Many mechanisms for gravitation have been suggested. It is interesting to consider one of these, which many people have thought of from time to time.
At first, one is quite excited and happy when he “discovers” it, but he soon finds that it is not correct. It was first discovered about 1750.
Suppose there were many particles moving in space at a very high speed in all directions and being only slightly absorbed in going through matter.
When they are absorbed, they give an impulse to the earth. However, since there are as many going one way as another, the impulses all balance.
But when the sun is nearby, the particles coming toward the earth through the sun are partially absorbed, so fewer of them are coming from the sun than are coming from the other side.
Therefore, the earth feels a net impulse toward the sun and it does not take one long to see that it is inversely as the square of the distance—because of the variation of the solid angle that the sun subtends as we vary the distance.
Problem I - drag
What is wrong with that machinery? It involves some new consequences which are not true. This particular idea has the following trouble:
the earth, in moving around the sun, would impinge on more particles which are coming from its forward side than from its hind side (when you run in the rain, the rain in your face is stronger than that on the back of your head!).
Therefore there would be more impulse given the earth from the front, and the earth would feel a resistance to motion and would be slowing up in its orbit.
One can calculate how long it would take for the earth to stop as a result of this resistance, and it would not take long enough for the earth to still be in its orbit, so this mechanism does not work.
No machinery has ever been invented that “explains” gravity without also predicting some other phenomenon that does not exist.
Problem II - heating
Maxwell argues that the temperature of bodies must tend to approach that at which
the average kinetic energy of a molecule of the body would be equal to the average kinetic energy of an ultra-mundane particle
and he states that the latter quantity must be much greater than the former
and concludes that ordinary matter should be incinerated within seconds under the Le Sage bombardment.
Problem III - energy
Maxwell also argued that the theory requires "an enormous expenditure of external power"
and therefore violating the conservation of energy as the fundamental principle of nature.
Importance of this theory
In spite of these problems Maxwell wrote:
Here, then, seems to be a path leading towards an explanation of the law of gravitation,
which, if it can be shown to be in other respects consistent with facts,
may turn out to be a royal road into the very arcana of science.
and Maxwell also said:
We have devoted more space to this theory than it seems to deserve, because it is ingenious,
and because it is the only theory of the cause of gravitation which has been so far developed
as to be capable of being attacked and defended.
Solution III - Solitons
Solitons in water
A soliton is a special kind of wave that acts like a particle. It continues without changing its shape, and keeps its identity even when it collides with other solitons.
The person who discovered the soliton was John Scott Russell in 1834. He called it "wave of translation", here is his description in his own words:
I was observing the motion of a boat which was rapidly drawn along a narrow channel by a pair of horses,
when the boat suddenly stopped – not so the mass of water in the channel which it had put in motion;
it accumulated round the prow of the vessel in a state of violent agitation, then suddenly leaving it behind,
rolled forward with great velocity, assuming the form of a large solitary elevation, a rounded, smooth and well-defined heap of water,
which continued its course along the channel apparently without change of form or diminution of speed.
I followed it on horseback, and overtook it still rolling on at a rate of some eight or nine miles an hour,
preserving its original figure some thirty feet long and a foot to a foot and a half in height.
Its height gradually diminished, and after a chase of one or two miles I lost it in the windings of the channel.
Such, in the month of August 1834, was my first chance interview with that singular and beautiful phenomenon
which I have called the Wave of Translation.
Russell spent some time making practical and theoretical investigations of these waves. He built wave tanks at his home and noticed some key properties:
The waves are stable, and can travel over very large distances (normal waves would tend to either flatten out, or steepen and topple over)
The speed depends on the size of the wave, and its width on the depth of water.
Unlike normal waves they will never merge – so a small wave is overtaken by a large one, rather than the two combining.
If a wave is too big for the depth of water, it splits into two, one big and one small.
Solitons in space
Solitons don't have to travel through water, there are electro-magnetic solitons.
So my theory is that over a long distance, there is an evolution of waves, some combine into being solitons, and only the solitons survive in the long run.
Waves are forming and dispersing all through the universe, but only the solitons live long enough to reach us.
So I claim that a barrage of solitons is constantly "bombarding" us from all directions. This solves the energy problem III of what creats them.
Solution II - Laser Cooling
There is a great explanation of laser cooling in this video by Sixty Symbols:
In "laser cooling" , we want to bring atoms to move slower and hence to be colder.
How Resonance Works?
Laser cooling works because of resonance. We all know resonance, from playing sitting in a swing as children.
The natural back and forth movement of the swing has a certain frequency - depended on the length of the ropes.
If someone pushes us a little each time, in the correct timing when we fall downwards, then our speed will increase more and more.
The push can be very gentle (a kid can push his big dad) - it will still get a bit amplitude eventually.
The important thing is the timing - that it resonates with the natural frequency of the swing.