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Gravitational Waves Detected

ldmitruk

ldmitruk

Active Member
arg-fallbackName="ldmitruk"/>
A big step forward in astronomy today as it was announced LIGO has detected gravitational waves for the first time. Once again a prediction of Einstein's Theory of General Relativity has been shown correct by hard working scientists. I wonder what gravitational waves will reveal about our universe in the future.
 
arg-fallbackName="DutchLiam84"/>
As I told my family, this is the beauty of a scientific theory, the ability of making testable predictions and have them come true. Suck it Nostradamus! This is very exciting!
 
arg-fallbackName="Laurens"/>
It feels awesome to live at such a time of discovery.

I can scarcely imagine what knowledge might unfold during my lifetime.
 
arg-fallbackName="Visaki"/>
I need to watch those videos when I get home, because I have no idea what the discovery of gravitational waves actually means. Sure it proves that Einstein was right but as far as I know that was already pretty certain.
 
arg-fallbackName="Deleted member 619"/>
I did a swift Q&A on this, if anyone's interested:


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, as I said earlier, 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=mc[sup]2[/sup]. 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`)/r[sup]2[/sup]. 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[sub]☉[/sub], 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, a cracking article HERE.

Feel free to share or ask questions.
 
arg-fallbackName="WarK"/>
Welcome back Hack :)

Does detection of gravitational waves by LIGO tell us anything more other than that gravitational waves are real? As far as I understand it, it's a confirmation of ideas we (well obviously not me but the physicists) already had, namely General Relativity. Did this experiment teach us anything new and/or unexpected?
 
arg-fallbackName="Deleted member 619"/>
WarK said:
Welcome back Hack :)

Does detection of gravitational waves by LIGO tell us anything more other than that gravitational waves are real? As far as I understand it, it's a confirmation of ideas we (well obviously not me but the physicists) already had, namely General Relativity. Did this experiment teach us anything new and/or unexpected?
Click to expand...

Not really. Indeed, it didn't really tell us that gravitational waves were real. They pretty much had to be, because they're a simple consequence of the fact that gravity propagates at a finite speed. Einstein was somewhat circumspect about them, but he didn't really have any need to be. The fact that they propagate at c directly leads to gravity travelling in waves.
 
arg-fallbackName="Deleted member 619"/>
Ta muchly, all of you.

Been enjoying your chromosome 2 stuff, by the way.
 
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