8 ms·

The Science of the Missing Gravitational Waves

91 points by pmcpinto 10y ago

dexwiz 10y ago
Can someone explain why it takes so long to form an image? The article reads like they still don't have enough data to see anything. From my understand of physical measurement, you start with a `blurry` image (or a graph with a wide peak), and it slowly comes into focus with more data. If the image is too faint because of the signal to instrument precision (noise) ratio is too low, you will never get an image, no matter how much data you have. I was bad at analytical chemistry, so my understanding may be completely wrong.
- InclinedPlane 10y ago
  > "If the image is too faint because of the signal to instrument precision (noise) ratio is too low, you will never get an image..." I'm curious why this makes sense to you? Does it make sense that you could use an ordinary film camera and take a picture with an arbitrarily short exposure, say a picosecond? With very, very low SNR it can take a long time to build up data. The reason why this is possible is because the real data, the signal, is correlated with itself, it builds up consistently with each addition of measurements. Noise, however, is uncorrelated, it's random, so it tends to evenly cancel (or even) itself out with additional measurements.
- pdonis 10y ago
  > The article reads like they still don't have enough data to see anything. That's because whatever signal is out there is quite a bit fainter than the initial estimates predicted it would be. If the signal were as strong as the initial estimates predicted, it would have been seen by now.
- hn9780470248775 10y ago
  If you're talking about making a map of the astrophysical or cosmological backgrounds of gravitational waves -- you're right. As you integrate (i.e. capture more data), the noise will tend to cancel out while the signal will reinforce itself. But the problem is that the signal-to-noise-ratio is so small -- essentially zero -- that, with current detector sensitivity, it would take literally forever to get an image with any features at all.
antognini 10y ago
There's a great deal that's not understood about supermassive black holes (SMBHs). This article deals with one of these open questions (Why is the GW background from SMBH mergers less than predicted?), but there are a number of other related problems. Here are a few off the top of my head: * How do SMBHs form? Is it from the merger of a bunch of stellar-mass black holes or do is it from the collapse of a huge gas cloud 1000s of times the mass of the Sun (or more) when the galaxy is first forming? * Why are the masses of SMBHs so tightly correlated to the masses of their host galaxies? This is known as the M-sigma relation and there's been a lot of research on this topic, in particular. The existence of this correlation implies that SMBHs are somehow involved in some sort of feedback mechanism with the rest of the galaxy, but this is very poorly understood. (There have been lots of different feedback mechanisms invoked, but it's been hard to discriminate between them to see what's really going on.) * How do SMBHs merge? We know that SMBHs are at the center of nearly all galaxies (if not all of them), and we know that galaxies merge. We don't usually see multiple SMBHs in a galaxy, so somehow the SMBHs must merge as well. But models of these mergers stall out at around a few light-years. At this distance, stars are too far away to influence the orbit, but gravitational waves are too weak to do anything. Somehow real SMBH binaries in the universe manage to overcome this problem, but how? This is known as the last parsec problem. * We see SMBHs driving huge, extremely powerful jets. What causes the formation of these jets? Why are they so collimated? The Blandford-Znajek process is usually invoked, but (at least in my opinion) while it's plausible, there's a fair amount of hand-waving and not as much observational evidence as one would like. * Not a question dealing with SMBHs specifically, but do black holes obey the No Hair Theorem? (Or, put another way, is GR correct in the strong gravity regime?) This is being tested with the Event Horizon telescope, which is attempting to observe the event horizon of the SMBH at the center of the Milky Way. They're fascinating objects, and due to their enormous size and energetics they are relevant to a huge number of problems in astrophysics and fundamental physics.
- ars 10y ago
  My theory: Black holes don't exist (time dilation prevents them from forming in a finite time). Dark matter is gravitational potential energy. (i.e. the potential energy of every star in a solar system falling into every other star, plus the energy of every galaxy falling into every other galaxy.) Cosmological redshift is actually gravitational redshift. (So dark energy is not necessary as a concept.) There is a lot more gravity out there in my theory. Don't forget that the relative motion of galaxies is inferred from redshift - if the cause of the redshift is not velocity then galaxies are not moving in the way we currently think they are. I wish I had the math to flesh these ideas out to see if they hold water.
yugai 10y ago
Come on, remember falsifiability, if the theory wins in any likely scenario it's not science but ideology
ChuckMcM 10y ago
This reminded me that one of the things I felt would be interesting for Apple to do, would be to drape a conductive net over the center of their new campus with supports to hold a receiver above it at the focal point, turning their headquarters building into a 1,000' diameter radio telescope.
- omegant 10y ago
  Is not being installed inside a city a big problem for interferences?
DiabloD3 10y ago
I started thinking the electric universe guys were a bunch of crackpots, but I'm wondering if they're actually right.
known 10y ago
missing = we are "unable" to detect

91 points by pmcpinto 10y ago

Can someone explain why it takes so long to form an image? The article reads like they still don't have enough data to see anything. From my understand of physical measurement, you start with a `blurry` image (or a graph with a wide peak), and it slowly comes into focus with more data. If the image is too faint because of the signal to instrument precision (noise) ratio is too low, you will never get an image, no matter how much data you have. I was bad at analytical chemistry, so my understanding may be completely wrong.

InclinedPlane 10y ago
> "If the image is too faint because of the signal to instrument precision (noise) ratio is too low, you will never get an image..." I'm curious why this makes sense to you? Does it make sense that you could use an ordinary film camera and take a picture with an arbitrarily short exposure, say a picosecond? With very, very low SNR it can take a long time to build up data. The reason why this is possible is because the real data, the signal, is correlated with itself, it builds up consistently with each addition of measurements. Noise, however, is uncorrelated, it's random, so it tends to evenly cancel (or even) itself out with additional measurements.
pdonis 10y ago
> The article reads like they still don't have enough data to see anything. That's because whatever signal is out there is quite a bit fainter than the initial estimates predicted it would be. If the signal were as strong as the initial estimates predicted, it would have been seen by now.
hn9780470248775 10y ago
If you're talking about making a map of the astrophysical or cosmological backgrounds of gravitational waves -- you're right. As you integrate (i.e. capture more data), the noise will tend to cancel out while the signal will reinforce itself. But the problem is that the signal-to-noise-ratio is so small -- essentially zero -- that, with current detector sensitivity, it would take literally forever to get an image with any features at all.

antognini 10y ago

There's a great deal that's not understood about supermassive black holes (SMBHs). This article deals with one of these open questions (Why is the GW background from SMBH mergers less than predicted?), but there are a number of other related problems. Here are a few off the top of my head: * How do SMBHs form? Is it from the merger of a bunch of stellar-mass black holes or do is it from the collapse of a huge gas cloud 1000s of times the mass of the Sun (or more) when the galaxy is first forming? * Why are the masses of SMBHs so tightly correlated to the masses of their host galaxies? This is known as the M-sigma relation and there's been a lot of research on this topic, in particular. The existence of this correlation implies that SMBHs are somehow involved in some sort of feedback mechanism with the rest of the galaxy, but this is very poorly understood. (There have been lots of different feedback mechanisms invoked, but it's been hard to discriminate between them to see what's really going on.) * How do SMBHs merge? We know that SMBHs are at the center of nearly all galaxies (if not all of them), and we know that galaxies merge. We don't usually see multiple SMBHs in a galaxy, so somehow the SMBHs must merge as well. But models of these mergers stall out at around a few light-years. At this distance, stars are too far away to influence the orbit, but gravitational waves are too weak to do anything. Somehow real SMBH binaries in the universe manage to overcome this problem, but how? This is known as the last parsec problem. * We see SMBHs driving huge, extremely powerful jets. What causes the formation of these jets? Why are they so collimated? The Blandford-Znajek process is usually invoked, but (at least in my opinion) while it's plausible, there's a fair amount of hand-waving and not as much observational evidence as one would like. * Not a question dealing with SMBHs specifically, but do black holes obey the No Hair Theorem? (Or, put another way, is GR correct in the strong gravity regime?) This is being tested with the Event Horizon telescope, which is attempting to observe the event horizon of the SMBH at the center of the Milky Way. They're fascinating objects, and due to their enormous size and energetics they are relevant to a huge number of problems in astrophysics and fundamental physics.

ars 10y ago
My theory: Black holes don't exist (time dilation prevents them from forming in a finite time). Dark matter is gravitational potential energy. (i.e. the potential energy of every star in a solar system falling into every other star, plus the energy of every galaxy falling into every other galaxy.) Cosmological redshift is actually gravitational redshift. (So dark energy is not necessary as a concept.) There is a lot more gravity out there in my theory. Don't forget that the relative motion of galaxies is inferred from redshift - if the cause of the redshift is not velocity then galaxies are not moving in the way we currently think they are. I wish I had the math to flesh these ideas out to see if they hold water.

yugai 10y ago

Come on, remember falsifiability, if the theory wins in any likely scenario it's not science but ideology

ChuckMcM 10y ago

This reminded me that one of the things I felt would be interesting for Apple to do, would be to drape a conductive net over the center of their new campus with supports to hold a receiver above it at the focal point, turning their headquarters building into a 1,000' diameter radio telescope.

omegant 10y ago
Is not being installed inside a city a big problem for interferences?

DiabloD3 10y ago

I started thinking the electric universe guys were a bunch of crackpots, but I'm wondering if they're actually right.

known 10y ago

missing = we are "unable" to detect