How does LIGO separate vibrations caused by a nearby truck from whatever reading that is required for gravitational waves?
Well, for one, there are two detectors, one in Louisiana and another in Washington.
LIGO Detects Gravitational Waves for Third Time
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Re: LIGO Detects Gravitational Waves for Third Time
#32How does LIGO separate vibrations caused by a nearby truck from whatever reading that is required for gravitational waves?
This is a complete guess, as I don't have any firsthand knowledge ... but I can only imagine that they have a whole array of seismographs on the premises, which they can use to clear noise from the main LIGO readings they are interested in.
Curious to know if this is the case from anyone who happens to know one way or the other :)
edit: the more I think about it, the more I think that random vibrations from passing trucks would be irrelevant ... it doesn't detect vibrations, it's measuring the speed of light between two points
Re: LIGO Detects Gravitational Waves for Third Time
#33Earlier quoted context omitted.
Black holes have mass, just like any other object in the universe - like a star, or a planet, or the sun. Consequently, they follow orbits just as any other mass would. In some cases, they're the local most massive object and any other masses move more in response. Other times they are near other black holes, and they orbit one another until they collide and merge. What makes black holes different is their density. T…
I guess this was the biggest question answering piece to me. When I think of a black hole, I assume it has a gigantic mass, enough that it's always the most massive local object, and subsequently pulls in all other things. I didn't realize that might not be the case. As black holes "absorb" everything that "falls" into them, do they continue to build mass then?
Yes.
Whether or not something is a black hole is dependent on its total mass and its radius. So anything can mathematically become a black hole if you compress it enough. The earth could be a black hole if it's total mass were compressed to something like 'less than the diameter of a grapefruit'. At that point space itself cannot contain the mass, physics breaks down and you get a singularity.
The moon would continue to orbit as it always did, since the moon's centre of mass is still exactly the same distance from the earth's centre of mass as it was before you pressed the 'compress button' on the north pole.
It takes incredible amounts of energy to cause this compression however. And this is why only the biggest stars become black holes. As the outward pressure of fusion diminishes because the hyrogen/helium/lithium/berylium/etc fuel runs out, the sheer gravitational pull of all that mass suddenly takes over and that inward momentum from all directions is enough to cause a singularity.
Re: LIGO Detects Gravitational Waves for Third Time
#34Earlier quoted context omitted.
> Do black holes "move?" Yes, like any other massive objects, black holes can have velocity and momentum. Two black holes, or a black hole and another object like a star, can orbit each other in a way that almost follows Newton's laws. > How is it that they could merge if they're stationary, unless they're pulling each other in I guess? This gets at what makes LIGO's findings interesting. Two black holes merge if the…
If we scale time to one-trillion-quadrillion years into the future, isn't is possible that all mass in the universe eventually coalesces into a massive universal super black hole? Or, does the expansion of the universe outstrip that?
Not an expert, but the evidence is pointing towards continued expansion until a 'big freeze'
https://en.wikipedia.org/wiki/Future_of_an_expanding_univers...
Re: LIGO Detects Gravitational Waves for Third Time
#35Great veritasium video about this latest wave: https://www.youtube.com/watch?v=NVKO7UCIlgs
What is involved with increasing sensitivity I wonder? Is it purely lengthening the arms? or are there other advancements required?
Hopefully one day we can have these things in space, isolated from noise and curvature of the earth and no need for vacuum equipment.
Re: LIGO Detects Gravitational Waves for Third Time
#36Earlier quoted context omitted.
These waves are extremely small, and we've just managed to build instruments sensitive enough to detect the very biggest ones. Earth bound instruments will no doubt get better, but to get a real jump in quality, you need instruments in the stillness of space: http://www.einstein-online.info/spotlights/eLISA
The info on eLISA is great. I am just waiting for the $10,000 shielding for high end speakers to keep gravity waves from interfering with the acoustic purity of the sound they produce. :-)
I will happily sell you such shielding for $10,000...
Re: LIGO Detects Gravitational Waves for Third Time
#37Earlier quoted context omitted.
Events big enough to be detected are quite rare, but the phenomenon you are asking about is more a financial reality than a "convenient coincidence" as you put it. There is a pretty steep curve connecting sensitivity and cost, so when the team that built LIGO was designing it, they used the best available models of colliding black hole event rates to estimate the sensitivity required to deliver a conclusive result in…
> If you're getting 10 events/second with a device like this, you probably overpaid for sensitivity Aside from issues processing and disentangling the overlapping events in a situation with that high of an event rate, more events would not be bad, so I'm not sure I'd call it "overpaying". Imagine the kind of population demographics that could be built up if we were detecting that many events.
Keep in mind that when LIGO was built at tremendous expense, gravitational waves were never conclusively detected, and just to get to this sensitivity it was a feat of engineering. It was unknown how long it would be or if they would ever detect a wave.
Just detecting the initial wave was one of the most important measurements in the history of physics. Now that we know that gravitational waves exist, and can give us great insight into the mysteries of the universe, there will be more efforts to detect waves at smaller amplitudes and different frequencies. That is one reason the eLISA project is going on [1].
1. https://en.wikipedia.org/wiki/Laser_Interferometer_Space_Ant...
Re: LIGO Detects Gravitational Waves for Third Time
#38How does LIGO separate vibrations caused by a nearby truck from whatever reading that is required for gravitational waves?
Here is a great video with explanations: https://www.youtube.com/watch?v=iphcyNWFD10
Short answer - they use lots of techniques - its super hard.
Re: LIGO Detects Gravitational Waves for Third Time
#39How does LIGO separate vibrations caused by a nearby truck from whatever reading that is required for gravitational waves?
This is a complete guess, as I don't have any firsthand knowledge ... but I can only imagine that they have a whole array of seismographs on the premises, which they can use to clear noise from the main LIGO readings they are interested in. Curious to know if this is the case from anyone who happens to know one way or the other :) edit: the more I think about it, the more I think that random vibrations from passing t…
vibrations from traffic, seismic events and even thunderstorms can be detected. If the mirrors or lasers move, it makes a difference. The sensitivity of these instruments are such that its akin to measuring the difference in the width of a human hair in the distance between here and alpha centauri. On the actual scale theyre measuring the slightest movement of the a fraction of a width of a proton.
Re: LIGO Detects Gravitational Waves for Third Time
#40Here's what I don't understand.
In the first detection, they mentioned that two black holes collapsed, emitted gravitational waves, and the resulting combined mass was less than then sum of two previous masses because energy was spent on gravitational wave generation. Hence it means, that due to gravitational interactions, objects leak mass. Now, we know that every object in the universe is gravitationally related to every other object, plus universe is expanding hence objects are constantly in flux with each other. The question is where all the leaked mass goes? Can this leakage account for dark matter? What about the space-time, does it function as a storage medium for this energy that now came from the leaked mass?
Please explain...