
Have Gravitational Waves Been Detected? - MKais
http://www.universetoday.com/110353/rumors-flying-nearly-as-fast-as-their-subject-have-gravitational-waves-been-detected
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sanxiyn
Of course gravitational waves have been detected. Detection was awarded Nobel
Prize in Physics in 1993. It has not been _directly_ detected, but BICEP2 will
not directly detect it either.

The significance is that this would be an experimental observation of cosmic
inflation. How it is observed (gravitational wave) is less important.

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frozenport
I understand that LIGO can detect something, but how do they know where it
came from? How can they register a disturbance in the spectra to a a source?
Do they really quickly point a ccd at the sky and hope they captured what
happened?

~~~
ausdemserail
CMB telescopes use microwave antennas (often feedhorns) to direct the
electromagnetic radiation onto some kind of detector. In the case of BICEP,
the detector is a superconducting bolometer, which senses small temperature
changes caused by CMB photons depositing themselves onto a resistive element.

To get data, a CMB telescope is scanned across the sky for several months (or
years), and the raw time signals are converted into a map of the microwave
sky.

LIGO is an entirely different category of scientific instrument; it is looking
for the direct influence of present-day gravitational waves on the motion of
terrestrial masses.

~~~
platz
I wonder if they're still going for LISA (> ligo). I guess LIGO wasn't
sensitive enough? [http://lisa.nasa.gov/](http://lisa.nasa.gov/)

~~~
ausdemserail
The first gravitational wave detectors weren't sensitive enough; there is a
second generation (including a more advanced version of LIGO) that is supposed
to come online in the next few years.

In parallel, people are also going forward with development for LISA. It had
to be scaled back a bit because NASA decided to pull out, but it's still
going.

~~~
astrosi
Just as a reason for doing this in parallel. Space based detectors (such as
LISA) are sensitive to a different frequency range than ground based detectors
such as LIGO and thus to different of astrophysical phenomena [1]

[1]
[http://www.ast.cam.ac.uk/~rhc26/sources/](http://www.ast.cam.ac.uk/~rhc26/sources/)

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nsxwolf
How did we get ahead of the waves? Or did they wrap around a curved universe
and come back to us?

~~~
ggdG
IANAC [1], but here's my Wikipedia-level 2 cents:

(Warning: leaky metaphors ahead!)

We stayed ahead of the primordial gravitational waves [2] for so long because
the expanding universe went through an "inflation" period: in a very short
time - immediately after the Big Bang - spacetime expanded at a rate that was
many orders of magnitude too big for phenomena like light or gravitational
waves to catch up to.

It leveled off quickly to a more gentle rate of expansion [3], but in the
meantime the universe has gotten so big that even its current age of 13.7
billion years isn't enough for us to be able to observe every object. Many
objects are so far from us that it will take much more than 13.7 billion years
for their photons to reach us. And no matter how distant the objects that will
'come into view' in the future, the light that appears the most distant to us
will always be the cosmic microwave background radiation.

So here we find ourselves, Earthly observers, sitting in the center of a
sphere with an apparent radius of 13.7 billion lightyears - called the
observable universe - at the edge of which we can see the immediate aftermath
of the Big Bang. No one knows how much bigger the total universe is w.r.t. to
the observable universe. It's hard to find out because we have no causal
relation to anything outside the observable universe. A safe bet IMHO (given
past experiences in the history of cosmology) is this: the entire universe is
way, way, way bigger than the observable universe.

[1] I Am Not A Cosmologist

[2] and also of the cosmic microwave background radiation

[3] sub light speed, at least for distances within the observable universe

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vl
In my layman understanding current prevailing theory is that acceleration of
expansion will reduce observable universe, and as consequence there is
basically no question of "size beyond observable universe" \- there is no
possible interaction with it and as such it doesn't exist.

[http://en.wikipedia.org/wiki/Accelerating_universe](http://en.wikipedia.org/wiki/Accelerating_universe)

~~~
lutusp
> In my layman understanding current prevailing theory is that acceleration of
> expansion will reduce observable universe, and as consequence there is
> basically no question of "size beyond observable universe" ...

Yes, but that was true before the Dark Energy discovery. It's predicted to
become much worse in the far distant future because of the acceleration caused
by Dark Energy, and eventually there will be comparatively small island
universes -- galactic clusters -- that will remain gravitationally bound far
into the future, after the remainder of the universe has receded from view.
This is because galactic clusters are below the threshold for being affected
(i.e. torn apart) by Dark Energy.

> there is no possible interaction with it and as such it doesn't exist.

Yes to the first, no to the second. At present, we cannot see beyond a certain
time horizon, but cosmological curvature measurements take this invisible
mass-energy into account even though it's not directly observable. Our present
conjecture that the universe is infinite in size (based on curvature
measurements) obviously implies a universe most of which isn't visible, but
all of which affects the measurements.

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akuchling
Sean Carroll's explanation of how this detection of gravitational waves could
set constraints on inflationary theories is helpful:

[http://www.preposterousuniverse.com/blog/2014/03/16/gravitat...](http://www.preposterousuniverse.com/blog/2014/03/16/gravitational-
waves-in-the-cosmic-microwave-background/)

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DonGateley
What has always puzzled me about this is why anyone would think that a local
change in a gravitational field would not propagate as a wave. What the hell
else could it do?

I do believe there are differential equations involved that make the field at
one point dependent on the field at another point after a period of time and
that's all that's required.

~~~
trhway
>why anyone would think that a local change in a gravitational field would not
propagate as a wave. What the hell else could it do?

propagate immediately. Wave is a propagation with finite speed (and the
expectation is for gravitational waves to have the same "c" ). There wouldn't
be "wave" in immediate propagation, i.e. with infinite speed.

~~~
DonGateley
Are their no other testable aspects of GR that would show gravity changes to
have finite propagation speed?

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andrelaszlo
[http://downforeveryoneorjustme.com/www.cfa.harvard.edu](http://downforeveryoneorjustme.com/www.cfa.harvard.edu)

> It's not just you! [http://www.cfa.harvard.edu](http://www.cfa.harvard.edu)
> looks down from here.

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aaron695
Not sure why this isn't top of HN. Isn't this huge?

Stream Monday 17th, 15:55 UTC -

[http://www.cfa.harvard.edu/news/news_conferences.html](http://www.cfa.harvard.edu/news/news_conferences.html)

~~~
lutusp
> Not sure why this isn't top of HN.

Gravitational waves beating a story about someone who Hula hooped for a rapt
audience of geeks? Get serious. :)

> Isn't this huge?

It could well be huge. Gravitational waves are the last confirmation of
general relativity that so far has no direct observational evidence.

I say "direct" because pulsars (compact, very massive collapsed stars that
emit radio pulses) have been observed to slow their pulse rates over time
consistent with the idea that they're radiating away some of their kinetic
energy in the form of gravitational waves. But this is indirect evidence at
best, and there are other possible explanations for the decline in pulse
rates.

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JacobAldridge
I'm looking forward to this as much as I did NASA's 2010 secretive massive
announcement of extraterrestrial life.

s/extraterrestrial life/arsenic-based life on earth

s/arsenic-based life on earth/something maybe

~~~
juliangamble
[http://en.wikipedia.org/wiki/GFAJ-1#Criticism](http://en.wikipedia.org/wiki/GFAJ-1#Criticism)

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batbomb
There's a good amount of preparation at Stanford astrophysics underway for
discussion of the results from the BICEP2 collaboration tomorrow.

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Pitarou
If you see a headline that asks a yes-no question, the answer is almost
always, "No."

~~~
InclinedPlane
If you don't know anything about the subject then deciding the answer to a
yes/no question without any data or logic is a useless exercise.

In this case the answer is almost certainly "yes", not least because
gravitational waves have already been detected anyway, though as with the
current experiment indirectly.

~~~
Pitarou
Damn! The one time I quote Betteridge's Law (thanks, hemmer), and it turns out
the answer is "yes".

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Pitarou
So far this is just hype, speculation, and an "aspiring science journalist"
(says so in the byline) trying to make a name for herself.

If she's right, big scoop and plaudits to her.

If she's wrong, nobody cares. She covered her ass with a question mark.

Smart woman. She'll go far, I'm sure.

