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Black Hole Merger & Gravity Waves

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 lowersharpnose 21 Feb 2016
I have read a bit about recent news of the detection of gravity waves from the merger of two black holes.

It is stated that ~3 solar masses was converted to GWs in a fraction of a second. This mass is the difference between the masses of the two black holes before and the resultant mass after merger.

Where did this mass come from - inside or outside the event horizons?
 sbc_10 21 Feb 2016
In reply to lowersharpnose:

Outside I presume. Otherwise you would be getting some kind of 'information' from inside the event horizon. Are these gravitational waves the result of space-time distorting as a result of mass being converted into energy??



 EdH 21 Feb 2016
In reply to lowersharpnose:

The energy is mostly coming from inside the event horizons (actually, there's some subtleties about energy in general relativity, but I think this is the right physical picture). Despite this, the gravity waves aren't actually extracting any information from inside the event horizons: the shape/ size of them is fixed by stuff outside. So there's no contradiction.

Related is that the information stored in a black hole is proportional to its surface area (this is not at all obvious, but there's good reasons to think its true!). On the other hand the radius of a black hole is proportional to its total mass. So even though the new bigger black hole has a smaller mass than the sum of the two initial ones, there's still plenty of "space" to store the information trapped in the initial ones!
In reply to EdH:

Can I not just sit on a bench watching the sunset and the waves whilst eating some chips?

(Sorry really will shut up now)
 Trevers 21 Feb 2016
In reply to sbc_10:

> Outside I presume. Otherwise you would be getting some kind of 'information' from inside the event horizon. Are these gravitational waves the result of space-time distorting as a result of mass being converted into energy??

The gravitational waves ARE the mass converted to energy. Think of it as gravitational radiation, as an analogue to electromagnetic radiation.

It's the gravitational waves that distort space-time as they pass through.
 Trevers 21 Feb 2016
In reply to Eeyore:

> Can I not just sit on a bench watching the sunset and the waves whilst eating some chips?

> (Sorry really will shut up now)

The laws of physics don't prohibit this so yes.
In reply to Trevers:


> The laws of physics don't prohibit this so yes.

Never was good at physics, a grade E confirms that. I'll settle for being happy.

(not yet midnight)
 felt 22 Feb 2016
In reply to EdH or Trevers or anyone who might know:

A couple of questions from the layperson:

1. I read that this event for 20 microsecs (?) or something gave out more watts than the combined light output of all the stars in the visible universe (this number being, as I understand it, 100 billion galaxies with 100 billion stars each in them; so a lot of stars, a sort of yottaosram) for the same period. Given that these holes are at the end of the day not that big -- three suns? -- how can that possibly be the case?

2. It seems fishy to me that the moment this machine is switched on we somehow manage to catch the biggest event ever in the history of everything. Isn't this akin to never watching telly, then finding one in the attic, switching it on and just coinciding with us winning the Eurovision Song Contest or the World Cup or similar?
 summo 22 Feb 2016
In reply to felt:
> 2. It seems fishy to me that the moment this machine is switched on we somehow manage to catch the biggest event ever in the history of everything.

it's not the biggest event ever, we can't actually see the edge of the universe in any direction, we have only been able to detect anything in the universe for the briefest of timescales, it is only big because it is the first event of it's kind for a human being to detect them. They also have masses of data that they still need to analyse, this event was in September the lead in to confirm the event takes time. The machines are off now for upgrades and others will being built that are more sensitive, news like this will just become the norm in a few decades.
Post edited at 06:25
In reply to felt:

The black holes where about 30 solar masses each, so those three solar masses are ~3 out of 60.

All of the three solar masses was converted in GWs in a fraction of a second, that is why it briefly emitted more energy that the rest of the galaxy put together.

A doubling of LIGO's sensitivity results in an 8-fold increase in the volume of space that can be searched. AIUI, LIGO had just been mad ~6 times more sensitive, whihch meant it was searching 216 times the volume of space that it was previously.

 felt 22 Feb 2016
In reply to lowersharpnose:

> All of the three solar masses was converted in GWs in a fraction of a second, that is why it briefly emitted more energy that the rest of the galaxy put together.

The figure I saw was not "the whole of the galaxy" but the whole of *all* the galaxies. Perhaps this was mistaken?

"radiated away at a peak rate of about 3.6×10 [superscript]49 watts – a level greater than the combined power of all light radiated by all the stars in the observable universe."
https://en.wikipedia.org/wiki/First_observation_of_gravitational_waves
 EdH 22 Feb 2016
In reply to felt:

For 1 it's because it happens so fast! Say the sun converts 1/100th its mass to energy over a lifetime of 10 billion years (its generating energy by fusion so only a fraction of its mass ever gets released as energy), whereas the black hole merger converts about 1 solar mass to energy over 0.01 seconds. Then the power of the black hole is equivalent to about (10 billion years)/(0.01 seconds)*100 suns , which comes out as the merger giving off the same power as 10^21 stars. This is about the same as the number of stars in the observable universe, so we're in roughly the right region.

For 2, there's still lots of uncertainty about how often these events happen. Before the detector was switched on they expected to see this size event at most about once a year, and probably a little bit less frequently than that. So, it could be that they just got lucky when they first turned it on, or maybe the astrophysical models used to predict how often these things happen are a bit off. There's lots of messy modelling of galaxies etc. involved, so the predictions may well not be so good.
 Trevers 22 Feb 2016
In reply to felt:

> 1. I read that this event for 20 microsecs (?) or something gave out more watts than the combined light output of all the stars in the visible universe (this number being, as I understand it, 100 billion galaxies with 100 billion stars each in them; so a lot of stars, a sort of yottaosram) for the same period. Given that these holes are at the end of the day not that big -- three suns? -- how can that possibly be the case?

This event is regarded as the most powerful ever witnessed (i.e not the most energetic). We can work it out with some back-of-an-envelope calculations. I'm going to use 0.5s as the time period for the observations since the graphs in the publication cover roughly that period:
http://journals.aps.org/prl/pdf/10.1103/PhysRevLett.116.061102

1 solar mass (Ms) = 2x10^30kg. The radiated energy equivalent of 3Ms is 1.8x10^47 Joules (using E=mc^2). So the average power output is 3.6x10^47 Watts!

The Sun produces energy through nuclear fusion: A simplified version of the process is that 4 Hydrogen nuclei (single protons) come together and fuse to form a Helium nucleus (2 protons, 2 neutrons). The mass of the Helium nucleus is approximately 99.25% the mass of the original protons. The energy comes from the missing 0.75%.

Let's assume that during The Sun's main sequence lifetime, 10% of the Hydrogen gets converted to Helium. That's 0.00075Ms over 10 billion years. Compare with our black holes: (3/0.00075) x 10x10^9 x 365.25 x 24 x 3600 x 2. Averaged across the half second I used, our black hole merger was 2.5 x 10^21 times more powerful than The Sun (2.5 thousand billion billion).

If we approximate our Universe as consisting of 100 billion galaxies containing 100 billion Sun-like stars, then the average power output of our black hole merger is a quarter of the power output of the rest of the observable Universe. When we consider that the power output of the black hole merger was not uniform over the split-second but rose to a peak, then we can see that, for a small fraction of a second, it was more powerful than everything else put together.

> 2. It seems fishy to me that the moment this machine is switched on we somehow manage to catch the biggest event ever in the history of everything. Isn't this akin to never watching telly, then finding one in the attic, switching it on and just coinciding with us winning the Eurovision Song Contest or the World Cup or similar?

Well it tells us something about our Universe - that black hole mergers are perhaps more common than we previously thought. That's why this new window we have on the Universe is so exciting, there are many incredible discoveries waiting to be made. Apparently there are some more announcements in the works from LIGO, I can't wait
 felt 22 Feb 2016
In reply to EdH and Trevers:

OK, good, thanks, I sort of get that now.

If I might ask another question -- and keeping with the World Cup analogy -- once it's been broadcast live the thing's all over (or they think it is, but there are repeats, highlights packages, &c, &c). But with this gravitational wave, won't the wave keep on coming for a long time -- for ever -- like some endless electromagnetic tsunami on YouTube, so we could catch it any time we wanted? Or is it that if our machines had blinked they would have missed it, like when you go to put the kettle on and miss the winning goal?
 wercat 22 Feb 2016
In reply to Trevers:
Would it not be more correct to say that the gravitational waves represent part of the conversion? There must have been a terrific amount of photonic radiation at sundry wavelengths. I might be terribly wrong, as perhaps it all hapened silently in the em spectrum and all the output was indeed spacetime perturbance.

Do we totally understand what happens to two merging event Horizons? Is there a point at which they would be disrupted enough for escape of electromagnetic waves as well?
Post edited at 09:08
 Trevers 22 Feb 2016
In reply to felt:

> OK, good, thanks, I sort of get that now.

> If I might ask another question -- and keeping with the World Cup analogy -- once it's been broadcast live the thing's all over (or they think it is, but there are repeats, highlights packages, &c, &c). But with this gravitational wave, won't the wave keep on coming for a long time -- for ever -- like some endless electromagnetic tsunami on YouTube, so we could catch it any time we wanted? Or is it that if our machines had blinked they would have missed it, like when you go to put the kettle on and miss the winning goal?

It is a case of blink and you miss it. The black holes would have been orbiting each other for (thousands/millions/billions) of years (deleted as applicable because I don't know) but it was only the final split second that was powerful enough for us to detect. Think of it as like a distant flash of light (except it's gravitational radiation, not electromagnetic). It's signal will continue to travel outwards at the speed of light, but it won't ever be detectable by us again.
 Trevers 22 Feb 2016
In reply to wercat:

> Would it not be more correct to say that the gravitational waves represent part of the conversion? There must have been a terrific amount of photonic radiation at sundry wavelengths. I might be terribly wrong, as perhaps it all hapened silently in the em spectrum and all the output was indeed spacetime perturbance.

For that, you'd need to ask someone much smarter than me!

If the black holes had considerable accretion disks, then there would have been some powerful EM radiation (but at those astronomical distances, perhaps too faint for us to see). I don't see why it would have necessarily peaked at the point of merger though.

As for anything more exotic, you'll need to ask Stephen Hawking.

The other problem is that our GW detection doesn't allow us to pinpoint where in the sky the waves were received from, so we'd have no idea where to train our telescopes!
 digby 22 Feb 2016
In reply to Trevers:

> The other problem is that our GW detection doesn't allow us to pinpoint where in the sky the waves were received from, so we'd have no idea where to train our telescopes!


I thought it did? The differing amounts of distortion in the 90 degree arms giving a vague indication of direction. When there are more detectors the accuracy will increase.
 Dauphin 22 Feb 2016
In reply to Trevers:

also EdH


Thanks for your input into this thread. Fascinating explanations, I thought the GW would continue to 'reverberate' around the universe and LIGO managed to pick up one of these echoes. Truly incredible that this death rattle of colliding black holes was picked up so soon.

D
 Trevers 22 Feb 2016
In reply to digby:

> I thought it did? The differing amounts of distortion in the 90 degree arms giving a vague indication of direction. When there are more detectors the accuracy will increase.

There are currently two LIGO detectors at opposite ends of the USA (Hanford and Livingston). Their slightly different orientations (due to the curvature of the Earth) give us some idea of orientation, but it's not nearly accurate enough to tell us exactly where on the sky we need to look (at those distances we're looking for a point source).

To get that kind of high resolution, we'd need a detector with 3 arms in x-y-z directions.

If eLISA goes ahead then the resolution we'll get from that will dwarf LIGO!
https://en.wikipedia.org/wiki/Evolved_Laser_Interferometer_Space_Antenna
 Trevers 22 Feb 2016
In reply to Dauphin:

> Thanks for your input into this thread. Fascinating explanations, I thought the GW would continue to 'reverberate' around the universe and LIGO managed to pick up one of these echoes. Truly incredible that this death rattle of colliding black holes was picked up so soon.

Not at all. I enjoy thinking about these things, and to be honest I was a bit dubious about the claim that it was more powerful than the rest of the Universe combined, and wanted to check it out for myself!

It sounds like you're thinking of the Microwave Background Radiation which is (in very simplified terms) an electromagnetic echo of the Big Bang which pervades the entire visible Universe.
 Coel Hellier 22 Feb 2016
In reply to felt:

> 2. It seems fishy to me that the moment this machine is switched on we somehow manage to catch the biggest event ever in the history of everything.

The point is that LIGO is the first detector capable of detecting such things. It is capable of detecting them out to a very large distance, so even if they are rare (in terms of events per galaxy) they could be common enough when sampling out to large distances.
 CurlyStevo 22 Feb 2016
In reply to Trevers:
I think that assumes the universe is definitely finite something I've always doubted ( and some respected astrophysicists doubt.).

I'm happy to see recently that the big bang theory has had some major doubt thrown over it, that's always seemed like an awful bodge of a theory to me and instinctively I don't believe any / much of it.
Post edited at 10:27
1
 Coel Hellier 22 Feb 2016
In reply to CurlyStevo:

> I'm happy to see recently that the big bang theory has had some major doubt thrown over it, ...

That's not really true. There are always discussions about different *variants* of the Big Bang model, but the basic model itself is pretty secure and has only got better supported as evidence has accumulated.
 Coel Hellier 22 Feb 2016
In reply to CurlyStevo:

The first link is discussing whether the Big Bang might have arisen out of a pre-existing state. This is indeed possible but does not cast doubt on the Big Bang model itself.

The second link is about the BICEP2 results, which were indeed wrong, but again that does not cast doubt on the basic Big Bang model itself.
 Offwidth 22 Feb 2016
In reply to CurlyStevo:
So what?... healthy scepticism is part of science and a requirement of any scientific model is that it can be disproved. That doesn't mean the 'big bang' model has major problems. Although when we have gut instincts like yours available, maybe we shouldn't bother?
Post edited at 11:02
2
 CurlyStevo 22 Feb 2016
In reply to Coel Hellier:
Did you read the first article, or perhaps you are arguing semantics?

It Opens with
"Big Bang, Deflated? Universe May Have Had No Beginning
In the new formulation, the universe was never a singularity, or an infinitely small and infinitely dense point of matter. In fact, the universe may have no beginning at all.

Our theory suggests that the age of the universe could be infinite,"

The big bang theory relies on a moment of expansion from a very highly possibly infinitely dense state 13.8 billion years ago. This article is saying this may never have happened and we have no right to say it did.

It then goes on to discuss several issues to the way the existing theories have been applied to the big bang theory and why they don't hold up.

I believe the second study was highlighting the only known actual evidence for the big bang is highly dubious and should not be trusted. The rest of the theory seems based on some pretty loose observations that the big bang theory has been extrapolated from.
Post edited at 11:20
 Dave Garnett 22 Feb 2016
In reply to Trevers:
.

> As for anything more exotic, you'll need to ask Stephen Hawking.

Brilliantly explained and illustrated here:

http://www.bbc.co.uk/programmes/p03gl17j

http://www.bbc.co.uk/programmes/p03h9y3b
Post edited at 11:08
 tony 22 Feb 2016
In reply to CurlyStevo:



> etc

I think the key line you should take from the second link is:
"I think in retrospect, they should have been more careful about making a big announcement,"
 CurlyStevo 22 Feb 2016
In reply to tony:

Oh I agree and I'm not pretending to be an expert or indeed dismissing the science that has been done in this area. I'm just saying there does seem to be a fair amount of doubt coming from various angles regarding the big bang theory.
 malk 22 Feb 2016
In reply to Coel Hellier: a few questions if you don't mind

how would the effects on earth from a black-hole merger in our galaxy compare with a supernova?
why has the event not been located in the sky using other detection methods? (x/gamma bursts)
what would be the effect of a merger of something like this: http://www.astronomy.com/news/2016/01/signs-of-second-largest-black-hole-in... with the supermassive black hole at the centre of our galaxy?
ps what do you think about the galactic superwave theory of extinctions?
 Coel Hellier 22 Feb 2016
In reply to CurlyStevo:

> The big bang theory relies on a moment of expansion from a very highly possibly infinitely dense state 13.8 billion years ago. This article is saying this may never have happened and we have no right to say it did.

No, the article is not saying that. The article is saying that that Big Bang 13.8 billion years ago might have arisen from a prior state. That is not at all a rejection of the standard Big Bang model.

> I believe the second study was highlighting the only known actual evidence for the big bang is highly dubious ...

No, not at all, there are a large number of other lines of evidence for the Big Bang. The BICEP2 results in 2014 were put forward as *additional* support for the Big Bang model, but there is a vast array of other evidence for it.

The Big Bang model was very strongly established before the 2014 BICEP2 results, and is still very strongly established even though the BICEP2 results have been shown to be incorrect.
 Coel Hellier 22 Feb 2016
In reply to malk:
> how would the effects on earth from a black-hole merger in our galaxy compare with a supernova?

The black-hole merger is more energetic, but is not likely to do us any harm. But then a supernova in our galaxy would not harm us unless it were very close.

> why has the event not been located in the sky using other detection methods? (x/gamma bursts)

Possible answers are: it was (there is a possible claim of a coincident GRB), or that it was too faint in gamma rays.
Post edited at 11:42
 Matt Rees 22 Feb 2016
In reply to Coel Hellier:

Very interesting Coel. Am I right in thinking that this discovery is interesting partly because the detection of gravity waves is a new way to observe previously unobservable events that emit very little (nothing?) other than gravity waves, due to their being related to black holes. Sort of like discovering a new sense that one has never had. I'm simultaneously boggling and awestruck. Thanks for your explanation in advance.
 Trevers 22 Feb 2016
In reply to CurlyStevo:

> Did you read the first article, or perhaps you are arguing semantics?

> It Opens with

> "Big Bang, Deflated? Universe May Have Had No Beginning

> In the new formulation, the universe was never a singularity, or an infinitely small and infinitely dense point of matter. In fact, the universe may have no beginning at all.

> Our theory suggests that the age of the universe could be infinite,"

> The big bang theory relies on a moment of expansion from a very highly possibly infinitely dense state 13.8 billion years ago. This article is saying this may never have happened and we have no right to say it did.

> It then goes on to discuss several issues to the way the existing theories have been applied to the big bang theory and why they don't hold up.

> I believe the second study was highlighting the only known actual evidence for the big bang is highly dubious and should not be trusted. The rest of the theory seems based on some pretty loose observations that the big bang theory has been extrapolated from.

Big Bang theory has not been discredited. Big Bang theory states that the Universe is expanding from an earlier, much denser state and there's plenty of evidence for this.

The livescience link concerns itself with the point of origin of the Big Bang (singularity or otherwise). I don't think we're going to come close to an answer until we have a unified theory of General Relativity and Quantum Mechanics.
 Trevers 22 Feb 2016
In reply to Coel Hellier:

> The black-hole merger is more energetic, but is not likely to do us any harm. But then a supernova in our galaxy would not harm us unless it were very close.

> Possible answers are: it was (there is a possible claim of a coincident GRB), or that it was too faint in gamma rays.

Interesting! Do you have a link?
 Trevers 22 Feb 2016
In reply to Matt Rees:

> Very interesting Coel. Am I right in thinking that this discovery is interesting partly because the detection of gravity waves is a new way to observe previously unobservable events that emit very little (nothing?) other than gravity waves, due to their being related to black holes. Sort of like discovering a new sense that one has never had. I'm simultaneously boggling and awestruck. Thanks for your explanation in advance.

Spot on! Yes, it's a whole new field of astronomy.
 CurlyStevo 22 Feb 2016
In reply to Coel Hellier:
OK regarding the prior state. They are saying that the universe maybe infinitely old and that it was never a singularity and also we have no right to say it started with a big bang in the first place. I'm somewhat in the dark about what parts of the big bang theory are left?

Are you saying the study the report highlighted is still allowing for expansion and retraction to a small dense area but just not a singularity, but not an infinitely small and infinitely dense point of matter, nor indeed a bang / explosion?

This does cast doubt over some of the more established / touted branches of the big bang theory right?
Post edited at 12:12
 Robert Durran 22 Feb 2016
In reply to CurlyStevo:

> I think that assumes the universe is definitely finite something I've always doubted ( and some respected astrophysicists doubt.).

Am I right in thinking that an infinite universe is compatible with a big bang - if the universe is infinite then it must have been infinite at the time of the big bang (since you can't have infinite expansion in a finite time) and so the big bang happened everywhere at the same time and the universe is now just a much bigger infinity in size than it used to be.
 Coel Hellier 22 Feb 2016
In reply to Trevers:

> Interesting! Do you have a link?

"Fermi Gamma-ray Burst Monitor ... observations at the time of the Laser Interferometer Gravitational-wave Observatory (LIGO)event GW150914 reveal the presence of a weak transient source above 50 keV, 0.4 s after the GW event was detected, ... Its localization is ill-constrained but consistent with the direction of GW150914."

http://arxiv.org/abs/1602.03920
moffatross 22 Feb 2016
In reply to Trevers:

> There are currently two LIGO detectors at opposite ends of the USA (Hanford and Livingston). Their slightly different orientations (due to the curvature of the Earth) give us some idea of orientation, but it's not nearly accurate enough to tell us exactly where on the sky we need to look (at those distances we're looking for a point source).

> To get that kind of high resolution, we'd need a detector with 3 arms in x-y-z directions.

> If eLISA goes ahead then the resolution we'll get from that will dwarf LIGO!


--------------------------------

Me & the sproggies went to a Glasgow Astronomy Society public lecture about gravitational waves a few years ago at which laser interferometry was well discussed, and IIRC, space based detectors were thought to be the only practical method of triangulating for a signal in 3 dimensions i.e. an Earth based detector just doesn't have enough space to work in (and I don't think even eLISA will have much directional resolution other then perpendicular to its two planes). I'd guess a great big tetrahedron could work better in that respect than a triangle but assume there are practicalities that make a triangle much, much easier to manage i.e. it doesn't much matter how far detector nodes drift, just so long as they can see each other and know how far apart they are from each other.

A decent gravitational resolution in 3d might allow radio and optical telescopes to be quickly pointed in the right direction to 'see' more events such as supernovae etc happening in near real time rather than staring at the same bit of space and hoping to get lucky. Whatever, it'd be well spent money, and I guess could be piggy-backed with other instrumentation such as solar. Incidentally, I understand that Glasgow University have made quite a contribution to the field so far, and one of the sproggies who's now working towards an Astrophysics MSc there, told me there was quite a buzz throughout his faculty at the announcement.
1
 Coel Hellier 22 Feb 2016
In reply to CurlyStevo:

> I'm somewhat in the dark about what parts of the big bang theory are left?

The Big Bang model is about extrapolating back to when the observed universe was a very hot and very small region, 13.8 billion years ago, with our observable universe expanding out of that.

If you *then* start asking about what caused that Big Bang, and start thinking about how the Big Bang might have arisen out of a previous state, then that is not a rejection of the Big Bang model.

In the same way, if one were to say that you were born <whatever> years ago, and explain *your* origins that way, it is not in conflict with that if we then start asking about how things were before you were born and the events that led to your birth.

> They are saying that the universe maybe infinitely old ...

If the Big Bang originated from a prior state, then perhaps the "ensemble" is infinitely old while "our universe" originated in the Big Bang 13.8 billion years ago.

> ... and that it was never a singularity ...

Whether or not our universe originated in a singularity is not part of the standard Big Bang model, since we don't have physics to deal with that.

> we have no right to say it started with a big bang in the first place.

That depends on what you mean by "it". "Our universe" started in the Big Bang; there may have been a prior state.

> just not a singularity, but not an infinitely small and infinitely dense point of matter, ...

Those things have never been part of the standard Big Bang model.

> This does cast doubt over some of the more established / touted branches of the big bang theory right?

No.

For more on this see: http://profmattstrassler.com/2014/03/21/did-the-universe-begin-with-a-singu...
 Coel Hellier 22 Feb 2016
In reply to Robert Durran:

> if the universe is infinite then it must have been infinite at the time of the big bang ...

Yes.

> ... and so the big bang happened everywhere at the same time ...

It's not really physical to consider the Big Bang as happening everywhere simultaneously in an infinite extent, since that violates causality and the finite speed of transmission of information.

If the BB were caused by a quantum-gravity fluctuation in a pre-existing state, then the effect of that would be finite in extent. Thus, even though the region would then have expanded greatly through the inflationary era, it would still be finite.

Thus, whether the universe is spatially infinite is a different question from what the size of the region that participated in our Big Bang is.

I wrote about this stuff at: https://coelsblog.wordpress.com/2015/12/30/how-many-big-bangs-a-philosophic...
 Coel Hellier 22 Feb 2016
In reply to Matt Rees:

> Am I right in thinking that this discovery is interesting partly because the detection of gravity waves is a new way to observe previously unobservable events that emit very little (nothing?) other than gravity waves, due to their being related to black holes.

Yes, and not only black holes, but also neutron stars and white dwarf stars (which are also small and dense and so have strong gravity).

There are rumours -- which I think are indeed only rumours -- that LIGO is currently detecting "a lot" of events, and that the announced event was only the first.
 CurlyStevo 22 Feb 2016
In reply to Coel Hellier:
> If the Big Bang originated from a prior state, then perhaps the "ensemble" is infinitely old while "our universe" originated in the Big Bang 13.8 billion years ago.
> That depends on what you mean by "it". "Our universe" started in the Big Bang; there may have been a prior state.

I have to disagree on what you have extrapolated from the article here I'm afraid.

The article clearly states:

"the universe may not have started with a bang."
"So when we say that the universe begins with a big bang, we really have no right to say that," Brandenberger told Live Science."
"In fact, the universe may have no beginning at all."

> Those things have never been part of the standard Big Bang model.

Well even the article you linked says:
"The connection with some kind of singularity dates back to the original Big Bang idea,"

Also the article I linked says:
"Big Bang under fire

According to the Big Bang theory, the universe was born about 13.8 billion years ago. All the matter that exists today was once squished into an infinitely dense, infinitely tiny, ultra-hot point called a singularity. This tiny fireball then exploded and gave rise to the early universe.
"


Sure I had already read some of that article before, but cheers anyway.
Post edited at 13:03
 Coel Hellier 22 Feb 2016
In reply to CurlyStevo:

> The article clearly states: "the universe may not have started with a bang."

And this all depends on what one means by "the universe".

If by that one means the observable universe that we see around us, then everything we see did indeed originate in a Big Bang 13.8 billion years ago. That is very strongly established and is not being doubted.

However, if by "the universe" one means the ensemble of all things, including the possible pre-existing state from which our Big Bang might have originated, then clearly *that* would not have originated in our Big Bang.

But, anyhow, the Big Bang model is not at all under threat or being doubted. One can only think that if one mistakes what "the Big Bang model" refers to.
 malk 22 Feb 2016
In reply to Coel Hellier: just a quicky..

how do we know the physical constants haven't changed over time? can this be tested and how would this variation influence cosmological theories?
 CurlyStevo 22 Feb 2016
In reply to Coel Hellier:
Seems to me the Big Bang Model means different things to different researchers Which is what I meant about semantics.

If now you are talking about a possible expansion and retraction of some subset of a possibly infinite universe (spatially and mass), with possibly no explosion and no mention of a singularity, then I have less issues with it! However I don't see many websites describing this model so it must be quite cutting edge / niche.

I disagree with your take on the article, it mentioned nothing of a big bang in only observable space and clearly casts major doubt over notions of it having occurred at all generally.

"the universe may not have started with a bang."
"So when we say that the universe begins with a big bang, we really have no right to say that," Brandenberger told Live Science."
"In fact, the universe may have no beginning at all."
Post edited at 13:13
 Coel Hellier 22 Feb 2016
In reply to CurlyStevo:

> However I don't see many websites describing this model so it must be quite cutting edge / niche.

No, it's not, it's the mainstream way that cosmologists think about the Big Bang. See, for example, that Matt Strassler article.

> I disagree with your take on the article, it mentioned nothing of a big bang in only observable space ...

Yes it does: "Either way, the universe was once very, very small and hot. "The fact that there's a hot fireball at very early times: that is confirmed," Brandenberg told Live Science."

> ... and clearly casts major doubt over notions of it having occurred at all generally.

No it doesn't.
 Coel Hellier 22 Feb 2016
In reply to malk:
> how do we know the physical constants haven't changed over time? can this be tested and how would this variation influence cosmological theories?

Yes, this can be tested to quite an extent. E.g.: http://arxiv.org/abs/1501.00560

"Constraint on the time variation of the fine-structure constant with the SDSS-III/BOSS DR12 quasar sample"

" we investigate the possible variation of the fine-structure constant over cosmological time-scales. ... and obtain delta-alpha/alpha of (0.9 +/- 1.8) X 10^-5 for the relative variation of the fine-structure constant. "

If the constants did vary over time, then yes this would have an effect on cosmological models.
Post edited at 13:17
 CurlyStevo 22 Feb 2016
In reply to Coel Hellier:
"> I disagree with your take on the article, it mentioned nothing of a big bang in only observable space ..."

> Yes it does: "Either way, the universe was once very, very small and hot. "The fact that there's a hot fireball at very early times: that is confirmed," Brandenberg told Live Science."

Where does that mention it only occurring in CURRENTLY observable space (/ a subset of the universe)? or a big bang? That quote is saying the entire universe was once in a very very small hot area.

Post edited at 13:20
 Coel Hellier 22 Feb 2016
In reply to CurlyStevo:
> That quote is saying the entire universe was once in a very very small area.

And as I said, there is ambiguity over that one might mean by "universe".

1) "universe" = the observable universe that we see around us that originated in a Big Bang 13.8 billion years ago.

2) "universe" = ensemble of all things, including the possible pre-existing state from which our Big Bang might have originated.

The article you're reading can be faulted for confusing and failing to distinguish between these two concepts, and your reading of it is similarly confused.

[I think that article shows that, either the writer of it has not properly understood the distinction between those two concepts, or is deliberately trying to hype something as more radical than it is.]
Post edited at 13:26
 malk 22 Feb 2016
In reply to Coel Hellier:


> 2) "universe" = ensemble of all things, including the possible pre-existing state from which our Big Bang might have originated.

are you trying to avoid the b or the m word?

 Coel Hellier 22 Feb 2016
In reply to malk:

> are you trying to avoid the b or the m word?

"m word" = multiverse??

"b word" = ????
 CurlyStevo 22 Feb 2016
In reply to Coel Hellier:
OK fair enough I see now. The article was confused. I still think it was clearly saying there was no big bang even if the reporting was poor.

http://earthsky.org/space/what-if-the-universe-had-no-beginning

"Are you seeing the stories this week suggesting that the Big Bang didn£t happen? According to astrophysicist Brian Koberlein £ a great science communicator at Rochester Institute of Technology with a popular page on G+ £ that£s not quite what the new research (published in early February 2015 Physics Letters B, has suggested. The new study isn£t suggesting there was no Big Bang, Koberlein says. It£s suggesting that the Big Bang did not start with a singularity £ a point in space-time when matter is infinitely dense, as at the center of a black hole. How can this be? Koberlein explains on his website:"

Regarding this definition of universe (as only meaning the observable universe when unqualified) and big bang theory its the first I've heard or read about it. Its not something you come across as a lay person with some minor interest in the subject.
Post edited at 13:39
 malk 22 Feb 2016
In reply to Coel Hellier:
b=branes,bulk?
http://en.wikipedia.org/wiki/Brane_cosmology
Post edited at 13:36
 malk 22 Feb 2016
In reply to CurlyStevo:

this looks a good read- i do still cling to an idea of some cyclicity: http://www.scientificamerican.com/article/a-recycled-universe/
 CurlyStevo 22 Feb 2016
In reply to malk:
I personally think as humans we like to think we are much more advanced than we are. Yet we still don't know the cause of most disease or how to cure it. We don't actually understand things as simple as human nutrition and more complex things like DNA or the actual workings of the brain we are a comparatively a long way off from understanding properly IMO.

As for theoretical astrophysics whilst I'm sure its super interesting to be involved in, so much of it just seems completely hypothetical to me. I guess things do become more concrete over time and some of those concrete things may stand the test of time many will not. I just find it very very hard to accept much of this stuff as any more than some logical thinking applied to a lot of unknowns which over time will change, often radically. Are we really past the equivalent era of the earth is flat with much of this stuff yet?
Post edited at 14:03
3
 Trevers 22 Feb 2016
In reply to CurlyStevo:

> " It's suggesting that the Big Bang did not start with a singularity, a point in space-time when matter is infinitely dense, as at the center of a black hole. "

FWIW, we don't really know that there is a singularity at the center of a black hole do we, only that the mass of the object is contained within the Schwarzchild Radius? Wasn't there talk of the possibility of a quark degeneracy pressure that could be preventing a complete collapse within the event horizon? Singularities are one of those things that most physicists don't really like to thing about. It's a few years since I studied physics though...
 Trevers 22 Feb 2016
In reply to malk:

> this looks a good read- i do still cling to an idea of some cyclicity: http://www.scientificamerican.com/article/a-recycled-universe/

Theories of the multiverse are way beyond my comprehension both mathematically and conceptually. However, I think this is one of those areas where we need to be wary of being led by the desire for the Universe to be a certain way. Cyclic theories have an aesthetic, almost religious appeal, and are much less disturbing than for example the idea of the Heat Death of the Universe. Einstein himself was driven to folly by the desire for the Universe to conform to his preconceptions!
 malk 22 Feb 2016
In reply to CurlyStevo:
good points - eg it was only a few years ago that the standard-model zero cosmological constant was shown to be non-zero..
Post edited at 14:39
 EdH 22 Feb 2016
In reply to CurlyStevo:

I think physicists do a very bad job of distinguishing between things that are on a firm footing and very likely to be true and wild speculation. In my opinion the hierarchy is something like

- The observable universe was once much smaller and hot enough that electrons weren't bound to protons to form hydrogen: almost certainly true, we can directly observe the effects around us, the physics is totally under theoretical and experimental control, and it seems impossible to think of reasonable alternatives.
- Even earlier, the observable universe was even hotter so that protons weren't bound into nuclei: very very likely to be true, the physics is well understood, and tested in present day experiments, and the predictions match observations very well.
- Even earlier: the observable universe went through a period of inflation and its size was exponentially increased: the general idea is probably true (something like say 90% or 99% or something). It explains a number of observations very well, but as yet there's no theoretical model that is totally consistent. So there's lots of open questions about how to make in happen, and the exact form it takes etc.
- Right at the start there was actually a singularity in space-time: probably not true. Such a singularity is our theories telling us we're using them in a regime where they dont work any more. And when they do this, we should listen and stop using them!
- Ideas about alternatives to this singularity or stuff before/ outside space time etc.: total speculation. The only reasonable candidate for a theory of quantum gravity is string theory, and this is a long long way away from being able to answer these sorts of cosmological questions.

In general, I think it's a good idea to be sceptical about press releases on new theoretical breakthroughs, especially if it's talking about quantum gravity! They are by no means necessarily reliable...
 Trevers 22 Feb 2016
In reply to EdH:

> - Ideas about alternatives to this singularity or stuff before/ outside space time etc.: total speculation. The only reasonable candidate for a theory of quantum gravity is string theory, and this is a long long way away from being able to answer these sorts of cosmological questions.

String theory is also pretty much untestable, at least for the present day. It's also highly ad hoc and more of a mathematical abstraction than a workable theory of reality. When you're having to invoke multiple hidden dimensions, it suggests to me that somewhere along the line, some understanding is missing.

General Relativity may be as difficult for the layman to get their head around as string theory, but it is good, hard science.

The public understanding of physics also suffers from the fact that theories are both right and wrong, relativity and quantum mechanics being the obvious examples. Just because they break down for certain ranges of parameters, doesn't mean that they don't make very accurate predictions in other areas and that they don't give us powerful insight into the way the Universe works.
 Coel Hellier 22 Feb 2016
In reply to CurlyStevo:

> We don't actually understand things as simple as human nutrition ...

The main reason for that is that, for ethical reasons, we can't run the large-scale controlled trials that would be necessary to properly understand nutrition.

But. anyhow, humans are among the most complex things around, so why would human nutrition be "simple"?

> As for theoretical astrophysics whilst I'm sure its super interesting to be involved in, so much of it just seems completely hypothetical to me.

No, not really, it's mostly based on a lot of solid evidence.
 EdH 22 Feb 2016
In reply to Trevers:

hmm, I agree with the pretty much untestable (at least for the very forseeable future), disagree with the ad hoc part, and strongly agree that some understanding is missing! But then i spend some proportion of my life working on string theory, so am not exactly neutral
 Trevers 22 Feb 2016
In reply to EdH:

> hmm, I agree with the pretty much untestable (at least for the very forseeable future), disagree with the ad hoc part, and strongly agree that some understanding is missing! But then i spend some proportion of my life working on string theory, so am not exactly neutral

Ah brilliant, where do you study?

I guess you can see why it seems pretty impenetrable to the layman. I've got a good conceptual understanding of GR and QM (although I don't remember the maths so well any more). I'm well aware of the problems in trying to reconcile the two. Having never actually studied it, I can't see where string theory comes from, or how it does reconcile the two. Is it possible to understand it without in depth maths, and are there any good books/resources on it?
 Offwidth 22 Feb 2016
In reply to Trevers:

Einstein didn't much like the idea of god playing dice but in the end we need to turn "like" buttons off in science and build theories that best fit the evidence. Einstein's main theories were both beautiful and simple but try and name a person who claims to conceptually understand their full scope (as opposed to following the math). There is no rule that the model needs to be simple, fully understandable or currently testable. People who talk about understanding things and actually mean it are probably not true scientists (at least not under the Popperian system... the philosophical definition btw, not the sex drug version). The current favoured models are just the best available and are often highly complicated (especially in nutrition!).
2
 EdH 22 Feb 2016
In reply to Trevers:

I'm in Trieste at the moment (though sadly not permanently, academia being what it is...!)

QM + GR is a problem because when you go to high energies processes involving virtual particles become increasingly important. For spin 0 and 1/2 particles these virtual particles mean you end up with divergences in your answer (e.g. your answers have sums that dont converge), but usually there are only a finite number of divergences so you can deal with them. Spin 1 particles are already a bit tricky, and for the divergences to be under control, particles have to be gauge bosons (e.g. photon, gluon etc.) or made up of other lower spin particles. Spin 2, i.e. a graviton, is even worse and at high energies it's impossible to calculate anything like a scattering amplitude for it.

In string theory, the particles come from excitations of a string, so when you calculate processes involving virtual particles there's a maximum energy they can have. At higher energies the process is actually strings scattering off each other, and it turns out that the answers from this are finite, without any divergences. Effectively because of their extra dimension compared to particles interactions happen over some non-zero distance and the dangerous high energy, i.e. short distance, processes get sort of blurred out.

Alternatively from the high energy perspective looking down, you start off with a string theory that we think is a consistent quantum mechanical theory. Then you calculate what the behaviour at low energies looks like, and you see it automatically includes a spin 2 particle that couples exactly like a graviton. So by chance it seems like you've stumbled on a good high energy theory that reproduces known low energy physics.

One reason people find string theory interesting is that there are many places where it could have just totally failed and been mathematically inconsistent but instead turned out fine for some subtle reason. It's kindof hard to describe in words, but somehow lots of things fit together in a unexpected way that mean it does actually seem to work.

There are still many many problems with connecting string theory to the real world though, and also in understanding what the theory really is, and how to fully define it. I dunno if these will get solved soon, they seem very hard, but you never know. In general any sort of quantum gravity is probably an going to be hard to explicitly test, just because it's only important at very high energies. On resources, I think Matt Strassler's blog is relatively balanced about the pros and cons , e.g. http://profmattstrassler.com/2014/01/23/quantum-field-theory-string-theory-...
 Offwidth 22 Feb 2016
In reply to EdH:

I feel for you. There is so much post doc talent on rolling temp contracts at the moment in the UK (alongside mass dishonest use of ZHCs for those people who would much rather have a proper part-time or fractional contract). Blatant and damaging exploitation by a managerial class who clearly don't give a shit about furthering knowledge and HE education.
 Root1 23 Feb 2016
In reply to felt:


I suspect it will be 10^38 yrs before England win the world cup again.
 Trevers 23 Feb 2016
In reply to EdH:

Thanks for that, fascinating stuff.

So, do the equations of QM fall nicely out of the maths of string theory, or is it not quite so convenient as that?
 felt 23 Feb 2016
In reply to Root1:

> 10^38

Ah, so that's how you style it. Does 10*38 work too or does that mean something else, like just times?

 Trevers 23 Feb 2016
In reply to felt:

10*38 is 10x38 = 380

10^38 is 10 to the power of 38
 EdH 23 Feb 2016
In reply to Trevers:
You make the stings quantum mechanical by construction, then from this a consistent quantum mechanical graviton falls out automatically (and on top of this there's no other way to get a consistent QM graviton that we know of.)
Post edited at 12:37
 Trevers 23 Feb 2016
In reply to EdH:

> You make the stings quantum mechanical by construction, then from this a consistent quantum mechanical graviton falls out automatically (and on top of this there's no other way to get a consistent QM graviton that we know of.)

Thanks

From that blog link you provided, I can see that it's not quite so ad hoc as I thought. I might see if I can find a good undergrad-level lecture course online to work through in my spare time.
 wercat 23 Feb 2016
In reply to felt:

10**38 was equivalent to 10^38 in some, probably archaic, computer syntax ...
 felt 23 Feb 2016
In reply to wercat:

I wonder why * is used when X seems to do the job perfectly well. Was it from that time when kids needed to learn their times table but X meant 18?
 Trevers 23 Feb 2016
In reply to felt:

> I wonder why * is used when X seems to do the job perfectly well. Was it from that time when kids needed to learn their times table but X meant 18?

Because x (or any other letter, but particularly x) is used in algebra and geometry constantly. It would get pretty confusing! It also makes complete sense from a programming point of view.

I'll spare you the details of cross and dot products of vectors and matrices
 felt 23 Feb 2016
In reply to Trevers:

If that's the case, and I'll take your word that it is, it's a wonder it was used in the first place.
 Rob Parsons 23 Feb 2016
In reply to felt:

> If that's the case, and I'll take your word that it is, it's a wonder it was used in the first place.

There is never any ambiguity in either hand-writing, or in properly typeset mathematics.

The 'problems' occur when using limited typesetting - as happens when typing up plain text using a keyboard, or when writing a computer program. In other words, the usage 'problems' showed up centuries after the mathematical conventions were first established!
 felt 23 Feb 2016
In reply to Rob Parsons:

> never any ambiguity in either handwriting

Ah, so that's what I must have been doing when I used to write my algebraic xs like the Chanel symbol.
 wercat 23 Feb 2016
In reply to felt:

it's not the only case - Military communication manuals used to stress the need to put a stroke through a 0 (Zero symbol) to prevent confusion with O-Oscar. Seven was to be handwritten with a stroke the continental way to prevent confusion with either 1 or J. This practice was adopted in computing quite early (IBM 3270 terminals used to have a character set where the Zero had a little dot at the centre to prevent confusion with O, unforgettable if you've had to use one for any length of time). The consequences in radio or line communications or programming/data representation may be catastrophic if one symbol is mistaken for another.

 Trevers 23 Feb 2016
In reply to wercat:

> 10**38 was equivalent to 10^38 in some, probably archaic, computer syntax ...

Thanks for reminding me about fortran
 wercat 24 Feb 2016
In reply to Trevers:
or 8080 assembler?

some would say :

"Old,

Not Obsolete.."

(reference to archaism, not **)
Post edited at 08:36
 DancingOnRock 24 Feb 2016
In reply to Rob Parsons:

Yes.

a=exp will give you a different result to a=e*p
 felt 24 Feb 2016
In reply to wercat:

> it's not the only case - Military communication manuals used to stress the need to put a stroke through a 0 (Zero symbol) to prevent confusion with O-Oscar. Seven was to be handwritten with a stroke the continental way to prevent confusion with either 1 or J.

Interesting. How was 5 distinguished from S, and 1 from either l or I?
 wercat 24 Feb 2016
In reply to felt:

I seem to remember some old manuals for morese operators that had a prescribed way of writing/forming letters. Number confusion was perhaps worse as alphabetics may have been thought less confused by context and number confusion could easily result in a message going to the wrong addressee or an incorrect timing or grid being read by the recipient
 Robert Durran 24 Feb 2016
In reply to wercat:

> I seem to remember some old manuals for morese operators that had a prescribed way of writing/forming letters.

Never before can a thread on here have mutated from something so fantastically interesting to something so fantastically dull.......
 felt 24 Feb 2016
In reply to Robert Durran:

Funny, I was thinking exactly the opposite.
 Robert Durran 24 Feb 2016
In reply to felt:

> Funny, I was thinking exactly the opposite.

What? You find man made arbitrary and trivial conventions more interesting than the majestic wonders of the cosmos?
 felt 24 Feb 2016
In reply to Robert Durran:

Yes, man is infinitely fascinating, and the cosmos lies within our brains. Having said that, I do like a nice bit of Hubble on the side at the weekend.
 wercat 24 Feb 2016
In reply to Robert Durran:
Both involve history. I find history interesting as well as the cosmos and computer science and quarks.

As an aside I also find the analogies between machine control and communications in the internet age and human communications command and control quite interesting.


As well as people's tendency to unnecessary offence.
Post edited at 14:50
 Robert Durran 24 Feb 2016
In reply to felt:

> .......the cosmos lies within our brains.

Eh, anything but. I think you are a bit confused.
 Trevers 24 Feb 2016
In reply to wercat:

> As well as people's tendency to unnecessary offence.

Arsehole
 wercat 24 Feb 2016
In reply to Trevers:

Oh well, we all have to make allowances!

Mind you it would have been quite justifiable to be telt off fer bean irreverlent which is an objective truth, rather than bean boren, which is rather subjectif
 Offwidth 24 Feb 2016
In reply to felt:

What about those of us who see it as a fun and interesting side-track of a really good thread?
 felt 24 Feb 2016
In reply to Offwidth:

No, quite, that's exactly my feeling; with my "exactly the opposite" I was hardly being serious, merely contrary towards someone introducing the first negative comment to what had been till then a remarkably polite and interesting thread.
 Trevers 24 Feb 2016
In reply to Offwidth:

> What about those of us who see it as a fun and interesting side-track of a really good thread?

I think it was an interesting aside. Only threads rarely seem to get back on track once they've been sidetracked

Gravitational waves are still blowing my little mind
 Brass Nipples 24 Feb 2016
In reply to Trevers:

You need to get a gravitational wave board, the surf is great...

 Robert Durran 24 Feb 2016
In reply to felt:
> No, quite, that's exactly my feeling; with my "exactly the opposite" I was hardly being serious, merely contrary towards someone introducing the first negative comment to what had been till then a remarkably polite and interesting thread.

Oh come on! It was just a harmless observation and in no way intended to be contentious; to be perfectly honest it never occurred to me that anyone could be so dull of mind as to disagree. No harm in the diversion about conventions for writing letters, but please have some perspective!


Anyway, can we get back to the wonders of the cosmos now please?
Post edited at 21:15
 wercat 24 Feb 2016
In reply to Robert Durran:
O Come on yourself - you carelessly try to cause offence and then accuse responders of being dull minded - Really, that is the way playground bullying is conducted - cause a stir and then accuse others of being in the wrong. Shame on you!

Get perspective yourself!

Now, the Cosmos ...
Post edited at 21:33
 Robert Durran 24 Feb 2016
In reply to wercat:
> O Come on yourself - you carelessly try to cause offence and then accuse responders of being dull minded.

Please read my post again. I didn't in any way try to cause offense; I sincerely didn't believe anyone could be so dull minded or lacking in perspective to be offended. Apologies if I made a misjudgement.
Post edited at 21:42
1
 Trevers 24 Feb 2016
In reply to lowersharpnose:

If it helps placate everyone, this is a piece of astrophysics from last year that blew my mind:

It's the formation of a star system 450 light years from Earth. That's fairly close in our Galaxy. Star systems form as vast disks of gas an dust, most of which condenses into the star in the centre. Planets form out of the rest of it and sweep out the remaining material as they orbit their parent star. It's a pretty violent process, rocks and asteroids flying all over the place, occasionally a planet even getting knocked out of it's course and flying into the parent star or off into interstellar space.

Anyway, they managed to capture a photo of the damn thing:

http://www.bbc.co.uk/news/science-environment-29932609

Amazing!
 wercat 24 Feb 2016
In reply to Robert Durran:

Accepted, but you do need to be careful with barbed hooks! They can get stuck
In reply to Robert Durran:

that's quite a non-apology apology, Robert!

 Robert Durran 24 Feb 2016
In reply to no_more_scotch_eggs:

> that's quite a non-apology apology, Robert!

>

Shhhhh...... I'm not sure whether I'm relieved or disappointed to have apparently got away with it........
 felt 25 Feb 2016
In reply to Robert Durran:

Hmm, I'll say no more, but only because I respected your uncle.
 Robert Durran 25 Feb 2016
In reply to felt:

> Hmm, I'll say no more, but only because I respected your uncle.

Because, deep down, you know he would have agreed with me?

Did he teach you maths?
 malk 25 Feb 2016
In reply to Robert Durran:

as a physicist, i'm with felt
 Robert Durran 25 Feb 2016
In reply to malk:
> as a physicist, i'm with felt

A dull minded physicist are you?

I'm more of a mathematician - it would be like finding the conventions for writing a multiplication symbol and an x more interesting than the whole of group theory. Only a fantastically dull minded mathematician would think like that.

Or the correct spelling of "benefitted" more interesting than the complete works of Shakespeare.........

I really genuinely cannot believe there is anything to discuss here.
Post edited at 13:41
 felt 25 Feb 2016
In reply to Robert Durran:

JHD, occasionally terrifying.

 Robert Durran 25 Feb 2016
In reply to felt:

> JHD, occasionally terrifying.

I believe that his ape impression which could go on for a disconcertingly long time was really quite disturbing in a classroom.
 felt 25 Feb 2016
In reply to Robert Durran:

Yes, but hey, this must be really dull for the others, much more so, dare I say, than arbitrary symbols, which have a considerable following.
 Robert Durran 25 Feb 2016
In reply to felt:

> Yes, but hey, this must be really dull for the others, much more so, dare I say, than arbitrary symbols, which have a considerable following.

You have a point, but my uncle was anything but dull (did you mountaineer with him?)

But yes, the thread should get back to gravity waves.
 felt 25 Feb 2016
In reply to Robert Durran:

No I did not, sadly, as I had no idea he was a latterday RLG Irving. But I've just reacquainted myself with the man by reading his kaleidoscopic account of the 75 Olympiad. Pithy.
 wercat 25 Feb 2016
In reply to Robert Durran:
good you used the word apparently!

by the way the interesting stuff is not the convention but the reason for it and, in military circles, the possible consequences of the errors it seeks to correct. "Send three and fourpence" and all that ..
Post edited at 18:02
 wercat 25 Feb 2016
In reply to no_more_scotch_eggs:

"that's quite a non-apology apology, Robert!"

that's why I added my rider to it! I feel a sanction coming on

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