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Posts Tagged ‘**physics**’

### Universe, Physics, Quantification of Earth: From “A short history of nearly everything” by Bill Bryson

Posted May 24, 2011

on:**“A short history of nearly everything” by Bill Bryson**

**Physics, the quantification of Earth, and the Universe**

The physicist **Michio Kaku** said: “In some sense, gravity does not exist; what moves the planets and stars is the **distortion of space and time**.”

Gravity is not a force but a byproduct of the warping of space-time, the “**ultimate sagging mattress**”.

This new understanding of the universe that time is an intrinsic dimension as space was offered by Albert Einstein through his **Special Theory of Relativity**.

Among other principles, Einstein realized that matter is energy that can be released under specific conditions so that energy is defined as the product of mass and the square of the speed of light c = 300,000 km/s.

In his attempt to unify classical and relativity laws, Einstein offered his General Theory of Relativity and introduced a constant in the formula to account for a stable Universe. Einstein declared that this constant was “the blunder of his life”, but scientists are now trying to calculate this constant because the universe is not only expanding but the galaxies are accelerating their flight away from the Milky Way.

In 1684, **Edmond Halley**, a superb scientist in his own right and in many disciplines, and the inventor of the deep-sea diving bell, visited Isaac Newton at Cambridge and asked him what is the shape of the planetary paths and the cause of these specific courses. Newton replied that it would be an ellipse and that he did the calculation, but could not retrieve his papers. The world had to wait another two years before Newton produced his masterwork: “Mathematical Principles of natural Philosophy” or better known as the “**Principia**”.

Newton set the **three laws of motion** and that for every action there is an opposite and equal reaction. His formula stated that force is proportional to the product of the masses and inversely proportional to the square of their corresponding distances. The constant of gravity was introduced, but would wait for **Henri Cavendish** to calculate it.

It is to be noted that most of his life, Newton was more serious in alchemy and religion than in anything else.

Henry Cavendish was born from a dukes families and was the most gifted English scientist of his age; he was shy to a degree bordering on disease since he would not meet with anyone and, when he visited the weekly scientific soirees of the naturalist Sir Joseph Banks, guests were advised not to look him straight in the face or address him directly.

** Cavendish** turned his palace into a large laboratory and experimented with electricity, heat, gravity, gases, and anything related to matter. He was the first to **isolate hydrogen**, combine it with oxygen to form water. Since he barely published his works many of his discoveries had to wait a century for someone else to re-discover the wheel.

For example, Cavendish anticipated the law of the** conservation of energy, Ohm’s law, Dalton’s law of partial pressures**, Richter’s law of reciprocal proportions, Charles’ law of gases, and the principles of electric conductivity. He also foreshadowed the work of Kelvin on the effect of** tidal friction** on slowing the rotation of the earth, and the effect of local atmospheric cooling, and on and on. He used to experiment on himself as many scientists of his century did, such as **Benjamin Franklin, Pilate de Rozier, and Lavoisier**.

In 1797, at the age of 67, Cavendish assembled **John Michell’s apparatus** that contained two 350-pound lead balls, which were suspended beside two smaller spheres. The idea was to measure the gravitational deflection of the smaller spheres by the larger ones to calculate the gravitational constant of Newton.

Cavendish took up position in an adjoining room and made his observations with a telescope aimed through a peephole. He **evaluated Earth weight** to around 13 billion pounds, a difference of 1% of today’s estimate and an estimate that Newton made 110 years ago without experimentation.

John Michell was a country parson who also perceived the wavelike nature of earthquakes, envisioned the possibility of black holes, and conducted experiments in magnetism and making telescopes. Michell died before he could use his apparatus which was delivered to Cavendish.

The 18^{th} century was feverish in measuring Eart: its shape, dimensions, volumes, mass, latitude and longitude, distance from the sun and planets and they came close to the present measurement except its longivity, and had to wait till 1953 for** Clair Patterson** (a male geologist) to estimate it to **4,550 million years** using lead isotopes in rocks that were created through heating.

**Einstein speaks his mind processes on the origin of General Relativity; (Nov. 21, 2009)**

This article is on how Einstein described his mind processes that lead to the theory of restricted relativity and then his concept for General Relativity.** **In 1905, restricted relativity discovered the equivalence of all systems of inertia for formulating physics equations.

From a cinematic perspective, there was no way to doubting relative movements. Still, there was the tendency among physicists to physically extend privileged significance to system of inertia. The question was “if speed is relative then, do we have to consider acceleration as absolute?”

Ernest Mach considered that inertia did not resist acceleration except when related to the acceleration toward other masses. This idea impressed Einstein greatly. Einstein said: ” First, I had to establish a law of gravitation field and suppress the concept of absolute simultaneity. Simplicity urged me to maintain Laplace’s “scalar gravity potential” and fine tune Poisson’s equation.

Given the theorem of inertia of energy then, inertia mass must be depended on gravitation potential; but my research left me skeptical. In classical mechanics, vertical acceleration in a vertical field of gravity is independent of the horizontal component of velocity; it follows that vertical acceleration is exercised independently of the internal kinetic energy of the body in movement.

I discovered that this independence did not exist in my draft theory; this evidence did not coincide with the affirmation that all bodies submit to the same acceleration in a gravitational field. Thus, the principle that there is equality between inertia mass and weight grew with striking significance. I was convinced of its validity, though I had no knowledge of the results of experiments done by Eotvos.”

Consequently, the principle of equality between inertia mass and weight would be explained as follows: in a homogeneous gravitational field, all movements are executed in relation to a system of coordinates accelerating uniformly as if in absence of gravity field. I conjectured that if this principle is applicable to any other events then it can be applied to system of coordinates **not accelerating uniformly**.

These reflections occupied me from 1908 to 1911 and I figured that the principle of relativity needed to be extended (equations should retain their forms in non uniform accelerations of coordinates) in order to account for a rational theory of gravitation; the physical explanation of coordinates (measured by rules and clocks) has to go.

I reasoned that if in reality “a field of gravitation used in system of inertia” did not exist it could still be served in the Galilean expression that “a material point in a 4-dimensional space is represented by the shortest straight line”. Minkowski has demonstrated that this metric of the square of the distance of the line is a function of the squares of the differential coordinates. If I introduced other coordinates by non linear transformation then the distance of the line stay homogeneous if coefficients dependent on coordinates are added to the metric (this is the Riemann metric in 4-dimension space not submitted to any gravity field). Thus, the coefficients describe the field of gravity in the selected system of coordinates; the physical significance is just related to the Riemannian metric. This dilemma was resolved in 1912.

Two other problems had to be resolved from 1912 to 1914 with the collaboration of Marcel Grossmann.

The first problem is stated as follows: “How can we transfer to a Riemannian metric a field law expressed in the language of restrained relativity?” I discovered that Ricci and Levi-Civia had answered it using infinitesimal differential calculus.

The second problem is: “what are the differential laws that determine the coefficients of Riemann?” I needed to resolve invariant differential forms of the second order of Riemann’s coefficients. It turned out that Riemann had also answered the problem using curb tensors.

“Two years before the publication of my theory on General Relativity” said Einstein “I thought that my equations could not be confirmed by experiments. I was convinced that an invariant law of gravitation relative to any transformations of coordinates was not compatible with the causality principle. Astronomic experiments proved me right in 1915.”

**Note**: I recall that during my last year in high school my physics teacher, an old Jesuit Brother, filled the blackboard with partial derivatives of Newton’s equation on the force applied to a mass; then he integrated and he got Einstein’s equation of energy which is mass multiplied by C square. At university, whenever I had problems to solve in classical mechanics on energy or momentum conservation I just applied the relativity equation for easy and quick results; pretty straightforward; not like the huge pain of describing or analyzing movements of an object in coordinate space.