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Author Topic: Gravitational Waves  (Read 22368 times)

Telecaster

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Gravitational Waves
« on: February 10, 2016, 05:42:51 pm »

Tomorrow at 10:30am (USA Eastern time) scientists working on the LIGO project will be holding a status update/press conference regarding their work. LIGO stands for Laser Interferometer Gravitational-Wave Observatory. Rumors have been circulating for the past month or so that LIGO has made the first ever direct detections of gravitational waves. These are waves or ripples caused by gravitational interactions, however not in space but rather of space. They're a prediction of Einstein's General theory of Relativity and have been surmised to exist, based on indirect observation, for quite some time. But surmising isn't the same thing as directly observing, and so GWs have until now remained officially theoretical. Given past instances of jumping the gun re. announcements of "discoveries" that turned out not to be valid (do a Web search on "BICEP2 results" for an example) the LIGO folks have reportedly been extra diligent in doing their work.

If the press conference confirms the rumors, as seems likely, this opens up a new field of study re. the behavior of gravity in extreme events (such as supernova explosions & black hole formation) and also at extremely small scales. This in turn should give us new insight into how both General Relativity and quantum mechanics could/might be superceded by a more complete theory not only encompassing both but also making new predictions of yet undiscovered natural phenomena.

Here's a good gravitational wave primer (though the ads are a bit much for my liking):

http://www.universetoday.com/127255/gravitational-waves-101/

Note: it's possible the press conference will turn out to be a non-event. Unlikely, though.

-Dave-
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Telecaster

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Re: Gravitational Waves
« Reply #2 on: February 11, 2016, 11:26:07 am »

Yep, as expected LIGO has detected gravitational waves. From a merger of two black holes ~1.3 billion light years distant from us, broadly in the direction of the Large Magellanic Cloud. The merger event was detected by both LIGO installations, one in Washington and the other in Louisiana, on 14 September of last year. This happened shortly after the "Advanced" version of LIGO went online. (It was anticipated that Advanced LIGO would detect GWs, if they actually existed, almost immediately. Which indeed happened. In fact it happened during a test run, though at full operational capability.) The observation matches the expected behavior of the merger, as derived from the equations of General Relativity, to an impressive degree. Einstein scores again (with a strong assist from astronomer Karl Schwarzchild, who in 1916 discovered gravitational waves lurking in the General Relativity equations)!

Another thing to note is that this detection not only confirms the existence of gravitational waves but also that of black holes! We already knew that the centers of galaxies contain objects of high density & small relative volume that emit no light. Now we know that the behavior of these objects, in a merger event, matches the predicted behavior of General Relativity's black hole solution. (We still don't know with any precision what's going on inside a black hole's event horizon, though…that's a task for a proper quantum theory of gravity to take on.)

So now we have a whole new way of doing astronomy, looking at the universe via gravitational rather than electromagnetic waves. There are additional LIGO detectors, spread out over the globe, due to come online in the near future. Right now we're doing the GW equivalent of looking up at the sky with Galileo's telescope. What might we find when we build detectors at the level of today's best telescopes?

-Dave-
« Last Edit: February 11, 2016, 12:04:08 pm by Telecaster »
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Rob C

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Re: Gravitational Waves
« Reply #3 on: February 11, 2016, 02:54:02 pm »

And to think that I find deep-digging within Photoshop a challenge.

;-(

Rob

Telecaster

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Re: Gravitational Waves
« Reply #4 on: February 11, 2016, 04:09:13 pm »

And to think that I find deep-digging within Photoshop a challenge.

;-(

No frowny face allowed. This is an exciting day, even a landmark one, in the history of astronomical observation. LIGO is the most sensitive & precise detection and measuring device ever built by us humans. And before long its capabilities will be upgraded by a factor of 3, bringing less powerful events than black hole mergers within its view. We have a whole new sense we can explore the skies with.

 :)  :D  ;D  8)

The attached pic is of LIGO Livingston, in Louisiana. The cartoon is via xkcd.

-Dave-
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pcgpcg

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Re: Gravitational Waves
« Reply #5 on: February 12, 2016, 02:54:08 pm »

Thanks for the link. I've been wondering what the effects of a gravity wave on my macro world were. I guess my body is momentarily distorted by an amount that is just almost unimaginably tiny. Also the explanation of how they are detected with a giant Michelson interferometer is very simple and easy to understand. All of this in ten minutes.

And to think that I find deep-digging within Photoshop a challenge.

On the contrary, I find mastering PS to be far more difficult than understanding the above tutorial link. Seriously. I was pleasantly surprised.
« Last Edit: February 12, 2016, 03:26:43 pm by pcgpcg »
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GrahamBy

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Re: Gravitational Waves
« Reply #6 on: February 12, 2016, 03:01:20 pm »

In 1988 I was at the Marcel Grossman meeting in Perth (the one in Australia). It was held there because a group in the physics department at UWA had built a resonating beam GW detector. We now know that the instrument itself was ridiculously small and the instrumentation way too noisy to work... but we got there :-)

And so the "our theory is more experimentally verified than yours" fight between the relativists and the Guantum folk goes on another round  ;D
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Telecaster

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Re: Gravitational Waves
« Reply #7 on: February 12, 2016, 04:55:47 pm »

Hehe…relativity refuses to give up.  :)

Another thing this gravitational wave detection does is set an upper bound on the mass of the putative graviton (the quantum of gravity, if in fact gravity is something that exists at such tiny scales). That upper bound is less than .000000000000000000000012 electronvolts. What a lightweight! By comparison even neutrinos are leadbutts.

-Dave-
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Ray

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Re: Gravitational Waves
« Reply #9 on: February 12, 2016, 06:58:09 pm »

Hehe…relativity refuses to give up.  :)

Another thing this gravitational wave detection does is set an upper bound on the mass of the putative graviton (the quantum of gravity, if in fact gravity is something that exists at such tiny scales). That upper bound is less than .000000000000000000000012 electronvolts. What a lightweight! By comparison even neutrinos are leadbutts.

-Dave-

For me, the most mind-boggling aspect of this Ligo system is its capacity to measure such tiny changes.

If I've understood correctly, the system consists of 4km-long interferometer arms, the lengths of which change as a result of the effects of gravitational waves, by a mere 1/10,000th the width of a proton. And as we all know, the physical size of a proton is very, very tiny, visible only through an electron microscope.

To get things into scale, if we imagine a hydrogen atom with its orbiting electron, as the size of a football field, then the proton at the centre of the atom would be about the size of a football, or perhaps even smaller; perhaps the size of a golf ball, with an electron the size of a grain of rice orbiting the outer perimeter of the football field.

How we could measure 1/10,000th the width of a proton with any accuracy is just incredible.
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pcgpcg

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Re: Gravitational Waves
« Reply #10 on: February 12, 2016, 11:35:28 pm »

I have a simple question for any physicists here. If I was a physicist myself I would be posting to a physics forum, but I’m not. I’ve been Googling and can’t find a satisfying answer to - what causes a gravitational wave?

I know that objects with mass warp spacetime. And when masses move through spacetime the warping also moves. So is it the case that if a mass is big enough and it accelerates through spacetime fast enough a wave is produced instead of a simple movement of the warping?

Is it like when I put my hand in water slowly the water moves, but if I put it in fast I create a wave?
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Ray

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Re: Gravitational Waves
« Reply #11 on: February 13, 2016, 08:10:39 am »

Is it like when I put my hand in water slowly the water moves, but if I put it in fast I create a wave?

I suspect this is the case, but I'm no authority. My immediate reaction to this news of the detection of gravitational waves, was the implication for the direct detection of Dark Energy and Dark Matter which comprise about 95% of the matter and energy of our universe, according to current theories.

Unfortunately it seems that  dark matter and energy do not exist in nearly dense enough 'clumps' to produce gravitational waves that could be detected by LIGO.

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Rob C

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Re: Gravitational Waves
« Reply #12 on: February 13, 2016, 09:30:55 am »

Ray, the measurement is nothing more than natural equipment expansion (in Louisiana, what else could you expect - even the rain comes preheated) creating an 'interesting' result that will bring in more funds - just like with NASA, though I gather they are getting less these days.

As to the rockets, nobody is going to live on Mars or even the Moon. Get over it; it's about military spending and the race to get an unassailable advantage from above, not human travel. Were but a tiny fraction of all that brass spent on me, it would make at least one person very happy!

;-)

Rob

stamper

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Re: Gravitational Waves
« Reply #13 on: February 13, 2016, 10:13:33 am »

I just wish that all of these scientists would spend their time and resources curing the problems on earth. A few months ago some of them were getting excited about water on Mars whilst water was ruining communities in the Uk. It took them a century to find out what Einstein had already predicted. How many billions/millions was spent on this fantasy project? Dreamers and wasters imo.  :( >:(

Eric Myrvaagnes

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Re: Gravitational Waves
« Reply #14 on: February 13, 2016, 10:18:06 am »

Hmmm. I wonder how long it will take for some major camera manufacturer to claim to have image stabilization that compensates for gravitational waves.   ;)
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-Eric Myrvaagnes (visit my website: http://myrvaagnes.com)

Robert Roaldi

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Re: Gravitational Waves
« Reply #15 on: February 13, 2016, 11:01:42 am »

I just wish that all of these scientists would spend their time and resources curing the problems on earth. A few months ago some of them were getting excited about water on Mars whilst water was ruining communities in the Uk. It took them a century to find out what Einstein had already predicted. How many billions/millions was spent on this fantasy project? Dreamers and wasters imo.  :( >:(

Why, do you think our politicians would listen to what scientists had to say?

You could make the same argument for every art gallery. Or the military. Or casinos. Or pro sports (oh wait, that was covered by casinos). How about if we shut down international tax havens. Or college sports (pro league farm teams more than educational opportunities). Or arms manufacturers. Or tobacco companies. Or subsidized corn growers. Feel free to add to the list.

How useful to society is it to produce millions of photos every minute that get uploaded to some server? Wouldn't all that time and money be better spent elsewhere?

We're conducting this conversation on a platform made possible because during the 1920s to 1950s, governments the world over (and a very few private labs) subsidized thousands and thousands of students and researchers that over time built up a body of knowledge we now call solid state physics.
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Robert

Torbjörn Tapani

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Re: Gravitational Waves
« Reply #16 on: February 13, 2016, 11:17:55 am »


The first integrated circuits were used to navigate to the moon. For what 50 kg of the same materials found in the earths crust. What a waste. We were better of when the projected number of computers in the world was about 5. No one was sharing useless cat pictures back then.

And LIGO... Who needs better quartz glass. What a complete waste of effort producing better optical glass. Useless I tell you.
I just wish that all of these scientists would spend their time and resources curing the problems on earth. A few months ago some of them were getting excited about water on Mars whilst water was ruining communities in the Uk. It took them a century to find out what Einstein had already predicted. How many billions/millions was spent on this fantasy project? Dreamers and wasters imo.  :( >:(
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Rob C

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Re: Gravitational Waves
« Reply #17 on: February 13, 2016, 11:39:45 am »

Extrapolation isn't an answer; stamper has a valid point.

Rob C

Rob C

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Re: Gravitational Waves
« Reply #18 on: February 13, 2016, 11:58:15 am »


We're conducting this conversation on a platform made possible because during the 1920s to 1950s, governments the world over (and a very few private labs) subsidized thousands and thousands of students and researchers that over time built up a body of knowledge we now call solid state physics.

Indeed, and I'm sure the intention was never for it to come to what the Internet is today. That's just what happens when good science gets into the domestic zone and we reach out for the lowest common denominator in search of profitting from it, spawning zillions of pointless messages per day, the main use-beneficiaries of which networks seem to be terrorists. The reluctance to mess with the 'freedom to communicate' this senseless crap means, essentially and consequentially, that it's left fairly wide open to them apart from the odd token closure; hey, there's money to be made - one day, they say - but the zillions still come in and nobody knows how to tax them because they can't find them!

Used to be thugs on the streets to worry about; now, those are the tiddlers. The real ones you never see because they have learned to be invisible unless making a marketing statement about something or another. Big Brother? Mother and family live in sunny California. They know everything about every one of us who 'nets.

Was that what was intended back in the day? Hey, maybe it really was. They say Satan's pretty old...

Telecaster

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Re: Gravitational Waves
« Reply #19 on: February 13, 2016, 04:01:18 pm »

I have a simple question for any physicists here. If I was a physicist myself I would be posting to a physics forum, but I’m not. I’ve been Googling and can’t find a satisfying answer to - what causes a gravitational wave?

I know that objects with mass warp spacetime. And when masses move through spacetime the warping also moves. So is it the case that if a mass is big enough and it accelerates through spacetime fast enough a wave is produced instead of a simple movement of the warping?

Is it like when I put my hand in water slowly the water moves, but if I put it in fast I create a wave?

A good question, and one that reminds me of an issue I have with the article I linked to above. At least twice in that article gravitational waves are referred to as propagating through space. This is wrong wrong wrong. GWs are oscillations of space. Or, more precisely, of spacetime. Mass, and the movement of objects with mass, not only warps & bends space…it also slows & accelerates the passage of time. Think of spacetime as a somewhat flexible 3D grid. We—along with stars, planets, galaxies, etc.—exist within this grid. GWs are the ripple-like warping & bending of that grid in response to the movement of massive objects. (By "massive" I mean anything that has mass. You and I create teeny tiny weak GWs—many orders of magnitude tinier than even the crazy small disturbances detected by LIGO—every time we breath in or out or blink our eyes. But the amplitudes of GWs will be greater with more massive objects moving at higher speeds.) When you move your hand slowly in water you still create a wave, but it's of low amplitude and is quickly dissipated. With faster movement you create a higher amplitude wave of longer duration.

As to the other stuff being expressed here: some people respond to new phenomena and new knowledge with curiosity & wonderment & even excitement, while others respond with dread & hostility & even rejection. All the rest follows from this.

-Dave-
« Last Edit: February 13, 2016, 04:16:16 pm by Telecaster »
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