Monday, 15 February 2016
Entertainment stuff from the week 8-14/2/16 (Gravity Wave Special)
Late last year, Lawrence Krauss tweeted the rumblings from within LIGO, that gravitational waves had been found, and that a Paper was pending.
Well, that Paper has now been published, and is undergoing critical analysis as we speak/read.
'Lawrence Krauss Reveals All - Gravitational Waves'
But what is it? And what are these 'gravitational waves'?
Are they colloquialisms for the silent applause, delivered by fans at gravy-making championships - the Gravy Invitational waves??
So what are they? Well, a friend asked for a layman's explanation of what gravitational waves are, via Facebook, and this is what i said:
[What 'gravitational waves' means is that] even the effects of gravity are affected by the spacetime constant 'c', commonly known as the 'speed of light'. So, if something with mass moves, then it'll take time for something somewhere else to notice. Hence the idea of ripples. If you throw a stone in a lake, it'll take time until a little plastic solider gets hit by a ripple, on the shore.
If two really massive (heavy) things spiral in towards each other and eventually collide, they'll be moving backwards and forwards very quickly, and so any LIGO you happen to have somewhere, will be most able to see the step down/up of gravitational tug as the masses move away/closer, to your position. The ripples are biggest, on the flat metaphorical lake of our cosmos, when the most massive things move about.
But in fact, even these ripples are far too small to observe directly, even coming from black holes, so LIGO has a huge array of mirrors and LASERs instead. Any gravitational wave, passing through, would ripple (distort) the 4km-across laboratory, causing the LASERs to get out of phase.
In the experiment's interferometer setup, the LASERs are made to deliberately destructively interfere, which means the output signal shows nothing at all. Unless the laboratory itself is warped, in which case the light doesn't fully cancel out, and so some light is seen.
And that's how they can find gravitational waves.
Is that all clear now? :-D
I should take this opportunity to correct a nuance in what i wrote two weeks ago - LISA Pathfinder is not actually involved in finding gravitational waves itself - Pathfinder is doing fundamental physics, studying the nature of gravity, under microgravity conditions.
ESA's eLISA (Evolved Laser Interferometer Space Antenna) is to be launched in the 2030s, when Pathfinder's done, and will be doing what LIGO does now, but on a much larger scale - over 5 million kilometres. To notice gravitational waves, you need something a lot bigger than the Pathfinder experiment's tiny craft - you need a huge interferometer.
You can easily look up video demonstrations of how an interferometer works, on the interwebs, including a demo by one of the guys who founded the LIDO experiment itself.
But then, why bother searching for that one, when i've linked it here? The man in the video is Rainer Weiss, who appears in the video below - 'The Announcement...'