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I'm part of the LIGO team responding to the AMA. If anyone on HN sees a good question that hasn't been answered, link it here and I'll sure we get to it!

by pinko 11y ago

pasbesoin 11y ago
I haven't looked into LIGO at all, so this is very likely not just off-the-cuff but out to lunch. But I'll ask: What if people start looking at the (very) precise timing of particle beam circulation e.g. at CERN? I would guess there is not sufficient resolution. And maybe it's beyond what's possible. But, thinking of additional avenues for measurement, and something that might be extant or require less build-out. And now, there would be something against which to compare anomalies, were they to be measurable.
danbruc 11y ago
I am not sure if it was already asked, I read the Reddit thread a day or two ago, but were there additional events after the first one or was it the only one so far?
- abecedarius 11y ago
  I'm just a bystander, but: the paper mentions another, weaker signal in the time period they wrote up (18 days IIRC). That one had an estimated false-signal rate of once in a couple years (the main one was more like once a century).
  - kgwgk 11y ago
    > (the main one was more like once a century). More like once in 200'000 years, actually.
    - abecedarius 11y ago
      Thanks.
ars 11y ago
Can I ask my question here? I saw somewhere that you adjusted for cosmological redshift. Did you also adjust for gravitational redshift as the gravity wave left the gravity well of the black holes? What about time dilation of the wave signal caused by gravity and orbital velocity?
ghayes 11y ago
Again, asking here since it's easier, but sorry if that wasn't the intent. To get a better understanding of what LIGO is observing, does every massive object create a gravitational wave as it moves? Do gravitational waves act similarly as to how moving a charged particle creates magnetic flux? Do we know from LIGO if gravitational waves propagate at exactly the speed of light?
- pacifist 11y ago
  Not on the team. Not even close. My under standing from other comments from the team is yes and yes. The reason we needed a collision of black holes was to get the signal up to where we can detect it. And they definitely said that this proves that gravitational waves propagate at the speed of light.
- versteegen 11y ago
  No, only accelerating objects create gravitational waves. (Massless particles have energy so also have gravitational fields and produce gravity waves when accelerating, by mass-energy equivalence.) The analogue of a gravity wave is not a magnetic field, which is created by a moving charge, but rather the electromagnetic radiation produced by an accelerating charge, e.g. synchrotron radiation or radio waves from an antenna.
BananaPelican 11y ago
(Also cheating by not linking to a Reddit post) I know this is speculative, but do you think it is possible and/or plausible that measurement precision could be improved to the point where we generate gravity waves to transmit data much as we do with EM waves?
- topquark 11y ago
  Another LIGO scientist here. It takes an overwhelming amount of energy to generate gravitational waves, and detecting them from terrestrial sources is about 20 orders of magnitude more difficult than the measurement we just made. Space, is extremely stiff; bending it enough to be detectable requires a huge amount of mass-energy.
- deleted 11y ago
  [deleted]
anotheryou 11y ago
How did they figure out where the black holes are? with just 2 "ears" I'd expect to be only able to determine a circle, but here is the picture they released: http://www.dailygalaxy.com/.a/6a00d8341bf7f753ef01b8d19e59ad970c-800wi http://www.dailygalaxy.com/.a/6a00d8341bf7f753ef01b8d19e59ad... Do i see a warped circle, or the bottom part of one? In the latter case I wonder how they found out. Are the L-shape sensors capable of seeing some direction depending on which way the phases shift first/last? If you'd build one of the sensors in reverse you'd see a reversed signal, no (and in between other amplitudes)? Given that they will have optimized the orientations of both stations this is probably how it worked and I'm seeing just part of a circle, right? That one lonely blob might be an unlikely mirrored version?
- dps1879 11y ago
  I love you me. Dont be like them and try to make your observations fit their theory. A theory is a guess only and period. Actually you are a wiser me.

I'm part of the LIGO team responding to the AMA. If anyone on HN sees a good question that hasn't been answered, link it here and I'll sure we get to it!

by pinko 11y ago

I'm part of the LIGO team responding to the AMA. If anyone on HN sees a good question that hasn't been answered, link it here and I'll sure we get to it!

pasbesoin 11y ago

I haven't looked into LIGO at all, so this is very likely not just off-the-cuff but out to lunch. But I'll ask: What if people start looking at the (very) precise timing of particle beam circulation e.g. at CERN? I would guess there is not sufficient resolution. And maybe it's beyond what's possible. But, thinking of additional avenues for measurement, and something that might be extant or require less build-out. And now, there would be something against which to compare anomalies, were they to be measurable.

danbruc 11y ago

I am not sure if it was already asked, I read the Reddit thread a day or two ago, but were there additional events after the first one or was it the only one so far?

abecedarius 11y ago
I'm just a bystander, but: the paper mentions another, weaker signal in the time period they wrote up (18 days IIRC). That one had an estimated false-signal rate of once in a couple years (the main one was more like once a century).
- kgwgk 11y ago
  > (the main one was more like once a century). More like once in 200'000 years, actually.
  - abecedarius 11y ago
    Thanks.

ars 11y ago

Can I ask my question here? I saw somewhere that you adjusted for cosmological redshift. Did you also adjust for gravitational redshift as the gravity wave left the gravity well of the black holes? What about time dilation of the wave signal caused by gravity and orbital velocity?

ghayes 11y ago

Again, asking here since it's easier, but sorry if that wasn't the intent. To get a better understanding of what LIGO is observing, does every massive object create a gravitational wave as it moves? Do gravitational waves act similarly as to how moving a charged particle creates magnetic flux? Do we know from LIGO if gravitational waves propagate at exactly the speed of light?

pacifist 11y ago
Not on the team. Not even close. My under standing from other comments from the team is yes and yes. The reason we needed a collision of black holes was to get the signal up to where we can detect it. And they definitely said that this proves that gravitational waves propagate at the speed of light.
versteegen 11y ago
No, only accelerating objects create gravitational waves. (Massless particles have energy so also have gravitational fields and produce gravity waves when accelerating, by mass-energy equivalence.) The analogue of a gravity wave is not a magnetic field, which is created by a moving charge, but rather the electromagnetic radiation produced by an accelerating charge, e.g. synchrotron radiation or radio waves from an antenna.

BananaPelican 11y ago

(Also cheating by not linking to a Reddit post) I know this is speculative, but do you think it is possible and/or plausible that measurement precision could be improved to the point where we generate gravity waves to transmit data much as we do with EM waves?

topquark 11y ago
Another LIGO scientist here. It takes an overwhelming amount of energy to generate gravitational waves, and detecting them from terrestrial sources is about 20 orders of magnitude more difficult than the measurement we just made. Space, is extremely stiff; bending it enough to be detectable requires a huge amount of mass-energy.
deleted 11y ago
[deleted]

anotheryou 11y ago

How did they figure out where the black holes are? with just 2 "ears" I'd expect to be only able to determine a circle, but here is the picture they released: http://www.dailygalaxy.com/.a/6a00d8341bf7f753ef01b8d19e59ad970c-800wi http://www.dailygalaxy.com/.a/6a00d8341bf7f753ef01b8d19e59ad... Do i see a warped circle, or the bottom part of one? In the latter case I wonder how they found out. Are the L-shape sensors capable of seeing some direction depending on which way the phases shift first/last? If you'd build one of the sensors in reverse you'd see a reversed signal, no (and in between other amplitudes)? Given that they will have optimized the orientations of both stations this is probably how it worked and I'm seeing just part of a circle, right? That one lonely blob might be an unlikely mirrored version?

dps1879 11y ago
I love you me. Dont be like them and try to make your observations fit their theory. A theory is a guess only and period. Actually you are a wiser me.