Thursday, August 31, 2017

Tresspassing on Einstein's Lawn by Amanda Gefter


  This book is a well-written, fascinating treatment of the lastest results in physics and cosmology in the context of the author's quest to understanding nothingness. Below is an inperfect summary for me to recall what I read.
Asking a yes or no question gets a bit of information. John Wheeler suspected that the universe is built up bit by bit by these measurements. Ours is a participatory universe. Wheeler like to say that the universe is a self-excited circuit, and that the boundary of the boundary is zero.
Wheeler "believed that the universe was right for observers because, somehow, observers create the universe." In special relativity the Lorenz transformation moves one path to another so that you are both loooking at the same world whatever your reference system (in unifom motion). With accelerated motion the parth through spacetime is curved. To match it up with a straight line path you need to curve space. "The wrinkles are gravity." "An inertial frame with a gravitational field is indistinguishable from an accelerated frame without a gravitational field."
Guth said, "...Today we think that the universe has zero values for all conserved quantities." Gravity has a negative contribution to the total energy. It always attracts and it takes energy to separate. It takes energy to bring electric charges together. Guth also said "Everything we see is in some sense nothing." Hawking said that we need to work from the top down, from the present to the past. We create the history of the universe.
"Something is real only if it's invariant." The same in every reference frame.  "..all the forces arise in essentially the same way--specifically, to account for the fact that things appear differently in different reference frames." An electron is described by a wave function which has a phase. If you step to the left you change the phase. The phases don't line up because you can't change it everywhere so you have to bend things which is electromagnetism which is a gauge force.  To "keep all reference frames on equal footing, you need a gauge force.
Chapter 7, Carving the World into Pieces, has much in it, and is too hard to adequately summarize. Gefter talks about the arrow of time and entropy which is a measure of hidden information. Temperature and pressure are shorthand for the detailed information about a gas. An individual molecule doesn't have a temperature. Gravitational entropy points in the opposite direction. It clumps stuff. Gravity is interesting at a black hole. The area of an event horizon can never decrease which resembles the second law of thermodynamics. Bekenstein claimed an event horizon's area is entropy. Hawking showed that black holes do radiate. The event horizon restructures the vacuum. It restricts the wavelengths of zero-point energy that can fit, spawning particles that wouldn't otherwise be there. The particles of Hawking radiation are observer-dependent. An accelerated observer sees a Rindler horizon which is like the event horizon of a black hole. Gravity and acceleration are equivalent. If space expands you get a deSitter event horizon, so we are surrounded by an event horizon. We each have our own universe.
The idea that the total amount of information in any region of three-dimensional space scales with the area of the two-dimensional boundary is called the holographic principle. Two descriptions--inside and outside the horizon--are complementary. The location of a bit becomes observer-dependent when gravity becomes important. Spacetime is no longer invariant.
Geometry, spacetime, doesn't fluctuate.
There isn't a single reality that all observers share. Wave-function collapse is observer-dependent. Interference in the two-slit experiment refers to a comparison between what is observed by one observer and what would be observed by another observer, a comparison between two different frames. If reality weren't observer dependent we wouldn't see interference. Interference cancels out the disagreements between our perspectives.
Light uses up its entire spacetime quotient on space, leaving none for time. It sees all of space in no time. Light is everywhere in a single instant. A photon sees a singularity. Horizons don't have horizons. The boundary of the boundary is zero. Eleven points in Chapter 15 summarize her results. The universe is nothing. If it were something it wouldn't be described by quantum mechanics.You need a broken symmetry to have information and information gives rise to the world. It from bit.


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