Tag Archives: black hole

Black Holes and Density

 A question asked of me by klcrace earlier inspired this article. 

Black Holes and Density.

Here is a good source of information on black holes:

Our atoms are mostly empty space, lots of room for things to fit into. Normally, the fields/forces around atoms keep them relatively far apart and the spaces in between remain mostly empty.  All mass have gravitational effects on surrounding masses and the more mass the higher those effects, but as long as the density remains below a certain point there is no black hole. It is not so much the mass that makes a black hole but the density – mass in a tiny space.

As a star gains mass, it’s outer mass compresses the inner material but the internal pressure keeps the atoms apart and the interior spaces empty. When a star grows too much or its internal pressure decreases because its fuel is depleted, it can collapse and when the density reaches a certain point, it technically becomes a “black hole”, one in which the gravitational pull is too great for light to escape. This is often accomplished by a stellar explosion that implodes the mass toward the center of the star, greatly increasing its density.

The mass is still the same but it is concentrated in such a small space (essentially zero space) that the density is enormous (essentially infinite), and the space around it is so severely warped that light does not get out. The density is self sustaining because the gravity of the masses within it is high enough to keep it together, except after much evaporation.

It is thought that much smaller masses can also be compressed by outside forces to the point that the small mass achieves black hole density, but none are known to exist. It would take enormous energy to accomplish this.

For example if you were able to compress a baseball enough, it would become a micro black hole. But it would have to be compressed so much that its outer radius would be essentially zero (much smaller than an atom).  The mass would still be that of a baseball, but the density would be so high that light could not get away from it. Space would be severely warped around this very tiny black hole, but only very very near its center, probably too small to be detected.  Gravity from such a source at the distance you would normally pick up the ball would be no more than for a regular baseball because the mass is still a baseball mass. If you could weigh it, (a real problem) it would weigh the same. It is the ratio of the mass to the radius that is important. Make the mass high enough and/or compress to an extremely small radius and you have a black hole.

Known and predicted black holes contain mass greater than our sun. Sometimes thousands and even billions of times greater. Yet the size of the space occupied by the mass in the black hole is still essentially zero. The gravity around such large masses is extremely high and will capture all light out to a certain radius, the event horizon. The event horizon can be far from the central mass depending on the amount of mass. The capture range is usually further out than the size of the central mass, and grows as the black hole captures more and more mass while the central region does not grow measurably, if at all.

Black holes can evaporate and if there is no nearby mass that it can capture to replenish itself with, a black hole could evaporate to a smaller mass than what was required to establish it. Smaller in mass than our own sun.

Black holes do typically have very high gravitational pulls, proportional to the mass inside and inversely to the distance to the center.  But a micro black hole could theoretically be floating around a lab that created it (such as with a high energy accelerator) and never be noticed as it would likely evaporate before it hit anything and even if it did encounter a part of the lab, it would be so tiny and have such small gravitational pull at atomic-size distances that it would not capture more “stuff” needed to grow. Likely it would just poof out of existence unnoticed.

At least I hope so.

What I want to emphasize it that any given mass has a certain gravitational pull at any given distance, black hole or not. Super-massive black holes at say 1000 light years away have the same gravitational effects as that of a group of stars of the same total mass that are close together (but not close enough to be a black hole) at the same 1000 light year distance. The difference is the black hole has much higher concentration of mass, occupies much less volume, and also warps space much more tightly than the group of stars with the same mass. The stars shine brightly and the black hole is, …well, black.


What’s Up with Gravity?

Gravity is a problem for physicists.

It not only affects mass, but all forms of energy. If you add energy to a mass, its gravitational effect is increased as well but only minutely because an enormous amount of energy is equivalent to a small amount of mass.

Gravity is weak, far weaker than electrostatic forces. Jump off a building and you go splat when you hit the earth. What took perhaps 20 stories to accelerate you to the splat speed is gravity. But the thousandths of an inch that you were stopped in was due to electrostatic forces. Electrostatic forces are the forces that keep your fingers from going through the keyboard.

Gravity also affects matter at a distance – forever like distances. Every atom in your body contributes to the earth’s attraction of the moon and the sun. Consider a molecule of water in the ocean. It is pulled as part of a tidal force by the sun and moon and it in return pulls on both the sun and the moon. Taken together it all adds up.

Gravity is not shieldable.  Elctrostatic effects are. You can build shields to protect you from most radiation and from electromagnetic fields. But gravity is different. If you could shield from gravity, you could build a big enough room to float around like spacemen. But the gravity force on a pea is just as strong no matter what you put around it.

Einstein developed a theory for gravitation – General Relativity – in which gravity is the effect of a distortion of space and time in the vicinity of mass. We can visualize that in the isolated case of the earth moving around the sun as a depression of a membrane representing space and time around the sun.

However, we can’t get our minds around that being the case when you or I standing on a set of scales. What space and what time are we distorting? How does an individual electron’s mass affect another one a mile away? A million miles away? What is going on?

Lets make a distinction: Gravity and Gravitation. “Gravitation” is the attractive influence that all objects exert on each other, whereas Gravity is the force that objects exert on each other due to their relative masses.  Maybe I can state it more simply: one is an influence (gravitation) and the other is a measurement (gravity). For example, a marine sergeant can influence a recruit to jump by yelling at him/her; how high they jump is a measurement. Gravitation is the attractive influence of you or I on the scales by the earth’s mass in relation to our mass. The scale indicates the weight. The force causing that scale’s hand to move is a measurement of gravity.


Fields are invisible lines drawn around objects to represent the points of equal strength of some measurable value. For example we can draw field lines around a magnet’s poles – points where the strength of the magnetic pull are equally strong. You have probably seen (or seen pictures of) magnetic filings on paper above a magnet. Those are lines of force that represent the effect of field gradients, not the points of equal strength that I’m making a point about here. The filings line up along gradients of the fields of the magnets, dipole to dipole so they create lines running from one pole to the other. These lines are often called fields. The ones I’m speaking about are equal strength fields that surround each pole. The filings are linked across those equal strength fields and bridge across the gradients, dipole to dipole.

Fields around single (isolated) objects, such as a charge field around an electron or such as a gravitational field around the same electron, are spaced outward like a shell, keeping the shape of the object but expanding as they go, unless interfered with by another field from another object. The difference is that other objects don’t interfere with the gravitational field (unless it is supermassive like a black hole) All points an equal distance from the object have the same intensity or measurable value. Field lines get weaker as you go away from the object due to the measurable effect becoming weaker as you move away This results in a field gradient from one field surface to the next.

A disturbance at the object (say somehow its mass doubles as two atoms merge) changes the fields at the speed of light, like a ripple in a pool of water. In other words, if the moon were somehow removed at a given moment, the earth would still feel the gravitational pull for just over 1 second (1.2 to 1.3 seconds). If the sun were removed at a given instant, we would not know about it (visually or gravitationally) for about 8.3 minutes.

A disturbance of the type where the mass doubles would cause the field shell that represents a given strength to jump to a distance further away from the mass center. The change would occur at the speed of light, so it is dependent on the distance to that field line or surface. It does not change instantaneously as some suppose and it does not change gradually as might otherwise be supposed. Therefore an object at that point would become affected by gravity at the same instant that light would arrive, not before.

The gravitational fields around an object have gradients that decrease with distance, but go on forever. An atom in your arm has a field that reaches the sun and beyond, but very very weakly and completely swamped (for measurement purposes) by all the other fields generated within the earth. Just the same, it does contribute. Everything adds up. Move your arm and the fields change throughout the universe at the speed of light.

Isolated static (electrical) charges affect each other though the gradients of the fields. They want to move toward each other if the charges are different and the fields tend to cancel or else move away from each other if the charges are alike. They move or experience forces across the gradients. Moving charges affect each other in different ways and their movement produces magnetic fields and magnetic fields also induce movement of charges. They are strongly attracted or forced apart if they are close together because any outside influence that would pull or push them are effectively shielded over relatively short distances by their environment.

What about gravity? Gravitational pull is very weak. What causes that weakness? Why don’t objects closer together (such as your fingers on the keyboard with the keyboard) strongly attract each other? Why doesn’t the massive earth crush us in its gravitational field?

My thoughts

These are just my thoughts, part of my personal theory of gravity. Feel free to discount it or shoot it down.

Isolated static gravitational objects also affect each other through gradients of the fields. Atoms, particles with mass, and all forms of energy are always moving. They jiggle. When they vibrate they do so in the gradient of another object’s gravitational field. I’m not talking about the vibration of one atom against another as being any significant part of the gravitational effect, but instead talking about the quarks and other ingredients of the atoms that are always in motion, those most intimate particles that have mass of their own. The gradients they encounter are also jiggling because the remote masses are ultimately composed of the component parts of atoms, and free particles, always moving.

They are affected only minutely by the gravitational field, which has a very small gradient over the volume of the effective mass of the particle, but they are affected nevertheless. The effect is somewhat like the small magnetic particles which form dipoles in magnetic fields and line up across the magnetic gradients, but these are not magnetic but instead gravitational. There is a gravitational tendency to move toward the other object’s mass, toward stronger gradients and away from smaller ones. Masses tend to congregate, group into crowds, pull together, clump up and possibly create cosmic objects, even suns and earths.

It is not that the gravitational field is so small. It is the competition of the gravitational field of our localized individual component masses within the earth’s gravitational field gradients embedded within the background of all the fields of all the masses of the universe also affecting us.

This competition is not present for electrostatic and electromagnetic fields, so they appear stronger – much stronger.

Our jiggling particles have masses that operate within a gradient that is quite small compared to the size of those masses. All the masses in the universe are contributing to the fields experienced by the particles in our body and the result is a small but measurable attraction that is normal (perpendicular) to the gravitational fields of the individual particles with a tendency to be pulled (a force) toward the center of those fields, force and/or movement toward the stronger gradient of the field. But the overall effect is small even though the earth is huge in relation to us.

When an object absorbs energy, its mass goes up because its jiggling goes up and it has a measurably (but very small) higher gravitational effect as it interacts with the field gradients. Cooling a mass to near absolute zero reduces the energy within the mass, those parts that bang against each other, but does not stop the motion of the quarks and other ingredients that make up the rest mass of the object’s atoms. So the gravitational attraction for that object does not diminish appreciably as it cools.

Bring objects closer together, and the gradients get higher at a quickening rate and the attraction gets higher and that effect swamps any energy effect due to cooling or heating. Just the same, the gradients from the masses of the rest of the universe are there all the time and tend to keep the gravitational force small compared to other forces generated by other fields which have limited effect. The gravitational effect can be quite large, but the gravitational force quite small. Gravitational fields around particularly large objects such as black holes and even our sun do get warped because space and time are also warped in those vicinities.

Space-Time Warping

What I leave unanswered with this paper so far is what gravity actually is. What I’ve described above is why I think that a field gradient makes things tend to have gravitational attraction and develop a force between them that we call gravity. I didn’t say anything about what makes the fields themselves. You can go to a certain point around an object and trace out a measurable effect and call it a field but you can’t say what caused the measurable effect without resorting to Newton or Einstein or perhaps gravitons.

In my opinion I have no quarrel with Einstein’s general relativity and its gravitational predictions or his development of the theory of gravity. It is a beautiful work. The mathematics are wonderful to behold and I don’t pretend to know anything about them other than they work and continue to stand up to careful study and experiments, and they also answer the question as to what makes the fields possible, why you can measure an effect at any distance from an object with mass.

It is a matter of relativity!  

 It is space-time warping, the same as with photons. Gravitation seems to be part of the same effects that I’ve been describing for quantum weirdness, and the fact that fields expand or adjust themselves at the speed of light helps make that case.

Fields as I’ve described them don’t move at the speed of light, they are static for static objects. Changes in the field at the source do adjust the fields at the speed of light. However, you can make a case for the changes to be constantly and forever moving the ripples because the masses within every atom (quarks, etc) are always moving and we and all our masses are forever moving on this earth and through the universe. In other words, the changes in the fields, though minute, are always moving at c and always present.

It may be these changes moving at the speed of light that is always running on zero-time zero-distance that are the foundation of action at a distance and gravitation in particular. Every particle in every atom is moving and so there are always field changes moving away at the speed of light, always attached to both the particle and the masses it encounters elsewhere in space and always applying a minute force on any mass it encounters wherever in the universe that might be.


I personally do not adhere to the idea that gravitons exist. Gravitons are a hypothetical theoretical particle that mediates the force of gravity within gravitational field theory. Such a particle would move at the speed of light and have a spin of 2. It would also be massless as a necessity of its speed. It has a lot of problems including “blowing up” (becoming infinite) in situations involving more than a couple of them at any time at energies in the ultraviolet range. The equations in the latter case cannot be renormalized. String theory helps the graviton, but it too has enormous problems.

If there is such a thing as a graviton, it is actually an effect of the changes in the ripples of the field that is caused by the motion of the components of the atoms or free flight particles. As such it could be conceivably be quantized and thus the ripples in the fields might be quantized. So maybe there is such a thing after all, but I’m not sure you can call it a particle and I’m not convinced it has to be a quantum object. The ripples I’m talking about moving from one mass to another are changes in the field that expands as it grows, and diminishes in strength as it goes flying out into space in all direction at once like a shell of a balloon expanding at c. That would be stretching the definition of a graviton quite a bit.

I think my way of looking at it is much simpler and has the effect of making sense to my feeble brain. I’ll leave it to Newton’s equations for most purposes and Einstein’s for special cases for the calculations. They work well. I’m sorry, but gravitons don’t excite me.

Copyright 2007 by James A. Tabb

Marietta, Ga.

aka  Oldtimer