Gravity, Energy, and Light Einstein and Newton 1

Newtonian Gravity Newton explains the universe using forces 2

Newton Newtonian gravitational theory is based on forces acting on one another. 1.An object at rest stays at rest and an object in motion stays in motion (in a straight line) until acted upon by another force. 2.F=MA (Force = Mass X Acceleration). The acceleration of Earth’s gravity is 9.8 m/s 2. Your weight is derived from Force of Earth pushing up on you/the acceleration resulting from Earth’s gravity – F/A=M. 3.For every action there is an equal and opposite reaction. From his laws, Newton derived the law of universal gravitation. 3

Newton’s Universal Mutual Gravitation Newton’s laws led him to conclude that: 1.Gravity is an Attractive force: It draws massive objects closer together 2.Gravity is a Universal force: It operates everywhere in the Universe. 3.Gravity is a Mutual force: It works between pairs of massive objects. 4.Gravitational force is proportional to the masses, and inversely proportional to the square of the distance between them. As an example: this is how Newton explained why the planets orbit the Sun.

Newton’s Universal Gravitation In Newtonian universal gravitation, gravitational effects propagate from place to place instantaneously. – This appears true to us due to the short distances within our solar system. For example: the sun and its effect on Earth. Newton’s laws make very successful predictions and are highly useful with respect to local phenomena; however, they lose accuracy as distances increase. 5

Enter Einstein Relativity 6

Einstein and E=MC 2 E=MC 2 is at the heart of Special Relativity. – This equation heralded the arrival of the atomic age and is evidence for the Big Bang. – It demonstrated that energy and matter are related and that a little matter can produce A LOT OF ENERGY. 7

E=MC 2 – A Demo Energy (in Joules) = Mass * the speed of light Squared. E = 1 gram * (300,000 Km/s) 2 – (1 g = lbs.) E = kg * (300,000,000 m/s) 2 E = 90,000,000,000,000 Joules (or 9 X Joules) 8

E=MC 2 – A Demo When we convert that to kilotons of TNT, we discover that 90,000,000,000,000 Joules is the equivalent of 21.5 kilotons of TNT. – (1 Joule of energy is equal to kilotons of TNT) The second atomic bomb that leveled Nagasaki had a yield of 21 kilotons. 9

Einstein and General Relativity General relativity is Einstein’s geometric theory of gravity. – In general relativity, space and time are combined into space-time. –

Einstein and General Relativity General relativity conceives of space-time as a fabric, which is warped by matter. – Stars, planets, galaxies and all other bodies made of matter warp space-time – the larger the mass of the object, the “greater the warping.” – Both visible matter, like you are made of, and dark matter warp the fabric of space-time. 11

Earth’s warping of the fabric of space-time is what maintains the Moons orbit. 12 Gravity Visualized Kje0yLg

Einstein and General Relativity For instance, the sun’s effect on space-time is greater than that of Earth (the sun warps – or dimples - the fabric of space-time more than Earth) because the sun is much more massive than Earth. Earth is held in orbit by the sun due to the sun’s greater warping of space-time. 13

Einstein and General Relativity Black holes are areas where space-time is so intensely warped that light cannot escape from their gravitational grasp. 14

Gravity Wells 15 The warping of space-time is known as a gravity well. A gravity well is a way to visualize a massive object’s gravitational field. The larger the body (the more mass) the more of a gravity well it creates. Stars have a “deep” gravity well. Asteroids and small moons have much shallower gravity wells. Anything on a planet or moon is considered to be at the bottom of the gravity well.

Gravity Wells Entering space from the surface of a planet or moon means climbing out of the gravity well, something that often takes a huge amount of energy. The larger a planet or moon's gravity well is, the more energy it takes to achieve escape velocity and blast a ship out of the gravity well. 16

Gravity Wells and Time Dilation Gravity Wells cause time dilation. The closer you are to a more massive object, the slower time passes. – Because of this phenomenon, we can say that the passage of time on Mars is not the same as the passage of time on Earth or Jupiter. Time will pass faster on Mars (shallower gravity well) than on Earth (deeper gravity well) or Jupiter (very deep gravity well). 17

Gravity Wells and Time Dilation – We have to make corrections for the relativity effect (time dilation) in our communication satellites, so they and we are on the “same clock.” These are small differences but if not corrected, would cause very large problems. 18

The gravity of matter bends light (also called gravitational lensing) This is Eddington’s eclipse experiment from Gravitational lensing is a prediction of relativity. Einstein's theory predicts that the direction of light propagation should be changed in a gravitational field, which is what happens. 19

Gravitational Lensing 20 Einstein’s Cross is a quasar that lies 8 billion light years away in the constellation Pegasus. It sits behind a galaxy that is 400 million light years away. Four images of the quasar appear around the galaxy because the intense gravity of the galaxy bends the light coming from the quasar.

Gravitational Lensing Light traveling around the lens splits and takes different paths, each traveling over a different amount of time. – Due to gravitational lensing, scientists were able to observe a supernova occur four different times as it was magnified by a massive galaxy. 21

The Speed of Light and Relativity Einstein stated that the fastest speed possible is the speed of light. – A photon travels at 186,000 miles/second He pointed out that nothing is instantaneous. Since light is the fastest thing in the universe, nothing can move as fast as light. – You can come close but you can never match it. 22

The Speed of Light and Relativity Moreover, at speeds near that of light, the fabric of space-time becomes contracted (warps) in the direction of the motion - slowing the passage of time. – If you are riding in a space ship near the speed of light, your clock will move slower than that of those you have left behind on Earth. 23

The Speed of Light and Relativity – Due to the effect of velocity on time, time is relative and can differ greatly depending on your frame of reference and the velocity with which you are moving. – This is called time dilation, which is the difference of elapsed time between two events as measured by observers moving relative to each other. 24

The Twin Paradox 25 This is a result of time dilation. Neil deGrasse Tyson on the Twin Paradox - outube.com/w atch?v=n2s1- RHuljo

Einstein and Newton Why Newton is wrong – Due to the constraint of the speed of light, instantaneous propagation of forces between objects is an impossibility. – This contradicts Newton’s law of universal gravitation and laws of motion. 26

Einstein and Newton However, Newton’s predictions for systems in which velocities are small compared to the speed of light (like one of our space ships) are accurate. – This is why we can discuss the structure of the Earth, planets, and other inhabitants of our solar system using Newtonian theory. 27