BellGab.com Archive

Quote from: area51drone on February 17, 2016, 07:37:38 PM
I've got more to say but I need to go do something so I'll just keep the conversation flowing with this..  I don't dislike GR, I'm simply asking is there any physical evidence that there can't be a body inside the event horizon? 

From what we understand about compressibility and the pressure-density relationship of matter under extreme circumstances we don't know of anything that can stand up to the extreme gravity inside. It should all be very nearly pointlike. Please don't get me wrong, that's by no means the whole story, surely there are quantum effects that are important at the singularity. The current thinking is that these will smooth out the singularity to prevent an infinity there. Many people also have other ideas about what might be in there from string theory also. But again, the horizon and external geometries reduce to GR within the observational error margins, as they must, for all these models.

Quote from: area51drone on February 17, 2016, 07:37:38 PM
You say no, but only give a model, which GR is, even though at least from all past experiments it has been proven to be true.  But it's still a model.   I'm asking you, is there anything physical, an experiment that has been done, might be able to be done (even in theory), or an observation of a distant body that proves beyond a shadow of a doubt that the mass is not a singular point (or ring, or whatever).   

You can get it from the Hawking radiation and gravitational waves will tell you a lot about whether or not there's a structure in there too given how black holes merge and ringdown. But there are other physical reasons why the mass has to be very localised to a small region near the center which is to do with our understanding of the properties of matter.

Quote from: area51drone on February 17, 2016, 07:37:38 PM
How can one say that GR is correct beyond the point we can see when there is no data to prove it?   Again, I'm not trying to ask this in a gotcha kind of way.    I just don't understand how mass/energy can fall to a single point in space.   

The least speculative option is GR given how well the other predictions all stand up to scrutiny. And thats my argument, given the success of GR anything that comes afterward has to reduce to GR in the appropriate limit, just like GR reproduces Newtonian mechanics in the appropriate limit. So it may be there's a spacetime crystal or phase transition to another universe inside a black hole or some other exotic thing. Observers are limited to what they can measure about black holes so we would have to hope that subtle distinctions exist between these options to distinguish the new theories predictions from vanilla GR, ie in the gravitational wave signature or some details of the black hole shadow, etc. These are quantities which are now on the cusp of being tested. Exciting times!

Quote from: area51drone on February 17, 2016, 07:37:38 PM
I'm not saying I can't understand why according to GR, I certainly could if I just accept that it is true everywhere (like you do), I just find it physically hard to believe because a singularity that is infinite seems like adding infinity+10 more stars shouldn't grow the event horizon, yet apparently it does.  Do you see what I'm saying?

Why should adding mass to a black hole NOT grow the event horizon? More mass means more curvature which means it's more difficult to escape the black hole at larger radii. I don't understand your objection to this point.

radius of event horizon = 2GM/c^2 where G is the gravitational constant, c the speed of light and M mass of the black hole. As M goes up, the radius of the event horizon goes up too.

Edited to add: I re-read your post and think you are mistaking mass for mass-density. The mass of the black hole is finite so M has a well-defined finite value. That mass must all be in a very small (point-like) region at the center of the black hole. This since mass divided by volume gives mass density if that mass is in an extremely small volume the mass density is very high. That mass density is what is finite, not the mass itself at r=0. Hope that helps.

Quote from: area51drone on February 17, 2016, 07:10:33 PM
You wouldn't say, that in a way, every large body has an event horizon where you cannot escape it's gravity (ignoring the ability to generate opposing forces, or coming at it with speed)?   Of course, a black hole is not a star, but what concrete example says that what is inside of a black hole is not simply matter in some form that does take up a reasonable amount of space?   

An event horizon is not a physical thing. It's a radius at which the escape velocity is equal to the speed of light.
Every body has an event horizon, it is the radius beyond which the body would need to be compressed to become a black hole. You have an event horizon smaller than a proton. If you were crushed to this radius your body would be entirely within the event horizon and your matter would have sufficient density to become a black hole. In fact, in all stellar modeling schemes you have to check if the radius is smaller than the event horizon defined by the interior mass at all radii inside the star. That's the difference between a star and a black hole a star has a surface which by definition is outside of the event horizon. A black hole has all mass within the event horizon.

Quote from: area51drone on February 17, 2016, 07:10:33 PM
So far all you've given examples of are the outside observations and calculations,

Which are all we'll ever have. No signals can get out.

Quote from: area51drone on February 17, 2016, 07:10:33 PM
which you admit DO break down at the singularity. 

They do, but that does not affect the horizon structure or the external geometry. Newtonian gravity breaks down at r=0 too, and so do Maxwell's laws. It's why the delta function was invented/discovered.

Quote from: area51drone on February 17, 2016, 07:10:33 PM
You don't know what happens even beyond the point where someone has gone from red to dark red to invisible.

Yes, I do. Everything up to the singularity is well defined and understood mathematically. The singularity is not. The outside observations agree with GR predictions. No matter how much you may dislike it, GR has a track record of working well and it does in this case too. It has a long line up of people hoping and praying to shoot it down and would not have lasted as long as it has if it did not work well. Everyone wants to be the guy to beat Einstein but it's proven very difficult to do.

Edited to add: Of course, GR is not the full picture, which would also give back the behavior of mass and density at the singularity. But any theory that replaces it pretty much has to keep all the stuff that GR does right in terms of the external and horizon geometry. It will "reduce" to GR in the appropriate limit. It *must* because GR matches so well with what we observe. There's not really any way around that.

Quote from: area51drone on February 17, 2016, 07:10:33 PM
In the ring case, is the singular ring a 2d ring or a ring rotated in 3 space, such that it makes a hollow sphere?

It's a 2D ring in the plane of rotation. There's a more complicated horizon structure, too.

It pains me to say this, but I have been underwhelmed and I went into it with low expectations. The first episode hit a high point for me and I've been pretty critical of the rest. The trip scene was great but the were-lizard dude was equal and opposite. No net gain.

I'm sort of left asking if we really needed this at all. I hope the finale blows the doors off but not holding my breath for that.

There's always Twin Peaks. No, I haven't learned my lesson yet.

Quote from: GravitySucks on February 17, 2016, 07:03:41 PM
Yeah, what ever happened to "Its intuitively obvious to the most casual observer. "

"It is left as an exercise for the reader to prove the effect occurs as stated."

Quote from: FearBoysWithBugs on February 17, 2016, 06:36:39 PM
I haven't read it yet, but this is not entirely hypothetical.  Some small organisms on Earth are dominated by things like surface tension of fluids and electrostatic charge.  Unfortunately they can't tell us that that feels like.

Yes it's true. These organisms would have a very different understanding of the cosmos than we would even if they could observe the outside world.

That paper also contains a great example of the size of the beings they consider. A caption reads "Above: They are very tiny" below a blank figure. Effective.

Quote from: FearBoysWithBugs on February 17, 2016, 06:33:25 PM
Ah, okay.  One additional question, sil vous plait.  Is it known whether this transformation from virtual to real particle take place when the paired virtual particle crosses the boundary of the event horizon, or once that paired virtual particle is incorporated into the mass of the black hole?

My gut says the best way to answer is that after deltaT has gone by and a particle still exists, the total energy of black hole + infalling doomed particle must be smaller than it was before.

Really it's a good question, and has a very difficult answer, since we're now dealing with the total energy, in the form of the energy momentum tensor, which must be dynamic. Plus the vacuum state is involved too. It's messy and I don't think I can give a better non-technical answer to it. The spacetime curvature has to change ever so slightly because there's less rest energy inside the horizon than there was previously. It's also difficult to answer the next followup question, which will (should?) be "deltaT for who?". I think that must be an observer in free-fall at the same distance from the black hole as the virtual particles came into existence, but it's also difficult to even say where those particle form exactly because of the wave particle duality, how localized are they, etc.

Quote from: rekcuf on February 17, 2016, 06:20:51 PM
You mean bellgab.com isn't a well respect science journal?

That's top corner material, right there

Quote from: Chronaut on February 16, 2016, 04:58:13 PM
In fact just a few weeks ago an ambitious but presently attainable experimental setup was described by André Füzfa in Physics Review D for generating a gravitational field, in his paper “How current loops and solenoids curve space-time”:
http://arxiv.org/abs/1504.00333

Chronaut, before I forget let me say thanks for posting this. In fact, we have a weekly journal club at work where we talk about interesting papers we've come across and I put this one on my stack. So when I saw the link it reminded me of another really interesting one that I think many people here may also find interesting.

This paper was posted in November 2015, it is a physics paper but only contains some light basic equations in the text and really stood out for me and captured my imagination. The paper is called "atomic beings and the discovery of gravity", and the general idea is to explore how difficult it would be for a civilization of tiny microscopic people to discover the force of gravity, since they would be so overwhelmed by electromagnetic phenomena in their day to day (which are fractions of a second to us) lives. The paper goes on to speculate that the nature of gravity might forever be obscured to such a civilization, with the beings coming up with more elaborate charge distributions needed to describe the universe, culminating in their theory of "dark charge"!
The analogy to our current situation in cosmology is that maybe some of our big conceptual problems come from seeing only a small corner of a much larger picture.
Was a really neat read. And can be found here:
http://arxiv.org/abs/1511.05431

Quote from: FearBoysWithBugs on February 17, 2016, 05:18:43 PM
This is the one aspect of Hawking Radiation that I never had a firm understanding of.  I assumed that the virtual particles were in pairs of positive and negative mass/energy, and that they should be captured in equal numbers by the black hole and therefore no resulting loss of mass.  Later, I saw an explanation that said that the negative mass/energy virtual particles were preferentially captured, but there was no further explanation.  Your phrasing above ("it doesn't matter which one) suggests to me that the virtual particles exist in a superstate of both positive and negative mass/energy and only drop down into one state after the capture of one and liberation of the other, with the captured particle being the negative mass/energy of the pair.

Would you mind explaining this briefly?

The uncertainty principle is what gives you virtual pairs. These have positive energy deltaE and exist for a time deltaT and satisfy deltaE*deltaT=constant  which is the uncertainty relation in terms of energy and time instead of position and momentum. They're both equivalent to one another. The virtual particles all have positive deltaE and exist for some time deltaT that is inversely proportional so more massive pairs last for shorter periods of time. The virtual pairs have opposite properties from one another, opposite charge, parity, spin, etc. so they are particle and anti-particle pairs (but even anti-matter carries positive energy and has positive rest mass). When the particles annihilate they release deltaE energy back into the vacuum.

When this happens near a black hole and one of the members of the pair is lost to the event horizon, the survivor has no twin to annihilate with. The survivor becomes a real particle with rest energy E0=m0*c^2 and kinetic energy Ek=p*c. This energy has to come from somewhere, so the virtual particle that fell into the hole must have the equivalent negative energy to counteract the survivor and balance the books. This negative energy contribution is subtracted from the black hole and correspondingly reduces it's mass and the size of the event horizon as well. The vacuum is kept at 0 net energy loss so there's no violation of the uncertainty principle and everything is top shelf. This tells you that Hawking radiation can be made of any kind of particle, normal matter, anti-matter, charged, neutral, whatever.

I think it's a very tidy and satisfying explanation for a very complicated phenomenon to describe mathematically.

Quote from: area51drone on February 17, 2016, 05:04:59 PM
Sorry, not a lot of time to respond, but in what way would a black hole with a singularity be different than a black hole that has the same mass with the physical dimensions of a large neutron star?    Don't you find it odd that a black hole's event horizon increases as it swallows up more mass, given that it is already infinite at a singular point?

It may not be truly singular at the center due to quantum gravity hijinx. A black hole has an event horizon, a neutron star does not. That means a black hole does not emit any radiation. Black holes are consistent with microlensing observations which set strong limits on the flux that can be coming from that object. All we can say about the mass inside the horizon is that it is sufficiently compact to have an event horizon so can't have any external structure and since we know about the type of degenerate pressure that can be generated by matter we don't know of anything that could form structure inside the horizon.

I don't find it odd that more mass increases the event horizon, since that's predicted by GR. It's spacetime curvature that makes up the external gravitational field, and you can think of Einstein's field equations as telling you how to translate mass into spacetime curvature. That's totally consistent.

If you're uncomfortable with the concept of an event horizon you're always free to transform to a frame where it doesn't exist and do your calculations there instead. Nothing wrong with taking the falling astronauts point of view.

Edited to add: Let me also say for completion that not all black holes have singular points - the rotating black hole solution (called the Kerr solution) has a singular ring. 

Quote from: rekcuf on February 17, 2016, 01:22:03 PM
Black hole production process: CONFIRMED! Oprah + Krispy Kremes + time  = 'supermassive Oprah singularity'

It's in the donut DATA! 

Publish before someone beats you to it

Quote from: FearBoysWithBugs on February 17, 2016, 12:38:25 PM
That reminds me, I really need more fiber in my diet.

You should try ColonBlow (TM & (c)).

Quote from: rekcuf on February 17, 2016, 12:29:10 PM
AO, I'm sure you're aware that creating mirco black hole in a lab (Large Hadron Collider) is theoretically possible. And you're correct; "doomsday" would not occur. A mirco black hole would only exist for a <fraction of a fraction> of a second, then poof out of existence. It would not have enough mass to sink to the earths core and continue growing.

Many claims have been made about creating a black hole but they come from quantum gravity, and no one really knows the exact details of that, energy scales to expect them to start showing up, etc. It is possible in many theories but I feel like it's more speculation whether it's possible in practice. Honestly I'd be less surprised to hear the LHC finds evidence of supersymmetry before it creates a tiny black hole. But it could be. And it would be kill a hell of a lot of those theories that forbid it.

The most extreme energy cosmic ray ever observed had around 50 times the energies that particles attain in the LHC, so if black hole production can occur around LHC energy scales they must be forming naturally in the upper atmosphere when these ultra high energy particle showers occur. Anyway, just navel gazing now and not much more to that thought ultimately

Quote from: area51drone on February 17, 2016, 10:41:41 AM
Okay, but how do we KNOW that mass actually collapses further?   I mean, the existence of what we observe as a "black hole" is pretty much proven.  But not what they are inside...   How do they know mass collapses to a singularity instead of just being really tight and in the case of a black hole, really big.   I mean, the calculations themselves break down, don't they?   I'm not meaning to say "we can't look into a black hole so you can never know" but is there some real solid proof beyond calculations that this must be true?

Has anyone ever actually created a tiny black hole that people worried about with the LHC?

The math says they collapse further, this really has more to do with the physics of matter and how to describe degeneracy than it has to do with the physics of black holes. Stars are much more complicated than black holes in fact.

It's also not at all true the math is useless to describe black holes, far from it. The math works fine and so does GR until you try to do a calculation at the exact center, r=0, and then you run into problems. This is the only place where the curvature become infinite so we really need quantum gravity for that part. But in the physics of the black hole exterior, how orbits behave, the lensing properties and accretion processes and mechanics in general are all well understood.

We have seen many black holes obscure and lens stars in the background, they behave as predicted by GR. We've seen stars torn apart by them that behave in the ways GR predicts black holes should behave, seen them in binary systems, seen disks around them, etc. There are a huge number of astronomical observations which support them and their mathematical description. The solid proof is composed of the observations of black holes themselves and the mathematical interpretation. Objects too massive to be stars exist and they behave in a consistent way with GR predicts they should. That much is non-negotiable. In fact the event horizon telescope is currently being used to image the shadow of the black hole at the center of the galaxy (sgr A*) directly which will give all kinds of strong field tests of GR.

Of course we have not been inside a black hole (and would not be able to return or send a signal out even if we had) nor have we ever created one in a lab (which would not a real breakthrough and not doomsday as many people speculate).

Quote from: area51drone on February 17, 2016, 05:01:55 AM
I've got another question about black holes, AO and Chron...   how do we know that mass is a point at the center of a black hole?   Why couldn't it be that it's just a really really big neutron star, or something?    I'm assuming there are some calculations that say the neutrons can't support that much mass and thus must collapse, but how do we know that for sure?

There's a fundamental limit to the amount of outward pressure matter can exert to keep a star stable called the Chandrasekhar limit. Put any more mass on a star that's at the limit and gravity beats pressure, collapsing the object. If it's a neutron star you're adding mass to, it will become a black hole (Or, possibly a quark star if those exist - but then there will be some even lower limit where quark degeneracy pressure is defeated and collapse to a black hole occurs). Regardless of the details (degenerate neutron matter or degenerate quark matter) anything over 3 solar masses with a radius smaller than 10 km is most likely a black hole. When you get into the 10s of solar masses range there's no question you're dealing with a stellar mass black hole.

Quote from: area51drone on February 17, 2016, 04:59:08 AM
I think most of us understand what a gravitational wave looked like (as a simple example) without the need for illustrations (even though they are cool).    What I'm having a hard time understanding is that, okay, say you have a rubber ball with the right orientation such that this wave is going to stretch it in spacetime.   Would that pass any energy to it in any kind of regular sense, ie would this hypothetical rubber ball be stretched to bounce if it were on a table made of mass that was not affected by the wave?

The table the ball is on would stetch too!
Imagine a set of nested concentric rings like the one shown above. They are all expanding and contracting in that same way. Just like a regular wave carries energy the coordinates of spacetime are distorted by a gravitational wave. This distortion can cause motion to occur relative to other objects. Feynman used the analogy of a sticky bead on a wire to show that the motion of the bead can cause friction on the stick, heating it up and therefore gravitational waves carry energy.
https://en.wikipedia.org/wiki/Sticky_bead_argument

Generally the kind of distortions LIGO measures are very weak, you need an interferometer with four km long arms to detect and fabry-perot etalons to multiply up to even longer effective length. The gravitational wave distortions stretch out the whole planet on km long wavelength scales but only change the pathlength by a smaller amount than the width of an atom. So they don't carry much energy at all for the purposes of detection.

Quote from: gabrielle on February 16, 2016, 08:13:31 PM
TL..is it just me, or does the explanation of how a gravitational wave moves seem sort of like a contraction?   ( getting ready to duck and hide)

The contradiction I'm guessing is the following (but please clarify if I make an assumption): Gravitational waves are made of the spacetime curvature. But spacetime curvature is caused by mass. So how can a wave travel through spacetime with no mass around?

When energy is radiated away from a system with mass and with some asymmetry (like colliding black holes) it sets up a disturbance in spacetime, like the wake of a boat passing by on a lake. This disturbance evolves through a wave equation, which means that an oscillation in one direction sets up an oscillation in another direction, which sets up an oscillation in another direction and on. So the wave can exist and travel on its own afterward even if there is no mass around anymore.

Consider the following. Suppose we have a set of test masses arranged in a ring. The effect of a gravitational wave is to distort the masses from being symmetrically arranged in a circle and is stretched into an ellipse that varies in time up and down and left and right. This is why a gravitational wave is "quadrupole" radiation. It stretches the ring out in two separate directions like this

In this image the wave is traveling toward you, "out" of your screen. The gravitational wave is not free to move masses around in arbitrary ways, it moves them back and forth rhythmically like this. The wave effect becomes really clear when we stack these things "on top" of one another to make a cylinder and let each of them react to the passage of a gravitational wave:

Remember this "surface" is really a bunch of individual masses arranged in a cylindrical shape. They are connected by lines only for illustrative purposes. In the absence of any wave the surface of the tube would be flat, and all the cross sections would be rings of equal size. As a gravitational wave comes through it distorts the spacetime (the points on the cylinder surface) in the same way that the single ring above is distorted. Set each of the rings that make up the cylinder moving in this same way and over time you can visualize what the gravitational wave does as it passes by. Each of the rings that makes up the cylinder is distorted in the same way. If you watch any one of the rings shown they each move up and down, left and right. This is easiest seen by watching the end of the cylinder. Including time really emphasizes the effect. Notice also that even though the rings all move in the same way, they are out of phase with one another. This is because the gravitational wave has a frequency so any given ring is not at the same point in the cycle of expansion and contraction as it's neighbors. This is the nature of the wave motion. Looking at the cylinder from the side makes the wave nature even more clear:

In this view, the left/right expansion and contraction are removed because we're looking at each ring from the side. Now we only see the up/down motion of the test masses that make up the ring. None of the rings are pushed around by the wave as you can see it's only the directions perpendicular to the direction of travel that are rhythmically affected by the wave.

In fact, this is the basic set up for the LIGO experiment. Roughly, imagine measuring the distance between the point at the very top of the ring and the point at the very right of the ring. As the gravitational wave passes by the distance between these points changes. If you could measure those distance changes you could measure how much a gravitational wave distorts the shape of the ring, how often, etc. and then learn something about how the wave was set up in the first place.

If I didn't answer or gave something too obscure please respond.
All the images are from this article that may help clarify things, but I think I pretty thoroughly cannibalized it with the above post.
http://www.universetoday.com/127255/gravitational-waves-101/

Quote from: ziznak on February 16, 2016, 11:54:38 AM
thats funny! there are some interesting stories online about how nintendo has tried to moderate certain aspects of the "miiverse" and streetpass/spotpass/flipnote that have allowed little perverted kids to draw penises on bowser and stuff.... there is probly an angry japanese man cursing your name right now at nintendo corp headquarters.

http://en.rocketnews24.com/2012/12/13/our-reporter-discovers-penis-disguised-as-goomba-nintendos-online-police-on-the-case-moments-later/

lol!
This. A thousand times this.

Quote from: Chronaut on February 15, 2016, 10:20:46 PM
Gravitational Meissner effect - that's a gem ;

Actually a beautiful result for such a short paper:
http://arxiv.org/abs/hep-th/9603077
He even finds an estimate for the maximum neutron star radius from the coherence length, which is in the ballpark with calculations from detailed equations of state. So it is quite an interesting paper for me. 

Quote from: Chronaut on February 15, 2016, 10:20:46 PM
Ever see Lockheed Martin's patent US5929732A, "Apparatus and method for amplifying a magnetic beam"?
https://patents.google.com/patent/US5929732A/en

If you can focus a magnetic field into a beam using other magnetic fields, it must be possible to focus a gravitational field into a beam as well.  Tractor beam, monsieur?

haha!
That's a great idea.
A bit harder to set up with mass quadrupoles since we will basically need to replace each fixed dipole with a black hole binary system. We will also need to keep them insulated from one another somehow so they don't turn into one giant N-body problem mess.

Minor technical hurdles. Because, do you know what's better than a lab scale tractor beam?
A solar system scale tractor beam!

Alternatively, would make a great "cosmic lighthouse" for anyone only interested in finding species that have the capability of detecting gravitational waves.

Quote from: zeebo on February 16, 2016, 02:03:07 AM
Me too.  We're always told nothing can escape the e. horizon and yet apparently something does and that's why black holes can eventually 'evaporate'.  Is this one of those squishy places where quantum and gravity theories don't quite gel with each other?

Nothing actually escapes the horizon with Hawking radiation. Since the vacuum is always bubbling with assorted quantum bric-a-brac, particle pairs are always popping out of the vacuum, annihilating one another and returning to the vacuum. These quantum fluctuations are required to have zero energy to balance nature's books. Such fluctuations occur all the time, even in empty space. Of course these particle-antiparticle pairs are fluctuating in the spacetime near black holes too. If one member of the pair (it doesn't matter which one) falls into the black hole, then it's partner no longer has anything to annihilate with and provided it is outside the event horizon it can escape. Since the escaping particle has mass (energy), it means it's partner must have negative mass (energy) within the black hole. This will annihilate some of the black hole mass and pay the mass debt for its partner.

To an outside observer it looks like the black hole emitted a particle and shrunk a tiny bit.

In fact there's nothing special about the event horizon, in GR it looks just like any other part of spacetime with finite curvature. You can even pick coordinates in which the horizon doesn't show up at all. It's only to us distant observers who are using particularly obvious coordinates that see an event horizon. An astronaut falling into a black hole, for example, doesn't notice anything special as he crosses the event horizon, but an observer outside the black hole won't ever hear anything more from his increasingly reddening after image.

Quote from: Chronaut on February 15, 2016, 09:55:53 PM
Niccce - this Menezes paper is gonna keep me company tonight =)  Most people aren't aware of the beautiful analogy between electric charge and "gravitational charge" and all of the wonderful parallels they share with magnetism and radiation, when the magnitude of the gravitational field is in the weak field limit.  Apparently Robert Forward wanted to build a toroidal gravitomagnetic inductor to experiment with possible propulsion applications in mind.  I wonder if we'll be able to harness plasma to try that out someday.  Iirc there's an open question about gravitational field symmetry with a mass current simultaneously flowing in both minor and major axis rotation.

I still love to peruse Robert Forward's inspiring papers on gravitation and experimental frontiers for antigravity research and the baffling physics of negative mass - you've probably read all that stuff but I though I'd mention them for anyone interested in this kind of thing.

When I first read about the gravitational Meissner effect I was really impressed. Since then I've always kept an eye out for strange optics or other obscure E&M that might have an analogue in weak field GR. It's just such a nice way of finding parallels between E&M and gravity I think it's very underappreciated and it bothers me it's not much known outside of GR circles.

Quote from: Chronaut on February 15, 2016, 08:42:37 PM
I'll have to amend my earlier answer gabrielle - it looks to me like the octupole and higher order radiation that carries linear momentum away from an inspiralling system comprised of unequal mass bodies, can only be absorbed by a system that also possesses an octupole moment.  So gravitational waves can't "push" just any body - only a body or system with the right properties could absorb that linear momentum and get pushed away from the source of the radiation.

A really interesting question with some very complex dynamics

That's right, they are emitted from specific configurations and interact with specific configurations. The wave equation that comes from the weak field limit looks just like any wave equation (ie, Maxwell) and so they have energy density, etc and can also have an analogue of an energy-density and momentum (Poynting) vector as well. This means they carry energy and momentum with them. The only difference is the waves are based on tensors rather than vectors, so the two index character of them means they have quadrupole character. Very interesting.
Article on GW energy-momentum (Poynting) vector here for those interested: http://arxiv.org/pdf/gr-qc/9801095.pdf
All that comes from the fascinating weak field GR expansion which looks just like Maxwells equations with mass and mass currents in place of charge and charge-current: https://en.wikipedia.org/wiki/Gravitoelectromagnetism
You can form a wave equation from these weak fields too, just like you can with Maxwell, and you get back a gravitational wave equation as you might expect. This wave equation then gives the speed of propagation as the speed of light. So it's an interesting result.

Quote from: Ciardelo on February 15, 2016, 01:27:58 PM

haha

Nice review Chronaut and FBWBugs.

I heard a tape of Lazar's claims somewhere. From what I remember his ideas were a lot of science-fiction word-salad to me. He picked some legitimate terms but arranged them in a way that didn't make much sense overall. I also remember that he was all prose, no math. Which does not help. The "gravity A" and "gravity B" business is nonsense.

However, to break the fourth wall with a knowing wink, Ununpentium was recognized as an element in December 2015 but only about 100 atoms of the stuff have ever been produced. Not quite on the island of stability either.
https://en.wikipedia.org/wiki/Ununpentium

Just picked up A Link Between Worlds for the 3DS.

It's awesome so far.

I named my character Dr. Ass, so when I pass people with streetview on they'll see it.

Very interesting paper posted to the arXiv last night. This group using Fermi observed a gamma-ray transient source with energy above 50 keV in a direction consistent with GW150914, which arrived some 0.4 seconds after the GW event was recorded.

Coincidence? Or has the first electromagnetic counterpart of a gravitational wave source already been seen?
http://arxiv.org/abs/1602.03920

These groups also tried searching for an electromagnetic counterpart but did not find anything. PAN-STARRS1, INTEGRAL and DECam all missed it but make a good case for the feasibility of future observations of EM counterparts to GW detections.
http://arxiv.org/abs/1602.04156
http://arxiv.org/abs/1602.04180
http://arxiv.org/abs/1602.04198

And ahoy Chronaut!

Quote from: Camazotz Automat on February 11, 2016, 06:21:25 PM
*** see post #1195:

Quote from: akwilly on February 12, 2016, 03:08:45 AM
very cool story but my question is what will we learn from this finding that we didn't already know? If it was predicted by Einstein 100 years ago what information will be a game changer and how if at all will it change anything scientists do?

Being able to study gravitational waves opens a completely new window to the Universe. Up until now we have used electromagnetic radiation to study signals from the stars and other objects in the sky. But electromagnetic waves do not tell the whole story. They can reveal only those processes that produce radio waves, visible light, X-rays, etc. Gravitational waves are entirely different than electromagnetic waves and are generated by sources which do not produce electromagnetic waves for example, two isolated black holes colliding are invisible to our conventional telescopes. But they are readily detectable using gravitational waves.

The announcement by LIGO is as revolutionary for astronomy and astrophysics as it was when Galileo used the first telescope.

In fact, the binary black hole system they made the announcement on emitted three solar masses worth of energy in gravitational waves. This is like take three Suns worth of mass, completely annihilating them and dropping all that energy into the fabric of the Universe itself. At the peak of the event the black hole merger was fifty times more powerful than the electromagnetic output of all the stars in the entire Universe combined. Yet we were completely blind to such an event up to this point. We need detectors like LIGO to see these kinds of events and simply can't study them otherwise. Think about all the mysterious signals we get from pointing telescopes and radio dishes upward - fast radio bursts, gamma ray bursts, X-ray transients - LIGO pulls back the veil on even more mysterious and exotic phenomena.

The next step will be when there are enough gravitational wave detectors to refine positions on the sky. Then we may be able to see an event with gravitational waves and turn our conventional telescopes toward it as well, or vice versa, and learn a lot more about the phenomena that we can see in both wave regimes, such as the surface structures of neutron stars for example.

Moreover, gravitational wave astronomy also allows for tests of general relativity in the strong field regime, at energies we have never before tested GR. This is key because we can't do those kind of tests on Earth and require the detailed study of astronomical sources for. The results announced yesterday all conform to Einstein's field equations but as more statistics are gathered and binary mergers are seen we will amass a lot of data about how gravity behaves from direct observations and how this may limit proposed theories of quantum gravity going forward. The first significant thing we seem to have answered though not directly addressed yesterday is that the speed of gravitational waves seems to be the same as the speed of light, this kills all theories that expect light and gravitational waves to propagate at different speeds.

It's a very important discovery, words like "landmark", "watershed" and "game-changer" can easily be used as labels. The LIGO team will win a nobel prize for this.

Incidentally an additional 12 papers were released on the arXiv yesterday, it sounds as if they have a total of eight candidate detections so far but the system reported on was by far the most significant and clear. An impressive discovery.

Quote from: maureen on February 10, 2016, 02:58:26 PM
Such a delight to have you back, AgentOrange!

We are riding the gravitational waves like the SilverSurfer- philosophizing and wondering.

Lovely!!  May the quarks be quirky and may the muons graze together!

Hi Maureen! Hope you are doing well.

Quote from: area51drone on February 10, 2016, 05:20:28 PM
All this Agent Orange ass kissing, and he STILL hasn't responded to my questions from years ago, AFAIK!   

Yeah sorry about that, I have them written down somewhere and had a substantial portion of a text wall written. But I'm not sure where they are now, and honestly I'm too lazy to go back and dig them out of their backup drive tomb.

It's been increasingly difficult to put up long posts. Last weekend was the exception for me lately. So I concede. Feel free to take points away from my column and add them to yours.