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Thread: Gravitational Waves

  1. #1
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    Smile Gravitational Waves

    Hello. Apparently these waves that were detected were very 'small' or weak by the time they got to Earth. Over time these waves I think I heard lose energy and or size as they travel across the Universe.

    How energetic would these waves be within a few astronomical units of the Black Holes themselves? I would like to know because apparently space time itself changes size when these waves pass..which means in
    the near vicinity of these things 1 meter of spacetime might be no distance at all.

    Thanks for your responses
    Bye
    G

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    I believe that gravity waves fall off as the square of the distance, and here at 1.3Gly away, they are on the order of .0001 proton diameters. You should be able to work out the gravitational flux at any point closer.

    Back of napkin calculations suggest to me that, at a distance of one light year, distortion detected by a strategically-placed LIGO would be on the order of 10 cm over its length (which I think is 4,000m).

    To wit:

    We are measuring distances of 1 /10,000th (10^-4) of a proton (10^-15), resulting in a distortion of 10^-19 over 4000m.

    One light year is about 1 billionth of the distance to us. So the force that close would be a billion squared, or 10^18.

    10^-18 divided by 10^-19 equals 10^-1.
    Last edited by DaveC426913; 2016-Feb-16 at 02:03 AM.

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    posted on another thread:

    But just for fun let’s look at how close we could get. Before the merger the two black holes have a diameter of about 212 and 170 kilometers respectively. After the merger the final black hole has a diameter of about 365 kilometers. If we were really close to the black holes, the tidal forces alone would kill us, so let’s assume we’re at least 10,000 kilometers from ground zero. At that distance the shift caused by the gravitational waves would be about one part in a thousand. If you were floating in space you would likely feel that, since a person would experience a shift of a millimeter or two. Would it hurt, or possibly harm you? That’s hard to say. It would really depend on how resilient humans are to gravitational wave distortion, and we don’t have any experimental data on that. If I were to guess I’d say as long as your space suit held up you’d be fine.
    http://www.forbes.com/sites/briankob.../#ac39ffb4aac3


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    Quote Originally Posted by Frog march View Post
    I'm not sure if a "shift" of a millimeter or two is an adequate description. The change in g would happen at light speed.

    I wonder if it is tantamount to a shock wave.

    I have a feeling it's enough to turn you into an expanding cloud of atoms.
    Last edited by DaveC426913; 2016-Feb-16 at 02:07 AM.

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    Quote Originally Posted by DaveC426913 View Post
    I'm not sure if a "shift" of a millimeter or two is an adequate description. The change in g would happen at light speed.

    I wonder if it is tantamount to a shock wave.

    I have a feeling it's enough to turn you into an expanding cloud of atoms.
    yes, I wouldn't be surprised myself.

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    I'm trying to figure this out. By the principle of equivalence, you would go from 0 to an incredible acceleration instantly, except it would happen to every atom in your body virtually simultaneously.

    I was comparing it to having every atom shifted simultaneously back and forth by one millimeter, between 100 and 10,000 times per second.

    Like being in a microwave - it excites every atom simultaneously.

    What power of microwave radiation would be required to induce a 1 millimeter amplitude vibration in a hunk of meat?
    Last edited by DaveC426913; 2016-Feb-16 at 04:18 AM.

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    It's going to depend on the wavelength surely?

    If the wavelength is many times longer than your body would you feel anything at all?

    If the frequency is 10,000 Hz and gravitational waves propagate at c, the wavelength is about 30km.

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    Quote Originally Posted by DaveC426913 View Post
    I believe that gravity waves fall off as the square of the distance, and here at 1.3Gly away, they are on the order of .0001 proton diameters.
    Something surprising, that I learned only from hints in some of the LIGO coverage, is that gravitational-wave amplitude falls off only as the inverse of the distance (sample reference, as well as Wikipedia). This helps explain why the first (strongest?) source detected was already so distant. Unlike EM radiation, in this case we can measure the amplitude rather than its square.

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    Correct. Here the amplitude is used in exactly the same way you would talk about the amplitude of an electric field, or the voltage amplitude. The intensity of the gravitational wave, like any intensity, is proportional to the amplitude2. The amount of power a gravitational wave carries falls off as inverse square. Luckily, we can measure its amplitude, and our ability to detect far away sources falls as 1/r .

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    There are more of these Gravitational Waves detectors planned around the world. Two of them are in Asia. Both the Chinese and Indian governments have given their approval.

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    Another comment on this from Amber Stuver:
    How far away do you have to be from this kind of black hole merger to live to tell the tale?
    Stuver: For the black hole binary we detected with gravitational waves, they produced a maximum change in the length of our 4 km (~2.5 mi) long arms [of] 1x10-18 meters (that is 1/1000 the diameter of a proton). We also estimate that these black holes were 1.3 billion light-years away.
    Now assume that we are 2 m (~6.5 ft) tall and floating outside the black holes at a distance equal to the Earth’s distance to the Sun. I estimate that you would feel alternately squished and stretched by about 165 nm (your height changes by more than this through the course of the day due to your vertebrae compressing while you are upright). This is more than survivable.
    http://gizmodo.com/your-questions-ab...red-1758269933

    Although the "speed of light" issue is an interesting complication.

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    Let me be the fly in the ointment. Think speghettification near the event, not something barely noticeable. Linearity should be fine, but not close to the event. This is speculative, but look at what we have:

    1) A three solar mass energy blast! Anything description of serenity seems ludicrous. It may be serene, but if so, that would be shocking news, and extremely non-intuitive.
    2) Entropy is greatly increased in an instant. [Surprisingly, the surface area of the event horizon is proportional to the black holes total entropy. The EH area shrinks with 3 solar mass loss, thus entropy is reduced associated with the b.h. This entropy change should, I think, manifest itself in the surrounding environment.]. This is not something small scale. [Added: I assume the greatest entropy (surface area) is that of the odd shaped EH envelope formed by the binary, thus making the entropy issue even more pronounced.]
    3) If confirmed, a gamma ray burst followed from this region with a ~ O.4 sec. delay. Serenity is the wrong word for describing these events. The delay seems to make some sense because the g.r.b. observed would have had the b.h. lensing effect and time dilation (and redshift?) applied to it.
    4) The shrinkage of the EH might have released some very energetic particles and photons from within this zone.
    5) This event had two masses going nuts, so wave propagation near this event should, perhaps, produce interference regions where the amplitudes slope might cause speghettification all by itself at certain points nearby?
    6) How often do serenity claims go south? Besides most binary orbits, is there serenity? The cosmological constant tried to force serenity upon a serene Static Universe. Look at the size of cat that brought in the house!
    7) Did I mention the energy release was ~ 3 solar masses? Super novae aren't that serene, really, though their energy release is diiferent.

    Are we not being a little naive in guessing that the boat would not rock when fishing at these holes. I know this is speculative, but that's where this gets fun, and this one is extra fun. I think it is a serious topic, so much so that no gravity pun will be used...this time.
    Last edited by George; 2016-Feb-24 at 09:13 PM.
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    Quote Originally Posted by George View Post
    Think speghettification near the event....
    You wouldn't be spaghettified. We need a new term! You'd be stretched one way and then the other, as shown in the animations. Then the large waves generated from the final merger would be past you, and you'd be back to your original configuration. What effect this would have on your individual atoms - and survival - I don't know. I do know it happens very quickly.

    Quote Originally Posted by George View Post
    2) Entropy is greatly increased in an instant. [Surprisingly, the surface area of the event horizon is proportional to the black holes total entropy. The EH area shrinks with 3 solar mass loss, thus entropy is reduced associated with the b.h. This entropy change should, I think, manifest itself in the surrounding environment.]. This is not something small scale.
    Yes, folks much smarter than me have figured that the surface area of the event horizon is proportional to the black hole's total entropy. The actual meaning of this is not exactly clear, at least to me. Offhandedly, I'm thinking this 3 solar mass measure of entropy loss is likely transferred and manifested in the gravitational waves. (?) Where/how else could it go? There could be a scientific paper here waiting to be written.

    Quote Originally Posted by George View Post
    4) The shrinkage of the EH might have released some very energetic particles and photons from within this zone.
    I don't see how. I imagine the gamma rays are coming from the two accretion disks slamming together.

    Quote Originally Posted by George View Post
    7) Did I mention the energy release was ~ 3 solar masses?
    Haha, I think you said that somewhere. All that energy goes into the gravitational waves. But it drops off with distance. Prior to merger, these black holes are going to be orbiting each other. You wouldn't want to be too close to this action in the first place.
    Everyone is entitled to his own opinion, but not his own facts.

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    Wiggling of atoms has something or other to do with temperature.
    Being in a rapidly fluctuating gravity field might cook you.

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    Quote Originally Posted by Cougar View Post
    You wouldn't be spaghettified. We need a new term! You'd be stretched one way and then the other, as shown in the animations. Then the large waves generated from the final merger would be past you, and you'd be back to your original configuration. What effect this would have on your individual atoms - and survival - I don't know. I do know it happens very quickly
    It depends on the slope ( gravity gradient) of the 3 solar mass wave. This can't be gentle, at least not on my mind. Amplitude and wavelength are important here. What is the gradient of such a wave at, say, 10,000 km from the pulse origin?

    Yes, folks much smarter than me have figured that the surface area of the event horizon is proportional to the black hole's total entropy. The actual meaning of this is not exactly clear, at least to me. Offhandedly, I'm thinking this 3 solar mass measure of entropy loss is likely transferred and manifested in the gravitational waves. (?)
    I am guessing not. Drop a ball bearing in calm water and the energy is transferred into the wave. The splash, however, represents the entropy increase to the universe as it is irreversible.

    So, is there no "splash" that would not cause havoc to our boat, ignoring the uber Wiemea wave?

    I don't see how. I imagine the gamma rays are coming from the two accretion disks slamming together.
    Inside a fixed EV, nothing escapes. Retract the prison wall and out some will go, I think.

    Haha, I think you said that somewhere. All that energy goes into the gravitational waves. But it drops off with distance. Prior to merger, these black holes are going to be orbiting each other. You wouldn't want to be too close to this action in the first place.
    Ok, but the bigger the wave, the bigger the splash, perhaps!
    Last edited by George; 2016-Feb-24 at 04:43 PM.
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    Quote Originally Posted by Squink View Post
    Wiggling of atoms has something or other to do with temperature.
    Being in a rapidly fluctuating gravity field might cook you.
    Splash!! . [Added: This is not the event splash, however, but something that happens along the wayve.]

    Also, the tidal stress near the EV -- for non-supermassive black holes-- is enough for speghettificaton, but how much more so when a ginormous gravity wave is added?!

    Both effects might cause any matter to produce a GRB, even with the gravity redshift. Not that I know, admittedly.
    Last edited by George; 2016-Feb-24 at 09:10 PM.
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    A colleague of mine forwarded this. All credit goes to Keith F. Lynch http://keithlynch.net/

    >> This surprises me, the equivalent of 3 solar masses radiated away in
    less than a second from 96 million miles away and we wouldn't notice?

    > It's not just the energy, but rather the effect it produces on whatever it interacts with (or not).

    Right. I just ran some numbers, and I came to the remarkable conclusion that the total solar power output (4E+26 watts) could harmlessly pass through you if it was in the form of gravitational waves rather than heat and light.

    I used the formula c^3 h^2 f^2 pi / (8 G) to convert strain to flux. G is the gravitational constant, h is the strain, c is the speed of light, and f is the frequency in Hz (250 in this case). The peak strain of the recent event was 1E-21, so I get apeak flux of 10 milliwatts per square meter.

    No wonder they always list the sensitivity of LIGO in terms of strain rather than in terms of watts per square meter. The latter doesn't sound nearly as impressive! Indeed, if the event had given off light rather than gravitation waves, it would have been not only bright enough to see from here, but bright enough to read by!

    As a sanity check, I divided the reported peak power output of the event, 3.6E49 watts, i.e. 200 solar masses per second annihilated, by the area of a sphere 1.3 billion light years in radius. I get about 20 milliwatts per square meter. What accounts for the factor of two discrepancy? Probably polarization. LIGO, if I understand correctly, is sensitive to only one of the two polarizations.

    ("Only" 3 solar masses were annihilated, because the event lasted less than a second.)

    Let's get closer to the event and see what happens. I hope you're reading this with a fixed font.

    Distance flux (W/m^2) strain N

    1.3E25 m (1.3E9 ly) 1E-2 1E-21 4E33
    1.3E22 m (1.3E6 ly) 1E+4 1E-18 4E39
    1.3E19 m (1.3E3 ly) 1E+10 1E-15 4E45
    1.3E16 m (1.3 ly) 1E+16 1E-12 4E51
    1.3E13 m (66 AU) 1E+22 1E-9 4E57
    1.3E10 m (8 M miles) 1E+28 1E-6 4E63

    The last column is the number of gravitons per square meter per second. I get that by multiplying the flux by the frequency and dividing by Plank's constant.

    In each case, I assume you're floating in space, in a good spacesuit, facing toward the event.

    I assume that a strain of one part in a million isn't going to hurt you, especially if it's front-to-back rather than head-to-toes. Note that that last distance is much less than 1 AU. 1E+28 watts per square meter -- your cross-sectional area is probably roughly one square meter -- means 25 times the sun's total power output is going through you. I wonder what it would feel like.

    Of course I'm also assuming it was a "clean" event, i.e. nothing but gravitational waves was given off. If it consisted of nothing but two black holes, that's pretty much certain. But if there was other stuff in the area, all bets are off. Indeed, there was a weak gamma ray burst half a second after the event, which may or may not be a coincidence. We don't know the direction of either the event or the gamma ray burst, except very roughly.

    > Supernovae radiate a huge amount of energy in neutrinos, but thesehardly affect anything else.

    Neutrinos aren't nearly as stealthy as gravitons. According to Randall Munroe, a typical supernova will emit 1E57 neutrinos, and they will be lethal at about 2 AU. During the peak tenth of a second of the event at the closest distance I list, 100,000 times as many gravitons will harmlessly pass through you as the *total* number of neutrinos given off by a supernova!

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    250 Hz sound has wavelength in room temperature air of 130 cm, in water of 6 m, and in flesh and bone slightly more.
    How much is a 170 cm man stretched or shrunk, head to toe, by sound of 250 Hz and 100 dB?
    By sound of 250 Hz and 0 dB?

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    I used the formula c^3 h^2 f^2 pi / (8 G) to convert strain to flux. G is the gravitational constant, h is the strain, c is the speed of light, and f is the frequency in Hz (250 in this case). The peak strain of the recent event was 1E-21, so I get a peak flux of 10 milliwatts per square meter.

    No wonder they always list the sensitivity of LIGO in terms of strain rather than in terms of watts per square meter. The latter doesn't sound nearly as impressive! Indeed, if the event had given off light rather than gravitation waves, it would have been not only bright enough to see from here, but bright enough to read by!
    If it were visible light energy, seen from Earth, this would be about a 20 mag. reduction when compared to the Sun –- 1E8 brightness difference using roughly 1 kw m^-2 for the Sun’s illuminance here. So it would be roughly equivalent to a -7 mag. star, which is much brighter than Venus, but dimmer than a crescent Moon. Very easily seen, but I doubt I could read by it, and I don’t read that quick.

    I assume that a strain of one part in a million isn't going to hurt you, especially if it's front-to-back rather than head-to-toes. Note that that last distance is much less than 1 AU. 1E+28 watts per square meter -- your cross-sectional area is probably roughly one square meter -- means 25 times the sun's total power output is going through you. I wonder what it would feel like.
    That makes sense, but what about at the 10,000 km distance used by another? This would make it 1 part in a thousand over 100 times in about 1/3 of a second. I would guess that this would at least be very loud to the ear drum and would be at an audible frequency. Here is a Youtube (w/commercial) of what it might sound like. Would it burst the ear drum?

    Of course I'm also assuming it was a "clean" event, i.e. nothing but gravitational waves was given off. If it consisted of nothing but two black holes, that's pretty much certain. But if there was other stuff in the area, all bets are off. Indeed, there was a weak gamma ray burst half a second after the event, which may or may not be a coincidence.
    I can’t imagine something of this magnitude being squeaky “clean”. There is still the question, at least for me, as to the impact from the entropy change. There must be a “splash” in there somewhere, which would help explain a grb. Can this event cause the “foam” to bust lose? How cool would that be?
    Last edited by George; 2016-Feb-25 at 05:40 PM.
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    Why should it not be "clean"? Systems with accretion discs need donor stars in orbit. Furthermore, it seems it has been shown that two merging black holes will eject any surrounding matter before coalescence.

    Personally, I strongly doubt the connection to that GRB is real.

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    Quote Originally Posted by Don Alexander View Post
    Personally, I strongly doubt the connection to that GRB is real.
    +1

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    Quote Originally Posted by Don Alexander View Post

    Personally, I strongly doubt the connection to that GRB is real.
    Have you considered the possibility of the gamma-ray photons from the GRB producing a signal in the interferometer(shedding its momentum to the mirrors and inducing the chirp)?

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    Quote Originally Posted by Staticman View Post
    Have you considered the possibility of the gamma-ray photons from the GRB producing a signal in the interferometer(shedding its momentum to the mirrors and inducing the chirp)?
    If that were possible, why hasn't ALIGO (& LIGO before it) seen this sort of thing from the many much more intense GRBs? As to it being possible, those gamma-ray photons don't make it through the atmosphere, so they can't get to a place where they could do what you suggest, and there aren't enough of them.
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    Quote Originally Posted by Don Alexander View Post
    Why should it not be "clean"? Systems with accretion discs need donor stars in orbit. Furthermore, it seems it has been shown that two merging black holes will eject any surrounding matter before coalescence.
    Maybe, but were pulsars supposed to have planets? I certainly am not qualified to say the modeling is oversimplified, especially given the likely sophistication needed to make such a model, but I would enjoy hearing about how the entropy change takes place as that, for me at least, is an interesting puzzle. If the surface area of the E.H. does represent the total entropy, and this surface area is greatly reduced with the merger, then how does the off-setting entropy increase manifest itself? If my refrigerator suddenly was (were?) to blast freeze everything inside, it would sure heat-up the kitchen!

    Personally, I strongly doubt the connection to that GRB is real.
    sundae.png ???
    Last edited by George; 2016-Feb-26 at 02:55 PM.
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    May I refer to: http://arxiv.org/abs/1602.07352

    Also, should the GWs themselves not be a strongly entropic signal? While weakly interacting, you have distortions of space-time moving out at the speed of light.

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    Quote Originally Posted by antoniseb View Post
    If that were possible, why hasn't ALIGO (& LIGO before it) seen this sort of thing from the many much more intense GRBs?
    The progress in terms of sensitivity from Ligo to Advanced Ligo has been remarkable, so it is reasonable to think that if detection of high energy EM waves is sensitivity dependent it wouldn't have been possible in the first decade of observation to detect them. On the other hand in the remote case the signal detected on september was actually from a GRB it was only the first few days of the engineering run, so it didn't have much time and there aren't so many GRBs in a few days coming the Earth's way. According to rumors there have been more signals detected after that first one in this first run.
    As to it being possible, those gamma-ray photons don't make it through the atmosphere, so they can't get to a place where they could do what you suggest,
    and there aren't enough of them.
    Surely, most gamma rays are absorbed by the atmosphere but the barrier is not perfect so you'll concede some photons may reach the surface, then a model of just what intensity of radiation is enough to produce the vibration of the mirrors that would be necessary to produce a signal of the form detected.

    Please note that I'm suggesting this putative source of signals as a very remote possibility but one that is neverthelees worth considering to avoid later chagrin and discredit of science. If that remote possibility ever materialized we would all know in time and it would still be an amazing engineering feat in terms of sensitivity of an instrument.

    My internet conversations with aLIGO workers lead me to think they haven't considered this possibility(maybe rightly so if there are really no theoretical grounds on which to consider it possible but I would like to hear some solid science ). At the very least there are no sensors in the interferometer dedicated to this particular source of noise.
    Last edited by Staticman; 2016-Feb-26 at 08:21 PM.

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    Quote Originally Posted by Staticman View Post
    T... most gamma rays are absorbed by the atmosphere but the barrier is not perfect so you'll concede some photons may reach the surface...
    No. They don't reach the surface, not even close, not even the highest mountaintops.
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    Quote Originally Posted by antoniseb View Post
    No. They don't reach the surface, not even close, not even the highest mountaintops.
    In science it is not so often that one can be so categorical, can you direct me to some reference?
    What would you consider the lowest frequency at wich EM waves can reach the surface?
    Last edited by Staticman; 2016-Feb-26 at 08:54 PM.

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    Quote Originally Posted by Staticman View Post
    What would you consider the lowest frequency at wich EM waves can reach the surface?
    Some long wave radio band, but I'm sure that isn't what you're asking about. You probably meant what is the highest frequency (shortest wavelength). That would be somewhere in the ultraviolet range that we recommend people avoid so they don't damage their skin.
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    Quote Originally Posted by antoniseb View Post
    Some long wave radio band, but I'm sure that isn't what you're asking about. You probably meant what is the highest frequency (shortest wavelength). That would be somewhere in the ultraviolet range that we recommend people avoid so they don't damage their skin.
    Oops, yeah that's what I mean. But I take that range to be the one in wich significant amounts of radiation can reach us, enough to be potentially harmful. But there must be some threshold in higher frequencies. One thing is that we may find it impossible to detect and another that there isn't none.

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