what I said earlier about bees humping and gravity being extremely weak. Such effects would not be detected simultaneously (or even close together) by detectors situated more than 2,000 miles apart.


Feel free to share or ask questions.

[Icarus]

WOW Hack, That was good stuff. Thank you for that.

[Tank]

Thank you for your insights and commentary Hack!

[Recusant]

Good to see you here again, hackenslash. I appreciate the informative write-up you've done, but it appears that you intended to include a link to Twistor59's article, which is missing.

[hackenslash]

Good to see you here again, hackenslash. I appreciate the informative write-up you've done, but it appears that you intended to include a link to Twistor59's article, which is missing.

Oops!

http://www.markushanke.net/on-gravitational-waves/

[chimp3]

What is cool about the scientific method is that what supports or disproves a current theory or leads to a new theory is still cool. Even the dead ends are fascinating. Tyson is really great at communicating why something is important in science. I am a fan of science.

[Recusant]

Thanks for the link, hackenslash. I found the piece generally informative, though the equations are beyond my abilities. The conversation in the comments section was also very interesting.