Exploring Gravity: Let's Think Together

[Tyger]

see my post "Why does Gravity occur? and let's start putting your thinking together with mine. They should fit very nicely.

 

[marcus]

Originally posted by Tyger
see my post "Why does Gravity occur? and let's start putting your thinking together with mine. They should fit very nicely.

I read your post earlier with interest but did not see how to respond. Frank Wilczek is an eminent particle physicist who has contributed to that discussion in the past 3 years

http://www.aip.org/web2/aiphome/pt/vol-55/iss-8/p10.shtml

You see right in the first sentence or so that he wants to explain the number 13E18 which is one of the major unexplained numbers that worried Dirac. Actually the reciprocal one over 13E18 which he calls "~10^-18" (very sloppy).

this number he calls "m_prot/M_Planck.
The ratio of the proton mass divided by the Planck mass.
It happens to be 1/13E18. A lot of people would like to explain
why that number is what it is, just as for so long they have wanted to explain 1/137.

Wilczeks trilogy in Physics Today is an important series. Here is the first

http://www.physicstoday.org/pt/vol-54/iss-6/p12.html

In the second paragraph he talks about Feynmann's interest in the fundamental constants (like 1/137) and in the third paragraph he talks about Dirac and his investigation of them.

The greatest theoretical physicists have always been obsessed with the fundamental constants---why they are what they are and what it means and why nature has these beautiful ratios and proportions built into her.

Wilczek is a very eminent HEP physicist with broad theoretical vision and his take on this may give us some guidance. His papers are 2001 and 2002 so it is kind of an updated view.

My own vision is insufficient to make any substantive contribution but I appreciate why the big guys are fascinated by Planck units (which are a way of summing up all these things) since they are the system of units BUILT OUT OF the fundamental constants and the system in which numbers like 1/137 and 13E18 appear most clearly.

I will think about your essay here but may not be able to reply in any helpful way.


Here are exerpts of your post just to have them handy:

[[ I think Gravity exists to hold a certain quantity in Nature constant.

In 1931 P.A.M. Dirac wrote a paper expounding on the fact that the quantities H, the Hubble Value, G, Newton's Constant, Ρ, the mean density of matter, and 1/T, the inverse age of the Universe were all apporx. 10^-41 when expressed in Electron (or Proton) mass units. This is known as Dirac's Large Number hypothesis. A necessary implication is that these "contants" vary.

An important model in Cosmology is the (somewhat misnamed) Big Bang Theory, the notion that the Universe started in a condensed state and expanded to it's current condition. Dirac's Hypothesis is consistent with it. More than a few authors have noted that Big Bang models are very sensitive to initial conditions, that small differences can lead to runaway expansion or immediate collapse. This is true even when we include the Dirac Hypothesis. However I refer to models which just combine the two as "naive models" for good reason, because they fail to take into account some very important and neccesary considerations. One is that all four of these quantiies must "track" appromately throughout the history of the Universe, and any initial mal-adjustment of conditions would cause them not to track. The naive models provided no mechanism to maintain such tracking.

After many attempts to make the naive models work I realized that something else was neccessary. I worked with electronic equipment and was well aquainted with fed-back systems. I could not escape this simple conclusion:

On the large scale the Universe acts as a fed-back system. And ordinary (Newtonian-Einsteinian) Gravity was part of the feedback mechanism.

In a fed-back system there is generally an input quantity and the output "tracks" the input. If the input is a constant current or voltage the output may be a constant voltage, and it serve to regulate the output potential. In such a case the input is usually described as a reference quantity.

Naturally we should want to know what the reference quantity is for our Universe. If we take G×T or H/Ρ we have a quantity with the approx. value of one in Dirac's units, with the dimensions of volume per unit mass per unit time, which represents the rate at which the Universe expands. R. Dicke has called this the Volumetric Rate of Expansion, and it seems to be the correct reference quantity.

There are three implications in all of this:

The Universe must operate on the large scale as a fed-back system.

Gravitation needs more "parts" than 1/R^2 Gravity to maintain the proper rate of expansion.

The third, not so easy to see, is that some of these mechanisms must operate faster than light. All these are neccesary to keep expansion or collapse at bay.

It's well established that 1/R^2 gravity fails on the large scale, on the scale of galaxies by a factor of ten, of clusters of galaxies by a factor of a hundred, for clusters of clusters by a thousand. It would seem that the other parts of Gravity take over here. For our purposes Gravity is any interaction that maintains the proper rate of expansion.]]

 

[marcus]

It is good to do what Dirac did but bad to do it his way. His way is history.

What started him off is the wide difference between the grav and elec forces when you look at, say, two electrons.

In natural units the "compton" is just the reciprocal of the mass
the proton compton is 13E18
and that means the proton mass is 1/13E18

the electron compton is 1836 times proton----1836 x 13 = 23868
so the electron compton is 23800E18, or 238E20
and the electron mass is 1/238E20

Imagine putting two electron one natural unit apart----this is an idealization. Then the force of electrostatic repulsion would be 1/137

On the other hand the gravitational attraction between them
would be the square of 1/238E20. Notice how small this is.

The force is (1/238)^2 times E-40.

So here I have gotten for you Dirac's famous 41 orders of magnitude. Actually if you compare 1/137 with the gravity force it is 42 orders of magnitude.

The point is that Dirac could not explain it, so he got the notion that it might have to do with the age of the universe. That idea is dead. But the need to explain it is still alive.
And Wilczek has some ideas of how to explain it. But they involve physics which has grown up between 1931 (when Dirac wrote) and now.

the main thing is you should not build units based on proton mass or electron mass Higgs boson mass or neutrino mass or Charley's mother's mass or the moon's mass or whatever. You build them out of really fundamental constants and don't pick out some arbitrary particle or atom. So you see that Wilczek is starting with Planck units and comparing other things to them---what is the proton mass compared with the basic natural mass unit? Why is it so small?

There is a lot of breaking news. Nature magazine a month or so back had an article about very strong evidence that area is actually quantized in units of the Planck area. Or certain areas are anyway. Mindboggling. My advice is if you are interested in basic physics then get accustomed to using the Planck units since that is where the modern analogs of Diracs ideas are happening

 

[Tyger]

I have to say

that I haven't yet "bought into" the Planck Mass viewpoint, at least not yet. Partly because it was a "rabbit pulled out of a hat". I suspect that there is a logarithmic relationshipe between the value of electric charge and other couplings and the strength of Gravity, and that is what the Wilczek articles basically says too, but in a very convoluted way. And I don't think your choice of unit of mass (or rest QM frequnecy, which is what is really important) is critical as long as your equations are consistent with it.

You know by now that I am not resistant to change, but on the other hand I don't follow the herd. I tend to be skeptical of any idea which becomes too popular, or is regarded as a matter of faith. I'm a student of the History of Physics, as well as Physics, and I know that most successful theories are based closely on observation and experiment, so I am leary of theories that are just based on mathematical extrapolation, as too many are today. There are huge bodies of experimental data waiting for a clear interpretation while people whittle away at some version of SuperSymmetry.

I think the next growth area in Physics is Astrophysics, including Solar Physics, but I'm afraid that most of the people involved don't know how or aren't willing to apply the proper kind of imagination to the task. I like Steven Weinberg's description of Magicians and Logicians to describe people with creative insight, and in my modest way I have enough of it to understand what he means, because I have been both from time to time. But you have to be willing to stray far from the safety of the herd, for if the herd were right there would be no problem to solve.

I must confess I am impressed with Wilczek, not so impressed with John Baez.