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Gravitational waves


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Author Topic: Gravitational waves  (Read 187 times)
mccoy
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« Reply #30 on: Feb 20, 2016 09:37 pm »

Guys, it turns out that GWs have a negligibile effect even near to the black holes collision we just witnessed. Someone has calculated that, at a distance of one AU (sun-earth distance) the strain would have been 10-7 that is,  imperceptible. Maybe some very faint sound effect would have been felt. I'm disappointed!!!

Such a titanic clash yields a really tiny effect in terms of gravitational waves. That's why they have been so elusive for decades.

By victor Toth

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A crude formula for the measured strain from the gravitational wave due to a binary star system is given by:
h∼2G2M1M2c4aD,h∼2G2M1M2c4aD,
where G∼6.674×10−11 m3/kg/s2G∼6.674×10−11 m3/kg/s2 is Newton's constant of gravity, M1M1 and M2M2 are the two masses, c=3×108 m/sc=3×108 m/s is the speed of light, aa is the separation between the stars and DD is the distance from the detector.
If you substitute M1=M2=30M⊙M1=M2=30M⊙, a=100 kma=100 km and D=421 MpcD=421 Mpc (after appropriate conversion of units, of course), for a separation of a=100 kma=100 km you get h=3×10−21h=3×10−21, so crude it might be, but the formula is not useless.
And it tells you that the strain is inversely proportional to distance. Which means that  if you were, say, 1 astronomical unit from the source, the strain would have been h∼3×10−7h∼3×10−7. This would have been easily detectable with a desktop experiment. (Very easily, as a matter of fact, as this strain exceed the sensitivity of the Michelson-Morley experiment from 1887 by ten orders of magnitude. Of course Michelson-Morley was not designed for this frequency range, but even so, it would have seen it for sure.)
Not only that, but since the gravitational wave emitted by GW150914 was in the audio frequency range, I suspect that humans would have heard it as the strain, acting as a momentary passing tidal effect, would have stressed their eardrums. That of course assumes that there were either no non-gravitational effects (e.g., deadly radiation from a disturbed accretion disk surrounding the coalescing binary) or the humans were well protected, so they could enjoy the "chirp" instead of having to flee for their lives...
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Steve Hydonus
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« Reply #31 on: Feb 23, 2016 01:42 am »

"Steve, I'm sorry that I'm not able to write so clearly, I'll have to try and simplify things. What I do usually is to rewrite what I grasped but of course I'm not a perfect explainer.
By the way, I'm not a scientist, lol, I'm a professional who likes scientific topics but has serious voids of knowledge in some subjects (for example, biology).

I'll write more topics on gravitational waves, with some very simple yet effective examples. Again, by writing these things I'm testing my own comprehension of such phenomena."

Quote from mccoy.

It seems to me that one of the great things about this discovery is that before we new about light traveling through space and the idea of dark matter which scientists do not seem to b able to describe currently. But gravitational waves adds another factor that can traverse space. Something else that is natural and not man made.

Steve
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« Reply #32 on: Feb 23, 2016 05:35 am »

Not my words:

"imagine letting your hands trail in the water on each side of a rubber raft and feeling the waves on the surface of the water brush your fingers — but neither really does it justice. “You have to sort of try to grasp new phenomena by analogy,” he explains, “but it's just a completely different way of viewing the universe...There's no sense that you can appeal to, because humans don't have a spacetime sensing sense."
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« Reply #33 on: Feb 23, 2016 10:54 pm »

Like Steve says, GWs are important because they are a new way to 'see' the universe. They convey information which is often not conveyed by electro magnetic waves and visible light. We are starting now to develop a new kind of telescopy. Also, GWs can go beyond the wall of CMBR, cosmic microwave background radiation, which is the absolute limit for visible light. Hence, GWs can relate info belonging to the first 300 000 years after creation.

Like SI says, we can only reason by analogy. The analogy of a pond (spacetime fabric) rippled by a stone thrown into it is very crude and not an exact one. GWs only occur in particular conditions, particularly, acceleration of a mass is necessary, which is not in conditions of circular or cylindrical simmetry. For example, a perfectly spherical body which rotates on its axis does not give rise to GWs. Irregularities in the spherical simmetry do give rise to GWs.
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« Reply #34 on: Feb 23, 2016 10:58 pm »

I'm seeing this as a group study. We are trying together to reach a better comprehension of this phenomenon, which is exceedingly tenuos and impercetible.

From the ligo.org site:

Quote
There are four main sources of gravitational waves caused by different kinds of motion and changing distributions of mass - continuous, inspiral, burst, and stochastic.

- See more at: http://www.ligo.org/science/GW-Sources.php#sthash.BstoAEMp.dpuf

The waves just detecte4d by LIGO are the inspiral waves

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« Reply #35 on: Feb 23, 2016 10:59 pm »

Inspiral waves:
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nspiral gravitational waves are generated during the end-of-life stage of binary systems where the two objects merge into one.  These systems are usually two neutron stars, two black holes, or a neutron star and a black hole whose orbits have degraded to the point that the two masses are about to coalesce.  As the two masses rotate around each other, their orbital distances decrease and their speeds increase, much like a spinning figure skater who draws his or her arms in close to their body.  This causes the frequency of the gravitational waves to increase until the moment of coalescence.  - See more at: http://www.ligo.org/science/GW-Inspiral.php#sthash.epf2kvAH.dpuf

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« Reply #36 on: Feb 23, 2016 11:22 pm »

Now, we have a plot which describes (by numerical modelling) the inspiral GWs created by the two colliding black holes above depicted:


The gravitational waves we can see are created by the two masses  which accelerate toward each other (increase their revolution velocity being attracted by each other's gravities). Every ripple we see is a revolution of the system.
When the masses gradually approach each other, there are two effects:
1)Their acceleration increases due to greater attraction because of shorter distance
2)Their masses increase because the velocity is relativistically increasing (approaching the speed of light).

The net effect is to increase the ampliture of the ripples (masses are greater and greater) and to increase the frequency (revolutions are faster and faster).

At the end the masses (black holes in our case) collide merging into a single body. TGhere are no more ripples since there are no more inspiraling masses.
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« Reply #37 on: Feb 23, 2016 11:41 pm »

Now, the last step. Pls Steve and others let me know if the plots and explanations are clear now. The recently detected waves are plotted in the following official graph



We can clearly see the ripples becoming gradually wider and more frequent, startign from time 0.3 seconds to time 0.42, when they are the highest and the closest.

At time 0.3 the black holes started to approach to each other, increasing significantly in velocity and mass. At 0.4 second the black holes are revolving around each other very, very closely, with velocity at about half lightspeed. The last spikes testify the moments just before the collision, after which there are no more gravitational waves (seconds 0.43 to 0.45) since there are no more two black holes, just a single, larger one which is spinning in a close to circular simmetry, hence radiating no gravitational waves.

The dramatic collision, where two bodies which total mass amounting at about 30 times our sun, has ended. The GWs detected are exceedingly and incredibly tenuos. I still can hardly believe the devices could detect them.
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« Reply #38 on: Feb 23, 2016 11:44 pm »

So, we have seen that the analogy to the ripples caused by a stoen thrown in a pond is valid in an inverse way.

First of all there are two 'stones' not just one. Then, the ripples are caused before the collision, by increasing acceleration of the black holes. after the collision there are no more ripples.
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« Reply #39 on: Feb 24, 2016 05:25 am »

This is the best explanation yet of the graph. However it looks to me that there r still some frequencies registering at the far rite. Because it has not gone flatline. Maybe they just consider it negligible. Or is it that even a black hole registers something although it doesnt appear significant with our current ability to plot gravitational waves.

mccoy wouldnt it b fascinating to have graphs like this to measure spaces between breaths and breaths per minute while meditating?

Now, the last step. Pls Steve and others let me know if the plots and explanations are clear now. The recently detected waves are plotted in the following official graph



We can clearly see the ripples becoming gradually wider and more frequent, startign from time 0.3 seconds to time 0.42, when they are the highest and the closest.

At time 0.3 the black holes started to approach to each other, increasing significantly in velocity and mass. At 0.4 second the black holes are revolving around each other very, very closely, with velocity at about half lightspeed. The last spikes testify the moments just before the collision, after which there are no more gravitational waves (seconds 0.43 to 0.45) since there are no more two black holes, just a single, larger one which is spinning in a close to circular simmetry, hence radiating no gravitational waves.

The dramatic collision, where two bodies which total mass amounting at about 30 times our sun, has ended. The GWs detected are exceedingly and incredibly tenuos. I still can hardly believe the devices could detect them.
« Last Edit: Feb 24, 2016 05:40 am by Steve Hydonus » Report Spam   Logged

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« Reply #40 on: Feb 24, 2016 10:19 am »

Steve, now it appears that you have little problems in construing the graphs, yes they are the best so far and show how similar the signal is in the two devices, located at the opposite angles of the USA.
The far left and far right sides of the graph might depict either background noise; the far right side may also depict smaller gravitational waves of the continuos type, emitted by the new blackhole while it's rotating on its axis, due to some imperfection in the spherical simmetry.
We do not have the whole recording so we cannot say, although it is very likely that we are dealing with background noise, random oscillations of the measurement device or even of the gravitational field itself. I'll try and see if a longer stretch of the recording is available.

What I did not understand yet how they could predict the event (smoother signal), maybe they just foresaw a set of possible patterns, encompassing the likely events. What is clear is that the computational power used by the project is immense.
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« Reply #41 on: Feb 24, 2016 10:22 am »

mccoy wouldnt it b fascinating to have graphs like this to measure spaces between breaths and breaths per minute while meditating?

Definitely so! Having a graph visualize the breath cycles on a monitor in front of you. This would entail an even greater identification with the breath and its cycle. My hong-sau wopuld sure benefit from it. I believe it's relatively simple but we'll have to search the practical details and the cost of such a system.
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« Reply #42 on: Feb 24, 2016 10:40 am »

A very well written article By Lawrence Krauss in the NY times.

http://www.nytimes.com/2016/02/14/opinion/sunday/finding-beauty-in-the-darkness.html?ref=topics&_r=0
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