# Gravity waves detected



## Brian G Turner (Feb 11, 2016)

Gravitational waves from black holes detected - BBC News



> "The fact that we are sitting here on Earth feeling the actual fabric of the Universe stretch and compress slightly due to the merger of black holes that occurred just over a billion years ago - I think that's phenomenal. It's amazing that when we first turned on our detectors, the Universe was ready and waiting to say 'hello'," the Glasgow University scientist told the BBC.



Something confuses me here - how were researchers able to target readings only from one specific gravitational encounter? If the universe is full of gravity waves, how do researchers separate one signal from all the noise - especially when the actual effect (the fraction of a width of an atom) is beyond tiny?

If the signal from two huge blackholes is so tiny, then are we really going to learn all that much about the universe from gravity waves? It comes across like trying to claim to be able to understand Mozart's symphonies through awareness only of the loudest bass note.

I know there's a lot of hype about this - Einstein was right about something! But we knew that he was right about most things. And yet, somehow, our understanding of how to apply gravity at the quantum level is an unsolvable puzzle - at least, so far. There remains something profoundly missing in our understanding of the universe, but this development doesn't really seem to add that much.

I am absolutely happy for anyone to argue otherwise.


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## TheEndIsNigh (Feb 11, 2016)

I'm not convinced.

I saw a program on the facility on "Horizon" maybe.

I seem to recall the guys there were saying the lasers were so sensative they had to ignore reading at some times of the day because a train could be detected quite a few miles away and it gave false positives or saturated the reading. Also from what I understand the wave would have to align perfectly along the long axis of one of the detectors. Since this woud happen only rarely and given the Earth's rotation only momentarily, I can't see how they know where the source of the wave was. Smoke and mirrors spring to mind.

Plus I'm an advocate of "gravity is faster than the speed of light" theory, which if true, to my mind would mean the thing would be too slow to spot a gravity wave.


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## Ursa major (Feb 11, 2016)

TheEndIsNigh said:


> I seem to recall the guys there were saying the lasers were so sensative they had to ignore reading at some times of the day because a train could be detected quite a few miles away and it gave false positives or saturated the reading.


That's why they use two** of them. The pattern they are saying represents the collapsing into each other of two black holes*** was detected and recorded at both those sites, and I'm pretty sure that while US trains are very long, they don't stretch from Louisiana to Washington State.


** - Although, I suppose, more would be useful. Unfortunately, the one in Italy (VIRGO) is off-line for a major upgrade and others have not yet been completed.

*** - Because the wave pattern at each detector closely matches the one predicted to be emitted by such an event.


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## Lew Rockwell Fan (Jun 4, 2016)

Ursa major said:


> while US trains are very long, they don't stretch from Louisiana to Washington State


A dramatic image though. Kind of makes me want to think up a plausible excuse for a train thousands of miles long. If it ran on a closed loop, it could connect to its own rear and be like a conveyer belt.


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## Ray McCarthy (Jun 8, 2016)

*LISA working better than expected!*
It's a test rig, the "real" one will be three satellites linked by lasers, millions of kilometres apart at a Lagrange point.

LISA Pathfinder free fall test beats expectations

ESA Science & Technology: Test cubes floating freely inside LISA Pathfinder

Gravitational spacecraft LISA Pathfinder opens Einstein’s universe

LISA Pathfinder exceeds expectations


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## Brian G Turner (Jun 8, 2016)

Are gravity waves supposed to be transverse or converse? I ask because my initial image was of a ripple in space/time - but now I wondered if it wasn't more likely to be stretching.


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## Ray McCarthy (Jun 8, 2016)

No idea, but if you have a tetrahedral set of masses and measure the distance change vs time (frequency and strength), you can detect from any direction, know direction and it will work for transverse or longitudinal waves. I don't even know if the question is meaningful, I suppose it is. I know about sound and electromagnetic. Sound can carried by longitudinal pressure variation in a gas. EM can be curiously regarded as longitudinal transmission of photos, or transverse magnetic and electric fields at right angles to each other. Aerials for radio can be responding to the magnetic field (loops), or primarily electric field (rod)*. Light detectors (IR, visible, UV) are usually photons causing a quantum photoelectric effect (one of Einstein's early papers), though there has been a suggestion that the retina uses dipoles rather than photoelectric cones for colour, the size then would explain the three (or four in some people) overlapping colour sensitivity curves. The rods may be photoelectric, which would explain lack of colour and higher sensitivity.

Gravity waves are very mysterious.

[* At lower radio frequencies the E field of an interference source is more powerful than the M field and a short rod will be very poor for reception of EM waves. A loop works well at low frequencies, LW & MW, so one radio technique is to have the loop for reception (every LW / MW radio ever made since 1922 with a built in aerial!) and a short telescopic aerial, or fixed rod, like on cheap VHF radio which picks up local interference much better and the radio signal badly, then the signal levels  and phase are adjusted so the interference is reduced. Naturally no domestic radios have this great feature, adds too much cost. No-one makes good domestic radios any longer.]


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## Brian G Turner (Jun 8, 2016)

I remember in basic physics all waves was classified as transverse or longitudinal, but sound was regarded as the only example of the latter.

In trying to imagine space/time as like a rubber mat (the popular analogy) it occurred to me that waves might be the stretching and compression of this, ie, longitudinal, rather than transverse ripples.


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## Ray McCarthy (Jun 8, 2016)

Brian Turner said:


> it occurred to me that waves might be the stretching and compression of this,


Yes, I agree, though that is just an analogy, I don't think it's really like a stretchy mat with depressions caused by mass.


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## Stephen Palmer (Jun 16, 2016)

More on these extraordinary discoveries.


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## Vertigo (Jun 16, 2016)

Interesting comment "...that propagate at the speed of light". I think it was always wishful thinking that they might be faster!


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## Ray McCarthy (Jun 16, 2016)

Vertigo said:


> I think it was always wishful thinking that they might be faster!


It wasn't scientific thinking


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## Ray McCarthy (Jul 1, 2016)

Another idea about gravity waves:
BAM! Astroboffins now have a second way of picking up black holes' collision super kicks

Needs new detector.


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## J Riff (Jul 2, 2016)

Was just listening to a description of how light actually goes nowhere, merely reflects its way about the universe. How much does a light particle weigh, once it gets here from, say, Andromeda Galaxy?
Gravity waves still mysterious. Mass attracts, that's all I remember.


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## Ray McCarthy (Jul 2, 2016)

Light (includes Radio, Infra-red and x-Rays, they are all the same thing) can be regarded as Electromagnetic waves, as described by Maxwell in the 19th Century, who predicted the invariant speed of Light and thus hinted at Relativity. Einstein built on his work. Electromagnetic waves can instead or at the same time be regarded as particles called Photons.

Photons are traditionally said to be massless. Otherwise they could never travel at the speed of light! (yes I know since light IS photons, that's mental!)

So a light particle weighs nothing, except that's a little misleading.  

Further reading (The proper answer is a little strange).
What is the mass of a photon?
If photons have no mass, how can they have momentum?
If photons have zero mass, why do they feel the effects of gravity? (Advanced) - Curious About Astronomy? Ask an Astronomer
Does light have mass?
Photon - Wikipedia, the free encyclopedia


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