Brief History of Time

A BRIEF HISTORY OF TIME

Dialogue Concerning the Two Chief World Systems by Galileo published in 1632
Two New Sciences by Galileo that was smuggled to a publisher in Holland. This was the birth of modern physics.
The City of God by St. Augustine (birth of the universe)
- time did not exist before the universe began.
Of the Heavens by Aristotle
Critique of Pure Reason by Immanuel Kant (birth of the universe)
H. G. Wells and the Time Machine


Knowing the world was round:
Shadow of the Earth on the moon was circular.
North Star appeared in different latitudes

Bertrand Russell on Astronomy

Galileo saw moons revolving around Jupiter so realized not everything has to revolve around the earth.

Newton concluded that there must be stars infinitely spread across the universe and the universe is infinite otherwise it would collapse on itself from attractive forces.

2 Theories:
1) General Theory of Relativity - shows how large objects a mile away from each other to millions of millions of millions of miles away from each other behave.
2) Quantum mechanics - shows how things at extremely molecular level work.
There is a continual search for a unified theory.

Chapter 2 - Space and Time

Galileo used balls rolling down a plane (slower so it can be observed).

Newton - a mass doubled (2M) in size will have greater attractive forces (double) than that of a normal size, M. But also is more difficult to accelerate because it is so large. These 2 things cancel each other out according to Newton's second law, which is why everything falls at the same rate. Law of attraction decreases exponentially with distance (square). So star double the distance will have 25% of the attractive forces. This predicts the motions of the moon, stars and planets with great accuracy.

Christenson Roemer - measured the speed of light in the late 1600s. He had known that there are times when the Earth and Jupiter are further apart and he noticed that the moons would go behind Jupiter and be eclipsed in uneven patterns. He noticed it took longer for it to be eclipsed the times when the earth was further away. So he assumed that light had a constant speed. And measured it to be 140,000 miles per second. (186,000 miles per second today).


Concept of cones in 4 dimensional space-time (3 dimensions of space and 1 dimension of time.) the cone appears because imagine a stone in a ripple of water and then the area in which that circular ripple spreads over time created a cone. Think of every event as having that same possible source. There is a future cone and a past cone. Example he uses. if the sun goes out now then it will take 8 minutes to reach earth. We are currently outside of that cone until 8 minutes later when the light reaches us then we are inside that cone.

Theory of relativity got rid of the notion of absolute time (which Newton proposed).
The higher the energy of light (frequency or number o light waves) the slower time gets. As you move away from the Earth's surface this frequency goes down, so time becomes faster away from the earth than on the surface. (Does this mean mountain climbers age faster? i did get a grey hair for the first time after Aconcagua; also is this the real reason why your heart rate goes up as u increase in elevation?)
(bottom of pg 33).

People higher up would see things down below as taking longer to happen because there are less light waves coming up. Also because the person up higher is moving faster than people down below. So if there were some twins. One lived on top of a mountain and the other lived at sea level. The twin on top of the mountain would age faster. Similarly if someone traveling at the speed of light came back several earth years later, then he would be much younger. This is called the 'twins paradox'.

Chapter 3: THE UNIVERSE IS EXPANDING
The milky way is a spiral galaxy that rotates every several hundred million years. Hubble predicted in 1924 that there were other galaxies but extremely far distances away from ours. He would use relative luminousness during the orbit of earth and also compare it to other stars that were of similar brightness and check its consistency. Also similarly the way Newton used a prism to refract light into the colors of the spectrum. We can now determine what elements the planets have by checking which wavelengths are sucked in by the elements on that planet and predict with relative accuracy which planets have what elements. Longest wavelengths are red and shortest are blue. A stationary star A, with a fixed wavelength of light being omitted from it and both earth and star A stay constant distances then the true color of the light will stay constant. However, if the star A is moving away from earth the wavelength gets longer so appears red and the star A that is moving closer to earth will have a shorter wavelength so will appear blue. This is the Doppler effect. other examples) the sound of a car having a different pitch when it passes in front of you verses further away (amplitude and note of the noise is different as distance changes); also a radar device that are used to measure speed from police officers.

Many people predicted that there would be as many blue galaxies as red galaxies; but Hubble found in 1929 that most galaxies were red. So that meant that galaxies were shifting away from the earth. He concluded also the farther the galaxy is away from us the faster it is moving away from us. (in other words increasing distance at an increasing rate). He would conclude this by the array of redness of the galaxies. Thus the universe is NOT static as many had thought previously but expanding. Disapproved Newton and Aristotle.

Alexander Friedmann - predicted that the universe was indeed static in that whereever you are in the universe it will look the same wherever you look out into space. There were 3 theories that could explain: (1) the universe started expanding since the big bang then would eventually contract (into the big crunch) the space time graph looked like a semi-circle and space itself would be shaped like a globe). (2) the universe is shaped like a saddle. Is expanding at an increasing rate. (3) that space is flat that it expanded quickly then now is increasing at a steady rate.

In 1965, Penzias and Wilson who were working at Bell Labs in NJ, were working with a sensitive microwave detector. They noticed the sensor was detecting microwaves in every direction on earth. If it was in the atmosphere it should be stronger if you aimed it at the horizon because you would get a larger concentration of waves then say aiming it right above you (lowest concentration). However it was identical across the entire sky. They concluded that it must be coming from something outside our solar system and galaxy (otherwise it would vary). They couldn't figure it out. Then some other scientists (DIck and Peebles from Princeton) theorized that the big bang would have started with extreme white light and since it has continued expanding ever since and expanding at an increasing rate, then that original white light would be viewed today as microwaves because it was so greatly red-shifted. THey won the nobel prize in 1978.

Hawking and Penrose completed a thesis that proved that everything started out in a singularity (ie. the big bang), with the use of general relativity. He had reversed the theory of black holes collapsing on themselves into zero, which was eventually a singularity; so that the reverse could also be true. Unfortunately the general theory of relativity broke down at extremely tiny levels and could not explain things at this level. Quantum Mechanics was needed. And thus a unifying theory is now needed called the Quantum theory of Gravity.

CHAPTER 4: THE UNCERTAINTY PRINCIPLE
Marquis de Laplace - believed that everything was completely deterministic and that everything could be predicted by scientific laws even human behavior, which was largely rejected for anyone that thought God could intervene in this universe. Planck had suggested that light, X rays and other waves are emitted in in certain packets called quanta. Also each quantum had a certain amount of energy that increased with frequency (or intensity). Werner Heisenberg formulated his 'Uncertainty principle'; that in order to predict the future position and velocity of a particle, one had to measure position and velocity accurately. The obvious way to do this was to shine light on the particle. However, as you shawn light on it, the energy from the quanta disturbed the path of the particle so the path could not be predicted. Also the more accurately the reading you wanted the shorter the wavelength you needed but the energy of the quantum would go up; so it even exacerbated the problem of locating the particle.
The uncertaintly principle then was the uncertainty of the position of the particle x uncertainty of the velocity x the mass of the particle can never be smaller than a certain quantity called Planck's constant.
In the 1920's Heisenberg, Schrodinger, Dirac came up with quantum mechanics, based on the uncertainty principle. Particles no longer had a separate, well defined position and velocity that could not be obvserved. Rather, they had a quantum state, which was a combination of position and velocity. So Leplace's dream of a completely deterministic model broke down (doesn't mean there isn't one though!). Einstein completely was against this model as he did not think that the universe was up to chance; 'God does not play dice'.
However, it was determined that waves and particles behave very similarly; if you pass a light through a two-slitted partition onto a screen behind it you get multiple fringes whether you use particles or waves. Even when you pass them through at the same time. This means that electrons must be passing to points at the same time!! (basically be at 2 places at once).
We learned at the atomic level that electrons of negative energy around a nucleus don't behave the same as planets and stars on the larger scale.
Neils Bohr in 1913 suggested that electrons orbit in only specified distances so the atom wouldn't collapse on itself (which people couldn't explain why it didn't before).
Einstein's theory brakes down during black holes and the big bang theory when there are huge infinite densities and should more closely resemble quantum mechanics.
4 types of force carrying particles:
1) Gravitational force - this force is universal. Every particle experiences it.
2) electromagnetic force - this force between 2 electrons is 1x10^40 stronger than gravity. On a very large scale the positive and negative forces cancel each other out. But at the atomic level they dominate.
3) Weak nuclear force - particles have different energies at different states and force changes depending on the state; think of the ball around a roulette table.
4) Nuclear Force -
DK's note: human emotions are much like various forces of a particle; except that it is explained differently.

CHAPTER 6: BLACK HOLES
- Wave / particle duality of quantum mechanics - meant that gravity might be able to have an effect on light. In late 1700s some one had come up with the idea that a star might be so big and powerful that it pulls the light back into its gravitational field. These are Black Holes.
- Hydrogen atoms keep bouncing into each and form heat; the heat becomes so hot that the atoms stop colliding and eventually stick together to form helium which is like a controlled hydrogen bomb reaction which gives off the light of the stars.
- much like a hot air balloon - these reactions are needed for expansionary forces so the star doesn't collapse on itself. there is an equilibrium until there is no fuel (Hydrogen) left and then the star collapses on itself. The larger the star the faster it eats the fuel because the gravitational force is larger. Our sun has about 5 billion years left before it runs out of fuel; then will likely explode; however much before this the earth will crash into the sun long before this.
- something that enters through the event horizon in a black hole will experience infinite density and the end of time. (Dante: "All hope abandon, ye who enter here.")

CHAPTER 8: THE ORIGIN AND FATE OF THE UNIVERSE
- studying black holes can help give understanding to the beginning of the universe especially if at the big bang and at a big crunch it approaches a singularity (where space-time becomes infinite).
- there have been different theories as the rate at which the universe may have expanded initially; likely by a concept called 'inflation' increasing at an increasing rate. The theory broke down because it did not support the variation that we see in the microwaves first witnessed at Bell Labs in NJ. So another modified version called chaotic inflation was developed which used quantum mechanics in its assumptions that there are repulsive forces in extremely high densities and the beginning of the universe had initially behaved in this way it seems; this came from Andrei Linde.
- in a concept called imaginary time (much like imaginary numbers, i in math), singularities do not exist because the laws of this universe could still hold. Hawking himself contradicts his old work of singularities by saying that in imaginary time there are no such thing. He gives the example of it looking much like the earth at the north and south poles and expanding and contracting with a maximum radius at the equator but things still work fine at the source where the poles are. The universe would be the biggest at the center (equator portion then contract into a big crunch at the south pole); However if we go back to 'real time' in which we live, then singularities would have to exist. Thus what is time? our current view and understanding of time is just the current system or model we use to explain everyday events. It could still be the incorrect model of the definition of time as it is not an all encompassing model. Imaginary time could really be what reality is.

CHAPTER 9: THE ARROW OF TIME
- The reason why things can't go backwards because of the 2nd law of thermodynamics; that entropy (chaos for lack of a better word) is exacerbated over time.
- There are at least 3 arrows of time:
(1) the thermodynamic arrow - direction of time in which disorder increases
(2) the psychological arrow - the direction of time in which we remember the past and not the future
(3) the cosmological arrow - the direction of time in which the universe expands rather than contracts

(1) and (2) are essection the same and always point int he same direction. Intelligent beings can only exist in the expanding phase of (3) because that is the way entropy works (start from an ordered state and then end in a disordered state; such as food being expelled eventually by heat.
DK: interesting that the universe could have only expanded in order for our knowledge to increase because disorder had to enter the world in order for us to gain knowledge.

CHAPTER 10: WORMHOLES and TIME TRAVEL
*** - Godel's incompleteness theorem is that it is impossible to prove all true statements through math
Limerick

There was a young lady of Wight
WHo travelled much faster than light
She departed one day
In a relative way
And arrived on the previous night
Interesting that there could be an infinite number of space time outcomes for history but we only live in one of those outcomes.
Christ's freedom was taken away from him because he already knew his destiny. He knew what had to be done; moreover he knew what was going to be done no matter what.

Up to now, most scientists have been too occupied with the development of new theories that describe what the universe is to ask the question why. On the other hand, the people whose business it is to ask why, the philosophers, have not been able to keep up with the advenceof scientific theories. In the 18th century, philosophers considered the whole of human knowledge, including science, to be their field and discussed questions such as: did the universe have a beginning? However, in the 19th and 20th centuries, science became too technical and mathematical for the philosophers, or anyone else except a few specialists. Philosophers reduced the scope of their inquires so much that Wittgenstein, the most famous philosopher of this century said, "The sole remaining task of philosophy is the analysis of language." What a comedown from the great tradition of philosophy from Aristotle to Kant!
However, if we do discover a complete theory, it should in time be understandable in broad principle by everyone, not just a few scientists. Then we shall all, philosophers, scientists, and just ordinary people, be able to take part in the discussion of the question of why it is that we and the universe exist. If we find the answer to that, it would be the ultimate triumph of human reason - for then we would know the mind of God.