6 ms·

Have Gravitational Waves Been Detected?

66 points by MKais 13y ago

frozenport 13y ago
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?
- raverbashing 13y ago
  Yeah, I think this is the interesting part, it wasn't detected by the "gravity wave detectors" but by something else. I think that they can point the source because the effects they detected means it could have only come from one place.
- theophrastus 13y ago
  wouldn't arrival of the same event at four or more points (at different times) determine the original sphere center of the wavefront?
- ausdemserail 13y ago
  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 13y ago
    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 13y ago
      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 13y ago
        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/
nsxwolf 13y ago
How did we get ahead of the waves? Or did they wrap around a curved universe and come back to us?
- dangrossman 13y ago
  Any echo of the big bang would be coming from all directions and going in all directions. It did not leave from here and come back, it left from some other point in the universe and is just reaching us. /not-a-scientist
  - contulluipeste 13y ago
    That's how the current estimation of the universe age was made (only it was about the background space temperature of about 4 Kelvin). This time, by measuring magnetic waves they seek to find a (even slight) difference in expanding directions. /not-a-scientist-either
- ggdG 13y ago
  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
Pitarou 13y ago
If you see a headline that asks a yes-no question, the answer is almost always, "No."
- hemmer 13y ago
  http://en.wikipedia.org/wiki/Betteridge%27s_law_of_headlines http://en.wikipedia.org/wiki/Betteridge%27s_law_of_headlines
- InclinedPlane 13y ago
  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 13y ago
    Damn! The one time I quote Betteridge's Law (thanks, hemmer), and it turns out the answer is "yes".
JacobAldridge 13y ago
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 13y ago
  http://en.wikipedia.org/wiki/GFAJ-1#Criticism http://en.wikipedia.org/wiki/GFAJ-1#Criticism
DonGateley 13y ago
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 13y ago
  >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 13y ago
    Are their no other testable aspects of GR that would show gravity changes to have finite propagation speed?
- pavlov 13y ago
  The assumption for the past 100 years has been that gravity propagates as a wave -- as mentioned in the article, it's the last untested prediction of Einstein's general relativity. But conclusive evidence has not been discovered.
  - renox 13y ago
    Untested, untested.. Directly observed is a better definition, the quasar observations are quite convincing.
- T-A 13y ago
  It's not that simple, due to the gauge invariance of the theory (not all mathematical degrees of freedom correspond to physical ones) and the approximations involved in deriving wave solutions. The argument was finally settled by Feynman's "sticky beads": http://en.wikipedia.org/wiki/Sticky_bead_argument http://en.wikipedia.org/wiki/Sticky_bead_argument
sanxiyn 13y ago
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.
batbomb 13y ago
There's a good amount of preparation at Stanford astrophysics underway for discussion of the results from the BICEP2 collaboration tomorrow.
aaron695 13y ago
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 13y ago
  > 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.
  - herewecome 13y ago
    Dude! Check out Walter Russell! Russellian Science!
- InclinedPlane 13y ago
  The headline doesn't help, that's for sure. The fact is that gravitational waves have been detected already, though indirectly, and a Nobel prize was awarded for the observations more than 20 years ago. That's not why the BICEP2 results are a big deal. The reason this news is important is two fold. One, the researchers were able to observe the effect of "b-mode" gravitational waves during the earliest moments of the big bang (within the first 10^-34 seconds) which reveal important details about the specifics of the big bang. They are indirectly observing an event which is older than all matter in the Universe, older than the cosmic microwave background, older than the cosmic neutrino background, older than dark matter even (which has a high likelihood of originating from the very early Universe when the 4 fundamental forces were still unified). Two, their observations are the first direct test for the theory of cosmic inflation which seems to have produced a definitive result and the result is significant evidence for inflation. That, in turn, translates some theories into realities. For example, we tend to hedge our bets when it comes to estimating the size of the Universe, because only so much of it is visible to us. In a Universe where inflation holds the non-visible Universe must be unimaginably huge compared to the visible portion of it by many orders of magnitude. Also, most inflationary theories effectively produce multiverses (this is hard to explain, basically it's like a foam of different regions of the universe which are effectively universes unto themselves due to speed of light / expansion rate constraints).
Pitarou 13y ago
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.
akuchling 13y ago
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/gravitational-waves-in-the-cosmic-microwave-background/ http://www.preposterousuniverse.com/blog/2014/03/16/gravitat...
andrelaszlo 13y ago
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.

66 points by MKais 13y ago

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?

raverbashing 13y ago
Yeah, I think this is the interesting part, it wasn't detected by the "gravity wave detectors" but by something else. I think that they can point the source because the effects they detected means it could have only come from one place.
theophrastus 13y ago
wouldn't arrival of the same event at four or more points (at different times) determine the original sphere center of the wavefront?
ausdemserail 13y ago
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 13y ago
  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 13y ago
    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 13y ago
      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/

nsxwolf 13y ago

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

dangrossman 13y ago
Any echo of the big bang would be coming from all directions and going in all directions. It did not leave from here and come back, it left from some other point in the universe and is just reaching us. /not-a-scientist
- contulluipeste 13y ago
  That's how the current estimation of the universe age was made (only it was about the background space temperature of about 4 Kelvin). This time, by measuring magnetic waves they seek to find a (even slight) difference in expanding directions. /not-a-scientist-either
ggdG 13y ago
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

Pitarou 13y ago

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

hemmer 13y ago
http://en.wikipedia.org/wiki/Betteridge%27s_law_of_headlines http://en.wikipedia.org/wiki/Betteridge%27s_law_of_headlines
InclinedPlane 13y ago
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 13y ago
  Damn! The one time I quote Betteridge's Law (thanks, hemmer), and it turns out the answer is "yes".

JacobAldridge 13y ago

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 13y ago
http://en.wikipedia.org/wiki/GFAJ-1#Criticism http://en.wikipedia.org/wiki/GFAJ-1#Criticism

DonGateley 13y ago

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 13y ago
>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 13y ago
  Are their no other testable aspects of GR that would show gravity changes to have finite propagation speed?
pavlov 13y ago
The assumption for the past 100 years has been that gravity propagates as a wave -- as mentioned in the article, it's the last untested prediction of Einstein's general relativity. But conclusive evidence has not been discovered.
- renox 13y ago
  Untested, untested.. Directly observed is a better definition, the quasar observations are quite convincing.
T-A 13y ago
It's not that simple, due to the gauge invariance of the theory (not all mathematical degrees of freedom correspond to physical ones) and the approximations involved in deriving wave solutions. The argument was finally settled by Feynman's "sticky beads": http://en.wikipedia.org/wiki/Sticky_bead_argument http://en.wikipedia.org/wiki/Sticky_bead_argument

sanxiyn 13y ago

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.

batbomb 13y ago

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

aaron695 13y ago

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 13y ago
> 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.
- herewecome 13y ago
  Dude! Check out Walter Russell! Russellian Science!
InclinedPlane 13y ago
The headline doesn't help, that's for sure. The fact is that gravitational waves have been detected already, though indirectly, and a Nobel prize was awarded for the observations more than 20 years ago. That's not why the BICEP2 results are a big deal. The reason this news is important is two fold. One, the researchers were able to observe the effect of "b-mode" gravitational waves during the earliest moments of the big bang (within the first 10^-34 seconds) which reveal important details about the specifics of the big bang. They are indirectly observing an event which is older than all matter in the Universe, older than the cosmic microwave background, older than the cosmic neutrino background, older than dark matter even (which has a high likelihood of originating from the very early Universe when the 4 fundamental forces were still unified). Two, their observations are the first direct test for the theory of cosmic inflation which seems to have produced a definitive result and the result is significant evidence for inflation. That, in turn, translates some theories into realities. For example, we tend to hedge our bets when it comes to estimating the size of the Universe, because only so much of it is visible to us. In a Universe where inflation holds the non-visible Universe must be unimaginably huge compared to the visible portion of it by many orders of magnitude. Also, most inflationary theories effectively produce multiverses (this is hard to explain, basically it's like a foam of different regions of the universe which are effectively universes unto themselves due to speed of light / expansion rate constraints).

Pitarou 13y ago

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.

akuchling 13y ago

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

andrelaszlo 13y ago

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.