
Physicists Detect Gravitational Waves, Proving Einstein Right - intull
http://www.nytimes.com/2016/02/12/science/ligo-gravitational-waves-black-holes-einstein.html
======
ScottBurson
This made me wonder how far we are from being able to create and detect
gravitons. The Wikipedia page on gravitons [0] addresses this question:

 _Unambiguous detection of individual gravitons, though not prohibited by any
fundamental law, is impossible with any physically reasonable detector. The
reason is the extremely low cross section for the interaction of gravitons
with matter. For example, a detector with the mass of Jupiter and 100%
efficiency, placed in close orbit around a neutron star, would only be
expected to observe one graviton every 10 years, even under the most favorable
conditions. [...]

However, experiments to detect gravitational waves, which may be viewed as
coherent states of many gravitons, are underway (such as LIGO and VIRGO).
Although these experiments cannot detect individual gravitons, they might
provide information about certain properties of the graviton. For example, if
gravitational waves were observed to propagate slower than c (the speed of
light in a vacuum), that would imply that the graviton has mass [...]._

Fascinating! I take it that the question of whether the graviton could have
mass is now considered to be well answered in the negative.

[0]
[https://en.wikipedia.org/wiki/Graviton](https://en.wikipedia.org/wiki/Graviton)

~~~
sandworm101
If gravitons have mass, then the universe is too strange to exist. Gravity is
an interaction that defines the presence of matter (see dark matter). For the
object that transmits that force between masses to itself have mass ... how
can a black hole then project gravity?

Imho whatever is carrying gravity between masses cannot itself have a mass.

~~~
contravariant
Force carrying particles in general don't have mass. Except that some of them
seem to do, which was rather puzzling for some time, but was solved using the
Higgs mechanism.

I can't think of an obvious reason the Higgs mechanism wouldn't work for
gravitons, but I could be mistaken, it's not exactly the most intuitive area
of physics.

Also, keep in mind that the strong force transmits the force between colour
charges while also having a colour charge itself, so it isn't entirely
inconceivable for the force transmitting the attraction between masses to have
a mass.

No clue if a massive graviton would allow for black holes, but it's not
entirely sure what black holes even are (especially quantum mechanically). At
the very least it's presumably possible for _some_ particles to escape it
(e.g. as Hawking radiation).

~~~
purpled_haze
> Force carrying particles in general don't have mass.

Massless particles don't have energy. Massless and energyless particles have
no speed. I have no interest in massless and energyless particles that stand
still.

~~~
cyphar
Photons are massless particles that have energy. All massless particles travel
at the speed of light.

~~~
purpled_haze
Protons are said to be massless, but a proton may have mass that is so small
that we cannot measure it easily. We can't currently say with 100% certainty
that it is massless- only that it is at most very, very small: < 1×10−18 eV/c2

~~~
Jweb_Guru
What? Protons most definitely have mass.

~~~
dwaxe
They obviously meant photons

~~~
purpled_haze
Yes, fingers kept typing wrong word.

------
pavpanchekha
I remember learning about the LIGO experiment back when it was being built, a
decade ago, and at the time it seemed so amazing: a giant tube of vacuum,
sealed underground and so sensitive that it could detect animals walking
nearby, listening to the moving and twisting of space itself… I guess we're
finally seeing that with immense human ingenuity and the most careful of
engineering, the universe will offer its secrets up to us.

This also means that between LIGO and ATLAS/CMS, the last few years have
screwed in the final screws on two of the big physics advances of the 20th
century: quantum field theory and general relativity are now both
experimentally complete, and both look nearly unassailed in their correctness.
The next steps for physics look increasingly abstruse: understanding the
exceptional cases, like black holes, holography, and the fundamentally
computational form of the universe. It's an exciting time, and it looks more
and more like we're close to the very bottom, since we have to look so far now
to find anything outside our models.

~~~
snowwrestler
Well we've accounted for about 5% of the universe--the stuff we know about.

Dark matter (about 25%) seems to only interact gravitationally, which means
that we've just, today, proven that we have an instrument that could possibly
observe it directly. To date, all our evidence for dark matter is indirect--
observing the otherwise unexplained behavior of normal matter. Today is the
gravitational equivalent to Galileo pointing his first telescope at the night
sky.

Dark energy (about 70%) still seems to be a total mystery.

And of course there is our inability to reconcile quantum mechanics with
gravity. With each further proof of the correctness of each of those theories,
the mystery of their apparent incompatibility deepens.

All of these factors lead me to believe that we may still have a long way to
go in our understanding of the physical universe. I hope I'm right.

This is also why I believe it is so important to pursue nuclear energy. If we
do invent further theories and experiments, it's likely that they will require
even greater energy levels than we can create now, and potentially imply even
greater dangers. If we can't learn to manage nuclear physics in a practical,
routine way, we'll never have a hope of going beyond it (if indeed there is a
"beyond.")

~~~
daveguy
How do we know dark matter is some mysterious form of matter and not just
small distributed particles (gas or solid) that are beyond our ability to
detect? Do we have proof of a specific, exotic, non-atomic matter?

~~~
snowwrestler
Scientists are pretty sure that dark matter is not just regular gas and dust
because the amount required to create the gravity we see, would be visible. It
would block or reflect a lot of the nearby starlight.

Just on the back of an envelope: If we assume the percentages in my post above
apply to an individual galaxy, then there has to be 5x as much dark matter
mass as lit mass. There's no way you could have 5x as much gas and dust in a
galaxy as stars, and not see it.

For comparison, the sun makes up about 99.8% of the Solar System mass (500x as
much mass as all the planets, dust, etc. combined).

~~~
JoeAltmaier
That always confused me. We have an Oort cloud, whose members we cannot
resolve very well/at all. Why do we assume only our star has such a thing? If
all stars did, that isn't enough mass to explain dark matter?

~~~
jdmichal
The total mass of the Oort cloud is guessed at (3×10^25 kg), or about five
Earth masses. With dark matter, we are talking about roughly 5.6x the amount
of the _total solar system_ mass. The Oort could would need to be about
371,691x more massive than it is.

[https://www.wolframalpha.com/input/?i=mass+of+the+solar+syst...](https://www.wolframalpha.com/input/?i=mass+of+the+solar+system+*+5.6+%2F+%283%C3%9710^25+kg%29)

~~~
CamperBob2
Could be an anthropic explanation for that. In a solar system with a
hypothetically-"normal" Oort cloud, comets and debris from the cloud might
wipe out life on the habitable inner planets every few hundred million years,
never allowing it to advance to human-like levels.

So we might be here only because our solar system is surrounded by an unusual
amount of nothing.

~~~
snowwrestler
But we also look at a lot of other stars in the sky. If every single one (or
almost every single one) had a massive 5x mass Oort cloud around it, it would
affect the light we see from that star.

Consider that we can currently detect differences in luminosity small enough
to tell whether an Earth-size planet is passing between us and the star. A 5x
mass Oort cloud would be thousands of times more mass than that. It would have
noticeable effect on luminosity.

And, while our sun has an Oort cloud, there are a lot of stars out there that
probably don't--too small, too big, too hot, too young, too old, etc.

------
kkylin
A conceptual issue that some of the commenters may have missed is that part of
the detection is done by matched filtering
([https://en.wikipedia.org/wiki/Matched_filter](https://en.wikipedia.org/wiki/Matched_filter)),
in which it is necessary to have a good idea of the signal you're looking for.
This detection has built upon analytical and numerical advances in relativity.
While people may not know about the prevalence of e.g. binary black hole
collisions, they have a pretty good idea of the signal that would result if
such a collision were to occur. Similarly with other potential sources like
binary neutron star collisions.

~~~
Panoramix
They also injected fake signals into the detector now and then, partly to keep
the analysts on their toes.

[http://www.ligo.org/news/blind-injection.php](http://www.ligo.org/news/blind-
injection.php)

~~~
bbcbasic
I don't think they are expected to tell its fake though? It's hard to do a
double blind experiment without a "placebo universe".

~~~
kordless
That's a rather loaded philosophical question you are asking there - assuming
you are serious about the double blind experiment.

------
losvedir
> _And then the ringing stopped as the two holes coalesced into a single black
> hole, a trapdoor in space with the equivalent mass of 62 suns. All in a
> fifth of a second, Earth time._

Am I reading this correctly, that shortly after the detector came online we
just happened to observe the exact moment a billion years ago that two black
holes collided?

Was that extremely coincidental? Or do these events happen all the time, and
so if it wasn't those two black holes it would be two others?

~~~
antognini
The predictions for the LIGO detection rate are very poor. They're based on a
sample of just a handful of binary pulsars observed in our Galaxy, which would
produce NS-NS mergers. The BH-BH merger rate is almost totally unconstrained,
although it is generally thought to be less than the NS-NS merger rate. So the
fact that a BH-BH merger was the first detection, and the fact that it was
detected so soon after the sensitivity increases is evidence that the BH-BH
merger rate is probably somewhat higher than expected. But we won't know for
sure until LIGO detects more events and the rate can be better constrained.
Sometimes you do just get lucky.

I should add that there are lots of selection biases and educated guesses in
all of this, too. The signal from BH-BH mergers is louder and easier to detect
from larger distances. At the same time, NSs are probably more common than
BHs, but it's not really clear whether there are more NS-NS binaries than BH-
BH binaries because NSs receive kicks from the supernova when they are born
but BHs (probably) do not. This may have the effect of blowing apart many
nascent NS-NS binaries but leaving the BH-BH binaries intact.

~~~
tomp
If this events are so rare (that we don't even know _how_ rare they are), how
is it possible that they achieved the required certainty (5 sigma)?

I guess you could count one _looong_ wave as a series of one-time
events/measurements, but it could as well be a _loooong_ interference.

~~~
21
This is about detection.

To put it another way, you need a single black swan to prove that black swans
exists (to whatever sigma).

~~~
pbhjpbhj
Isn't the point though that the gravitational wave observatories are looking
specifically for "black swans" rather than just observing swans generally. So
when a swan with a lower reflectivity is observed then it now fits the "black
swan" profile. Could be just a swan covered in soot; you need more data to
show that this swan is always black or that the lower reflectivity wasn't
caused by a measuring anomaly, etc.

I may have pushed the analogy too far!

------
scrumper
From the abstract of the paper, energy equivalent to three solar masses were
radiated away in gravitational waves. That's a simply incredible amount!

Possibly stupid question: Given how far away it was, and that the inverse
square law applies, would the effect of these waves be visible on the human
scale if we were closer? We can see the effects of the compression of
spacetime with LIGO after all, so presumably we could?

~~~
bzbarsky
This thing was a billion light years away. Say it were closer; let's put it at
a single light year away.

LIGO measures wave amplitude, as far as I can tell, which goes down linearly
with distance (unlike wave energy, which goes down quadratically, since it's
proportional to square of the amplitude). So we could expect to see an effect
about a billion times bigger.

The detected effect was a change in metric of one part in 6e20 if I'm not
mistaken: (4e-3 * (diameter of proton))/4km based on the article's claim of
"four one-thousandths of the diameter of a proton". So at one light year
distance we could expect an effect of one part in 6e11.

Not really visible on the human scale, seems to me. You could detect it easily
with something like the Mössbauer effect, I expect. Your typical lab bench
laser interferometer has errors on the order of 1 in 1e6 as far as I can tell,
so probably wouldn't be able to pick this up.

Disclaimer: I could be totally off on what a lab bench laser interferometer
can do. I'm pretty confident in the rest of the numbers above.

~~~
swombat
On the other hand, we may well detect the 3 solar masses radiated away as
energy. That decreases as an inverse square law, so as one solar mass is about
10^30kg, and 1kg gives off about 10^17 J, we're talking about an explosion
releasing something around 10^47 J. For comparison, a 1 kiloton nuclear bomb
gives off about 10^15 J.

So, inverse square that explosion... 1 light year is about 10^16m, so we
square that and get 10^32m, so we're now talking about ... 10^15 J.

So, unless my maths is all off (which is possible), if this happened about a
light year away, whoever's on the side facing towards the blast wouldn't get
to observe very much because they'd feel as if a 1kt nuke just went off above
their head. Not a great way to start the day.

Chances are it would wipe out life on Earth too, through the ensuing side-
effects like lighting the atmosphere on fire, sterilising half the planet,
significantly heating up the oceans, possibly even stripping part of the
atmosphere away, etc.

For a great novel based around a strikingly similar premise to what was just
observed (and the main reason I even bothered to calculate this), _Diaspora_
by Greg Egan is a fantastic book.

~~~
bzbarsky
The big question is how much of the energy would get transferred in practice.

I agree that 3 solar masses worth of electromagnetic radiation at 1 light year
distance would feel like a nuke going off. What I don't know is to what extent
the energy of the equivalent gravitational waves (which _would_ have a lot of
energy I agree) would actually get transferred to things we care about, like
the atmosphere and us. If it's a few percent, say, we'd clearly be in trouble.
If it's more like what neutrinos do, it would probably be detectable but
probably not by unaided human senses.

I tried doing some quick looking around for estimates of gravitational wave
coupling and energy transfer and didn't find anything so far...

~~~
platz
I would like to understand why a gravitational wave distorts length in
relation to normal gravity wells; specifically is this particular to waves?
Why don't lengths get distorted in a normal gravity well, or do they? In
essence, what is different between a gravity wave and a gravity well, which i
understand _both_ distort space, but only the wave distorts it in a way we can
measure? Does the gravity well change lengths proportionally in all directions
and thus isnt measurable?

~~~
bzbarsky
A gravity well also distorts lengths, as best I understand (which is not very
well, to be honest; take everything I'm saying here with a big grain of salt).

The difference in terms of detection is that the wave does this in a time-
varying, periodic fashion.

For something like LIGO, we're trying to measure length changes on the order
of 1e-18 meters. We're not actually measuring the lengths of LIGO's arms to
that accuracy, though. What we're measuring is the difference between the
times light takes to travel down those arms. And even that's hard to measure
on an absolute scale, so what we really measure is how that difference changes
in time.

Or put another way, the effect of Earth's gravitational well is not really
distinguishable from inaccuracies in making the two legs of the interferometer
equal length to start with, and is a much smaller effect than those
inaccuracies. Again, if I understand this right...

~~~
swombat
Actually, we have ample proof of the distortion of spacetime in a gravity well
- gravitational lensing. It's an observed effect around very massive objects
and we have been able to see it at work very well. Also, arguably, the fact
that we're not falling towards the sky is itself evidence of a spacetime
gradient near the Earth, but that was also explained by Newton's Law of
Gravitation.

But back in 1916, Einstein also theorised, as part of his general theory of
gravitation, that there would be such things as gravity waves, caused by very
massive objects moving through spacetime making 4-dimensional ripples appear
in spacetime. Until today, that was just an unproven theory, though everyone
believed it was likely to be true. There is now solid evidence to back it.

~~~
platz
Agree... my question, though poorly worded, is less about proof of spacetime
gradients (they do in the ways you describe).

It's more about understanding what the measurable effects of a gravitational
well on earth has on the LIGO experimental setup (or a similar one with
infinite precision), in the absence of gravitational waves.

~~~
swombat
Well, something like LIGO can only measure gravitational waves, because it
looks for changes in the geometry of spacetime. If you were to move the LIGO
in and out of Earth's gravitational well, I guess then it would record a
shift.

------
hun-nemethpeter
According to this paper (
[https://dcc.ligo.org/LIGO-P150914/public](https://dcc.ligo.org/LIGO-P150914/public)
) they detected the signal first at Livingston, Louisiana and 6.9ms later in
Hanford, Washington. The distance between them according to wikipedia (
[https://en.wikipedia.org/wiki/LIGO](https://en.wikipedia.org/wiki/LIGO) ) is
3002km (Ok, the 3002 km distance is on the Earth). If the gravity wave travel
at the speed of light they should detect 10ms later (300 000/3002 sec = 1/100
sec = 10ms ). From these data the gravity travels at 434 000km/sec instead of
300 000km/sec. Almost 50% faster then light... Is there any error in my calc?

~~~
glial
I think your calculation assumes that the waves are traveling parallel to the
line connecting Livingston/Hanford. In the diagram below, 's' is the source of
the waves.

    
    
        H-----L-------s
    

If instead the waves are traveling perpendicularly to the line between those
two cities, they should be detected at the same time.

    
    
           s
          /|\
         / | \
        L-----H
    

Since the measured time difference is between 0ms and 10ms, the reality is
probably somewhere in between these two extremes.

~~~
hoodoof
Weird, that's exactly what I was thinking.

------
kachnuv_ocasek
Paper here:
[https://dcc.ligo.org/LIGO-P150914/public](https://dcc.ligo.org/LIGO-P150914/public)

------
stevebmark
How do the detectors work? In my mind they don't make physical sense. They're
saying the distance between the mirrors changes, but I don't understand how
that's possible in this context.

Let's say a gravitational wave compresses space. To someone inside that
compressed space, there should be no noticeable difference. Light will still
flow the same way through the compressed space at the same speed _relative to
the compression_. Matter will behave identically, because both light and
matter are part of the fabric of that space. As I understand it, the only way
the mirror lengths could change is if space is created or destroyed.

If that doesn't make sense, consider the 2d analogy of drawings living on
paper. Assume also that light moves only along the surface of the paper. If
you bend the paper, the light will bend with it. But when you bend the paper,
the creatures living on the paper can't know it's bent. The fabric of the
paper is still identical. Even if some of the paper gets compressed in one
direction, it will still have the same amount of particles, so any light
travelling through there will hit the same amount of resistance. And
stretching the paper, even if you're a drawing on the part being stretched,
would have no effect. A 2d creature looking at something 1 foot away, even if
the paper is stretched to 10 feet, won't see any difference, because the
fabric light travels through is also stretched.

The only way I can see this making sense is if light travels independent of
the fabric of space, but it's my understanding that light travels _through_
it, not independent of it?

~~~
yosyp
I think the crucial detail you are missing from the article is this:

 _" According to the equations physicists have settled on, gravitational waves
would compress space in one direction and stretch it in another as they
traveled outward."_

LIGO is two sets of 2 L-shaped antennas spread far apart on the globe, so that
we can compare the compression of space in orthogonal directions and measure
the very short delay between the gravitational wave hitting the first detector
followed by the second. In this case, that difference was 7 milliseconds,
which is also consistent with the speed of gravitational waves (also the speed
of light)

~~~
stevebmark
I still don't understand. It doesn't matter where the compression happens,
because it should be undetectable to any light/matter that's fundamentally a
part of that space? If one of the arms gets compressed - the matter will be
compressed too, so light still has the same density and amount of space to
travel through?

~~~
vickychijwani
Check the comic posted by AdrianN, it explains what you're missing. Basically
light takes longer to travel stretched space (but matter does not, as you
correctly said).

~~~
stevebmark
I see. If that's true, then light travels through a higher dimension, and this
is definitive proof of at least a fourth spatial dimension. Otherwise there
would be nothing for the 3d space to ripple through, or for light to travel
through.

I'm surprised I haven't heard that light travels independent of 3d space
compression before. That would also imply that if you enter a black hole with
your feet at the bottom, you would see them _visibly_ stretched far away from
you (noticeably? I'm not sure) because light would take longer in the
distortion to reach your eyes.

~~~
enugu
Doubts about higher dimensions and general relativity is common and a crucial
point, so I dont think you should get downvoted.

Some points which might be helpful. We have a way, using the concept of a
manifold, for ants on a surface like a sphere or a dougnut to figure this out
without appealing to a third dimension. One could imagining say ant
geographers making maps of portions of the surface, and noting how common
regions covered in two different maps have different labels/coordinates. One
can then figure out a definition of when two collections of maps(called an
atlas) are equivalent and then show that an atlas for a plane, sphere,
doughnut are mutually nonequivalent.

But all this is topology and involves global considerations. What is relevant
here is local curvature. We can also do this appealing to an extra dimensions.
Now, you used the example of a folded paper and you are correct that for an
ant on the surface, the curvature is indetectable. The curvature of the paper
is extrinsic and not intrinsic. We say that is isometric to flat space, and
its curvature tensor is 0.

On the other hand, if the ant was on the surface of a ball, it could figure
out this curvature intrinsically, for instance, by measuring sum of the angles
of a triangle or the distance between parallel lines keeps shrinking. Not only
is this intrinsic, but it is locally measurable. One cant have maps, even for
a small area of the earth's surface, without some kind of distortion because
of this intrinsic curvature.

An additional complexity - in GR, spacetime is curved rather that just space.
Also, dont take 'curvature' too literally, it is just a way of measuring
deviation from numbers that you would get in the flat scenario.

For more read up on manifolds, riemann curvature. John Baez had some essays on
the geometric meaning of the curvature tensor in terms of the volume of a ball
relative to the usual flat Euclidean case.

------
chrismbarr
For someone like me who knows next to nothing about this, that video was
extremely well produced and it explained everything i was wondering about.

~~~
tptacek
Jonathan Corum has had a fun career to watch; he's (I think?) a student of
Tufte's. I discovered him with brunch.org; also, check out his style.org.

------
wslh
Weird nobody mentioned here the excellent threads on this topic here
[https://www.reddit.com/r/science/comments/458ppo/ligo_makes_...](https://www.reddit.com/r/science/comments/458ppo/ligo_makes_gravitational_wave_announcement_today/)
and here
[https://www.reddit.com/r/askscience/comments/458vhd/gravitat...](https://www.reddit.com/r/askscience/comments/458vhd/gravitational_wave_megathread/)

------
Roodgorf
Are there any potential competing theories this detection could also support?
I'm wondering how much room there is here for confirmation bias, but I suppose
that's a pretty hard thing to measure without the benefit of hindsight.

~~~
Steuard
Even before this discovery, it's been pretty solidly established that any
alternative theory to General Relativity would need to behave essentially
identically to GR in the limits where we've been able to test it. So, for
example, the "low energy limit" of string theory is general relativity (plus
other content, in most cases). I'm not sure whether the loop quantum gravity
folks have a working low-curvature limit yet (I'm out of touch), but that
would be a requirement for them, too.

At first glance, I'd guess that this discovery only strengthens that
conclusion: even a small deviation from GR might well change the detailed
behavior of an immensely high curvature situation like a black hole merger,
and what we saw seems to have been a spot on match for the GR-based models.

~~~
davrosthedalek
Well, they extracted a lot from the waveform: Distance, the two masses, the
resulting mass. I could imagine that a competing theory gives the same
waveform maybe with different values for these parameters.

~~~
pdonis
A "competing theory" would first have to match the GR predictions in all the
other regimes where it's already been tested. But doing that is an extremely
strong constraint on a theory, to the point where the only theory that can
meet it is GR itself. Physicists know this because alternative theories to GR
have been constructed and tested, and they have all failed. See, for example,
here:

[https://en.wikipedia.org/wiki/Alternatives_to_general_relati...](https://en.wikipedia.org/wiki/Alternatives_to_general_relativity#Results_of_testing_theories)

~~~
effie
That's a very common sentiment, but a mistaken one. Theories do not get
accepted only if they match the predictions of the previous theories. People
value other features besides accuracy of predictions, like simplicity and
explanatory power. Just recall how Kopernik's theory of solar system got
accepted. It had worse predictions than Ptolemy's scheme at the time it was
introduced; Ptolemy's scheme was way better in accuracy, but utterly complex
and explained little.

~~~
pdonis
You're missing the point. I agree that matching the predictions of
_experiments_ (not previous theories--I'm talking about experimental results
that match the predictions of GR, not just those predictions themselves) is
not a _sufficient_ condition for a theory to be accepted (which is what you
are saying); but it is certainly a _necessary_ condition (which is what I was
saying).

 _> Just recall how Kopernik's theory of solar system got accepted. It had
worse predictions than Ptolemy's scheme at the time it was introduced_

Yes, and it wasn't accepted at the time it was introduced. Actually,
Copernicus' theory in its original form was never really "accepted"; what was
accepted was Kepler's reformulation using elliptical orbits, based on Brahe's
more accurate observations. Kepler's model was _more_ accurate than Ptolemy's,
and that was a key factor in its acceptance.

~~~
effie
I agree with you that if a new theory was to replace the old one for making
specific set of predictions, it should give predictions of similar or better
accuracy. But I do not think _that replacement_ is necessary for the new
theory to compete or be accepted; it is the new benefit it brings, whatever
its nature may be, that is crucial. The two can temporarily both be accepted
to coexist, if both have their strengths. For example, quantum theory does not
make the same predictions as classical theory when it comes to classical
experiments (mechanics, basic EM phenomena) and is largely useless in that
domain. It only gives probabilities of results of specified experiments of
certain kinds; it does not reproduce the old predictions (like definite
trajectories, Moon phases or solar eclipses), but provides new results (like
resonance frequencies of atoms and molecules and their bond energies). Similar
thing can happen with a new theory of gravity; it may not give the same
prediction for Mercury perihelion precession, but it may be able to explain
other things, like why the inverse square law, why no repulsive gravity or why
the mutual gravity force between electrons is so much lower than the mutual EM
force. Explanation for oddities in Mercury motion could then wait for further
data and repetition of calculations. It is natural to expect of any new theory
to bring new results, but demanding that it reproduces all the old ones along
is too much. That happens rarely and such expectation only prevents any new
ideas from being considered.

~~~
pdonis
_> quantum theory does not make the same predictions as classical theory when
it comes to classical experiments (mechanics, basic EM phenomena)_

Yes, it does. Do you know how the classical limit of quantum theory works?
That limit is what allows us to use classical physics in the domain where it
works. If that limit didn't work, we would have a serious problem with
consistency.

 _> It only gives probabilities of results of specified experiments of certain
kinds; it does not reproduce the old predictions (like definite trajectories,
Moon phases or solar eclipses)_

Are you aware that all of those "old predictions" can indeed be derived from
quantum theory, using the classical limit I described above? The reason that
works is that, in the classical limit, quantum theory predicts a probability
of 1 for one result--the classical result.

 _> It is natural to expect of any new theory to bring new results, but
demanding that it reproduces all the old ones along is too much._

You appear to have a mistaken understanding of how new theories get accepted.
New theories that don't reproduce all of the predictions of the theory they
replace, in the domains where the old theory is verified by experiment, are
not accepted. If general relativity had not reproduced all of the predictions
of Newtonian gravity in the weak field, slow motion limit, it would not have
been accepted. And if quantum theory had not reproduced all of the predictions
of classical physics in the classical limit, it would not have been accepted.

~~~
effie
As I wrote above, I agree with you on the requirements for replacement theory.
My point is that a new theory of a phenomenon does not need to replace and
reproduce all the results of the old theory to be considered worthwile,
competing, acceptable.

~~~
pdonis
Can you give an example of a new theory that was considered worthwhile even
though it didn't replace and reproduce all the results of the old theory? I'm
not aware of any. (The Copernicus example given upthread is not a valid
example, as I said in response to that post.)

~~~
effie
Schroedinger's theory of hydrogen atom and his wave mechanics (1926). It
explained positions of emission lines of excited hydrogen, but it didn't
explain how the atoms lose excitation energy as there is no _c_ and no
spontaneous emission in that theory. Larmor's older theory (1897) explained
how the energy is lost - by EM radiation - and gave formula connecting
acceleration and losses that is used to this day.

Joseph Larmor, LXIII, _On the theory of the Magnetic Influence on Spectra ;
and on the Radiation from moving Ions_ , Philosophical Magazine Series 5 Vol.
44, Iss. 271, 1897

Erwin Schrodinger, _Quantisierung als Eigenwertproblem_. Annalen der Phys. 384
(4) (1926)

~~~
pdonis
_> Schroedinger's theory of hydrogen atom and his wave mechanics (1926)._

This was not a "new theory" that was competing with any "old theories". It was
a tentative model in a regime where _no_ previous theory existed, and it was
never claimed to cover anything outside that limited regime. It wasn't
competing with any other theories, because there were no other theories to
compete with. The question of whether or not Schrodinger's model reproduced
the predictions of the "old" theory never arose, because there was no "old"
theory. (Technically, there was a sort of "old" theory of the hydrogen atom--
Bohr's model--but Schrodinger's model did reproduce all of its correct
predictions, plus it added more correct predictions of things that the Bohr
model got wrong.)

The position with regard to gravitational waves is very different; we already
have a comprehensive, fundamental theory--General Relativity--that explains
them. Any alternative theory that only explained GWs, and didn't also explain
all the other experimental results that GR explains, would be a nonstarter.

 _> Larmor's older theory (1897)_

This wasn't a separate "theory" at all; it was just a derivation of a
particular formula using an already known theory, Maxwell's Equations.

~~~
effie
Schroedinger theory certainly was a new theory of the atom and later of
molecules at that time, successfully competing and largely replacing classical
EM models of atoms and molecules such as Larmor's theory of molecules,
although it didn't cover the EM radiation aspect and EM theory needs to be
used in parallel with Schroedinger's to get, say, intensities of emission
lines. I think this is a good example of what I was saying in the first post.
It is the new benefit that the theory brings, not reproduction of every single
result of the previous theories, that makes the new theory interesting and
helps its adoption. Cases where the new theory completely replaces the old
theory and reproduces all of its positive results happen too, but are not the
only way how new knowledge is adopted.

~~~
pdonis
_> I think this is a good example of what I was saying in the first post. It
is the new benefit that the theory brings, not reproduction of every single
result of the previous theories_

Of course Schrodinger's model didn't reproduce the results of classical EM
with regard to the atom. It wasn't supposed to, because those results of
classical EM were _wrong_. In other words, there wasn't a correct "old theory"
that covered the regime the Schrodinger model covered (the atom)--there was
only a wrong "old theory".

As far as using Schrodinger's model plus classical EM theory to get results
like emission line intensities, there also there was no correct "old theory";
there was only a wrong "old theory" (classical EM by itself, which did not
predict emission lines at all, let alone their intensities--it predicted a
continuous emission spectrum). Also, this hybrid classical-quantum model was
known to be incomplete at the time; it was only used because nobody had yet
figured out how to quantize the EM field.

 _> It is the new benefit that the theory brings, not reproduction of every
single result of the previous theories_

Once again, this is _not_ the situation under discussion in this thread
(gravitational waves). In the case you describe, the results of the previous
theories were _wrong_ in the regime the new model covered, so there was
nothing to reproduce; there was no correct "old theory" for the new theory to
compete with.

In the case of gravitational waves, we have a _correct_ "old theory"\--General
Relativity--so any new theory that did not match that _correct_ old theory
would be a nonstarter. I am not aware of any case where a new theory was
accepted as interesting when there was a correct old theory covering the same
regime and the new theory did not reproduce its results.

~~~
effie
> _It wasn 't supposed to, because those results of classical EM were wrong._

You're badly mistaken. Although nobody succeeded in obtaining the emission
line frequencies of gases out of the classical EM theory, the theory did
correctly give other results consistent with observations. One of them is the
formula for emission intensity that connects energy radiated with second
derivative of electric moment; it goes back to Larmor's work. This _was_ the
result the new theory would preferably reproduce or at least be consistent
with. Wave mechanics wasn't consistent with it - the hydrogen atom oscillates
indefinitely in wave mechanics. Schroedinger himself viewed this as a
deficiency and planned to get back to it - check the ending part of his
seminal papers on wave mechanics. The classical formula is taught to this day
both in macroscopic EM theory and quantum optics courses, although there are
some deficiencies and problems about the formula that Larmor did not know.

> _In the case of gravitational waves, we have a correct "old
> theory"\--General Relativity--so any new theory that did not match that
> correct old theory would be a nonstarter._

I do not think any physics theory could even be "correct" in the sense of
Platonic ideals, but I do not know what you mean by "correct". I do not claim
a new theory could completely replace the old one before it could deliver the
same or better results. I claim theory has value and is accepted based on its
new benefits, not its superiority in every aspect the old theory was superior
before. Calling incomplete theory non-starter makes no sense to me, as all
theories, including General Relativity, are incomplete.

~~~
pdonis
_> You're badly mistaken._

No, I'm not; you're just mistaken about which classical results I was
referring to. I meant the results of classical EM that predicted that atoms
could not exist--because the electrons would radiate until they fell into the
nucleus. And what classical formula tells you how much the electrons will
radiate because of their acceleration due to responding to the electric field
of the nucleus? Larmor's formula.

In other words, Larmor's formula was not a "theory"\--it was a particular
result derived within a theory. The particular _result_ happened to be
correct, within a particular limited domain; but the underlying _theory_ that
was used to derive it could not explain _why_ it was correct--because the same
theory, and indeed the same particular result--the same formula--made other
predictions that were obviously egregiously wrong (like predicting that atoms
would collapse).

 _> nobody succeeded in obtaining the emission line frequencies of gases out
of the classical EM theory_

You're drastically understating the failure of classical EM here. It's not
that classical EM couldn't predict the particular frequencies of emission
lines. It's that classical EM couldn't predict the _existence_ of emission
lines at all. Classical EM predicted that atoms would emit a continuous
spectrum of radiation--not radiation sharply peaked at particular frequencies.

 _> The classical formula is taught to this day both in macroscopic EM theory
and quantum optics courses_

Sure, because _within its domain of validity_ , it works fine as an
approximation. But that's all it is--an approximation. And we explain why the
approximation works, and why it works only within a particular domain of
validity, by reference to the more complete underlying theory--quantum
electrodynamics.

 _> I do not know what you mean by "correct"._

I mean "makes predictions that match the results of experiments".

------
euske
I sometimes wonder why tech people like space-related stuff so much. It is a
major news indeed and a feat of science and technology, but why is space so
popular? Because it's otherworldly, large-scale and kind of making you feel
empowered or united? I'm probably more interested in mundane, obscure and
humble stuff, so this disproportionate popularity of space-related news is
always baffling to me.

~~~
mturmon
In grappling with this question myself -- it's a good question -- I've
concluded the interest is in understanding and predicting the behavior of a
system based on a few laws.

The system is quite complex and full of exotic objects, so ordinary real world
intuition is a poor guide. And the laws are couched in a mathematical language
that is also foreign to our everyday world.

Yet, predictions can be made and tested. It's an intellectual puzzle like
"what does this very tight loop do?", or "how does the Y combinator work?" \--
but in a different arena.

------
ericjang
The mechanical and software engineering underlying these research endeavors is
breathtaking. The laser apparatus, LISA pathfinder, ELISA - how on earth do
they calibrate/debug/test such complex systems?

... and I shudder to think that more often than not, anything I code in C/C++
will segfault on first run.

~~~
pif
Don't worry, their code segfaulted umpteen times, too :-)

------
boardwaalk
If they build a third observatory, can they triangulate where in the universe
the events are occurring?

~~~
stouset
My intuition is that this is unlikely, but I'd love to see someone do the
math. Given the scale of interstellar distances, any locations on our planet
(and even in our solar system) are going to effectively function as a single
point. Given arbitrarily-accurate measurement, it could work, but I'd bet
physical limitations will prevent that from being a possibility.

To my mind, it'd be roughly like trying to triangulate an earthquake in France
with three sensors in a 1mm^3 cube in NYC (scale is probably way off, I
definitely didn't do the math).

~~~
Florin_Andrei
It would work. The delta-t is a few miliseconds. This gives enough precision
for a decent estimate of the direction of the signal.

Now estimating the distance is a different matter.

~~~
swamp40
The gravity waves redshift just like any other wave. So, they _have_ estimated
a distance: 1.3B light-years.

------
jcoffland
I wonder of this means the space version of these antennas, eLISA, will get
more funding. Using space seems like a much better way to access long distance
laser conduits in a vacuum needed to detect gravitational waves.

~~~
gammarator
Since the LISA has longer baselines, it measures gravitational waves of
different frequencies, from different phenomena--supermassive black hole
coalescence, not these (mere!) stellar mass black holes. So the experiments
are complimentary

------
ernesto95
I generally dislike idolatry and pinning mayor scientific advancement on one
single person, but honestly, Einstein really was something else.

~~~
dheera
In all honesty I do think Einstein is getting too much credit today. I'd paste
the list of co-authors here to congratulate them but HN doesn't allow comments
that large. The list is available here for reference, and I think every one of
them deserves credit for this.

    
    
      http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.116.061102
    

On another note, I feel like the importance of this finding is less in proving
Einstein's theory; having taken a formal relativity class and an degree in
Physics, I think GR itself is an astounding mathematical framework for
describing spacetime, to which Einstein deserves credit, but the existence of
gravitational waves is completely natural consequence of the equations within.
It's not very different from the existence of light being a natural
consequence of Maxwell's equations.

I'd say the true importance of this discovery is in successfully creating an
_experimental apparatus_ to detect what was previously almost universally
agreed to probably exist but thought to be nearly impossible to detect. What's
truly exciting isn't proving Einstein right, but the possibilities of what
we'll be able to to detect with this apparatus in the future. So it's the team
that built the apparatus which truly deserves the credit today.

------
nilkn
I hope Kip Thorne gets a Nobel Prize for this, ideally while he's still alive.

~~~
mikeyouse
Pedanticly, it'd have to be while he was alive since the Nobel Committee won't
nominate anyone who's deceased. Rosalind Franklin would've surely received one
for her work on DNA (among others who passed before their work was
recognized).

------
terryf
It was mentioned that during this event, three sun's mass equivalents were
turned into gravity waves, I guess that means that matter particles were
turned into gravitons.

But what happens to them? Is there any way to turn them back into matter? If
not, then at some point, will all matter in the universe end up as gravitons?

Also, if an object moving through space creates gravitational waves, doesn't
that violate the law that states that a non-accelerating object will not
lose/gain any energy? Because if you have to emit gravitons as you move in
space, and emitting them requires energy or matter expenditure, then an object
moving through space will slowly lose all it's mass?

------
nappy-doo
Does anyone know if G-Waves are effected by velocity, like EM-Waves are?

In other words, if two bodies are moving relative to one another, one emits
G-Waves, and one detects them. Are the waves at the detector doppler shifted
in frequency by the relative velocities?

~~~
lutorm
I don't see how they could not be. I think that shift arises from
transformations between different coordinate frames, it doesn't matter what
you're observing.

------
chejazi
_Lost in the transformation was three solar masses’ worth of energy, vaporized
into gravitational waves in an unseen and barely felt apocalypse. As visible
light, that energy would be equivalent to the brightness of a billion trillion
suns._

Beautiful.

------
peter303
Note this is a stellar black hole merger of several tens of solar masses.
Imagine the disturbance of a galactic core black hole mergers of millions of
stellar masses. These are probably much rarer, but do occur when galaxies
merge.

~~~
swombat
Oooh, I can do another back of the envelope calculation here! (cf
[https://news.ycombinator.com/item?id=11081838](https://news.ycombinator.com/item?id=11081838)
)

If this happened in the centre of the Milky Way, we're about 25k light years
away.

Let's say 2 1 million solar masses black holes merged there... and they also
gave off about 3/60 of their mass as radiation, that's about 100'000 solar
masses being radiated 25k light years away.

Using my calculation in the other post, we're talking 10^52 Joules. Across a
distance of 25'000 light years, or about 10^20 metres, that's then decreased
by 10^40 (inverse square) so we're left with about 10^12 Joules...

Which is good news! If that happened in the Milky Way, we would probably
survive it - though we'd definitely notice some strange atmospheric effects...

------
jshelly
Does anyone else get a bit depressed when you consider how insignificant we
are?

~~~
venomsnake
No. But with so much interesting things left to find I start to really really
hate the concept of mortality :(

~~~
grif-fin
I could not agree more. Everyday I wake up and I think why is it that we gave
up on massive wave of research on immortality/life extension.

------
4k
I have a question: what does this mean for theoretical physics? (except for
Einstein was right) Does it settle any major debates? Does it make any
competing theory more or less likely?

Sorry I am not vary knowledgeable on the topic.

~~~
Steuard
It's by far the most explicit verification we've ever had that black holes
exist in pretty nearly the exact form predicted by Einstein's equations of
general relativity, which is pretty cool. It provides the tightest limits on
any possible mass for the graviton (the presumed particle carrying the
gravitational force, which is generally believed to be massless but you always
have to wonder about more exotic possibilities). It gives a stunningly clear
confirmation that modern numerical simulations of relativistic dynamics are an
accurate reflection of nature. (And by the same token, it presumably puts
limits on the strength of any potential deviation in the laws of physics from
the equations used in designing those simulations.) And it probably does
something to give preference to models of _astrophysics_ in which binary
systems with these characteristics are common.

Beyond that, I guess I'd say that this particular signal doesn't feel like
that much of a _surprise_ : we were already pretty confident that if a black
hole binary were to merge, a signal more or less like this would be an
expected result. The scientists were evidently surprised that their very first
signal was so strong (this one was even borderline detectable by the previous
version of LIGO), which may teach us something, but it's not revolutionary.

------
QuadrupleA
One thing I don't quite understand - how can the "chirp" from LIGO be
unambiguously categorized as extraterrestrial in origin? The waveform shown
onscreen in the NYtimes video looks like an extremely noisy signal - not sure
if that's the actual sampled data or just an artistic rendition. Couldn't
there be a variety of physical disturbances that explain a sine-tone sweep
like that, given how sensitive the instrument is to physical vibrations?

~~~
cft
There are two independent sites, 2000 miles apart. Additionally, each site has
two perpendicular experiments: one shows contraction when the perpendicular
one shows expansion. Orientations at both sites are aligned I presume.

~~~
bobinator606
And there is a third which was offline at the time, and 2 more being worked
on. This is no the last experiment.

------
AYBABTME
So what does this mean about the future, now? What new capability do we have?
What is possible now that wasn't possible before?

------
ttflee
How could this result be reproduced in an independent repetition, then?

~~~
astrosi
In a very real way it was. There were two completely geographically separate
instruments which recorded the same signal with a delay that is consistent
with the light travel time between them.

In the future this will get better when VIRGO in Italy and KAGRA [2] in Japan
come online. Then we will have 4 independent detectors which will be able to
verify that same signal is observed at the same time.

Obviously of course given the transient nature of what is being observed once
the merger has occurred it will very rapidly stop producing gravitational
waves so we will not be able to measure the same event again.

[1]:
[https://en.wikipedia.org/wiki/Virgo_interferometer](https://en.wikipedia.org/wiki/Virgo_interferometer)

[2]:
[https://en.wikipedia.org/wiki/KAGRA](https://en.wikipedia.org/wiki/KAGRA)

------
goshx
This is live now: [https://www.theguardian.com/science/across-the-
universe/live...](https://www.theguardian.com/science/across-the-
universe/live/2016/feb/11/gravitational-wave-announcement-latest-physics-
einstein-ligo-black-holes-live)

------
amai
Wow, the list of authors to the paper is three pages long:

[https://dcc.ligo.org/public/0122/P150914/014/LIGO-P150914_De...](https://dcc.ligo.org/public/0122/P150914/014/LIGO-P150914_Detection_of_GW150914.pdf)

------
amai
On November 25, 1915 (at the time of WWI) Einstein presented the actual
Einstein field equations to the Prussian Academy of Sciences. Almost exactly
100 years later on September 14, 2015 LIGO observed the first gravitational-
wave signal. Is that a coincidence?

~~~
flexie
Yes

------
programd
The original science paper is here [0]

[0]
[http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.116...](http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.116.061102)

------
drelihan
ok, so some of the best minds on Earth can build a machine to detect
gravitational waves from an event 1.3B light years away. This is an incredible
motivation for those of us on what is possible with technology in simple
terrestrial projects.

------
soneca
Honest question: there is any example of Einstein being proved _wrong_?

Was he indeed always right on his theories for phenomenons before they could
be proved by experiments; or is that the case that we only hear about when he
is proved right?

~~~
marcoperaza
He was a proponent of hidden variable theory, which tried to reconcile quantum
mechanics with determinism, famously saying "God does not play dice". People
often say that hidden variable theories were proven impossible, and thus
Einstein was proven wrong. That's not quite true, and only _local_ hidden
variables have been ruled out.

~~~
lamontcg
It also disparages his contribution to the scientific discussion to just state
that he was "proven wrong".

Bohr's argument in the discussion was a bit of a mess and I couldn't pull
anything out of his rebuttal to EPR other than an assertion that QM behaves
the way it does and not to pay any attention to the man behind the curtain.
Its a very philosophical argument with very little scientific content and he
just proposes that the QM math is correct because its correct, as far as I can
tell.

EPR made a logical cogent argument. It was based on the philosophical
principle of the locality of physics. They translated that into the
mathematics of Quantum Mechanics and proposed a simple experimental test.
Later that was refined by Bell and tested experimentally by Aspect and others.
It was the Einstein-Podolsky-Rosen paper that laid the groundwork of how to
test the non-locality/hidden-variables of QM though.

EPR moved the scientific discussion forwards much more than Bohr did, but it
turns out the test they proposed showed that the position they favored was
incorrect.

Also Einstein was arguing first and foremost that physics must be _local_.
That's in opposition to the "spooky action at a distance" bit that he didn't
like. Since local hidden variables are ruled out then he really was proven
"wrong".

TL;DR I think Bohr's argument is rubbish, and Einstein's is solid, but the
Universe is a bitch and doesn't care...

------
gnaritas
No they haven't proven Einstein right, they've failed to prove him wrong; that
distinction is the essence of science. Theories are never proven right, they
can only be proven wrong.

------
IanDrake
Is the speed of light affected by the gravitational fluctuations mentioned in
the article?

Or, put another way, is the speed of light only a constant because we measure
it in constant gravity?

~~~
delecti
Any observer will observe the same speed of light in their location.

Any effect of gravitational fluctuations in spacetime on the speed of light is
a bit like a car driving on a race track that has treadmills scattered around
it pointing in various directions and speeds. The car's speedometer will
always read the same value because it's measuring the speed of its tires on
whatever it's driving on.

------
wuliwong
I am not sure why but I am really hung up on the quote “Finally, astronomy
grew ears. We never had ears before.” They are detecting gravitational waves
not sound waves.

~~~
fsloth
Any vibration is just a signal. We don't actually have a direct experience
with a sound, hearing is our brains interpreting the nerve signals generated
by tiny organelles jiggling in our ears. What is concrete then, is only the
shape of the signal, but not the medium through which it propagates.

This device just acts like a gigantic hearing device. Except it's not pressure
waves, but the fabric of the universe which reverbates.

Note that the frequency of the signal is indeed in the audible range.

Anyway, I was a bit irritated of this same phrase, but because I tought radio
astronomers had been listening to skies for quite some time now.

~~~
wuliwong
I think it bothers me because it is focusing on the sound that some small
piece of this operation creates when the amazing thing is to be able to
measure gravitational waves. Who cares if you hook the output of some piece of
LIGO up to a speaker or not and make a noise? Unplug that speaker and these
results are just as amazing.

------
dschiptsov
But there is no "fabric of space-time". Time is a mental concept, it cannot be
detected.

Whatever they have detected or calculated is something else.

------
sytelus
Better video directly from LIGO/Caltech:
[https://www.youtube.com/watch?v=wrqbfT8qcBc](https://www.youtube.com/watch?v=wrqbfT8qcBc)

And here's more detailed from PBS Space: [https://www.youtube.com/watch?v=gw-
i_VKd6Wo](https://www.youtube.com/watch?v=gw-i_VKd6Wo)

------
giomasce
I really wonder what the researcher sitting bored at their computer looking at
random data thought when they noticed the interesting event!

~~~
akuchling
[http://www.sciencemag.org/news/2016/02/here-s-first-
person-s...](http://www.sciencemag.org/news/2016/02/here-s-first-person-spot-
those-gravitational-waves)

" On 14 September 2015, while Drago was on the phone with a LIGO colleague in
Italy, his pipeline sent him an email alert—of which he receives about one
each day—telling him that both LIGO detectors had registered an “event” (a
nonroutine reading) 3 minutes earlier, at 11:50:45 a.m. local time. It was a
big one. “The signal-to-noise ratio was quite high—24 as opposed to [the more
typical] 10,” he says."

------
known
A hole that is less than the sum of its parts. Three suns’ worth of mass has
been turned into energy, in the form of gravitational waves;

The coalescing holes pumped 50 times more energy into space this way than the
whole of the rest of the universe emitted in light, radio waves, X-rays and
gamma rays combined.

------
brownbat
Einstein wasn't sure at first. It was Feynman who introduced the thought
experiment that settled the debate in the physics community:

[https://en.wikipedia.org/wiki/Sticky_bead_argument](https://en.wikipedia.org/wiki/Sticky_bead_argument)

~~~
gaur
Not sure why this received downvotes. There was significant debate until the
1950s about whether gravitational waves were real phenomena or just coordinate
artifacts. The sticky bead argument played a big role in settling the issue.

------
kamaal
Tangential question. With blackholes merging, can more and more merge some
time in future, creating a net gravitational pull to slow down the expansion
of the universe and then may be eventually cause the universe to collapse into
that continually merging mega black hole.

~~~
gus_massa
The gravity pull of the new black hole is essentially equal to the sum of the
gravity pull of the two isolated black holes, and it's essentially equal to
the gravity pull of the two stars before they transformed into black holes. So
merging black holes don't increase the pull.

Actually, in each transformation there is an explosion and part of the mass
goes away (try to not be very close). So the total mass in the final black
hole is smaller than the mass in the initial stars, the rest are debris
forming a nebula or something around the black hole.

(And, as the other commenter said, gravity is too weak.)

------
oldo-nicho
I'm interested to know how they can be so sure that the change in distance
between the two arms of LIGO is attributed to gravitational waves? I would of
thought that miniscule movements in the Earth's crust would be a more likely
culprit.

~~~
oldo-nicho
Ahh, just realised that there are two instruments located on either side of
the states, so if both instruments register the same event then it is unlikely
to be tectonic movement...

------
fucsia
_once shot up the outside of one of the antenna arms in Louisiana, and a truck
crashed into one of the arms in Hanford_

Does this mean an actual truck, a vehicle? Did they accidentally hurt someone?

I liked this quote: _The future for the dark side looks bright._

------
srkiranraj
I understood how LIGO works but one question I have is, how did scientists
conclude the gravitational waves they detected are from a collision of 2 black
holes that happened before 1.3 Billion/Million years ago.

Could someone explain ?

------
jakeogh
Technical details and hints on future results:
[https://news.ycombinator.com/item?id=11092982](https://news.ycombinator.com/item?id=11092982)

------
onetimePete
Would such a gravity wave cause a tsunami on a world circling the two black
holes?

------
rdli
Live stream from the NSF:
[https://www.youtube.com/user/VideosatNSF/live](https://www.youtube.com/user/VideosatNSF/live)

------
jharohit
For those who missed the live announcement by the team
[https://youtu.be/aEPIwEJmZyE?t=27m13s](https://youtu.be/aEPIwEJmZyE?t=27m13s)

------
JabavuAdams
Where can I find out more about how thermal effects in the LIGO optics are
controlled for?

Basically, I want to understand how it's possible to measure a distance change
on the femtometer scale.

~~~
selimthegrim
You probably want to read about their active isolation measures. Then you
should find anything by Vladimir Braginsky you can get your hands on. This is
a good start: [http://www.amazon.com/Quantum-Measurement-Vladimir-B-
Bragins...](http://www.amazon.com/Quantum-Measurement-Vladimir-B-
Braginsky/dp/0521484138)

~~~
JabavuAdams
More accessible / concise info on the vibration isolation, here:
[https://news.ycombinator.com/item?id=11084282](https://news.ycombinator.com/item?id=11084282)

------
elorant
Are gravitational waves supposed to be that weak or is it because of the
distance between us and those black holes? Do they lose power as they travel
through space?

~~~
kordless
Think of waves in a pond when you drop a rock in. The energy spreads out as it
travels into the farthest reaches of the pond.

~~~
davrosthedalek
Only that in space, it drops even faster: The wavefront carries the same
energy, but spread out over ever increasing length/area. For gravitational
waves (or radio waves) they form spheres, not circles, and the surface size
scales with r^2, not r. (Also water waves are /complicated/)

~~~
bzbarsky
Right, but LIGO detects wave amplitude, not wave energy, which goes down as
1/r.

~~~
davrosthedalek
Oh, interesting point! I now have to wrap my head around that information
transfer normally means energy transfer...

------
msie
So does this verification of gravitational waves help with Physics theory-
building? Have people really doubted Einstein : the existence of gravitational
waves?

------
hendekagon
Has anyone converted the spectrograms given in the paper, or better still the
raw data, into sound yet ? Each location in each ear please!

~~~
astrosi
The data release contains the data converted to sound if you scroll to the
bottom [1].

I don't think anyone has combined them as you suggest though!

[1]
[https://losc.ligo.org/events/GW150914/](https://losc.ligo.org/events/GW150914/)

------
pinkrooftop
Would it be possible to listen for information transmitted via gravitational
waves? Would there be any benefit over radio?

~~~
nickhalfasleep
This event was the equivalent of three of our suns turned into pure energy.
Pretty expensive to send a message.

~~~
yk
Burning a few suns per message would significantly reduce spam.

~~~
wanderfowl
Your post advocates a

( ) technical ( ) legislative ( ) market-based ( ) vigilante (X) Physics-based

approach to fighting spam. Your idea will not work. Here is why it won't work.
(One or more of the following may apply to your particular idea, and it may
have other flaws which used to vary from state to state before a bad federal
law was passed.)

(X) The amount of energy involved would likely destroy the planet.

(X) Many email users cannot afford to lose business or alienate potential
employers

Specifically, your plan fails to account for

(X) The relative sparseness of non-dark energy in our vicinity

(X) Huge existing software investment in SMTP

and the following philosophical objections may also apply:

(X) Incompatiblity with open source or open source licenses

(X) I don't want the government reading my email

Furthermore, this is what I think about you:

(X) Sorry dude, but I don't think it would work.

(I'm sorry, but I couldn't resist)

------
pkrumins
Can't wait until this discovery can be utilized to creating some kind of a new
technology! Such as time travel!

------
ridgeguy
Obligatory......

[http://xkcd.com/1642/](http://xkcd.com/1642/)

------
jstalin
Does gravity move at the speed of light?

~~~
ddingus
The videos say the waves do move at exactly the speed of light. They are
massless.

------
spullara
As with most physics experiments for the last 40 years, nothing new was
discovered that we didn’t already predict. Confirming something widely
believed to be true isn't nearly as valuable as finding out we don't
understand something. This is actually one of the reasons I dropped out of my
physics phd program.

~~~
gammarator
Because this is astrophysics and not particle physics, this discovery is just
the beginning! We don't know the rates of these mergers, the distribution of
the masses of the binary components, what electromagnetic signature
accompanies the events (if any)...

We've known gravity waves existed since the Hulse-Taylor pulsar, so just
observing them for the first time is not nearly as interesting as the science
to come in the next decade. Advanced LIGO is a powerful new tool that will
open up exciting new observations.

------
ksec
And we are one step closer Gravity Shockwave Generating Division Tool.

------
xCathedra
Could someone explain what possible applications this might produce?

~~~
ddingus
It's super early, and detection seems at the limits of our technology.

This is just understanding at present. That, in itself is worth it.

As that understanding develops, and our tech advances, engineering may be able
to apply it in useful ways, maybe object detection above a specified mass? New
ways to visualize things?

One "application" is to serve as a ruler to measure out tech with. The limits
are there, putting these observations just within reach.

Now that we have some confirmation, we also have the metrics as well as the
compelling new science that may arise from all of this as a strong motivation
to advance.

It's like being able to detect color for the first time. At first we
understand what color is, then we refine, and after iterations, engineering,
experiments, we get to a place where we see it all in color.

Applications will follow.

These waves being confirmed are like a new sense. Crude, but real. We can now
follow this new perception to its conclusion, just as we have many other
things.

We don't always know what that conclusion will be, or the form an application
may take, but we do know we won't actualize any of it if we don't do the
basic, hard, expensive work needed first.

------
UhUhUhUh
1.1. billion and 40 years vs. pencil and paper and a few years. That should
tell us something about education, mode of thinking and research. And a few
other things.

------
known
Did collision of 2 black holes prove E = MC2

------
swehner
The "proving Einstein right" part would be more fitting if there was some
independent evidence of the collision. As it is it seems to go in circles.

But that's the NYT I guess.

~~~
sandworm101
Maybe we will get lucky and literally see two black holes merge somewhere
nearby. But I think these detectors will be the last of our concerns with all
the praying and bunker building going on. Bruce Willis won't save us from that
one.

------
hiphopyo
Does this bring us any closer to warp drives?

~~~
drdeca
Uh, I guess it might help with testing things that would?

Iirc the idea would be that inferometers would be used to test things like
that.

I don't think we (humanity) will achieve warp drives, though, I do support the
attempt.

------
lobster_johnson
Dicussed here:
[https://news.ycombinator.com/item?id=11079462](https://news.ycombinator.com/item?id=11079462)

~~~
tfgg
To be fair, that article is pre-announcement and doesn't have much detail on
the actual discovery.

Actual paper here:
[http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.116...](http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.116.061102)

------
meganvito
the wave can come from two slits, one beam comes later maybe

------
meganvito
the wave can from two different slits, so one beam travels longer

------
frandroid
> The future for the dark side looks bright.

Oh no you didn't.

------
exodust
I wonder if gravitational waves are responsible for the video starting
automatically without me clicking play.

~~~
mikeash
Yes, in that any given event is ultimately the result of all previous events
within its past light cone.

------
josephv
I swear a big bang theory rerun about this was on last night. Sheldon detected
waves at the north pole, but they were actually a blender turned on by the
rest of the gang. He's embarrassed and goes home. Leonard beds Penny. Decent
episode.

------
brudgers
I am a bit skeptical of the conclusion given the methods. Here, there's no
observable phenomena independent of the test apparatus that corresponds to the
proposed cause. The conclusion is circular.

1\. Theory predicts gravitational waves when massive objects collide and that
the gravitational waves would have an effect that could be measured by the
experimental instruments.

2\. The experimental instruments measure something.

3\. This is considered proof that massive objects collided.

4\. Therefore gravitational waves exist.

To reframe my skepticism, the experiment measures something. The conclusion as
to what it measures, however, is unsupported by statistical inference or
direct experience of a causal phenomenon. That's not to say that what the
phenomena measured -- the earth resonating -- is uninteresting or unimportant
or even inconsistent with the theory of gravitational waves.

Yet, I don't find the possibility of a geophysical cause -- i.e. that the
earth maintains consistent dimensions at a sub-atomic scale -- the many orders
of magnitude less likely than gravitational waves necessary to reach a
conclusion. In particular, I find natural fluctuation to be more likely
because the experiment acknowledges its existence.

For a point of comparison, consider the Perihelion precession of Mercury that
provides evidence in support of general relativity. The theory was used to
predict the results of an observable event. The experimenters trained their
telescopes at a particular location and particular time and observed phenomena
consistent with a prediction based on the theory. The same is true of the
Higgs. In both cases the experiment is of the form "when X, I will observe Y."

The reasoning here is:

    
    
      If X, then Y.
      Y, therefore X.
    

It treats an ordinary implication as mutual implication.

~~~
dragonwriter
I think your argument fails for a few reasons:

(1) It simply fails to understand the scientific method, which is empiricism,
not mathematical/logical proof. Scientific evidence is essentially failed
disproof, not logical proof.

(2) It mischaracterizes the nature of the prediction, which includes not
merely that _something_ will be measured, but that a particular pattern will
be measured.

(3) It proposes unspecified "geophysical causes" as an alternate explanation,
but there was no pre-existing geophysical model which predicted the pattern
observed. (Any after-the-fact geophysical -- or other -- alternative
explanation which explains the observed pattern would also need to perform
differently on some other test to be verifiably different, and then we could
do the test to distinguish the source.)

(4) It misstates the reasoning to contrast it with other experiments, this is
exactly "when X, I will observe Y" (where X is "I construct detectors of a
particular type in more than one location" and Y is "I will periodically
detect particular patterns of signals on those detectors -- not just one of
them alone -- which the model predicts will be produced by collisions of
massive, distant objects.")

~~~
brudgers
Under the theory of science as the study of what is falsifiable, there's
nothing here to falsify because there is no way to disprove that a conjectured
but unobserved collision of two massive bodies was something else or didn't
occur. Which is to say that it is impossible to falsify that a conjecture is a
conjecture.

That there is not a geophysical theory, doesn't have a bearing on the
correctness of the gravitational wave theory one way or the other...anymore
than the absence of a helio-centric model for the solar system made the
geocentric model more correct or the absence of a theory of oxygen made the
theory of pholgiston more correct. More importantly, both these incorrect
theories had reasonable explanatory power to the point that they were useful.

The reason they were useful theories is because they were predictive,
pholgiston allowed a person to calculate the weight of ashes after burning and
the geocentric solar model made the prediction of the location of stars
possible with reasonable precision. On the other hand, theories that offer
conclusions about unfalsifiable propositions are what Carnap and the Vienna
circle termed "metaphysics".

The conclusion that the experiment justifies is that the Earth resonates.
There is no external event to which the measurements can be correlated to
establish causality. There's no confidence interval. It's a case where the
observations confirm a pre-existing world view under the same human cognitive
structures by which seashells on mountain tops confirm a world-wide flood. It
assumes that because we live on the Earth we know everything about it.

Anyway, it's a case of over-reaching with the conclusions. It's an argument
from design.

~~~
dragonwriter
> Under the theory of science as the study of what is falsifiable, there's
> nothing here to falsify because there is no way to disprove that a
> conjectured but unobserved collision of two massive bodies was something
> else or didn't occur.

Yes, there is: if the predicted kind of observations did not occur, it would
imply one of two things:

(1) the model of gravity waves and their generation and propagation on which
the prediction was based was incorrect, or

(2) the expectation of large-object collisions on which the prediction was
_also_ based is incorrect.

Now, were that the case, _distinguishing_ which of those assumptions was false
would require coming up with a new set of experiments that would have
different results if the first was correct and the second false than if those
were flipped, and yet a different set of results if both were false.

> That there is not a geophysical theory, doesn't have a bearing on the
> correctness of the gravitational wave theory one way or the other

Science isn't about correctness, its about continuous refinement of models
which better predict observations. The absence of a better alternative model
doesn't "prove" that a given model is "correct", but science deals with
neither proof (except in the negative sense) nor correctness. (Further, the
model of gravity waves being tested here is an implication of broader models
whose other implications have also withstood attempts to falsify them.)

------
known
Everyday we're getting sun rays
[https://en.wikipedia.org/wiki/Crepuscular_rays](https://en.wikipedia.org/wiki/Crepuscular_rays)

Why are we surprised at gravitational waves when 2 black holes collided?

~~~
delecti
We actually aren't surprised. This confirms a theory we've been reasonably
confident about for about 100 years.

This is less "wow, look at what an unexpected result we found!" and more that
we finally managed to measure something we've been looking for.

~~~
macintux
Not only expected, but the predicted wave forms were virtually perfect. We
knew what to look for, and we even knew what we saw as soon as we saw it.

------
oldmanjay
A detector of this sensitivity seems like a boon for spying. Rather difficult
to relocate, fortunately, but it makes me wonder about the future of the
technology. No one would have looked at the first computer and envisioned an
iPhone.

~~~
shmerl
_> No one would have looked at the first computer and envisioned an iPhone._

Not really. Portable computers were envisioned quite a long time ago.

~~~
oldmanjay
Not before they were solid state. Computers had their own buildings and relied
on glass tubes for operation. Screens weren't on the radar. Operators were
highly educated. But technology did bring us to a point where the vision
became more focused, and led to what we have today.

There are many possible paths to rebutting my statement, which to be clear is
idle morning musing, but your objection doesn't hold water.

~~~
j1vms
I agree that you do make a point. There is really no way for us to know what
is to come. Sometimes we think we are looking at a square, but it really is a
cube and we are just unable to look beyond are current perspective for
whatever reason.

I would say one obstacle that stands in the way of "spying" on objects moving
on the Earth's surface is that the gravitational wave energy emitted by
accelerating objects on Earth would be "too small" for current detectors. Not
to mention that there would be the issue of how to filter gravitational wave
noise, and/or isolate frequencies. However, if it possible to build an
amplifier or filter to resolve these issues, that remains to be seen - or
maybe somebody else could chime in.

edit: typos, clarity

~~~
j1vms
ok, here's an idea that someone might either build on or refute: would it be
possible to build an amplifier of gravitational waves using some arrangement
of microscopic and/or macroscopic objects having a "known" defined 3D physical
relationship (say in a lattice), and under known interactional forces
(including EM). You would have to take into account the uncertainty principle
in system parameter measurement, though the propagating gravitational wave
should have a deterministic effect on the potential well and thus the quantum
wave(s) of the system(s). Thus, amplification through propagation in the
space-time of the system might be feasible. This is of course all hand-waving,
and very rough.

------
aabbccdd
I'm wondering no-one mentioned Electric Universe which is the greatest
opponent of this gravitational hocus-pocus religion. It would be much more
beneficial to the humanity to focus smart peoples' attention to Birkeland
currents or plasma or to the recent experiments of the SAFIRE project. They
have several series on their youtube channel:

[https://www.youtube.com/user/ThunderboltsProject/videos](https://www.youtube.com/user/ThunderboltsProject/videos)

~~~
vecter
You ... must be trolling.

