Albert Einstein

1. Albert Einstein By Laura Salazar

2. Short Info. • Albert Einstein (March 14, 1879-April 18, 1955) was a German theoretical physicist who is widely considered to have been one of the greatest physicists of all time. • While best known for the theory of relativity, he was awarded the 1921 Nobel Prize in physics. • Some of his contributions to physics include; The Annus Mirabilis Papers, Theory of Relativity, Special Relativity, General Relativity, Mass-Energy Equivalence, Conservation of Mass and Energy, and Fast Moving Object.

3. The Annus Mirabilis Papers • His paper on the particulate nature of light put forward the idea that certain experimental results, notably the photoelectric effect, could simply understood from the postulate that light interacts with matter as discrete “packets” of energy and which seemed to contradict wave theories of light. • This was the only work of Einstein’s that he himself pronounced as “revolutionary”. • His paper on Brownian motion explained the random movement of very small objects as direct evidence of molecular action, thus supporting the atomic theory.

4. Cont. • His paper on electrodynamics of moving bodies proposed the radical theory of special relativity, which showed that if speed of light is the same when measured by any observer no matter how they are moving, then real physical consequence must follow. • This paper also argued that the idea of a luminiferous aether- one of the leading theoretical entities in physics at the time- was superfluous. • In his paper on the equivalence of matter and energy, Einstein deduced from his equations of special relativity that would later become the most famous expression in all of science: : E = mc²,suggesting that tiny amounts of mass could be converted into huge amounts of energy. • All four papers are today recognized as tremendous achievements.

5. Theory of Relativity • The theory of relativity, refers specifically to two theories: Albert Einstein’s special relativity and general relativity.

6. Special Relativity • Special relativity is a theory of the structure of space time. It was introduced in Einstein’s 1905 paper “on the Electrodynamics of Moving Bodies”. • Special relativity is based on two postulates which are the same for all observers in mechanics: 1) The laws of physics are the same for all observers in uniform motion relative to one another 2) The speed of light in a vacuum is the same for all observers, regardless of their motion or of the motion of the source of light. • The resultant theory has many surprising consequences. • Time dilation: Moving clocks tick slower than an observer’s “stationary” clock.

7. Cont. • Length Contraction: Objects are shorter along the direction in which they are moving. • Relativity of Simultaneity: Two events that appear simultaneous to an observer A will not be an observer B is moving with respect to A. • E = mc²; energy and mass are equivalent and interchangeable.

8. General Relativity • General relativity is a theory of gravitation developed by Einstein in the years 1907-1915. • The development of general relativity began with the equivalence principle, under which the states of accelerated motion and being as rest in a gravitational field are physically identical. • An object in free fall is falling because that is how objects move when there is no force being exerted on them, instead of this being due to the force of gravity it is the case in classical mechanics. • This is incompatible with classical mechanics and special relativity because in those theories, moving objects cannot accelerate with respect to each other, but objects in free fall do so.

9. Cont. • To resolve this difficulty Einstein first proposed that space time is curved. In 1915, he devised the Einstein field equations which relate the curve tune of space time with the mass, energy, and momentum within it. • Einstein’s relativity theory says that when substance reaches the speed of light, its mass transforms into energy. • Some of the consequences of general relativity are: 1) Time goes slower at lower gravitational potentials. This is called gravitational time dilation. 2) Orbits process in a way unexpected in Newton’s theory of gravity. 3) Even rays of light bend in the presence of a gravitational field. 4) The universe is expanding, and the far parts of it are moving away from us faster than the speed of light. 5) Frame- dragging, in which a rotating mass “drags along” the space time around it. • Technically, general relativity is a metric theory of gravitation whose defining feature is its use of the Einstein field equations. The solutions of the field equations are metric tensors which define the topology of the space time and how objects move intertially.

10. Mass-Energy Equivalence • Mass-energy equivalence is the concept that all mass has an energy equivalence, and all energy has a mass equivalence. This is expressed quantitatively using the special relativity equation: E = mc² • E= energy equivalent to the mass • M= mass • C=speed of light

11. Conservation of Mass and Energy • With the concept of mass-energy equivalence, we combine together the conservation of mass and the conservation of energy, allowing mass to be converted to forms of active energy while still retaining mass. • Active energy in the form of kinetic energy or radiation can be converted to particles which have rest mass. • The total amount of mass and energy in a closed system remains constant. Energy cannot be created or destroyed, and in all of its forms, trapped energy exhibits mass. • In relativity theory, mass and energy are two forms of the same thing and neither one appears without the other.

12. Fast Moving Object • A fast-moving object moving at near to the speed of light cannot be accelerated to the speed of light, regardless of how much energy we put into the system. • As we apply a constant force on such an object, its speed does not appear to increase by the amount specified by E=1/2 mv2. Instead, the energy provided to it continues to appear as mass, even as the role of velocity increase nearly stops. • The objects relativistic mass increases, in what is called mass dilation. The relativistic mass of an object is expressed as a function of its relative speed to that of light. • The relativistic mass which appears associated with a single fast-moving object is an observer-dependent quantity, and the part of it which is associated with a single objects kinetic energy is just as observer-dependent as the kinetic energy itself.

13. Cont. • Either one may be made to disappear entirely, by proper choice of inertial frame. For this reason, mass in special relativity is usually chosen to be rest mass or invariant mass, which is a quantity which is not frame-dependent. • There is no part of invariant mass for single objects which depends on kinetic energy. • Although a part of the invariant mass for systems of objects may depend may depend on the kinetic energy of some of the objects in the system, this part of the mass is not observer-dependent, and cannot be made to disappear by choice of observers. • Since it is already defined as that energy which is present in the particular inertial frame where the contribution of kinetic energy to invariant mass is minimized.