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Gravitational Wave Memory

12/09/2021 10:06 PM

When an electromagnetic wave propagates through space, the space returns to its original state after the wave passes. When a gravitational wave travels past a point, theoretically, a "scar" is left in spacetime, a memory of the gravitational wave. Spacetime may not return to it's former state. Gravitational waves are very difficult to detect, and these "scars" are an order of magnitude more difficult, but it just may be possible.

Gravitational waves may leave a lasting mark on the universe. (Image credit: Shutterstock)

https://www.livescience.com/65441-gravitational-wave-memory.html

https://en.wikipedia.org/wiki/Gravitational_memory_effect

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#1

Re: Gravitational Wave Memory

12/09/2021 11:38 PM

Interesting and I look forward to the day when these even harder-to-detect gravitational memories are discovered.

The theorists keep predicting smaller and smaller fluctuations to detect. Is there a limit to how tiny of a signal we can detect? I know technology keeps improving in these efforts and yesterday's limits inform how to improve for the next smaller limit but how far can we go? Is it really turtles all the way down?

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#3
In reply to #1

Re: Gravitational Wave Memory

12/10/2021 7:14 AM

A Planck wavelength....Hmm,...maybe I will ask a carpenter...

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#20
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Re: Gravitational Wave Memory

12/16/2021 5:40 PM
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#2

Re: Gravitational Wave Memory

12/10/2021 7:10 AM

Great fleas have little fleas upon

their back to bite'em,and little fleas

have lesser fleas,and so infinitum,

and the great fleas themselves,

in turn,have greater fleas to go on,

while those again have greater still,and so on...August De Morgan

----------------------------------------------------------------------------------------------

I wonder if there are monster rogue waves in gravity as there are in the oceans?

What would be the effect on surrounding matter if there were such waves?

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#7
In reply to #2

Re: Gravitational Wave Memory

12/10/2021 10:58 AM

Do gravity waves behave like water waves,lifting the objects that they pass under or in this case,through?

Could an effect on local gravity be detected as a wave passed through?

Jus' thinkin'...

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#12
In reply to #7

Re: Gravitational Wave Memory

12/10/2021 8:19 PM

The LIGO detectors are interferometers. When a gravitational wave passes, there will be a fringe shift as the distance between different legs of the interferometers varies. If it is a true gravitational wave and not terrestrial noise, there will be correlation between the two interferometers.

https://www.ligo.caltech.edu/page/ligo-detectors

Here is an example of a linearly polarized (plus polarization) gravitational wave.

See this.

https://en.wikipedia.org/wiki/Gravitational_wave

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#4

Re: Gravitational Wave Memory

12/10/2021 7:22 AM

As I watch water water spiral down the drain,and see all of the water on the edges of the sink hole,there is nothing in the center.

Since all matter is spaghetti-fied as it goes into a black hole,it may accumulate like strings or pellets, of indescribable density, around a center mass,made up of strings,like the core of a golf ball.Or perhaps like the rings of Saturn.

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#5
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Re: Gravitational Wave Memory

12/10/2021 10:30 AM

From our distant vantage point, time passes slower and slower for an object falling into the gravitational field of a black hole, until it comes to a complete stop at the event horizon. So, as far as we are concerned, nothing falls into the hole but remains stuck above the event horizon.

For the hapless victim falling into a black hole, all would seem normal (except for that pesky spaghetti thing), but if he could observe events far away, centuries and eons would pass by more and more quickly. As he falls through the event horizon, infinite time will have passed on the outside.

Actually, for a galactic black hole, the tidal force at the event horizon is not that great and the spaghetti problem doesn't occur until inside the hole.

https://forum.cosmoquest.org/showthread.php?177054-Tidal-Forces-in-Supermassive-Black-Holes

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#6
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Re: Gravitational Wave Memory

12/10/2021 10:46 AM

If he could see future events,that would mean that future events are fixed,and that the future is immutable,so there is really no such thing as free will,only an illusion of free will.

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#8
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Re: Gravitational Wave Memory

12/10/2021 11:13 AM

No, he is not seeing his future. He is seeing the future as it unfolds the same as we are. It just unfolds much faster for him. The question of whether the future is fixed or determined by "free will" or quantum uncertainty is not relevant.

If he spent 1 year close to a black hole and then escaped back to his home planet, he might find that thousands of years had gone by there and all his friends (and maybe favorite countries) are gone. It's the same situation as if he had been travelling close to the speed of light.

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#9
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Re: Gravitational Wave Memory

12/10/2021 11:25 AM

There is an empty hole in the center of a whirlpool,as it drains down the sink,so if the same exists in a black hole,and everything is caught up in the event horizon,what is at the bottom of the "hole"- could this be used as a wormhole?

Perhaps it is like the focusing point on a water nozzle,and sprays matter out into another dimension of time or space,of course the time would be reversed,First in First out(FIFO). The "other" space time would expand proportionally as it acquired more matter and energy,maintaining a steady concentration.It is harder to inflate a balloon at first,so it may expand slower in the beginning,but inflate quicker as it expands.

A. E. said that energy and matter are the same thing,so matter is simply a concentrated form of energy.The energy leaving the black hole center may be so concentrated that it emerges as matter particles that "boil" or "evaporate" into energy when the pressure is released.

Perhaps these virtual particles that pop in and out of our spacetime are evaporating particles of mass spewed out by black holes formed on the "Other Side".

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#10
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Re: Gravitational Wave Memory

12/10/2021 12:10 PM

From my fading memories, I recall that nobody knows what actually happens to energy/matter (stuff) as it crosses the event horizon. At least this is unknown from the perspective of the falling object. From an outsider's perspective, the object never reaches the event horizon, let alone crosses through it. The widely held belief of spaghettification approaching and during transition is just a well-educated guess as foundational physical laws of our universe change for the hapless object.

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#13
In reply to #5

Re: Gravitational Wave Memory

12/12/2021 12:16 AM

"... until it comes to a complete stop at the event horizon. So, as far as we are concerned, nothing falls into the hole but remains stuck above the event horizon..."

LIGO detections of gravitational waves due to the merging of black holes with black holes or neutron stars would seem to contradict the idea that nothing falls into a black hole due to getting stuck at the event horizon from our perspective.

It appears that massive objects from our perspective indeed do merge with black holes with the orbital frequency increasing until merger, to my understanding.

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#14
In reply to #13

Re: Gravitational Wave Memory

12/12/2021 9:55 PM

That is an interesting point. The gravitational field from the matter that previously fell into a black hole obviously extends through the event horizon. If it didn't then I propose an event horizon and black hole wouldn't exist at all. I suppose this also means that gravitational fields propagate faster than the speed of light in a vacuum.

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#16
In reply to #14

Re: Gravitational Wave Memory

12/14/2021 10:12 AM

Here is the way I understand it:

I don't think you can say a gravitational field propagates. A gravitational field is just the shape of space-time. It doesn't have to get out of a black hole, it is the black hole.

Gravitational waves propagate at the speed of light as the gravitational field varies due to, for example, the rapid motion of very dense objects, e.g. orbiting black holes.

https://www.physicsforums.com/threads/how-does-gravity-get-out-of-a-black-hole.856841/

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#18
In reply to #16

Re: Gravitational Wave Memory

12/14/2021 2:34 PM

I've been thinking about my comment, too. Whenever spacetime warps and/or velocities approach "c", one should not default to the Newtonian mechanics our brains instinctively use. I think the crux of the puzzle is precisely the time dilation effect you pointed out earlier.

Since outside observers will never experience inner objects crossing the event horizon, the gravitational field from that "falling" object will always be present to the outside observer even though the falling object will quickly cross the event horizon from the object's time perspective.

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#15
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Re: Gravitational Wave Memory

12/14/2021 9:51 AM

"... until it comes to a complete stop at the event horizon. So, as far as we are concerned, nothing falls into the hole but remains stuck above the event horizon..."

To clarify, an object falling into a black hole doesn't come to a stop from our viewpoint. It just appears to move slower and slower, never actually reaching the event horizon.

"To a distant observer, clocks near a black hole would appear to tick more slowly than those further away from the black hole.[90] Due to this effect, known as gravitational time dilation, an object falling into a black hole appears to slow as it approaches the event horizon, taking an infinite time to reach it. To a distant observer, clocks near a black hole would appear to tick more slowly than those further away from the black hole.[90] Due to this effect, known as gravitational time dilation, an object falling into a black hole appears to slow as it approaches the event horizon, taking an infinite time to reach it."

https://en.wikipedia.org/wiki/Black_hole

https://en.wikipedia.org/wiki/Black_hole#CITEREFCarroll2004

The gravitational field is outside of the hole. A single object has a stationary gravitational field that does not emit gravitational radiation. The combined gravitational field of two orbiting massive objects is not stationary but varies as the objects rotate about each other. This variation radiates gravitational waves.

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#19
In reply to #15

Re: Gravitational Wave Memory

12/16/2021 11:40 AM

"...object falling into a black hole appears to slow as it approaches the event horizon, taking an infinite time to reach it ..."

.

So, the theoretical slowing is not just the radial component of motion but all components (including tangential), right?

...and the gravitational waves produced by some massive thing like a neutron star falling into a black hole are probably radiated while the massive object is spiraling outside the event horizon. Presumably gravitational waves don't radiate out from inside the event horizon...

So, if from our frame of reference time perspective, if massive objects slow to speeds for which crossing the event horizon will take an eternity, and this is not abrupt but some smooth curve, it seems unlikely we would see the frequency increase until it disappears.

Also I would expect extremely lumpy super massive black holes, more akin to a cluster of grapes than racketball as eternity is a long enough time that whatever was previously caught will still be at the horizon when the next thing falls in.

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#11

Re: Gravitational Wave Memory

12/10/2021 12:20 PM

It’s interesting… but as a layman view, and I’m giving myself way too much credit… for this to develop, where there always appear to be new particles being discovered all the time…

A physicist I can’t recall the his name or his exact quote… but it went something like this a breakthrough would be no new particles have been discovered (because so many were being discovered) I think it was being applied to the Nobel prize.

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#17

Re: Gravitational Wave Memory

12/14/2021 2:24 PM

The strongest material ever made....will be mass-less. Being that EM can be super-positioned, a field barrier could theoretically be much stronger and denser than any mass. Such a barrier should allow us to manufacture a perfect vacuum. And such a barrier should prevent static and external fields too.

This would allow us to see space in it's natural environment. Empty.

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