Compressed Matter

[Crazycowbob]

I've been reviewing some of my physics, and upon thinking about black holes, a question popped into my head.

Maybe some of you more studied folks can add some clearification :)

I know that under the emense gravity of a black hole, atoms are pulled so strongly together that they collapse, forming a ball of neutrons, protons, and electrons with essentually no space between.

What I'm wondering is, pre-big bang, when all the matter of the whole universe was in one spot, was everything compressed even further? Did the bonds between quarks break, and leave a mass of quarks and leptons, or where even those broken into even more basic particles by gravity?

I know under Relativity, the situation, like black holes, is considered a singularity, but I was under the impression that quantum theory more or less made the idea of a singularity obsolete, providing a better understanding of what goes on in such phenomena than general relativity had been able to.


Educationalizing is most definately welcomed over here :-D

[Yllanes]

The classical picture (GR) for a BH or the Big Bang is a singularity. Singularity would mean no quarks or anything we know: it's a finite amount of matter in a point. This probably means that the classical picture is no good there. We don't know the quantum picture.

There are some ideas. For example, current research in quantum cosmology suggests that there wasn't an initial singularity. Rather, if we go backwards in time matter is compressed up to a point and then rebounds. These ideas are still on very shaky ground.

[Schneibster]

Well, now.

First of all, it's worth noting that when atoms are compressed down to where the electrons and protons get smashed together, if there is enough energy, you wind up with a ball of neutrons; the protons and electrons combine, IOW. The environment in which a black hole is theoretically created is the center of a supernova; and we know that slightly smaller supernovae create neutron stars, so this is relatively well understood, because we can see neutron stars and cannot account for our observations in any other reasonable way. So most likely, what exists initially inside the event horizon of a black hole is a ball of neutrons. What happens to anything that falls into it after that, we cannot ever know; once the event horizon has formed, the only way anything can get out is Hawking radiation, which means that all we see is a "gas" of escaping particles. We get no details from this about what's inside of the hole, other than mass, charge, and spin. This last is the relatively famous "no hair" theorem, "a black hole has no hair," a rather amusing statement meaning that the internal characteristics of a black hole are impossible to determine; its only characteristics are those of the whole hole (heh), rather than any constituent of it.

Now, your question is more interesting than that. But you need to understand what the differences are between the interior of a black hole and the Big Bang to understand the answers I'll give, and before I start, I need to be sure that you understand that while this is all theory, the vast bulk of it cannot have been any other way. The biggest difference between a black hole and the Big Bang is that we are outside any black hole we can observe, but we are inside the results of the Big Bang. Therefore we have physical evidence we can examine that can tell us about detailed characteristics of what happened back then, a situation we can never be in with respect to a black hole.

Another important point to understand is that the statements about the visible universe being, for example, the size of a pea, make people think that the WHOLE universe was the size of a pea; this is not the case. We can only see out so far, because looking outward is necessarily looking back in time, because the velocity of light is finite. Thus, in a universe of limited duration, there cannot have been any light before its beginning, and thus any point at a distance further than light could have traveled in the amount of time since the beginning is invisible- it is "beyond our horizon." What is being said is not that the universe was finite and the size of a pea; the universe has always been infinite. What is being said is that the visible universe was the size of a pea. This is an important distinction.

OK, now we have a better idea of what we're talking about. We're talking about an enormous density, all of the matter in the visible universe packed into an incredibly small space. There is an implication to this: there is a law of thermodynamics that says that temperature and pressure are related to one another, and vary directly. In other words, as the pressure increases, so does the temperature. In practical terms, you can observe this when you pump up a bicycle tire. The pump and the tire get hot. And there is another law that relates pressure and density similarly. So the density of the universe is so high that the temperature is enormous, far, far beyond the temperature even at the center of an exploding supernova. At these temperatures and pressures, the very characteristics of protons and neutrons become "smeared."

You are probably aware that protons and neutrons are made of smaller particles called quarks; specifically, of three members each, of two types: up and down. Two ups and a down are a proton; two downs and an up are a neutron. Now, this enormous pressure and temperature mean that there is plenty of kinetic energy in these quarks, so much that they can easily turn into one another with only a very small change in their kinetic energy relative to the total that they have. Not only that, but it turns out there are four more kinds of quarks, strange, charm, top, and bottom, that they can turn into; we don't see these much these days, because they all decay into up and down quarks pretty quickly, but back then, there was so much energy around that they could pretty much freely interconvert into one another. And to top it all off, quarks are held together in threes by the strong force, and the strong force has a characteristic called "asymptotic freedom:" this means that if the quarks have enough energy, they don't have to stay together all the time, but if they don't have enough, then they are confined into the "bags" we call protons and neutrons (and a bunch of other particles, too, all called "hadrons," but because the heavier quarks decay so quickly, none of these lasts very long, and you wind up with protons and neutrons). So the enormous pressure of the universe had the interesting property that instead of pushing things together so much they couldn't do anything, it actually pushed them together so much that they COULD do anything, just about.

Another interesting thing is that when things get hot enough and high enough pressure, the forces we know of get "smashed" into a single force. For example, above a certain temperature, you can't tell the difference between the weak force and the electromagnetic force. We can actually slam particles together hard enough these days that we can reach that realm. At another higher temperature, this "electroweak" force can't be told any more from the strong force, the one that holds the quarks together; and this is pretty well above the temperature where the quarks begin to experience asymptotic freedom. We haven't made any accelerators that can make particles "hot" enough to enter the "strongelectroweak" realm, but we are finishing up one at CERN called the Large Hadron Collider or LHC that should be able to show asymptotic freedom, and we already have some that we believe have just entered this realm, the Tevatron and a few others. The last threshold is the one where the "strongelectroweak" force gets smashed together with gravity. We know really very little about this, primarily because we have not managed to synthesize an effective quantum theory of gravity; until we do, we cannot even imagine really what this would be like.

So take all this interchangeability, of both particles and forces, and this enormous pressure and temperature, and that's what things were like right at the Big Bang.

There is another realm beyond this: it doesn't just keep going down and down, cosmologists believe. What they believe is that there was another state of the universe before the Big Bang, called the "inflationary universe," which is when the dimensions went from being small to being big. But this isn't even really a theory yet; there's too little evidence left over because the Big Bang erased a lot of it. But it's a pretty strong hypothesis, there is some evidence left over, and it explains that evidence pretty well; it's just that it hasn't predicted anything yet, and there are also some interesting competing hypotheses out there. But if we get into that, we're going to be off into a tangent about string theory, and ekpyrotics, and a bunch of other stuff that's pretty speculative still at this time. Basically, the interchangeability, and the pressure and temperature, are what you need to keep in mind.

[Crazycowbob]

Thanks! That does help clear some things up. I have been reading through "Relativity", and "A Brief History of Time", and am absolutely fascinated with theoretical physics. (Even though it's really a bit more in depth than what my Mechanical Engineering degree is requiring)

Are there any other books on the subject you particularly recommend?

And do forgive me if I ask a lot of questions, answers always seem to bring out more!

Now, I've got to go back and hit my Calc. book, been a while and I need to brush up on the math of all this :D

[Schneibster]

Both excellent sources. I'd suggest a not-very-well-known book by Vincent Icke called "The Force of Symmetry," which will give you a pretty good grounding in some of the more difficult parts of modern particle and field physics without an inordinate amount of math; "Perfect Symmetry" by Heinz Pagels, a really good overview of physics up to the start of the string revolution, with a bunch of really good cosmology including a review of the inflationary universe scenario of the Big Bang theory; and Brian Greene's "The Elegant Universe," for a good overview of string physics. Some physicists you will meet here or around elsewhere are not very complimentary about string physics; IMHO, it is worth learning about anyway, because it at least shows what the consensus view of the majority of physicists is looking at. For some alternatives, I suggest research into Roger Penrose's "Twistors," and into Loop Quantum Gravity, which are two rival theories to string theory. I'd say that'll do to go on with.

[l0rca]

Yllanes, you live in Madrid? I live in Rota dude.

[Yllanes]

Yllanes, you live in Madrid?
Yes.
I live in Rota dude.
Good. We need more JREFers in Spain.

[l0rca]

Are you a hot girl?

[Yllanes]

Are you a hot girl?

Afraid not. I'm a guy.

[l0rca]

Thus, in a universe of limited duration, there cannot have been any light before its beginning, and thus any point at a distance further than light could have traveled in the amount of time since the beginning is invisible- it is "beyond our horizon." What is being said is not that the universe was finite and the size of a pea; the universe has always been infinite. What is being said is that the visible universe was the size of a pea. This is an important distinction.

Are you considering the multiverse theory, or considering the term universe in another way?

Some physicists you will meet here or around elsewhere are not very complimentary about string physics

I don't know. I look kindly on it. String Theory might be a simple man's nightmare, but I think it provides a fundamental complexity that isn't found in simple particles much. Other theories attempt to split the fundamental forces into differant entities depending on the temperature, which M-Theory tries to relieve. I guess you could say I'm holding my breath on the next generation of Hadon colliders.

[Thanz]

Are there any other books on the subject you particularly recommend?
I am currently reading "A Short History of Nearly Everything" by Bill Bryson, and I am quite enjoying it. It does, as the title suggests, go into more than just the big bang etc., but it does review those topics. Quite a good read, and enjoyable for someone (like me) who has not taken any science beyond high school.

[Crazycowbob]

Okay, continuing in this vein, here's a question that should put me in waaay over my head (At least until I get a bit further along in my degree :-D)

As far as the 4 fundamental forces are concerned, are they all instintaneous? Unless I missed some important classes, I know magnetic fields themselves are not made up of photons, but can cause their discharge, meaning photons carry the EM force, but the force itself is felt instantly by anything within it's range, am I correct? The same for gravity (though we have not as of yet found a "carrier" for gravity), an object's gravity is felt instantly by everything within it's influence, otherwise Pluto would orbit a spot far behind the suns motion in the galaxy would it not?

What I'm curious about is how are the forces, particularly Gravity, transmitted? It would seem to me that Gravity could not be transmitted by any particle, as it would have to travel faster than light to function. I just find the ideas behind the forces very enigmatic, and have so far been unable to locate a good explaination of how things exactly work.

Technical explainations are more than welcome, just keep in mind my calculus is not up to speed at the moment. :)

[Yllanes]

As far as the 4 fundamental forces are concerned, are they all instintaneous?


Gravity and the electromagnetic field travel at c, there is no instantaneous action at a distance.


What I'm curious about is how are the forces, particularly Gravity, transmitted? It would seem to me that Gravity could not be transmitted by any particle, as it would have to travel faster than light to function. I just find the ideas behind the forces very enigmatic, and have so far been unable to locate a good explaination of how things exactly work.
Gravity is not described as an interaction in GR. It is the effect of the geometry of spacetime. It is not instantaneous, if you move a planet, its gravitational field will move at c. This is the current picture, the future picture may very well be protagonised by the graviton, a massless particle of spin 2.

The other three forces are mediated by particles. The range of a force is greater the smaller the mass of the carrier. An interaction with infinite range (EM) has massless carriers (photons). The nuclear forces have a very short range because they are carried by massive particles.

[69dodge]

I have been reading through "Relativity" [...]By Einstein?

Also good is "The Evolution of Physics: from Early Concepts to Relativity and Quanta" by him and Leopold Infeld.

[69dodge]

The same for gravity (though we have not as of yet found a "carrier" for gravity), an object's gravity is felt instantly by everything within it's influence, otherwise Pluto would orbit a spot far behind the suns motion in the galaxy would it not?In Newtonian theory, gravity is instantaneous. In relativity, it's not; however, it's more complicated than in Newtonian theory---it's not as simple as Pluto just being pulled toward where the sun was a while ago. The net effect of the complications is that Pluto's orbit ends up being practically the same as if Pluto were being pulled toward where the sun is now, as Newtonian theory supposes it is.

[Crazycowbob]

In Newtonian theory, gravity is instantaneous. In relativity, it's not; however, it's more complicated than in Newtonian theory---it's not as simple as Pluto just being pulled toward where the sun was a while ago. The net effect of the complications is that Pluto's orbit ends up being practically the same as if Pluto were being pulled toward where the sun is now, as Newtonian theory supposes it is.

Are there any particular sources I can look up to get a better understanding of this? I'm very interested in learning more :)

[Zygar]

Are there any particular sources I can look up to get a better understanding of this? I'm very interested in learning more :)

Really any source on the theory of relativity will explain this concept.

The outcome is "practically" the same, but Relativity's predictions are far more accurate. Infact, the difference was enough to resolve the Vulcan (http://en.wikipedia.org/wiki/Vulcan_%28hypothetical_planet%29) hypothesis.

[Schneibster]

Hee hee, actually, regarding instantaneous forces, there's something really interesting to talk about. I've talked about it here before; I'll give a link in a moment. It turns out that the fact that charged particles obey SR, and that the transmission of the electromagnetic force is not instantaneous but propagates at the speed of light, is responsible for the existence of magnetism; and it further turns out that the reason that the color (strong) force acts the way it does is that the magnetic component is dominant, which implies some rather curious things about how the color force manifests.

Here (http://forums.randi.org/showthread.php?p=1227083) is the thread. Cecil had a cool experience here, and I was happy to share in it, along with epepke and some others.

[chracatoa]

Another important point to understand is that the statements about the visible universe being, for example, the size of a pea, make people think that the WHOLE universe was the size of a pea; this is not the case. We can only see out so far, because looking outward is necessarily looking back in time, because the velocity of light is finite. Thus, in a universe of limited duration, there cannot have been any light before its beginning, and thus any point at a distance further than light could have traveled in the amount of time since the beginning is invisible- it is "beyond our horizon."

Yes, but if the big bang is right, the universe would have to expand faster than the speed of light if there are parts of it that are invisible for us. Or am I completely off base here?

[Zygar]

Hee hee, actually, regarding instantaneous forces, there's something really interesting to talk about. I've talked about it here before; I'll give a link in a moment. It turns out that the fact that charged particles obey SR, and that the transmission of the electromagnetic force is not instantaneous but propagates at the speed of light, is responsible for the existence of magnetism; and it further turns out that the reason that the color (strong) force acts the way it does is that the magnetic component is dominant, which implies some rather curious things about how the color force manifests.

Here (http://forums.randi.org/showthread.php?p=1227083) is the thread. Cecil had a cool experience here, and I was happy to share in it, along with epepke and some others.

That's very interesting. But now that it is pointed out, it makes sense.

[Yllanes]

Yes, but if the big bang is right, the universe would have to expand faster than the speed of light if there are parts of it that are invisible for us. Or am I completely off base here?

The Big Bang is compatible with an infinite universe. As Schneibster said, only the observable universe was the size of a pea, the whole would have always been infinite. Even if the universe is finite, with all of it the size of a pea a long time ago, its radius is bigger than its age times the speed of light. This is not in contradiction with SR. You can read this tutorial (http://www.astro.ucla.edu/~wright/cosmolog.htm) or start with these two FAQ:

How can the Universe be infinite if it was all concentrated into a point at the Big Bang? (http://www.astro.ucla.edu/~wright/infpoint.html)

If the Universe is only 10 billion years old, how can we see objects that are now 30 billion light years away? (http://www.astro.ucla.edu/~wright/cosmology_faq.html#DN)

[scotth]

Just dropping off a few more book ideas....

"Einstein's Theory of Relativity" by Max Born is my favorite. After reading a stack of 'popularizations' that left me unsatisfied, this book had enough detail to make me happy.

Also, the relativity primer in Brian Greene's "Elegant Universe" presents some of the concepts in a brilliantly clear manner.

[Zygar]

Yes, but if the big bang is right, the universe would have to expand faster than the speed of light if there are parts of it that are invisible for us. Or am I completely off base here?

The matter from the Big Bang didn't expand at that rate. Space itself was expanding faster than light. The indirect result is that the matter was moving faster than light. But since it was not moving faster than light relative to space itself, no laws are broken.

[RecoveringYuppy]

Hee hee, actually, regarding instantaneous forces, there's something really interesting to talk about. I've talked about it here before; I'll give a link in a moment. It turns out that the fact that charged particles obey SR, and that the transmission of the electromagnetic force is not instantaneous but propagates at the speed of light, is responsible for the existence of magnetism; [snip].
I may be repeating a point since this conversation spans threads.

There should also be an force analogous to magnetism for gravity also. Since gravity propagates at the speed of light a spinning massive body should exert a torque on another nearby spinning massive body.

[Schneibster]

Hmmm, might that be the origin of "gravity waves?"

Hey, I wonder what's going on at LIGO? Haven't checked that out recently.

[RecoveringYuppy]

Hmmm, might that be the origin of "gravity waves?"
I don't know which concept came first but wave propagation of gravity would be another way in which gravity should be analogous to electricity and magnetism.

[Schneibster]

No, I was wrong- that's at least partly frame dragging. IIRC. Yllanes will no doubt step in and correct me if I don't.

Frame dragging means that the actual spacetime surrounding a spinning massive object is twisted by the spin, as opposed to just being curved by the mass. Or anyway that's a good way to understand it from a layman's POV, which I try not to get too far beyond.

[RecoveringYuppy]

I don't think you're wrong. I think frame dragging, gravity waves, and the magnetic analog (gravitomagnetism???) I referred to are all closely related.

The magnetic analogy goes like this: In a circular loop of wire with with non moving charges a charged particle at a distance is not affected by the wire because all charges within the wire are balanced out. An equal number of protons and electrons. But start a current moving in the wire and the situation changes. At first glance the charges are still balanced but the electrons moving away from the isolated charge are now exchanging virtual photons with the isolated charge that are red shifted while the ones from the side of the circle with the current moving toward it are blue shifted. A similar thing happens with mass and gravity. If a mass is rotating, the mass on one side is seen as receding leading to "red shifted" gravity waves and the other side is seen as approaching and "blue shifted" gravity waves. That leads directly to frame dragging and magnetic analog. And then given that there is a magnetic analog that leads to wave propagation. So I think they are all closely related.


BTW Is LIGO still in operation? Has LISA made any progress? Has Gravity B produced results yet?

[Schneibster]

I did a post on those two experiments here (http://forums.randi.org/showthread.php?t=70492). There'll be some more interesting stuff over there shortly, too, I think. Feel free to join in.

[RecoveringYuppy]

Thanks. Hadn't seen that thread yet.

[69dodge]

Are there any particular sources I can look up to get a better understanding of this? I'm very interested in learning more :)Here's something: Does Gravity Travel at the Speed of Light? (http://www2.corepower.com:8080/~relfaq/grav_speed.html)

[chracatoa]

You can read this tutorial (http://www.astro.ucla.edu/~wright/cosmolog.htm)

Very nice tutorial. I will spend some time reading it. I thought that the Big Bang included the entire universe, not only the observable universe.

Now, let us assume there is something beyond our observable universe. Will we be able to see something in the distant future or it will remain invisible for us forever? Perhaps we cannot even speculate about it...

[joobz]

Hee hee, actually, regarding instantaneous forces, there's something really interesting to talk about. I've talked about it here before; I'll give a link in a moment. It turns out that the fact that charged particles obey SR, and that the transmission of the electromagnetic force is not instantaneous but propagates at the speed of light, is responsible for the existence of magnetism; and it further turns out that the reason that the color (strong) force acts the way it does is that the magnetic component is dominant, which implies some rather curious things about how the color force manifests.

Here (http://forums.randi.org/showthread.php?p=1227083) is the thread. Cecil had a cool experience here, and I was happy to share in it, along with epepke and some others.
So magnetism is a type of electro doppler effect?

[Cuddles]

Very nice tutorial. I will spend some time reading it. I thought that the Big Bang included the entire universe, not only the observable universe.

It depends on your definition of "universe" and "big bang". Popular thinking currently is that the universe is quite possibly infinite, or at least close enough that it can be seen on a clear day, but that the observable universe is, obviously, finite. In this case we can either refer to what is observable as "the universe" or to the entire infinite space as "the universe". Equally, the big bang can either refer to the start of the whole thing, the end of the inflationary period or just the origin of the observable universe (in most theories incorporating inflation the last two are the same, and in most without inflation the first and third are the same). It is easy to get confused when different people are using different definitions.

Now, let us assume there is something beyond our observable universe. Will we be able to see something in the distant future or it will remain invisible for us forever? Perhaps we cannot even speculate about it...

Maybe. We can speculate about it, but without knowing the the shape, extent and actual amount of energy and mass in the universe it is impossible to say for sure. If the universe is closed and heavier than the critical mass it will eventually stop expanding and collapse back, which would mean that things outside will become visible in the future (unless light slows down as well, which is also possible). The most likely outcome at the moment is that the universe will expand forever, and in fact its expansion will accelerate. This will mean that while the observable space becomes larger, the actual matter will become more widely spaced and things visible now will pass over the horizon, eventually leading to every particle effectively living in its own isolated universe, since it will not be possible for any of them to interact with any others.

[RenaissanceBiker]

Are you a hot girl?

That is both the saddest and funniest thing I have ever read on this forum.

[Schneibster]

So magnetism is a type of electro doppler effect?No, it's actually just a reduction in the effect of the electric field caused by relativistic foreshortening.

[RecoveringYuppy]

Doesn't an explanation based on considering the Doppler effect on the exchanged virtual particles lead to a consistent explanation also?

[RecoveringYuppy]

In Newtonian theory, gravity is instantaneous.
Isn't it more like Newtonian theory didn't even address the speed that gravity might propagate? I think most of the situations considered involved bodies whose gravitational field hadn't changed in millions of years. So the question of how fast a gravitational change might propagate didn't even arise. All gravitational fields considered were pretty much static.

[RecoveringYuppy]

The same for gravity (though we have not as of yet found a "carrier" for gravity), an object's gravity is felt instantly by everything within it's influence, otherwise Pluto would orbit a spot far behind the suns motion in the galaxy would it not?
One simple point about this seems to have gone unmentioned. Pluto is as much in orbit around the galaxy as the Sun is. Just as the Moon is in orbit around the Sun as the Earth is. Regardless of the more complicated concept of what speed gravity might propagate at, Pluto is in no danger of the Sun leaving it behind.

For most practical purposes, including the orbits of the planets about stars and the stars about the galaxy, the propagation speed of gravity is a moot point. The stars and the galaxies are homogeneous and static enough that the gravity field propagated everywhere a long time ago. And the field that gets here tomorrow or next year isn't going to be much different from the one that is here today.

[scotth]

Isn't it more like Newtonian theory didn't even address the speed that gravity might propagate? I think most of the situations considered involved bodies whose gravitational field hadn't changed in millions of years. So the question of how fast a gravitational change might propagate didn't even arise. All gravitational fields considered were pretty much static.

Actually, I think 69dodge had that one correct.

That Newtonian gravity propogated at the speed of light was a central problem with it in Einstein's view, once he had created Special Relativity.

And clearly, static isn't the case either. The planets move about and have gravity of their own that effects each other and other smaller bodies for certain.

There was no allowance for any propogation time due to the constant movement of the planets, thus instantaneous.

[RecoveringYuppy]

@scotth

But did Newton (or anyone for that matter) ever explicitly say that gravity propagates at some speed or that the force vector points at where the planet is now or at some earlier point? I think not. I think it was centuries before anyone even came across a situation where it made a difference that prompted the question. And when the question did come up people had to try it both ways to find out that both approaches still had problems.

Basically I'm making a small point that I don't think Newton was prescient enough to have even considered the question or to even realize he might have implied something about the question. When 19th century scientists realized this previously unaddressed question made a difference they had to answer it.

[scotth]

Basically I'm making a small point that I don't think Newton was prescient enough to have even considered the question or to even realize he might have implied something about the question. When 19th century scientists realized this previously unaddressed question made a difference they had to answer it.

That is not the impression that I had... I hope to be able to find the passages (probably of the Principia) that led me to believe otherwise.

I do think Newton considered it and instantaneous action was his conclusion. Now, can I support that? This will be a tough one I bet.

[RecoveringYuppy]

I've read Principia but probably not with this particular question in mind. I do remember reading something about some of the early attempts at explanations for the anomolous precession of perihelions. One early writer on that subject speculated about gravity taking time and pointed out they had no way to know and had to assume gravity was instantaneous.

I suppose it is also possible that Newton himself explicity thought or said it was instantaneous but that no one took him seriously. He was at odds with almost everyone of his time over how actions could propagate over distance.

[ynot]

How does the speed of terminal velocity (falling through our atmosphere) relate to the speed of gravity?

[Unnamed]

How does the speed of terminal velocity (falling through our atmosphere) relate to the speed of gravity?
I doesn't. The terminal velocity concept does not depend in any appreciable way on the speed of gravity.

[RecoveringYuppy]

How does the speed of terminal velocity (falling through our atmosphere) relate to the speed of gravity?
Gravity is an acceleration, not a speed. Terminal velocity goes up with increasing gravity and down with increasing friction. On a planet with no atmosphere, terminal velocity would equal escape velocity.

[Zygar]

I doesn't. The terminal velocity concept does not depend in any appreciable way on the speed of gravity.

It most certainly does, although you mean acceleration of gravity. It is a balancing equation between air resistance and the force of gravity.

[Unnamed]

It most certainly does, although you mean acceleration of gravity. It is a balancing equation between air resistance and the force of gravity.
Maybe ynot meant the acceleration of gravity, but I meant the speed of propagation of the gravitational field, which was the subject being discussed for several posts until now.

[RecoveringYuppy]

Yes, it's not related to the speed of propagation of gravity, but is related to the strength of gravity.

[l0rca]

That is both the saddest and funniest thing I have ever read on this forum.

Maybe you are a blond. ;)