LIGO is very serious about doing blinded test runs, even going as far as writing the whole paper before they check whether the signal was real. There's only a couple of people in the entire collaboration who even know when the blinded test runs occur. In any case, this rumor has been going around for a couple of months, so if it's true, we should know soon. Between this and the LHC blip, I'm quite excited about the next couple of months.
Can you explain that a bit more? I'm fascinated but don't quite get the rationale behind having not even the authors of the paper know the results. What is their process?
It means you have to develop your experimental method prior to seeing the data, so you can't try a dozen different ways of slicing that data up until you get the result you want.
Yeah. This is what's absolutely missing in many scientific fields, and seems to be the reason for so many results turning out to be utter bullshit (hello, psychology). There's a strong push coming from research community to make this approach, which is known as 'study pre-registration', mandatory.
Presumably pre-registration could also help with positive results bias.
Assuming the registration was made public, one could mandate that something had to be produced from the study, if only a statement that nothing was found.
Wouldn't solve the problem but would presumably aid meta-studies?
It's not really feasible for most research (although there are plenty of needed improvements along these lines). Big physics projects are unusual in that they are enormous undertakings of 100s or 1000s of PhDs, and few or no other experiments will take data that can cross-check the results. (For instance, no other machine will produce the conditions at the LHC for several decades at least, which is why they go to the fantastic expense of building two completely separate general purpose detectors.) Devoting ~5 full-time PhDs for the sake of super-duper methodological rigor is doable for LIGO, but not for smaller experiments.
Well, keep in mind that if hundreds of scientists take their chance on the same data using different methods, we basically have the same problem. One of them will be the lucky one that took the approach that shows the favorable results, whether the results are truly there or not.
Another level of experimental blinding would be to avoid conferring with the other observatory (there are two components to LIGO, one in Hanford, WA and one in Livingston, LA) for confirmation/correlation until after one site's evaluation is complete. I don't know whether this is the current practice.
In any case, if the observatories are actually able to detect gravitational waves and if there are no theoretical obstacles, eventually two black holes will merge, which will produce a completely fantastic observation consisting of a rapidly rising frequency (as the two BHs circle each other closer and closer, shedding their orbital energy as gravitational waves), followed by a very loud cosmological pop as the BHs finally collapse into each other.
My impression (from well off to the side in a tangentially related field, mind you) has been that false positives are common enough in the individual detectors that they really do need the comparison with the other location's data as a filter. (Not common enough for an actual coincidence to be at all likely, though.) I'm happy to be corrected if I'm wrong, of course! But I think the system has only been designed to be reliable as a whole.
> But I think the system has only been designed to be reliable as a whole.
Yes, absolutely, I only meant that initial evaluations might be more objective if the two observatories cannot compare notes (at first) -- that might lead to a kind of confirmation bias. Only after one observatory satisfies itself that they have a sufficiently unambiguous signal should they be allowed to correlate with the other observatory's results.
Considering the absence of plausible signals to date, this idea might be bending over backwards to avoid observational bias.
I see your point, but I still have a sense that the false positive rate is just too high. I don't know the actual false positive rate, but I've somehow pictured maybe a dozen or so very brief (<1 sec?) signals per year. Under anything like those circumstances, an accidental coincidence would still be vanishingly unlikely (since there are 3x10^7 sec/year, it would be something like a one in a million chance), but the collaboration can't be expected to do full, detailed analysis of false signals a dozen times a year.
> ... I still have a sense that the false positive rate is just too high.
That might be true in principle, but considering what's at stake, I think the investigators will bend over backward to avoid making a claim that isn't ironclad. Remember that in real science, investigators look for explanations that will falsify their results, and only give credence to results that resist sincere efforts at falsification. (Contract this to the outlook of a pseudoscientist, who only looks for reasons to confirm his results.)
Remember the incident in which some investigators claimed that neutrinos were exceeding the speed of light? In truth, they were looking for reasons to confirm their result, not falsify it. They were wrong, the real cause was a bad connection and ... they were pressured to resign their positions.
> ... the collaboration can't be expected to do full, detailed analysis of false signals a dozen times a year.
That's true, but they could instead choose a handful of genuinely peculiar signals, signals unlikely to have natural causes, and try to falsify those.
As above, there are a handful of cosmological sources that would produce -- not a brief signal -- but a pattern of signals, like a rising tone created by merging black holes. Those would be more interesting, as well as being easier to compare to false terrestrial sources.
It would take infinite time to an observer outside the horizon. It would probably look something like a cell dividing, in reverse, over infinite time, such that the end result is indistinguishable from a single hole.
This is the exact same conceptual issue as the formation of a single black hole (BH). Consider a spherical shell of matter (i.e. GR dust) collapsing inwards to form a BH. As the dust particles get closer and closer together, one can roughly say that time slows down for them and that none of the particles ever pass through their mutual horizon. Rather, the argument goes, the particles just becomes exponentially close to where that horizon would form. From the outside, this is indistinguishable from a BH for all practical purposes, since the only way to isolate the still-free dust particles is to zoom exponentially close to the horizon and then drag yourself out (which requires an exponential amount of energy).
The problem with this argument is that there is no preferred global time coordinate with respect to which you declare that "the BH has formed". Rather, the spacetime events corresponding to "each dust particle crosses their mutual horizon" (i.e., "the formation of the BH"), along with the rest of the interior of the BH, comprise an additional spacetime region you can choose to attach to your manifold or not. This is a free choice because causality flows one-way across the boundary; no experiments outside the BH can be sensitive to whether the region "really" exists. There are multiple ways to extend the normal time coordinates (at infinity) into the interior of the BH, and a natural choice is the proper time of in-falling particles/observers. In that case, the BH definitely forms at a finite values of that time coordinate.
Merging two existing BHs doesn't introduce new fundamental issues. Quantum mechanics does introduce new fundamental issues, but formally the jury is still out on whether it resolves this question. The majority opinion is that the interior of the BH exists just as much as regions beyond your cosmological horizon (in an expanding cosmology) exist, from which you are likewise causally disconnected
> This is the exact same conceptual issue as the formation of a single black hole (BH).
I know. No one has ever explained how those can form either.
> From the outside, this is indistinguishable from a BH for all practical purposes
Except without the physics breaking properties of black holes. So not the same at all.
> The problem with this argument is that there is no preferred global time coordinate with respect to which you declare that "the BH has formed".
I don't need a global time, my own time frame is perfectly fine with me. If a black hole can never form, as viewed by me, then black holes don't exist.
> This is a free choice because causality flows one-way across the boundary
This presupposes the black hole exists already, but we have not gotten there yet. First it has to form, and it can not.
> and a natural choice is the proper time of in-falling particles/observers. In that case, the BH definitely forms at a finite values of that time coordinate.
It gets interesting here - what does happen from the POV of that particle? I suspect it never sees a black hole. This particle is moving exponentially close to the speed of light, relative to the center of mass of the forming black hole.
This means that time is stopped for the center of mass of the black hole from the POV of the particle, which means the center of mass can never form a black hole since it can never do anything at all (since time is stopped for it).
Arguing that, because the event horizon collapses the time dimension (from the perspective of a distant observer), therefore BHs aren't real, is like saying that sum(2^-n,(n,1,oo)) can't equal 1 because it's an infinite series and an infinity of additions takes too long.
Think of black holes as objects of great mass, that have very bright accretion disks, surrounding an event horizon that is perpetually almost forming a singularity but never quite completes it (from the perspective of someone far from the horizon).
> This means that time is stopped for the center of mass of the black hole ...
From the perspective of a distant observer, the time horizon is located at the event horizon.
The evidence is non-existent. The only evidence is for supermassive objects, not event horizons.
> Arguing that ... BHs aren't real, is like saying ... an infinite series and an infinity of additions takes too long.
That's a terrible argument. One is an actual physical process, the other is a mathematical abstraction. Do you not understand infinity? Infinity means you can't actually do it. It doesn't mean you can't calculate it.
> Think of black holes as objects of great mass, that have very bright accretion disks, surrounding an event horizon that is perpetually almost forming a singularity but never quite completes it (from the perspective of someone far from the horizon).
Eh? If it never forms a singularity, it has no event horizon. i.e. it has none of the physic breaking properties of black holes.
And accretion disks don't have to be bright BTW, as stuff falls in time dilation makes them much less bright (they "slow down", and emit photons less often).
> From the perspective of a distant observer, the time horizon is located at the event horizon.
When I say center of mass of the black hole I am naming the object I am talking about, not describing the location of the time horizon. Sorry if it was confusing.
If you're familiar with Occam's razor, you know that, for a given phenomenon, the simplest explanation is to be preferred. There certainly are massive objects at the center of most galaxies, and the most economical explanation is that they're black holes. No one is closing the book on these ideas -- that would be unscientific -- but there is strong evidence that these things are black holes.
That they exist is beyond question. That they have super-high masses confined to a small space is beyond question. General Relativity then fills in the blanks in our observations.
> That's a terrible argument. One is an actual physical process, the other is a mathematical abstraction.
So is General Relativity. But because nature follows the same rules, General Relativity accurately predicts many aspects of reality (certainly not all).
> And accretion disks don't have to be bright BTW ...
Well, yes, they do -- they're giving up a huge amount of gravitational potential energy, and that energy must be conserved -- it's converted to kinetic energy, it becomes heat and light.
Consider a satellite in an elliptical orbit. At the orbital apoapsis, potential energy is highest and kinetic energy is lowest. Not surprisingly, this is the point of smallest velocity. Now consider periapsis -- it's the reverse: lowest potential energy, highest kinetic energy, therefore highest velocity.
In a normal planetary elliptical orbit with no friction, even though the two kinds of energy are constantly changing, they sum to a constant at each point in the orbit, so there's no net dissipation of energy. But as matter falls into a black hole, in order for it to pass through the event horizon, it must give up most of its energy (both potential and kinetic). Most of that energy is converted into heat and light.
Most accretion disks preserve the rotational momentum of the infalling mass, so they're in the form of disks surrounding the event horizon. In theory, mass could fall directly into the BH without any rotation -- in that case, there would still be a huge energy conversion process and much radiated energy. Sp accretion disks are very bright.
Here's a graphic of the imagined BH from "Interstellar", thought to be fairly accurate as movie graphics go:
> Eh? If it never forms a singularity, it has no event horizon.
Yes, and by the same reasoning, because a Calculus limit expression never gets to its limit, therefore Calculus is bunk. My point? Just as (1+1/n)^n approaches e as n approaches infinity (http://www.wolframalpha.com/input/?i=limit+n+-%3E+inf%2C+%28...), a black hole approaches its final form as mass approaches it from the perspective of a distant observer.
You might as well have argued that, because this classic-physics gravitational equation:
f = (G m1 m2) / r^2
assumes that all the mass is a dimensionless point at the center of the central body, therefore if m1 and m2 occupy the same point in space, the result is infinite, therefore (because infinity isn't a number) Newtonian gravitation is bunk.
> There certainly are massive objects at the center of most galaxies, and the most economical explanation is that they're black holes
That is just not true. To be a black hole it must first be possible for black holes to exist, otherwise they are simply supermassive object - to us they would look EXACTLY the same!
A black hole is NOT the simplest explanation! It's the most complicated one. You are using your razor very incorrectly.
> That they exist is beyond question.
Absolutely not true. That massive objects exist? Sure. Are they black holes? Not so clear.
> That they have super-high masses confined to a small space is beyond question. General Relativity then fills in the blanks in our observations.
No, actually General Relativity does NOT fill in the blanks - it claims things are impossible. The math does the equivalent of divide by zero.
> So is General Relativity. [a mathematical abstraction]
Great, so since GR predicts it would take infinite time, I guess case closed. Since infinite time, by definition, can not actually happen, it means black holes can not form. Just because you can calculate what something will do doesn't mean it will actually do it.
> Well, yes, they do -- they're giving up a huge amount of gravitational potential energy, and that energy must be conserved -- it's converted to kinetic energy, it becomes heat and light.
Kinetic energy does not become heat and light. Kinetic energy is velocity. To make heat and light you need some other process. Have you never heard of conservation of momentum?
On top of that, the discs are dim because time is dilated to nothing not because there is no energy there.
> But as matter falls into a black hole, in order for it to pass through the event horizon, it must give up most of its energy (both potential and kinetic). .... in that case, there would still be a huge energy conversion process .... Most of that energy is converted into heat and light.
How in the world are you writing this stuff? You can't just "give up" velocity. You have to transfer that velocity to something else. You can't just wave your hands and say "magic". Friction might cause objects to equalize in velocity, but can not actually reduce velocity (only share it amongst the objects).
> a black hole approaches its final form as mass approaches it from the perspective of a distant observer.
And takes infinite time to do so, and since right now is not infinitely in the future, right now, today, black holes do not exist.
Infinite. Do you not understand that word? It means forever, it means it never actually does it, just gets closer and closer.
> therefore if m1 and m2 occupy the same point in space, the result is infinite, therefore (because infinity isn't a number) Newtonian gravitation is bunk.
Nice question, wrong conclusion. The actual conclusion is that since infinity is not actually seen in the real world (as opposed to math), there must be some method that prevents the two masses from ever occupying the same spot.
Your argument is entirely backward, you think that if infinity shows up in the math then it must show up in the real world. No. If infinity shows up in the math then your math is wrong, or incomplete. In this case there is something else that prevents r from hitting zero.
>> it's converted to kinetic energy, it becomes heat and light.
> Kinetic energy does not become heat and light.
So have you told the LHC people that they're misguided for thinking they can produce the Higgs Boson by colliding protons together? I'm sure you can persuade them how wrong they are.
Electromagnetic energy (heat and light) is a kind of kinetic energy.
But you know what? I've decided not to try to correct all the errors you've made. If you actually understood physics, you wouldn't have objected to the things you have (you might have found a better reason to object).
> Friction might cause objects to equalize in velocity, but can not actually reduce velocity ...
Wow. Those fools in Europe are sure misguided to have spent so much money on a circular 17 mile pipe dream. if only they had consulted with you before building that monstrous contraption. They actually think their gadget can convert near-light-speed velocities into many other kinds of energy, including electromagnetic, and the creation of particles from energy and the reverse. Do them a favor -- set them straight, as you've set me straight.
The LHC collides TWO protons! The net velocity between them is zero.
You seem to know at least some physics, how can you possibly not know this?
But in your black hole scenario there are not two opposite velocities adding up at the horizon.
You can not just directly turn velocity into light, it's not possible, you need another object.
> Electromagnetic energy (heat and light) is a kind of kinetic energy.
Some people define only two kinds of energy: Potential and Kinetic, in that definition electromagnetic energy is a type of kinetic energy, and velocity is a type of kinetic energy.
But it does NOT follow that electromagnetic energy is the same as velocity energy!
It's like an apple is a fruit and an orange is a fruit, but an apple is not an orange.
> They actually think their gadget can convert near-light-speed velocities into many other kinds of energy, including electromagnetic, and the creation of particles from energy and the reverse.
I take it you've never heard of conservation of momentum? You can not just turn the velocity into other things, you have to react it with something else (which is what I said - go back and read it). In this case they react it with a proton going the other way.
They could also react it with the earth, or a slab of metal.
None of these apply to a black hole.
We have also gotten way off topic from time dilation.
> The LHC collides TWO protons! The net velocity between them is zero.
Yes, but only because their original velocity has been converted into other forms of kinetic energy, like heat and light, among other things like Higgs bosons. Here is what you said:
> Kinetic energy does not become heat and light.
I proved your statement to be false. End of story. Now stop trolling.
Is this like some kind of contest to you to see if you win? Even if you win, you'll still be wrong.
Instead of focusing on that, why not actually learn something?
"To make heat and light you need some other process." For example, another proton to crash into. You can't just directly convert the velocity to energy, you need another object take the velocity from you.
Quote from the above article: "LIGO's detectors, at their current sensitivity, could pick up only gravitational waves of frequencies well above 10 Hertz. So if they have picked up a signal, they would have captured the final stages of the drama, when the black holes circle more than 10 times per second, speeding up to several thousand times a second just before they merge. Simulations show that the resulting waves, if played as an audible sound, resemble a bird’s ‘chirp’ (http://www.ligo.org/science/GW-Inspiral.php) (http://www.ligo.org/science/GW-Overview/sounds/chirp40-1300H...)."
My original remark from yesterday, to which you ignorantly objected: "... eventually two black holes will merge, which will produce a completely fantastic observation consisting of a rapidly rising frequency (as the two BHs circle each other closer and closer, shedding their orbital energy as gravitational waves), followed by a very loud cosmological pop as the BHs finally collapse into each other."
I have said exactly the same thing the entire time, only you kept ignoring it. Or, to be charitable, maybe just not understanding it. Just because you don't understand the words I said, doesn't mean I didn't say it.
Do you need me to quote myself?
Also, I take it you did not ever study physics? If you did you would know this on your own without me telling you.
What I said, over and over, is you can not turn velocity into light directly, you have to transfer that velocity to something else. In an event horizon there is nothing to transfer the velocity to, since everything is moving more or less at the same speed.
I don't know why you can't seem to absorb this. I really don't. It's basic highschool physics, plus I've said it over and over and over and over. In as many different ways as I can think of.
> Apart from the fact that heat and light are kinetic energy.
Are you totally incapable of absorbing information? I know that sounds insulting, but I am serious. You keep saying the same wrong thing over and over despite being told different.
You are wrong. Period.
It's like you have a mental block stopping you from understanding this, I don't get it.
> ... eventually two black holes will merge, which will produce a completely fantastic observation consisting of a rapidly rising frequency (as the two BHs circle each other closer and closer, shedding their orbital energy as gravitational waves), followed by a very loud cosmological pop as the BHs finally collapse into each other."
Back to this, very nice. The problem is that they won't actually do this - time dilation means it will take infinite time for this to happen, so we'll never see this.
Not sure what the point of telling you this is though. If you can't understand Conservation of Momentum there is zero chance you'll understand relativity.
Try this - stop arguing with me. Clearly I'm not the teacher for you.
Go find some other people - show them this thread if you like. Then have them explain Conservation of Momentum to you. Also ask them to explain the difference between kinetic and electromagnetic energy.
Please do that before replying, otherwise we'll just be going in a circle.
> I have said exactly the same thing the entire time
This is a lie -- you keep changing your claim to keep up with the facts other people provide you with. Examples below.
> What I said, over and over, is you can not turn velocity into light directly, you have to transfer that velocity to something else.
That's not what you said originally, and you are now lying. You said that "Kinetic energy does not become heat and light. Kinetic energy is velocity." Both statements are false (velocity is one of many examples of kinetic energy but the reverse claim is an error of omission), and I provided the literature references, which you refused to read.
You earlier said:
> Friction might cause objects to equalize in velocity, but can not actually reduce velocity (only share it amongst the objects).
Totally false -- velocity is not conserved, energy is conserved. There's no conservation of velocity law. If you were a scientist, if you knew anything about physics and possessed intellectual integrity, you would drop a lump of clay, watch it abruptly stop at the floor as it efficiently converts velocity into heat. Or two billiard balls on a collision course, or two protons at the LHC, etc. etc..
> Clearly I'm not the teacher for you.
"The teacher?" You're utterly ignorant and a narcissist to boot. You're severely mentally ill, unfortunately there's no cure for malignant narcissism (https://en.wikipedia.org/wiki/Malignant_narcissism).
We're done -- you have to learn this on your own without embarrassing yourself further in this public forum. Have a nice day.
> velocity is not conserved, energy is conserved. There's no conservation of velocity law
But there is, it's called Conservation of Momentum. It's velocity times mass. Go look it up - it will take just a few seconds on google. I'll wait.
> you would drop a lump of clay, watch it abruptly stop at the floor as it efficiently converts velocity into heat
No, it transferred its velocity to the entire planet.
> Or two billiard balls on a collision course
One has positive velocity, the other negative. They cancel out.
But go try making two billiard balls stop when they are both going the same way (as in your example about particles near the event horizon). You can't. Try it - maybe it will help. You have to transfer the velocity to something else.
> We're done -- you have to learn this on your own without embarrassing yourself further in this public forum. Have a nice day.
Oh, we were done ages ago.
One you do learn some physics you'll recall this conversion and cringe in embarrassment, not at your ignorance, but at your refusal to learn.
Your attempt at "diagnosing me" doesn't perturb me, because I know this stuff backward and forwards. Your obstinacy just amuses me. This stuff is so basic your comments are just laughable.
"One you do learn some physics you'll recall this conversion and cringe in embarrassment, not at your ignorance, but at your refusal to learn."
Just FYI, your conversational partner's website says:
"Paul Lutus has a wide background in science and technology. He designed spacecraft components for the NASA Space Shuttle and created a mathematical model of the solar system used by the Jet Propulsion Laboratory during the Viking Mars mission."
Am I sure? I've done no verification. But while I'm occasionally frustrated with the holder of that account I've seen no particular reason to believe that they are not who they claim to be. I am sure that the account holder claims to be Paul Lutus, as the link is on his profile.
'How is it possible that someone with a "wide background in science" has not heard about conservation of momentum?'
It's probably not; but this comment thread (wading through the jibes, snipes, and nonsense) doesn't seem to demonstrate with much clarity that he hasn't.
I appreciate that you refuse to accept an explanation until it completely makes sense to you, but it sounds like you're attached at a gut level to some basic misconceptions. (In particular: it's not just that local clocks appear to run at different rates, it's that ticks of two separated clocks do not always have a meaningful one-to-one mapping, so it's often not possible to assign a sensible time that a particular event happens according to a clock held by an outside observer.) Those misconceptions won't be cleared up unless you're staring the math in the face.
Grab an intro GR textbook and work through it. There are free ones online.
I did, after I studied it more is when I realized black holes can't form. That's when I found that others have noticed it to, and called it an "eternally collapsing object" (ECO).
> so it's often not possible to assign a sensible time that a particular event happens according to a clock held by an outside observer.
That's not completely accurate. The two can not assign the SAME time to some event happening - it might happen at different times for the two.
But it IS possible to say when the even will happen from ONE of their points of view. It just might not be the same time as what the other one sees.
NB I haven't studied it at all, beyond a high school level AP class touching on special relativity 20 years ago. That said, this was spinning in my head last night and now totally makes sense to me. From the faller's perspective time slows down until the black hole evaporates in front of you (Hawking radiation), leaving you in a universe a billion years in the future. Or if the hole is eternal, you get crushed by every particle ever destined for that black hole hitting you at once (since the rest of the universe speeds up from your perspective). Not to mention the inward-facing part of your brain would not be able to send signals to the outward-facing part, so you'd be pretty screwed there too.
That said, I doubt physicists would have overlooked this for 100 years when they pretty consistently say you'd fall into the hole unscathed and not even know you'd passed the horizon, so I'm sure this is wrong.
Hawking radiation is just spontaneous quantum particle pairs caused by the strong gravitational field, where one reaches escape velocity, reducing the mass of the object. This would still occur, whether you call it Hawking radiation or not.
Yes, I'm well aware of the reasons to dispute the reality of the manifold patch corresponding to the interior of the BH, which are based directly on the arguments I gave above. But this
> But it IS possible to say when the even will happen from ONE of their points of view. It just might not be the same time as what the other one sees
is again demonstrating that you don't understand how time coordinates work in GR. There is not a unique way to extent an observer's proper time to a time coordinate on an entire manifold, and different extensions are incompatible. Some of those extensions, as I said, give a finite time for BH formation.
I think you're more interested in axe-grinding that teaching or learning, so I'm going to call it quits on this one.
> Why do people just seem to completely ignore relativity when dealing with black holes?
It's true that, at and below the event horizon, spacetime curvature is such that time hasn't its usual meaning, but this doesn't mean two BHs cannot orbit closer and closer and eventually merge. Such events take place primarily outside the event horizon. This video --
-- diagrams stars orbiting close to the BH said to be at the center of our galaxy (in fact these orbits give us an estimate of the BH's mass).
So if stars can orbit a BH, then a BH can orbit a BH, and the latter would orbit in normal spacetime, at least until the merger.
> Because of time dilation this merger will take infinite time.
Only from the perspective of the event horizon and below. Remember that "above" the event horizon, time still has its usual meaning, even though it's greatly modified compared to time on Earth's surface (which is also slightly dilated in GR).
> But they will take infinite time to actually merge though.
Yes, from the perspective of a distant observer. From the perspective of an observer falling into the BH, time will pass in the usual way, indeed it must.
> The closer they get to that event horizon the slower time goes, so they will take longer and longer to orbit.
Only from the perspective of a distant observer. This might explain why black holes last as long as they do, from the perspective of a distant observer. For all we know, they all blow up in short order from the perspective of an observer falling into one.
> If, us, that distant observer, never see the black holes merge, then what does that mean for the gravity waves?
The black holes don't need to merge to create gravity waves, they only need to orbit each other. It turns out that all orbiting bodies create gravity waves, but in most cases the waves are too weak to detect. For black holes, because of their great mass and sometimes close separation, there is a good chance they will create detectable gravity waves.
The idea is, if there are no gravity waves, then two black holes could orbit forever with the same separation (no loss of energy). But if gravity waves are real, then the black holes will eventually merge, due to the loss of energy the waves represent.
There is already good indirect evidence for gravity waves:
The idea here is that the period of orbiting pulsars will change due to the loss of energy represented by the gravity waves. In some cases we can see the change of orbital period, and it's consistent with the expected energy of the gravitational waves (which have not been directly observed).
"In 2014, researchers on another US experiment, called BICEP2, [0] called a press conference to announce the discovery of gravitational waves, but others have since pointed out that the signal could be due entirely to space dust."
The BICEP2 team thought they detected gravitational waves with their Cosmic Microwave Background (CMB ) measurements from their Antarctic observatory.[0],[1],[2] By chance the ESA had the Planck observation satellite measuring a broader spectrum. Matching the two observations the BICEP2 measurements were capturing light interference from space dust in-between the observatory and the source. [3]
If gravitational waves are found, this will be the biggest thing since Smoot and COBE [4] and confirmation of the Gurth Inflation theory. [5]
> The BICEP2 team thought they detected gravitational waves with their Cosmic Microwave Background (CMB ) measurements from their Antarctic observatory. By chance the ESA had the Planck observation satellite measuring a broader spectrum. Matching the two observations the BICEP2 measurements were capturing light interference from space dust in-between the observatory and the source.
This is a bit different, though. BICEP2 was claiming a detection of a polarization signal in the cosmic microwave background, which if present, would point to existence of primorial gravitational waves resulting from cosmic inflation. But, as you note, the multi-wavelength observations of Planck (not taken by chance, but part of a carefully planned all-sky survey with somewhat coarser resolution compared to BICEP2) showed that the polarization signal measured by BICEP2 was consistent with foreground dust, rather than primordial gravitational waves.
> If gravitational waves are found, this will be the biggest thing since Smoot and COBE and confirmation of the Gurth Inflation theory.
It will be huge, but the gravitational waves LIGO would detect are not primordial or from inflation, but rather from supernovae and compact binary mergers (neutron star pairs, stellar-mass black hole pairs, etc.). So a LIGO gravitational wave detection would not provide any evidence for or against inflation. But it would tell us a lot about stellar explosions and the evolution of compact binaries.
EDIT: I should note that LIGO could detect or place constraints on some "exotic" gravitational wave sources – cosmic strings, for example.
"It will be huge, but the gravitational waves LIGO would detect are not primordial or from inflation, but rather from supernovae and compact binary mergers (neutron star pairs, stellar-mass black hole pairs, etc.)."
I missed this. How do they tell the difference? (Interferomety?)
Generally, the difference is direct vs indirect detection. LIGO aims to directly detect gravitational waves as they pass Earth by measuring the change in length of two parallel arms (using interferometry). In contrast, BICEP2 was looking for a polarization signal in the cosmic microwave background (CMB) which would occur if there were primordial gravitational waves (but this signal could also be mimicked by foreground dust).
So BICEP2's claimed detection wasn't a direct detection of gravitational waves. BICEP2 detected polarization (specifically B-mode polarization[0]) in the CMB. The BICEP2 team initially thought the amount of foreground dust was too low to explain the degree of polarization they observed, so they attributed the polarization to primordial gravitational waves affecting the cosmic microwave background. As you noted, Planck had multiple bands and so could more effectively determine the amount of foreground dust. Using a joint BICEP2+Planck dataset, the teams determined the signal could be explained by foreground dust.
In contrast, LIGO is attempting to directly measure gravitational waves from:
1) discrete, individual events, such as a merger of neutron stars. As the objects inspiral, they emit gravitational waves, with the emission becoming stronger (and, presumably higher frequency) as the objects near final merger. At final coalescence, a burst of gravitational waves is emitted. It is hoped/expected that this burst (plus some GW emission leading up to the merger) will be detected by LIGO for individual sources.
2) A gravitational wave background from the ensemble of events too far away to detect individually, but whose sum adds up to enough to be detectable. In contrast to the above, this will be some linear combination of all the passing waves from distant individual events, from a variety of directions.
The frequency of the gravitational waves depends on the bodies involved. With LIGO's 2km arms, it is sensitive to a range of frequencies which correspond to expectations for stellar-mass compact binaries. The LISA project[1] would have longer baselines and so would be sensitive to mergers of more massive objects, such as supermassive black hole pairs. So, the baseline of your gravitational wave experiment determines what you can possibly measure. This graphic shows at which frequencies various phenomena emit[2]. Based on that graphic, LIGO may be sensitive to the frequencies corresponding to primordial gravitational waves, but they are likely far far below LIGO's detection ability. My impression is that direct detection of primordial gravitational waves will not be possible for a while, if ever. Rather, they may be detected indirectly, via the imprint they leave on the CMB polarization (as BICEP2 tried).
By the way, I should have mentioned that we already have indirect evidence for gravitational waves, from the orbital decay of binary pulsars such as PSR B1913+16 [0]. The observed orbital decay has an excellent match with the orbital decay predicted using general relativity and gravitational waves. [1] shows the agreement, with the line being a theoretical prediction and not a fit.
Off-topic, but if anyone has a chance to go tour the LIGO facilities, definitely take it! It is a very interesting experience, and highly educational, even for those that don't have a physics background. I've been to the one in Livingston while studying at LSU, and even after several years, I'm still astounded at the precision of the technology used there.
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[ 2.8 ms ] story [ 127 ms ] threadAssuming the registration was made public, one could mandate that something had to be produced from the study, if only a statement that nothing was found.
Wouldn't solve the problem but would presumably aid meta-studies?
In any case, if the observatories are actually able to detect gravitational waves and if there are no theoretical obstacles, eventually two black holes will merge, which will produce a completely fantastic observation consisting of a rapidly rising frequency (as the two BHs circle each other closer and closer, shedding their orbital energy as gravitational waves), followed by a very loud cosmological pop as the BHs finally collapse into each other.
Yes, absolutely, I only meant that initial evaluations might be more objective if the two observatories cannot compare notes (at first) -- that might lead to a kind of confirmation bias. Only after one observatory satisfies itself that they have a sufficiently unambiguous signal should they be allowed to correlate with the other observatory's results.
Considering the absence of plausible signals to date, this idea might be bending over backwards to avoid observational bias.
That might be true in principle, but considering what's at stake, I think the investigators will bend over backward to avoid making a claim that isn't ironclad. Remember that in real science, investigators look for explanations that will falsify their results, and only give credence to results that resist sincere efforts at falsification. (Contract this to the outlook of a pseudoscientist, who only looks for reasons to confirm his results.)
Remember the incident in which some investigators claimed that neutrinos were exceeding the speed of light? In truth, they were looking for reasons to confirm their result, not falsify it. They were wrong, the real cause was a bad connection and ... they were pressured to resign their positions.
https://en.wikipedia.org/wiki/Faster-than-light_neutrino_ano...
> ... the collaboration can't be expected to do full, detailed analysis of false signals a dozen times a year.
That's true, but they could instead choose a handful of genuinely peculiar signals, signals unlikely to have natural causes, and try to falsify those.
As above, there are a handful of cosmological sources that would produce -- not a brief signal -- but a pattern of signals, like a rising tone created by merging black holes. Those would be more interesting, as well as being easier to compare to false terrestrial sources.
I've heard this so many times, and I still don't see how it's possible! Because of time dilation this merger will take infinite time.
No one has ever explained this satisfactorily to me. Why do people just seem to completely ignore relativity when dealing with black holes?
The problem with this argument is that there is no preferred global time coordinate with respect to which you declare that "the BH has formed". Rather, the spacetime events corresponding to "each dust particle crosses their mutual horizon" (i.e., "the formation of the BH"), along with the rest of the interior of the BH, comprise an additional spacetime region you can choose to attach to your manifold or not. This is a free choice because causality flows one-way across the boundary; no experiments outside the BH can be sensitive to whether the region "really" exists. There are multiple ways to extend the normal time coordinates (at infinity) into the interior of the BH, and a natural choice is the proper time of in-falling particles/observers. In that case, the BH definitely forms at a finite values of that time coordinate.
Merging two existing BHs doesn't introduce new fundamental issues. Quantum mechanics does introduce new fundamental issues, but formally the jury is still out on whether it resolves this question. The majority opinion is that the interior of the BH exists just as much as regions beyond your cosmological horizon (in an expanding cosmology) exist, from which you are likewise causally disconnected
I know. No one has ever explained how those can form either.
> From the outside, this is indistinguishable from a BH for all practical purposes
Except without the physics breaking properties of black holes. So not the same at all.
> The problem with this argument is that there is no preferred global time coordinate with respect to which you declare that "the BH has formed".
I don't need a global time, my own time frame is perfectly fine with me. If a black hole can never form, as viewed by me, then black holes don't exist.
> This is a free choice because causality flows one-way across the boundary
This presupposes the black hole exists already, but we have not gotten there yet. First it has to form, and it can not.
> and a natural choice is the proper time of in-falling particles/observers. In that case, the BH definitely forms at a finite values of that time coordinate.
It gets interesting here - what does happen from the POV of that particle? I suspect it never sees a black hole. This particle is moving exponentially close to the speed of light, relative to the center of mass of the forming black hole.
This means that time is stopped for the center of mass of the black hole from the POV of the particle, which means the center of mass can never form a black hole since it can never do anything at all (since time is stopped for it).
But they do -- the evidence is copious:
http://www.galacticcenter.astro.ucla.edu/animations.html
Arguing that, because the event horizon collapses the time dimension (from the perspective of a distant observer), therefore BHs aren't real, is like saying that sum(2^-n,(n,1,oo)) can't equal 1 because it's an infinite series and an infinity of additions takes too long.
Think of black holes as objects of great mass, that have very bright accretion disks, surrounding an event horizon that is perpetually almost forming a singularity but never quite completes it (from the perspective of someone far from the horizon).
> This means that time is stopped for the center of mass of the black hole ...
From the perspective of a distant observer, the time horizon is located at the event horizon.
The evidence is non-existent. The only evidence is for supermassive objects, not event horizons.
> Arguing that ... BHs aren't real, is like saying ... an infinite series and an infinity of additions takes too long.
That's a terrible argument. One is an actual physical process, the other is a mathematical abstraction. Do you not understand infinity? Infinity means you can't actually do it. It doesn't mean you can't calculate it.
> Think of black holes as objects of great mass, that have very bright accretion disks, surrounding an event horizon that is perpetually almost forming a singularity but never quite completes it (from the perspective of someone far from the horizon).
Eh? If it never forms a singularity, it has no event horizon. i.e. it has none of the physic breaking properties of black holes.
And accretion disks don't have to be bright BTW, as stuff falls in time dilation makes them much less bright (they "slow down", and emit photons less often).
> From the perspective of a distant observer, the time horizon is located at the event horizon.
When I say center of mass of the black hole I am naming the object I am talking about, not describing the location of the time horizon. Sorry if it was confusing.
> The evidence is non-existent.
If you're familiar with Occam's razor, you know that, for a given phenomenon, the simplest explanation is to be preferred. There certainly are massive objects at the center of most galaxies, and the most economical explanation is that they're black holes. No one is closing the book on these ideas -- that would be unscientific -- but there is strong evidence that these things are black holes.
That they exist is beyond question. That they have super-high masses confined to a small space is beyond question. General Relativity then fills in the blanks in our observations.
> That's a terrible argument. One is an actual physical process, the other is a mathematical abstraction.
So is General Relativity. But because nature follows the same rules, General Relativity accurately predicts many aspects of reality (certainly not all).
> And accretion disks don't have to be bright BTW ...
Well, yes, they do -- they're giving up a huge amount of gravitational potential energy, and that energy must be conserved -- it's converted to kinetic energy, it becomes heat and light.
Consider a satellite in an elliptical orbit. At the orbital apoapsis, potential energy is highest and kinetic energy is lowest. Not surprisingly, this is the point of smallest velocity. Now consider periapsis -- it's the reverse: lowest potential energy, highest kinetic energy, therefore highest velocity.
In a normal planetary elliptical orbit with no friction, even though the two kinds of energy are constantly changing, they sum to a constant at each point in the orbit, so there's no net dissipation of energy. But as matter falls into a black hole, in order for it to pass through the event horizon, it must give up most of its energy (both potential and kinetic). Most of that energy is converted into heat and light.
Most accretion disks preserve the rotational momentum of the infalling mass, so they're in the form of disks surrounding the event horizon. In theory, mass could fall directly into the BH without any rotation -- in that case, there would still be a huge energy conversion process and much radiated energy. Sp accretion disks are very bright.
Here's a graphic of the imagined BH from "Interstellar", thought to be fairly accurate as movie graphics go:
http://www.wired.com/2014/10/astrophysics-interstellar-black...
> Eh? If it never forms a singularity, it has no event horizon.
Yes, and by the same reasoning, because a Calculus limit expression never gets to its limit, therefore Calculus is bunk. My point? Just as (1+1/n)^n approaches e as n approaches infinity (http://www.wolframalpha.com/input/?i=limit+n+-%3E+inf%2C+%28...), a black hole approaches its final form as mass approaches it from the perspective of a distant observer.
You might as well have argued that, because this classic-physics gravitational equation:
f = (G m1 m2) / r^2
assumes that all the mass is a dimensionless point at the center of the central body, therefore if m1 and m2 occupy the same point in space, the result is infinite, therefore (because infinity isn't a number) Newtonian gravitation is bunk.
That is just not true. To be a black hole it must first be possible for black holes to exist, otherwise they are simply supermassive object - to us they would look EXACTLY the same!
A black hole is NOT the simplest explanation! It's the most complicated one. You are using your razor very incorrectly.
> That they exist is beyond question.
Absolutely not true. That massive objects exist? Sure. Are they black holes? Not so clear.
> That they have super-high masses confined to a small space is beyond question. General Relativity then fills in the blanks in our observations.
No, actually General Relativity does NOT fill in the blanks - it claims things are impossible. The math does the equivalent of divide by zero.
> So is General Relativity. [a mathematical abstraction]
Great, so since GR predicts it would take infinite time, I guess case closed. Since infinite time, by definition, can not actually happen, it means black holes can not form. Just because you can calculate what something will do doesn't mean it will actually do it.
> Well, yes, they do -- they're giving up a huge amount of gravitational potential energy, and that energy must be conserved -- it's converted to kinetic energy, it becomes heat and light.
Kinetic energy does not become heat and light. Kinetic energy is velocity. To make heat and light you need some other process. Have you never heard of conservation of momentum?
On top of that, the discs are dim because time is dilated to nothing not because there is no energy there.
> But as matter falls into a black hole, in order for it to pass through the event horizon, it must give up most of its energy (both potential and kinetic). .... in that case, there would still be a huge energy conversion process .... Most of that energy is converted into heat and light.
How in the world are you writing this stuff? You can't just "give up" velocity. You have to transfer that velocity to something else. You can't just wave your hands and say "magic". Friction might cause objects to equalize in velocity, but can not actually reduce velocity (only share it amongst the objects).
> a black hole approaches its final form as mass approaches it from the perspective of a distant observer.
And takes infinite time to do so, and since right now is not infinitely in the future, right now, today, black holes do not exist.
Infinite. Do you not understand that word? It means forever, it means it never actually does it, just gets closer and closer.
> therefore if m1 and m2 occupy the same point in space, the result is infinite, therefore (because infinity isn't a number) Newtonian gravitation is bunk.
Nice question, wrong conclusion. The actual conclusion is that since infinity is not actually seen in the real world (as opposed to math), there must be some method that prevents the two masses from ever occupying the same spot.
Your argument is entirely backward, you think that if infinity shows up in the math then it must show up in the real world. No. If infinity shows up in the math then your math is wrong, or incomplete. In this case there is something else that prevents r from hitting zero.
Maybe you should read this: https://en.wikipedia.org/wiki/Domain_of_a_function
> Kinetic energy does not become heat and light.
So have you told the LHC people that they're misguided for thinking they can produce the Higgs Boson by colliding protons together? I'm sure you can persuade them how wrong they are.
> Kinetic energy is velocity.
Yes, among many other things: http://physics.info/energy/ (see the table "Types of kinetic energy")
Electromagnetic energy (heat and light) is a kind of kinetic energy.
But you know what? I've decided not to try to correct all the errors you've made. If you actually understood physics, you wouldn't have objected to the things you have (you might have found a better reason to object).
> Friction might cause objects to equalize in velocity, but can not actually reduce velocity ...
Wow. Those fools in Europe are sure misguided to have spent so much money on a circular 17 mile pipe dream. if only they had consulted with you before building that monstrous contraption. They actually think their gadget can convert near-light-speed velocities into many other kinds of energy, including electromagnetic, and the creation of particles from energy and the reverse. Do them a favor -- set them straight, as you've set me straight.
The LHC collides TWO protons! The net velocity between them is zero.
You seem to know at least some physics, how can you possibly not know this?
But in your black hole scenario there are not two opposite velocities adding up at the horizon.
You can not just directly turn velocity into light, it's not possible, you need another object.
> Electromagnetic energy (heat and light) is a kind of kinetic energy.
Some people define only two kinds of energy: Potential and Kinetic, in that definition electromagnetic energy is a type of kinetic energy, and velocity is a type of kinetic energy.
But it does NOT follow that electromagnetic energy is the same as velocity energy!
It's like an apple is a fruit and an orange is a fruit, but an apple is not an orange.
> They actually think their gadget can convert near-light-speed velocities into many other kinds of energy, including electromagnetic, and the creation of particles from energy and the reverse.
I take it you've never heard of conservation of momentum? You can not just turn the velocity into other things, you have to react it with something else (which is what I said - go back and read it). In this case they react it with a proton going the other way.
They could also react it with the earth, or a slab of metal.
None of these apply to a black hole.
We have also gotten way off topic from time dilation.
Yes, but only because their original velocity has been converted into other forms of kinetic energy, like heat and light, among other things like Higgs bosons. Here is what you said:
> Kinetic energy does not become heat and light.
I proved your statement to be false. End of story. Now stop trolling.
You most certain did not.
Is this like some kind of contest to you to see if you win? Even if you win, you'll still be wrong.
Instead of focusing on that, why not actually learn something?
"To make heat and light you need some other process." For example, another proton to crash into. You can't just directly convert the velocity to energy, you need another object take the velocity from you.
> Kinetic energy does not become heat and light.
Now:
> "To make heat and light you need some other process."
Translation: "You were right." Apart from the fact that heat and light are kinetic energy.
Further reading: http://www.scientificamerican.com/article/gravitational-wave...
Quote from the above article: "LIGO's detectors, at their current sensitivity, could pick up only gravitational waves of frequencies well above 10 Hertz. So if they have picked up a signal, they would have captured the final stages of the drama, when the black holes circle more than 10 times per second, speeding up to several thousand times a second just before they merge. Simulations show that the resulting waves, if played as an audible sound, resemble a bird’s ‘chirp’ (http://www.ligo.org/science/GW-Inspiral.php) (http://www.ligo.org/science/GW-Overview/sounds/chirp40-1300H...)."
My original remark from yesterday, to which you ignorantly objected: "... eventually two black holes will merge, which will produce a completely fantastic observation consisting of a rapidly rising frequency (as the two BHs circle each other closer and closer, shedding their orbital energy as gravitational waves), followed by a very loud cosmological pop as the BHs finally collapse into each other."
I have said exactly the same thing the entire time, only you kept ignoring it. Or, to be charitable, maybe just not understanding it. Just because you don't understand the words I said, doesn't mean I didn't say it.
Do you need me to quote myself?
Also, I take it you did not ever study physics? If you did you would know this on your own without me telling you.
What I said, over and over, is you can not turn velocity into light directly, you have to transfer that velocity to something else. In an event horizon there is nothing to transfer the velocity to, since everything is moving more or less at the same speed.
I don't know why you can't seem to absorb this. I really don't. It's basic highschool physics, plus I've said it over and over and over and over. In as many different ways as I can think of.
> Apart from the fact that heat and light are kinetic energy.
Are you totally incapable of absorbing information? I know that sounds insulting, but I am serious. You keep saying the same wrong thing over and over despite being told different.
You are wrong. Period.
It's like you have a mental block stopping you from understanding this, I don't get it.
> ... eventually two black holes will merge, which will produce a completely fantastic observation consisting of a rapidly rising frequency (as the two BHs circle each other closer and closer, shedding their orbital energy as gravitational waves), followed by a very loud cosmological pop as the BHs finally collapse into each other."
Back to this, very nice. The problem is that they won't actually do this - time dilation means it will take infinite time for this to happen, so we'll never see this.
Not sure what the point of telling you this is though. If you can't understand Conservation of Momentum there is zero chance you'll understand relativity.
Try this - stop arguing with me. Clearly I'm not the teacher for you.
Go find some other people - show them this thread if you like. Then have them explain Conservation of Momentum to you. Also ask them to explain the difference between kinetic and electromagnetic energy.
Please do that before replying, otherwise we'll just be going in a circle.
This is a lie -- you keep changing your claim to keep up with the facts other people provide you with. Examples below.
> What I said, over and over, is you can not turn velocity into light directly, you have to transfer that velocity to something else.
That's not what you said originally, and you are now lying. You said that "Kinetic energy does not become heat and light. Kinetic energy is velocity." Both statements are false (velocity is one of many examples of kinetic energy but the reverse claim is an error of omission), and I provided the literature references, which you refused to read.
You earlier said:
> Friction might cause objects to equalize in velocity, but can not actually reduce velocity (only share it amongst the objects).
Totally false -- velocity is not conserved, energy is conserved. There's no conservation of velocity law. If you were a scientist, if you knew anything about physics and possessed intellectual integrity, you would drop a lump of clay, watch it abruptly stop at the floor as it efficiently converts velocity into heat. Or two billiard balls on a collision course, or two protons at the LHC, etc. etc..
> Clearly I'm not the teacher for you.
"The teacher?" You're utterly ignorant and a narcissist to boot. You're severely mentally ill, unfortunately there's no cure for malignant narcissism (https://en.wikipedia.org/wiki/Malignant_narcissism).
We're done -- you have to learn this on your own without embarrassing yourself further in this public forum. Have a nice day.
But there is, it's called Conservation of Momentum. It's velocity times mass. Go look it up - it will take just a few seconds on google. I'll wait.
> you would drop a lump of clay, watch it abruptly stop at the floor as it efficiently converts velocity into heat
No, it transferred its velocity to the entire planet.
> Or two billiard balls on a collision course
One has positive velocity, the other negative. They cancel out.
But go try making two billiard balls stop when they are both going the same way (as in your example about particles near the event horizon). You can't. Try it - maybe it will help. You have to transfer the velocity to something else.
> We're done -- you have to learn this on your own without embarrassing yourself further in this public forum. Have a nice day.
Oh, we were done ages ago.
One you do learn some physics you'll recall this conversion and cringe in embarrassment, not at your ignorance, but at your refusal to learn.
Your attempt at "diagnosing me" doesn't perturb me, because I know this stuff backward and forwards. Your obstinacy just amuses me. This stuff is so basic your comments are just laughable.
Just FYI, your conversational partner's website says:
"Paul Lutus has a wide background in science and technology. He designed spacecraft components for the NASA Space Shuttle and created a mathematical model of the solar system used by the Jet Propulsion Laboratory during the Viking Mars mission."
Are you sure it's the same person?
'How is it possible that someone with a "wide background in science" has not heard about conservation of momentum?'
It's probably not; but this comment thread (wading through the jibes, snipes, and nonsense) doesn't seem to demonstrate with much clarity that he hasn't.
Grab an intro GR textbook and work through it. There are free ones online.
> so it's often not possible to assign a sensible time that a particular event happens according to a clock held by an outside observer.
That's not completely accurate. The two can not assign the SAME time to some event happening - it might happen at different times for the two.
But it IS possible to say when the even will happen from ONE of their points of view. It just might not be the same time as what the other one sees.
That said, I doubt physicists would have overlooked this for 100 years when they pretty consistently say you'd fall into the hole unscathed and not even know you'd passed the horizon, so I'm sure this is wrong.
There would not be Hawking radiation since the black hole has not formed.
> That said, I doubt physicists would have overlooked this for 100 years
Other people have noticed this too: https://en.wikipedia.org/wiki/Eternally_collapsing_object
It doesn't seem to get as much attention, I think because there is less interesting math there to do research on.
> But it IS possible to say when the even will happen from ONE of their points of view. It just might not be the same time as what the other one sees
is again demonstrating that you don't understand how time coordinates work in GR. There is not a unique way to extent an observer's proper time to a time coordinate on an entire manifold, and different extensions are incompatible. Some of those extensions, as I said, give a finite time for BH formation.
I think you're more interested in axe-grinding that teaching or learning, so I'm going to call it quits on this one.
It's true that, at and below the event horizon, spacetime curvature is such that time hasn't its usual meaning, but this doesn't mean two BHs cannot orbit closer and closer and eventually merge. Such events take place primarily outside the event horizon. This video --
http://www.galacticcenter.astro.ucla.edu/animations.html
-- diagrams stars orbiting close to the BH said to be at the center of our galaxy (in fact these orbits give us an estimate of the BH's mass).
So if stars can orbit a BH, then a BH can orbit a BH, and the latter would orbit in normal spacetime, at least until the merger.
> Because of time dilation this merger will take infinite time.
Only from the perspective of the event horizon and below. Remember that "above" the event horizon, time still has its usual meaning, even though it's greatly modified compared to time on Earth's surface (which is also slightly dilated in GR).
> Remember that "above" the event horizon, time still has its usual meaning
The closer they get to that event horizon the slower time goes, so they will take longer and longer to orbit.
Yes, from the perspective of a distant observer. From the perspective of an observer falling into the BH, time will pass in the usual way, indeed it must.
> The closer they get to that event horizon the slower time goes, so they will take longer and longer to orbit.
Only from the perspective of a distant observer. This might explain why black holes last as long as they do, from the perspective of a distant observer. For all we know, they all blow up in short order from the perspective of an observer falling into one.
If, us, that distant observer, never see the black holes merge, then what does that mean for the gravity waves?
The black holes don't need to merge to create gravity waves, they only need to orbit each other. It turns out that all orbiting bodies create gravity waves, but in most cases the waves are too weak to detect. For black holes, because of their great mass and sometimes close separation, there is a good chance they will create detectable gravity waves.
The idea is, if there are no gravity waves, then two black holes could orbit forever with the same separation (no loss of energy). But if gravity waves are real, then the black holes will eventually merge, due to the loss of energy the waves represent.
There is already good indirect evidence for gravity waves:
https://en.wikipedia.org/wiki/Gravitational_wave
The idea here is that the period of orbiting pulsars will change due to the loss of energy represented by the gravity waves. In some cases we can see the change of orbital period, and it's consistent with the expected energy of the gravitational waves (which have not been directly observed).
http://www.ligo.org/news/blind-injection.php
The BICEP2 team thought they detected gravitational waves with their Cosmic Microwave Background (CMB ) measurements from their Antarctic observatory.[0],[1],[2] By chance the ESA had the Planck observation satellite measuring a broader spectrum. Matching the two observations the BICEP2 measurements were capturing light interference from space dust in-between the observatory and the source. [3]
If gravitational waves are found, this will be the biggest thing since Smoot and COBE [4] and confirmation of the Gurth Inflation theory. [5]
[0] http://www.theguardian.com/science/2014/mar/17/primordial-gr...
[1] https://www.cfa.harvard.edu/CMB/bicep2/
[2] https://www.cfa.harvard.edu/CMB/bicep2/science.html
[3] http://www.theguardian.com/science/2014/sep/22/gravitational...
[4] http://aether.lbl.gov/www/projects/cobe/ and https://en.wikipedia.org/wiki/George_Smoot
[5] http://www.nytimes.com/2014/03/18/science/space/detection-of...
This is a bit different, though. BICEP2 was claiming a detection of a polarization signal in the cosmic microwave background, which if present, would point to existence of primorial gravitational waves resulting from cosmic inflation. But, as you note, the multi-wavelength observations of Planck (not taken by chance, but part of a carefully planned all-sky survey with somewhat coarser resolution compared to BICEP2) showed that the polarization signal measured by BICEP2 was consistent with foreground dust, rather than primordial gravitational waves.
> If gravitational waves are found, this will be the biggest thing since Smoot and COBE and confirmation of the Gurth Inflation theory.
It will be huge, but the gravitational waves LIGO would detect are not primordial or from inflation, but rather from supernovae and compact binary mergers (neutron star pairs, stellar-mass black hole pairs, etc.). So a LIGO gravitational wave detection would not provide any evidence for or against inflation. But it would tell us a lot about stellar explosions and the evolution of compact binaries.
EDIT: I should note that LIGO could detect or place constraints on some "exotic" gravitational wave sources – cosmic strings, for example.
I missed this. How do they tell the difference? (Interferomety?)
So BICEP2's claimed detection wasn't a direct detection of gravitational waves. BICEP2 detected polarization (specifically B-mode polarization[0]) in the CMB. The BICEP2 team initially thought the amount of foreground dust was too low to explain the degree of polarization they observed, so they attributed the polarization to primordial gravitational waves affecting the cosmic microwave background. As you noted, Planck had multiple bands and so could more effectively determine the amount of foreground dust. Using a joint BICEP2+Planck dataset, the teams determined the signal could be explained by foreground dust.
In contrast, LIGO is attempting to directly measure gravitational waves from:
1) discrete, individual events, such as a merger of neutron stars. As the objects inspiral, they emit gravitational waves, with the emission becoming stronger (and, presumably higher frequency) as the objects near final merger. At final coalescence, a burst of gravitational waves is emitted. It is hoped/expected that this burst (plus some GW emission leading up to the merger) will be detected by LIGO for individual sources.
2) A gravitational wave background from the ensemble of events too far away to detect individually, but whose sum adds up to enough to be detectable. In contrast to the above, this will be some linear combination of all the passing waves from distant individual events, from a variety of directions.
The frequency of the gravitational waves depends on the bodies involved. With LIGO's 2km arms, it is sensitive to a range of frequencies which correspond to expectations for stellar-mass compact binaries. The LISA project[1] would have longer baselines and so would be sensitive to mergers of more massive objects, such as supermassive black hole pairs. So, the baseline of your gravitational wave experiment determines what you can possibly measure. This graphic shows at which frequencies various phenomena emit[2]. Based on that graphic, LIGO may be sensitive to the frequencies corresponding to primordial gravitational waves, but they are likely far far below LIGO's detection ability. My impression is that direct detection of primordial gravitational waves will not be possible for a while, if ever. Rather, they may be detected indirectly, via the imprint they leave on the CMB polarization (as BICEP2 tried).
[0] https://en.wikipedia.org/wiki/Cosmic_microwave_background#Po...
[1] http://lisa.nasa.gov/
[2] https://en.wikipedia.org/wiki/File:The_Gravitational_wave_sp...
EDIT: Added new first paragraph and reworded the rest for clarity/flow.
By the way, I should have mentioned that we already have indirect evidence for gravitational waves, from the orbital decay of binary pulsars such as PSR B1913+16 [0]. The observed orbital decay has an excellent match with the orbital decay predicted using general relativity and gravitational waves. [1] shows the agreement, with the line being a theoretical prediction and not a fit.
[0] https://en.wikipedia.org/wiki/PSR_B1913%2B16
[1] https://en.wikipedia.org/wiki/PSR_B1913%2B16#/media/File:PSR...