Nature of Time (FQXi competition & Rovelli's paper)

[atyy]

If Marni Dee Sheppeard, Carl Brannen and Louise Riofrio vote for each other, then one or more of them may win a prize.

There's zillions of essays. Any you would recommend for those of us who don't have the time to read all of them?

 

[Count Iblis]

Julian Barbour has a good essay. I may vote for him. I'm going to ask the FQXI organizers to extend the voting deadline. Dec. 15 is ridiculously close to the submission deadline. And many people are very busy right before the Holidays. Why not allow people to vote until after the New Year?

 

[atyy]

Julian Barbour has a good essay. I may vote for him. I'm going to ask the FQXI organizers to extend the voting deadline. Dec. 15 is ridiculously close to the submission deadline. And many people are very busy right before the Holidays. Why not allow people to vote until after the New Year?

Yes, Barbour's essay is superb. I hadn't seen the timeless least action before, but that really shows how close Newton and Einstein are. And he's got a great ending.

 

[RandallB]

The mainstream view is essentially trying to answer the question 'which arrow of time is the most fundamental'?.

And most physicists would say the thermodynamic arrow. Its the one we have the most intuition for in everyday life and is the consequence for most other arrows (except the cosmological arrow).

How does one discribe "arrow of time"?

And where "most other arrows" (I assume mainstream versions as needed for GR or QM), that may be incompatable with each other, all have a common consequence of the "thermodynamic arrow":

* What is it about the "cosmological arrow" that it does not give the "thermodynamic" as a result?
* Does the cosmological have a result in the thermodynamic context that can be compared with the accepted thermodynamic arrow?
* Does that, or what does, explain what it is about the "cosmological arrow" that does allow it to have a it have accepted thermodynamic arrow as a consequence??​

 

[plack]

Clock may be no more time than odometer is velocity

However... Two observers may have best possible clocks, but relative to each other, one always has a better clock.

So probability that both observers measure time equally is not 100%, even under best of circumstance

This is where clock becomes time. When there is conceptual inability to get better notion of time than the best possible clock can give you:

http://toph.synthasite.com/"

Here is the postulate:

"Rate of a moving clock at speed V (relative to at-rest clock) is equivalent to relativistic rate at speed V*P, where P is probability that time of random event can be measured equally by both clocks."​

 

[starkind]

"…the unchanging block universe view of space-time is best replaced by an evolving block universe which extends as time evolves, with the potential of the future continually becoming the certainty of the past; space-time itself evolves, as do the entities within it."

http://arxiv.org/abs/0812.0240
On the Flow of Time
George F R Ellis
9 pages, 2 figures. Essay for the Fqxi essay contest on THE NATURE OF TIME
(Submitted on 1 Dec 2008)

From post #19 this thread, by Marcus

This statement, seemingly meaningful, confuses me, and serves, I think, as a focal point showing the conceptual problems stemming from language. In short, our language was developed over millennia to describe events in the classical world of three dimensions of space evolving along a single line of time. Such language seems to me to be misleading when speaking of conditions under other kinds of dimensional groupings, such as block time.

Block time is spoken of elsewhere as a frozen river, which is also a problematic image. In this analogy, the length of the river, normally a dimension of space, is compared to a length of time. Given that we can make meaningful statements using such comparisons, we have to be careful that our comparisons reflect the sacrifice of a spatial dimension in order to allow us to image a span of time. This is not so easy to do as it may seem.

Consider, for example, the concept of an individual entity. Suppose we look at a microorganism, such as an amoeba, under a microscope. The amoeba is easily visible as a defined entity, having a particular shape evolving in time. There is no difficulty seeing which part of the slide is the amoeba and which is not. But if we extend the range of block time the amoeba has room to explore its environment, and its position cannot be simply localized. Given long enough time, every part of the slide may be explored by the amoeba, and given our sacrifice of a space dimension for a time dimension, the shape of the amoeba changes from essentially spherical to essentially linear, in analogy to a world becoming a world line.

Now we may see the identity problem. Amoebas reproduce by fission. We may say that a single amoeba becomes two amoebas. But in the block time view, there is no difference between the parent amoeba and the daughter amoebas. Their world line looks more like the branching of a tree. Is one amoeba the parent and the other the daughter? Are there two amoebas in block time, or only one, or are there three? This to show that a clear identity in our usual perceptual set of three space and one time, is not clear at all in other sets of dimensions, such as we imagine in block time.

Thus the suggestion that block time evolves is not so simple. Block time is totally deterministic. Conditions at one surface of the block time (the beginning, in our ordinary language) completely determine conditions at any place in the block. In block time, the past and the future are set in place and unchangeable. There is no single surface called "now". An evolution of block time would require that the future, and the past, can "change". Clearly this change cannot be along the time dimension of the block. It has to change in another direction in time.

So a changing block time has to have two dimensions of space and two dimensions of time. Two of space because we sacrificed a space dimension (length) for a time dimension (past and future). Two of time because the frozen river is now seen to be not a single river, but a group of rivers, each of which is frozen, and each of which is similar but not the same as other rivers in the group. Perhaps it is as if the frozen river is more like a frozen lake. And are there other frozen lakes stacked above and below the one described here?

It is possible, from this line of reasoning, and from the space-time equivalence principle, to suggest that we must accept that there is not a single preferred line of time, but that there are as many directions in time as there are in space. Each point-like event in our perceptual 3+1 becomes its own universe, with its own set of time dimensions, and identity as we know it disappears entirely. All humanity can be viewed as a single being. All life can be viewed as a single being. All the universe is one. All the multiverse is one. Every definition and distinction is merely an illusory artifact of position.

Can we modify our natural language to reflect this kind of indefinite multiverse? When we speak of an event in the past, do we have to consider that the past is not a fact, but a point of view? Is the future not a set of probable outcomes, but a set of all possible outcomes? Then what outcomes are not possible?

I am thinking that the true shape of the multiverse will not be revealed by looking at what is possible, but instead must be formulated by defining out what is not possible. What set of actions can lead to a multiverse in which some outcome is eliminated? For example, if I never travel to Australia, I can be certain that I will never have an auto accident in Brisbane. Then what happens to the multiverse in which I decide I must go to Brisbane?

Are there any actions that must be totally forbidden in every multiverse? If there are such impossible actions, they must be the boundary conditions of the multiverse.