Anti-electric universe

March 7, 2019

The Elegant Universe

Filed under: Uncategorized — davidlpf @ 3:45 am

By Brian Greene

(This a partial write-up on the book so far hopefully have the full review by early next week. I’ve really better back on schedule. )

The book is about why and string theory came about. The why is there was a conflict between relativity and quantum mechanics, well the two theories of relativity special and general relativity. Special relativity deals with things as their velocity approaches the light. Imagine that in a totally dark region of space there is you and an object in the far distance, like a cube. Now one you is suddenly travelling toward each other at a constant velocity. Now since you don’t have any reference points to compare your motion to. As you pass each other you notice that the length of the cube has shrink and from the cube point of view you have shrink in direction of motion. Now to measure the amount of time has passed you make a simple clock. You have two mirrors with the reflecting surfaces facing each other and you drill a hole for a laser and a receiver. You shine the laser and one trip from the laser to the other mirror you make that equal to one unit of time. Now when are travelling near the speed of light with the clock travelling with you. You notice instead of going straight up and down the light beam is travelling at an angle and the distance it takes is longer so it each unit of time is longer so the amount of time that passes by is slower. Also as a consequence of this the amount of energy it takes to accelerate things closer to the speed of light gets exponentially higher to the point near the speed of light where there is not enough energy in universe to accelerate the object.

General relativity came about because Einstein who came up with special relativity realized that when an object came into the the influence of a larger objects gravitational field the force would have to travel faster than the speed of light. He realized the fabric of the universe was a four dimensional grid consisting of three spatial dimensions and time. A simplistic way to think about it is to stretch out a rubber sheet of garbage bag out. Now you place something like a bowling ball or a basketball in the center and then roll a smaller object onto the sheet and it will eventually follow a path into the larger object. Now in real life the shape that the objects make is much more complicated because it is in for dimensions and also the smaller object if it has enough velocity it will orbit around the larger object.

Quantum mechanics deals with things on the very small scales and the motions are more based on probability than how things work in macroscopic we are use to. Quantum mechanics actually describes 3 out 4 forces in nature these are electromagnetic, weak and strong force. These forces have particle that transmit the force between particles. The photon or light particle has no mass and transmits the electromagnetic force. The weak force and transmitted by the gauge bosons and they have a mass, this keeps the atoms together. Finally there is the strong force which keeps particles called quarks together using particles called gluons.

One thing that started the journey into the quantum world was black body radiation. A black body is a perfect absorber and emitter of radiation. One example I am very use to is an old fashioned wood fuelled kitchen stove. In the firebox portion of the stove you start and build a fire, the metal shell of the stove absorbs the radiation on the inside of the stove and emits the radiation in the form of heat into the room. In most of these stoves you have an oven which is an empty space that is closed off and if take out all the air in the oven the only way energy is transmitted is by radiative heating. When physicist originally did the calculation on the system there would be an infinite amount of energy in the system. They eventually found that no matter the wavelength they all had the same amount of energy. Max Planck made a guess that the energy came in clumps. If the wavelength of a wave had little energy in each wave then there were more waves then waves with more energy. If the wave had to much energy than that wave was not in the system. In space objects like asteroids, comets, planets and moons absorb radiation form the nearby star and emits it back into space.

Another experiment that led to the discovery of quantum mechanics was the photoelectric effect. If you set up an simple circuit with a lamp hooked to a battery and on one wire to the lamp you cut the circuit and attach part of the wire to each plate and place the plates facing each other. No you shine a light with a filter on it, so you only get on wavelength like red coming out, you notice the light bulb does not come on, you try different filters until you get the light bulb to shine. It did not matter how bright the light shinning on the plate it only depended on the wavelength. Why is it certain only wavelengths turned on the bulb. Einstein figured that you needed a certain amount of energy to allow an electron to leave the plate and it was dependent on the wavelength of the light.

A third experiment that started to shine a light on the quantum realm was Youngs double slit experiment. You just need a light source, a screen with at least two slots in it that you block the slots and a detector (a wall can be used). You set up the experiment with the light source one side of the screen and the detector on the other. First you open one slot and shine the light and you notice a band of light in front where the slot was on the screen. Then you close the slot and open the other and you notice something similar on the other side. Then you open both slots and notice there are more than two bands. What is interesting is if can just send pulses of light you notice spots on the detector than you see a pattern starting to appear, it is the same as you let in all the light in at once. So there was no way to predict exactly where each particle would fall at each moment.

The conflict arose you have quantum mechanics that seems to work on small particles with discrete amount of energy that you couldn’t really predict with certainly where they would go but you could predict within a certain probability of where they would land. On the other hand you had large objects that seem to attract each other depending how much they warped spacetime.

(sorry that is all for now.)


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