Right About Time? by Sean Gryb and Flavio Mercati

Sean: "In SD, there is one frame where physics is scale invariant. That frame behaves much like an either."

Clever etherists know that, in a frame moving relative to the ether, the speed of light is variable:

http://www.jstor.org/stable/3653092

The Mystery of the Einstein-Poincaré Connection, Olivier Darrigol: "It is clear from the context that Poincaré meant here to apply the postulate [of constancy of the speed of light] only in an ether-bound frame, in which case he could indeed state that it had been "accepted by everybody." In 1900 and in later writings he defined the apparent time of a moving observer in such a way that the velocity of light measured by this observer would be the same as if he were at rest (with respect to the ether). This does not mean, however, that he meant the postulate to apply in any inertial frame. From his point of view, the true velocity of light in a moving frame was not a constant but was given by the Galilean law of addition of velocities."

Does the same variation of the speed of light exist in Shape Dynamics?

Pentcho Valev

Sorry!

It turns out we are allies in this matter

http://fqxi.org/community/forum/topic/1413

Originally the Michelson-Morley experiment confirmed Newton's emission theory of light:

http://www.amazon.com/Relativity-Its-Roots-Banesh-Hoffmann/dp/0486406768

Relativity and Its Roots, Banesh Hoffmann: "Moreover, if light consists of particles, as Einstein had suggested in his paper submitted just thirteen weeks before this one, the second principle seems absurd: A stone thrown from a speeding train can do far more damage than one thrown from a train at rest; the speed of the particle is not independent of the motion of the object emitting it. And if we take light to consist of particles and assume that these particles obey Newton's laws, they will conform to Newtonian relativity and thus automatically account for the null result of the Michelson-Morley experiment without recourse to contracting lengths, local time, or Lorentz transformations. Yet, as we have seen, Einstein resisted the temptation to account for the null result in terms of particles of light and simple, familiar Newtonian ideas, and introduced as his second postulate something that was more or less obvious when thought of in terms of waves in an ether."

http://www.aip.org/history/einstein/essay-einstein-relativity.htm

John Stachel: "An emission theory is perfectly compatible with the relativity principle. Thus, the M-M experiment presented no problem; nor is stellar abberration difficult to explain on this basis."

http://www.philoscience.unibe.ch/documents/kursarchiv/SS07/Norton.pdf

John Norton: "These efforts were long misled by an exaggeration of the importance of one experiment, the Michelson-Morley experiment, even though Einstein later had trouble recalling if he even knew of the experiment prior to his 1905 paper. This one experiment, in isolation, has little force. Its null result happened to be fully compatible with Newton's own emission theory of light. Located in the context of late 19th century electrodynamics when ether-based, wave theories of light predominated, however, it presented a serious problem that exercised the greatest theoretician of the day."

http://philsci-archive.pitt.edu/1743/2/Norton.pdf

John Norton: "In addition to his work as editor of the Einstein papers in finding source material, Stachel assembled the many small clues that reveal Einstein's serious consideration of an emission theory of light; and he gave us the crucial insight that Einstein regarded the Michelson-Morley experiment as evidence for the principle of relativity, whereas later writers almost universally use it as support for the light postulate of special relativity. Even today, this point needs emphasis. The Michelson-Morley experiment is fully compatible with an emission theory of light that CONTRADICTS THE LIGHT POSTULATE."

Pentcho Valev pvalev@yahoo.com

Sean,

I think the traditional emphasis on measurement only compounds the confusion about time. We perceive time as a series of events and measurement only re-enforces this perception, but physics is supposed to be about understanding the underlaying dynamic processes, not just how to model them. It is not that reality consists of a four dimensional geometry in which all events are somehow suspended, but that the changing configuration of what is, turns future potential into actual events, then replaces them. To wit, the earth doesn't travel a fourth dimension from yesterday to tomorrow, but that tomorrow becomes yesterday because the earth rotates.

Einstein said time is what you measure with a clock and a clock consists of two components, the hands, representing the present and the face, representing the events. Blocktime, as a declarative explanation of spacetime, argues only the face is real and all those events simply exist as their own present. It says time is like a book or dvd, where all the scenes already exist and it's simply a matter of where you are in that four dimensional geometry.

It's not the face, the events, which are real and the present is an illusion, but the present, that which exists, that is real and the events which are transitory. So it's not the hands moving around the face, but the events coming into being and being replaced. An example I go into is Schrodinger's cat; Quantum theory uses an external timeline, ie, going from past to future. But that pushes a determined past onto a probabilistic future and it branches out into multiple realities. If we eliminate that external timeline and just let time emerge from the process, then it is the actual occurrence of the events which determines the fate of the cat. To use a less loaded example, prior to a race, there are as many potential winners as runners, but after the race has occurred and the events reduced the possible outcomes to one, there is only one result.

The present isn't some dimensionless point on a timeline, because duration doesn't exist external to the present, but is the state of the present between measured events.

It is a dynamic reality, much of which is traveling at the speed of light and much of which is seemingly stable for periods far longer than our lives. Out of this flood of input, our minds select very limited bits of information to coalesce into each thought, thus the sense of the present as a frozen moment.

John Merryman

Sean and Flavio,

Interesting essay.

"Consider a world with no scale and no time. In this world, only 3 dimensional Platonic shapes exist. This kind of world has a technical name, it is a fixed point of renormalization {"fixed" because such a world does not flow since the renormalization scale is meaningless. This cannot yet be our world because nothing happens in this world. Now, allow for something to happen and call this "something" a measurement. One thing we know about measurements is that they can never be perfect. We can only compare the smallest objects of our device to larger objects and coarse grain the rest. Try as we may, we can never fully resolve the Platonic shapes of the fixed point. Thus, coarse graining by real measurements produces ow away from the xed point."

This quote makes me think of the cosmological constant as the fixed point of renormalization and the accompanying dynamic stress energy tensor as your measurement. As Eddington stated:

"matter does not cause the curvature of space-time. It is the curvature"

I look forward to reading more in depth. We may have quite a bit in common.

Regards,

Jeff

I would like you to read my essay "Billy Pilgrim Blues". I cover the same issues as your essay, but in a very different way. Please honestly tell me what you think.

Sean,

Thank you for your comments and taking the time to read my essay.

Clocks do not have to be cyclic. I used the example of a perfect cyclic timepiece to isolate time from all other factors. The Earth spins on its axis and the stars move in relationship to each other, but the Earth is different each day and the stars burn a little of their store of hydrogen each momentum. Entropy is very much a part of Astronomy. At the quantum scale, when enthopy change is harder to come by, postion relationships between indivual particles are uncertain. Please show me a way to mark time that does not change enthopy.

All the best,

Jeff

Dear Sean,

I'd like to remark only that

1. Einstein the physicist was agree to simplify mathematics, in particular, he used the 3-dimensional simplified version of the Pythagorean theorem in the form x2 y2 z2 = t2 ( i.e in a rectanglular box, the square of the space diagonal is equal to the sum of squares of the three sides ). Purely mathematically, however, it is not correct, because it is valid only for even x and y ( for example 3,4,12,13, etc ). But Einstein equation IS NOT valid for positive odd x and y, actually ( please, see Pythagorean Quadruple and Euler Brick problems, and my FQXi essay also )

2. On time. Mathematically speaking, Einstein's time is an attempt to introduce a new kind of complex number of the type ( x x' x'' yi ) as a kind of displacement. Thus,it could be difficult ( beyond popular science ) to deduce taking time theory seriously from this sort of attempt. The minus sign has important sense here, because it is a part of complex number algebra.

Entropy still exists for systems out of equilibrium, it is just a far more difficult calculation to find the value of the change in entropy for non-equilibrium systems. Humans and the Sun still obey the second law of thermodynamics.

In macroscopic systems the entropy change is clearly defined (but sometime hard to calculate). At the very small scale (atomic scale) the change in entropy can be undefined.

Dear Sean Gryb,

"an experiment by Michelson and Morley ... measured the speed of light to be

independent of how an observer was moving". Isn't the speed of a wave in general independent of how its source as well as its many possible observers are moving?

Eckard