Fighting the Hard Fight

[chromosphere]

Corri,

Wow! Lots of deep questions in there. I will do my best to answer them.

new theory that Newtonian Physics is not holding up at the galaxy level. Nothing proven yet... but has serious potential.

Actually, the idea that gravity might have a slightly different form than Newtonian only measurable at large scales (e.g. galactic scales) has been around for awhile. Occasionally new data will pop up, or someone will make a new stab at how the equation should look to fit the data.

According to Newton, the gravitational force is proportional to the inverse square of the distance between the two objects. So if you double the distance between two objects, the force will decrease by a factor of 4. Tripling the distance would cause it to decrease by a factor of 9, and so on. This equation, Newton's Universal Law of Gravity, has been shown to be VERY good at predicting observed motions in gravitational fields.

However, there are other observations that don't fit with this Law. If you take a galaxy full of stars and gas and put it in motion around a massive central object (typical scenario for a spiral galaxy) the speed of rotation of the stars should decrease with increasing distance from the center. We see the same thing with the planets in our solar system (how many are there again? LOL). But when we observe the rotational speed of stars in our galaxy, the speed of objects remains roughly constant with distance from the center.

There are two basic ways that people have used to explain this observation. One is dark matter, which we can go into if you want. The other is that the equation of gravity is slightly different than Newton's Law. If you experiment for example with the power, instead of it being inverse square it is inverse to the 2.3 power, you can make orbiting objects move differently. The trick is to tweak that number or the equation in such a way that you get the observed motion in galaxies, WITHOUT affecting the equation enough that it doesn't correctly predict the orbits of planets. People have been able to do this.

The problem is that there are many other motions in space, and tweaking the Law of Gravity in the way proposed to solve the galactic rotation problem creates conflict with some of those other motions. So the majority of scientists do not support the "tweak" model.

No one, not even Einstein, could figure out why gravity is such a weak force, but it is theorized, that gravity is woven, somehow into the space/time theory... the fabric of the universe.

First, figuring out WHY gravity is a weak force would be more of a philosophical question. Gravity just is what it is.

Second, the notion that gravity is woven into spacetime is essentially Einstein's Theory of General Relativity. The presence of mass warps spacetime. Objects are not orbiting in response to a centripetal force of gravity, they are following the curvature of space caused by the massive object. Einstein's theory has been successful primarily because it correctly predicts all observed motion, AND motions that Newton's Law could not predict, such as the bending of the path of starlight.

So I got to thnking. At the quantum level, gravity does not behave as it does at the macro level. This consfused Einstein. K. I get that.

You have basically described the great conundrum of modern physics. At the microscopic level, we can describe 3 of the 4 forces using a particle model (quantum physics). The missing one is gravity. But we have this great model for how gravity works at the macroscopic level. Unfortunately, that model (Relativity) cannot be molded to work at the microscopic level, at least not in the same way as the other 3 forces. Also, gravity is so weak that we do not have laboratory equipment sensitive enough to measure its properties at the microscopic level. Many people have made attempts to create a model (so called String Theory models) to explain the 3 quantum forces and gravity together, but while they look good on paper, there is no laboratory verification at this time.

So... what if... gravity defines the closed system? And systems within systems? What if it is merely an indicator of they system with which you are dealing, rather than a manifestation of the system?

I'll have to admit I am a bit confused as to the point you are trying to make here. Can you elaborate?

bodies that have mass exhibit certain levels of gravity that will always be pre-empted by the stronger forces, such as EMP and strong and weak nuclear forces.

While it is true that the other forces are stronger, gravity is preiminent at the macroscopic level. This is because the nuclear forces are only strong on very small scales, on the order of the size of an atomic nucleus. And the electromagtic force is generally zero outside the atom because most are electrically neutral. Gravity is the only long range force that always points in the same direction, toward the mass. So yes, the other forces do dominate at very small scales.

But... if gravity were any stronger than it is... how is it... that we would even be able to survive? If gravity operated at the quantum level as it does at the Newtonian level, how it is that you and I would have the ability to think? To walk upright... to have a neuron fire?

It seems as if you are skirting near the anthropic principle here. Are you asking if gravity were STRONGER than it currently is, how would it affect us? There is no reason to think that gravity does not operate at small scales, it is just very weak and thus essentially does not influence the behavior of particles. But it would be definitely true that if gravity were stronger than it is now, it would completely change the character of our universe, not just us.

Photons have no mass... why, then, would gravity have the same affect on them that it does on say... a planet?

But see, gravity does have the same effect on a photon as it does on a planet, given the difference in the properties of a photon and a planet. Scientists have demonstrated conclusively that the path of photons are altered by the presence of mass in the exact same way that a planet's path is altered to make it orbit, through the warping of spacetime. The difference in path being related to the energy of the object in question. Imagine taking a bed-sized rubber sheet and stretching it taut. Now put a bowling ball in the center (the massive object). Now start shooting marbles across the sheet. If you shoot them slowly, they will circle around the bowling ball. If you shoot them quickly, they will just move in a slightly curved line. That is the difference between orbits and the bent path of photons.

Why would gravity have the same affect on a galaxy that it does on a planet?

Why would it not? Galaxies are made up of the same material as planets, the only difference being that galaxies appear to have large quantities of matter that does not interact with light surrounding them. The presence of this "dark matter" affects the motion of the galaxy in the same way as if there was a large quantity of normal matter surrounding the galaxy. It is just that this matter is electromagnetically neutral and thus we cannot see it with electromagnetic waves (i.e. light). This is not unprecedented. There are many forms of matter that we cannot see with light. The only real question is what exactly is this dark matter made of.

If it did... the whole big bang would never have happened... yes? No?

Unfortunately that is a question that is impossible to answer definitively at this time. We really do not know how tweaking the fundamental properties of the universe would have affected the event called the Big Bang. All we can really say is how it would likely have affected the evolution of the universe post-Big Bang. Yes, if gravity were different than we observe it, the universe would be a MUCH different place.

The problem that a lot of people get into here is trying to predict exactly how different it would be. One of those problematic predictions has to do with the presence of life. There are many that say if you change only slightly the properties of the universe, life could not exist, thus this is evidence that the universe was designed in a certain way so that life would be created. Some of those take that one step further and use it as proof of a Designer, i.e. God. The problems with that argument are three-fold. One, we do not really know enough about life, especially how it starts, to really say anything conclusive about the probability of it starting under given conditions. All we can say is that life, as it manifests itself on the Earth, would be unlikely if the fundamental properties of the universe were to change. But even then we still don't have a good model for exactly how life began on the Earth to definitively say.

Second, we have NO way of knowing that changing the form of gravity slightly would not alter some other property(s) of the universe so that life, even life as we know it, could still develop. String Theory purports that all of the fundamental properties are connected in some way. So tweaking one would cause a change in all. Since we do not know the exact form of that connectedness, there is no way to predict (at this time) how changing one would affect the other.

Finally, evolution itself gives an answer to the anthropic principle. Let us just postulate that tweaking some or all of the parameters of the universe would cause it to not be able to support life or even itself. I.e. if gravity were much stronger, the universe would have just quickly collapsed on itself. If gravity were much weaker galaxies and stars would have never formed. In essence, the universe would have "died" quickly. But who is to say that many universes have not be formed by many "Big Bangs", each with different sets of fundamental properties. The ones with bad mixes of properties just "die", while the one that comes along with just the right mix "lives." Isn't it interesting how amazingly parallel that is to the theory of biological evolution. Adaptations that are favorable (e.g. a set of properties that works well together) survive while unfavorable sets do not. It could even been that the very first universe to be formed with the right mix was then able to propogate its properties into future universes (a series of "bangs" and "crunches") much in the same way that natural selection drives the changing of Earth's species toward adapations that work. I find that rather elegant personally.

One more quote then I'll wrap up ... for now

WHY WOULD gravity operate in a dense field, like a black hole, the same way it would in empty space... if it did... waht sense would THAT make?

You are absolutely right here. Einsteins Relativity AND Newton's Laws are ineffective at predicting the environment inside a black hole. Clearly there is a higher order model that is needed. String Theory does have promise, we just need to be patient for the laboratory equipment to catch up with the theoretical possibilities.

Basically, your questions do drive at the heart of what is puzzling the astrophysical community today. So while I may be able to "answer" your questions, I must admit that those answers are very tentative. But then again, that is the nature of science.

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