LIGO gravitational wave announcement

macdoc said:
I think there is a conceptal issue here....you don't "notice" curved space you notice the change in gravity that causes the change to the curve in space which a gravitational wave engenders.

Collapsing orbiting black holes managed to dispose of 3 solar masses in a very short time with an incredible amount of accompanying sturm und drang as Einsteins equation of mass and energy was demonstrated.....the result of that was a sudden change in gravity.....if you were outside the blast and radiation zone ....I doubt very much you would "notice" a gravitational wave of exceedingly short duration moving at the speed of light.
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I accept your last sentence. However, I have been finding difficulty in constructing any kind of intellectual representation of this event.

Consider: the arms of LIGO were squeezed by a length equivalent to a fraction of the diameter of a proton. We didn't notice this (by normal unaided sense organs). Was that simply because the effect was so small on account of the great distance from the event? If so, what would be the case if we were so close that the LIGO arms were squeezed by a hundred metres? If a pulse of energy were to squeeze the Channel Tunnel by a similar fraction of its length, that would be very ńoticeable, even if it happened in a tiny instant of time. If we were closer, would such catastrophic disruption be caused, or would the wave pass through us leaving us unscathed?
 
Craig B said:
Yes, I was wondering what would have happened if we had been much closer to the event, so that let's say the arms of the LIGO momentarily changed length by a hundred metres. Would that have caused utter disruption of all material structures, including the planet, or would it just have rippled past leaving things as unaffected as is a cork floating on a pond agitated by a breeze?
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Craig B said:
carlosy said:
So, how close would a human had to be to notice the gravitational wave itself (not the energy blast / em-waves) on his own body? Would that even be possible?
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I already asked that, more or less, at #108.
I was wondering what would have happened if we had been much closer to the event, so that let's say the arms of the LIGO momentarily changed length by a hundred metres. Would that have caused utter disruption of all material structures, including the planet, or would it just have rippled past leaving things as unaffected as is a cork floating on a pond agitated by a breeze?​
The responses I received haven't really enlightened me, I must admit.
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I think that if you were close enough to the BBH (binary black hole) merger for the arm lengths to have changed by that much due to GW, the tidal effects of the BBH merger would have been far more severe! :)

The BOTE calculation I did in #262 in this thread should provide a sufficient basis for estimating how close you'd to be for a stretching and squeezing of the 4 km arms of 100m. You could also estimate the tidal force across a 4 km arm at that distance from a 60 sol mass BH (say). Of course, that close the 'linear approximations' would likely be invalid; you'd need to do a full, strong-field set of calculations, but as I think you'd be ripped to shreds by the tidal forces anyway, such a more accurate calculation seems an overkill.
 
macdoc said:
This is incorrect...

What do thing the big flash was? .....the gravitational wave was a RESULT of the ginormous conversion of mass to energy....we didn't see the flash...anything within a solar system distance was blasted to whatever raw bits apply by that 50 x output of all the stars in the universe flash.

The gravitational wave occurred because of the abrupt change in mass that occurred as a result of the conversion of mass to energy.
That change in mass generated the gravitational wave,.
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Don't think so. The gravitational wave is result of the two black holes orbiting each other, not any unrelated abrupt change in mass. Orbiting bodies radiate gravitational waves which requires energy.
 
~

smartcooky said:
I don't think you even need the math actually, I think all you have to do is look at what the two theories propose

If gravity were a force as Newton suggested, but travelling at c then the lag of one object orbiting the other would exist.... the forces would not "point" directly at each other
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Right. But I was trying to explain how an EU fan would view this. I think that they'd likely conclude that 'gravity' must have an ~infinite speed, because otherwise there'd be this lag, and because Newton's law is close enough.

However, gravity is not a force, its a three dimensional distortion of the fabric of spacetime. That distortion "exists where it exists" regardless of the relative speeds of the two objects.

<snip>
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That's where the EU acolytes, well most of them, will object. They have no time for all this math-based nonsense! It's obvious that gravity is a force, and if the math of GR produces black holes - which they see, mathematically, as pure nonsense ("can't divide by zero! weren't we taught that in school!") - that only further proves that "the mainstream" has completely lost touch with reality.

Do I think any of this makes sense? No. But I do think it's not far from what EU supporters believe.
 
JeanTate said:
I think that if you were close enough to the BBH (binary black hole) merger for the arm lengths to have changed by that much due to GW, the tidal effects of the BBH merger would have been far more severe! :)

The BOTE calculation I did in #262 in this thread should provide a sufficient basis for estimating how close you'd to be for a stretching and squeezing of the 4 km arms of 100m. You could also estimate the tidal force across a 4 km arm at that distance from a 60 sol mass BH (say). Of course, that close the 'linear approximations' would likely be invalid; you'd need to do a full, strong-field set of calculations, but as I think you'd be ripped to shreds by the tidal forces anyway, such a more accurate calculation seems an overkill.
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To the lay reader, wishing to see the results of the calculations performed by more scientific minds, you are saying this: the only disruptive physical effect which might result from the merging of the black holes would result from tidal forces. If that is so, I understand it, and it aids my comprehension of the event.
 
Ummm it's not only tidal effects...tidal affects were a constant as the black holes orbited - when they merged tho, 3 solar masses turned to energy.
Tidal effects of that collapse are the least of your worries in that cosmic neighborhood.

That event created both a huge energy release AND a sudden change in gravity which produced the wave we recorded.

Ongoing tidal effects of the single remaining larger black hole would be different than the orbiting pair was.
 
Craig B said:
Consider: the arms of LIGO were squeezed by a length equivalent to a fraction of the diameter of a proton. We didn't notice this (by normal unaided sense organs). Was that simply because the effect was so small on account of the great distance from the event? If so, what would be the case if we were so close that the LIGO arms were squeezed by a hundred metres? If a pulse of energy were to squeeze the Channel Tunnel by a similar fraction of its length, that would be very ńoticeable, even if it happened in a tiny instant of time. If we were closer, would such catastrophic disruption be caused, or would the wave pass through us leaving us unscathed?
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I have NO evidence for this, its just speculation, but possibly, it could go unnoticed because the whole of local spacetime, and everything in it is distorted too.

If a passing GW makes you 10% shorter for an instant, would you notice if every molecule, every atom, every subatomic particle in you and surrounding you, was also made shorter by 10%. In other words, if your surrounding environment changes and you change with it, would you sense the change?
 
While the tidal effects were (almost) constant in intensity, the freqency of the tides would have changed as the two bodies approached each other. The normal tides would be pretty horrific because of the mass differences between each of the black holes. Not a pleasent environment at all, even without the collapse. The crazy thing is that, after the merger the tides should decrease!

Would have been interesting to see if hypothetical close by instrumentation could continue to detect orbital tidal effects AFTER the merger. Could the bodies still exist and orbit each other inside the event horizon? Would the event horizon then be distorted by them in that case (forming a spinning oblate). My un-informed guess is that they wouldn't, otherwise we would still see gravitational waves from them.

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there are always tidal affects near any large orbiting masses....we see them every day on earth.
I think the questioner means ripples as the gravity changed due to the conversion... the ripples we see in the gravitational wave record. But as those are moving at the speed of light ....kinda hard to imagine there would be any "feel".

LIGOgraph-615x300.jpg


If you were near enough to "feel" those ripples.....I think there were other things to worry about going on. :D
 
To the lay reader, wishing to see the results of the calculations performed by more scientific minds, you are saying this: the only disruptive physical effect which might result from the merging of the black holes would result from tidal forces. If that is so, I understand it, and it aids my comprehension of the event.
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since 3 solar masses were turned to energy in an instant....a change in tidal forces would be the least of your concerns.
 
I wonder if there are any tidal effects of a planet being in orbit around two orbiting black holes? It would orbiting the common centre of gravity and it should make little difference if it was one black hole of the same mass instead.

Though when the two black holes merged and lose mass the orbit would be slightly higher.
 
rjh01 said:
I wonder if there are any tidal effects of a planet being in orbit around two orbiting black holes? It would orbiting the common centre of gravity and it should make little difference if it was one black hole of the same mass instead.

Though when the two black holes merged and lose mass the orbit would be slightly higher.
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A pair of BHs with a combined 65 solar masses revolving around each other are doing so in a very, very deep gravitational well, so I think a planet would have to be orbiting a BLOODY long way away from the centre of mass in order to even survive intact without being ripped apart by tidal forces.

Even if it was far enough away, it would have to be even further (in the order of many light years) to survive the sudden release of three solar masses in energy when the two merged.

Put it this way. AIUI. the merger released more energy that a typical Type II Supernova, and if one of those happens within 20 LY of us, we're toast! (don't worry, the nearest candidate star for a Supernova is α Vir a.k.a. Spica and its 260 LY away)
 
smartcooky said:
A pair of BHs with a combined 65 solar masses revolving around each other are doing so in a very, very deep gravitational well, so I think a planet would have to be orbiting a BLOODY long way away from the centre of mass in order to even survive intact without being ripped apart by tidal forces.

Even if it was far enough away, it would have to be even further (in the order of many light years) to survive the sudden release of three solar masses in energy when the two merged.

Put it this way. AIUI. the merger released more energy that a typical Type II Supernova, and if one of those happens within 20 LY of us, we're toast! (don't worry, the nearest candidate star for a Supernova is α Vir a.k.a. Spica and its 260 LY away)
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The issue is whether such an amount of energy emitted as gravitational waves would have a different effect from an equivalent amount of electromagnetic radiation. It is reasonably clear that three solar masses of gamma rays would be very destructive. But three solar masses of energy in the form of gravitational waves? What does that do to objects it encounters?
 
macdoc said:
What any sudden change in gravity would do to a nearby mass :D

Here is a good explanation exactly on your question



http://www.space.com/31896-gravitational-waves-black-holes-sutter-op-ed.html
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Yes, but I don't think it really answers the question. It implies that you could but it is so feeble that you wouldn't, which of course we know. But would you if you were closer?

I suspect you wouldn't even if you were very close (aside from EM issues). The reason is that your size and maybe even planets are very small compared to the wavelength of the gravity wave.

To use the water analogy, a wave peaking near a beach could pull your pants off depending on orientation because the wavelength is comparable to your body size and has different effects on different parts of your body in the same instant.

Now think of swimming in a tsunami in the open ocean with a wavelength that can be miles long.

How long are these gravity waves?
 
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