Gravitational waves, potential, and creationism

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stoppedcaring
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Gravitational waves, potential, and creationism

Postby stoppedcaring » Tue Aug 26, 2014 6:34 pm UTC

Some particularly convoluted versions of young-earth creationism propose that God created the universe moving inward from the observable edge, at the speed of light, over a period of 13.8 billion years, such that all the light from the farthest and nearest reaches of the universe reached our solar system (created last) simultaneously; this simultaneous appearance is represented as consistent with an instantaneous creation supposedly described in Genesis. It's a creative way to get around the infamous starlight problem faced by young-earth creationism.

Here's a rough diagram (the red lines represent the light from the galaxies approaching the center):

Image

There are plenty of problems with this, not the least of which is the implication that all collision and tidal structures we observe must be no older than 6,000 years (which makes the existence of stellar streams greater than 20,000 lightyears long and bow shock trails greater than 100,000 lightyears long rather suspicious). But the more interesting problem is the gravitational wave prediction it would seem to make.

If the universe were spherical and created from the outside in radially at the speed of light, then light wouldn't be the only thing heading inward with the red lines. The gravitational potential of all that mass would be traveling inward in the form of one gigantic gravitational wave. 6,000 years ago, when our solar system was finally created (in this model), the gravitational potential would all meet in the center (ostensibly damped by some miracle so as not to obliterate the newly-formed solar system) and begin to propagate back outward as gravitational potential from one side of the universe started to affect the opposite side:

Image

Now unless I miss my guess, a gravitational potential wave consisting of the entire other half of the universe ought to produce some sort of an effect. What would the amplitude of such a gravitational wave be? Would such a wave produce any visible effect on stars, planets, etc that it passed through? Does this model therefore make testable predictions about cruciform oscillation observable in stars and dust clouds 3,000 lightyears from us?

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WarDaft
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Re: Gravitational waves, potential, and creationism

Postby WarDaft » Wed Aug 27, 2014 6:21 pm UTC

Do we actually have any model of what gravity would do if new mass suddenly popped into existence? That... doesn't sound like something that would go well with the laws of gravity.


Also, they've posited a deceptive god assembling a universe to look like something other than how it was "actually" made just to perpetuate their belief.
This is basically Descartes' evil demon, and needs no consideration before being summarily dismissed.
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Re: Gravitational waves, potential, and creationism

Postby eSOANEM » Wed Aug 27, 2014 9:42 pm UTC

New energy appearing from nothing would just be a discontinuity in the stress-energy tensor. GR can, in principle (numerically at least) handle such cases I believe using a green's function type method.
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stoppedcaring
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Re: Gravitational waves, potential, and creationism

Postby stoppedcaring » Thu Aug 28, 2014 8:40 pm UTC

Perhaps I can recast the question in a more straightforward fashion.

Consider a Kardashev-III civilization with a Dyson swarm large enough to enclose an entire galaxy. Suppose this civilization wants to create a new galaxy with a new galactic core, so they arrange their pre-charged Dyson swarm in an empty region of space with particle beam cannons on each spacecraft in the swarm. They all simultaneously fire a pulse of particles at 99.99999% the speed of light at the center of the void; when they meet, they fuse and collapse instantaneously, creating a supermassive black hole of mass M_smbc.

What are the characteristics of the gravitational wave propagating outward from the formation of that black hole? What would that wave look like at a radius of, say, 920 parsecs, in terms of the variable M_smbc?

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Re: Gravitational waves, potential, and creationism

Postby Tyndmyr » Fri Aug 29, 2014 3:48 pm UTC

My guess is that they'll simply twerk it in some way to claim that god totally set up the gravity to already be visible to us as well. No observational evidence will convince someone determined that a omnipotent god wanted things this way. I've argued with creationists for decades, and only recently come to terms with just how futile it is. It literally doesn't matter how perfect your refutation is, they'll simply jump to some other expanation, because they are not seeking truth, but a justification for an extant belief.

It appears to be best to simply ignore the arguments altogether, and teach them actual knowledge when possible. Whatever knowledge, it doesn't much matter, but actual science. Scientific theories have predictive values, and serve as useful tools. Creationism does not. Therefore, when they need to get things done, they'll start using the useful thing. It ain't a fast process, but science has basically gotten this far by being useful.

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Re: Gravitational waves, potential, and creationism

Postby lgw » Fri Aug 29, 2014 11:43 pm UTC

Tyndmyr wrote:My guess is that they'll simply twerk it in some way to claim that god totally set up the gravity to already be visible to us as well.


And thus Tyndmyr's Theory of Twerking was born. The jiggling is evidence of gravity waves sent by God to make us happy. I'm a believer.
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Re: Gravitational waves, potential, and creationism

Postby Quizatzhaderac » Wed Sep 03, 2014 7:03 pm UTC

Adding a finite mass instantaneously would create a gravity wave of infinite frequency, and hence infinite energy. Adding energy from nowhere over 24 hours is something GR can handle.

In both cases the resulting gravity wave would cause gravity to pull outward and inward. Objects moving longitudinally will also be accelerated latitudinally one way, then the over. Likewise object moving latitudinally will be accelerated longitudinally one way, then the over. Same thing after it passes through center, but switch outward and inward.

So astronomers should except to see object 6,00 lyrs away blueshift, tilt on their axises, redshift, the tilt back.

If the wave is energetic or concentrated enough to form a black hole at the center it'll stay a back hole and no wave will emerge. The black holes energy would be the energy of the rest of the universe / (period energy was added over/ Planck time)1. Using Wolfram alpha and assuming it all happened on the first day we get a mere 2,100 tonnes, which would evaporate in 13 minutes.

Since the wave's period is longer then the black hole's lifetime, the black hole basically wouldn't form, but the amplitude at the center (assuming perfectly symmetric) should be enough for Hawking radiation/ pair production to occur.

In the case of the Dyson-swarm-cannon-beam, you'd basically form a Kugelblitz black hole, and lose all signs of how it was created.
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Re: Gravitational waves, potential, and creationism

Postby Hypnosifl » Thu Sep 04, 2014 3:03 pm UTC

stoppedcaring wrote:Perhaps I can recast the question in a more straightforward fashion.

Consider a Kardashev-III civilization with a Dyson swarm large enough to enclose an entire galaxy. Suppose this civilization wants to create a new galaxy with a new galactic core, so they arrange their pre-charged Dyson swarm in an empty region of space with particle beam cannons on each spacecraft in the swarm. They all simultaneously fire a pulse of particles at 99.99999% the speed of light at the center of the void; when they meet, they fuse and collapse instantaneously, creating a supermassive black hole of mass M_smbc.

What are the characteristics of the gravitational wave propagating outward from the formation of that black hole? What would that wave look like at a radius of, say, 920 parsecs, in terms of the variable M_smbc?

If the swarm were arranged in a spherical shell and all fired inward at the center simultaneously, the matter/energy density would be spherically symmetric at all times (or at least very close to it on large scales, ignoring the small gaps between members of the swarm and the beams they fire), in which case no gravitational waves would be created at all. Gravitational waves depend on the quadrupole moment of the source (unlike electromagnetic waves which depend on the dipole moment, see here for some discussion) and this means spherically symmetric configurations like a star with oscillating radius don't emit gravitational waves, as mentioned here.

BTW, do you remember where you read the creationist theory you describe in your OP? I've heard of another creationist model in which the universe is supposed to be a finite collection of matter with gravitational time dilation allowing for creation to last seven days at the center (where Earth is, naturally) while lasting much longer farther out, but I've never heard the idea of a wave of creation traveling inwards.

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Re: Gravitational waves, potential, and creationism

Postby stoppedcaring » Thu Sep 04, 2014 4:54 pm UTC

Hypnosifl wrote:
stoppedcaring wrote:Perhaps I can recast the question in a more straightforward fashion.

Consider a Kardashev-III civilization with a Dyson swarm large enough to enclose an entire galaxy. Suppose this civilization wants to create a new galaxy with a new galactic core, so they arrange their pre-charged Dyson swarm in an empty region of space with particle beam cannons on each spacecraft in the swarm. They all simultaneously fire a pulse of particles at 99.99999% the speed of light at the center of the void; when they meet, they fuse and collapse instantaneously, creating a supermassive black hole of mass M_smbc.

What are the characteristics of the gravitational wave propagating outward from the formation of that black hole? What would that wave look like at a radius of, say, 920 parsecs, in terms of the variable M_smbc?

If the swarm were arranged in a spherical shell and all fired inward at the center simultaneously, the matter/energy density would be spherically symmetric at all times (or at least very close to it on large scales, ignoring the small gaps between members of the swarm and the beams they fire), in which case no gravitational waves would be created at all. Gravitational waves depend on the quadrupole moment of the source (unlike electromagnetic waves which depend on the dipole moment, see here for some discussion) and this means spherically symmetric configurations like a star with oscillating radius don't emit gravitational waves, as mentioned here.

That would be the case outside the sphere, but what about for an observer at some random point inside the sphere? At time t0, it is enclosed in a shell and thus experiences no gravity. At time t1, when that shell of mass crosses the location of the observer, the observer will begin to experience a pull of gravity toward the center. At time tinfinity, the observer will experience the entire gravitational force of the black hole. What is the change in gravitational force going to look like over that time duration, and thus how is the change in gravitational potential going to propagate outward from the center?

BTW, do you remember where you read the creationist theory you describe in your OP? I've heard of another creationist model in which the universe is supposed to be a finite collection of matter with gravitational time dilation allowing for creation to last seven days at the center (where Earth is, naturally) while lasting much longer farther out, but I've never heard the idea of a wave of creation traveling inwards.

This is the updated version from Jason Lisle. He doesn't actually come right out and describe it in these terms, because he wants to say it all happened simultaneously using his anisotropic synchrony convention model, but this is what he's advancing.

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Re: Gravitational waves, potential, and creationism

Postby Hypnosifl » Thu Sep 04, 2014 6:57 pm UTC

stoppedcaring wrote:That would be the case outside the sphere, but what about for an observer at some random point inside the sphere? At time t0, it is enclosed in a shell and thus experiences no gravity. At time t1, when that shell of mass crosses the location of the observer, the observer will begin to experience a pull of gravity toward the center. At time tinfinity, the observer will experience the entire gravitational force of the black hole. What is the change in gravitational force going to look like over that time duration, and thus how is the change in gravitational potential going to propagate outward from the center?

I think the gravitational potential would change but in a way that didn't involve gravitational waves, in the same way the Coulomb force from a charge moving at constant velocity will change as its distance from you changes, but no electromagnetic waves will be involved since the second derivative of the dipole moment is zero (see the physics FAQ link I posted for some discussion of changing fields without waves in both EM and GR).
stoppedcaring wrote:This is the updated version from Jason Lisle. He doesn't actually come right out and describe it in these terms, because he wants to say it all happened simultaneously using his anisotropic synchrony convention model, but this is what he's advancing.

Thanks. Googling a little, it seems like he's basically just arguing that distant stars were all created along the past light cone of the Earth on the "fourth day of creation", and that God for some reason chooses a simultaneity convention in which the simultaneity surface would hug the past light cone (but deviating from it just slightly so the simultaneity surface can be a space-like surface rather than a light-like one), I image there's not really any way to say what general relativity should predict would happen in such a magical scenario. And his paper basically just goes on and on about his wonderful new simultaneity convention without even attempting to say anything about the physics of suddenly-appearing stars (for example, if the average density in regions where stars had been created was above that which general relativity says would be needed to give the universe positive curvature, would space somehow transform from infinite and flat to a finite hypersphere?)

stoppedcaring
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Re: Gravitational waves, potential, and creationism

Postby stoppedcaring » Thu Sep 04, 2014 8:12 pm UTC

Hypnosifl wrote:
stoppedcaring wrote:That would be the case outside the sphere, but what about for an observer at some random point inside the sphere? At time t0, it is enclosed in a shell and thus experiences no gravity. At time t1, when that shell of mass crosses the location of the observer, the observer will begin to experience a pull of gravity toward the center. At time tinfinity, the observer will experience the entire gravitational force of the black hole. What is the change in gravitational force going to look like over that time duration, and thus how is the change in gravitational potential going to propagate outward from the center?

I think the gravitational potential would change but in a way that didn't involve gravitational waves, in the same way the Coulomb force from a charge moving at constant velocity will change as its distance from you changes, but no electromagnetic waves will be involved since the second derivative of the dipole moment is zero (see the physics FAQ link I posted for some discussion of changing fields without waves in both EM and GR).

Okay, then...so what effect would the wave-of-change-in-gravitational-potential have on galaxies?

Lisle's model implies that the light from everything on one side of the universe is still propagating out into the other side of the universe -- that the light from everything in the direction of Orion is just now reaching stars 6,017 lightyears in the opposite direction. If there were giant mirrors set up 3,008 lightyears away, we should just now see the reflection of the stars opposite them bouncing back to us, while a giant mirror 3,009 lightyears away would still be blank. Obviously, no such mirrors exist...but the gravitational potential travels at the same speed as light, and that ought to produce visible effects, no?

stoppedcaring wrote:This is the updated version from Jason Lisle. He doesn't actually come right out and describe it in these terms, because he wants to say it all happened simultaneously using his anisotropic synchrony convention model, but this is what he's advancing.

Thanks. Googling a little, it seems like he's basically just arguing that distant stars were all created along the past light cone of the Earth on the "fourth day of creation", and that God for some reason chooses a simultaneity convention in which the simultaneity surface would hug the past light cone (but deviating from it just slightly so the simultaneity surface can be a space-like surface rather than a light-like one), I image there's not really any way to say what general relativity should predict would happen in such a magical scenario. And his paper basically just goes on and on about his wonderful new simultaneity convention without even attempting to say anything about the physics of suddenly-appearing stars (for example, if the average density in regions where stars had been created was above that which general relativity says would be needed to give the universe positive curvature, would space somehow transform from infinite and flat to a finite hypersphere?)

Oh, the positive curvature of space is a good point.

Does the measured flatness of space imply a certain minimum size of the universe significantly larger than the 86 billion lightyears we see?

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Re: Gravitational waves, potential, and creationism

Postby Hypnosifl » Thu Sep 04, 2014 11:13 pm UTC

stoppedcaring wrote:Okay, then...so what effect would the wave-of-change-in-gravitational-potential have on galaxies?

Lisle's model implies that the light from everything on one side of the universe is still propagating out into the other side of the universe -- that the light from everything in the direction of Orion is just now reaching stars 6,017 lightyears in the opposite direction. If there were giant mirrors set up 3,008 lightyears away, we should just now see the reflection of the stars opposite them bouncing back to us, while a giant mirror 3,009 lightyears away would still be blank. Obviously, no such mirrors exist...but the gravitational potential travels at the same speed as light, and that ought to produce visible effects, no?

Good points, I don't know enough about general relativity to even begin to try a calculation though. One point that occurs to me, though, is that since Lisle's model in which matter just pops into existence probably can't even be modeled in GR, the more "realistic" version would probably be something like what you suggest where you'd have a preexisting spherical shell that would start shooting matter inwards...in that case any star would feel the potential from the opposite side of the shell than the one it was closest to, even if it didn't yet feel the effects of all the matter that had been shot in from the opposite side. Not sure how that would effect things, or how it would effect each star's motion 6000 years after it was "created" by the matter shot in from the shell (speaking of motion, Lisle makes no attempt to explain the pattern of redshift increasing with distance, from what I can see in the paper--he just says "I will further stipulate that the consensus understanding of galactic distances, redshifts, and universal expansion is basically correct", even though that would seem to imply that God deceptively assigned all galaxies just the right pattern of redshift to match what would be expected in a standard cosmological model where matter emerged from a Big Bang and fills space evenly)
stoppedcaring wrote:Oh, the positive curvature of space is a good point.

Does the measured flatness of space imply a certain minimum size of the universe significantly larger than the 86 billion lightyears we see?

Again I don't know how to do the calculation, but it does seem like if you had a giant "island universe" filled with galaxies in a larger empty space (one which was asymptotically flat, meaning curvature approached zero far from the island), then leaving aside weird ideas about how it originated and just assuming it had been there for more years than its diameter in light-years, the curvature of space inside the island might well turn out to be measurable depending on the size of the island. Assuming the density of galaxies inside the island was basically spherically symmetric, I think the curvature inside should be given by the "interior Schwarzschild metric" shown here, maybe someone can say what kind of measurable effects that metric would have if we assume the density of matter is similar to that of the observable universe but different values are chosen for the radius of the edge of the island.


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